Disertación/Tesis

Clique aqui para acessar os arquivos diretamente da Biblioteca Digital de Teses e Dissertações da UFRN

2024
Disertaciones
1
  • RAMON DE OLIVEIRA SILVA JUNIOR
  • Source wavelet estimation with machine learning and generalized seismic wavelets

  • Líder : GILBERTO CORSO
  • MIEMBROS DE LA BANCA :
  • RAMON CRISTIAN FERNANDES ARAUJO
  • GILBERTO CORSO
  • JOAO MEDEIROS DE ARAUJO
  • SERGIO LUIZ EDUARDO FERREIRA DA SILVA
  • Data: 24-abr-2024


  • Resumen Espectáculo
  • Source wavelet estimation from seismic data is an important task in the subsurface imaging effort. In this study, we intend to test a Machine Learning (ML) approach to obtain the wavelet parameters from seismograms. For the sake of simplicity, it is usually assumed that the Ricker wavelet is a good approximation for the seismic source waveform. However, the attenuation caused by propagation in heterogeneous media and specific water phenomena distort the frequency content of the wavelet, an effect not adequately represented by Ricker. To correct this phenomenon, we work with the Generalized Seismic Wavelet (GSW), which is a recently proposed generalization of the Ricker wavelet. The Ricker has just one parameter, the fundamental frequency. On the other hand, the GSW has two parameters: the same fundamental frequency and the order of the fractional time derivative of the Gaussian function; the latter controls the wavelet’s shape and asymmetry in time domain. For a specific value of this additional parameter, the GSW becomes the Ricker wavelet. Using the seismogram as input, machine learning models are trained to output the generalized wavelet parameters that best explain the data. The source wavelet is then estimated as the WSG whose parameters are those provided by the model. The proposed methodology was tested and validated with synthetic seismic data, in which a marine acquisition in deep waters was modeled, using a simplified velocity model obtained from Gato do Mato, an oil field located in the Santos basin, Brazil. We propagate an acoustic wave using the following acquisition geometry: one source placed at the surface and 50 receivers placed at 2100 m in depth, spaced 100 m apart from one another in the horizontal direction. We performed one thousand numerical propagations using the GSW with different parameterizations as the source waveform. Furthermore, we randomly selected 70% of the data for training, and the other 30% for testing. Three ML algorithms have been considered for regression: Extreme Gradient Boosting (XGBoost), Bayesian Ridge  and the Random Forest. The results were satisfactory, achieving good accuracy in estimating the GSW parameters.

2
  • JOSÉ LUAN ARAÚJO AGUIAR
  • The Study of Stellar Eruptions in Open Clusters using TESS Light Curves

  • Líder : BRUNO LEONARDO CANTO MARTINS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • MARCELO BORGES FERNANDES
  • Data: 09-may-2024


  • Resumen Espectáculo
  • Stellar magnetic fields are directly linked to fundamental stellar parameters such as age and mass, and they can give rise to extremely energetic events known as flares. These events correspond to significant explosions that occur on the surface of stars due to variations in the lines of these magnetic fields. The study of these phenomena can provide insights into the behavior of stellar magnetic activity, influencing the space weather in the stellar system’s vicinity, including the atmospheric conditions of nearby planets. In this work, we investigate the activity of these flares in 15 open clusters of different ages, utilizing short-cadence TESS light curves. Our study is based on the analysis of 3892 light curves from 1518 stars, resulting in the identification of 2288 flares. The properties of these flares, such as equivalent duration, and energy in the TESS band, were calculated for each event. The results revealed a decrease in the occurrence of flares with increasing cluster age. Most flares, with 1092 events, were observed in the Pleiades, hundreds of events in the Hyades and α Persei, and a few dozen in Alessi 13, IC 2602, and Praesepe. The observed flares energy varies from 4.154×10³² to 2.892×10³⁵ ergs. No flares were identified in clusters older than one billion years. When comparing Praesepe and Hyades, both approximately 700 million years, significant differences in the frequency of flares were observed. Although flare activity decreases with age, other astrophysical properties, such as variations in periods of high and low magnetic activity, directly influence the flare frequency rate.

Tesis
1
  • MARIANA CRISTINA DE LIMA
  • Supergravity Solutions on AdS_{3,4,5,6,7} and the AdS/CFT Correspondence

  • Líder : DMITRY MELNIKOV
  • MIEMBROS DE LA BANCA :
  • ALESSANDRO TOMASIELLO
  • DIEGO TRANCANELLI
  • DMITRY MELNIKOV
  • EMANUELE ORAZI
  • HORATIU STEFAN NASTASE
  • THIAGO SIMONETTI FLEURY
  • Data: 25-ene-2024


  • Resumen Espectáculo
  • The AdS/CFT conjecture states an equivalence between a theory of quantum gravtivy and a theory without gravity.
    It relates complementary regimes of the coupling constant and has been exhaustively investigated since its birth.
    A key tool, but not the only one, is symmetry. As we will see, there is a match between the symmetries of the two
    sides. We can say that this thesis is the union of two projects with the same goals, but working in different
    geometries. Both projects are focused on the spin-2 field perturbation of either type IIA or IIB families of 10-
    dimensional supergravity solutions. The perturbation of the metric is particularly interesting because of its
    universality. In the first project, the metric has an AdS3 factor. In the second one, we have five families and each
    of them has an AdS factor: AdS2, AdS4, AdS5, AdS6, and AdS7.
    The “first project”, the one on AdS3\times M7, is interesting from the point of view of AdS/CFT correspondence
    because it is dual to a d=2 CFT, which, in turn, possesses an infinite number of symmetry generators. In the last
    few years, new important examples of such correspondence were constructed in the papers \
    cite{Eberhardt:2017pty}, \cite{Eberhardt:2018ouy} and \cite{Eberhardt:2019qcl}. In this thesis, we will
    investigate a less supersymmetric solutions. We will study the Kaluza-Klein spectrum of the spin two fluctuation
    which is dual to the stress-energy tensor according to the conjecture.
    In the “second project" we investigate five families at once and show that all of them admit a certain combination
    of the warp factors as a solution. Such combination together with the respective spectra we call universal minimal
    solution.

2
  • MOISÉS PEREIRA DA SILVA
  • Rotação Estelar e Ambiente Galáctico

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • ALAN ALVES BRITO
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • RAIMUNDO SILVA JUNIOR
  • SILVIA HELENA PAIXAO ALENCAR
  • Data: 29-ene-2024


  • Resumen Espectáculo
  • In this work, we study the distributions of rotational velocities, along with the kinematics and chemical
    abundances, of dwarf stars from different disk populations, in order to comprehend the relationship between these
    observables and the Galactic environment. The Milky Way is home to several structures, including the stellar halo,
    the bulge, the thin disk, and the thick disk, each inhabited by stars with unique origins and formation processes,
    associated with distinct chemical and kinematic properties. However, due to interactions and dynamic processes,
    such as radial migration, these populations mix and, as a result, our solar neighborhood is composed of stars
    formed at different times and in different regions of the Galaxy. As a result of the present work, utilizing Chemical
    and rotational information, we disentangled the canonical populations of the Galactic disk and reproduce the main
    properties of these populations such as chemical enrichment, age, kinematics, orbital velocity gradients and the
    ratio of local density. Additionally, we also shed light on the origin of stellar angular momentum and the statistical
    nature of the distribution of projected rotational velocity, v sin i, of the disk components and demonstrate a possible
    spatial coupling of this observable with the Galactic environment. Our results suggest that the rotational velocities
    of stars are not only defined by their evolutionary processes, but also by their sites of formation. Through estimates
    of birth radii, we find that the entropic index q of the v sin i distributions depends on the shear of the Galaxy’s
    differential rotation, revealing that stellar rotation is closely linked to events unfolding on global scales.
    Furthermore, we observed that the rotational properties of some stars are possibly associated with the effects of the
    Galactic bar. Finally, our results indicate that the rotational shear of the Milky Way increases in outer regions of the
    disk.

3
  • MARCOS SANTOS NUNES
  • Study of Ferrite Nanoparticles for Potential Applications in Permanent Magnets and Magnetic Hyperthermia: Analysis of
    Magnetic and Structural Properties.

  • Líder : JOAO MEDEIROS DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • ANA LUCIA DANTAS
  • ANDREA PAESANO JUNIOR
  • FELIPE BOHN
  • JOSE HUMBERTO DE ARAUJO
  • JOÃO MARIA SOARES
  • MARCO ANTONIO MORALES TORRES
  • Data: 23-feb-2024


  • Resumen Espectáculo
  • The quest to enhance magnetic properties through core@shell nanoparticles and the investigation of the heating effect
    of magnetic nanoparticles using an alternating magnetic field have sparked intense scientific and technological interest.
    Significant advancements in this field have been driven by progress in the production techniques of nanoscale magnetic
    materials, enabling diverse applications such as permanent magnets, biomedical applications, and magnetic hyperthermia. This
    thesis addresses two distinct nanostructured systems. The first focuses on the synthesis of 𝐶𝑜𝐹𝑒2𝑂4@𝐶𝑜𝐹𝑒2 nanocomposites
    with core@shell structure using a method that does not involve special reagents or gases. The process involved the preparation
    of glutaraldehyde-crosslinked chitosan beads containing 𝐶𝑜𝐹𝑒2𝑂4 nanoparticles, followed by high-temperature and vacuum
    thermal treatment. The CO gas released during this process facilitated the reduction of 𝐹𝑒3+and 𝐶𝑜2+ ions to their zero-valent
    states. After the synthesis, the structural, morphological, and magnetic properties of the samples were investigated. X-ray
    diffraction analysis, transmission electron microscopy (TEM), and Mössbauer spectroscopy revealed the presence of the desired
    magnetic phases. TEM images confirmed the core@shell structure. Magnetic characterization indicated exchange-coupling
    between the phases under certain synthesis conditions, resulting in a maximum energy product (𝐵𝐻)𝑚𝑎𝑥= 0.67 MGOe. The
    thickness of the CoFe$_2$ phase (≈ 9.0 nm) aligns with the theoretical limit expected by the Kneller-Hawig theory, which is
    10.2 nm, for exchange coupling at the interface. The second system involves the synthesis and study of the magnetic properties
    of Manganese Ferrite 𝑀𝑛𝐹𝑒2𝑂4 nanoparticles. In this part of the work, 𝑀𝑛𝐹𝑒2𝑂4 nanoparticles were synthesized using the
    same method as the previous system but with conventional thermal treatment in the presence of air. Samples with various sizes
    were obtained by thermal treatments at different temperatures, resulting in particle sizes ranging from 7.8 to 13.3 nm. At 300 K,
    the saturation magnetization of the nanoparticles varied from 16.2 to 35.8 emu/g. Low-temperature Mössbauer spectroscopy
    showed the presence of monophasic 𝑀𝑛𝐹𝑒2𝑂4. For all samples, the Mössbauer results at 300 K suggested superparamagnetic
    behavior. AC and DC susceptibility measurements indicated that below the blocking temperature, the system behaves as a
    superspin glass. Specific Loss Power (SLP) measurements were conducted at a frequency of 74 kHz and AC field amplitude of
    247 Oe. The sample thermally treated at 600 °C, with a dispersion prepared at a concentration of 1.0 mg/mL, exhibited the
    highest SLP of 129.1 W/g.

4
  • ÁLVARO SANTOS DE JESUS
  • Search for Dark Sectors: Beyond the Standard Model of Particle Physics

  • Líder : FARINALDO DA SILVA QUEIROZ
  • MIEMBROS DE LA BANCA :
  • FARINALDO DA SILVA QUEIROZ
  • MANOEL SILVA DE VASCONCELOS
  • RAIMUNDO SILVA JUNIOR
  • TEREZA CRISTINA DA ROCHA MENDES
  • TÉSSIO ROGÉRIO NOBREGA BORJA DE MELO
  • VICTOR PAULO BARROS GONÇALVES
  • Data: 05-abr-2024


  • Resumen Espectáculo
  • The Standard Model of Particle Physics is one of the best theoretical models in the history of physics. However, there is a growing number of pieces of evidence pointing to the fact that the model is, in fact, incomplete. In this work, we discuss the existence and properties of extensions to the Standard Model called Dark Sectors, presenting methods of detection for these new particles and possible candidates, such as WIMP dark matter, Axion-Like Particles, and the Dark Photon. Firstly, we use a famous extension to the Standard Model known as the Two Higgs Doublet Model augmented by a new $U(1)_{L_\mu - L_\tau}$ gauge symmetry to propose a solution to the muon anomalous magnetic moment tension while presenting a viable dark matter candidate simultaneously. Then, we propose an experiment for searching dark sector particles in Brazil by repurposing some subsystems of the currently inactive UVX synchrotron light generator, named ``Search for Dark Sectors'' (SeDS). Within the framework of SeDS, we find that, if constructed, this experiment has the potential to produce appealing results in the search for dark photons and Axion-Like Particles, being able to search for regions on the parameter space $\{m_{A^\prime}, \epsilon^2\}$ for dark photons and $\{g_{aee},m_a\}$ for the Axion-Like particles that are currently unexplored by other experiments in the literature, thus being a promising experiment in the search for dark sectors.

5
  • FABRIZIO GIOVANNI OLIVIERO
  • Majorana Fermi surface state in a network of quantum spin chains

  • Líder : RODRIGO GONCALVES PEREIRA
  • MIEMBROS DE LA BANCA :
  • FERNANDO IEMINI DE REZENDE AGUIAR
  • DMITRY MELNIKOV
  • PEDRO ROGÉRIO SÉRGI GOMES
  • RAFAEL CHAVES SOUTO ARAUJO
  • RODRIGO GONCALVES PEREIRA
  • Data: 25-abr-2024


  • Resumen Espectáculo
  • Half a century ago, Anderson’s resonating valence bond theory initiated a compelling research subject in condensed matter
    physics: the exploration of the nature of quantum spin liquids. Today, the understanding of these phases of matter is deeply
    connected to the concept of quantum entanglement. In a broad context, quantum spin liquids refer to systems wherein the
    effective degrees of freedom are described by local magnetic moments residing on the lattice, exhibiting an absence of long-
    range order even at very low temperatures. In addition, the ground-state wave function displays significant entanglement, and
    excitations manifest fractionalization. In particular, this thesis is focused on the study of the chiral spin liquids that can be
    found in Mott insulators that break time-reversal and parity symmetry. Starting from junctions composed of critical spin-1
    chains, we construct a honeycomb network hosting a chiral spin liquid with gapless spectrum. The low-energy modes are
    characterized by spin-1 Majorana fermions, which give rise to a legitimate two-dimensional state that harbors a Fermi
    surface when the interactions at the junctions are adjusted close to chiral fixed points with staggered chirality. We explore the
    physical properties and stability of the chiral spin liquid phase against boundary perturbations, employing well-controlled
    analytical methods within the effective field theory of the network. Additionally, we establish evident connections with the
    excitation spectrum derived from parton constructions on the kagome lattice.

6
  • JONATHAN PESSOA CORREIA
  • Investigating DNA molecules using statistical physics tools

  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • RAIMUNDO SILVA JUNIOR
  • GILBERTO CORSO
  • UMBERTO LAINO FULCO
  • FERNANDA SELINGARDI MATIAS
  • ANTONIO DE MACEDO FILHO
  • Data: 30-abr-2024


  • Resumen Espectáculo
  • Abstract: We investigate various statistical techniques for analyzing DNA sequences, concentrating on four key species: humans, coronaviruses, maize, and soybeans. These species were chosen because of their significance in medicine, biology, the economy, the treatment of sickness, and agriculture. We examined the structure and dynamics of the DNA sequences of these species using techniques like Chaos Game Representation, Multifractal Detrended Fluctuation Analysis, and the complexity-entropy plane. Additionally, we used models based on Tsallis statistics to characterize the distribution of base pair lengths in human DNA, and we used Bayesian statistics to determine which model best fit these distributions.

    The findings demonstrated a power law association in the genetic sequences under investigation, emphasizing the persistence of their composition and the existence of multifractal features. These results highlight the intricacy and challenge of genetic makeup prediction while also highlighting the potential of these statistical tools to advance our knowledge of DNA sequences and their applications to technology, agriculture, and health. The results open up new avenues for investigation, recommending the use of these approaches on a larger variety of creatures in an effort to fully explore the enormous genetic complexity that exists.}

7
  • RAPHAEL BENJAMIM DE OLIVEIRA
  • Influence of deformation on mechanical, electronic and adsorption properties in nanostructures

  • Líder : LEONARDO DANTAS MACHADO
  • MIEMBROS DE LA BANCA :
  • CRISTIANO FRANCISCO WOELLNER
  • DOUGLAS SOARES GALVAO
  • EDIMILSON FÉLIX DA SILVA
  • LEONARDO DANTAS MACHADO
  • UMBERTO LAINO FULCO
  • Data: 29-may-2024


  • Resumen Espectáculo
  • Two-dimensional nanostructures are of growing interest in science due to their exceptional mechanical,
    electronic, and thermal properties. As theoretical and experimental studies have advanced, analyzing how such
    properties can be manipulated, especially by applying strain, has become necessary.
    Our work is focused on analyzing how deformation, whether uniaxial or biaxial, affects some properties of
    nanostructured materials. We studied materials composed only of carbon, such as graphene, α-graphyne, β-graphyne,
    and ɣ-graphyne, and materials composed of two or more types of atoms, such as boron nitride and sheets composed of
    carbon, boron, and nitrogen. These analyses are done through computational physics simulations. In the simulations
    focused on mechanical properties, we use both classical methods (molecular dynamics) and quantum methods (Density
    Functional Theory). In the study of the electronic properties, we used Density Functional Theory (DFT). When
    studying the adsorption of gases, we used Monte Carlo simulations in the Grand canonical ensemble.
    In this document, we present the results obtained, as well as perspectives for future calculations.

2023
Disertaciones
1
  • SHAYDINA DUARTE NEVES DA SILVA
  • Computational Models for silence distribution in Soundscapes

  • Líder : GILBERTO CORSO
  • MIEMBROS DE LA BANCA :
  • GILBERTO CORSO
  • GUSTAVO ZAMPIER DOS SANTOS LIMA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • RENATA SANTORO DE SOUSA LIMA
  • ROBERTO ANDRÉ KRAENKEL
  • Data: 06-mar-2023


  • Resumen Espectáculo
  • The soundscape, or acoustic landscape, is a concept that has received a great attention from ecologists, animal behaviorists and urban planners. The understanding and modeling of soundscape measurements in physics is still incipient. The duration of silence times in a soundscape is defined using a microphone and a typical sound intensity threshold; above the threshold, sound is perceived, below the threshold, silence is defined. In many soundscapes it was observed that the statistics of silence durations does not depend on the used threshold and follows a power law. In this dissertation, we build a null model for the statistics of silences: a microphone is placed in the center of a square matrix and sound emitters are randomly drawn in the matrix. Given a threshold, the sound is heard or not, depending on the sound intensity reaching the microphone. Assuming a squared decay of intensity and having all emitters the same power, only emitters within a critical radius are detected at the microphone. Under these conditions, the proposed model resembles a Bernoulli experiment, in which success consists of sound detection, and failure consists of inaudible sound at the microphone. The ratio between the area of the circle and the matrix defines the success probability of Bernoulli's experiment. Furthermore, the statistic between two successes follows a geometric distribution. Computer simulations confirm the theoretically established geometric distribution. Alternative tests with non-constant power have been performed, but the observed distribution in simulations is still a exponential type, and not a power law type.

2
  • MARIANA TEIXEIRA DE CASTRO
  • Stellar flares detected in light curves from the TESS mission.

  • Líder : IZAN DE CASTRO LEÃO
  • MIEMBROS DE LA BANCA :
  • IZAN DE CASTRO LEÃO
  • BRUNO LEONARDO CANTO MARTINS
  • JOSE RENAN DE MEDEIROS
  • MARCELO BORGES FERNANDES
  • Data: 12-may-2023


  • Resumen Espectáculo
  • Stellar flares originate from the release of a large amount of energy resulting from variations in the magnetic field of a
    star. These phenomena can be used as important observational markers of the magnetic activity of low-mass stars and also
    influence the atmospheric and biological conditions of planets in their surroundings. In hot subdwarf stars (sdBs), such
    phenomena are presumed to be caused by events external to the star due to its interaction with the magnetic field of a binary
    pair. This Master's Dissertation aims at the detection and basic characterization of eruption signatures in light curves collected
    by the Transiting Exoplanet Survey Satellite (TESS) mission. Starting from an initial sample of 924 stars belonging to the TESS
    Objects of Interest (TOIs) catalog, observed in sectors 31 to 40, we identified potential eruption events in 52 stars. We
    additionally considered two sdB stars previously studied in the literature, for which we identified, from the TESS light curves,
    eruption events in the form of giant magnetic pulses. A statistical analysis based on the color-magnitude diagram of our
    working sample reveals a tendency for more flares to occur and to have higher energy in main sequence stars compared to those
    out from the main sequence, as well as for cool stars compared to hot stars. These results agree with the fact that main sequence
    stars and cool stars have more developed convective zones, and therefore higher magnetic activity, than evolved or hot stars. In
    general, this dissertation provides new constraints for further studies on stellar magnetic activity and eruptions.

3
  • MARIANA TEIXEIRA DE CASTRO
  • Stellar flares detected in light curves from the TESS mission.

  • Líder : IZAN DE CASTRO LEÃO
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • MARCELO BORGES FERNANDES
  • Data: 12-may-2023


  • Resumen Espectáculo
  • Stellar flares originate from the release of a large amount of energy resulting from variations in the magnetic field of a
    star. These phenomena can be used as important observational markers of the magnetic activity of low-mass stars and also
    influence the atmospheric and biological conditions of planets in their surroundings. In hot subdwarf stars (sdBs), such
    phenomena are presumed to be caused by events external to the star due to its interaction with the magnetic field of a binary
    pair. This Master's Dissertation aims at the detection and basic characterization of eruption signatures in light curves collected
    by the Transiting Exoplanet Survey Satellite (TESS) mission. Starting from an initial sample of 924 stars belonging to the TESS
    Objects of Interest (TOIs) catalog, observed in sectors 31 to 40, we identified potential eruption events in 52 stars. We
    additionally considered two sdB stars previously studied in the literature, for which we identified, from the TESS light curves,
    eruption events in the form of giant magnetic pulses. A statistical analysis based on the color-magnitude diagram of our
    working sample reveals a tendency for more flares to occur and to have higher energy in main sequence stars compared to those
    out from the main sequence, as well as for cool stars compared to hot stars. These results agree with the fact that main sequence
    stars and cool stars have more developed convective zones, and therefore higher magnetic activity, than evolved or hot stars. In
    general, this dissertation provides new constraints for further studies on stellar magnetic activity and eruptions.

4
  • ALBERTO BEZERRA DE PALHARES JÚNIOR
  • QAOA Applied to the Portfolio Optimization Problem

  • Líder : RAFAEL CHAVES SOUTO ARAUJO
  • MIEMBROS DE LA BANCA :
  • RAFAEL CHAVES SOUTO ARAUJO
  • DMITRY MELNIKOV
  • NADJA KOLB BERNARDES
  • ASKERY ALEXANDRE CANABARRO BARBOSA DA SILVA
  • Data: 12-jun-2023


  • Resumen Espectáculo
  • Quantum computing is no longer in its early stages. There already exists quantum computers with more qubits than a classical
    computer is capable of simulating. This current stage is considered intermediate and is therefore called the NISQ era (noisy
    intermediate-scale quantum). The main feature of this current stage is that there are still not enough qubits to perform quantum
    error correction, hence the noisy name. In this context of quantum computing without quantum error correction and with an
    intermediate number of qubits, variational algorithms gained prominence and, among them, there is one called QAOA
    (quantum approximate optimization algorithm). As the name suggests, this is a quantum algorithm that approximates the
    solution of optimization problems. The objective of this work was to apply this algorithm to solve an optimization problem in
    the finance area known as portfolio optimization. This application took place both in an ideal way (without noise) and in a way
    consistent with the current capacity of quantum computers (with noise). Both were simulated using IBM's Python tool for
    simulation and access of quantum computers via cloud called Qiskit. The results suggest that the QAOA performance with
    noise was, as expected, worse than the ideal case, but still satisfactory within the limitations of the method.

5
  • MARCELO FERREIRA DA SILVA
  • Is the speed of light varying by using  Planck satellite and galaxy clusters observations?

  • Líder : RODRIGO FERNANDES LIRA DE HOLANDA
  • MIEMBROS DE LA BANCA :
  • RAIMUNDO SILVA JUNIOR
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • SAULO HENRIQUE PEREIRA
  • Data: 11-ago-2023


  • Resumen Espectáculo
  • The speed of light plays a fundamental role throughout the theoretical physics. Any variation in this quantity can  lead to deep modifications on  our understanding of nature. In this dissertation, we performed a test for  temporal constancy of  speed of light by using   measurements from the Planck satellite (more precisely, the values of $\Omega_M$ and $\Omega_b$), the galaxy clusters gas mass fraction and SNe data. However, cosmological analyzes via galaxy clusters strongly depend on the mass measurements  of these structures. In our analyses, we considered three different values for the mass calibration factor ($K$) found in the literature, one of them coming from the Planck observations. We found that when the value of $K$ used was not that of the Planck satellite, a possible temporal variation of the speed of light was verified. This result shows a possible tension between the constancy of the speed of light, the values of $\Omega_M$ and $\Omega_b$ (from Satellite Planck) and the values of $K$ obtained independently from that of the Planck satellite.

6
  • DÊNIS GIOVANNI DE MEDEIROS DANTAS
  • Mechanical Properties of Naphthylenes

  • Líder : LEONARDO DANTAS MACHADO
  • MIEMBROS DE LA BANCA :
  • CLAUDIONOR GOMES BEZERRA
  • LEONARDO DANTAS MACHADO
  • SERGIO ANDRÉ FONTES AZEVEDO
  • UMBERTO LAINO FULCO
  • Data: 24-ago-2023


  • Resumen Espectáculo
  • Since its discovery and synthesis in 2004, graphene has been gaining increasing attention in the scientific community due to its
    broad applicability in various technological fields. Over the years, new carbon-based two-dimensional materials have been
    discovered, and one of the most recent ones, discovered in 2019, is the Naphthylene. This material consists of a family of three
    structures known as alpha, beta, and gamma. In this study, we investigate the mechanical properties of these materials through

    uniaxial deformation using two distinct methods: (i) classical molecular dynamics (MD) employing the LAMMPS (Large-
    scale Atomic Molecular Massively Parallel Simulator) program in conjunction with the Tersoff three-body interatomic

    potential; and (ii) quantum simulations based on density functional theory (DFT) using the SIESTA code. We compare the
    results obtained from both methods and analyze how vacancy defects in different carbons affect the mechanical properties of
    naphthylenes. We found that the results obtained with MD for naphthylene-alpha show good agreement with the quantum
    method. The naphthylene-beta structure exhibited the highest elastic constant and the least susceptibility to failure, comparable
    to graphene. Naphthylene-gamma was found to be the least resistant to fractures. None of the studied materials are isotropic;
    they exhibit different elastic constants and distinct non-uniform stress distributions when deformed in different directions.

7
  • MARIA INÊS ARRUDA GONÇALVES
  • Title: Sistemas binários resolvidos espectroscopicamente e astrometricamente (WB) como um teste de teorias de gravitação

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • IZAN DE CASTRO LEÃO
  • JAILSON SOUZA DE ALCANIZ
  • JOSE RENAN DE MEDEIROS
  • Data: 01-sep-2023


  • Resumen Espectáculo
  • The proposition of the dark matter theory was a milestone in understanding the structure and evolution of the Universe. Throughout history, astronomical observations have revealed that the amount of visible matter is not enough to explain the dynamics of galaxies and the rotation curves of spiral galaxies. This has led to the emergence of different theories of gravitation that seek to provide an explanation for this phenomenon. One of the most prominent theories is the Modified Newtonian Dynamics (MOND), which proposes a modification of Newton's law of gravitation in the low acceleration regimes ). MOND has been widely studied and tested as an alternative to the dark matter hypothesis, raising questions about its validity and limitations. One way to test theories of gravitation, including MOND, is through the study of resolved spectroscopic and astrometric binary systems, known as wide binaries. These systems consist of two stars that are sufficiently distant from each other, allowing their orbits and gravitational interactions to be observed and analyzed. In this dissertation, a detailed study of wide binaries was conducted as a test for theories of gravitation, with a focus on MOND. To obtain a study with the best data available so far, data obtained by the Gaia mission and the HARPS spectrograph were used, providing precise information about angular separation, spatial velocity, radial velocity, among other properties of these binary systems. Through the analysis of this data, the implications of gravitation theories, especially MOND, for the dynamics of these systems were investigated. Careful analyses of the properties of binary systems, combined with Gaia and HARPS data, allowed for a rigorous assessment of gravitation theories and their performance in explaining observations. The results obtained, although preliminary due to the still limited size of the sample, provided valuable information about the validity of MOND, the dark matter theory, and their ability to explain the dynamics of wide binaries, as well as the analogous problem of rotation curves of spiral galaxies.

8
  • MATHEUS PHELLIPE BRASIL DE SOUSA
  • Temperature influence of neuronal ephaptic coupling via Hodgkin-Huxley model

  • Líder : GUSTAVO ZAMPIER DOS SANTOS LIMA
  • MIEMBROS DE LA BANCA :
  • GILBERTO CORSO
  • GUSTAVO ZAMPIER DOS SANTOS LIMA
  • MARCELO DE MEIRA SANTOS LIMA
  • Data: 22-sep-2023


  • Resumen Espectáculo
  • Several studies have already shown the importance of synaptic, chemical or electrical, communication in
    maintaining various biological functions in the human body, as well as its sensitivity to temperature variations. In
    addition, to neuronal communication, there is another type of communication, called ephaptic communication.
    Ephaptic communication arises from electrical fields generated by a neuron or neuron population. This
    communication, which is still little explored, has been gaining prominence because several hypotheses have been
    raised about its biological function. Therefore, this work aims to introduce the ephaptic entrainment term into the
    Hodgkin and Huxley model, as well as the term responsible for temperature variation in the model. The results of
    this work were compared with empirical results and results obtained via hybrid model simulation. To obtain the
    results, we varied the temperature in a symmetrical interval, around 0ºC, and separated the neuronal activity into
    two regimes: Subthreshold and Suprathreshold. To analyse the subthreshold results, we used circular statistics to
    evaluate the phase differences between the neuronal potential and the external ephaptic signal. In the
    suprathreshold regime, we used the Inter-Spike Interval (ISI) to evaluate the model’s firing frequency, the
    Population Vector to obtain the phase preferences between the neuronal potential and the ephaptic signal, and we
    ended by using Spike Field Coherence (SFC) to measure the synchronization between the signals. The results
    obtained in this work, by simulating the adapted Hodgkin and Huxley model, not only resemble the results in the
    literature, but also show that temperature can influence ephaptic entrainment.

9
  • SILVIA LUCIA CORREA ANGEL
  • Standard Model of Electroweak Interactions


  • Líder : FARINALDO DA SILVA QUEIROZ
  • MIEMBROS DE LA BANCA :
  • FARINALDO DA SILVA QUEIROZ
  • DMITRY MELNIKOV
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • PAULO SÉRGIO RODRIGUES DA SILVA
  • TÉSSIO ROGÉRIO NOBREGA BORJA DE MELO
  • Data: 22-sep-2023


  • Resumen Espectáculo
  • The Standard Model of Particle Physics (SM) constitutes a successful theoretical framework that gathers all the current knowledge about the fundamental interactions of nature (except gravity) and the matter that surrounds us. Its success is due to numerous theoretical predictions that were subsequently experimentally confirmed. This dissertation thoroughly examines each of the essential elements for its understanding, as well as the need to expand its boundaries to solve phenomena still unexplained, particularly the enigma of dark matter, the nature of which is unknown.


10
  • JOAB MORAIS VARELA
  • Entanglement detection in pure states with a Quantum Classifier Algorithm

  • Líder : RAFAEL CHAVES SOUTO ARAUJO
  • MIEMBROS DE LA BANCA :
  • RAFAEL CHAVES SOUTO ARAUJO
  • JOAO MEDEIROS DE ARAUJO
  • ASKERY ALEXANDRE CANABARRO BARBOSA DA SILVA
  • Data: 14-dic-2023


  • Resumen Espectáculo
  • Entangled states proved to be an essential resource for information processing, however, its classification is still an open problem.
    The objective of this work is to apply machine learning methods based on distance metrics to make a quantum state classification.
    The classification method implementation was made using classical and quantum algorithms also comparing the performance and
    efficiency of both. However, it should be noted that all quantum computation processes made in this work used simulators provided
    by the SDK Qiskit. No real quantum computers were used to implement the quantum methods due to the qubit quantity that exceeds
    the available open-access quantum computers of the IBM Q-Experience. The classical results obtained in this work make a good
    classification of quantum states with a precision rate between $70\%$ and $80\%$. The quantum predictions may have a lower
    precision, due to some simplifications made in the data pre-processing step, showing that quantum algorithms for entanglement
    classification probably will require a higher number of qubits than the currently available ones.

11
  • JOÃO VICTOR FERREIRA LACERDA AIRES
  • Tidal effects on Hot Jupiters

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • SYLVIO FERRAZ DE MELLO
  • Data: 15-dic-2023


  • Resumen Espectáculo
  • Tides are direct consequences of the gravitational interaction between celestial bodies. In the Earth context, the tidal interaction in the Earth-Moon system is directly
    observed in both increasing or decreasing of the oceanic level, once our planet’s surface is mostly covered by water. However, the discovery of gas giants exopla-
    nets in close-in orbits around their host stars (called hot jupiters), made us question what would be the consequences of such extreme tides. In this master’s thesis,
    we use the tidal evolution equations (both lonely and together with the stellar magnetic braking equations) to simulate how the presence of hot jupiters around
    main sequence stars with masses in the range 0.5 M ⊙ < M ⋆ < 1.1 M ⊙ , affects both planetary orbits and host star’s rotation.

Tesis
1
  • TIBÉRIO AZEVEDO PEREIRA
  • Deep learning anomaly detector for numerical relativistic waveforms

  • Líder : RICCARDO STURANI
  • MIEMBROS DE LA BANCA :
  • LEO GOUVEA MEDEIROS
  • LUCIANO CASARINI
  • RAIMUNDO SILVA JUNIOR
  • RICCARDO STURANI
  • VALERIO MARRA
  • Data: 26-ene-2023


  • Resumen Espectáculo
  • Gravitational Wave Astronomy is an emerging field revealing hidden information from Astrophysics and Cosmology. The
    increasing volume of observational data and Numerical Relativity simulations has promoted several analyzes and modeling
    of compact binaries’ gravitational waves. Specially, Machine Learning has become a great support to boost research. In this
    project, we developed a U-Net Deep Learning model that detects possible anomalous waveforms in a Numerical Relativity
    catalog. We use binary black hole simulations with varying masses and spins. We categorized seven different anomaly types
    during the coalescence stages with a dataset of dominant and higher modes waveforms.

2
  • BERNARDO FORTON ODLAVSON GONÇALVES
  • Investigating the rotation, the magnetism and the chemical abundances of solar-type stars through evolutionary models and spectroscopy: from the pre-main sequence to the red giant

  • Líder : MATTHIEU SEBASTIEN CASTRO
  • MIEMBROS DE LA BANCA :
  • JORGE LUIS MELENDEZ MORENO
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • LEO ALBERTO GIRARDI
  • MATTHIEU SEBASTIEN CASTRO
  • RAIMUNDO SILVA JUNIOR
  • Data: 31-ene-2023


  • Resumen Espectáculo
  • The study of the rotational evolution of the Sun and solar-type stars is undoubtedly one of the fields of stellar
    astrophysics in major evidence today. There are numerous issues that are still far from being fully understood, which makes
    research in this field intense and dynamic. Among these issues are the understanding of the phenomena that influence the
    angular momentum of stars during their formation, still in the Pre-Main Sequence phase; the understanding of the
    mechanisms that act in the stellar interiors throughout evolution, which end up determining, for example, the rotation profile
    of a solid body observed on the Sun; or which transport mechanisms act in evolved stars, which undergo profound changes in
    their structure, and manifest peculiar phenomena such as lithium enrichment and alterations in many chemical abundances. In
    all cases, we know that stellar magnetism plays a prominent role, however, it is still far from being fully understood. In this
    thesis we use models computed with the Toulouse-Geneva Stellar Evolution Code (TGEC) to study the rotational evolution of
    four samples of solar-type stars, in addition to revisiting studies with analogous stars from open clusters. In our analysis, we
    used two different magnetic brake prescriptions, which simulate the loss of angular momentum due to stellar winds.
    Additionally, we also studied a sample of giant solar-type stars that are rich in lithium, investigating the possible relationship
    with the magnetic character of some of these stars. As far as main sequence stars are concerned, we found some convergences
    and some discrepancies between our models and the stellar samples studied. We found that the sample with seismological
    data, composed of stars of intermediate and older ages, is not well restricted for a study on the rotation and magnetic
    evolution of the Sun. The sample of low-activity stars appears to be affected by a decrease in magnetic braking despite
    differences in metallicity, although targets with higher metallicity seem to better follow our evolutionary paths. Finally, wefound a mismatch between our rotation evolution tracks and the position of the youngest stars. As for lithium-rich giant stars,
    we found that stars previously classified as red giants (RGB) may be in a different evolutionary state. Furthermore, we found
    that most stars in our sample with surface magnetic field detection show at least moderate rotation speeds, but even then, we
    were unable to detect a magnetic field in two rapidly rotating stars. Because of our small sample of magnetic giants, it is
    difficult to determine whether the presence of a surface magnetic field and the Li-enrichment phenomena in giants could be
    somehow linked.

3
  • YOXARA SÁNCHEZ VILLAMIZAR
  • Physics Beyond the Standard Model using 3-3-1 Models

  • Líder : FARINALDO DA SILVA QUEIROZ
  • MIEMBROS DE LA BANCA :
  • FARINALDO DA SILVA QUEIROZ
  • SANDRO FONSECA DE SOUZA
  • ALEX GOMES DIAS
  • ALEXANDRE ALVES
  • GUSTAVO GIL DA SILVEIRA
  • VICTOR PAULO BARROS GONÇALVES
  • Data: 07-feb-2023


  • Resumen Espectáculo
  • Several open problems in the Standard Model call us to search for new physics.
    In this work, we investigate viable solutions to these issues. We focus on models based
    on an extended gauge group, known as 3-3-1 models. Considering the result from
    the gµ − 2 experiment E989 at Fermilab laboratory, we assess whether 3-3-1 models
    can explain the anomaly observed by the gµ − 2 collaboration, which favored a new
    physics’ interpretation with over 4σ of confidence level at the beginning of 2020. Later,
    we discuss how these 3-3-1 models could be extended to successfully explain the gµ − 2
    anomaly while agreeing with current and future colliders. Further, we dive into the de-
    tails of the 3-3-1 models and carry out a Monte Carlo Simulation of the Large Hadron
    Collider to obtain lower mass bounds on the masses of the new gauge bosons, namely
    the Z ′ field. Moreover, we forecast the mass reach for the Z′ gauge boson in the LHC
    at High-Luminosity and High-Energy. Given that dark matter is present in several
    models discussed in this thesis, we therefore investigate the interaction between the
    dark matter in one of these models known as 3-3-1 LHN and collider searches. Our
    results also compare the experimental relic density of dark matter with our candidates.
    Besides, numerous flavor anomalies have emerged recently. Then, we assume flavor-
    changing interactions mediated by a gauge boson Z′ , at tree level, analyzing the SM
    0
    0
    deviations in the K 0 − K , D 0 − D , Bd0 − B0 d and Bs0 − B0 s meson systems. Here, we use
    updated data on the mass difference of the four meson systems, and we derive lower
    mass bounds on Z′ at two different parameterizations of the quark mixing matrices. By
    focusing on a model based on the SU(3) gauge group, we put our results in perspective
    with current and future hadron colliders to conclude that mass meson systems can give
    rise to much more stringent bounds than those at high-energy colliders and that recent
    new physics interpretations of the b → s and R( D ∗ ) anomalies are unfavorable.

4
  • HERNÁN GUILLERMO BUENO XAVIER
  • Network construction of non-Abelian topological phases

  • Líder : RODRIGO GONCALVES PEREIRA
  • MIEMBROS DE LA BANCA :
  • RODRIGO GONCALVES PEREIRA
  • DMITRY MELNIKOV
  • TOMMASO MACRI
  • EDUARDO MIRANDA
  • HERMANN FREIRE FERREIRA LIMA E SILVA
  • Data: 05-may-2023


  • Resumen Espectáculo
  • In this thesis we use a network of chiral junctions to realize non-Abelian topological phases in two dimensions. Our
    construction is based on boundary fixed points of low-energy field theories describing Y junctions of critical spin-chain
    models. To set the stage, we first study a single junction of gapless spin-1 chains belonging to the SU(2)_2 universality class,
    whose spectrum includes fractional excitations such as Majorana fermions. We find that chiral fixed points appear as special
    points on a transition line that separates two regimes described by open boundary conditions. Remarkably, along this transition
    the junction behaves as a tunable spin circulator as the spin conductance varies continuously with the coupling constant of a
    marginal boundary operator. We then construct a family of topological chiral spin liquids departing from a honeycomb
    network made of critical spin-S chains. The chiral spin liquid phase harbors SU(2)_{k=2S} anyons, which stem from the
    underlying Wess-Zumino-Witten models that describe the constituent spin chains of the network. The network exhibits
    quantized spin and thermal Hall conductances. We illustrate our construction by inspecting the topological properties of the
    SU(2)_2 model. We find that this model has emergent Ising anyons, with spinons acting as vortex excitations that bind
    Majorana zero modes. We also show that the ground state of this network is threefold degenerate on the torus, asserting its
    non-Abelian character. Our work provides a controllable analytical framework to study non-Abelian topological phases,
    sheding new light on the stability of such phases in artificial quantum materials.

5
  • LUCAS GIOVANNI DA POSSA CARAMÊS
  • Lévy walks inside annuli and spherical shells with absorbing boundaries

  • Líder : MADRAS VISWANATHAN GANDHI MOHAN
  • MIEMBROS DE LA BANCA :
  • CLAUDIONOR GOMES BEZERRA
  • ERNESTO CARNEIRO PESSOA RAPOSO
  • JOAO MEDEIROS DE ARAUJO
  • LEONARDO DANTAS MACHADO
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MARCOS GOMES ELEUTERIO DA LUZ
  • Data: 29-may-2023


  • Resumen Espectáculo
  • The Lévy Flight Foraging Hypothesis proposes that organisms have evolved to use
    Lévy walks as an effective exploration strategy. There is substantial evidence in the
    literature supporting the notion that Lévy inverse square walks are optimal for foraging
    with revisits, regardless of dimensionality. However, more rigorous mathematical
    demonstrations of this phenomenon are still needed, especially for dimensions higher
    than 2. We investigate the foraging problem by considering the simpler case of concentric
    annuli or spherical shells, which is closely related to the full problem. By analyzing this
    approach, we show that Lévy inverse square walks are the optimal search strategy in the
    limit of foraging with revisits. This result is a strong evidence supporting the Lévy Flight
    Foraging Hypothesis in dimensions greater than 1

6
  • FELIPE BRUNO MEDEIROS DOS SANTOS
  • Impact of Extensions of Gravity on Inflation and Reheating

  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • RAIMUNDO SILVA JUNIOR
  • FARINALDO DA SILVA QUEIROZ
  • LEO GOUVEA MEDEIROS
  • FELIPE TOVAR FALCIANO
  • FRANCISCO DE ASSIS DE BRITO
  • Data: 26-jun-2023


  • Resumen Espectáculo
  • In this work, we investigate the impact of extensions of gravity in cosmic inflationary scenarios, in which a scalar
    field, dubbed inflaton is considered as responsible for the accelerated expansion of the primordial Universe. In particular, we
    will see how such changes affect the cosmic microwave background radiation temperature power spectrum, determined with
    great precision by the most recent experiments that investigate it. Initially, we consider that the inflaton is non-minimally
    coupled to gravity, and we will check the predictions for two specific models. The first one is characterized by the β -
    exponential potential, which generalizes the well-known power-law inflation, and it is motivated by brane dynamics; the next
    model arises from a supergravity realization, usually called the Witten-O’Raifeartaigh inflation. Through a statistical analysis,
    we will establish constraints on cosmological parameters of the specific models, determining if there is any preference from
    data for the presence of a non-minimal coupling. The connection of such models with the reheating period is investigated next,
    in a way that we seek to establish the relation between the duration and temperature of reheating with the properties of the
    model. By choosing the Witten-O’Raifeartaigh one, we use the results of the previous analysis to numerically model the post-
    inflationary era, in a way that non-linear effects on the growth of perturbations of the field are considered, resulting in an
    amplification of said fluctuations through a preheating process. These fluctuations can be responsible for the formations of
    long-lived structures dubbed oscillons, argued as a possible source of primordial gravitational waves. Finally, we check the
    possibility of application of the β-exponential scenario to the warm inflation picture, in which the energy dissipation of the
    field into radiation is realized at the same time that inflation proceeds, with the degree of dissipation impacting greatly the
    predictions of a given model. We will see that for the β-exponential model, it is possible to make the strong dissipation regime
    concordant with the swampland conditions, recently investigated in the literature in the context of warm inflation.

7
  • JOSIEL MENDONÇA SOARES DE SOUZA
  • Late-Time Cosmology With Third Generation Gravitational Wave Observatories

  • Líder : RICCARDO STURANI
  • MIEMBROS DE LA BANCA :
  • ODYLIO DENYS DE AGUIAR
  • RAFAEL DA COSTA NUNES
  • RAIMUNDO SILVA JUNIOR
  • RICCARDO STURANI
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • Data: 12-jul-2023


  • Resumen Espectáculo
  • With the first detection of gravitational waves in 2015 by the observatories LIGO Hanford and
    Livingston, a new window opened to the study of astronomy, astrophysics, and cosmology. With
    gravitational waves emitted by binary systems of compact objects, such as binaries of black holes
    and neutron stars, we can measure directly their luminosity distances dL , similar to type Ia super-
    novae called standard candles. Thus, these gravitational wave sources received the name standard
    sirens, in analogy with the standard candles. If an electromagnetic counterpart of these sources
    is available, as the signal GW170817, we can identify directly their sky position, and so, their host
    galaxies and redshifts z. Thus, having a relationship dL − z through detections of gravitational
    waves with electromagnetic counterparts, we can perform cosmological tests, such as measur-
    ing H0 , performing Bayesian model selection, and constraining cosmographic parameters, among
    others. In this work, we explore the strength of the planned ground-based third generation obser-
    vatories, Einstein Telescope and Cosmic Explorer to probe the evolution of the Universe’s expan-
    sion. We start presenting our software GWDALI developed to estimate uncertainties in gravita-
    tional wave parameters via Fisher-Matrix and beyond Gaussianity approach of likelihoods. We
    also explore how much the synergy between third generation observatories can improve mea-
    surements of luminosity distances of bright standard sirens (standard sirens with electromagnetic
    counterparts) to get the best cosmological constants from dL − z relationships. Finally, we deal
    with the cosmography approach, forecasting the maximum accuracy in the measurements of the
    first three cosmographic parameters, Hubble constant H0, deceleration parameter q0 , and jerk j0
    with Einstein Telescope.

8
  • GABRIEL LUZ ALMEIDA
  • Classical Amplitudes in Gravitational-Wave Physics

  • Líder : RICCARDO STURANI
  • MIEMBROS DE LA BANCA :
  • LAURA BERNARD
  • WALTER GOLDBERGER
  • DMITRY MELNIKOV
  • EMANUELE ORAZI
  • RICCARDO STURANI
  • Data: 18-jul-2023


  • Resumen Espectáculo
  • The recent detections of gravitational waves from coalescing binaries by the LIGO and Virgo interferometers not
    only opened a new window of observation into the Universe but also revived interest in the relativistic two-body problem. In
    this thesis, after presenting the general theory of gravitational waves, we review the effective field theory approach within the
    so-called Non-Relativistic General Relativity. In this framework, the different scales involved in the problem define different
    dynamical regions, with short scales describing the conservative interaction between the two bodies and long-distance scales
    accounting for gravitational-wave processes. At higher orders, however, radiation modes start to affect the conservative
    dynamics of the system through the so-called tail effect.
    We then study emission amplitudes for the class of nonlinear processes of tails, which are processes of order G_N^2, and
    represent the effect of scattering gravitational radiation off the static background curvature, including not only mass tails but
    also the “failed” tails due to the angular momentum of the source. As originally shown in our work, some of these amplitudes
    present anomalies, which are then properly understood and corrected with field theory tools which have straightforward
    counterpart in traditional methods. We also investigate the relation between emission and self-energy diagrams and, in
    particular, show that a correction to the anomalous self-energy diagrams is necessary to correctly account for conservative
    terms that arise from radiative processes. From this, we obtain the correct contribution to the conservative 5PN stemming from
    the electric quadrupole angular momentum failed tail, correcting previous results of the literature. Besides this, we also
    compute for the first time the conservative contributions from the angular momentum failed tail, for arbitrary multipole
    moments.
    Subsequently, we explore the natural higher-order extension (of order G_N^3) of the mass tails, called tails of tails, for generic
    electric and magnetic multipoles. As we will see, both long- and short-distance divergences are encountered, which are then
    properly understood and dealt with in terms of standard renormalization techniques. In this case, we are able to resum the
    logarithmic contributions through the integration of the renormalization group equation.
    Thus, in this thesis, we have extended the post-Newtonian perturbative expansion in the particularly thorny region of processes
    involving the mixture of radiative and potential modes.

9
  • GABRIEL LUZ ALMEIDA
  • Classical Amplitudes in Gravitational-Wave Physics

  • Líder : RICCARDO STURANI
  • MIEMBROS DE LA BANCA :
  • DMITRY MELNIKOV
  • EMANUELE ORAZI
  • LAURA BERNARD
  • RICCARDO STURANI
  • WALTER GOLDBERGER
  • Data: 18-jul-2023


  • Resumen Espectáculo
  • The recent detections of gravitational waves from coalescing binaries by the LIGO and Virgo interferometers not
    only opened a new window of observation into the Universe but also revived interest in the relativistic two-body problem. In
    this thesis, after presenting the general theory of gravitational waves, we review the effective field theory approach within the
    so-called Non-Relativistic General Relativity. In this framework, the different scales involved in the problem define different
    dynamical regions, with short scales describing the conservative interaction between the two bodies and long-distance scales
    accounting for gravitational-wave processes. At higher orders, however, radiation modes start to affect the conservative
    dynamics of the system through the so-called tail effect.
    We then study emission amplitudes for the class of nonlinear processes of tails, which are processes of order G_N^2, and
    represent the effect of scattering gravitational radiation off the static background curvature, including not only mass tails but
    also the “failed” tails due to the angular momentum of the source. As originally shown in our work, some of these amplitudes
    present anomalies, which are then properly understood and corrected with field theory tools which have straightforward
    counterpart in traditional methods. We also investigate the relation between emission and self-energy diagrams and, in
    particular, show that a correction to the anomalous self-energy diagrams is necessary to correctly account for conservative
    terms that arise from radiative processes. From this, we obtain the correct contribution to the conservative 5PN stemming from
    the electric quadrupole angular momentum failed tail, correcting previous results of the literature. Besides this, we also
    compute for the first time the conservative contributions from the angular momentum failed tail, for arbitrary multipole
    moments.
    Subsequently, we explore the natural higher-order extension (of order G_N^3) of the mass tails, called tails of tails, for generic
    electric and magnetic multipoles. As we will see, both long- and short-distance divergences are encountered, which are then
    properly understood and dealt with in terms of standard renormalization techniques. In this case, we are able to resum the
    logarithmic contributions through the integration of the renormalization group equation.
    Thus, in this thesis, we have extended the post-Newtonian perturbative expansion in the particularly thorny region of processes
    involving the mixture of radiative and potential modes.

10
  • JOAO CARLOS ROCHA DE ARAUJO
  • Magnetic interactions between superparamagnetic nanoparticles and their influence on hyperthermia phenomenon

  • Líder : FELIPE BOHN
  • MIEMBROS DE LA BANCA :
  • DALBER RUBEN SANCHES CANDELA
  • FELIPE BOHN
  • JOÃO MARIA SOARES
  • JULIANO CASAGRANDE DENARDIN
  • MARCO ANTONIO MORALES TORRES
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 21-jul-2023


  • Resumen Espectáculo
  • The effect of heating magnetic nanoparticles from the application of an alternating magnetic field has aroused great interest in the scientific community. In the biomedical field, for example, this effect is used in cancer therapy through magnetic hyperthermia. However, the factors that can influence the heating of these materials are not yet fully understood and have generated several discussions, with discrepancies between the results presented in the literature. Although superparamagnetic systems have been widely explored for applications in magnetic hyperthermia, in most cases the effects of magnetic interactions between nanoparticles on the heating efficiency of these materials are completely neglected. In this work, we aim experimental investigation on the existence of magnetic interactions between superparamagnetic nanoparticles and their influence on magnetic hyperthermia. From the production and structural, morphological, magnetic, and calorimetric characterization of nanoparticles MgFe2O4,  γ-Fe2O3, ZnFe2O4, and CuFe2O4 it was made a systematic investigation of the magnetic properties of these samples, which led to the belief that they are associated with the existence of exchange interactions in the system. For this study, it was first confirmed that the samples consist of pure ferrite nanoparticles, without secondary phases and superparamagnetic behavior at room temperature. Nevertheless, it was found that the magnetic response of these samples is not well described by the well-known Langevin function, even taking into account the size distribution of the nanoparticles. To address the reasons for such a deviation of non-interacting behavior of a superparamagnetic system, from equilibrium and dynamic magnetization measurements, it was considered a theoretical approach based on modified Weiss mean field approximation, in which it was used to describe the nature of the interactions presente in the samples. From the results, positive values were found for the parameter  θ associated with the mean field and which is directly related to the interactions within the system. This result suggests the existence of magnetizing effects due to interactions in the system, which, according to the Weiss mean field theory, are fingerprints of the presence of exchange forces between nanoparticles. In addition, it was shown that the equilibrium susceptibility initial and the relaxation time are strongly affected by such interactions, directly influencing the Specific Loss Power (SLP), a key parameter in the context of magnetic hyperthermia.

11
  • HEITOR DA SILVA
  • Nonlinear dynamics in quantum fluids of light

  • Líder : TOMMASO MACRI
  • MIEMBROS DE LA BANCA :
  • TOMMASO MACRI
  • LEONARDO DANTAS MACHADO
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MIGUEL ÁNGEL GARCÍA MARCH
  • ROMAIN PIERRE MARCEL BACHELARD
  • Data: 25-jul-2023


  • Resumen Espectáculo
  • Nonlinear dynamics in quantum fluids of light

12
  • ARTHUR LANNE RICARDO DE SOUZA
  • Using Ti1−xCux thin films as temperature sensors applied for the study of the Anomalous Nernst Effect in multilayer
    ferromagnetic structures

  • Líder : MARCIO ASSOLIN CORREA
  • MIEMBROS DE LA BANCA :
  • MARCIO ASSOLIN CORREA
  • FELIPE BOHN
  • JOAO MEDEIROS DE ARAUJO
  • MATHEUS GAMINO GOMES
  • ALEXANDRE DA CAS VIEGAS
  • DANNIEL FERREIRA DE OLIVEIRA
  • Data: 28-jul-2023


  • Resumen Espectáculo
  • Nowadays, it is increasingly necessary to develop clean energy sources as well as energy-efficient electronic devices. In this
    context, the Anomalous Nernst Effect (ANE) has the potential for energy-efficient and sustainable integrated systems
    applications. This work presents a proposal for the applicability of the thermal sensorial properties of the alloy Titanium-
    Copper (TiCu) integrated into nanostructured ferromagnetic systems for the study of the Anomalous Nernst Effect. For this
    purpose, we produced and investigated the ability of Ti1−xCux thin films to act as temperature sensors based on the variation of
    electrical resistance (RTD sensors). We used the magnetron sputtering technique to deposit Ti1−xCux films in three
    compositions: Ti0.74Cu0.26, Ti0.70Cu0.30, and Ti0.54Cu0.46. We tested the performance of Ti1−xCux films produced as a potential
    temperature sensor through temperature variation protocols in the range between 35 and 110 °C. Among the compositions
    produced, the film Ti0.70Cu0.30 showed the most promising results. The Ti0.70Cu0.30 film showed linearity and stability in the
    thermoresistive response, as well as excellent thermal sensitivity, quantified by the TCR coefficient α. The α obtained for the
    film Ti0.70Cu0.30 was −1.99 × 10−3°C−1. We integrated the Ti0.70Cu0.30 film into a TiCu/Insulator/NiFe multilayer ferromagnetic
    nanostructure and compared it with a TiCu/NiFe nanostructure to study the influence of the insulating layer, especially on the
    magnetic behavior. As an insulating material, we use Kapton. Both samples showed soft magnetic behavior, characterized by
    low values of the coercive field (Hc) and saturation field (Hs). The presence of the insulating layer influenced a slight
    difference in the coercivity of the multilayer structures, for TiCu/Isolate/NiFe Hc ≈ 5 Oe and for TiCu/NiFe Hc ≈ 9 Oe, due to
    the flexibility of the surface of the Kapton better accommodated the particles during the deposition process. However, in
    practice, the magnetic behavior of the two structures is similar. We investigated the Anomalous Nernst Effect through the
    voltage VANE, using three values for the applied temperature gradient ∇T. The voltage VANE of the samples showed smooth
    behavior as a function of the magnetic field, with low coercivity and saturation field, as well as the magnetic behavior. The
    TiCu sensor was able to read the temperature variations during all stages of the voltage measurement process VANE in both
    samples for the three values of ∇T. We calculated the Anomalous Nernst Coefficient (SN) for the TiCu/Insulator/NiFe sample,

    where we obtained SN = 0.60 μV/K, and for the TiCu/NiFe sample, SN = 0.46 μV/K. These values are in agreement with SN
    values reported in the literature for NiFe monolayer structures at room temperature. Therefore, Ti0.70Cu0.30 film is an excellent
    candidate to act as an RTD-type temperature sensor, with potential applicability in different systems.

13
  • DANIEL BORGES SILVA
  • Pseudospin topological behavior and topological edge states in a two-dimensional photonic crystal composed of Si rods in a triangular lattice

  • Líder : CLAUDIONOR GOMES BEZERRA
  • MIEMBROS DE LA BANCA :
  • ANDRE JORGE CARVALHO CHAVES
  • CARLOS HUMBERTO OLIVEIRA COSTA
  • CLAUDIONOR GOMES BEZERRA
  • DORY HELIO AIRES DE LIMA ANSELMO
  • FELIPE ARRUDA DE ARAÚJO PINHEIRO
  • MADRAS VISWANATHAN GANDHI MOHAN
  • Data: 25-ago-2023


  • Resumen Espectáculo
  • In this work we propose a two-dimensional topological photonic system of Si rods, whose unit cell is composed of six artificial atoms located on the sites of a triangular lattice. By perturbing the original lattice, by alternately increasing (type A) and shrinking (type B) the radius of the rods, we find edge modes that are highly localized at the interface between the type A and type B photonic crystals. The proposed structure is robust against complex defects and allows transmission of the propagating electromagnetic waves without any reflection. The interface edge modes present a typical behavior corresponding to that of a topological insulator. More specifically, the edge mode presents a pseudospin topological behavior. Our numerical results show the robustness, originating from the topological protection, of this mode against defects, disorder, and reflection. Also, the localization at the interface state permits the confinement of the light, where the interface behaves as a waveguide for the propagation of electromagnetic waves. The geometric perturbation considered here can easily be implemented using nanolithography.

14
  • ISAAC EDSON CRUZ RAMALHO MENDONÇA
  • cosmologia observacional e vínculos em possíveis desvios da física padrão

  • Líder : RODRIGO FERNANDES LIRA DE HOLANDA
  • MIEMBROS DE LA BANCA :
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • IZAN DE CASTRO LEÃO
  • RAIMUNDO SILVA JUNIOR
  • RAFAEL DA COSTA NUNES
  • SAULO HENRIQUE PEREIRA
  • Data: 08-dic-2023


  • Resumen Espectáculo
  • The ΛCDM model, also known as the concordance model of Cosmology , is the
    best to describe the different phases of evolution of the universe and agrees with most
    observational data. However, in recent years, several problems have emerged that have
    challenged this model. In order to explain some of these problems, many alternative models
    have been proposed, such as the addition of new dynamic fluids modeled by different fields,
    modifications of Einstein’s general relativity and deeper modifications to standard physics,
    such as the possibility of varying fundamental constants. In this thesis, using the most
    recent observational data, we test possible deviations from the theory of general relativity,
    as well as possible temporal variations in the speed of light. As results, we did not obtain
    departures from the standard physics, however, more restrictive constraints should be
    performed in the future with better observational data.

2022
Disertaciones
1
  • TALES CARNEIRO DOS SANTOS
  • Topological data analysis in functional neural networks under Ayahuasca effect.

  • Líder : MADRAS VISWANATHAN GANDHI MOHAN
  • MIEMBROS DE LA BANCA :
  • ALINE AMABILE VIOL BARBOSA
  • FERNANDO ANTÔNIO NÓBREGA SANTOS
  • GUSTAVO ZAMPIER DOS SANTOS LIMA
  • IRAM MARCELO GLÉRIA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • Data: 16-feb-2022


  • Resumen Espectáculo
  • An area of great interest for scientists today is the study of real complex systems. An example of a complex system is
    the human brain, an essential component of life. The present study makes use of complex systems methods to investigate, in an
    exploratory way, the brain connectivity in a comparative way before and after the ingestion of Ayahuasca tea. The complex
    systems tools used for this work focused on investigating the connectivity between brain regions, based on fMRI data. These
    fMRI data were represented through simplicial complexes, in order to enable the use of specific techniques for the assessment
    of brain connectivity. The three measures used to assess brain connectivity were: (i) Euler entropy; (ii) the curvature; (iii) and
    persistent entropy. Using appropriate statistical tests, it was possible to observe changes in the phase transition point of the
    complex system in question. For the curvature, no significant changes were observed, however a relevant change in the
    participation profile of the nodes during the system phase transition was observed. As for the persistent entropy, a decrease in
    its value was observed for the two-dimensional simplices. In this way, the present study expands the understanding of the
    impact of Ayahuasca on the brain and opens the door to future studies regarding brain connectivity under the action of
    psychedelics.

2
  • PAULO DOUGLAS SANTOS DE LIMA
  • Acoustic Full Waveform Inversion using Hamiltonian Monte Carlo

  • Líder : JOAO MEDEIROS DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • JOAO MEDEIROS DE ARAUJO
  • GILBERTO CORSO
  • MAURO SANTOS FERREIRA
  • Data: 24-feb-2022


  • Resumen Espectáculo
  • Full Waveform Inversion (FWI) is a high-resolution technique used to estimate an ensemble of subsurface models
    that describe the physical structure of Earth's interior considering the entire seismic wavefield. Hamiltonian Monte Carlo
    (HMC) method has acquired great attention in solving seismic inversion problems due to its capacity of sampling on high-
    dimensional model spaces by avoiding the random walk behavior. In this work, we verify the feasibility of using the HMC
    method on the FWI problem under the acoustic wave approximation. We consider as laboratory two synthetic velocity models
    under different data variance scenarios. The results suggest that the inversion process is strongly dependent on data variance
    and on the choice of mass matrix, implying that more efforts are necessary to real data applications.

3
  • RAFAEL ÁVILA MACÊDO
  • Chiral phases and Landau-forbidden transitions in one dimension

  • Líder : RODRIGO GONCALVES PEREIRA
  • MIEMBROS DE LA BANCA :
  • ALVARO FERRAZ FILHO
  • FRANCISCO CASTILHO ALCARAZ
  • RODRIGO GONCALVES PEREIRA
  • Data: 11-mar-2022


  • Resumen Espectáculo
  • The common lore in statistical physics suggests that phases and transitions of matter are generally classified by what is called
    the Landau-Ginzburg-Wilson paradigm. In two dimensions, however, quantum models can exhibit ``deconfined'' continuous
    transitions between ordered phases, which are forbidden by the Landau classification. On this thesis, we introduce a one-
    dimensional quantum spin model with three ordered phases: A chiral spin state, where the system orders into three-spin
    ``fluxes'', an antiferromagnetic state, and a novel phase which we denote as the Klein paramagnet. We find that all transitions
    from the chiral phase are continuous and beyond the Landau paradigm.

4
  • MATHEUS FILIPE SANTOS ALVES
  • Gravitational waves in theories of quadratic gravitation

  • Líder : LEO GOUVEA MEDEIROS
  • MIEMBROS DE LA BANCA :
  • ANTONIO DUARTE PEREIRA JUNIOR
  • LEO GOUVEA MEDEIROS
  • RODRIGO SANTOS BUFALO
  • Data: 16-mar-2022


  • Resumen Espectáculo
  • The success of General Relativity in describing gravitational phenomena is unquestionable. Despite this, there are conceptual problems in General Relativity, such as the presence of singularities in solutions to the Einstein equation, energy and dark matter, in addition to the fact that the theory is not renormalizable, which makes it impossible to quantize it in a conventional way. One way to try to circumvent these problems is to use the so-called theories of modified gravitation. In the scope of this work we will focus our study on the quadratic gravitation model that has been receiving attention due to its application in the context of quantum gravity as it is a renormalizable theory. After a brief review of the theory of gravitational waves in General Relativity, the proposed gravitation is explored. The quadratic gravity field equations are deduced, linearized, and then solutions of these equations are studied. In addition, a detailed study of the degrees of freedom in this theory of gravitation is made. An analysis of the emission of gravitational waves by binary point black hole systems is also made and, in particular, we study the orbital dynamics and the waveform that would be observed by a detector. Finally, we compare the results with General Relativity and obtain constraints in the parameters of the theory.

5
  • JOÃO VICTOR TOMAZ DE LIMA
  • ABORDAGENS ROBUSTAS PARA PROBLEMAS INVERSOS BASEADOS NAS ESTATÍSTICAS GENERALIZADAS DE RÉNYI, TSALLIS E DE KANIADAKIS

  • Líder : GUSTAVO ZAMPIER DOS SANTOS LIMA
  • MIEMBROS DE LA BANCA :
  • GUSTAVO ZAMPIER DOS SANTOS LIMA
  • JOAO MEDEIROS DE ARAUJO
  • SERGIO LUIZ EDUARDO FERREIRA DA SILVA
  • SERGIO R. LOPES
  • Data: 18-mar-2022


  • Resumen Espectáculo
  • In general, inverse problems can be faced as a task of optimizing a functional that promotes the fit between the experimental data and the data calculated from a physical model. Commonly, the objective function known as "least squares function" — which is based on Gaussian statistics — is used for this task, however this approach presents serious difficulties in a context in which the noises don't obey the Gaussian statistics. The type of non-Gaussian noise that we investigated in this work are the outliers, which are characterized as discrepant measures that contaminate the sample and make it difficult to interpretation of the experimental data.

       In this dissertation we approach the generalization of the inverse problem through the generalization of Gaussian statistics in the context of Rényi, Tsallis and Kaniadakis statistics. In this sense, we discuss the error distributions in the non-Gaussian context and the generalized objective functions that derive from these statistics and evaluate their robustness through the so-called Influence Function (objective function gradient).  

       We exemplify the robustness of generalized methodologies using numerical experiments. In particular, we use the inverse problem generalization in a seismic inversion problem with high contamination from outliers.

       Our results show that the generalized inverse problem is resistant to outliers. Furthermore, we identified that the best data inversion performance occurs when the entropic index of each generalized statistic is associated with objective functions proportional to the inverse of the error amplitude. We argue that at such a limit the three approaches are resistant to outliers and are also equivalent. Furthermore, this approach suggests a lower computational cost for the inversion process due to the reduction of numerical simulations to be performed and the rapid convergence of the optimization process.

6
  • JACINTO PAULO DA SILVA NETO
  • A Right-handed Neutrino Dark Matter Phenomenology

  • Líder : FARINALDO DA SILVA QUEIROZ
  • MIEMBROS DE LA BANCA :
  • CLARISSA MARTINS SIQUEIRA
  • FARINALDO DA SILVA QUEIROZ
  • JAILSON SOUZA DE ALCANIZ
  • PAULO SÉRGIO RODRIGUES DA SILVA
  • Data: 08-abr-2022


  • Resumen Espectáculo
  • Right-handed neutrinos appear in several extensions beyond the Standard Model, specially in connection to neutrino masses.
    Motivated by this, we present a model of right-handed neutrino dark matter that interacts with Standard Model particles
    through a new gauge symmetry as well as via mass mixing between the new vector field and the Z boson, and investigate
    different production mechanisms. We derive the dark matter relic density in the Standard Cosmological Model, when the
    Hubble rate is faster than usual, when dark matter decouples in a matter domination epoch, and when it decouples in a
    radiation domination regime, which is then followed by a matter domination era. The direct detection rate features a
    spin-independent but velocity suppressed operators, as well as a spin-dependent operator when the mass mixing is correctly
    accounted for. We put all these results into perspective with existing flavor physics, atomic parity violation, and collider
    bounds. Lastly, we outline the region of parameter space in which a weak scale right-handed neutrino dark matter stands as a
    viable dark matter candidate.

7
  • RAABE MELO DE OLIVEIRA
  • Percolation in the Quantum Internet Network

  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • ERVIN KAMINSKI LENZI
  • LUCIANO RODRIGUES DA SILVA
  • RAFAEL CHAVES SOUTO ARAUJO
  • SAMURAÍ GOMES DE AGUIAR BRITO
  • Data: 06-may-2022


  • Resumen Espectáculo
  • The area of Network Science has drawn a lot of attention from the scientific community due to its importance and
    interdisciplinary, promoting the integration of several other fields of knowledge. This is mainly due to the fact that this area
    allows us to simulate real systems and formulate theoretical models about a wide range of phenomena. The Quantum Internet
    is included in a series of potential new applications, called Quantum Technologies 2.0. This type of technology, in theory, will
    revolutionize the way we communicate. In principle, the Quantum Internet is based on the conjecture of distributing
    entanglement between the sites that constitute it, with the aim of performing tasks that are not possible using the current
    Internet. This work provides a statistical analysis, through the Percolation Theory, of the Quantum Internet network.
    Percolation theory allows a simple and sophisticated description for a phase transition based on an order parameter. In this
    dissertation, we begin with a general presentation of the concepts and foundations of Network Theory and Percolation Theory,
    where our study is based. Then, we reproduce the Quantum Internet model through optical fibers (OFBQI) for𝜌= 0.0002,
    where𝜌is the density of sites in the network. Combining the concepts studied and the OFBQI model, we investigated the point
    at which a phase transition from the percolating network to a disconnected network occurs. We use as an order parameter the
    relative size of the largest percolating cluster,𝑚=𝑁𝐺/𝑁, where𝑁𝐺is the size of the largest connected component (a
    sub-graph) and𝑁is the size of the network. We show, through the Binder cumulative, that the fraction of sites removed that
    completely disconnects the network occurs in𝑓𝑐= 0.659, which turns out to be independent of the size of the system. Finally,
    we find the critical percolation exponents𝛽,𝛾,𝜈,𝜎,𝜏and the fractal dimension of the percolating cluster𝑑𝑓for the Quantum
    Internet Network.

8
  • GUSTAVO KAIQUE DA SILVA GUILHERME
  • Estudo das propriedades estruturais, magnéticas, e eletrocatalíticas de compósitos de Fe-W e Fe-Mo para aplicação na
    reação de evolução de oxigênio

  • Líder : MARCO ANTONIO MORALES TORRES
  • MIEMBROS DE LA BANCA :
  • ANDREA PAESANO JUNIOR
  • JOSE HUMBERTO DE ARAUJO
  • MARCO ANTONIO MORALES TORRES
  • Data: 30-may-2022


  • Resumen Espectáculo
  • The world energy demand grows year after year and because of the environmental impact of fossil fuels consumption, it is
    urgent the search for a sustainable energy source. Hydrogen is a great candidate for this post, but his large-scale production still
    faces some adversities. The cleanest way to produce this fuel is from the water electrolysis, which occurs through two half-
    reactions, the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The last one has slower kinetics,
    which makes the total process not efficient. Thus, it is important to chose the right catalyst, however, nowadays the frequently
    used cayalyst are based on rare and consequently more expensive materials, such as Pt and Ru. In this context, it is necessary
    to search for catalysts of cheaper materials. Therefore, this work is dedicated to the synthesis and analysis of the physical
    and electrochemical properties of Fe-W and Fe-Mo nanocomposites for application as OER catalyst. The nanocomposites were
    produced by the sol-gel method, their structural characterizations were performed through X-ray difraction (XRD), their
    magnetic properties studied by vibrating-sample magnetometry (VSM) and by Mössbauer spectroscopy (MS), and their
    electrochemical specicities were based on linear scan voltammetry (LSV), electrochemically active area (ECSA) and
    electrochemical impedance spectroscopy (EIS) measurements. Thus, for the system Fe-W, a nanocomposite containing two
    distinct phases was obtained, Fe and Fe6W6C, and for the system Fe-Mo a composite that has the metals Fe, Mo and possibly
    a non-homogeneous alloy of these two metals. The magnetic characterizations pointed to soft ferromagnetic materials, with
    low remanent and coercive elds. On the other hand, the electrochemical measurements showed to be promising because both
    composites presented overpotential values classied as ideal and very close to RuO2 in electrolysis in alkaline medium.

9
  • ZILMAR CANDIDO DE SANTANA JUNIOR
  • Testing the dark matter density evolution law with the large-scale structure

  • Líder : RODRIGO FERNANDES LIRA DE HOLANDA
  • MIEMBROS DE LA BANCA :
  • JOAO RAFAEL LUCIO DOS SANTOS
  • RAIMUNDO SILVA JUNIOR
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • Data: 09-jun-2022


  • Resumen Espectáculo
  • The main purpose of this work is to propose an observational test for the dark matter density evolution law. We allow a deviation from the standard law such as
    ρ_{DM}∝ (1+z)^{3+ε}, where ε = 0 recovers the canonical result. As observational sources, 40 measurements of the gas mass fraction of galaxy clusters on the
    interval 0.078 ≤ z ≤ 1.063 and 18 points of measurements of Baryon Acoustic Oscillations on the interval 0.11 ≤ z ≤ 2.4 were used.
    The Baryon Acoustic Oscillations data were used to infer the angular diameter distance to the galaxy clusters. From the statistical analyses,
    we obtained ε =0 within 2σ c.l., in full agreement with recent results that used other observational quantities. Our results are independent of a
    specific model of interaction in the dark sector.

10
  • DENNIS RODOLFO AQUILES BARBOSA LIMA
  • Random Braid Gates for Topological Quantum Circuits

  • Líder : DMITRY MELNIKOV
  • MIEMBROS DE LA BANCA :
  • ALEKSANDR NIKOLAIEVICH PINZUL
  • DMITRY MELNIKOV
  • FRANCESCO TOPPAN
  • RODRIGO GONCALVES PEREIRA
  • THIAGO SIMONETTI FLEURY
  • Data: 25-jul-2022


  • Resumen Espectáculo
  • Abelian anyons are many-body states of electrons characterized by a permutation phase between 0 and π. The non-abelian
    generalization of this concept was proposed by Kitaev to make fault-tolerant quantum computers. For non-abelian anyons,
    the phased permutation operators give rise to matrix representations of the permutation group, among them the braid
    groups. Knot Theory and Braid Group have all the tools that are needed to build quantum braid circuits. Taking advantage of
    existing technologies of study of transport properties of interacting systems, we use the T-matrix formalism to analyze
    random T-matrix models and random R-matrix models as circuits of random braids. A special attention is given to Chalker-
    Coddington’s percolation model and renormalization approaches that rely on solving systems of linear equations or
    performing tensor contractions. As a simple example we introduce a quasi-1D random braid model in polynomial
    representation and analyze its transmission probability distribution.

11
  • JEDSON FERNANDES DE AMORIM
  • Light Propagation in Quasiperiodic Cylindrical Systems With Graphene

  • Líder : DORY HELIO AIRES DE LIMA ANSELMO
  • MIEMBROS DE LA BANCA :
  • DORY HELIO AIRES DE LIMA ANSELMO
  • CLAUDIONOR GOMES BEZERRA
  • MANOEL SILVA DE VASCONCELOS
  • JOAO MILTON PEREIRA JUNIOR
  • Data: 16-ago-2022


  • Resumen Espectáculo
  • In this work, we will focus on the analysis of transmittance, reflectance, and absorption spectra of light in cylindrical quasiperiodic structures with and without graphene. In chapter one we introduce some remarkable developments in photonic crystals, semiconductors, and the concept of quasicrystals. In chapter two we will make a review of Fibonacci, Octonacci, Double—Period, and Thue--Morse sequences, and how the concept of quasiperiodic crystals arose mainly due to Dan Shechtman's work. We also review graphene's main properties and finish the chapter by showing relevant works in the area of light propagation through cylindrical photonic crystals. In chapter three we develop a general transfer-matrix method in cylindrical geometry using Maxwell's equations, which is particularized to TE or TM modes, and in the cases with and without a conductor that obeys Ohm's law. Afterwards, in chapter four we use the mathematical model of the earlier chapter and make an analysis of transmittance, reflectance, and absorption spectra for both TE and TM modes, with embedded graphene and without graphene at all. Finally, in the last chapter, we will make some conclusions about the results of the Cylindrical Photonic Quasiperiodic Crystals analyzed, possible applications, and perspectives of study on this topic.

12
  • DASAEV OLIVEIRA FONTINELE
  • ON THE RELATIONS BETWEEN HABITABLE ZONE AND CIRCUNSTELLAR DEBRIS DISK

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • HELOISA MARIA BOECHAT-ROBERTY
  • Data: 20-dic-2022


  • Resumen Espectáculo
  • There are several studies related to the presence of debris disk with metallicity, rotation and age of stars. However, little is
    known in the literature about the relationship between the presence of a debris disk and the circumstellar habitability zone and
    how the range of the habitability zone affects the disk. To carry out this work, we selected the main catalog of (Cotten & Song
    2016), this catalog contains 507 stars showing potential excess infrared, without ambiguities, from observations made with the
    WISE satellite.
    For a better understanding of the profile of the stars present in the catalog, the Cor-Magnitude GAIA was built, based on the
    methodologies of (Messias et al. 2022) and (Gordon et al. 2021), for the exhibition of the work. We can see in this diagram that
    only 171 stars belong to the Main Sequence, this selection was made due to the evolutionary stage of the stars, it is susceptible
    to important biases, which can influence the results obtained. With the sample of Main Sequence stars, the (Kopparapu et al.
    2014) model was applied to calculate the Circumstellar Habitability Zones. As this model has a temperature limit of 2700K to
    7200K, only 83 stars fall within the approached limit. By calculating the distance from the habitability zone, it was possible to
    separate the sample into 3 small groups: stars that have a debris disk radius greater than the outer radius of the conservative
    ZH; stars that have the radius of the debris disk inside the conservative ZH; stars that have a debris disk radius smaller than the
    inner radius of the conservative ZH. Finally, we compare our results with the mean radius of the asteroid belt in order to
    observe systems with architecture similar to the solar one.

Tesis
1
  • RONIEL DE LIMA ARAÚJO
  • Studies of the structural, electronic, optical, vibrational and thermodynamic properties of neurotransmitters and levodopa
    in the DFT formalism.

  • Líder : UMBERTO LAINO FULCO
  • MIEMBROS DE LA BANCA :
  • ANTONIO DE MACEDO FILHO
  • CARLOS ANTONIO BARBOZA
  • DORY HELIO AIRES DE LIMA ANSELMO
  • EUDENILSON LINS DE ALBUQUERQUE
  • LUCIANO RODRIGUES DA SILVA
  • MARCELO LEITE LYRA
  • UMBERTO LAINO FULCO
  • Data: 18-feb-2022


  • Resumen Espectáculo
  • In this work, we will present a study of the structural, electronic, optical, vibrational and thermodynamic properties of the
    crystals of dopamine, l-dopa, noradrenaline and adrenaline, through computer simulations in the DFT formalism (Density
    Functional Theory), where the generalized gradient approximation (GGA-PBE) and the hybrid functional HSE06 were used.
    From the experimental data of the four crystal structures, the optimization of the crystal geometry, calculation of the density of
    states and band structure, optical absorption, dielectric function, refractive index, optical conductivity, reflectivity, loss
    function, infrared and Raman spectrum and also Debye temperature, enthalpy, free energy, T*entropy and heat capacity were
    performed. The new lattice parameters found showed good agreement with the experimental values. Through the functional
    GGA-PBE (HSE06), we found that: dopamine presented an indirect band gap E=3.8 eV (4.70 eV), for noradrenaline we
    obtained an indirect band gap E=3.48 eV (4.40 eV), for adrenaline an indirect band gap E=3.53 eV (4.60 eV) and a direct band
    gap E=3.09 eV (3.60 eV) was obtained for the l-dopa crystal. The analysis of the densities of electronic states made it possible
    to identify the contributions per atom to the states of the valence and conduction bands. In the optical properties,it is possible
    to observe an absorption of light in the ultraviolet region, and a greater sensitivity in the absorption of polarized radiation in the
    100 direction, for dopamine, noradrenaline and l-dopa, while adrenaline presents a greater absorption ofpolarized light with
    the polarization direction 001. IR and Raman spectra werecalculated,and vibration modes analyzed. The thermal capacity at
    room temperature found was: 210.01 cal/cell.K, 121 cal/cell.K, 182 cal/cell.K and 103 cal/cell.K, for dopamine,l-dopa,
    noradrenaline and adrenaline, respectively.

2
  • WAGNER DE ALMEIDA BARBOSA
  • TARGET-ORIENTED FULL WAVEFORM INVERSION BASED ON PATCHED GREEN'S
    FUNCTION METHOD AND RENY'S STATISTICS

  • Líder : JOAO MEDEIROS DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • CLAUDIONOR GOMES BEZERRA
  • GILBERTO CORSO
  • JOAO MEDEIROS DE ARAUJO
  • MARCOS ANTONIO ANACLETO
  • MAURO SANTOS FERREIRA
  • Data: 10-mar-2022


  • Resumen Espectáculo
  • We propose an efficient methodology for the complete version of the wave oriented to atarget area through
    the Patched Green’s Function-(PGF) method. The method consists of separating the velocity model into
    two regions of interest, “external” and “target” regions. When trying the verylarge system it can be
    considered as projected arrays. In addition, we address a situation in whichthe observed data is
    contaminated with noise. In this scenario, we formulate a FWI rubased on themaximization of the
    Reney statistic together with the PGF method, we build a robust objective function in this scenario scenario.
    Results relevant to the results obtained with the results-based version of the FWI, based on the results
    obtained with the PGF methodology, related to the results obtained with the results-based method of the
    FWI based on the results statistics based on the FWI, especially not -Gaussians. The main advantage of the
    PGF method is that it is able to optimize the approximate methods of thecontinuous method in each ideal
    method, it is worth emphasizing that mathematically the PGF methodis mathematically exact and does not
    involve the PGF method is thus a computationally approximated cost to precision, robust of the FWI based
    in the Reney statistic to data with non-Gaussian noise, it maybe related to the entropic index, especially for
    the value ofα→2/3.

3
  • ALLYSON IRINEU ARAÚJO LIMA
  • Investigação de propriedades de transporte eletrônico e caracterização multifractal de bandas de energias de sequências GA no DNA humano

  • Líder : MANOEL SILVA DE VASCONCELOS
  • MIEMBROS DE LA BANCA :
  • ANTONIO DE MACEDO FILHO
  • CLAUDIONOR GOMES BEZERRA
  • DAVID LIMA AZEVEDO
  • DORY HELIO AIRES DE LIMA ANSELMO
  • MANOEL SILVA DE VASCONCELOS
  • UMBERTO LAINO FULCO
  • Data: 22-mar-2022


  • Resumen Espectáculo
  • In this work, we analyze the location and fractal properties of  the energy spectrum in a genomic system, formed by seven types of pure GA sequences (G-Guanine and A-Adenine) found on human  chromosome 7. We use 2 methods to find the Hamiltonian solutions in the tight-binding approximation: transfer matrix and negative eigenvalue method developed by Dean.

    Through the transfer matrix method we obtained: Energy diagram, Electronic Transmittance Spectrum and Lyapunov Coefficient. By means of the negative eigenvalues method, we determined: Energy Diagram and Electronic Density of States.

    The investigation of the multifractal behavior of energy bands took place  through the singularity spectrum f(α), which was calculated using an algorithm based on the theorems of Shannon, Eggelston and Billingsley, in addition, by the study of law of potency. In our results, the Energy Diagram revealed a fractal behavior similar to the Cantor random set. Comparing all the  sequences studied here, the results of the multifractal analysis of energy band distributions showed typical behavior of

    multifractal systems (spectrum with inverted parabola shape).

4
  • JOSÉ JAYSON XAVIER DE SOUSA
  • CoFe2O4@BiFeO3 Nanoparticles: Synthesis, Characterization and Signatures of Spin Disorder

  • Líder : FELIPE BOHN
  • MIEMBROS DE LA BANCA :
  • CLAUDIONOR GOMES BEZERRA
  • FELIPE BOHN
  • FERNANDO LUIS DE ARAUJO MACHADO
  • JOÃO MARIA SOARES
  • MARCO ANTONIO MORALES TORRES
  • RODOLFO BEZERRA DA SILVA
  • Data: 13-abr-2022


  • Resumen Espectáculo
  • Nanoscale magnetic systems, such as ferrites, perovskites and core@shell structures, are a group of promising materials, due to their vast technological potential and the possibility of advancing the understanding of fundamental physics related to nanoscale materials. Taking this into account, we synthesize CoFe2O4@BiFeO3 core/shell nanoparticles by coprecipitation and systematically investigate the structural, morphological, and magnetic properties in such nanostructured system. Through structural and morphological characterization, we demonstrate the obtainment of core@shell nanostructure with pure phases. By performing a broad experimental magnetic analysis, we evaluate the magnetic response for the precursor phases, as well as for the core@shell nanostructure. For this latter, we identify fingerprints of the wasp-waisted behavior and exchange bias effect, disclosing the exchange coupling between the phases taking place at the interface. Further, we reveal the exchange coupling between core and shell is strongly affected by a spin glass behavior arisen from the spin disorder in the CoFe2O4@BiFeO3 core/shell nanoparticles. After all, our findings allow us to place the used procedures taking into account the processes of adapted coprecipitation and calcination as a feasible route to the production of high-quality core@shell nanostructures. However, in order not to be bound by a single method, core@shell samples CoFe2O4@BiFeO3 with three core sizes and their precursors were synthesized through hydrothermal synthesis. This second set of samples also showed promising results, as the material obtained showed pure phases for all samples and strong indications of magnetic coupling between the phases that make up the core and the shell, indicating great efficiency of the hydrothermal method.

5
  • JOÃO GUSTAVO DA SILVA SANTOS
  • Analysis of themechanisms of magnetic relaxation in bilayers through the magnetoimpedance effect

  • Líder : MARCIO ASSOLIN CORREA
  • MIEMBROS DE LA BANCA :
  • JOSÉ FILIPE VILELA VAZ
  • ANTONIO AZEVEDO DA COSTA
  • EDIMILSON FÉLIX DA SILVA
  • LEONARDO DANTAS MACHADO
  • MARCIO ASSOLIN CORREA
  • MATHEUS GAMINO GOMES
  • Data: 29-abr-2022


  • Resumen Espectáculo
  • The manipulation and transport of electronic spin angular momentum has been used in the development of high
    performance devices. In this context, the magnetic thin film emerges as a promising candidate for the fabrication of sensor
    elements, as it presents a stability of magnetic properties, even in increasingly reduced dimensions. Therefore, knowing well the
    phenomena involved in the dynamics of magnetization of this type of material is an important step for the development of
    technology and science. Thus, our work was divided into two converging lines of investigation, where the essence of research in
    these two branches has in common a global objective; to study the mechanisms of magnetic relaxation in samples structured in
    bilayers using the magnetoimpedance technique. We focused on finding the effective damping parameter of the samples and
    understandinghoweachtypeofmagneticrelaxationmechanismcontributedtotheinvestigatedsystemviathe
    magnetoimpedance effect. However, this research presented a great challenge, as it brings innovations in the way of investigating
    the dynamics of magnetization in an insulating material through the magnetoimpedance effect. This technique ensures the broad
    characterization of magnetization dynamics in ferrimagnetic insulating material, making it possible to analyze the behavior of
    magnetization with respect to frequency sweep and external magnetic field simultaneously. With the success of this research, we
    consolidated the implementation of a technique that investigates the dynamics ofmagnetization in ferromagnetic insulating
    materials

6
  • MILTON GOMES DE SOUZA NETTO
  • Relativistic gravitational redshift in a stellar environment and open cluster kinematics - M67, a unique laboratory

  • Líder : IZAN DE CASTRO LEÃO
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • HELIO JAQUES ROCHA PINTO
  • IZAN DE CASTRO LEÃO
  • JAILSON SOUZA DE ALCANIZ
  • JOSE RENAN DE MEDEIROS
  • RAIMUNDO SILVA JUNIOR
  • Data: 02-may-2022


  • Resumen Espectáculo
  • Stellar clusters provide key information for studying from stellar origins to the Galactic structure, and even for fundamental
    physics tests. In particular, Messier 67 (M67) is an important open cluster because it has similar metallicity and age to the Sun.
    We present an observational study of different phenomena that can affect radial velocity (RV) measurements of stars
    belonging to M67, for solving information about the cluster kinematics, as well as for a unique test of General Relativity.
    Based on a recent technique, the difference between two independent RV measurements, spectroscopic and astrometric, of
    stars belonging to a given cluster, allows empirically detecting, for example, the cluster’s global movement and the
    gravitational redshift predicted by General Relativity. Spectroscopic and astrometric RV measurements were obtained from
    public archives of the HARPS spectrometer and the Gaia satellite, respectively. Two initial samples, of 1278 and 144 stars,
    were carefully selected, resulting in a final sample of 74 stars. We detected quantitatively the gravitational redshift (GR) in
    M67, thus adding a new support to the General Theory of Relativity. We also detected for the first time an apparent rotational
    (or shear) motion of M67, with a rotation gradient of ~ 66 m/s/pc. With these results, a new database with RV values
    representing unbiased measurements are provided as a by-product of this Thesis. Finally, we calculated from newer data a
    virial mass of 1980 +/- 100 M and a tidal radius of 14.2 +/- 0.3 pc for M67, in agreement with previous estimates. Overall, the
    empirical determination of the cluster rotation is very useful for kinematic studies, either of the cluster itself or on its relation
    with the Galactic structure. In addition, the present study contributes to fulfilling a gap among the tests of General Relativity,
    since this theory has been little tested in stellar environments.

7
  • RUTE MELO DE OLIVEIRA
  • Connecting geographical complex networks q-Statistical

  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • CONSTANTINO TSALLIS
  • JOAO MEDEIROS DE ARAUJO
  • JOSÉ SOARES DE ANDRADE JÚNIOR
  • LUCIANO RODRIGUES DA SILVA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • SAMURAÍ GOMES DE AGUIAR BRITO
  • Data: 13-may-2022


  • Resumen Espectáculo
  • Networks are abound in nature, therefore, Network science is a very interdisciplinary theory and has been
    widely successfully used to study huge connected systems. The nonextensive statistical mechanics
    naturally emerge from the limitations of the BoltzmannGibbs statistic, being capable to describe systems
    in the regimes where the standard statistical mechanics fails. Nowadays the connections between these
    two areas are well known. In this thesis we study a d-dimensional geographically located network
    (characterized by the index αG ≥ 0; d = 1, 2, 3, 4) whose links are weighted through a predefined random
    probability distribution, namely P(w). In this model, each site has an evolving degree ki and a local
    energy εi ≡ Pki j=1 wij/2 (i = 1, 2, ..., N) that depend on the weights of the links connected to it. At the
    thermodynamic limit, the energy distribution is the form p(ε) ∝ exp(−βqε)_q , where exp(z)_q is the q-
    exponential defined by exp(z)_q ≡ [1 + (1−q)z] 1/(1−q) which optimizes the non-additive entropy Sq and
    when q → 1 the Boltzmann-Gibbs entropy is recovered. The parameters q and βq depends only on αA/d,
    thus exhibiting universality. Also, we provide here strong numerical evidence that a isomorphism appears
    to emerge connecting the energy q-exponential distribution (with q = 4/3 and βqω0 = 10/3) with a specific
    geographic growth random model based on preferential attachment through exponentially-distributed
    weighted links.

8
  • CARLOS AUGUSTO DE MORAES IGLESIAS
  • Uma investigação sobre a existência de desigualdades fundamentais em processos magnéticos no regime linear

  • Líder : FELIPE BOHN
  • MIEMBROS DE LA BANCA :
  • FELIPE BOHN
  • MARCIO ASSOLIN CORREA
  • SUZANA NOBREGA DE MEDEIROS
  • EDIMILSON FÉLIX DA SILVA
  • JOAO PAULO SINNECKER
  • FERNANDO LUIS DE ARAUJO MACHADO
  • RUBEM LUÍS SOMMER
  • Data: 24-jun-2022


  • Resumen Espectáculo
  • The study of nanostructured materials, more specifically, magnetic nanoparticles systems, is a topic challenging the scientific community. Such systems, besides presenting very interesting properties from the point of view of fundamental physics, such as superparamagnetism, superferromagnetism and spin glass, are of multidisciplinar interest due to their huge potential in nanotechnology and biotechnology applications. Specifically, biomedical applications, such as magnetic hyperthermia therapies, require the use of nanoparticles with reduced dimensions under the action of low amplitude alternating magnetic fields. In this context, the so-called Linear Response Theory (LRT) receives enormous attention, since it corresponds to an excellent candidate for the description of processes in the low fields regime. Furthermore, fundamental parameters of magnetic systems that are extremely important for maximizing the efficiency of nanoparticles in medical and technological applications, such as magnetic susceptibility, are obtained within the validity limits of this theory. In this thesis we investigate the existence of fundamental limits and inequalities in magnetic processes in which nanoparticle systems are under the action of low amplitude magnetic fields, that is, in processes in which the Linear Response Theory proves to be valid. First, considering magnetic processes in thermodynamic equilibrium, we find inequalities associated to the equilibrium magnetic susceptibility, saturation magnetization and effective anisotropy constant in blocked magnetic nanoparticles systems. By means of an experimental evaluation, using a sample of barium hexaferrite nanoparticles (BaFe12O19), we verify that such inequalities, in fact, are not violated. Still in the context of equilibrium processes, we show that the inequality found for the susceptibility in blocked nanoparticles must also be valid for non-interacting superparamagnetic systems. Through the evaluation of the experimental results obtained in superparamagnetic systems of magnetite (Fe3O4), magnesium ferrite (MgFe2O4) and zinc ferrite (MgFe2O4), we verify that this inequality is violated in all cases, a fact that we believe to be a signature of the existence of correlations mediated by exchange forces between nanoparticles within the systems. Next, considering dynamic processes, we also obtain inequalities associated to the real and imaginary components of the dynamic susceptibility in addition to the power limit that can be generated through the interaction of alternating magnetic fields with superparamagnetic nanoparticles. In order to evaluate the validity of our theoretical approach also for magnetodynamic processes, we carry out calorimetric procedures under alternating magnetic field effect using the same superparamagnetic samples considered in the equilibrium processes and verify the total agreement of the experimental results with our theoretical expectations. In summary, in this thesis we unequivocally demonstrate the existence of fundamental inequalities that limit the behavior of magnetically blocked and superparamagnetic non-interacting nanoparticle systems in addition to the implications of their violations. Such results are promising tools for maximizing the efficiency of magnetic nanoparticles in biotechnological and biomedical applications since they elucidate the real impacts of effects that are still poorly understood in the literature, such as the effect of inter-particle interactions in magnetic processes.

9
  • JOSÉ ROBERTO DA SILVA
  • Electronic transport in quasi-periodic nanostrutrures

  • Líder : LUIZ FELIPE CAVALCANTI PEREIRA
  • MIEMBROS DE LA BANCA :
  • JONAS ROMERO FONSECA DE LIMA
  • CLAUDIA GOMES DA ROCHA
  • ANDERSON LUIZ DA ROCHA BARBOSA
  • LEONARDO DANTAS MACHADO
  • LUIZ FELIPE CAVALCANTI PEREIRA
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 29-jun-2022


  • Resumen Espectáculo
  • In this work the electronics and transport properties of Fibonacci superlattice formed by nanostructures with quasi-periodic perturbations are investigated. The calculations of transport are based in the recursive method of Greens function (RGF) within of the ap- proximation tight binding (TB). In our calculations we explore neighbors first and second interaction. In ours models we try to investigate linear, double chain and graphene nano- ribbons. Two types of perturbations are investigated. The first consist in quasi-periodic perturbation by substitutional doping (PQD). The second is featured by modulation of the Fermi velocity (MVF). In both the cases the perturbations are achieved by replication of pure and defectives blocks in the central part of the structure. Ours results show that the replication of the blocks in the scattering center reduces substantially the conduc- tance, producing a series of dips that are inducing to gaps in determined energy level. This behavior is characteristic of systems in strongly localized regime. In some situations we demonstrate that theses gaps are induced by a Anderson localization regime. This effect occurs due to interference and to electronic confinement that leads to quasi-bound states. Theses states are clearly observed in the calculation of the local states density (LDOS). Besides that, we show that the modulation these perturbations provoke effects different in armchair and zigzag nanoribbons. We show too that the transport properties can to be tuned continuously by variation quasiperiodic of the length of the central part. Additionally, the results obtained in this work can to provide a new approach for the study of the control of the electronic response of one-dimensional nanostructures.

10
  • LUCAS MARQUES DA SILVA
  • Study of the influence of doping and coupling of magnetic phases on the (BH)max of BaFe12O19

  • Líder : JOSE HUMBERTO DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • JOSE HUMBERTO DE ARAUJO
  • FELIPE BOHN
  • MARCO ANTONIO MORALES TORRES
  • JOSÉ FERNANDO MORAIS LOPES MARIANO
  • ANDREA PAESANO JUNIOR
  • Data: 01-jul-2022


  • Resumen Espectáculo
  • The M-type barium hexaferrite (BaFe12O19), an iron oxide with hexagonal geometry, is a material that play an important technological role in applications such as permanente magnets, microwave devices and magnetic recording. In this work, we study the influence of two experimental approaches used to improve the maximum energy product, (BH)max, of barium hexaferrite: doping with lanthanum (La) and cobalt (Co), and the coupling of magnetic phases. In the first one, we produced samples of barium hexaferrite, using the Ionic Coordination Reaction (ICR) method, doped with a fixed amount of La and a variable amount of cobalt, Ba0.7La0.3Fe12-xCoxO19, x = (0.0, 0.25, 0.50, 0.75 and 1.0). In the second, through the polyol process, we coated samples of pure and impurity-free barium hexaferrite (also obtained by the ICR method) with superparamagnetic nanoparticles of cobalt ferrite (CoFe2O4), obtaining coupled nanocomposites of BaFe12O19/CoFe2O4 with

    different proportions. Then, these samples were submitted to a reductive process in a hydrogen atmosphere, where there was a partial reduction of cobalt ferrite, giving rise to a new nanocomposite of the BaFe12O19/CoFe2O4@CoFe2 type. These samples were characterized by the use of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), as a function of magnetic field and temperature and Mössbauer spectroscopy. In the first approach, XRD measurements showed the presence of a small amount of α-Fe2O3 in the doped samples. The SEM images revealed a morphology like nanorod, smaller than the critical limit for single-domain particles. Optimized magnetic properties were achieved for the sample with concentration of Co x = 0.25. Furthermore, this sample displayed the highest value of (BH)max of 6.98 kJ/m3 (0.877 MGOe), which corresponds to a significant improvement of 8% over the pure sample. For the second approach, XRD analyzis revealed the presence of two phases, BaFe12O19 and CoFe2O4, for the as prepared nanocomposites, and three phases, BaFe12O19, CoFe2O4 and CoFe2, for the nanocomposites after reduction. The TEM micrographs showed that the different phases are structurally coupled. Magnetization (Mr) and remanent demagnetization (Md) measurements were performed at room temperature. Through Mr and Md it was possible to make the Henkel and δm plots of the nanocomposites that provided information about the nature of the interactions between the phases and about the magnetic behavior. We detected a coupling of the exchange-spring type between the phases of the nanocomposites.

11
  • JOSIAS VALENTIM SANTANA
  • Effects of radiative transfer on different techniques for tracking the magnetic field in the interstellar medium

  • Líder : IZAN DE CASTRO LEÃO
  • MIEMBROS DE LA BANCA :
  • IZAN DE CASTRO LEÃO
  • BRUNO LEONARDO CANTO MARTINS
  • JOSE RENAN DE MEDEIROS
  • CARLOS EDUARDO FERREIRA LOPES
  • DANIEL BRITO DE FREITAS
  • Data: 14-jul-2022


  • Resumen Espectáculo
  • Stellar clusters provide key information for studying from stellar origins to the Galactic structure, and even for fundamental
    physics tests. In particular, Messier 67 (M67) is an important open cluster because it has similar metallicity and age to the Sun.
    We present an observational study of different phenomena that can affect radial velocity (RV) measurements of stars
    belonging to M67, for solving information about the cluster kinematics, as well as for a unique test of General Relativity.
    Based on a recent technique, the difference between two independent RV measurements, spectroscopic and astrometric, of
    stars belonging to a given cluster, allows empirically detecting, for example, the cluster’s global movement and the
    gravitational redshift predicted by General Relativity. Spectroscopic and astrometric RV measurements were obtained from
    public archives of the HARPS spectrometer and the Gaia satellite, respectively. Two initial samples, of 1278 and 144 stars,
    were carefully selected, resulting in a final sample of 74 stars. We detected quantitatively the gravitational redshift (GR) in
    M67, thus adding a new support to the General Theory of Relativity. We also detected for the first time an apparent rotational
    (or shear) motion of M67, with a rotation gradient of ~ 66 m/s/pc. With these results, a new database with RV values
    representing unbiased measurements are provided as a by-product of this Thesis. Finally, we calculated from newer data a
    virial mass of 1980 +/- 100 M and a tidal radius of 14.2 +/- 0.3 pc for M67, in agreement with previous estimates. Overall, the
    empirical determination of the cluster rotation is very useful for kinematic studies, either of the cluster itself or on its relation
    with the Galactic structure. In addition, the present study contributes to fulfilling a gap among the tests of General Relativity,
    since this theory has been little tested in stellar environments.

12
  • JAILSSON SILVA LIMA
  • Mechanical properties of carbon and boron nitride nanostructures: a molecular dynamics study

  • Líder : LEONARDO DANTAS MACHADO
  • MIEMBROS DE LA BANCA :
  • LEONARDO DANTAS MACHADO
  • DORY HELIO AIRES DE LIMA ANSELMO
  • MADRAS VISWANATHAN GANDHI MOHAN
  • ALEXANDRE FONTES DA FONSECA
  • SERGIO ANDRÉ FONTES AZEVEDO
  • Data: 08-ago-2022


  • Resumen Espectáculo
  • The discovery of graphene and its exceptional properties has motivated research on two-dimensional (2D) materials for over a decade. Since then, several other 2D materials with diverse properties have been discovered, such as hexagonal boron nitride (h-BN). More recently, two-dimensional materials have been combined into hybrid structures, leading to the creation of solids with adjustable properties. In this document, the mechanical properties of hybrid nanostructures composed of graphene and h-BN were investigated using classical molecular dynamics. Two types of arrangements were considered: (i) square sheets of graphene containing circular and hexagonal h-BN domains and (ii) square sheets of h-BN containing circular, hexagonal, triangular and double triangular graphene domains. The results obtained here show that, for both types of structures, the Young's modulus of the hybrid structure depends essentially on the fraction of h-BN and graphene in the structure, with Young's modulus values decreasing linearly as the concentration of h-BN increases in (i) and increasing with increasing graphene in (ii). We also analyze the temporal evolution of the fracture patters and of the stress concentration during the simulations. From this analysis we conclude that the fracture always starts in the interface region between graphene and h-BN, because it was found that the B-C and C-N bonds are weaker than the C-C and B-N bonds. Finally, we observe for both types of arrangements that the mechanical properties of the hybrid structures are not altered when the sheet length and the domain diameter are increased proportionally. This indicates that our results may be valid for much larger structures than those tested here, such as those that are synthesized experimentally.

13
  • YGOR PARÁ SILVA
  • Effects of Curvature in Two - Dimensional Condensed Matter Systems

  • Líder : TOMMASO MACRI
  • MIEMBROS DE LA BANCA :
  • LEO GOUVEA MEDEIROS
  • RODRIGO GONCALVES PEREIRA
  • TOMMASO MACRI
  • VAN SÉRGIO DA SILVA ALVES
  • VÍVIAN VANESSA FRANÇA HENN
  • Data: 23-ago-2022


  • Resumen Espectáculo
  • The influence of curved background on the properties of Condensed Matter systems is a significant question for a broad class of physical applications. They catch the curiosity of people because of their interesting features in a rich interface between many research areas. In this thesis we introduce an analytically solvable model of Dirac fermions with imaginary mass on the sphere. We show the existence of an infinite sequence of exceptional points (EP), which depend on the radius (curvature) of the sphere. We employ quench dynamics to characterize curvature-dependent Non-Hermitian phase transitions. We demonstrate that the existence of singular points of the Loschmidt echo and the fidelity are an unambiguous signature of geometric EPs that distinguish between different phases of the model. Also, we use numerical techniques to solve the Bose-Hubbard hamiltonian that simulates the hyperbolic geometry. In this system, we attempt to verify whether we can observe a bound-states comprising a pair of atoms in the presence of repulsive interactions in a hyperbolic lattice. This system is a playground to simulate a space with negative curvature, that is difficult to simulate in a euclidean space without distortions.

14
  • ROSEANE DE LIMA GOMES
  • On the nature of photometric variability in TESS stars with planetary transits

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • CARLOS EDUARDO FERREIRA LOPES
  • DANIEL BRITO DE FREITAS
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • Data: 01-nov-2022


  • Resumen Espectáculo
  • Different space missions are revolutionizing our understanding of stellar variability, revealing a new view of dynamic phenomena associated with stars in different regions of the HR diagram. Furthermore, environments with planet-hosting stars have proved to be complex and primordial laboratories for the understanding of star-planet relationships, where much of the information about this interaction is revealed by the photometric behavior of the star including rotation, pulsation and transient events. Rotation is a parameter that can be characterized by the detection of spots on the surface of the star and plays, in fact, an important role in controlling stellar evolution and in a potential scenario of planetary habitability. In this sense, the study of periodicities in stars with planets, from photometric observations, such as those associated with the KEPLER and TESS missions, opens new perspectives for the study of different stellar properties, including rotation and magnetic activity. In this work, we carried out a search for signatures of photometric variability in the light curves of 2215 TOI's (Tess Objects of Interest) stars with planets discovered by the TESS telescope, via planetary transit. For objects with clear photometric modulation, we determined their periodicities by applying the BLS, FFT, Lomb-Scargle and Wavelet techniques. The results of this analysis are described in Canto et al. (2020), where, from the total of 2215 stars, we found 289 TOI's with rotation signature, 13 TOI's with pulsation signature subdivided into 5 different classes, 316 TOI's with ambiguous variability, 1586 TOI's with low signal-to-noise ratio and 11 eclipsing binary TOI's. We studied the Porb / Prot × Porb distribution of stars with rotation signature and identified a possible synchronicity between the rotational period and the orbit of the innermost planet for some of them. In addition, in this subsample we found 30 stars that present eruption events, a phenomenon of great importance in the study of planetary habitability, as they are events that can impact the development and continuity of biological activity. Likewise, recent studies on pulsating stars have shown that carbon, one of the fundamental elements for the existence of life, may be being released into the interstellar medium through these variables, which makes our subsample of 13 TOI's more interesting as they are targets with potential planets. Finally, we made a solid characterization of the evolutionary state of the analyzed stellar sample, from a Color-Magnitude Diagram with data from GAIA, and we identified 1511 stars as probable members of the Main Sequence (MS) and 546 evolved stars, which reveals us that the distribution of our sample is predominantly from MS, including stars with rotation signature.

15
  • GESIEL RODRIGUES DA SILVA NETO
  • Spherically symmetric solutions and inflation in higher-derivative theories of gravity

  • Líder : LEO GOUVEA MEDEIROS
  • MIEMBROS DE LA BANCA :
  • EMANUELE ORAZI
  • ILYA LVOVICH SHAPIRO
  • JAILSON SOUZA DE ALCANIZ
  • LEO GOUVEA MEDEIROS
  • RAIMUNDO SILVA JUNIOR
  • Data: 18-nov-2022


  • Resumen Espectáculo
  • Extensions of general relativity in which higher-order curvature corrections are included in Einstein-Hilbert's action have received increasing attention mainly by model building in high-energy physics --- string theory and quantum gravity --- and in the accelerated expansion of the very early universe. In this PhD thesis, we proposed a higher-order gravity, characterized by the inclusion of all correction terms up to the second-order involving the Ricci scalar. From then on, we approached two topics of interest. The first topic concerns the investigation of spherically symmetric solutions, where we explored weak-field regime and black hole solutions. We obtained all solutions in the weak-field regime and also addressed the issue of the possibility of existence of non-Schwarzschild black hole solutions. In turn, the second topic involves research in the context of cosmic inflation, motivated by the success of the Starobinsky model. In this sense, we developed a detailed research of Starobinsky+$R^{3}$ and Starobinsky+$R^{3}+R\square R$ inflationary models, confronting them with the most recent observational data from the Planck satellite and the BICEP3/Keck Array.

16
  • JOÃO MARCELO MACHADO
  • A study on magnetic activity and rotation of M dwarf stars from Kepler, K2 and TESS missions

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • RAIMUNDO SILVA JUNIOR
  • ADRIANA BENETTI MARQUES VALIO
  • MARCELO EMÍLIO
  • Data: 12-dic-2022


  • Resumen Espectáculo
  • Despite being the most abundant stars in the Galaxy, M dwarfs are one of the least known objects in terms of their physical properties, especially regarding its magnetic activity and the underlying dynamo mechanism. Thus, a broad study on different activity diagnostics and their relationship with stellar rotation is necessary. In this work we performed a spectroscopic survey of 122 M dwarfs present in the Southern Continuous Viewing Zone (CVZ) of the TESS space mission, based on

    observations with the Gemini and SOAR telescopes. We obtained at least one optical spectrum for each star, with R ≈ 2000, from which we measured the chromospheric emission in the Hα line. Our sample has 21 stars with measured rotation periods (������������ ), of which 12 were determined in this work from TESS light curves. The active fraction of the stars in our sample is consistent with that expected for field M dwarfs, confirming that late spectral-type stars generally remain active longer than early-type stars. Two stars presented enough rotation to be considered magnetically saturated, although they are at activity levels below the saturation region in the rotation-activity diagram, indicating the possibility that M dwarfs with short periods also present inactivity in Hα. We also analyzed a sample of 1788 field M dwarfs from Kepler and K2 missions, for which we investigated the distributions of ������������ and the photometric activity index ������, associated with the standard deviation of the light curve, using color-magnitude diagrams with accurate distance and magnitude data from Gaia mission. We note that the stars with the highest values of ������ in the sample (≳ 10000 ppm) are in general very young, with isochronal ages ≤ 50 Myr. We

    compared the photometric index with canonical chromospheric and coronal activity indicators in order to validate it as a proxy

    for magnetic activity in low-mass stars. Based on this index, we also studied the rotation-activity diagram, taking into account the transition to fully convective stars (≈ 0.35 ���), where we noticed the same distribution between these stars and those partially convective in both saturated and unsaturated regimes, suggesting a solar-like dynamo behavior, even for stars without

    the presence of a tacocline

2021
Disertaciones
1
  • JONATHAN PESSOA CORREIA
  • Size distribution of human DNA encoding via information theory

  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • RAIMUNDO SILVA JUNIOR
  • DORY HELIO AIRES DE LIMA ANSELMO
  • ANTONIO DE MACEDO FILHO
  • Data: 12-feb-2021


  • Resumen Espectáculo
  • We analyze the coding sequence for the Homo Sapiens via a model that naturally embraces correlations among the
    bases in DNA sequences of living organisms. The model is based on the Shannon entropy's optimization, which is the core of all statistical arguments. As a result, we propose the double-exponential law distribution function of the length of DNA measured in base pairs (bp). The results show that the Short-Range-Correlations (SRC), always present in coding DNA sequences, are appropriately captured through the double-exponential distribution and adequately describes the cumulative length distribution of DNA bases. Based on this model, we use an Empirical cumulative distribution function and the database of proteins compiled by the Ensembl Project to show consistency with the data.

2
  • LUCAS RODRIGUES DELGADO DE FREITAS
  • Gapless excitations in Kitaev materials with defects

  • Líder : RODRIGO GONCALVES PEREIRA
  • MIEMBROS DE LA BANCA :
  • EDUARDO MIRANDA
  • LEONARDO DANTAS MACHADO
  • RODRIGO GONCALVES PEREIRA
  • Data: 26-mar-2021


  • Resumen Espectáculo
  • A quantum spin liquid is a magnetic phase of matter remarkable for its ground state long-range entanglement and fractional excitations. A quantum spin liquid appears in the well-known Kitaev honeycomb spin-half model. In a magnetic field, there is a phase transition to a topological phase with an energy gap in the bulk and chiral Majorana fermions at the edge However, recent nuclear magnetic resonance experiments suggest excitations without a gap in this phase, signalled by a power-law dependence of the spin-lattice relaxation rate at low temperatures. In this work, I propose a mechanism to account for this experimental result. I use the localization of chiral Majorana modes in defects to explain the presence of gapless modes in the bulk. Treating the weak interaction between the chiral modes in the defects within a mean-field approximation, I find that these modes remain gapless when the interaction is below a critical value that depends on the magnetic field strength. I used the effective low-energy theory to calculate the spin-lattice relaxation rate and found a behavior that agrees with the experimental result.

3
  • LEONARDO DE QUEIROZ DANTAS
  • Magnetic Polaritons in Gyromagnetic Medium with Graphene Layer

  • Líder : DORY HELIO AIRES DE LIMA ANSELMO
  • MIEMBROS DE LA BANCA :
  • DORY HELIO AIRES DE LIMA ANSELMO
  • MANOEL SILVA DE VASCONCELOS
  • NILSON SENA DE ALMEIDA
  • Data: 09-abr-2021


  • Resumen Espectáculo
  • In this work we present the theoretical study on magnetic polaritons (magnon-polaritons) in a system formed by a semi-infinite gyromagnetic medium (ferromagnetic or antiferromagnetic), with a layer of graphene at the interface between this medium and the vacuum. Thus, the analytical and numerical calculations were reviewed for cases in which a static magnetic field is applied parallel to the interface, and we propose a new case, in which the magnetic field is applied perpendicularly to the interface between the media. The results found show that, for the case of perpendicular magnetic field, there was the formation of magnetic surface polariton modes, characterizing the photon-magnon coupling. In this case, the numerical results showed that these modes propagate reciprocally, that is, independent of the direction of the wave vector for both magnetic media (ferromagnetic and antiferromagnetic). In contrast, bulk modes were not found, characterizing an independent behavior between photon and magnon in the gyromagnetic bulk. The inclusion of the graphene layer also made it possible to control the surface modes by varying the parameters existing in the optical conductivity in graphene, such as the chemical potential and the scattering rate.

4
  • GABRIEL MORENO CUNHA
  • Ephaptic Coupling in Hybrid Neuronal Model

  • Líder : GUSTAVO ZAMPIER DOS SANTOS LIMA
  • MIEMBROS DE LA BANCA :
  • GILBERTO CORSO
  • GUSTAVO ZAMPIER DOS SANTOS LIMA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MARCELO DE MEIRA SANTOS LIMA
  • SERGIO R. LOPES
  • Data: 26-jul-2021


  • Resumen Espectáculo
  • There is growing interest in the impact of electrical fields generated in the brain. Transmembrane ionic currents originate electric fields in the extracellular space and are capable of affecting nearby neurons, a phenomenon called ephatic communication. In the present work, the Quadratic Integrate-and-Fire model was adapted to include the ephatic coupling behavior and its results were compared to the empirical results. Therefore, the analysis tools were divided according to the neuronal activity regime. For the subthreshold regime, circular statistics were used to describe the phase differences between the stimulus signal and the modeled membrane response; In the suprathreshold regime, the Population Vector and Spike Field Coherence were used to estimate phase preferences and the coupling intensity between the stimulus and the spikes of the model. The subthreshold phase difference was sensitive to the characteristic membrane response time, as well as the frequency of the stimulus given to the model. On the other hand, the intensity of the coupling between spikes and stimulus was sensitive to the intensity of noise added to the stimulus signal and also to the stimulus frequency. The preferential phase of spikes are sensitive, according to the model, only to the stimulus frequency. Such results are consistent with the results observed in empirical experiments on ephatic neuronal coupling. It was observed that the Quadratic Integrate-e-Fire model with ephatic coupling is able to successfully model this neuronal communication. Thus, the model makes it possible to pursue further studies on the physiological importance of ephatic coupling in the brain, including significant implications for our understanding of brain processing for neuroscience.

5
  • CAMILA PEREIRA RAMOS
  • Abundances from the Boltzmann Equation 

  • Líder : FARINALDO DA SILVA QUEIROZ
  • MIEMBROS DE LA BANCA :
  • AION VIANA
  • ALEX GOMES DIAS
  • CLARISSA MARTINS SIQUEIRA
  • FARINALDO DA SILVA QUEIROZ
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • Data: 30-jul-2021


  • Resumen Espectáculo
  • Observational data that support the existence of dark matter (DM) has been largely documented, pointing to the presence of a non-baryonic matter that is responsible for around 25% of the energy budget of the Universe. However, such type of matter has not been detected so far, and the standard model of particle physics (SM) does not have an explanation for DM. In this work, the weakly interacting massive particles (WIMPs), the main candidates for DM, are presented. It is then the main goal to show that this DM candidate generates the abundance required to obtain the estimated amount of DM in the Universe. This result is obtained by solving the Boltzmann equation, in the early Universe scenario.

6
  • HELCIO FELIPPE JUNIOR
  • Pearson matrices as density operators: A test of the entropic brain hypothesis using the von Neumann entropy

  • Líder : MADRAS VISWANATHAN GANDHI MOHAN
  • MIEMBROS DE LA BANCA :
  • ALINE AMABILE VIOL BARBOSA
  • DRAULIO BARROS DE ARAUJO
  • ERNESTO CARNEIRO PESSOA RAPOSO
  • FERNANDA PALHANO XAVIER DE FONTES
  • MADRAS VISWANATHAN GANDHI MOHAN
  • Data: 30-jul-2021


  • Resumen Espectáculo
  • The entropic brain hypothesis states that key functional parameters should exhibit increased entropy during psychedelic
    induced altered brain states. This hypothesis has gained significant support over the years, particularly via thresholding Pearson
    correlation matrices of functional connectivity networks. However, the thresholding procedure is known to have drawbacks,
    mainly its arbitrariness in the threshold value selection. In this work, we propose an entirely objective, threshold independent
    method of entropy estimation. Let R be a generic N×N Pearson correlation matrix. We define ρ = R/N and prove that ρ
    satisfies the necessary conditions for a density operator. Therefore, the von Neumann entropy S = –tr(ρlnρ ) can be directly
    calculated from the Pearson matrix. We then calculate the entropy of functional correlations of the human brain. Consistent
    with the entropic brain hypothesis, we find that entropy increases during the acute effects of the psychedelic indigenous
    beverage ayahuasca.

7
  • LUÍS FELIPE MARTINS DE ALMEIDA MORENA REIS
  • Emission of Gravitational Waves in Quadratic Theories of Gravity

  • Líder : LEO GOUVEA MEDEIROS
  • MIEMBROS DE LA BANCA :
  • LEO GOUVEA MEDEIROS
  • RICCARDO STURANI
  • RODRIGO ROCHA CUZINATTO
  • Data: 23-sep-2021


  • Resumen Espectáculo
  • Despite the unquestionable success of General Relativity (GR) in being able to describe and predict several gravitational
    phenomena, this theory still has some internal issues of interest for cosmology and high energy physics, e.g. singularities, dark
    energy, cosmology of the early universe, quantum gravity, etc. Extended theories of gravity, which consist of modifications in
    GR, have been shown to be a possible solution to these problems. Therefore, in this work we will study a quadratic theory of
    gravity, where the terms 𝛼𝑅 2 and 𝛾𝑅 𝜈𝜉 𝑅 𝜈𝜉 are added to the Einstein-Hilbert action with 𝛼 and 𝛾 being dimensionless coupling
    constants. This theory is usually present\ in several works being linked to the renormalization issues of gravity. In this work we
    will study the main aspects of this quadratic theory, focusing mainly on the properties of new fields that manifest themselves in
    the theory through the solution of linearized field equations. Thus, we will analyze the role that these fields play in the orbital
    evolution of a point mass system in a circular orbit due to
    the emission of gravitational waves.

Tesis
1
  • SERGIO LUIZ EDUARDO FERREIRA DA SILVA
  • Full-Waveform Inversion Based on Generalized Statistical Mechanics

  • Líder : GILBERTO CORSO
  • MIEMBROS DE LA BANCA :
  • GILBERTO CORSO
  • JOAO MEDEIROS DE ARAUJO
  • RAIMUNDO SILVA JUNIOR
  • JORGE LUIS LOPEZ
  • WAGNER MOREIRA LUPINACCI
  • Data: 29-ene-2021


  • Resumen Espectáculo
  • The subsurface imaging is a central procedure in seismic exploration and, consequently, a topic of great economic interest. In general, the seismic data inversion process is employed to estimate the physical parameters of the subsurface. In geophysical applications, seismic inversion is usually formulated as an optimization problem that aims to minimize the difference between the modeled data and the observed data through the Gauss' law of error, which is closely linked to the Boltzmann-Gibbs statistical mechanics. In this approach, errors are assumed to be distributed according to a Gaussian distribution. However, in practice, especially in non-linear problems, errors are seldom Gaussian and, therefore, this approach may fail to reconstruct physical models, especially when there are outliers in the data set. Thus, the error laws determined by  non-Gaussian statistics are essential for a robust seismic inversion. In this way, we present in this work new methodologies for the execution of seismic inversions based on non-Gaussian statistics. In particular, the generalized statistics in the sense of Tsallis and Kaniadakis are considered to solve a challenging problem of seismic inversion, called, Full-Waveform Inversion. In this work, we present the foundation and formalism of the FWI based on generalized statistical mechanics, as well as the results of several numerical tests carried out on two different subsurface models: (i) we consider a very dense seismic acquisition geometry in a Marmousi case study; and then, (ii) we employ an OBN acquisition in a case study with a representative model of the Brazilian pre-salt field. At the end, we compare the conventional FWI with the FWI based on Tsallis and Kaniadakis statistics. The results suggest that the FWI based on generalized statistical mechanics is a powerful
    methodology, especially in noisy environments. In addition to the proposed methodology to provide better reconstruction of  the subsurface models, no computational cost is added compared to the conventional approach.

2
  • ASNAKEW BEWKETU BELETE
  • The variability properties of active galactic nuclei and their intractions with the host galaxies

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • JOSE RENAN DE MEDEIROS
  • BRUNO LEONARDO CANTO MARTINS
  • IZAN DE CASTRO LEÃO
  • JAILSON SOUZA DE ALCANIZ
  • ZULEMA ABRAHAM
  • Data: 29-ene-2021


  • Resumen Espectáculo
  • Active galactic nuclei (AGNs), a compact regions that consist of a super-massive
    black hole surrounded by an accretion disk in the center of massive galaxies, have
    long been known in their unique observational properties. Strong variability has
    been identified as one of those properties that can be used to probe the interior of
    the system. Also, most astrophysical objects, like AGNs, are possibly associated
    with continuous nonlinear stochastic systems due to their complexity in nature. It
    has been indicated that quasars, a sub-class of AGN, are among complex systems
    that have nonlinear time series characterized by fractal behavior and also by sudden
    bursts of very large amplitude, implying that the dynamical evolution of quasars
    is nonlinear (i.e., described by nonlinear stochastic differential equations). Addi-
    tionally, there is a suggestion that extragalactic radio sources are intermittent on
    timescales of ∼ 10 4 - 10 5 yr. Despite the complex nature of AGNs, astronomers
    have been trying to investigate the variability properties of AGNs using linear tech-
    niques, such as structure function, periodogram, Fourier analysis, etc. However,
    most valuable information in a complex system signal is contained by its irregu-
    lar structures and transient phenomena called singularities. Thus, particularly in
    physics, it is important to analyze irregular structures in a signal to deduce proper-
    ties about the underlying physical phenomena. Moreover, among other evidences,
    the recently discovered tight correlation between super-massive black hole mass and
    the host galaxy bulge properties revealed the fact that AGNs are not isolated objects
    -they interact and co-evolve with their host galaxies. The interaction mechanisms
    are thought to be through AGN feedback and feeding, and have been known to af-
    fect both the observational properties of AGNs, and the properties and kinematics
    of the gas in the surrounding environment, thereby regulating AGN- host galaxy
    co-evolution. Thus, understanding the types of variabilities along with their driv-
    ing physical mechanisms and the physics behind the AGN-host galaxy interaction
    mechanisms(AGNfeedbackandfeeding)providesapotentiallysignificantinforma-
    tion to constrain the nature of AGNs and get a full picture to construct a universal
    model to study the co-evolution of the two physically connected systems. The AGN-
    host galaxy interaction can easily be studied by modelling the kinematics of gas (in
    all form) in the nuclear/circumnuclear regions of the host galaxy.
    In this thesis I studied the nonlinear (multifractal) signature printed in the long-
    term light curves of different classes of AGNs and its correlation with different AGN
    and other observational parameters, and whether multifractality is an intrinsic be-
    haviour of AGNs and it can be affected by extrinsic variations (e.g., gravitational
    lensing). I applied the one-dimensional multifractal detrended moving average and
    the wavelet transform modulus maxima approachs to characterize the nonlinearity
    presented in the light curves. In addition, I also present the analysis of the kinemat-
    ics of CO molecular gas in the nuclear and circumnuclear regions of three nearby
    Seyfert galaxies, NGC 4968, NGC 4845, and MCG-06-30-15, by using their bright
    CO(2-1) emission line as a tracer. I used two different softwares, the 3D-Based Anal-
    ysis of Rotating Object via Line Observations (3 D BAROLO) and DiskFit, to model
    the kinematics of cold CO molecular gas in these three galaxies.
    I found that AGNs are strongly nonlinear and intermitent systems, and nonlinearity
    is an intrinsic behaviour of AGNs (i.e., the degree of nonlinearity does not change
    with cosmological redshift), indicating that AGNs are really complex systems, and
    the information contained in their light curves cannot be fully captured by linear
    analysis techniques. The nonlinear behaviour of AGNs is found to be affected by
    extrinsic variation (gravitational lensing). Moreover, the degree of nonlinearity is
    found to be inversly correlated with wavelength, the shorter the wavelength the
    vii
    stronger the nonlinearity, and strongly correlated with fractaional variability ampli-
    tude. I did not find any significant correlation between the degree of nonlinearity
    and AGN parameters such as black hole mass, the size of the Broad-Line Region
    (BLR), and continuum luminostiy. However, an important correlation is observed
    between the degree of nonlinearity and the Eddington ratio. I also found that re-
    processing in the BLR introduces additional nonlinearity, i.e., the reprocessing in the
    BLR increases the nonlinearity of the ionizing continuum.
    Circular motion is found to be the dominant kinematics of the CO molecular gas
    in the inner molecular disk of the three nearby Seyfert galaxies, NGC 4968, NGC
    4845 and MCG-06-30-15, mainly in NGC 4845 and MCG-06-30-15. However, there
    is a clear evidence for the presence of non-circular motions in the central regions of
    NGC 4968 and NGC 4845. The strongest non-circular motion is detected in the nu-
    clear region of NGC 4968, mainly in the minor kinematic axis, with velocity ∼ 115
    km s
    − 1 . For NGC 4968, the Ω b
    pattern speed for the bar put corotation at 3.5 kpc
    and inner Lindblad resonance (ILR) ring at R = 300pc, which corresponds to the CO
    ring. Moreover, of all DiskFit models, bisymmetric model is found to be the best-
    fit model, indicating that the observed non-circular motions, mainly in NGC 4968,
    could be due the molecular gas in the disk of the galaxy being perturbed by the nu-
    clear barred structure. Considering the CO-to-H 2 conversion factor α in the interval
    [0.8, 3.2], the molecular mass in the molecular disk of each galaxy is estimated to be
    ∼ 2.8 × 10 9 (α= 0.8) and ∼ 11 × 10 9 (α=3.2) for NGC 4968, ∼ 4 × 10 9 (α= 0.8) and ∼ 16
    × 10 9 (α= 3.2) for NGC 4845, and ∼ 0.3 × 10 9 (α= 0.8) and ∼ 1.2 × 10 9 (α= 3.2) for
    MCG-06-30-15. For the galaxy NGC 4968, the computation of the torques exerted by
    the stellar bar on the gas are positive inside the molecular ring, and negative inside,
    revealing that the gas is accumulating in the inner Lindblad resonance.

3
  • LESSANDRO JORGE DE LIMA
  • Computational Models for Thermoelectric Effects Studies in Thin Films and the Medium Range Potts Model (q = 3)

  • Líder : JOAO MEDEIROS DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • FELIPE BOHN
  • JOAO MEDEIROS DE ARAUJO
  • LÚCIO STRAZZABOSCO DORNELES
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MARCIO ASSOLIN CORREA
  • SERGIO ANDRÉ FONTES AZEVEDO
  • Data: 25-feb-2021


  • Resumen Espectáculo
  • In this thesis we present the results of two works in computational physics on the thermoelectric effects in thin films and the medium-range Potts model (q = 3). In the first, we seek to obtain the magnetic behavior and thermoelectric response of Co2FeAl/W films from numerical calculations, we compare experiment and theory, we explore the possibility of obtaining evolution of the magnetic response and the thermoelectric voltage with the magnitude and direction of the magnetic field. We show that the thermoelectric voltage curves can be obtained from a change in the Stoner-Wohlfarth model by the association and experimental parameters used in the longitudinal spin Seebeck effect experiment. In the second, we seek to find the so-called X and Y exponents, for the medium-range Potts model, which describes the transition from one universality class to another as the range of interactions increases. Such an effect is called a crossover phenomenon. We present the results obtained so far for the medium-range Potts model. We use the Metropolis algorithm to perform numerical Monte Carlo simulations of the Potts model of the state q = 3. With this algorithm we simulate systems with network sizes, L, equal to 32, 46, 64, 92, 128, 182 and 256. We found that as the range of interactions, Rm increases, the critical exponents α/ν, β/ν and γ/ν vary. Therefore, in this work we try to use two algorithms in two applications involving thin films and the Potts model (q = 3).

4
  • LEANDRO DE ALMEIDA
  • Using Gravitational Microlensing to search low-mass exoplanets
  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • EDER MARTIOLI
  • FRANCISCO JOSÉ JABLONSKI
  • JEFFERSON SOARES DA COSTA
  • JOAO RODRIGO SOUZA LEAO
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • Data: 18-mar-2021


  • Resumen Espectáculo
  • Gravitational lenses were proposed by Albert Einstein in the course of developing the theory of general relativity.
    Einstein observed that massive objects curve space-time and thus the path of light that passes close to these objects undergo deflection effects and the light is then deflected in these vicinities. The gravitational lens regime can be divided into three categories: strong lenses, weak lenses, and microlensing. This thesis is focused on the latter, the gravitational microlensing.
    Gravitational Microlensing (GM) events happen when, from the observer's perspective, there is an alignment between two stars, one in the background (source) and another in the foreground (lens). This alignment causes the light from the source to deviate from its original path. This deviation of light generates a magnification of the brightness of the background star and if the two stars have relative movements, a characteristic light curve is then produced. If the lens star has a planet, we can infer its presence by carefully analyzing this light curve and determining the mass fractions of the system and also the apparent major semi-axis. This technique differs from the others because it is the only one that can detect small planets beyond the snow line of its stars. These planets are essential for filling the census of exoplanets that we have in our galaxy. In this work, we focus on
    finding low-mass planets in solar-type stars. For this, we use the semi-analytical method of solving the lens equation and we propose the parameterization of the shortest distance between the path of the source star and the main lens (impact parameter $\mu_0 $) and the angle that the source path makes with the relative axis of the system (angle of impact $\alpha$). This parameterization forces the source path to pass through the region of interest of the event in which it would be possible to detect low mass planets, increasing the probability of detecting planets with the mass of the Earth. We applied our parameterization in GM events available in the literature and also in light curves of events observed at the Pico dos Dias Observatory (OPD) in the observational campaigns of 2018, 2019, and 2020, which were part of this doctorate together with
    the MicroFun collaboration from "Ohio State University ". In this thesis, we present a detailed discussion of planetary caustic in GM events and the effects on the formation of light curves in an event involving a planet with a mass similar to that of Earth. We present in detail the methodology for photometric observation of GM events monitored at the OPD. We also present a possible detection of 3 candidates for exoplanets, one of them using data observed in the OPD during this doctorate. In this work, we analyze the topology of GM events that produce light curves in which the detection of planets with a mass similar to that of Earth is possible.

5
  • GABRIEL CAMPELO DE MELO FERRAZ
  • Spin Chain Network Construction of Chiral Spin Liquids

  • Líder : RODRIGO GONCALVES PEREIRA
  • MIEMBROS DE LA BANCA :
  • AMIR ORDACGI CALDEIRA
  • MARIANA MALARD SALES
  • RAFAEL CHAVES SOUTO ARAUJO
  • RODRIGO GONCALVES PEREIRA
  • TOMMASO MACRI
  • Data: 26-mar-2021


  • Resumen Espectáculo
  • In this thesis work, it was sought to present a new construction method of a chiral spin quantum liquid formed from Heisenberg spin chains. The spin chains, initially assembled in trios, were coupled in the form of Y junctions. In each Y junction, a chiral interaction was added between the three spins at the edges of each chain, in addition to the exchange interaction between neighbouring spins in the bulk of the chains. Through the previous study of an isolated Y junction its extension was investigated here by establishing the set of these junctions in the form of a hexagonal network of spin chains. The theoretical analysis was based on low energies using the bosonization technique and applying invariant boundary conditions to the bosonic modes or the chains' spin currents. It was concluded, with the established chiral spin liquid, that the CSL is of the Kalmeyer-Laughlin type, which its elementary excitations correspond to spinons, fractional magnetic excitations of semonic statistics. The chiral spin liquid found is also accompanied by a quantized spin Hall conductance and edge modes at the network boundaries. The (gapped)spectrum of the spinons and the stability of the chiral liquid were studied through the backscattering perturbation between the chiral bosonic fields of neighboring hexagons and an effective tight-binding model for spinons. The theory was able to predict a phase transition when the spinon gap closes, resulting in the condensation of the spinons or the formation of a stable CSL. As a perspective, the method developed in this work can be extended to other topological phases of matter and eventually be useful in the application of topological quantum computing.

6
  • MÁRCIO ASSUNÇÃO TEIXEIRA
  • SIMUTOOLS: A specter simulation tool for NIRPS

  • Líder : BRUNO LEONARDO CANTO MARTINS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • EDUARDO JANOT PACHECO
  • HELOISA MARIA BOECHAT-ROBERTY
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • Data: 07-abr-2021


  • Resumen Espectáculo
  • With the possibility of using the variation in radial velocity to find exoplanets, that has begun with the discovery of 51 Pegasi b, the exoplanet scene has been a target of great interest. From this pioneer discovery up to now, various spectrometers were and have been built with the purpose of searching for exoplanets. In this context, NIRPS (Near Infra-Red Planet Searcher) is included, a spectrometer which will be mounted jointly to HARPS (High Accuracy Radial velocity Planet Searcher), in Chile, and will operate in the near infrared range, with the goal of searching for explanets orbiting low mass stars. In this work, we present a program developed for NIRPS, SIMUTOOLS, which will simulate the specter that reachs the detector (H4RG). These simulations expect to: anticipate any particularity that may happen to the instrument, or the detector, so that it may be corrected beforehand, prior to NIRPS’ functioning; and also test and calibrate the data reduction software (DRS). This code was successful in its simulations, presenting the particularities of each type of observation, showing intrinsic
    effects due to the instrument, the difference between high accuracy and high efficiency modes and, lastly, the simulation of specters from different M stars, in which we may also realize the influence from atmospheric absorption in the observation.

7
  • DESIANE MAIARA GOMES DOS SANTOS
  • Scale-free behavior in hailstone sequences generated by the Collatz map

  • Líder : MADRAS VISWANATHAN GANDHI MOHAN
  • MIEMBROS DE LA BANCA :
  • DORY HELIO AIRES DE LIMA ANSELMO
  • ERNESTO CARNEIRO PESSOA RAPOSO
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MARCIO ASSOLIN CORREA
  • MARCOS GOMES ELEUTERIO DA LUZ
  • RICARDO VIANA
  • Data: 23-abr-2021


  • Resumen Espectáculo
  • The Collatz conjecture, perhaps the most elementary unsolved problem in mathematics, claims that for all positive integers $n$, the map $n\mapsto n/2$ for even $n$ and $n \mapsto 3n+1$ for odd $n$ reaches 1 after a finite number of iterations. We examine the Collatz map's orbits, known as hailstone sequences, and ask whether or not they exhibit scale-invariant behavior, in analogy with certain processes observed in real physical systems. We develop an efficient way to generate orbits for extremely large $n$'s (e.g., higher than $n \approx 10^{3,000}$), allowing to statistically analyze very long sequences. We find strong evidence of a scale-free power law for the Collatz map. We analytically derive the scaling exponents, displaying excellent agreement with the numerical estimations. The scale-free sequences seen in the Collatz dynamics are consistent with geometric Brownian motion with drift, which is compatible with the validity of the Collatz conjecture. Our results lead to another conjecture (conceivably testable through direct, nonetheless very time consuming, numerical simulations): given an initial $n$, the average number of iterations needed to reach $1$ is proportional, to lowest order, to $log[n]$.

8
  • MARCUS VINÍCIUS PINHEIRO LOPES
  • Thermoelectric effects in Co2FeAl/W bilayers with uniaxial and cubic anisotropies

  • Líder : MARCIO ASSOLIN CORREA
  • MIEMBROS DE LA BANCA :
  • THIAGO JOSÉ DE ALMEIDA MORI
  • FELIPE BOHN
  • MARCIO ASSOLIN CORREA
  • MAURICIO ROBERTO BOMIO DELMONTE
  • MÁRCIO MEDEIROS SOARES
  • Data: 26-abr-2021


  • Resumen Espectáculo
  • The conversion of temperature gradients applied to magnetic materials has been the subject of study for its importance in the possibility of building devices that take advantage of it. The application of these temperature variations generate electrical responses due to the production of spin and charge currents that gave rise to an area of spintronics, the spin caloritronics. From these currents it is possible to measure the thermoelectric voltage in magnetic materials, produced by the direct conversion of the temperature gradient into electrical voltage. In this work, this thermovoltage is mainly associated with two phenomena, the Seebeck spin (SSE) and anomalous Nernst (ANE) effects. Both are investigated in samples of Co2FeAl/W (CFA/W) grown on silicon (Si) and gallium arsenide (GaAs) substrates. The samples were prepared by magnetron sputtering with the substrate under to distinct temperature conditions during deposition, from 300 K up to 773 K. Here, the bilayers were deposited onto oriented substrates in order to induce magnetocrystalline anisotropy, thus allowing the obtainment of systems with an overlap of anisotropies such as uniaxial and cubic. The samples were characterized from the structural and magnetic point of views. Specifically, the structural characterization was performed by X-ray diffractometry (XRD), while the quasi-static magnetic behavior was obtained through magnetization curves measured using a Vibrating Sample Magnetometer (VSM). Thermoelectric response was explored via longitudinal Spin Seebeck effect (LSSE). In this configuration, the temperature gradient is normal to the plane of the film, and the external magnetic field lies in the plane. Then, the thermoelectric voltage is measured with electrical contacts fixed in the film plane. Computer simulations were also carried out using the adapted Stoner-Wohlfarth model, which together with the experimental data show that the thermoelectric response of the samples is the result of the interaction between the uniaxial and cubic contributions of magnetocrystalline anisotropy. The results place CFA grown onto GaAs substrate as a promising candidate for active elements in spintronic devices.

9
  • REBECCA DE MOURA BRAZ DINIZ
  • Continuous Phase Transition in a Diluted Block Voter Model with Sociophysical and Biophysical Applications

  • Líder : JOAO MEDEIROS DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • ALEXANDRE DA SILVA ROSAS
  • CLAUDIONOR GOMES BEZERRA
  • JOAO MEDEIROS DE ARAUJO
  • MADRAS VISWANATHAN GANDHI MOHAN
  • RAIMUNDO NOGUEIRA DA COSTA FILHO
  • Data: 26-may-2021


  • Resumen Espectáculo
  • The Diluted Block Voter Model gives a biophysical interpretation of a continuous phase transition in a magnetic network system, we also give some insights into the sociophysical context of elections. We simulated a regular square lattice of N spins variable with two states σi = ±1, and edge L = √N . Each spin can receive the outflow influence of the persuasive cluster spins (NPCS), a randomly chosen square block. This chosen adjacente spin have q resistance to accept the outflow influence. So, it rejects the PCS influence with probability q and agrees with the majority of PCS with probability (1 - q). The dilution is due to the fraction f of sites with no resistance q = 0 while the complementary 1 - f sites effective have q resistance, named qc its critical value when phase transition occurs. Our parameters of interests are qc, f and NPCS. We calculate the magnetization, susceptibility and Binder’s cumulant of the system to map the phase transition showing that some configuration of parameters lead us to a null magnetization region. We compare the results of large groups of influence with the mean-field theory and we use the finite scale size theory. In biophysical terms, in some configurations of vaccine efficiency q, contagion group NPCS, and campaign absences f, we have an ordered phase (magnetization > 0) Where there is an epidemic propagation. In social terms, for some configuration of social temperature q, Social pressure NPCS and social neglect f, we have a disordered phase (null magnetization)where there is no consensus.

10
  • ACÁCIO SILVEIRA DE MELO
  • Anomalous Nernst Effect in magnetostrictive films on flexible substrate

  • Líder : MARCIO ASSOLIN CORREA
  • MIEMBROS DE LA BANCA :
  • CLAUDIONOR GOMES BEZERRA
  • FELIPE BOHN
  • JOAO PAULO SINNECKER
  • JULIAN PENKOV GESHEV
  • MARCIO ASSOLIN CORREA
  • MATHEUS GAMINO GOMES
  • Data: 04-jun-2021


  • Resumen Espectáculo
  • The anomalous Nersnt effect (ANE) in nanostructured magnetic materials is a key phenomenon for optimizing control and using internal energy in electronic devices. In this work, we will explore the magnetic properties and ANE in a flexible magnetostrictive film with uniaxial anisotropy induced and subjected to mechanical stress, in addition, we will promote an integration between the ANE effect and the magnetostrictive phenomena, which in turn, in_uences the effective anisotropy of Films. Therefore, a theoretical study of the behavior of magnetization in this system will be presented, so that we can understand how it will influence the thermoelectric voltage response. At the same time, we will integrate this study with the experimental data obtained, in this way we can manipulate the ANE through the magnetic field and the applied mechanical stress. Theoretically, we calculate the magnetization behavior and the thermoelectric voltage response from the theoretical approach to planar geometry, with magnetic free energy density that takes into account the induced contributions of uniaxial and magnetoelastic anisotropy. Experimentally, we verified changes in the effective magnetic anisotropy, changing the applied stress, and explored the anomalous Nernst effect, as a powerful tool to investigate the magnetic properties of magnetostrictive materials. We found agreement between the experiment and the numerical calculations, thus elucidating the magnetic behavior and the thermoelectric voltage response. Finally, evidence was provided to confirm the validity of the theoretical approach to describe the magnetic properties and the anomalous Nernst effect in ferromagnetic magnetostrictive films with uniaxial magnetic anisotropy and subjected to external stresses.
11
  • ANA CAROLINA MATTIUCI FIGUEIREDO
  • A study of the binary systems rotation and their relationship with stellar and orbital parameters

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • GABRIEL ARMANDO PELLEGATTI FRANCO
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MARCELO EMÍLIO
  • MATTHIEU SEBASTIEN CASTRO
  • SILVIA HELENA PAIXAO ALENCAR
  • Data: 10-jun-2021


  • Resumen Espectáculo
  • Stellar rotation is an important parameter to be considered in the study of stellar evolution and structure, as
    it relates to several equally relevant parameters such as mass and temperature and influences the chemical composition of the
    star. In binary systems the study of rotation allows us to understand the tidal effects that a system can suffer and the process
    that makes the system achieve synchronization and circularization. To understand how rotation behaves and relates to other
    stellar parameters in binary systems, we use a method of analyzing light curves and measuring the rotation period. We apply
    this method to light curves of the CoRoT and TESS space missions in stars belonging to eclipsing and spectroscopic binary
    systems. In addition, we analyzed the relationships between other parameters such as orbital period and eccentricity, projected
    rotational velocity and effective temperature, among others. We finished this study with correlation diagrams to have an
    overview between the different groups of binaries. We obtained excellent results in determining the rotation period for 70
    eclipsing binary systems, 26 spectroscopic binary systems and 15 systems belonging to the Taurus-Auriga region. We reaffirm
    the values of the eccentricities for 18 eclipsing binary systems and found 38 synchronized systems of which 12 are
    synchronized and circularized. For the spectroscopic systems, we found that for the stars of the main sequence, the shorter the
    orbital period, the greater the probability of the system being synchronized, however, it is possible to find red giants of long
    period synchronized. We also found that the correlations between rotation, orbital parameters, mass and temperature change
    according to the different types of binary systems.

12
  • RAFAEL RAMON FERREIRA
  • SPECTROSCOPIC STUDY OF CHROMOSPHERIC ACTIVITY IN SOLAR TYPE STARS: The search for characterizing analogs stars in  Maunder minimum

  • Líder : MATTHIEU SEBASTIEN CASTRO
  • MIEMBROS DE LA BANCA :
  • ADRIANA BENETTI MARQUES VALIO
  • GUSTAVO FREDERICO PORTO DE MELLO
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • SILVIA HELENA PAIXAO ALENCAR
  • Data: 11-jun-2021


  • Resumen Espectáculo
  • Since the first observations of sunspots made by Thomas Harriot and subsequently by Galileo and several other scientists, astronomers looking for methods to better understand the magnetic phenomena in the Sun and in solar-type stars. It is well established that the first indicators used to characterize magnetic activity were sunspots. It is also worth highlighting one of the most intriguing phenomena of the evolution of solar magnetism known as Maunder's minimum, which occurred specifically between 1645 and 1715. What makes this minimum of activity is enigmatic is the registration of very few sunspots and practically no variability in the area. over 70 years, remaining to this day without a consolidated explanation. In the twentieth century, with the advancement of observational techniques related to spectroscopy, astronomers began to make observations of solar/stellar activity also through the spectra. The solar/stellar chromospheric activity, has been the subject of exhaustive treatment over the last six decades in the literature. The main spectroscopic indicators come from the Ca II H\&K resonant lines, particularly the indicators SMW and the index with photosphere correction RHK are the main ones. Spectroscopic measurements of the activity of solar-type stars have been carried out since 1960, in an attempt to answer the question of how unique the magnetic evolution of the Sun is in relation to other solar-type stars. All this background has allowed to determine that stars of the solar type have activity cycles, in the case of the Sun a primary cycle of 11 years is well established and a possible secondary cycle of 88 years. In our work we obtained as main results: 1) The characterization and determination of the activity cycle of the solar analog HD43587, as well as estimates of its rotational period and characterization of the magnetic field; 2) Development of theoretical tools to estimate the observations of stellar spots globally in other stars of the solar type; 3) Analysis and determination of the activity cycle of 30 stars of the solar type indicated in the literature as in the state of Maunder Minimum; 4) Calibration of activity indexes based on the Ca II H&K lines using the Coudé spectrograph located at the Pico dos Dias Observatory.

13
  • ANDRÉ CHAVES DE BRITO
  • About Medium Infrared Excess in Binary Spectroscopic Systems

  • Líder : BRUNO LEONARDO CANTO MARTINS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • EDUARDO JANOT PACHECO
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • MARCOS PEREZ DIAZ
  • Data: 30-jun-2021


  • Resumen Espectáculo
  • The presence of circumstellar material is seen as a powerful indicator for the formation of

    planetary systems similar to our Solar System. It is known that nearby binary stars have a more extensive

    habitability zone when compared to individual stars, making them the target of several researches,

    however, studies on debris discs in systems of this nature are still incipient. Faced with this con-

    juncture, it is sought through this thesis, debris discs in spectroscopic binary systems. The sample

    was obtained from the WEBDA database, initially containing 25 open agglomerates with the lar-

    gest populations of spectroscopic binary stars available, totaling 1033 candidates. The search for

    excess in the infrared occurred in the 3.4 μm, 4.6 μm, 12 μm and 22 μm bands of WISE and was

    performed through a comparison from the SEDs (Spectral Energy Distribution) obtained by the

    photometric data from the GAIA missions, 2MASS and WISE and the synthesized curve genera-

    ted by the BT-Settl model, available on the virtual platform VOSA (Observatory Sed Analyzer).

    The stars with excess in the infrared have passed through visual inspection and had their galactic

    latitudes checked, resulting in a final sample with 6 confirmed spectroscopic binary systems with

    disc presence. After these procedures, the main parameters that characterize the debris discs were

    calculated and, among other results, it was possible to verify that non-evolved binary spectroscopic

    systems, belonging and open agglomerates, can house stable circumbinary debris discs.

14
  • EVERSON FRAZÃO DA SILVA
  • Absorption in Photonic Quasicrystals

  • Líder : MANOEL SILVA DE VASCONCELOS
  • MIEMBROS DE LA BANCA :
  • DORY HELIO AIRES DE LIMA ANSELMO
  • EUDENILSON LINS DE ALBUQUERQUE
  • JOAO MILTON PEREIRA JUNIOR
  • MANOEL SILVA DE VASCONCELOS
  • RAIMUNDO NOGUEIRA DA COSTA FILHO
  • Data: 27-jul-2021


  • Resumen Espectáculo
  • After Yablonovitch's pioneering work (in 1987) on photonic crystals, there was a growing interest in studies on the propagation
    of electromagnetic waves in periodic multilayers, mainly because of the possibility of guiding, allowing or prohibiting the
    propagation of light in certain frequency bands with the use of band gaps. On the other hand, after Kohmoto's pioneering work
    (also in 1987), the study of photonic quasi-crystals has been receiving a lot of attention. Photonic quasi-crystals exhibit long-
    range order, non-translational symmetry and a characteristic in the auto-similarity optical spectra, a very interesting property in
    fractal studies. In this doctoral thesis, we have study absorption and optical transmission spectra in multilayers, by using the
    theory of photonic quasi-crystals. The technique that we use for the calculation of the optical spectrum is the technique of the
    transfer matrix. The photonic quasi-crystals we studied are formed by the sequences of Octonacci and Dodecanacci. Also,
    Graphenes are materials that have received a lot of attention for their optoelectronic properties, even in the absence of a band
    gap. In this thesis we use graphene at the interfaces between the layers to obtain the spectra and compare the results with the
    case without Graphenes. We also investigated the effect of the chemical potential for the control of band gaps in these
    structures, as well as the influence of the oblique incidence. The study of coherent perfect absorption has been quite
    highlighted also in recent years, mainly for several technological applications, such as modulators, Bragg reflectors, plasmon
    structures, among others. On the other hand, Hermitian systems, previously present only in quantum mechanics, had their
    studies expanded to acoustic and electronic systems. Non-Hermitian systems had their equivalent in optical systems where
    what we call parity-time symmetry (PT symmetry) occurs, where the refractive indices of the material satisfy the condition n
    (x) = n * (- x). In this thesis, we also calculated the transmission spectrum in a photonic crystal with PT symmetry, which are
    formed by quasi-periodic sequences well known in the literature, namely: Fibonacci, Thue Morse and Double Period. In our
    results, we have shown the existence of high transmission peaks as a result of the definition of PT symmetry in photonic quasi-
    crystals.

15
  • ALINE NASCIMENTO LINS
  • Short distance tests of General Relativity From Astronomy

  • Líder : RICCARDO STURANI
  • MIEMBROS DE LA BANCA :
  • DMITRY MELNIKOV
  • FRANCISCO DE ASSIS DE BRITO
  • GEORGE EMANUEL AVRAAM MATSAS
  • RAISSA FERNANDES PESSOA MENDES
  • RICCARDO STURANI
  • Data: 25-ago-2021


  • Resumen Espectáculo
  • Recent detections of gravitational waves, together with the increasing precision of electromagnetic observations of neutron
    stars and black holes, have expanded the possibility of testing the theory of General Relativity. In this work, we parameterize
    extensions of General Relativity (GR), adding terms of high curvature, built from the fourth powers of the Riemann tensor,
    therefore, departing from GR in the ultraviolet (UV). The presence of these operators modifies the gravitational potential
    between compact objects, as well as their multipole moments. Through an Effective Field Theory approach, we calculate the
    corrections to the gravitational potential and radiative multipole within the post-Newtonian approximation to GR and obtain
    also the equations of motion for the spin and these quantities are directly comparable with astronomical observations.

16
  • HEBERTT LEANDRO SILVA
  • Gravitational Waves Fundamental: Applications in Astrophysics and Cosmology

  • Líder : RICCARDO STURANI
  • MIEMBROS DE LA BANCA :
  • RICCARDO STURANI
  • LEO GOUVEA MEDEIROS
  • RAIMUNDO SILVA JUNIOR
  • JAILSON SOUZA DE ALCANIZ
  • VALERIO MARRA
  • Data: 16-sep-2021


  • Resumen Espectáculo
  • The detection of gravitational waves, predicted by General Relativity, opened up possibilities to study physics previously unexplored. Based on affirmation, the present work is divided into two parts. First, we analyze an effect derived from geodesic deviation equation, called memory effects. We propose a model, representing a simplified description of astrophysical source emitting radiation and analyse its effect on detector a far away from the source after the radiation has passed. The particular memory effect we investigate is due to the change in longitudinal modes, rather than the well-study memory effect in radiative modes. The toy model proposed assumes spherical symmetry in which the entire source initially at rest is converted into radiation. Both longitudinal and transverse(radiative) modes contribute to the Riemann tensor and interact with the detector and the possibility of detecting time varying longitudinal modes is studied. In the second part of the  thesis, we propose a way to measure the Hubble constant,which enters the relationship between the redshift z and luminosity distance $d_L$, and it is a crucial parameter in Cosmology that provides a measure of the Universe expansion rate. The application consists of measuring $ H_0 $ using the gravitational wave detections from binary black hole coalescences whose amplitude depends inversely on the luminosity distance $d_L$ without electromagnetic counterparts enabling a measure of the {\it{redshift}}. The method consists of breaking the degeneracy between $H_0$ and the redshift by using the statistical information on the astrophysical binary black hole population using the source distribution as a function of redshift.

17
  • JOSÉ CARLOS DE SOUZA CARNEIRO
  • Synthesis of superparamagnetic magnetite nanoparticles: coated with PVP and doped with neodymium and gadolinium.

  • Líder : JOSE HUMBERTO DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • EDIMILSON FÉLIX DA SILVA
  • IGOR FROTA DE VASCONCELOS
  • JOSE HUMBERTO DE ARAUJO
  • JOÃO MARIA SOARES
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 24-sep-2021


  • Resumen Espectáculo
  • The synthesis of superparamagnetic magnetite nanoparticles has been a prominent topic in the field of condensed matter research due to its applicability in biomedicine and other technologies. In this work, we describe the synthesis of nanoparticles of pure magnetite, magnetite coated with polyvinylpyrrolidone polymer (PVP), and PVP-coated magnetite doped with neodymium and gadolinium. We studied the structural and magnetic properties by X-ray diffraction (XRD), magnetization measurements (VSM), transmission electron microscopy (MET), and Mössbauer spectroscopy. The nanoparticles showed superparamagnetic behavior at room temperature. The values obtained for saturation magnetization, coercivity, and remanence indicated the superparamagnetic nature of the samples obtained. The presented approach provides an easy route to prepare PVP-coated magnetite nanoparticles, as well as ones doped with neodymium and gadolinium.

18
  • MICHELLE QUEIROZ DA SILVA
  • Coprecipitação; moagem de alta energia; ilmenita; titanohematita; vidros de spin.

  • Líder : FELIPE BOHN
  • MIEMBROS DE LA BANCA :
  • EDIMILSON FÉLIX DA SILVA
  • FELIPE BOHN
  • JOÃO MARIA SOARES
  • RODOLFO BEZERRA DA SILVA
  • SERGIO ANDRÉ FONTES AZEVEDO
  • SUZANA ARAÚJO BARBOSA
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 30-sep-2021


  • Resumen Espectáculo
  • Iron oxides and titanium oxides are of great scientific importance due to their magnetic, electrical, morphological, and physical-chemical properties, all of which enable various applications such as catalytic processes, semiconductors, spintronics, among others. Among the mixed binary oxides, systems of the type Fe2-yTiO3, a series of solid solutions with compositions between hematite (α-Fe2O3) and Ilmenite (FeTiO3), have attracted the interest of theoretical and experimental areas due to their magnetic characteristics (antiferromagnetic with weak ferromagnetism). In this work, we synthesized compounds of the type xTiO2-(1-x) Fe3O4 by means of high-energy ball milling, with x = 0.2; 0.4; 0.6; 0.8, of which we selected the concentration x = 0.2 for a more detailed analysis. For the synthesis of the composites, we used the precursor powders TiO2 (anatase) and Fe3O4 (synthesized here by means of co-precipitation), and both were stoichiometrically mixed and milled in a ball mill for 24 hours. Subsequently, we submitted  he resulting samples to heat treatment at temperatures of  700°C, 900°C and 1100°C for 3 h. After that, the composites were characterized through X-ray diffraction, vibrant sample magnetometry, and Mössbauer spectroscopy. We used the Physical Properties Measurements System – PPMS to obtain ZFC/FC curves, magnetic susceptibility, and magnetization by different treatment temperatures. For just milled samples, the X-ray diffraction analysis did not show the formation of new crystalline phases. For the milled sample submitted to heat treatment, the presence of ilmenite (FeTiO3) and hematite (α-Fe2O3) was observed, with the former presenting phase concentration of 100% at the temperature of 1100°C. Magnetic analysis and Mössbauer spectroscopy revealed the presence of Fe2+ and Fe3+ ions. The combined system FeTiO3 - α-Fe2O3 is characterized as titanohematites. The sample calcined at a temperature of 700°C also showed behavior compatible with the dynamics of spin glasses. The results found suggest to the obtainment of high-quality FeTiO3-αFe2O3 and FeTiO3 composites from syntheses and accessible thermal treatments with several applications in the field of Condensed Matter Physics.

19
  • EDWIN HUMBERTO FAGUA DUARTE
  • Optimized methods for Full Waveform Inversion in 3D

  • Líder : JOAO MEDEIROS DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • CLAUDIONOR GOMES BEZERRA
  • GILBERTO CORSO
  • JESSÉ CARVALHO COSTA
  • JOAO MEDEIROS DE ARAUJO
  • JORGE LUIS LOPEZ
  • REYNAM DA CRUZ PESTANA
  • Data: 21-oct-2021


  • Resumen Espectáculo
  • Full waveform inversion (FWI) is one of the most studied techniques today to recover subsurface parameters that affect
    wave propagation. One of the main difficulties in applying FWI in 3D seismic surveys is its high computational cost. This
    problem has been solved with the advancement of computational technology, but there are still difficulties to apply a FWI to real
    3D data. In this work are studied implemented to optimize a FWI, as which are based on the physical properties of waves. To
    this end, this work was done in two parts. In the first part, the encoded simultaneous sources technique was used, in which the
    FWI gradient is calculated by simultaneously propagating information from several sources grouped in one or several subgroups,
    taking advantage of the superposition principle of the wave equation. In order to reduce the crosstalk noise that appears in the
    gradient calculation using simultaneous sources, two encoding schemes have been proposed, by phase rotation and by static
    limited to a period of the dominant frequency. In phase rotation encoding a phase rotation is applied to each shot where the
    rotation angle is chosen randomly for each shot. In static coding the traces of each shot are temporally shifted and the value of
    this shift is chosen randomly for each shot having a maximum value of one period of the dominant frequency of the data. With
    the help of numerical tests on synthetic 2D data to demonstrate that the proposed schemes have a faster convergence than
    encodings by polarization (multiply by +1 or -1 randomly each shot) and by static without being limited. In the second part, a
    workflow was developed to apply a FWI to real data acquired in the Brazilian pre-salt region. This data was obtained with an
    Ocean Bottom Node (OBN) 3D acquisition, where the receivers are spread at the ocean bottom. In the developed workflow,
    several existing techniques are combined to optimize the use of memory and processing, which take advantage of wave
    propagation properties. On the OBN data for inversions made using sources and receivers decimation strategies to reduce
    computational cost. The encoded source schemes studied in the first part were also tested. These testicles also use various
    functions with the objective of an intention of melody and a resolution of inversions. It was verified that the inversions recovered
    information related to the pre-salt reservoir and that both decimation and source coding strategies reduced the computational cost
    of FWI without compromising the quality of the inversion.

20
  • FRANCISCO ALEXANDRE DE OLIVEIRA FEITOSA
  • Propagation of electromagnetic waves in Kolakoski quasicrystal with graphene

  • Líder : CLAUDIONOR GOMES BEZERRA
  • MIEMBROS DE LA BANCA :
  • CARLOS HUMBERTO OLIVEIRA COSTA
  • CLAUDIONOR GOMES BEZERRA
  • DORY HELIO AIRES DE LIMA ANSELMO
  • MANOEL SILVA DE VASCONCELOS
  • SERGIO ANDRÉ FONTES AZEVEDO
  • VAMBERTO DIAS DE MELLO
  • Data: 22-oct-2021


  • Resumen Espectáculo
  • In this work, we simulate the incidence of electromagnetic waves in an one-dimensional photonic quasicrystal composed of multilayers following the Kolakoski sequence with graphene embedded at the interfaces. The system is formed by the juxtaposition of two blocks of different dielectric materials, A and B, with A being silicon dioxide, (SiO2) and B being titanium dioxide, (T iO2). Between the blocks A and B we insert layers of graphene. We used the Transfer Matrix Method, which simplifies the algebra involved, to perform the numerical calculation that generated the data analyzed in this work. Next, we present the objectives of this work: generate the necessary data to establish the transmission and reflection spectra, investigate the effects of the graphene monolayer and evaluate the effects of the quasiperiodicity on the physical behavior of the system. To do so, we impose variations on the following parameters of the system: angle of incidence, chemical potential of graphene, Kolakoski generation index and the type of electromagnetic propagation mode. The results obtained reveal that the presence of graphene reduces the transmissivity across the entire frequency range and also induces a band gap in the low frequency transmission. Furthermore, we observe that the band gap produced by graphene is omnidirectional and that its thickness increases with the increase of graphene’s chemical potential, which can be adjusted by the value of the electrical voltage. Furthermore, we identified frequency ranges that present a Bragg gap

21
  • NIZOMAR DE SOUSA GONÇALVES
  • Sobre a relação entre excesso no infravermelho médio e a atividade cromosférica de estrelas do campo.

  • Líder : BRUNO LEONARDO CANTO MARTINS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • EDUARDO JANOT PACHECO
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • MARCELO BORGES FERNANDES
  • Data: 22-nov-2021


  • Resumen Espectáculo
  • Circumstellar disks are components of the formation of planetary systems and, at the same time, a product of these processes.
    On the other hand, debris disks are vestiges of the planetary formation process, indicating the formation of planetary systems.
    Note that the most important stages of circumstellar disks are: the protoplanetary disk and the secondary disk (or debris disk),
    which can be associated with stellar ages. The chromospheric activity index, logR’HK, is used as a star age tracer. Thus, it is
    reasonable to seek a relationship between chromospheric activity index and the presence of a circumstellar disc, however,
    studies of this nature are still rare. In this scenario, we look for circumstellar disks in a sample of 2845 field stars with known
    chromospheric activities. We searched for infrared excess, using WISE data in the bands 3.4 μm, 4.6 μm, 12 μm and 22 μm.
    These data, in turn, were combined with data from the 2MASS and GAIA missions to generate a Spectral Energy Distribution
    (SED) on the VOSA virtual platform and the SED curves were synthesized by the BT-Settl model. The infrared excess was
    characterized by the excess significance and the stars that were candidates to host circumstellar disks underwent visual
    inspection of the images, as well as their galactic latitudes were verified. At the end of this process, four stars were confirmed
    with circumstellar disks, classified as debris disks. The parameters that characterize the debris disks (temperature, luminosity
    fraction, radius and mass) were calculated and compared with the results in the literature. We observe that the luminosity
    fraction and mass of debris disks decrease with the age of the star systems. Finally, we found that the debris disks in our
    sample were found around more chromospherically active stars. In comparison with the results in the literature, there seems to
    be an anti-correlation between the luminosity fraction of the debris disks and the chromospheric activity index.

22
  • FRANCISCO DE ASSIS CHAVES DE BRITO
  • Infrared Excess and Debris Discs in M67 Cluster Stars

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • HELIO JAQUES ROCHA PINTO
  • BRUNO LEONARDO CANTO MARTINS
  • HELOISA MARIA BOECHAT-ROBERTY
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • Data: 21-dic-2021


  • Resumen Espectáculo
  • The search for circumstellar material orbiting different star families is one of the most studied topics in Stellar
    Astronomy, mainly because the presence of this material indicates the existence of exoplanets. In addition, their physical
    properties can tell us how much a planetary system may resemble the Solar System, indicating how this system may evolve.
    Current studies show the presence of circumstellar material with temperatures close to those found in the asteroid belt of the
    Solar System, but with widely varying dimensions and compositions. Although most studies of circumstellar dust and disks
    reveal that this material tends to disappear for stellar ages exceeding 300-400 million years, there are research showing that
    debris disks can be found orbiting stars with ages on the order of the solar age, i.e., 4 to 5 billion years. The main objective of
    this doctoral thesis is to search for debris disks that orbit stars of the Open Cluster M67, which is close to the age of the Sun.
    From this point of view M67 Cluster may contain stars at different evolutionary stages and may offer unique conditions to
    search for debris disks. It should be noted that this aspect will offer conditions to better understand how circumstellar debris
    disks evolve with age. This study adopted the strategy of searching for infrared excess in M67 stars, using observations
    collected by the WISE Mission, which provides fluxes at wavelengths corresponding to the bands 3.3 - 4.7 - 12 and 22 μm. O diagnóstico para identificação do excesso consistiu na comparação entre distribuições espectrais de energia, m.
    The diagnostics to identify the excess in M67 stars compared the spectral distributions of energy, built from theoretical models, and observational fluxes obtained at different wavelengths, extending from about 0.5 to 22 μm. O diagnóstico para identificação do excesso consistiu na comparação entre distribuições espectrais de energia, m, covering observations made by
    the Gaia Mission, 2MASS Project and WISE Mission. From an initial sample of 1520 stars, members of M67, 1380 stars were
    identified, presenting observations at WISE wavelengths 3.3 - 4.7 - 12 and 22 μm. O diagnóstico para identificação do excesso consistiu na comparação entre distribuições espectrais de energia, m, defined as bands W1, W2, W3 and W4
    respectively. These stars with WISE measurements also showed observations in the G, G RP and G BP bands of Gaia, as well
    as in the J, H and K bands of 2MASS. From the sample of 1380 stars, three objects designated J085103.24+114547.3,
    J085202.94+105932.7 and J085116.70+114529.6 show excesses with physical meaning (SNR > 3), absence of contamination
    by other sources or artifacts and circular images. These results point to a fraction of 0.2% of M67 stars with an excess at 22
    μm. O diagnóstico para identificação do excesso consistiu na comparação entre distribuições espectrais de energia, m, a value far below that cited in the literature for stars on the order of or with greater ages than the solar age, which is about
    4%. Considering that this excess is associated with the presence of circumstellar material, defined as debris disk, we used
    standard models to estimate the physical parameters associated with the disks: luminosity fraction, radius, mass and
    temperature. Although the temperatures of the material, between 225 and 300 K, are on the order of the temperatures known
    for the solar Zodiacal Cloud, the values obtained for the luminosity fraction and the mass, respectively 10 4 and 10 5 times
    higher than the Zodiacal Cloud values, show that the material around the stars J085103.24+114547.3, J085202.94+105932.7
    and J085116.70+114529.6 is brighter and denser than what is expected at the age of M67. Such material must also be
    composed of second-generation dust and debris and no longer be composed of material from the planetary formation phase.
    This unusual characteristic, that is, brighter and denser material, seems to indicate the presence of one or more replenishment
    mechanisms in these regions, through violent collisions between asteroids, planetesimals and planets.

2020
Disertaciones
1
  • BRUNO HENRIQUE SOUSA NOGUEIRA
  • Connectivities in critical two-dimensional Q-Potts Model.

  • Líder : JACOPO VITI
  • MIEMBROS DE LA BANCA :
  • JACOPO VITI
  • MOHAMMAD ALI RAJABPOUR
  • RODRIGO GONCALVES PEREIRA
  • Data: 12-mar-2020


  • Resumen Espectáculo
  • The conformal field theory has been show as a valuable asset in theoretical physics over the course of the last decades. In this work such theory was used as a way to evaluate four-point boundary connectivities in a two-dimensional model, where bonds are dictated by the Q-Potts model. For this model Q has integer values and 1 ≤ Q ≤ 4, that define unitary statistical models. In this paper we use a formal extension that Q  have real values and  0 ≤ Q ≤ 4$, range were still possible to evaluate connectivities as solutions of a differential equation  in conformal field theory. Such computations were made in order to obtain the universal ratio and inspect the consistency of results for $Q$ enclosed by two integers. Thereby, we were able to evaluate the universal ratio for diversified statistical models and achieve relevant results, in the sense that we showed the existence of a consistency or uniformity between the universal ratio and Q.

2
  • ÁLVARO SANTOS DE JESUS
  • Phenomenology of the Type-I Seesaw Mechanism

  • Líder : FARINALDO DA SILVA QUEIROZ
  • MIEMBROS DE LA BANCA :
  • FARINALDO DA SILVA QUEIROZ
  • CARLOS ANTÔNIO DE SOUSA PIRES
  • DIEGO ALEJANDRO COGOLLO APONTE
  • Data: 22-may-2020


  • Resumen Espectáculo
  • Neutrinos are elementary particles present on many phenomena in nature, from nuclear physics, such as the beta decay, to cosmology, where neutrinos have an essential role in the evolution of theuniverse.IntheStandardModelofParticlePhysics,neutrinosarehypothesizedtobemassless left-handed particles. However, with the discovery of the neutrino oscillations, it became known that the neutrinos are massive particles, which is direct evidence against the Standard Model. Therefore, there is a necessity for models beyond the Standard Model that can explain how the neutrinos become massive. In this work, we are going to study the Type-I Seesaw Mechanism, which is a model that explains how the neutrinos become massive by adding right-handed neutrinos (RHN) and the hypothesis that neutrinos can be Majorana particles. Even though this is a very simple model to explain the neutrinos masses, it also predicts the existence of several prohibited events, such as lepton flavor violation and lepton number violation processes. To analyze the consequences of the Type-I Seesaw Mechanism, we are going to study processes that have the RHN signature, as well as its phenomenology by using colliders and rare decays, so that we can obtain bounds on the RHN physical properties

3
  • FABRIZIO GIOVANNI OLIVIERO
  • Gapless chiral spin liquid from a parton mean-field theory on the kagome lattice

  • Líder : RODRIGO GONCALVES PEREIRA
  • MIEMBROS DE LA BANCA :
  • ALVARO FERRAZ FILHO
  • ERIC DE CASTRO E ANDRADE
  • RODRIGO GONCALVES PEREIRA
  • Data: 17-jun-2020


  • Resumen Espectáculo
  • Quantum spin liquids are among the most studied phases of matter which depart from the paradigm of symmetry
    breaking order and Fermi-liquid theory. In this work, we investigated a spin-1/2 Heisenberg model on the kagome lattice with
    exchange interaction Jd between spins connected by the diagonals of the hexagons and a staggered chiral interaction Jχ that
    couples the three spins in the triangles. Applying parton construction, we show that the model can exhibit a gapless chiral
    quantum spin liquid phase in the regime of dominant Jχ . The gapless phase is equivalent to the one found in other mean-field
    solutions based on Majorana fermions with symmetry protected line Fermi surfaces. Our goal is to study the changes in the
    spectrum of the spinons as a function of the ratio Jd/Jχ for two different cases of a specific ansatz in the mean-field theory. We
    expect that in the regime of relevant Jd , a non-coplanar ordered magnetic state appears, the cuboc-2 state. The apparent phase
    transition is analyzed in terms of the mean-field orders parameters and the search for instabilities in generalized susceptibility.
    This work provides a unique example of a phase transition between a chiral spin liquid and a non-trivial ordered magnetic
    state.

4
  • RAPHAEL BENJAMIM DE OLIVEIRA
  • Storage and release of H2 in two-dimensional materials

  • Líder : LEONARDO DANTAS MACHADO
  • MIEMBROS DE LA BANCA :
  • DAIANE DAMASCENO BORGES
  • LEONARDO DANTAS MACHADO
  • UMBERTO LAINO FULCO
  • Data: 10-ago-2020


  • Resumen Espectáculo
  • Two-dimensional (2D) carbon-based materials have been extensively investigated in recent years, due to their excellent mechanical, thermal and electronic properties. Among the discoveries that have emerged from these investigations, we would like to highlight here the possibility of controlling several properties in these materials using mechanical strain. In our work, we used the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) program to analyze whether  deformation could be used to release adsorbed gases in 2D materials. To determine if this was possible, we first examined whether the strain altered the interaction between the adsorbed gas and four structures: graphene, α-graphyne, β-graphyne, and ɣ-graphyne. Towards this end, we inserted a H2 molecule at a height z from the surface of each material, and changed its position to determine the interaction energy throughout the surface. Analysis of the results revealed that the strain reduced the attractive interaction between H2 and all of the investigated 2D materials. To confirm that the amount of adsorbed gas would decrease in the presence of deformation, we performed Monte Carlo simulations in the grand canonical ensemble, using structures with and without deformation. Our results confirmed that the strain reduced the amount of adsorbed gas on the surface of all of the investigated materials. Thus, we conclude that deformation can be applied to any of the studied materials to partially release the adsorbed gas. Comparing the studied materials, we observed that ɣ-graphyne showed the best performance at low pressures, and that α-graphyne showed the best performance at pressures near one atmosphere.

Tesis
1
  • ALYSON BRUNO FONSECA NEVES
  • Effective field theory and geometry of long molecules

  • Líder : DMITRY MELNIKOV
  • MIEMBROS DE LA BANCA :
  • DIONISIO BAZEIA FILHO
  • DMITRY MELNIKOV
  • RAIMUNDO SILVA JUNIOR
  • RICCARDO STURANI
  • VITOR BARBANTI PEREIRA LEITE
  • Data: 03-mar-2020


  • Resumen Espectáculo
  • The goal of this thesis is to construct an effective description of the dynamics of curves in three dimensions applicable in the context of protein physics. The model is intended to reproduce a variety of geometric characteristics observed in real proteins, assuming that proteins can be approximated by long continuous curves. The degrees of freedom in the effective description are parameterized by the curvature and torsion functions. The minimal necessary model is constructed in terms of an energy functional depending on four phenomenological parameters. We discuss static configurations of the effective model, which appear in two different classes: minima of the effective potential and soliton-like configurations interpolating between pairs of minima. In proteins such classes correspond to most common secondary structures (alpha-helices and beta-strands) and motifs connecting those structures (loops, turns, hairpins etc.) In order to obtain the values for the parameters, the solutions of the model are compared with real protein structures extracted from the Protein Data Bank. A very specific relation between the curvature and torsion predicted by the model allows us to universally fix three of the parameters of the model. We show that the fourth parameter is not universal. It controls the characteristic size of the motifs connecting alpha-helices and beta-strands and may be used to explain the absence of beta-strands in some proteins and their abundance in the others. In the most appealing scenario the model features ``stable'' alpha-helices and ``metastable'' beta-strands. We study the classical and quantum stability of the metastable configurations. We derive estimates for the temperatures of classical phase transitions and show that quantum transitions are suppressed. We also discuss how realistic discrete proteins “stabilize” beta strands and hairpin-like motifs.

2
  • GIVAL PORDEUS DA SILVA NETO
  • Theory and Applications of Reduced Relativistic Gas in Cosmology

  • Líder : LEO GOUVEA MEDEIROS
  • MIEMBROS DE LA BANCA :
  • FRANCISCO DE ASSIS DE BRITO
  • LEO GOUVEA MEDEIROS
  • LUCIANO CASARINI
  • RAIMUNDO SILVA JUNIOR
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • RONALDO CARLOTTO BATISTA
  • Data: 06-mar-2020


  • Resumen Espectáculo
  • The Reduced Relativistic Gas (RRG) is a simplified version of the ideal relativistic gas, where it is assumed that all particles have the same momentum magnitude. Although this is a very idealized situation, the resulting model preserves the phenomenology of the Maxwell-Boltzmann distribution and, in some situations, can be described as a perfect fluid, without introducing large errors. The perfect fluid description of RRG model was already used to study the warmness of dark matter, massive neutrinos and interaction of baryons and photons before recombination, showing very good agreement with previous works based on the full Einstein-Boltzmann system of equations. In order to understand these results and construct a more general and formal framework for RRG, we develop a theoretical description of first-order cosmological perturbations of RRG, based on a distribution function which encodes the simplifying assumption that all particles have the same momentum magnitude. From this function, we derive the full set of Einstein-Boltzmann equations for RRG and study quantities beyond the perfect fluid approximation. We derive an analytical expression that relates the parameter of warmness to the mass of the particle and also we explicitly verify that the non-relativistic and ultra-relativistic limits are recovered. Furthermore, using RRG to describe warm dark matter (WDM), we show that for particles with m keV, the perfect fluid approximation is valid on scales with k 10 h/Mpc, for most of the universe evolution. We also determined the initial conditions for RRG in the early universe and studied the evolution of the potential in a toy model composed only of RRG. Finally, we study in a semi-analytical way the sub-horizon evolution of the density contrast of the WDM in a model with WDM, radiation, and , where the WDM is described by the RRG.

3
  • RAFAELA MEDEIROS DE SOUZA
  • Domain Walls Nucleation and Maximum Energy Product in Magnetic Core@Shell Nanocylinders 

  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ARTUR DA SILVA CARRICO
  • FELIPE BOHN
  • SUZANA NOBREGA DE MEDEIROS
  • LEONARDO LINHARES OLIVEIRA
  • SILAS SARMENTO PEDROSA
  • Data: 06-mar-2020


  • Resumen Espectáculo
  • Ferromagnetic structures in confined geometries have attracted great interest, as geometric confinement opens new routes for manipulating fundamental magnetic properties required by major applications such as logic devices, magnetic sensors, nano-oscillators and magnetic memories. We report a theoretical study of the impact of dipolar interaction on the magnetic phases of the core@shell (Fe@Py) rectangular nanocylinders.Our results indicate that the dipolar interaction between the core and the shell is capable of causing significant changes in the magnetic phases of the isolated Fe cylinder and the Py ring. We show that the geometric parameters of flat Fe@Py core@shell cylinders can be chosen in such a way to control the nucleation of domain walls in the Py shell. It is also possible to fine-tuning the domain wall position and width by using only magnetic energies. On the other hand, bimagnetic nanoparticles combining different functionalities of two magnetic materials opens new perspectives for key applications such as permanent magnets, recording media, and magnetic hyperthermia. A theoretical analysis of the impact of the composition of FeP t@CoFe2 and FeP t@Fe bimagnetic nanocylinders on the maximum energy product (BH)max was performed. (BH)max is the determining parameter of the permanent magnet quality. The best composition is determined by the competing trends imposed by the dipolar energy and a ferromagnetic core@shell interface exchange energy. It was observed that the dipolar interaction has a negative impact on the intensity of (BH)max for shell thicknesses above a theresehold value, which depends on the material. The results show that the best shell material is the one with highest exchange stiffness.

4
  • ARTHUR GONÇALVES CAVALCANTI
  • Study of Quantum Defect Properties in the Holographic Approach

  • Líder : DMITRY MELNIKOV
  • MIEMBROS DE LA BANCA :
  • BRUNO CARNEIRO DA CUNHA
  • DMITRY MELNIKOV
  • JACOPO VITI
  • RODRIGO GONCALVES PEREIRA
  • THIAGO SIMONETTI FLEURY
  • Data: 09-jun-2020


  • Resumen Espectáculo
  • In this thesis, we present a review of the proposal for AdS/BCFT by T. Takayanagi for the holographic description of
    boundary systems, in particular, boundary conformal field theories (BCFTs). Motivated by a better understanding of the
    proposed duality, we employ entanglement entropy as a probe of familiar properties of impurities and defects. We discuss the
    configurations that provide examples of the renormalization group (GR) flow of defect entropy, as well as fixed points of GR.
    In addition, we built new solutions in BCFT’s dual holography through the application of differenteomorphisms between
    systems without temperature and with temperature. With that, we studied some thermodynamic systems far from equilibrium,
    in particular local quenchs, showing a model for the dynamic behavior of the entanglement itself due to the quantum defect.

5
  • JADSON TADEU SOUZA DANTAS
  • Vortex Stabilization in Coupled Cylindrical Ferromagnetic Nanostructures

  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ANA LUCIA DANTAS
  • ARTUR DA SILVA CARRICO
  • FABIO HENRIQUE SILVA SALES
  • LEONARDO LINHARES OLIVEIRA
  • MARIA DAS GRACAS DIAS DA SILVA
  • SERGIO MURILO DA SILVA BRAGA MARTINS JUNIOR
  • Data: 31-jul-2020


  • Resumen Espectáculo
  • Great discoveries in fundamental research very often lead to a new technology era. This is about to happen in nanomagnetism. Currently, there are promising perspectives of micro-wave nanoantenna’s design, based on the use of systems consisting of soft ferromagnetic nanoelements suitably designed to hold interacting magnetic vortices. Besides, there are demands for controlling the vortices chiralities. Experimental reports indicate that the vortex pair excitation spectra and magnetoresistance depend on the vortices chiralities. Furthermore, the synchronization of the vortex’s dynamics, owing to vortices interaction, leads to high-quality microwave spectra, with narrow emission lines, as desired for nanoantennas. The vortex magnetic profile results from a competition between the trends imposed by the exchange and the dipolar energies. Nanostructuring brings new elements and promising perspectives of tailoring the vortex magnetic profile of soft ferromagnetic nanoelements to suit device application demands. Placing two nanoelements together, if the nanoelements distance is comparable to its own geometrical dimensions, one may modify the intrinsic vortex profile of the soft material, because the dipolar field in each nanoelement may have a considerable contribution emanating from the other nanoelement. We have investigated the magnetic structure at remanence of pairs of vortices of a pair of identical and coaxial 21 nm height Fe circular nanocylinders with the diameter ranging from 81 nm to 129 nm, and the uniaxial anisotropy easy axis in the plane of the circular faces. In addition, we have investigated similar Py systems for comparison purposes. We have shown that by choosing appropriate values of the nanocylinders distance, one may control the dipolar interaction strength, allowing to set the relative chirality of the vortices in pairs of circular Fe nanoelements, as required for device applications. Furthermore, we have shown that the vortices chiralities and locations in the nanocylinders may be controlled by using external fields of moderate strength. For circular nanocylinders pairs, we have used preparations routes with the external field-aligned either in the x-axis direction, parallel the easy axis of the Fe uniaxial anisotropy, or in the y-axis direction, perpendicular to the easy axis of the Fe uniaxial anisotropy. We have shown that owing to the impact of the uniaxial anisotropy in the sequence of magnetic phases along either the x-axis or the y-axis preparation route, and the remnant state may be either a same chirality vortex pair or an opposite chirality vortex pair. In the case of Py nanocylinders, there is no uniaxial anisotropy. Our results show that for Py nanocylinder pairs, the magnetic pattern at remanence does not depend on the direction of the in-plane external field used in the preparation route. We notice that one may have surprising features from the dipolar interaction between the Fe nanoelements. For instance, we have found that isolated 21 nm height and 129 nm diameter Fe nanocylinders hold a vortex at remanence. However, contrary to intuition, coaxial pairs of these nanocylinders, placed one on top of the other at short distances, may display, instead, an almost uniform state at remanence. This might be valuable information for designing nano-oscillators based on pair of vortices. We have also investigated the remnant state of pairs of identical elliptical 25nm height Fe nanocylinders with face-to-face distance ranging from 20nm to 60nm. The Fe nanocylinders uniaxial anisotropy easy axis is in the plane of the elliptical faces pointing along the minor axis direction. To induce vortex nucleation, we have used the preparation route with the external field along the minor axis direction. We have shown that controlling the dipolar interaction strength by changing the elliptical nanoelements distance, one may design the magnetic structure of four interacting vortices at remanence. For instance, we investigated pairs of Fe (195 nm x 305 nm x 25 nm) nanocylinders, each with a 195 nm and 305nm long minor and major axes, respectively. The isolated Fe nanocylinders hold a single vortex at the center at remanence. A pair of these nanocylinders, with a 35 nm face-to-face distance, instead, shows a pair of opposite chirality vortices in each nanocylinder. We have shown that there are relevant changes in the strength of the dipolar and local fields, owing to the change of the magnetic structure that results from vortices motion. We suggest that this may affect the restoring torques for vortices oscillations around the equilibrium positions.

6
  • ISAAC DE MACÊDO FÉLIX
  • Heat Conduction in Quasi-Periodic Graphene-hBN Nanoribbons

  • Líder : LUIZ FELIPE CAVALCANTI PEREIRA
  • MIEMBROS DE LA BANCA :
  • ALEXANDRE FONTES DA FONSECA
  • ANDERSON LUIZ DA ROCHA BARBOSA
  • LEONARDO DANTAS MACHADO
  • LUIZ FELIPE CAVALCANTI PEREIRA
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 04-ago-2020


  • Resumen Espectáculo
  • The development of nanotechnology requires an increasing understanding of the phenomena related to nanoscale heat transport, in order to find promising strategies for thermal management in miniaturized electronic devices. In this sense, semiconductor superlattices (whose phonons are the main heat carriers) have been shown to be an ideal platform for the exploration of these phenomena, as they allow to control their physical properties by adjusting only their superlattice period (supercell size). In the present study, non-equilibrium molecular dynamics simulations were performed to investigate thermal transport in graphene-hBN superlattices in the face of a gradual deviation from their periodicity. For this purpose, quasiperiodic nanoribbons were built, which lie between periodic and disordered medium, distributing the domains of graphene and hBN in their supercells according to the Fibonacci, Thue-Morse and Double-Period sequences, which exhibit controlled growth from the periodic case. The results revealed a similar behavior for the three sequences analysed. In the periodic case, there is a non-monotonic behavior of the thermal conductivity with the superlattice period, which is a consequence of the crossover from the coherent (phonons wave-like) to incoherent (phonons particle-like) thermal transport regime, as has been reported in the literature. However, as the translation symmetry of the nanoribbons degrade with the quasiperiodicity of the supercell, the coherent thermal transport regime is gradually suppressed due to the diffuse scattering of phonons in different length scales. This allows to reduce its thermal conductivity in a controlled manner, being able to provide a value up to 60 % smaller than the thermal conductivity of its periodic counterpart. This finding opens a new horizon for the control of nanoscale heat transport and presents a valuable strategy for the development of new thermoelectric materials.

7
  • DIEGO ALVES DE BARROS
  • Synthesis and Characterization of NdCo Magnetic Nanostructures Covered with PVP

  • Líder : JOSE HUMBERTO DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • JOSE HUMBERTO DE ARAUJO
  • LUCIANO RODRIGUES DA SILVA
  • LÁZARO LUIS DE LIMA SOUSA
  • MARCO ANTONIO MORALES TORRES
  • RODOLFO BEZERRA DA SILVA
  • THOMAS DUMELOW
  • Data: 31-ago-2020


  • Resumen Espectáculo
  • Rare earth (RE) intermetallic compounds and transition metals (TM) are widely used in the production of permanent magnets and have, in general, ferromagnetic behavior. Most of these compounds are produced in an arc furnace or in ball mills, physical methods that do not allow controlling many variables in the process. Currently, much of the research in this area is related to the production of these compounds through chemical methods. In this work, we propose a process for the synthesis of magnetic nanoparticles of the NdCo type via the polyol method, with the use of PVP, for five samples with variation in the molar proportions of the compounds. PVP was used to protect the particles against aggregation and oxidation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements were performed for structural and morphological analysis, respectively. DC magnetization measurements, vibrant sample magnetometry at 5 K and 300 K and magnetic thermogravimetry (MTG), were performed for magnetic characterization. The XRD measurements showed the formation of the NdCo2, Nd2Co7, Nd5Co19 and Nd2Co17 phases, with predominance of the Nd2Co17 phase, for four of the five samples, for four of the five samples. The diffractogram network parameters were obtained through the rietveld refinement and showed that the average crystallite sizes ranged from 6.5 nm to 20.7 nm. Through TEM it was possible to observe ellipsoidal and spherical nanoparticles, distributed in a PVP matrix, with size distributions ranging from 6.1 nm to 12.4 nm, and which crystallographic planes and their respective phases contributed to the formation of the images. The DC magnetization measurements as a function of temperature indicated the Curie temperatures (Tc) of the phases and are in accordance with the literature and XRD measurements, the magnetization values showed elevations in the vicinity of Tc which are related to the PVP phase shift to high temperatures, and the consequent formation of metastable phases, rich in Cobalt, reported in the literature. The ferromagnetic behavior was observed in all samples at both 5 K and 300 K in the measurements of magnetometry of vibrant sample. With the TGM magnetic thermogravimetry measurements, the transition temperatures for the phases reported in the previous measurements were obtained, including for the metastable phases, through the simple interpolation method.

8
  • ÉRIC CARVALHO ROCHA
  • Complex analytical structure of stable Lévy distributions

  • Líder : MADRAS VISWANATHAN GANDHI MOHAN
  • MIEMBROS DE LA BANCA :
  • DORY HELIO AIRES DE LIMA ANSELMO
  • ERNESTO CARNEIRO PESSOA RAPOSO
  • LUCIANO RODRIGUES DA SILVA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MARCOS GOMES ELEUTERIO DA LUZ
  • Data: 23-sep-2020


  • Resumen Espectáculo
  • The almost ubiquitous Lévy α-stable distributions lack general closed-form expressions in terms of elementary functions—Gaussian and Cauchy cases being notable exceptions. To better understand this 80-year-old conundrum, we study the complex analytic continuation pα (z), z ∈ C , of the Lévy α-stable distribution family pα (x), x ∈ R, parametrized by 0 < α ≤ 2. We first extend known but intricate results, and give a new proof that pα (z) is holomorphic on the entire complex plane for 0 < α ≤ 2, whereas pα (z) is not even meromorphic on C for 0 < α < 1. Next, we unveil the complete complex analytic structure of pα (z) using domain coloring. Finally, motivated by these insights, we argue, that possibly, there cannot be closed-form expressions in terms of elementary functions for pα (x) for general α.

9
  • IVANDSON PRAEIRO DE SOUSA
  • Avalanche and interavalanche-intervals statisics in time-series.

  • Líder : GILBERTO CORSO
  • MIEMBROS DE LA BANCA :
  • FELIPE BOHN
  • GILBERTO CORSO
  • GUSTAVO ZAMPIER DOS SANTOS LIMA
  • JOSÉ GARCIA VIVAS MIRANDA
  • LUCIANO RODRIGUES DA SILVA
  • SERGIO R. LOPES
  • Data: 23-oct-2020


  • Resumen Espectáculo
  • In this work, we present empirical results obtained through the analysis of time series of three different complex systems: barkhausen noise signals in magnetic systems, accelerometer signals that recorded motor activity in rodents and acoustic signals that recorded background noise in some ecosystems ( soundscapes). In particular, we found that the time series of these three systems have a common feature: intermittency, all with some time interval distributed according to a power law. More precisely, in the case of Barkhausen noise, we obtained an exponential distribution for waiting times, in contrast to the already well-known power law for avalanche durations. For the accelerometer signals obtained in mice, we show that there is an alternation between a distribution of the
    power law form for the durations of the avalanches of motor activity and an exponential distribution for the quiet intervals. In the case of acoustic time series, we show that there is an alternation between a lognormal distribution for the intervals of acoustic activity (the sound times) and a power law for the intervals of quiet for all analyzed ecosystems.

10
  • NÚBIA RIBEIRO MACHADO
  • Dynamics of magnetization and Barkhausen noise in ferromagnetic

  • Líder : FELIPE BOHN
  • MIEMBROS DE LA BANCA :
  • FELIPE BOHN
  • GUSTAVO ZAMPIER DOS SANTOS LIMA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MARCIO ASSOLIN CORREA
  • RUBEM LUÍS SOMMER
  • SERGIO LUIZ ALVES DE QUEIROZ
  • Data: 03-dic-2020


  • Resumen Espectáculo
  • Since its discovery in 1919, Barkhasen noise (BN) has been widely used as an important tool to characterize soft magnetic materials, to understand the complex magnetization process and, in particular, to investigate the dynamics of domain walls. In recent years, BN has attracted great interest as an example of the manifestation of crackling noise in magnetic systems. In the particular case of the dynamics of domain walls and BN, most studies concentrate on explaining statistical properties such as the distributions of area and duration of jumps, average area and power spectrum, which can be described by power laws with exponents, τ, α, 1/σνz e ϑ  respectively. These power laws, which present a cutoff, are considered as a characteristic of the critical behavior of the magnetization process. In this work, we focus on the study of  Barkhausen noise in ferromagnetic multilayer films using the traditional inductive method and the statistical properties of  Barkhausen jumps. Specifically, were obtained Barkhausen noise time series for multilayer films with Co77Fe23B10(10 nm)/Ag(2 nm), Co77Fe23B10(10 nm)/Ta(2 nm) ,  Ni81Fe19(10nm)/Ag(2 nm) e Ni81Fe19(10nm)/Ta(2 nm) and structures consisting of 10, 15, 25 and 50 stacked bilayers. Motivated by the results obtained in polycrystalline and amorphous films with diferent thicknesses, through the method, we investigate the dynamics of magnetization through critical exponents of the distributions of area, duration, average area and power spectrum, obtained experimentally, to understand the efects the dimensionality of the system and the range of interactions on exponents due to the movement of domain walls. From theoretical predictions of models that describe the dynamics of a ferromagnetic domain wall driven by an external magnetic field through a disordered environment, it was observed that the exponents obtained experimentally, when compared to theoretical models, present three-dimensional magnetic behavior with long-range dipolar interaction, regardless of the number of stacked bilayers, the spacer and the field frequency suggesting a single universality class for the set of exponents. In particular, dependence on exponents τ and α for polycrystalline multilayers was not observed, a fingerprint of field theory-medium that describes three-dimensional polycrystalline magnetic materials. Our resuls reveal an artificially structured three-dimensional DWs dynamics due to the act of stacking bilayers with two-dimensional magnetic behavior. Finally, we raise possibilities of the coupling between the layers as an indicator of the stability of the exponents

11
  • LEONARDO RIBEIRO COLAÇO
  • COSMOLOGICAL BOUNDS ON A POSSIBLE TIME VARIATION OF THE FINE STRUCTURE CONSTANT AND THE COSMIC DISTANCE DUALITY RELATION

  • Líder : RODRIGO FERNANDES LIRA DE HOLANDA
  • MIEMBROS DE LA BANCA :
  • FRANCISCO DE ASSIS DE BRITO
  • LEO GOUVEA MEDEIROS
  • RAIMUNDO SILVA JUNIOR
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • RONALDO CARLOTTO BATISTA
  • SAULO HENRIQUE PEREIRA
  • Data: 11-dic-2020


  • Resumen Espectáculo
  • In recent years, with the advent of increasingly robust and accurate astronomical observations, further investigations of the role of fundamental constants of nature has become a fascinating field of research, because any space-time variation of these constants would indicate the presence of a new physics and would put in check the relativistic cosmology itself, based on the Cosmological Principle.In this thesis, by using galaxy clusters observations, type Ia Supernovae measurements, and Strong Gravitational Lensing Systems we propose three methods to probe a possible time variation of the fine structure constant (). Such possible variation is investigated in the specific context of the Runaway Dilaton model, which was originated from string theories. We conclude that, although the observational bounds obtained on a possible variation of  () are not competitive with those from quasar spectroscopy (), our proposals provide completely independent bounds with different redshift intervals. Finally, a test to probe a possible deviation of the cosmic distance duality relation (CDDR) is also proposed, , by using scaling-relation measurements from galaxy clusters properties plus type Ia supernova. The cosmological bounds obtained on possible deviations from the relation are compatible with the limits present in the literature and point to the validity of the duality relation.

12
  • CORNÉLIO RODRIGUES FILHO
  • Pseudo-Escalares na Teoria de Klebanov-Strassler

  • Líder : DMITRY MELNIKOV
  • MIEMBROS DE LA BANCA :
  • DMITRY MELNIKOV
  • LEO GOUVEA MEDEIROS
  • RICCARDO STURANI
  • HORATIU STEFAN NASTASE
  • NELSON RICARDO DE FREITAS BRAGA
  • Data: 17-dic-2020


  • Resumen Espectáculo
  • Nesta tese descrevemos o setor pseudo-escalar $0^{-+}$ da teoria de Klebanov-Strassler. Este setor completa a construção holográfica para os estados mais leves de glueballs, que são singletos perante a simetria global $SU(2)\times SU(2)$. Nós derivamos as equações lineares da supergravidade para o setor pseudo-escalar e analisamos o seu espectro. O sistema de equações apresenta compatibilidade com seis automodos, como esperado pela supersimetria. Nossa análise numérica permite de forma confiável extrair quatro torres de autovalores. Tais valores mostram boa compatibilidade com os resultados do setor  escalar $0^{++}$, que já são conhecidos através de outro trabalho. Assumindo as massas de $0^{++}$ como uma referência, nós comparamos os estados mais leves do espectro holográfico com os resultados de Yang-Mills na rede para $SU(3)$ e $SU(\infty)$.

13
  • ANTONIA VERUSKA BENEVIDES PINHEIRO
  • Study of magnetic couplings in CoFe2O4@CoFe2 nanostructures dispersed in Ag matrix

  • Líder : SUZANA NOBREGA DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • RAIR MACÊDO
  • DORY HELIO AIRES DE LIMA ANSELMO
  • FELIPE BOHN
  • JOÃO MARIA SOARES
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 18-dic-2020


  • Resumen Espectáculo
  • Using the coprecipitation method, samples (precursors) of the CoFe2O4-Ag nanocomposite were synthesized, varying the concentration of CoFe2O4. These samples were subjected to thermal reduction, under H2 atmosphere at 350 °C, for different time intervals in order to obtain a core-shell nanostructure of CoFe2O4@CoFe2 dispersed in the Ag matrix. Through X-ray diffractometry, it was observed the phases CoFe2O4, CoFe2 and Ag,, where the peak of CoFe2 (shell) becomes more evident for samples reduced for a longer time. Rietveld refinements provide values for the size of CoFe2O4 nanoparticles (core) which decrease size with the increase in the reduction time, from 30 to 90 minutes. This decrease was also observed in Transmission Electron Microscopy images, and is around 0.5 nm. Meanwhile, the shell thickness (δCF) changes from 2.5 nm to 3 nm between samples with a lower concentration of CoFe2O4 reduced by 30 and 90 minutes. The nanoparticles of Ag, in the precursor samples, have diameters of 11 nm, but this value increases to ≈ 15 - 20 nm after the heat treatment. Magnetization measurements, at 300 K, reveal a decrease in the coercive field (Hc) as δCF increases, and the behavior of the curves suggests an exchange spring coupling. A phenomenological model was developed to describe the behavior of magnetic interactions in relation to the distance between the core shell nanoparticles, Dnc, based on the analysis of  Henkel and δm plots which are obtained through the relationship between the remaining reverse and direct magnetizations. For small Dnc distances, there is a greater contribution of dipolar interactions. When Dnc increases, the exchange interactions are more pronounced, as the contribution due to coupling at the core-shell interface is evidenced. Magnetization measurements as a function of the field in 4 K by zero field cooling and field cooling under a 1 T cooling field exhibit a horizontal shift in the curves, which can be attributed to freezing spins at the core-shell interface. It was found that the field of exchange bias (HEB) in samples with lesser δCF is approximately double that presented in samples with thicker δCF. This increase in HEB is related to the ratio of the surface area on one disordered layer to the volume of the ferromagnetic layer.

2019
Disertaciones
1
  • JOSIEL MENDONÇA SOARES DE SOUZA
  • Discriminating Cosmological Expansion Models With Third Generation Gravitational Waves Detectors

  • Líder : RICCARDO STURANI
  • MIEMBROS DE LA BANCA :
  • JAILSON SOUZA DE ALCANIZ
  • RICCARDO STURANI
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • Data: 26-feb-2019


  • Resumen Espectáculo
  • At the dawn of Gravitational Wave Astronomy, new avenues have been opened to test and
    constrain cosmological models. By simulating standard sirens detected by the third generation ground-
    based gravitational wave detector, Einstein Telescope, we show how we one can discriminate among
    different cosmological models. In this work, we use 10-year projected data of Einstein Telescope to compare
    the standard cosmological model (the Lambda CDM) with models using different phenomenological
    parametrizations of the equation of state for the dark energy.

2
  • HERNÁN GUILLERMO BUENO XAVIER
  •  An Effective Model for Strongly Correlated Electrons

  • Líder : ALVARO FERRAZ FILHO
  • MIEMBROS DE LA BANCA :
  • ALVARO FERRAZ FILHO
  • EVGENII KOCHETOV
  • RODRIGO GONCALVES PEREIRA
  • Data: 28-feb-2019


  • Resumen Espectáculo
  • In this work we examine an alternative effective formulation for the $t$-$J$ model which is believed
    to capture the essential physics behind the underdoped regime of the high-$T_c$ cuprates. After recasting
    the original problem in this new representation, we check the consistency of our procedure and discuss
    some physical consequences of such a representation including, the crossover between the regimes of small
    and large Fermi surfaces which is observed experimentally. We then explore the possiblity of constructing a
    path integral representation for the $t$-$J$ quantum partition function departing from the proposed
    formulation. Finally, we use the latter formalism to derive a continuum effective field theory in $(2+1)$
    spacetime dimensions which features small hole-like pockets near the nodal regions of the Brillouin zone
    along with an unconventional mechanism for superconductivity.

3
  • PABLO JOSÉ LIMA SOARES
  • Polaritons in photonic crystals interspersed with graphene

  • Líder : EUDENILSON LINS DE ALBUQUERQUE
  • MIEMBROS DE LA BANCA :
  • EUDENILSON LINS DE ALBUQUERQUE
  • UMBERTO LAINO FULCO
  • FABIO FERREIRA DE MEDEIROS
  • Data: 08-ago-2019


  • Resumen Espectáculo
  • We presented an electromagnetic wave propagation in periodic and quasiperiodic (Fibonacci type) multilayer structures, intercalated by a graphene layer, using a theoretical model based on a transfer matrix treatment to simplify the algebra which can be otherwise quite heavy. The multilayer structure is composed by two materials A and B with positive and negative refraction indexes in the terahertz (THz) region. Medium A is a semiconductor (silicon carbide - SiC), with a plasmon-phonon dielectric function and a constant magnetic permeability. Medium B is a metamaterial (lithium tantalate - LiTaO3) with a plasmon-polariton type dielectric function and a Drude type magnetic permeability. We discussed the photonic band gap spectra for both the ideal cases, where the refractive index dependent on the frequency of one of the materials can be considered constant in the the frequency range investigated, as well as the more realistic case, taking into account a frequency-dependent refraction index for both materials. The so-called zero-gap region of the mean refractive index  of the photonic structure is also investigated. We also presented a quantitative analysis of the results, pointing out the distribution of the allowed photonic bandwidths for high generations, which gives a good insight about their localization and power laws.

4
  • SAMIHR VALENTIM HERMES
  • Quantum Boltzmann Equation and BBGKY Hierarchy

  • Líder : TOMMASO MACRI
  • MIEMBROS DE LA BANCA :
  • DORY HELIO AIRES DE LIMA ANSELMO
  • SIMONE PAGANELLI
  • TOMMASO MACRI
  • Data: 04-oct-2019


  • Resumen Espectáculo
  • In this work we will focus in statistical physics applied to problems of Bose-Einstien condensation at finite temperatures. We begin by a brief introduction to the classical methods, already well established by fundamental courses. Afterwards, starting from a kinetic theory, we will obtain the equations of motion for the atoms in the condensate state, as well as for the Bogoliubov quasiparticles of the thermal cloud of excited atoms. Through this kinetic description, we will also obtain, from quantum principles of quantum mechanics, the Born-Bogoliubov-Green-Kirkwood-Ygon (BBGKY) hierarchy, which can be truncated to obtain the Boltzmann-Vlasov Equation. Finally, we will use the same microscopic principles to study the damping of collective excitations of the Bose-Einstein condensate in the thermal regime.

5
  • YOXARA SÁNCHEZ VILLAMIZAR
  • Phenomenology of the Type-II seesaw model

  • Líder : FARINALDO DA SILVA QUEIROZ
  • MIEMBROS DE LA BANCA :
  • DIEGO ALEJANDRO COGOLLO APONTE
  • CARLOS ANTÔNIO DE SOUSA PIRES
  • FARINALDO DA SILVA QUEIROZ
  • Data: 29-nov-2019


  • Resumen Espectáculo
  • In this dissertation the theoretical and experimental aspects of the type-II seesaw model will be reviewed. The type-II seesaw is a mechanism that generates neutrino masses by adding a weak-scalar triplet to the Standard Model spectrum. This model is phenomenologically attractive  because it can generate neutrino masses without invoking new physics effects at very high energy scales. We revisit the constraints coming from the $\rho$-parameter and electroweak precision data. Later we discuss collider signatures of the type II seesaw model focusing on the Large Hadron Collider. We exhibit the viable parameter space of the type II seesaw model and show the complementarity between collider physics and lepton flavor violation. This dissertation represents a first-step to our goal which is to assess the High-Luminosity and High Energy LHC sensitivity to the type II seesaw model in connection to lepton flavor violation and neutrino mass ordering.

6
  • ARTHUR LANNE RICARDO DE SOUZA
  • Integration of the tape casting and magnetron sputtering techniques for the development of moldable multifunctional systems

  • Líder : MARCIO ASSOLIN CORREA
  • MIEMBROS DE LA BANCA :
  • Antonio Carlos Silva da Costa
  • BRUNO RICARDO DE CARVALHO
  • MARCIO ASSOLIN CORREA
  • Data: 17-dic-2019


  • Resumen Espectáculo
  • The increased demand for low-power and high-performance electronic systems has been driving the discovery of new materials and the study of their physical and chemical properties. In this sense, the integration of different techniques allows us to develop multifunctional materials with specific properties and characteristics for certain technological applications. In this scenario, this work presents a proposal for the production of hybrid materials through the integration between tape casting and magnetron sputtering techniques. To this end, the magnetron sputtering technique was used to grow trilayered thin films nanostructures of Ni81Fe19/Cr/Ni81Fe19, using as substrates Al2O3 and ZrO2 ceramic flexible sheet produced by the tape casting technique. As a comparison standard, similar films were grown onto amorphous rigid substrate (glass), which has been widely studied in the literature. The slurries, suspensions of ceramic materials, presented the pseudoplastic behavior, which is recommended for the tape casting technique. The films were produced with a fixed total thickness of 300 nm, but varying the thickness of the Ni81Fe19 layers between 75 and 142.5 nm and the Cr layer thickness between 15 and 150 nm. The structural characterization revealed that the change of the used substrate did not modify the structural properties of Ni81Fe19 films. The magnetic measurements reveal that films produced onto flexible sheet show an evolution of the contribution of out-of-plane anisotropy with the increase of Ni81Fe19 layer thickness, as well as the dependence of magnetic properties with the Ni81Fe19 layer thickness, results that mirroring the magnetic properties found in Ni81Fe19 thin films on the glass in the literature. Based on these results, we were able to keep the magnetic properties of the Ni81Fe19 alloy, even when the flexible sheet of Al2O3 and ZrO2 ceramic tapes were employed. Thus we conclude that the flexible sheets are excellent candidates for moldable device applications as ceramic-magnetic coating.

Tesis
1
  • JOSÉ ARCÊNIO DOS SANTOS LOURENÇO
  • Kondo effect in a PT-symmetric non-Hermitian Hamiltonian

  • Líder : RODRIGO GONCALVES PEREIRA
  • MIEMBROS DE LA BANCA :
  • DMITRY MELNIKOV
  • DORY HELIO AIRES DE LIMA ANSELMO
  • LUIS GREGORIO DIAS DA SILVA
  • MARIA CAROLINA DE OLIVEIRA AGUIAR
  • RODRIGO GONCALVES PEREIRA
  • Data: 19-mar-2019


  • Resumen Espectáculo
  • The non-Hermitian physics along with strong correlations allows the appearance of new effects
    in open quantum many-body systems with balanced gain and loss. In this work, we proposed a
    generalized Anderson impurity model that presents the inclusion of non-Hermitian hopping terms between
    an embedded quantum dot and two wires. Such non-Hermitian hopping terms are symmetric under the
    combined action of parity (P) and time reversal (T ). We mapped the model in the regime of a localized
    state occupied by a single electron leading to the PT -symmetric Kondo model . We analyzed the
    interaction effects by applying the perturbative renormalization group approach. We found that the Kondo
    effect persists if the couplings are below a critical value, which corresponds to the exceptional point of the
    non-Hermitian Kondo interaction. We observed that in the regime of the spontaneous breaking of PT -
    symmetry, the Kondo effect is suppressed and the low energy properties are governed by a local-moment
    fixed point with zero conductance.

2
  • RICARDO BORGES DA COSTA
  • Pré-defesa Doutorado

  • Líder : ALEXANDRE BARBOSA DE OLIVEIRA
  • MIEMBROS DE LA BANCA :
  • ALEXANDRE BARBOSA DE OLIVEIRA
  • DORY HELIO AIRES DE LIMA ANSELMO
  • MARCIO ASSOLIN CORREA
  • CARLOS CHESMAN DE ARAUJO FEITOSA
  • JOÃO MARIA SOARES
  • ROBERTO LÁZARO RODRIGUEZ SUAREZ
  • Data: 07-jun-2019


  • Resumen Espectáculo
  • Pré-defesa Doutorado

3
  • RODRIGO DA SILVA SOBRINHO
  • Infrared excess in rotational stars analogs to the Sun: Looking for exo-asteroid belts

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • EDUARDO JANOT PACHECO
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • MARIA LIDUINA DAS CHAGAS
  • Data: 27-jun-2019


  • Resumen Espectáculo
  • Observations of circunstelar matter disks provide a powerful tool for our understanding of planetary systems dynamics. Analogs to the Solar System asteroid belts, such disks results, mainly, from the collision of remaining solid material from the planetary formation process. Even if the current literature describe the presence of circunstelar disk in hundreds of Main Sequence stars, its detection around stars similar to the Sun is still very uncommom. In this context, this present study is focused on the search for debris disk orbiting stars with superficial physical parameters similar to solar values, including, particularly, rotation period, from photometric observations in the infrared, in
    the 3.4, 4.6, 12 and 22 μm bands, made by the space mission WISE (Wide-field Infrared Survey Explorer). As central object, a sample of 881 stars was defined with effective temperature, metallicity, gravity and rotation period similar to solar values. These stars, defined here as rotational analog to the Sun, have a well determined rotation period, calculated from photometric modulation identified in light curves obtained by the space telescope Kepler. Six stars, KIC 1868785, 7267949, 7435796, 10533222, 11352643, and KIC 11666436, present clear signs of infrared excess, a revealing diagnosis of the presence of circunstellar matter orbiting them. The disks of matter detected are much more dense and luminous than the Solar System zodiacal dust, pointing to a origin associated to recent violent events.

4
  • WILLIAM JOUSE COSTA DA SILVA
  • OBSERVATIONAL CONSTRAINTS ON NONADDITIVE COSMOLOGICAL MODELS: FROM BULK VISCOSITY TO DYNAMICS

  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • JAILSON SOUZA DE ALCANIZ
  • LEO GOUVEA MEDEIROS
  • LUCIANO RODRIGUES DA SILVA
  • RAIMUNDO SILVA JUNIOR
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • VALERIO MARRA
  • Data: 28-ago-2019


  • Resumen Espectáculo
  • From current cosmological observations, dark matter and dark energy are the energetic components that dominate the evolution and dynamics of the present universe, as baryonic matter and radiation have a share of less than 5% of total cosmic energy. Although necessary to describe some observational data the nature of the dark sector remains a mystery to cosmology. In this thesis, we study a cosmological models scenarios with bulk viscosity. Endowed with an alternative interpretation of the bulk viscosity and the dynamics of the Universe from the microscopic effects based in the nonadditive Statistical Mechanics we propose a extended ΛCDM model. This scenario take account nonadditive effects about the energy equipartition theorem as well as an interpretation of the viscous dark matter through nonextensive/dissipative correspondence (NexDC). In order to impose observational constraints on model parameters and compare models, we implement a Bayesian Analysis considering data from the type Ia supernovae, baryon acoustic oscillations and cosmic background radiation. The results obtained were that the non-extensive viscosity effect is discarded at 1σ confidence, but at 2σ we have a scenario with viscosity. From a model comparison point of view, the proposed models have unfavorable inconclusive evidence regarding the ΛCDM. In the second part of the thesis, we consider a description of viscous dark energy in the scope of universe dynamics modified by nonadditive theory as well as the standard. In order to impose observational limits, we performed a Bayesian Analysis using data from cosmic chronometers, type Ia supernova, baryonic acoustic oscillations, and cosmic background radiation. As a results of the analysis, we obtain that a bulk viscosity is discarded in 1σ in the dark energy context. In the comparison models, we can conclude that the viscous dark energy models are also discarded compared to the ΛCDM model.

5
  • CLAUDIVAN MOREIRA DE SOUZA
  • THERMOMAGNETIC EFFECTS ON MAGNETIC NANOPARTICLES AGGLOMERATES

  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ANA LUCIA DANTAS
  • ARTUR DA SILVA CARRICO
  • FELIPE BOHN
  • LEONARDO LINHARES OLIVEIRA
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 25-oct-2019


  • Resumen Espectáculo
  • Recent research has studied the magnetic properties of nanoparticle superparamagnetic clusters with the possibility of applications in drug delivery control systems, magnetic resonance imaging, magnetic hyperthermia, etc. At the same time, several researchers have studied the phenomenon of thermal hysteresis under different circumstances and systems. Another object that has concentrated efforts in current research is the magnetocaloric effect on different structures focusing on the application in magnetic cooling technology. The objective of this work is to investigate the phenomenon of thermal hysteresis in superparamagnetic clusters of magnetite (Fe3O4) and Gadolinium (Gd) with spherical and ellipsoidal geometry and to analyze the impact of dipolar interaction on the thermal stability of as well as to investigate the magnetocaloric effect on Gd nanoparticle clusters. For this, we investigated the thermal magnetization curve of clusters with different eccentricities, with the size of the order of hundreds of nanometers composed of particles of Fe3O4 from 9 nm to 12 nm in diameter and Gd particles of 5.5 nm to 20 nm, with

    variable density and evenly distributed in the clusters. We consider a temperature range from 200 to 1200 K, calculate the cooling and heating curves, as well as analyze the magnetic phases of the system under the effect of a low and constant external magnetic field. The entropy range  was calculated for an external field range for Gd ellipsoidal cluster systems. In our model, we do not consider effects of magnetocrystalline anisotropy. The anisotropy present in the system comes from the shape of the clusters and the dipolar interaction that naturally produces an anisotropic effect. We observe that the dipolar field

    has a relevant contribution in the formation of thermal hysteresis. In spherical clusters we do not observe the formation of thermal hysteresis, in these clusters the sequence of magnetic phases in the cooling and heating branch are identical. In ellipsoidal clusters of eccentricity 0.97, the formation of thermal hysteresis associated with a sequence of magnetic phases characteristic of the ellipse was strongly influenced by the action of the dipolar field of the nanoparticles. The inverse magnetocaloric effect was observed in high eccentricity ellipsoidal clusters that have the Antiferromagnetic state as the natural state of magnetization. The results indicate that the magnetic phases that lead to the emergence of thermal hysteresis result from the competition between Zeemann, thermal and dipolar energies associated with the effect of the cluster topology. Therefore, in the systems analyzed in this study, the above parameters can control the appearance and characterization of thermal hysteresis and magnetocaloric effect.

6
  • SERGIO MURILO DA SILVA BRAGA MARTINS JUNIOR
  • Generalized Dynamics for Nanostructured Magnetic Systems

  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ANA LUCIA DANTAS
  • ARTUR DA SILVA CARRICO
  • JOSE HUMBERTO DE ARAUJO
  • LEONARDO LINHARES OLIVEIRA
  • SILAS SARMENTO PEDROSA
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 13-nov-2019


  • Resumen Espectáculo
  • Microwave emission by magnetic materials at well-localized frequencies is of great interest for future nanotechnology applications. Theoretical models were developed in this work to study the excitation spectra of nanostructured magnetic systems. We use micromagnetic simulations, the Landau-Lifshitz resolvent matrix and a generalized dynamic susceptibility tensor. The first part of this work is devoted to setting the Landau-Lifshitz equations of motion for a nanostructured system composed, according to the micromagnetic theory, and the elements of the Landau-Lifshitz equations resolvent matrix, as well as the elements of the dynamic susceptibility tensor. The theoretical models are then applied to describe the excitation spectra of systems such as uniformly magnetized ferromagnetic nanostripes, domain walls of ferromagnetic nanostripes coupled to antiferromagnetic vicinal substrates and magnetic vortices of circular nanodisks. The resolvent matrix allows obtaining the spectral density of states, and is applied to the study the spectra of domain walls, allowing the characterization of some modes of walls oscillations in a frequency range below the magnetic domain spectral band. Using the dynamic susceptibility tensor, the spatial distribution of resonance modes along the entire nanostructure could be identified. Thus, the similarities and differences between the domain, domain wall and vortex magnetic excitations can be investigated using the theoretical models developed in this study. Thus, we suggest, it possible to predict microwave field values to excite each of the observed oscillation modes.

7
  • LUCIANO LUIZ ALENCAR DE OLIVEIRA
  • A ROTAÇÃO ESTELAR REVELADA PELA MODULAÇÃO FOTOMÉTRICA

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • LEONARDO ANDRADE DE ALMEIDA
  • MARIA LIDUINA DAS CHAGAS
  • Data: 16-dic-2019


  • Resumen Espectáculo
  • Rotation is one of the most important parameters in astrophysics and its effects are observed in all evolutionary stage, since the beginning. This present work shows an analysis of the rotation from photometric measures along the Hertzsprung-Russell diagram (HR diagram), for stars in different evolutionary stages, such as: main sequence, subgiants, giants, bright giants and supergiants Ib. We use stellar evolution models with rotation, in which the metallicity are z = 0, 002 and z = 0, 014, presented respectively by Georgy et al. (2013b) and Ekström et al. (2012). Through the measurement of angular rotation velocities, presented in the models, we estimate the rotation period for each evolutionary track (with masses ranging from 0, 8M
     < M ≤ 20M
    ) and consequently we determine the rotation isoperiodic lines using the interpolation technique cubic spline for a effective temperature region 3.500 < Tef ≤ 10.500 K and luminosity −1, 0 < Log (L/L
    ) ≤ 5, 5. The interpolation technique was utilized to the mean values ±5% of the desired measurements, which are 5, 15, 25, 50 and 100 days. Combining the isoperiods with the distribution of our sample’s rotation period values, we observe that there is a significant congruence between the theoretical data and the observational data, even though another analysis may indicate a divergence. In addition, our results show that the discontinuity of the rotation period happens gradually and in every luminosity class, in the vertical direction (depending only on the stellar mass), as well as in the horizontal direction (depending on the effective temperature) in the HR

    diagram.

8
  • SUZIERLY ROQUE DE LIRA ARAUJO
  • On the photometric variability of white dwarf stars

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • LEONARDO ANDRADE DE ALMEIDA
  • MARIA LIDUINA DAS CHAGAS
  • Data: 17-dic-2019


  • Resumen Espectáculo
  • Photometric variability can provide important information about white dwarfs, whether related to rotation or the presence of companions - planetary, substellar or stellar-remnant. The rotation can provide clues to the physics of white dwarf formation, once it is a remnant of their angular momentum, which went through several stages of stellar evolution. The presence of substellar companions or stellar-remnant provides clues about the final stages of stellar evolution and plays an important role in that evolution. The high photometric precision and the large amount of data provided by space missions, such as Kepler and K2, combined with the correct tools, make it possible to analyze the photometric variability of white dwarf stars. In order to detect the relative periodicities, present in the light curve obtained by these space missions, several mathematical transformations have been applied, such as the Fourier transform, one of the most used in astrophysics, and the Wavelet, which has been applied in a wide range of areas, including Statistics, Geophysics, Image Coding and Compression, Turbulence and Astrophysics. The Wavelet transform is a powerful tool, since it has functions located in both frequency and time, allowing the detection of the temporal evolution of various phenomena, which makes it ideal for analyzing non-stationary signals. In this context, we use these tools in order to study the photometric variability of 25 white dwarf stars observed by the Kepler mission. From the light curves of these stars, we analyze the Lomb-Scargle periodograms, determine the possible physical mechanisms responsible for the detected modulations and perform local and global wavelet spectra. The first one is interpreted as the signal energy distribution, while the second one is the temporal integration of the local map. Finally, we discuss the physical meaning of the results by establishing a comparative study between the periodicities determined in this work and those found in literature.

9
  • JOSE EDVALDO DE LIMA JUNIOR
  • On the Incidence of Debris Disk orbiting in main Post Sequence Stars.

  • Líder : BRUNO LEONARDO CANTO MARTINS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • IZAN DE CASTRO LEÃO
  • JOSE RENAN DE MEDEIROS
  • LEONARDO ANDRADE DE ALMEIDA
  • RODRIGO DA SILVA SOBRINHO
  • Data: 19-dic-2019


  • Resumen Espectáculo
  • In this work we look for debris discs around main post sequence using the infrared excess identified from the spectral energy distribution (SED) and visual inspection of the images provided by bands of the WISE satellite for each star. Our sample is compose of red giant and white dwarfs stars. The red giants sample have 6676 of Pinsonneault et al. (2018) catalog and 360 of Ceillier et al. (2018). In the catalog of  Fusillo et al. (2017) there are 12,359 stars that are inside (VST ATLAS) catalog, out of them these authors selected 4200 stars through Pwd function (probabilities of being white dwarfs). Out of the selected stars 351 of the stars are in the 2MASS (Cutri et al. 2003) catalog at the bands 1.24 mm, 1.63 mm and 2.16 mm  (J, H and K, respectively) and 220 stars have WISE (Cutri et al. 2013) fluxes at bands 3.4 mm, 4.6 mm, 12 mm and 22 mm (W1, W2, W3 and W4, respectively) where Only 41 of these stars have significance greater than   (Ribas et al. 2012) and 31 stars show excess infrared on the bands W1 and W2 according to their SEDs of the BT-DUSTY model. Finally, 7 of these stars were selected from the visual inspection for W1 and W2 bands. For the final sample of 7 stars, we calculate the disc temperature (), luminosity fraction (, inner radius () and mass of the disc ().

10
  • DANIELLY FREIRE DA SILVA
  • Infrared Excess and Debris Disk around Kepler Subgiant Stars

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • JOSE RENAN DE MEDEIROS
  • BRUNO LEONARDO CANTO MARTINS
  • IZAN DE CASTRO LEÃO
  • ANTONIO CARLOS DA SILVA MIRANDA
  • RODRIGO DA SILVA SOBRINHO
  • Data: 20-dic-2019


  • Resumen Espectáculo
  • Studies about circumstellar material in different evolutionary stages has been increasingly developing due to the emergence of high photometric resolution space missions, covering an even larger spectrum of infrared wavelength. Among them, Spitzer, Herschel and WISE, for instance, present a particular aspect by offering observations in wavelength compatible to the temperature of the Solar System's Asteroid Belt and Zodiacal Cloud. In this present thesis, a search for debris disk is performed around 34030 objects, defined in the literature as being in the Main Sequence, observed by the Kepler mission and based on the WISE mission photometric information. At first, a diagnosis is performed on the presence of infrared excess on these stars, this detection is potentially associated to the presence of circumstellar material. Then, a study is made about the evolutionary stage of the sample, including their location on the HR diagram. This analysis was done based on data from the GAIA mission and showed that only about 16500 stars are actually Main Sequence, with around 17000 presenting characteristics of Subgiants or binary systems, according to their location. By utilizing data treatment tools, including VOSA, this work has shown the presence of debris disk around 35 Main Sequence stars, 13 Subgiants and one anomalous star, with well defined locations in the HR diagram, raising questions about the physical characteristics of these disks in relation to the stellar age. The Main Sequence stars possess debris disks that are more massive and more luminous than the Solar System's Asteroid Belt and Zodiacal Cloud, bringing up the possibility that the disk was refueled with additional material, produced by violent stochastic events, including the disintegration of large bodies such as planets or massive asteroids. In Subgiants stars, on average, the mass and luminosity of the disks are in the same order as the values seen in the Main Sequence stars, this is incompatible with the notion that these disks are first generation remnants and have survived the first evolutionary stages. Therefore, such results seem to point to the presence of dynamical physical processes happening in the circumstellar environment during the Subgiant stage, refueling the disks with material produced in this stellar evolutionary stage. The Subgiants' disks presented in this work can not be explained solely by the evolutionary context or under the consideration that they were preserved during the passage from the Main Sequence to the Subgiant stage and along the evolution outside the Main Sequence.

2018
Disertaciones
1
  • RUTE MELO DE OLIVEIRA
  • Preferential Attachment in Network: Dissimilarity Model

  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • LUCIANO RODRIGUES DA SILVA
  • MARCOS VINICIUS CANDIDO HENRIQUES
  • RAIMUNDO SILVA JUNIOR
  • SAMURAÍ GOMES DE AGUIAR BRITO
  • Data: 02-mar-2018


  • Resumen Espectáculo
  •  Many systems can be represented by complex networks once that they are characterized by
    several constituents interacting with each other. Because that, the study of the networks has become very popular in the scientific community, in the different areas of research. Seeking to understand the behavior of some real systems, many models were proposed. In this work, we elaborate and discuss a complex dynamic network model, based on the Bianconi-Barabasi model. We changed the preferential attachment rule by inserting a factor representing a dissimilarity between the sites. The dissimilarity factor informs us about the differences between the fitness parameter. Our model is represented by the following preferential attachment rule: Πi= (|ηi-ηj|ki)\(Σ|ηi-ηj|kj). In this way, two factors are responsible by the competition for links: (i) connectivity, the most connected sites are favorable to receive more connections, and (ii) dissimilarity, sites with different fitness are more likely to establish connections. We numerically computed, the connectivity distribution of the network P(k), the connectivity temporal evolution of the sites and others intrinsic properties in the study of networks. An interesting result studied was the degree distribution entropy, which revealed invariant by the network's size, as expected, however, changes with m (number of links at each step of time).

2
  • CARLOS AUGUSTO DE MORAES IGLESIAS
  • Thermal behavior in the non-adiabatic regime of superparamagnetic nanoparticles in an alternating magnetic field

  • Líder : FELIPE BOHN
  • MIEMBROS DE LA BANCA :
  • ANA LUCIA DANTAS
  • FELIPE BOHN
  • LUIZ FELIPE CAVALCANTI PEREIRA
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 09-mar-2018


  • Resumen Espectáculo
  • The phenomena of raising the temperature of magnetic nanoparticles under an alternating magnetic field, known as magnetic hyperthermia, is an outstanding field, which gives rise to challenges in the context of fundamental physics and providing new roads to applications, such as in the cancer treatment and in the control of thermally activated drug delivery. Thus, the complete understanding of the behavior of these systems with reduced dimensions becomes a key point and the optimization of the production processes and the properties of these materials, a challenging task. In this work, we perform a theoretical and experimental investigation of the magnetic hyperthermia in MgO.Fe2O3 and FeO.Fe2O3 superparamagnetic nanoparticles. Specifically, we aim to fully understand the influence of the composition, nanoparticle size, as well as amplitude and frequency of the field on the specific absorption rate of the samples. Here, we propose a theoretical model to describe the thermal behavior of magnetic nanoparticles, providing further insights on well-known parameters found in literature. To test the robustness of the approach, we apply the theoretical model to describe the magnetic hyperthermia curves obtained experimentally. To obtain the magnetic hyperthermia curves, an experimental system is developed, making possible to generate magnetic fields with frequency up to 100 kHz and amplitude up to 200 Oe. The excellent agreement between theoretical and experimental results provides support to confirm the validity of our approach to describe the thermal behavior of magnetic nanoparticles.

3
  • LUCAS MARQUES DA SILVA
  • Synthesis, structural and magnetic characterization of barium hexaferrites doped with La3+ and Co2+

  • Líder : JOSE HUMBERTO DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • JOSE HUMBERTO DE ARAUJO
  • SUZANA NOBREGA DE MEDEIROS
  • JOÃO MARIA SOARES
  • Data: 06-abr-2018


  • Resumen Espectáculo
  • The barium hexaferrite, an iron oxide of hexagonal geometry, currently plays an important technological role in applications such as permanent magnets, microwave devices, and magnetic recording. In this work, we investigated the effects of doping with La3+ and Co2+ ions on the magnetic and structural properties of barium hexaferrite. Two series of samples were produced, Ba1-αLaαFe12-xCoxO19 with α=0.30, x=(0.0, 0.25, 0.50, 0.75, and 1.0) and α=0.10, x=(0.25 and 0.50). The samples were synthesized by the Ionic Coordination Reaction technique in chitosan polymer matrix and calcined in air 900 °C/4 h. The characterization was performed by X-ray diffractometry, scanning electron microscopy, vibrating sample magnetometry, Mössbauer spectroscopy and physical properties measurement system. The X-ray diffractograms revealed the presence of the BaFe12O19 type crystalline phase in all samples, with mean particle size ranging from 71 - 58 nm, decreasing with doping. The electron micrographs presented a particle morphology in the form of nanorods and nanoplates, with lengths and diameters varying around 190 nm and 70 nm, respectively. The analysis detected impurities of α-Fe2O3 and γ-Fe2O3, for the series with α=0.30. 

4
  • GREYSON JANUÁRIO COELHO SILVA
  • Gauge symmetries, effective fields theories and curves in three dimensions

  • Líder : DMITRY MELNIKOV
  • MIEMBROS DE LA BANCA :
  • DIONISIO BAZEIA FILHO
  • DMITRY MELNIKOV
  • FARINALDO DA SILVA QUEIROZ
  • MADRAS VISWANATHAN GANDHI MOHAN
  • Data: 11-abr-2018


  • Resumen Espectáculo
  • The effective theories of curves described by gauge theories are analyzed with the intent to apply them to modeling physics of extended quasi-one dimensional systems, such as protein molecules, elastic cords, or even vortices in superconductivity. In this study one perceives how the geometry of curves, apparently simple, can be related to subjects of paramount importance for Physics or even Biology. In this work we start with Frenet equations that model curves and consequently introduce gauge symmetries, the spontaneous symmetry breaking, as well as solitary waves. With the aid of the idea of effective gauge theories, the mathematical framework is elaborated to produce an energy functional, through which one can arrive at the equations that govern the dynamics of curves, being prototypes of long molecules. It was shown graphically that the most simple theoretical model can adapt the basic secondary structures of proteins, called $\alpha$-helix and $\beta$-strand. The properties of the potential of the theory have been analyzed together with  characteristics of the structure of curves such as folds, which reflect the supersecondary structures of proteins (structural motifs). The classical and quantum stability properties have been studied using the standard field theory methods. It was shown that the motifs, realized in the model as static solitons, are unstable configurations in the limit of infinite smooth curves, which preserve translational symmetry.

5
  • JOÃO MARCELO MACHADO
  • ROTATION, MAGNETIC ACTIVITY AND THE OCCURRENCE OF HOT JUPITERS IN COOL STARS

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JEFFERSON SOARES DA COSTA
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • THARCISYO SA E SOUSA DUARTE
  • Data: 13-abr-2018


  • Resumen Espectáculo
  • Rotation is fundamental in Stellar Astrophysics for being responsible for several phenomena with impact on the stellar formation and evolution, such as the generation and topology of the associated magnetic fields and the angular momentum transfer. It is known that all stars undergo rotational braking as they evolve, showing a transition in the values of rotational measurements from the F spectral type. A possible explanation for this phenomenon is the magnetic activity, sustained by the dynamo process and differential rotation, another possible explanation regards the dissipation due to gravitational tides in the cases of binary stars or stars with detected exoplanets. In this work, we developed a theoretical model to describe the frequency distributions of projected rotational velocities, vsini, for approximately 10.000 stars of F, G, and K spectral types, including a sample of solar twins. We studied the rotational braking due to magnetic nature from the study of chromospheric activity by analyzing the log R’HK indicator, associated with the Ca II H and K lines, and the coronal activity through measurements of X-ray flux. To study the gravitational mechanism we take into account a sample of 46 stars hosting extrasolar planets known as hot Jupiters (HJs), detected through transit and radial velocity methods. We also explored the dependence between stellar rotation and orbital parameters and discussed possible processes of formation and migration of HJs, by analyzing the spin-orbit misalignment, or obliquity (λ), and the eccentricity of these systems. Our theoretical model is valid since it recovers the Skumanich law, which is fundamental in the context of gyrochronology, and properly describes the stars with low rotation values. From the solar twins’ sample, we have also determined that the internal distribution of angular momentum may be one of the factors associated with the rotational transition observed between stars whose convective and radiative envelopes are found in different depths. From the observational point of view, we did not notice a direct dependence between rotation and the presence of HJs, however we showed a clear correlation between the values of vsini and activity, so that the rotational braking is more probably connected to the mass loss from magnetically-coupled winds. Exploring the planetary sample we noticed a slight tendency for more massive HJs to be found in aligned orbits. Revisiting previous works, we have determined that stars with temperatures lower than ~ 6020K and masses lower than ~ 1.15M are found in approximately aligned systems, whereas stars above these limits exhibit a great dispersion in the values of λ. We also noticed a dependence between λ and the spectral type, where F stars show a great spread in the obliquity values. These three results may be related to the fact that stars with these characteristics undergo weak tidal dissipation due to their thin convective zones, resulting in a slow orbital realignment in the respective systems.

6
  • TIBÉRIO AZEVEDO PEREIRA
  • 3+1 formalism in General Relativity

  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • RAIMUNDO SILVA JUNIOR
  • RICCARDO STURANI
  • Maria Aldinez Dantas
  • Data: 27-abr-2018


  • Resumen Espectáculo
  • The study of new solutions in General Relativity motivated investigations of Cauchy problems for alternative gravitational regimes, which led to the need to elaborate techniques to split the spacetime into three plus one dimensions. The 3+1 formalism arises as a mathematical tool for decomposing the components of the metric and the curvature. The central mechanism found in the literature is known as the ADM formalism, developed initially as an attempt to construct a theory of canonical quantum gravity, which later its formulation was applied to evolve the Einstein equation numerically. As a subfield of Gravitation, the Numerical Relativity investigates phenomena in strong field systems and other scenarios which are not possible to solve analytically. In this dissertation, we will present an introduction to the 3+1 formalism, as well as gauge and initial conditions to prepare some gravitational systems. To consolidate this theoretical approach, we will show techniques of Numerical Relativity to evolve the spacetime from of given initial configurations.

7
  • GESIEL RODRIGUES DA SILVA NETO
  • Spherically Symmetric Solutions in Starobinsky-Podolsky Gravitation

  • Líder : LEO GOUVEA MEDEIROS
  • MIEMBROS DE LA BANCA :
  • LEO GOUVEA MEDEIROS
  • RAIMUNDO SILVA JUNIOR
  • CÁSSIUS ANDERSON MIQUELE DE MELO
  • Data: 02-may-2018


  • Resumen Espectáculo
  • Extensions of General Relativity have received increasing attention over the last few decades due to motivations coming from high-energy physics, astrophysics, and cosmology. The non-renormalizability of Einstein’s gravitation and the search for a coherent quantum theory of gravity drove the rising of higher-derivative gravity during the 1960s. Today, robust observational data indicate that modified gravity theories are possible candidates in describing evolution of the Universe. In this dissertation, the model called Starobinsky-Podolsky gravitation is proposed, which includes higher-order corrections of the curvature invariants. Here, the Einstein-Hilbert action is supplemented by a quadratic correction of the Ricci scalar R plus a derivative contraction term of R. After a review of Einstein’s gravitation and an exposition about Schwarzschild black holes, the proposed gravitation is explored. The field equations of Starobinsky-Podolsky gravity are deduced and then spherically symmetric solutions are studied. Its Newtonian limit is developed and analyzed. Finally, an analysis of the black holes solutions is made, in particular, under which conditions only Schwarzschild black holes can occur.

8
  • POLYANNA DO VALE GUEDES
  • Kaniadakis Statistical Study of the Distribution of Human Chromosome Sizes

  • Líder : DORY HELIO AIRES DE LIMA ANSELMO
  • MIEMBROS DE LA BANCA :
  • DORY HELIO AIRES DE LIMA ANSELMO
  • RAIMUNDO SILVA JUNIOR
  • VAMBERTO DIAS DE MELLO
  • Data: 04-may-2018


  • Resumen Espectáculo
  • In this dissertation, we investigated the non-coding DNA of the 24 human chromosomes, through the generalized statistics. This study, carried out with the recent generalizations of the Standard Theory of Statistical Mechanics, has been more important and analyzed as the statistical properties of the genetic sequences, in order to obtain information about the size distributions. In works already carried out on non-coding human DNA the use of q-exponential distributions of Tsallis generalized formalism through the maximization of non-extensive entropy is reported to study the size distribution of these sequences. In this dissertation, we broaden these studies through the use of k-statistics originating from Kaniadakis generalized formalism. Namely, a brief comparison between the two analyzes is interesting. We present the values of the deformation parameters k, in Kaniadakis formalism, and the entropic index q in the Tsallis formalism, which describe the size distributions for all the chromosomes of the non-coding human DNA.

9
  • ROSEANE DE LIMA GOMES
  • Infrared Excess and Magnetic Activity in Main Sequence Stars

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • JOSE RENAN DE MEDEIROS
  • BRUNO LEONARDO CANTO MARTINS
  • ANTONIO CARLOS DA SILVA MIRANDA
  • Data: 20-jul-2018


  • Resumen Espectáculo
  • There are several studies related to chromospheric and coronal magnetic activity, as a determinant of age, as well as the relations with metallicity and rotation of stars. However, the relationship between magnetic 

    Abstract:

    There are several studies related to chromospheric and coronal magnetic activity, as a determinant of age, as well as the relations with metallicity and rotation of stars. However, the relationship between magnetic activity and the excess of stellar infrared (IR) radiation, which indicates the presence of circumstellar discs or planets, is not yet well known. For the accomplishment of this unprecedented study, we selected 128 stars, from the catalog Eiroa et al. (2013), with spectral type F, G and K, class of luminosity V and that have values for the fluxes Ca II (-5.4 < logR’HK < -4.0) and X-ray, indicators the magnetic activity in the chromosphere and in the corona of the star, respectively. These parameters were related to infrared fluxes in the WISE (3.4 µm and 22 µm), IRAS (12 µm and 25 µm), AKARI (9 µm and 18 µm) and SPITZER / MIPS (24 µm and 70 µm) photometric bands for a subsample of 33 stars that shows IR excess, in order to study the behavior of magnetic activity in the presence of circumstellar discs. In this context, we noticed that the medium IR fluxes increase as the Ca II flux decreases, this tendency is also shown to be increased for the higher temperature stars. In addition, we observed a similar anticorrelation between coronal emission and IR flux, but with greater evidence for type G stars. For the far IR, we noticed a weak correlation with the chromospheric and coronal activity. In a last analysis, we observed the correlation between R’HK and RX of the sample which, as expected, agrees with several works present in the literature, we also noticed that such behavior does not differentiate in the presence, or not, of circumstellar discs.

10
  • RENATO FERREIRA DUTRA
  • Photonic Equivalent to Hofstadter Butterfly

  • Líder : MANOEL SILVA DE VASCONCELOS
  • MIEMBROS DE LA BANCA :
  • MANOEL SILVA DE VASCONCELOS
  • EUDENILSON LINS DE ALBUQUERQUE
  • FABIO FERREIRA DE MEDEIROS
  • Data: 25-jul-2018


  • Resumen Espectáculo
  • In the present work we do the theoretical study of the propagation of electromagnetic waves in a multilayer system, whose refractive index of each layer is modulated by the function that describes the potential of the one-dimensional Harper model. We apply the transfer matrix method to obtain the transmittance spectra as a function of the reduced frequency w/w0. In order to identify possible edge states or topological states, we calculate the transmittance spectrum as a function of w/w0 and the parameter f for three cases: first, when layer thicknesses are given by the optical-length ratio Ijdj=l0/4, where Ij is the refractive index of the layer j; the second, when all thicknesses of the layers are equal, dj=d; and finally when the thicknesses of the layers are related by  d2j=2d2j+1. In addition, we obtained the transmittance spectrum as a function of the periodicity control parameter b. At the critical point l=0.5, we reproduce the photon equivalent of the Hofstadter butterfly, which corresponds to a critical state in the metal-insulating transition, that is, for l >0.5, the system is equivalent to a state and when l >0.5, the system is equivalent to an insulating state.

11
  • JOAO CARLOS ROCHA DE ARAUJO
  • : Losses mechanisms in blocked and unlocked magnetic nanoparticles submitted to an alternating magnetic field

  • Líder : FELIPE BOHN
  • MIEMBROS DE LA BANCA :
  • FELIPE BOHN
  • JOHN CARLOS MANTILLA OCHOA
  • RODOLFO BEZERRA DA SILVA
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 27-jul-2018


  • Resumen Espectáculo
  • The heating of magnetic nanoparticles submitted to an alternating magnetic field has attracted increasing interest of the scientific community in recent years. It is a consequence of the wide employment of nanoparticles and magnetic hyperthermia in, for instance, biomedical applications, such as drug delivery thermally activated and as a therapy for cancer treatment. When nanoparticles are under the influence of the alternating magnetic field, the heating is a result of physical mechanisms as magnetic relaxation and hysteresis loss, both directly associated with the magnetization reversion in this systems. In this work we aim to investigate the loss mechanisms in magnetic nanoparticles, as well as the thermal behavior of suspensions of nanoparticles dispersed in water, when submitted to an alternating magnetic field. To this end, we produce two sets of samples with distinct characteristics and investigate the structural, morphologic, magnetic and calorimetric properties in order to understand the effect of the particle size, composition and magnetic behavior on the loss mechanisms in magnetic hyperthermia. The first set of samples consists of magnesium ferrite MgFe2O4 annealed at 400 °C, 500 °C, 600 °C e 1000 °C, presenting particles with different diameters. The second set is composed by cobalt doped magnesium ferrites Mg1-xCox Fe2O4 with x = 0:0, 0:2, 0:5, 0:8 and 1:0, annealed at 1000 °C, allowing the evaluation of the influence of both, particle diameter and composition on the loss mechanisms. From these sets, particles in blocked and superparamagnetic states are obtained and we investigate the contributions of hysteresis loss, Brownian relaxation and Néel relaxation to the magnetic hyperthermia. Specifically, the experimental results reveal that the blocked particles present losses primarily associated with the hysteresis loss and Brownian relaxation, while the superparamagnetic ones have losses due to Néel relaxation. The results also disclose the dependence of such mechanism with the anisotropy field, this latter an important parameter in the process

12
  • JOSÉ ROBERTO MOREIRA DA SILVA
  • Topological Phonon States in One-Dimensional Quasicrystals

  • Líder : MANOEL SILVA DE VASCONCELOS
  • MIEMBROS DE LA BANCA :
  • MANOEL SILVA DE VASCONCELOS
  • DORY HELIO AIRES DE LIMA ANSELMO
  • JOSE DE MIRANDA HENRIQUES NETO
  • Data: 30-jul-2018


  • Resumen Espectáculo
  • Theoretical models for predicting the properties of quasicrystalline materials have been of considerable interest to the scientific community recently. However, they are mainly related to the optical and electronic characteristics of the system, and a study of the elementary oscillations, such as phonons, of one-dimensional quasicrystalline lattices is still necessary. Recently published works have shown that the localization properties of the Harper model can be modeled in a quasicrystal through the Hamiltonian of Aubry-André, considering the immeasurable potential with the lattice parameter. This model proved to present itself as a topological insulator, exhibiting border states and nontrivial phases for the electronic case. Motivated by these results, in this work, we present a study on the vibrational properties of one-dimensional quasi-crystals, highlighting the topological states of edge. For this, we model a one-dimensional quasicristal through the Aubry-André model with the potential parameter defined by the golden ratio (b = (1+) / 2). We performed the numerical calculations from the exact numerical diagonalization of the Hamiltonian. In our results, we find the multifractal frequency spectrum known as the "Hofstadter's butterfly", which emerges as a critical state of a transition from metal-insulating type states to the value of modulation of the dimensionless spring constant of 1.0. We also show by calculating the wavelength, that there exist certain states that cross the largest gaps of the spectrum (as a function of the phi phase) are edge states in the system, where there are state locations in them.

13
  • GUSTAVO MIASATO SILVA
  • Universality, Criticality, Fractal, Power law, diffusion, Marathons.
  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • LUCIANO RODRIGUES DA SILVA
  • RAIMUNDO NOGUEIRA DA COSTA FILHO
  • RAIMUNDO SILVA JUNIOR
  • Data: 17-ago-2018


  • Resumen Espectáculo
  • The aim of this work is the analysis of the distribution of time intervals  measured among participants who cross the finish line consecutively in marathons and half marathons. More specifically, if  is the finish time of the i-th finisher, the time interval between him or her and the next one will be , . N is the finishers total number. After analysing different set of data, we verified that the distribuition is of power law type , with. Our study used data set from marathons and half marathons across several countries and years. Besides the power law encountered, two other results that we consider relevant are the fact that the distributions show the same universality class, that is, the same exponent, and that it is invariant in space and time, meaning that it is independent of the place and year of the event. We believe that the same procedure can be applied to different competitions.

14
  • BERNARDO FORTON ODLAVSON GONÇALVES
  • Lithium-rich giant stars: a study of the chemical anomaly and the magnetic field of those objects

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • JEFFERSON SOARES DA COSTA
  • THARCISYO SA E SOUSA DUARTE
  • Data: 10-sep-2018


  • Resumen Espectáculo
  • According to the standard theory of stellar evolution, low-mass stars (spectral type K and G) must reach the beginning of the main sequence (ZAMS) with Li abundance near the meteorological value, which is ∼3.3 dex, and hold a high abundance until they reach the first dredge-up zone in the Red Giant Branch (RGB). After completion of the dilution processes, in the red clump, such stars should present a relatively low Li abundance. However, approximately 1-2% of all observed K and G giant stars have an abnormally high Li abundance (≥ 1.5dex). It is possible to find in the literature many attempts to reconcile theory and observation, but none of them is capable of explaining all the scenarios in which these chemical anomalies occur.

     

    Our work aims to present a new study of lithium-rich G and K spectral type stars and analyze the possible existence of particular characteristics to the lithium-rich stars that present detected magnetic field. We assemble a sample of 20 giant stars — taken from Charbonnel e Balachandran (2000), Kumar, Reddy e Lambert (2011), and Lèbre et al. (2009) — and calculate their fundamental parameters and the longitudinal magnetic field for a sub-sample of stars with observed high-resolution spectra available at PolarBase (Petit et al., 2014). Concerning the evolutionary states, we have used parallaxes recently provided by ESA’s Gaia spacecraft. To do so, we use the spectral analysis tool iSpec (Blanco-Cuaresma et al.,2014) and the Least-Squares Deconvolution (LSD) technique (Donati et al., 1997). We obtained results for fundamental parameters and Li abundance using the same procedure for all stars. Thus, we have the reliability in comparing stars from different samples that possibly had their spectra treated in different ways. We obtained relations between Li abundance, rotation velocity, and presence of a magnetic field according to what is predicted in the literature. We conclude that each star needs to be analyzed individually and with greater spectroscopic detail so that the real nature of its Li abundance is unraveled. The 12C/13C isotopic ratio, and the C/N elemental ratio, need to be investigated so that we can determine precisely the position of some stars (from our sample) on the H-R diagram.

15
  • GUILHERME AUGUSTO DIAS MONTEIRO
  • Application of DCDFT and MSL in the determination of variability periods of

    eclipsing m-dwarf pairs

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • THARCISYO SA E SOUSA DUARTE
  • Data: 10-sep-2018


  • Resumen Espectáculo
  • In order to identify the periodicities of stars and to determine their various causes, studies begun millennia ago have reached a new level, unexpected until the end of last century. The discovery of the first exoplanet aroused one of the oldest questions of the human being: “Are we alone in the universe? ”. To answer this question, so-called planet-hunting satellites such as CoRoT and Kepler have been designed. They have observed hundreds of thousands of stars with unprecedented accuracy and duration. The light curves acquired by these satellites could present periodic variations from intermittences of the most diverse sources and their study allows to us a better understand of stars. In this work, codes were developed based on the DCDFT and MSL techniques that, implemented in an automation routine, allowed the determination of the orbital periods of 12 eclipsing binaries, composed by M Dwarfs and observed with Kepler satellite. The results from this analysis, compared to those pre-existing in the literature, enabled the evaluation of these methods. From this, it was possible to verify the inefficiency of the MSL for short periods, even with the reduction in search range, although the method was able to determine longer periods without difficulties. Meanwhile, the DCDFT was able to identify most of the periods correctly, with the exception of three cases where eclipses had an equivalent dimensions, leading the method to find only half the correct period.

Tesis
1
  • FRANCISCO ADRIANO DE LIMA SANTIAGO
  • Magnetostatic Modes and Optical Reflection Spectrum in Aperiodic Rare Earth Superlattices

  • Líder : DORY HELIO AIRES DE LIMA ANSELMO
  • MIEMBROS DE LA BANCA :
  • DORY HELIO AIRES DE LIMA ANSELMO
  • CLAUDIONOR GOMES BEZERRA
  • MANOEL SILVA DE VASCONCELOS
  • NILSON SENA DE ALMEIDA
  • RAIMUNDO NOGUEIRA DA COSTA FILHO
  • Data: 25-ene-2018


  • Resumen Espectáculo
  • In this thesis we present a theoretical study of the propagation of magnons in the

    magnetostatic regime and of electromagnetic waves in aperiodic superlattices of rare earths formed by dysprosium (Dy) and holmium (Ho). The superlattices studied are the quasiperiodic Fibonacci and the deterministic aperiodic Thue-Morse and Double-Period, all of which are constructed through the periodic stacking of unit cells, which are formed by a two-layer substitution rule of type A/B, where this rule depends on the type of sequence considered for the construction of the superlattice. As a consequence of the periodic of the unit cells, it is possible to apply Bloch’s theorem, which together with the matrix-transfer method, allows us to find the bulk and surface magnetostatic modes. These modes present a self-similar behavior of the volume bands, so, at the limit of the generation number , these spectra become a Cantor-type fractal set. It has also been verified scaling and localization properties of these modes, which are different for Dy and Ho. In the propagation of electromagnetic waves we analyze the optical spectrum of reflection (or reflectance) for the same rare earth superlattices. We use here the Drude model to determine the dielectric function of rare earths, which are metals, so we have that reflection is dominant for these systems. We also use the Maxwell equations and the matrix-transfer method, which allows us to obtain the reflection coefficients. Therefore, we analyzed in these structures the spectra for the normal incidence of s-polarized (TE waves) and p-polarized waves (TM waves), where it was observed that they present an autosimilar behavior and a mirror symmetry in their spectra in the near infrared region, with reflectance for both polarizations. In the oblique incidence it was observed that the reflectance is sensitive to the variation of the angle, also varying with the type of superlattice and its generation, where the spectra are different for Dy and Ho. In the far infrared region we have seen that reflectance is dominant in rare earths, as is expected for metals.

2
  • SÉRGIO ORLANDO DE SOUZA BATISTA
  • Electromagnetism, Classical Mechanics, Statistical Mechanics, Quantum Mechanics.

  • Líder : SUZANA NOBREGA DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • FELIPE BOHN
  • JOSE HUMBERTO DE ARAUJO
  • RODOLFO BEZERRA DA SILVA
  • SUZANA NOBREGA DE MEDEIROS
  • TIBERIO MAGNO DE LIMA ALVES
  • WILSON ACCHAR
  • Data: 25-jul-2018


  • Resumen Espectáculo
  • Electromagnetism, Classical Mechanics, Statistical Mechanics, Quantum Mechanics.

3
  • LÁZARO LUIS DE LIMA SOUSA
  • STUDY OF DOUBLE PEROVISKITA $La_2MnFeO_6$ PREPARED BY SOLID STATE REACTION

  • Líder : JOSE HUMBERTO DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • FERNANDO LUIS DE ARAUJO MACHADO
  • GUSTAVO DE OLIVEIRA GURGEL REBOUCAS
  • JOSE HUMBERTO DE ARAUJO
  • MARCO ANTONIO MORALES TORRES
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 30-jul-2018


  • Resumen Espectáculo
  • In this work, three samples of $La_2MnFeO_6$  (LFMO) were prepared by solid state reaction, heat treated at 1200 $^{\circ}C$ at treatment times equivalent to 24, 48 and 96 $hrs$, each identified by name LFMO24, LFMO48 and LFMO96, respectively. The obtained structures are double-$perovskite$, monoclinic with spatial group $ P2_1 / n $ and lattice parameters given by $a$ = 5.52 Å, $b$ = 5.51 Å and $c$ = 7.81 Å. The sample crystallite sizes are equivalent to 361.0 $nm$ (LFMO24), 348.9 $nm$ (LFMO48) and 370.83 $nm$ (LFMO96). According to the specific heat (HC) measurements, the LFMO's have a ferrimagnetic phase transition of approximately 10 $K$, according to data adjustment using the mean field theory. Phase transitions due to charge location were observed, occurring at different temperatures depending on the degree of ordering of each system, in which the most disorganized state tends to have this transition tending to 140 $K$. An excess in HC is identified and modulated according to the sum of the defects of Frenkel and Schottky, where LFMO24 and LFMO48 presented smaller and greater amount of defects, respectively. The contribution of the crystalline lattice was stipulated using the Thirring Model, with Debye temperatures of the order of the expected for this type of material. DC, AC and magnetic hysteresis magnetization measurements confirm the existence of weak ferromagnetism behavior at room temperature in all LFMOs, in samples LFMO48 and LFMO96 it is assigned directly to the atoms of $Mn$, but in LFMO24, sample that presented higher value of magnetization at this temperature, there is an increase provided to the $Fe$ ions, in spite of the $M$ spectroscopy for the $^{57}Fe$, to show a doublet. The real part of the AC susceptibility, $\chi_{AC}^{'}$, complemented by different theoretical models, confirms a cluster-glass type phase, generated by agglomerates in a certain temperature range in the LFMO's, by about 30 $K$, where $\chi_ AC^{'}$ shows peaks that vary with frequency $f$. The strong presence of the Griffiths phase in the $1/\ chi_{AC}^{'} curves of LFMO48 and LFMO96 suggest that this phase is initiated at 65 $K$, occurring differently at LFMO24.

4
  • MARIA APARECIDA DOS SANTOS
  • RESTRICTIONS OF INFLATIONARY MODELS β-EXPONENTIAL
    USING BACKGROUND COSMIC RADIATION DATA

  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • FABIO CABRAL CARVALHO
  • JAILSON SOUZA DE ALCANIZ
  • LEO GOUVEA MEDEIROS
  • RAIMUNDO SILVA JUNIOR
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • Data: 31-jul-2018


  • Resumen Espectáculo
  • In recent years, the inflationary scenario has become one of the most important models in the description of the Universe in its early instants. It initially emerges as a solution to the problems of standard cosmology, but has mainly stood out as the mechanism capable of generating the initial perturbations that gave rise to the large-scale structures of the Universe. Their theoretical predictions can be tested with the current observational data, which allow to restrict several classes of inflationary models present in the literature. Thus, in this work we analyze a class of generalized inflationary models proposed by Alcaniz and Carvalho [1], known as β-exponential inflation and we show that this type of potential can arise in the context of brane cosmology, in which the field describing the size-extra dimension is interpreted as the inflaton. We discuss the observational viability of this class of models in the light of the latest Cosmic Radiation Background (RCF) data obtained by the Planck satellite through a Bayesian analysis and impose constraints on the model parameters. We find that the RCF data weakly prefer the standard model ΛCDM in relation to the β-exponential inflation. However, when the current local measurements of the Hubble parameter, H0, are considered, the β-exponential model is moderately preferred in relation to the ΛCDM cosmology, making the study of this class of inflationary models interesting in the current context of H0 voltage.

5
  • JOSE CRISANTO DA COSTA NETO
  • Formal power series for the stable distributions of Lévy: the symmetric case.

  • Líder : MADRAS VISWANATHAN GANDHI MOHAN
  • MIEMBROS DE LA BANCA :
  • DORY HELIO AIRES DE LIMA ANSELMO
  • ERNESTO CARNEIRO PESSOA RAPOSO
  • JOAO MEDEIROS DE ARAUJO
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MARCOS GOMES ELEUTERIO DA LUZ
  • Data: 17-ago-2018


  • Resumen Espectáculo
  • A relevant problem in Statistical Physics and Mathematical Physics is to derive numerically precise expressions and exact analytical forms to calculate the distributions of Lévy α-stable P_α(x;β). In practice, these distributions are usually expressed in terms of the Fourier Integral of its characteristic function. In fact, known closed-form expressions are relatively scarce given the huge space of parameters: 0 < α ≤ 2 (Lévy index), -1 ≤ β ≤ 1 (asymmetry), σ > 0 (scale) and - ∞ < µ < ∞ (offset). In the formal context, important exact results rely on special functions,

    such as the Meijer-G, Fox-H functions and finite sum of hypergeometric functions, with only a few exceptional cases expressed

    in terms of elementary functions (Gaussian and Cauchy distributions). From a more practical point of view, methods such as series expansions, e.g., allow an estimation of the Lévy distributions with high numerical precision, but most of the approaches are restricted to a small subset of the parameters and, although sophisticated, this algorithms are time-consuming. As an additional contribution to this problem, we propose new methods to describe the symmetric stable distributions, with parameters β = 0, µ = 0, σ = 1. We obtain a description through a closed analytical form, via series of formal power making use of the Borel regularization sum procedure (for α = 2/M, M = 1, 2, 3...). Furthermore we obtain an approximate expression (for 0 < α ≤ 2) by dividing the domain of the integration variable into sub-intervals (windows), performing proper series expansion

    inside each window, and then calculating the integrals term by term.

6
  • ANALINE PINTO VALERIANO BANDEIRA
  • PROPRIEDADES ESTÁTICAS E DINÂMICAS DE SUPER-REDES E MULTICAMADAS QUASIPERIÓDICAS"

  • Líder : CLAUDIONOR GOMES BEZERRA
  • MIEMBROS DE LA BANCA :
  • CLAUDIONOR GOMES BEZERRA
  • DORY HELIO AIRES DE LIMA ANSELMO
  • LEONARDO DANTAS MACHADO
  • CARLOS HUMBERTO OLIVEIRA COSTA
  • JOAO MILTON PEREIRA JUNIOR
  • Data: 30-ago-2018


  • Resumen Espectáculo
  • In this study, we investigate the static and dynamics properties of magnetic multilayer and thin film systems, respectively. The propagation of spin waves was investigated in a quasiperiodic superlattice which structure was built according to the so-called Octonacci sequence, composed by two simple cubic ferromagnetic materials interacting through bilinear and biquadratic exchange couplings at their interfaces. The ferromagnetic materials are described by the Heisenberg model, and a transfer matrix treatment is employed, with the calculations performed for the exchange-dominated regime, taking into account the random phase approximation (RPA) to obtain the band and transmittance spectra. In addition, the influence of the biquadratic coupling on the band and transmittance spectra is discussed. We also performed an investigation of the static magnetic properties of nanometric films, with low symmetry crystallographic growth directions ([211] and [321]), by using two quasiperiodic models. For the model 1, the magnetic thin films are stacked quasiperiodically, with the non-magnetic spacers having the same thickness, while for the model 2, the non-magnetic spacers follows the quasiperiodicity, with different thicknesses. For both models the quasiperiodicity is according to the Fibonacci and Octonacci quasiperiodic sequences. The theoretical modelling is based on a realistic magnetic energy taking in account the Zeeman, cubic and uniaxial anisotropy terms, besides the bilinear and biquadratic couplings. From the equilibrium configurations magnetization, magnetoresistance and phase diagrams are obtained

     

7
  • BRUNO LUSTOSA DE MOURA
  • ASTEROSSISMOLOGIA E ESPECTROSCOPIA DE ESTRELAS GIGANTES DO CLUM

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • JEFFERSON SOARES DA COSTA
  • FRÉDÉRIC BAUDIN
  • MARCELO EMÍLIO
  • MARIA CRISTINA DE ASSIS RABELLO SOARES
  • Data: 31-oct-2018


  • Resumen Espectáculo
  • The pulsation of the stars has become, from decades to now, one of the main mechanisms to obtain information about their interiors. With the advent of the missions, the need to understand how
    global parameters of the star behaved in relation to the modes is crucial to the entire study of stellar evolution, especially in the Red Giant Branch. Many computational codes use inferential statistics for gather
    information, all very peculiar to evolutionary states since the main sequence
    until the asymptotic giant branch. Our work was to develop a tool
    which will serve as a basis for new trials and works, within the Asteroseismology of Clump stars, which obtain the values of maximum oscillation frequency and the separations between these frequencies are pillars for stellar physical understanding. Herein to this, the correct modeling associated with the inclusion of metallicity obtained
    from spectroscopy, may generate changes, not yet fully understood
    in the seismic scales relations for mass and radius. In this way, the study of seismology of Clump stars may be the key to a promising scenario for Archeology Galactic and for the complete understanding of processes in the stellar interior.

8
  • GERDIVANE FERREIRA DUARTE
  • Statistical Properties of Real Complex Networks

  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • ANTONIO DE MACEDO FILHO
  • LUCIANO RODRIGUES DA SILVA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MARCO ANTONIO ALVES DA SILVA
  • RAIMUNDO SILVA JUNIOR
  • Data: 14-nov-2018


  • Resumen Espectáculo
  • We present a study of social networks based on the analysis of Brazilian and Portuguese family names (surnames). We construct networks whose nodes are names of families and whose edges represent parental relations between two families (each individual). From these networks we extract the connectivity distribution, clustering coefficient, shortest path and centrality. We find that the connectivity distribution follows an approximate power law. We associate the number of hubs, centrality and entropy to the degree of miscegenation in the societies in both countries. Our results show that Portuguese society has a higher miscegenation degree than Brazilian society. All networks analyzed lead to approximate inverse square power laws in the degree distribution. We conclude that this parameter tends to be independent of the network size considered. The assortative mixing of all networks is negative, showing that the more connected vertices are connected to vertices with lower connectivity. Finally, the network of surnames presents some small world characteristics.

9
  • RAFAEL LEAL DA SILVA

  • Synthesis and characterization of nanostructures of samarium doped ferrites and coated with polymers.

  • Líder : JOSE HUMBERTO DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • GUSTAVO DE OLIVEIRA GURGEL REBOUCAS
  • JOSE ALZAMIR PEREIRA DA COSTA
  • JOSE HUMBERTO DE ARAUJO
  • MARCO ANTONIO MORALES TORRES
  • RODOLFO BEZERRA DA SILVA
  • UBIRATAN CORREIA SILVA
  • Data: 29-nov-2018


  • Resumen Espectáculo
  • This work was shown in the physical and characterization of nanoparticles magnetite and ferrite of cobalt doped with Sm: Fe 2.68Sm0.32O4 and CoFe (2-x) SmxO4 (x = 0.05, 0.10, 0.15 and 0.20). As magnetite nanoparticles were produced using the polyol method, where the polymer polyvinylpyrrolidone (PVP) was used for protection as nanoparticles of the oxidation. As nanoparticles of Sm-doped cobalt ferragens, they were constructed by the ionic rope reaction (ICR) method and covered by a chitosan matrix.
    A crystal structure and magnetic properties were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy and DC magnetometry.
    A magnetite sample has a print size distribution having a diameter of 5.2 nm. As the bees presented under the superparamagnetic effect of 4 × 105 J / m3 at 5 K. In a constant environment, the MH presented the has a single paramagnetic component, while the 5 K is a saturation magnetization of 18.9 emu / ha MH curve , field cooling (FC) has a displacement with a bias shift field of ~ 110 Oe. The benefits are discussed in terms of spatial distribution of actions, as determined by Mössbauer spectroscopy. Immunization of magnetocrystalline anisotropy.
    The cobalt silver samples are coated by the chitosan biopolymer, with a variable variation of the Sm-ion concentration dependent sizes, ranging from 9.49 nm to 5.62 nm. The coercive field values, saturation magnetization and anisotropy were subjected to structural changes with doping. A theological dose was made taking into account the form of distribution of particles, blocked and superparamagnetic. The mega-sounds spectrum was when performance was used in three sixths in each of the crystallographic groups, at room temperature and at 12 K. The results were calculated in relation to the random distribution of Smenoe A and B levels. were for applications of an AC magnetic field of 70.5 kHz and intensity of 200 Oe. The value was maximum for the sampling of a series of 12.09 W / g, which aims to use hyperthermia.

10
  • PIERRE NIAU AKMANSOY
  • Nonlinear Electrodynamics Constrains

  • Líder : LEO GOUVEA MEDEIROS
  • MIEMBROS DE LA BANCA :
  • LEO GOUVEA MEDEIROS
  • FARINALDO DA SILVA QUEIROZ
  • JACOPO VITI
  • BRUTO MAX PIMENTEL ESCOBAR
  • RODRIGO SANTOS BUFALO
  • Data: 14-dic-2018


  • Resumen Espectáculo
  • Nonlinear electrodynamics (NLED) are a generalization of Maxwell's electrodynamics that arises and is used in several fields such as: gravitation, classical consequences of the quantum vacuum, low energy limits of string theories etc. Because of this, it's an important task to evaluate the empirical validity of these theories by comparing their predictions with the corresponding experimental measurements. In this thesis, the ionization energy of the hydrogen atom and the photon-photon scattering cross section recently observed by the ATLAS Collaboration with ultraperipheral collisions of lead ions are used.

     

    The way in which Born-Infeld-like theories, a class of NLED, modify the Coulomb potential produced by the hydrogen atom's nucleus is calculated. Then, using the perturbation theory, the first order correction of the ground state energy is derived. It is remarkable that, although this class of NLED behaves identically in the low energy limit, each theory produces a slightly different correction. This is due to the framework of perturbation theory which forces the use of the complete Lagrangian. Comparison with the measurement of the ionization energy constrains the parameter b, which characterizes this class of theories, to be b≥10^21 V/m.

     

    The direct interaction between photons is one of the most striking features of NLED. Therefore, the cross section for γγγγ scattering acquires a contribution due to nonlinear corrections to Maxwell's Lagrangian besides the Standard Model ones. In the equivalent photon approximation, the complete scattering cross section for PbPb→PbPb+γγin ultraperipheral collisions is derived through the convolution of the subprocess cross section γγγγ with the photon fluxes produced by the ions. Comparison of the complete cross section with the experimental measurement obtained by the ATLAS Collaboration yields the most precise constrain for the nonlinear parameters α~β≤2x10^-10 GeV^-4 ≈ 10^-47 m^3/J.

2017
Disertaciones
1
  • LARISSA DE FARIAS RIBEIRO
  • Networks without typical scale; Alternative models and computational techniques.
  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • LUCIANO RODRIGUES DA SILVA
  • MAURICIO LOPES DE ALMEIDA
  • RAIMUNDO SILVA JUNIOR
  • TIAGO DE MEDEIROS VIEIRA
  • Data: 13-ene-2017


  • Resumen Espectáculo
  • We are embedded in a networked world, and in the last few years network studies and their
     properties have expanded considerably. The main reason is that several systems can be 
    modeled through so-called complex networks. Examples of systems easily modeled as networks are: 
    the society, the Web, the brain, among others. To understand the behavior of these systems, several 
    models in the area of Complex Networks have been proposed. Barabási and Albert proposed 
    a model that included two basic mechanisms (growth and preferential bonding),
     reproducing a characteristic behavior in some real systems: distribution of 
    connectivity in power law. As a consequence of the Barabási and Albert model,
     other network models emerged, considering different types of factors included i
    n the preferential link mechanism.
     Models that use this mechanism satisfactorily explain the
     emergence of distributions that follow power law in real networks.
     However, the preferred connection is not the only mechanism through which a network can grow and 
    generate this type of connectivity distribution. Therefore, in this work we analyze two models that use
    different mechanisms of preferential linkage and that are able to generate networks without a typical scale:
     the vertex copy model and the deconstruction model of Poisson networks. We compare the results 
    with the networks derived from the Barabási and
     Albert model,
     because 
    we believe that studying di
2
  • NATHAN LIMA PESSOA
  • Tailoring domain walls in NiFe nanorings, in dipolar coupled cylindrical core-shell structures

  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ARTUR DA SILVA CARRICO
  • JOSE HUMBERTO DE ARAUJO
  • GUSTAVO DE OLIVEIRA GURGEL REBOUCAS
  • Data: 25-ene-2017


  • Resumen Espectáculo
  • Nanostructured magnetic systems have been the focus of intense research effort in recent years. From the pure theoretical point of view, the interest focus on new magnetic phases that might emerge from dipolar effects in systems, with geometric constrictions, with dimensions of the order of fundamental magnetic lengths. There is also a large interest from the viewpoint of applications, such as magnetic sensors, nano-oscillators and new designs of magnetic memories. Motivated by recent experimental results, showing the possibility of domain wall confinement in ferromagnetic nanorings, by magnetic constrictions like notches and asymmetries, in addition to studies which reveal a strong 

3
  • LEANDRO DE ALMEIDA
  • The Study of Gravitational Microlensing and the Discovery of Far Exoplanets
  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • FRANCISCO JOSÉ JABLONSKI
  • Data: 10-feb-2017


  • Resumen Espectáculo
  • Abstract: In the last decade, the number of exoplanets discovered has grown exponentially, mainly due to Kepler observations which, along with observations of the K2 mission, announced the discovery of 1284 planets at once in 2016. These discoveries were done using the planetary transit method, which has low sensitivity for low-mass planets far away from their stars. Thus most of the discoveries of giant planets were of orbits close to their stars. In contrast, the gravitational microlensing technique is sensitive to low-mass planets orbiting between $ 0.5 $ AU and $ 10 $ $ AU $. Because it depends only on the combined gravitational field of the star-planet, this technique can detect planets around low brightness stars, which would be difficult for other techniques that depend on star emitted light. Until now, astronomers have discovered 47 planets through this technique, which is relatively low number, when compared to the other methods like transit and radial velocity. In this dissertation we show in detail the equations behind the gravitational microlensing theory and its applications to detect distant low-mass planets. We focus on the characterization of systems with closed topology, where the planet has between 10^-5 and10^-6 of the mass of the star and with a semi-major axis about 1 AU (planet with Earth-like mass around 1AU of a star with Sun-like mass). We also present a suggestion of parameterization for the impact parameter \mu_0 and the impact angle \alpha in order to reduce the search time consuming for light curves generated from systems with close topology. We present the main steps for the development of two algorithms that use the semi-analytical method of solution of the lens equation and the brute force of simulation method Inverse Ray Shooting (IRS) respectively. These codes simulate the topology and light curve of microlensing events, and were used to simulate our systems presented in this dissertation. As a main result, we demonstrate the ability of the model to generate theoretical curves and compared these light curves with real microlensing events.

4
  • DANYELLE PRISCILA DA SILVA
  • Experimental Study of the Binary System Samário Ferro
  • Líder : JOSE HUMBERTO DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • JOSE HUMBERTO DE ARAUJO
  • SUZANA NOBREGA DE MEDEIROS
  • JOÃO MARIA SOARES
  • Data: 14-feb-2017


  • Resumen Espectáculo
  • Intermetallic alloys composed of a rare earth element and a transition metal have attracted great scientific interest in the last decades. Such interest occurs because these types of materials possess magnetic properties that make them strong candidates for the production of permanent high performance magnets. There are a large number of compounds that can be formed from the combination of a rare earth element and a 3d transition metal. In this work was carried out an experimental study of one of these combinations, the samarium iron system. The samples used in this study were alloys prepared by arc melt, with the following concentrations: Sm30Fe70, Sm40Fe60, Sm50Fe50, Sm70Fe30 and Sm80Fe20. Subsequently, they were investigated by X-ray diffraction, metallography, thermomagnetic analysis and magnetometry. In these samples three intermediates were identified: Sm2Fe17, SmFe3 and SmFe2. The network parameters and Curie temperatures of these compounds were determined. The magnetic properties of the first three samples (Sm30Fe70, Sm40Fe60 and Sm50Fe50) were consistent with the ratio and magnetic characteristics of the intermetallic compounds present. However, for the last two samples (Sm70Fe30 and Sm80Fe20), the study indicated a possible formation of metastable phases. There was also a dependence of the magnetic properties on the samarium concentration.

5
  • CACIANO SOARES COSTA
  • The Blume-Capel Model in a Gaussian Random Field

  • Líder : FRANCISCO ALEXANDRE DA COSTA
  • MIEMBROS DE LA BANCA :
  • FRANCISCO ALEXANDRE DA COSTA
  • JOAO MEDEIROS DE ARAUJO
  • LUCIANO RODRIGUES DA SILVA
  • GISLENE MICARLA BORGES DE LIMA
  • Data: 24-feb-2017


  • Resumen Espectáculo
  • In this work we investigate the infinite ranged Blume-Capel model (BC), under a random field following a Gaussian distribution. The model is exactly soluble and from the corresponding free energy density we have obtained a wealthy of phase diagrams. We initially revisit the BC model under a uniform crystal field and in zero magnetic field. This allowed us to regain the well-known mean-field results for this model. In the next step we revised the Kaufman-Kanner work on the BC model under a bimodal random magnetic field and uniform crystal field. In the case we paid special attention to crystal field versus temperature phase diagrams.

    Finally, we investigated the phase diagrams for the Gaussian random field case. The obtained phase diagrams display a rich variety of critical phenomena, with the presence of tricritical points, in some cases, related to the occurrence of  both frist-oder and continuous transition lines.     

6
  • RONIEL DE LIMA ARAÚJO
  • Structural, electronic, optical and vibrational properties of L-Threonine crystal: Computational simulations in DFT formalism.

  • Líder : UMBERTO LAINO FULCO
  • MIEMBROS DE LA BANCA :
  • UMBERTO LAINO FULCO
  • CARLOS ANTONIO BARBOZA
  • MANOEL SILVA DE VASCONCELOS
  • ANTONIO DE MACEDO FILHO
  • Data: 17-mar-2017


  • Resumen Espectáculo
  • In this work, we study the structural, electronic, optical and vibrational properties of orthorhombic l-threonine crystals, obtained through computational simulations in the DFT formalism (Density Functional Theory), the local density approximations (LDA-CAPZ) and the generalized gradient (GGA-PBE). L-threonine is an essential aminoacid that plays an important role in biological systems, being the last of the 20 aminoacids that make up the proteins, to be identified. For the crystal l-threonine, the optimization of crystalline geometry, network parameters, angles and inter atomic distances, band structure, state-by-atom density, optical absorption, dielectric function, refractive index, Optical conductivity, loss function, infrared spectrum and Raman. The calculated network parameters are close to the experimental results, a band gap direct E(Γ → Γ)=5,06 eV and band gap indirect E(X→S)=4,91 eV were obtained within the GGA and LDA level, respectively. The analysis of the electron states density allowed to identify the contributions per atom for the states of the valence and conduction bands, in the optical properties it is possible to observe a sensitivity to the plane of incident light polarization 001. A good agreement was obtained between the vibrational spectra IR and Raman theoretical and experimental data of the crystal l-threonine.

7
  • ACÁCIO SILVEIRA DE MELO
  • Meander-line Multilayer Magnetoimpedance: Magnetization dynamics in ferromagnetic trilayers

  • Líder : MARCIO ASSOLIN CORREA
  • MIEMBROS DE LA BANCA :
  • MARCIO ASSOLIN CORREA
  • TOMMASO MACRI
  • ANTÔNIO MARCOS HELGUEIRA DE ANDRADE
  • Data: 23-mar-2017


  • Resumen Espectáculo
  • The magnetoimpedance effect (MI) is an interesting tool for a completely analysis of the magnetic nanostructures, since is possible to observe the magnetization dynamics behavior at a wide range of frequency and external magnetic field,  in both saturated and unsaturated regimes.  In the last years studies about the MI effect as a function of sample geometry has been performed. In particular in trilayer systems and meander-lines samples, separately.  Based on this, here we seeks the integration  between these two geometry (trilayer and meander-line) and the structural and magnetic properties (quasi-static and dynamics) are explored in [NiFe/Cr/NiFe] trilayered samples. The samples were produced by Magnetron Sputtering technique under glass amorphous substrate with thicknesses of 75 - 142.5 nm for the ferromagnetic layer and 15-150 nm for the Cr layer, totalizing 10 samples. However, the total thicknesses of the trilayered samples are remained constant of 300 nm, irrespectively of the produced sample. Associated with this, for each set of thicknesses three in-plane substrate geometry were explored. The first one, a rectangular geometry, traditionally studied, the last two a meander-line geometry are studied. In particular, to reach these geometry for the samples, masks were used during the deposition process.  The structural characterization, trough X-ray diffraction, shows a crystalline behavior with a [111] texture, usually found for NiFe thin films grown onto amorphous substrate. The quasi-static characterization was performed through magnetization curves, obtained from a Vibrating Sample Magnetometer (VSM), with external magnetic field applied in the film-plane for distinct direction with respect to the mains axis of the samples, to verify the anisotropy behavior. In a general point of view, the magnetization curves reveal the isotropic behavior in the film-plane and a strongly dependence with the NiFe thicknesses.  On the other hand, a weak dependence with the sample geometry (rectangular or meander-line) is observed, as expected. Finally, for the magnetization dynamics study the magnetoimpedance effect was used in a wide range of field ( 700 Oe) and frequency (0.5 up to 3.0 GHz). Besides, two field configuration between the external magnetic field and the drive current were explored, named by longitudinal and transverse measurements. The MI measurements present a double or multiple peaks structures, characteristic of the FMR contribution in the MI variations in this frequency range. With respect to the MI effect dependence,  as a function of the thicknesses ratio of the NiFe and Cr layers,  is possible to observe a strongly influence of the out-of-plane magnetic anisotropy in the peaks structures in the MI curves, mainly for the samples with thick NiFe layer.  Lastly, the MI curves as a function of the sample geometry reveal changes in the dynamics magnetization, carrying asymmetric MI curves and a complexity in the peak structure.

8
  • PEDRO RICARDO VASCONCELOS DE MORAES JÚNIOR
  • A MULTIFRACTAL ORIGIN FOR THE TURBULENCE IN THE INTERSTELLAR MEDIUM

  • Líder : DANIEL BRITO DE FREITAS
  • MIEMBROS DE LA BANCA :
  • DANIEL BRITO DE FREITAS
  • BRUNO LEONARDO CANTO MARTINS
  • CAIO FÁBIO TEIXEIRA CORREIA
  • Data: 13-abr-2017


  • Resumen Espectáculo
  • In recent years studies on complex systems have been gaining strength and tools to be able to simulate and verify their behavior statistically. Much of this is due to many systems that have come to behave in a nonlinear and dissipative way. For these cases conventional geometries such as Euclidean is not possible for the prowess of explaining it, with this the geometry of the fractals emerged as an important alternative for the treatment of this medium, being laws of scales(power) applying very well for this system being exemplified in the form of time series and surfaces (two-dimensional and three-dimensional geometries).Thus a variety of methods we recounted for this treatment, among them are the analysis via exponent of Hurst and multifractal analysis. Our work aims to propose a new method to analyze two-dimensional images multi-fractally, being these images coming from clouds simulations of the interstellar medium. First step was to generate 12 MHD simulations in which they differed from values of pressure and magnetic field, then generated the 2D image that is applied on them the multifractal MFDMA treatment method. With the application of this method it is possible to evaluate the images through a frame containing the exponents of multifractal analysis, being possible to evaluate the scale behavior in the images and verify the degree of complexity, and to find out which sources cause multifractality, using two methods of multifractal analysis that are shuffling the original image data and replacing the original data from the Fourier transform. The results show that for all images the shuffling method can destroy the multifractal source of the original image and still behave like a monofractal, While the other method is ineffective, concluding that nonlinear factors are not included among the sources and indicating as a source of multifractality the long-range correlations. Another important result is the relation of the degree of multifractality ∆h with the pressure.

9
  • LOUIS GUSTAVO DA COSTA SOBRAL E SÁ
  • Thermal and mechanical properties of NHG under strain

  • Líder : LUIZ FELIPE CAVALCANTI PEREIRA
  • MIEMBROS DE LA BANCA :
  • LEONARDO DANTAS MACHADO
  • LUIZ FELIPE CAVALCANTI PEREIRA
  • SERGIO ANDRÉ FONTES AZEVEDO
  • Data: 24-jul-2017


  • Resumen Espectáculo
  • One and two-dimensional materials, such nanowires, nanotubes, graphene, and boron nitride, triggered enormous interest due to their potential application in novel electronic and heat management devices. In contrast to three-dimensional bulk materials, thermal transport in low-dimensions can be quite different. Graphene exhibits extraordinary physical properties, including an extremely high thermal conductivity. A novel graphene-derived two- dimensional crystal with a C2N stoichiometry and evenly distributed holes and nitrogen atoms in its basal plane, nitrogenated holey graphene (NHG), has recently been synthesized. Here we report an investigation of the thermal conductivity of NHG via non-equilibrium molecular dynamics simulations based on the Tersoff interatomic potential. We perform an analysis of finite-size effects and extrapolate our simulation results to estimate the properties of very large NHG sheets. The intrinsic thermal conductivity of NHG at room temperature was found to be 67.23 W/m-K, with an effective phonon mean free path of 16.84 nm. Both quantities are much smaller than the corresponding ones for graphene. Under uniaxial or biaxial strain we observe an increase in thermal conductivity and the corresponding effective phonon mean-free-path, although not as pronounced as in graphene. 

10
  • ALLYSON IRINEU ARAÚJO LIMA
  • Investigation of Optical and Electronic [(CH3) 2 NH2] Zn (HCOO) 3
  • Líder : MANOEL SILVA DE VASCONCELOS
  • MIEMBROS DE LA BANCA :
  • MANOEL SILVA DE VASCONCELOS
  • UMBERTO LAINO FULCO
  • JOSE DE MIRANDA HENRIQUES NETO
  • Data: 07-ago-2017


  • Resumen Espectáculo
  • The structural, electronic and optical properties of [(CH3)2NH2] Zn (HCOO)3 Triclinic were determined by first principles calculations developed in the Density Functional Theory (DFT) as encoded in the CASTEP Software, using Local density approximation (LDA) and generalized gradient approximation (GGA). A good agreement between the calculated and experimental network parameters was obtained. In the GGA approach, the results of the optimization were more compatible with the experimental data, presenting in the worst margin of error +0,87% for the network parameter a. In addition, we found that this material is a broad band gap semiconductor, with values of 3,67 eV (LDA) and 4,23 eV (GGA) in energy band gap, while in the optical properties we observed an isotropic behavior in the GGA approximation and a semi -isotropic for the LDA approach. In this work we obtained the Optimization of Crystalline Structure, Electronic Banding Structure, State Density, Dielectric Function and Optical Absorption of these materials for the two approaches.

11
  • RAIMUNDO NAZARENO DA SILVA CONCEIÇÃO FILHO
  • Synthesis and Characterization of Magnetic Nanoparticles of the Cobalt Samarium System

  • Líder : JOSE HUMBERTO DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • ARTUR DA SILVA CARRICO
  • GUSTAVO DE OLIVEIRA GURGEL REBOUCAS
  • JOSE HUMBERTO DE ARAUJO
  • MARCO ANTONIO MORALES TORRES
  • Data: 01-sep-2017


  • Resumen Espectáculo
  • In this work we used the chemical polyol method for the preparation of Sm-Co nanoparticles. The synthesized samples were named in the following forms: ARS-0%; ARS-5%, ARS-7% and ARS-9%, being the percentages referring to the variation of Acetic Acid used in the synthesis. The structural characterization was performed by     X-ray diffraction and transmission electron microscopy (TEM). The structural parameters were determined by the Rietvelt method using the Maud software. The following phases were identified: SmCo7; Sm2CO7; Sm2Co17 and Sm5Co19. For the study of magnetic properties, measurements with the vibrating sample magnetometer were used to obtain magnetization curves as a function of the magnetic field applied at room temperature. The PPMS was used to measure magnetization curves as a function of temperature. The Curie temperatures obtained are in accordance with the phases obtained by the structural characterization methods. Images of the samples were obtained through the SEM and MET for morphological study and determination of the size of the nanoparticles of the samples. Our results show the feasibility of the polyol method to obtain Sm-Co nanoparticles and the influence of Acetic Acid in the synthesis process.

Tesis
1
  • TIBERIO MAGNO DE LIMA ALVES
  • Static magnetic properties of magnetic nanopowders (Co1,2Fe1,8-xMnxO4 – CoFe2O4) and thin films (FeCuNbSiB): Theory and experiment

  • Líder : CLAUDIONOR GOMES BEZERRA
  • MIEMBROS DE LA BANCA :
  • CLAUDIONOR GOMES BEZERRA
  • FELIPE BOHN
  • SUZANA NOBREGA DE MEDEIROS
  • FERNANDO LUIS DE ARAUJO MACHADO
  • JACQUES COUSTEAU DA SILVA BORGES
  • VAMBERTO DIAS DE MELLO
  • Data: 26-ene-2017


  • Resumen Espectáculo
  • Magnetic nanostructures have received great attention from the academic community, not only due to their various technological applications, but from basic physics point of view, displaying behaviors, effects and properties of great interest. In this context, we can mention the anisotropic magnetic properties of FeCuNbSiB ferromagnetic thin films, cobalt ferrites nanopowders with Fe−Mn substitution (Co1,2Fe1,8-xMnxO4) and also stoichiometric cobalt ferrite itself (CoFe2O4). In this work, we have developed three models and numerical systems based on coherent rotation of the magnetization, one for each cited sample above, in order to describe and/or quantifying such anisotropic effects. Through modeling and simulation processes, we found that thin films of FeCuNbSiB, produced by magnetron sputtering technique, had a texture formation of anisotropy axes that can be modeled by a statistical distribution. The numerical calculations applied in longitudinal, transverse and polar measurements of magnetization indicated that, indeed, the dominant mechanism in the magnetic hysteresis of thin films studied here is consistent with coherent rotation of magnetization. The simulations indicated the behavior of difficult saturation in magnetic hysteresis curves of Co1,2Fe1,8-xMnxO4 nanopowders, at low temperature, could be modeled by a superposition of cubic and uniaxial [001] easy plane configuration anisotropies, compatible with a tetragonal symmetry. The wasp-waisted behavior in magnetic hysteresis curves of CoFe2O4 nanopowder could be attributed to effects of dipolar interactions between crystallites with a uniaxial anisotropy in easy plane configuration.

2
  • ELOISE CRISTINA DE SOUZA RODRIGUES
  • Synthesis and characterization of α-Fe and magnetite nanocomposite for biomedicalk applications

  • Líder : MARCO ANTONIO MORALES TORRES
  • MIEMBROS DE LA BANCA :
  • JOSE HUMBERTO DE ARAUJO
  • JOÃO MARIA SOARES
  • MARCO ANTONIO MORALES TORRES
  • NELSON ORLANDO MORENO SALAZAR
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 03-feb-2017


  • Resumen Espectáculo
  • Iron Oxide nanoparticles have been used em several biomedical applications  due to their biocompatibility and biodegradability. Among these applications, magnetic hyperthermia of tumors has been proposed as an alternative treatment of several neoplastic diseases. In this work, we have used high energy ball milling to produce iron oxide  nanoparticles with sizes smaller than 70 nm. We have prepared two groups of samples, the first group is composed of magnetite and α-Fe, the second group is composed of magnetite, wüstite and α-Fe nanoparticles. To improve the sample´s dispersibility in aqueous medium, the samples were functionalized with oleic acid and Pluronic-F127 three-block copolymer. The structural and chemical properties of samples were studied through x-ray diffraction, transmission electron microscopy (TEM) and Mössbauer spectroscopy. The magnetic properties were studied through AC susceptibility and DC magnetization as a function of temperature and field.  From the Mössbauer studies we noticed a significant fraction of Fe2,5+ located in octahedral sites of iron oxide, this result indicates that the samples  has a an stoichiometry similar to pure magnetite. The magnetic measurements showed the Verwey transition at about 120 K. From the TEM images we verified that the wüstite phase is formed on the surface of magnetite nanoparticles. Therefore, we showed that the wüstite phase and oleic acid surfactant prevent the magnetite nanoparticles from further oxidation. The shift of hystereis loops observed in the field-cooled samples was ascribed to exchange interaction between the wüstite and magnetite phases. The AC susceptibility showed characteristic peaks of magnetite wall domains, this result indicated that a fraction of particles are multidomain. The samples were submitted to an AC magnetic field and we observed an increase in temperature of e 11º C and 53º C for samples functionalized and bare, respectively. The combination of magnetic properties, the ability to release heat in presence of an AC field, and the stability of particles in aqueous suspension suggest that these samples are good candidates for magnetic hyperthermia.

3
  • CRISLANE DE SOUZA SANTOS
  • The Raychaudhuri Equation and the Non-Attractive Character of f(R) Gravity

  • Líder : JANILO SANTOS
  • MIEMBROS DE LA BANCA :
  • EDÉSIO MIGUEL BARBOZA JÚNIOR
  • JAILSON SOUZA DE ALCANIZ
  • JANILO SANTOS
  • RAIMUNDO SILVA JUNIOR
  • RICCARDO STURANI
  • Data: 24-mar-2017


  • Resumen Espectáculo
  • The observational evidence of the accelerated expansion of the Universe has been the main reason for a revision of the cosmological evolution as predicted by General Relativity (GR). Currently there are two main approaches to solving this problem: by introducing in the Einstein’s equations a term which represent a new kind of fluid (the so-called dark energy) possessing exotic features or by the modification of the gravitation theory. In this thesis we focus on the second approach, particularly the theories know as f(R) theories of gravity, which have received many attention in the last years. In this framework, the Raychaudhuri equation makes possible to examine the whole of spacetime structures without specific solutions of Einstein’s equations, playing so a central role to the understanding of gravitational attraction in Astrophysics and Cosmology. In the general relativity theory of gravity without a cosmological constant, a non-positive contribution from the spacetime to Raychaudhuri’s equation is usually interpreted as manifestation of the attractive character of gravity. In this case, particular energy conditions - indeed the strong energy condition - must be assumed in order to guarantee this attractive character. In the context of f(R) theories of gravity however, even assuming the standard energy conditions we may have a positive contribution to Raychaudhuri’s equation. Besides giving us a simple way to explain the observed accelerated expansion of the Universe, this fact opens the possibility of a repulsive character of this kind of gravity. In this thesis we address the attractive/non-attractive character of f(R) theories of gravity at the light of Raychaudhuri’s equation and make use of the strong energy condition, jointly with recente estimated values for the cosmographic parameters, in order to put bounds on a paradigmatic class of f(R) theories of gravity. 

4
  • CARLENE PAULA SILVA DE FARIAS
  • Competing Orders in Strongly Correlated Systems: from Ordered Magnetism to Spin Liquid Phases.

  • Líder : ALVARO FERRAZ FILHO
  • MIEMBROS DE LA BANCA :
  • ALVARO FERRAZ FILHO
  • RODRIGO GONCALVES PEREIRA
  • TOMMASO MACRI
  • PASCOAL PAGLIUSO
  • SERGIO GARCIA MAGALHÃES
  • Data: 10-abr-2017


  • Resumen Espectáculo
  • The main objective of this thesis is to investigate the competing ordered phases in the metallic heavy fermion compound URu2Si2,  which displays a body-centered tetragonal lattice. We first provide a study case of the competition between antiferromagnetic (AF) and spin liquid (SL) phases. The antiferromagnetic state is study with spin-wave theory. Whereas the spin liquid analysis is carry out in an algebraic spin liquid representation. In the second part, we describe an effective theory for Raman scattering experiments at these particularly phases. We provide insight about the hidden order phase displayed by the heavy fermion compound URu2 Si2 .

5
  • FRANCISCO JÂNIO CAVALCANTE
  • Evolution of the magnetic brake index for solar-type stars

  • Líder : DANIEL BRITO DE FREITAS
  • MIEMBROS DE LA BANCA :
  • DANIEL BRITO DE FREITAS
  • BRUNO LEONARDO CANTO MARTINS
  • JOSE RENAN DE MEDEIROS
  • EDUARDO JANOT PACHECO
  • MACKSON MATHEUS FRANÇA NEPOMUCENO
  • Data: 26-may-2017


  • Resumen Espectáculo
  • The present work is based on the effects of the magnetic braking for the evolution of the loss of
    angular momentum and, consequently, the relation between stellar rotation and age. In general, this
    rate of loss defined by dJ/dt depends on the angular velocity Ω in the form dJ/dt ∝ Ω^{q}, where
    q is a parameter of the non-extensive statistical mechanics. In the context of stellar rotation, this
    parameter is directly related to the braking index. For q equal to the unit, the magnetic field
    saturation scenario is recovered. Such an approach was proposed and investigated by de Freitas
    and De Medeiros for unsaturated field stars. In this thesis, we propose a new non-extensive
    approach to the evolution of stellar rotation based on the Reiners and Mohanty model. We
    developed a non-extensive version of the Reiners and Mohanty torque, and compared with the
    model proposed by de Freitas and De Medeiros, using a velocity sample (v seni) for ~16000 stars
    F and G field. As a result, we show that the Kawaler and Reiners-Mohanty models exhibit strong
    discrepancies in relation to the domain of validity of the entropic index q. These discrepancies are
    mainly due to the sensitivity of the stellar radius. Our results also showed that the modified Kawaler
    model is consistent within a wide mass range, while the Reiners and Mohanty model is restricted
    to masses smaller than G6 stars.
    We also devoted part of this thesis to studying the evolutionary behavior of the magnetic braking
    index for stars outside the main sequence. In this approach, we consider that the brake index
    undergoes a variation along the evolution of the star, that is, it is not a constant, but depends on the
    effect of dI /dt. Thus, we justify the fact that G-type giant stars are governed by the same Skumanich
    law. However, they must be corrected by one factor. In this thesis, we show that this factor is due
    to non-conservation of the volume of the star, which becomes more evident in later evolutionary
    stages, as is the case of the giants. We found that the dI/dt effect is best considering that the star
    volume is not conserved.

6
  • SUZANA ARAÚJO BARBOSA
  • Synthesis and Characterization of Nanocomposites of Ni-Cu and Halide CuCl Systems

  • Líder : MARCO ANTONIO MORALES TORRES
  • MIEMBROS DE LA BANCA :
  • MARCO ANTONIO MORALES TORRES
  • JOSE HUMBERTO DE ARAUJO
  • SUZANA NOBREGA DE MEDEIROS
  • JOSE ALZAMIR PEREIRA DA COSTA
  • JOSÉ ANTONIO HUAMANÍ COAQUIRA
  • Data: 28-ago-2017


  • Resumen Espectáculo
  • The aim of this work is to synthesize and study crystalline, non-aggregated and monodispersed nanoparticles of three systems containing Ni and/or Cu. The samples were prepared through the sol-gel method assisted by chitosan polymer. The first system is a nanocomposite with average particle size of 9-27 nm. The phases are mainly Ni, α-NiH and β-NiH. The α-NiH phase showed a significant magnetic contribution at temperatures below 50 and the hydrides were chemically stable when stored in air along several months. The second system is an ionic semiconductor of Cu(I)Cl with spherical particles and with average diameter of 9 nm. The third system consists of the solid solution of Ni and Cu atoms, and these samples are a mixing of NixCu(1-x) (0,50<x<0,92) alloys with average particle sizes in the range of 11-90 nm. The transmission electron microscopy images seems to reveal Cu rich alloy phases near to the particles surface, and Ni rich alloys located at the center. Magnetic measurements as a function of temperature in the range of 300-800 K showed evidences of magnetic transitions related to alloys with 75<x<92. For temperatures below Tc of the Ni92Cu8 alloy, it was observed a magnetic signal due to the Hopkinson phase. For T>Tc we noticed a feature related to the Griffiths phase which is due to Ni clusters dispersed in the Cu rich alloy phase. The critical parameters for this phase are in close agreement with the literature. The analysis of the hysteresis curves revealed an enhancement of the magnetocrystalline anisotropy constant (Keff) and this result was ascribed to the development of a surface magnetic anisotropy. The Griffiths phase and the Keff effect seem to be related the Cu rich alloy phase, which may be located at the nanoparticles surface. Experiments in samples subjected to AC magnetic field showed absorption specific rates with increasing values in agreement with the whole Ni content of the samples. The maximum variation of temperatures occurred for intervals of 200 s, indicating that these samples have potential for use in magneto hyperthermia in the treatment of tumors.

7
  • THIAGO CRISOSTOMO CARLOS NUNES
  • Role of dimensionality in complex networks: Connections with nonextensive statistical mechanics

  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • ANTONIO DE MACEDO FILHO
  • DANIEL JUDSON BEZERRA SOARES
  • JOAO MEDEIROS DE ARAUJO
  • LUCIANO RODRIGUES DA SILVA
  • RAIMUNDO SILVA JUNIOR
  • SAMURAÍ GOMES DE AGUIAR BRITO
  • Data: 08-sep-2017


  • Resumen Espectáculo
  • Scale-free networks are quite popular nowadays since many systems are well represented by such structures. In order to study these systems, several models were proposed. However, most of them do not take into account the node-to-node Euclidean distance, i.e., the geographical distance. In real networks, the distance between sites can be very relevant, e.g., those cases where it is intended to minimize costs. Within this scenario we studied the role of dimensionality d in the Bianconi-Barabási model with a preferential attachment growth involving Euclidean distances. The preferential attachment in this model follows the rule , where  characterizes the fitness of the i-th site and is randomly chosen within the (0, 1] interval. We verified that the degree distribution P(k) for dimensions d = 1,2,3, 4 are well fitted by ,   is the q-exponential function naturally emerging within nonextensive statistical mechanics. We determine the index q and  as functions of the quantities and d, and numerically verify that both present a universal behavior with respect to the scaled variable  The same behavior also has been displayed by the dynamical 𝛽 exponent which characterizes the steadily growing number of links of a given site.

8
  • CRISTÓVÃO PORCIANO DO NASCIMENTO JÚNIOR
  • Synthesis, Structural and dielectric characterization of iron niobate.

  • Líder : SUZANA NOBREGA DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • CARLOS CHESMAN DE ARAUJO FEITOSA
  • SERGIO ANDRÉ FONTES AZEVEDO
  • SUZANA NOBREGA DE MEDEIROS
  • TIBERIO MAGNO DE LIMA ALVES
  • UILAME UMBELINO GOMES
  • Data: 14-sep-2017


  • Resumen Espectáculo
  • Iron niobate (FeNbO4) has been applied to the photodiode in solar energy converters,
    gas sensors, photo detectors, and electronic devices. However, a full description of your
    dielectric properties is still scarceness so. By using a high energy mill, was prepared three
    kinds of samples (24, 48 and 72 hours) of precursors. After milling process, the resultant
    ponders were to calcinate for precisely 4 hours and in a temperature of 1 300 celsius.
    We used a hydraulic press about 1570 Kgf to produce samples. Next, samples were calcinated during a time considered the same for all of them and underwent to dielectric
    characterization. In the way to characterize the samples, the formers were submitted to
    X rays, scanning electronic microscopy and X rays uorescence. Results have been shown
    that samples milling by 24 hours, has 94.48% of FeNbO4 and 5.52% of Fe2O3, by 48h
    has 97.82% of FeNbO4 and 2,18% de Fe2O3, and by 72h 93,68% of FeNbO4 and 6.32% of
    Fe2O3. Dielectric properties were analyzed through I-V characteristic curves and complex
    dialectic permitivity against frequency. Characteristic curves exhibited semiconductors
    electronic devices behave like thyristor class. Furthermore, actual work constitutes a fully
    new route to sintering iron niobate. Results still indicated the samples have potential
    application in the electronic devices.

9
  • NEYMAR PEREIRA DA COSTA
  • PROPRIEDADES TERMOELÉTRICAS DE FILMES NANOMÉTRICOS DE LIGAS DE TELURIO SELENIO E ANTIMONIO PRODUZIDOS POR MAGNETRON SPUTTERING DC.

  • Líder : CARLOS CHESMAN DE ARAUJO FEITOSA
  • MIEMBROS DE LA BANCA :
  • ALEXANDRE BARBOSA DE OLIVEIRA
  • CARLOS CHESMAN DE ARAUJO FEITOSA
  • CHARLIE SALVADOR GONCALVES
  • CLÁUDIO BENEDITO SILVA FURTADO
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 14-sep-2017


  • Resumen Espectáculo
  • The present thesis discusses a semiconductor target production method whose material is obtained from commercial thermoelectric modules. The targets are used in a magnetron sputtering system. The materials consist of two semiconductor ternary alloys, one made of bismuth telluride and antimony, characterized as type P and the other of bismuth selenide and telluride, characterized as type N. These alloys of Bi2Te3-ySey and Bi2-xSbxTe3 systems exhibit high-performance thermoelectric properties within an ambient temperature range. Based on these data, thermoelectric films of nanometric thickness were produced in two batches, whose samples were submitted to post-production thermal treatments. We investigated the thermoelectric properties of films, at ambient temperature in the physical property measurement system (PPMS). To that end, the thermal transport option (TTO), which makes it possible to acquire data on physical quantities such as Seebeck coefficient α, thermal conductivity κ and electrical resistivity ρ, was applied. These quantities were used to calculate the power factor and figure of merit, which is an adimensional factor that determines how promising the material is for energy conversion and thermoelectric refrigeration applications. Measures of voltage current using the four-point collinear method showed that the type P semiconductor can be used as a thermal keying sensor. An important perspective is the development of a substrate, using films as planar thermoelements, thereby functioning as a thermoelectric device capable of promoting thermal gradients in applications for other systems such as magnetic-galvanometric.

10
  • SILAS SARMENTO PEDROSA
  • Dipolar effects on the magnetic phases of superparamagnetic clusters

  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ANA LUCIA DANTAS
  • ARTUR DA SILVA CARRICO
  • GUSTAVO DE OLIVEIRA GURGEL REBOUCAS
  • JOSE HUMBERTO DE ARAUJO
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 15-sep-2017


  • Resumen Espectáculo
  • Superparamagnetic nanoparticles clusters are currently driving considerable research attention. The interest stems from chances of designing systems with promising potential for technological applications, and from the fundamental viewpoint, tailoring new magnetic phases. The initial magnetic susceptibility and the stray field, at remanence, are key features for the optimization of magnetic systems for biomedical applications. Also, the existence of dipolar ferromagnetism, in the absence of exchange energy, has been one of the focus of magnetism for decades. We report a theoretical discussion of the impact of the dipolar interactions on the magnetic phases of superparamagnetic nanoparticles confined in spherical and ellipsoidal clusters. We consider Fe3O4 nanoparticles, with size ranging from 9nm to 12nm, arranged with uniform density in hundreds nanometer size volumes. We show that the magnetic phases, and the initial susceptibility, are controlled by the dipolar interaction. Also, the topological nanoparticle arrangement, the nanoparticle size, and the packing density, are key features. We show that the dipolar interaction alone may stabilize classical magnetic phases, well known for systems with large content of exchange and anisotropy energies. In addition, we have found that at remanence the nanoparticles clusters magnetic phase have a unique property. The dipolar energy leads to thermal stabilization of the individual nanoparticles moments. Large nanoparticles densities may allow nearly full thermal value of the nanoparticles magnetic moments. Despite this, the nanoparticles cluster is superparamagnetic, with a rather small stray field at remanence, as required for biomedical safety. Nanoparticle clustering in large eccentricity ellipsoidal volumes are promising systems for both low field and large field biomedical applications. For low field applications, there is a large increase in the initial susceptibility, with enhancement in the efficacy of vector targeting and also for hyperthermia absorption rate. For high field applications, the enhancement of the stray is much stronger than that for spherical clusters. Our theoretical model reproduces typical properties of Fe3O4 nanoparticles spherical clusters, as well as intriguing results for Fe and Co quasi-one-dimensional systems.

11
  • FRANCYS ANTHONY DA SILVA
  • Rotation and Activity of F, G, and K type stars observed by CoRoT and KEPLER satellites

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • FRÉDÉRIC BAUDIN
  • MARCELO EMÍLIO
  • MARIA CRISTINA DE ASSIS RABELLO SOARES
  • Data: 01-dic-2017


  • Resumen Espectáculo
  • The question of how typical the Sun is within the class of solar-type stars,  in terms of activity and rotation has been the subject of active investigation over the past three decades. Recently, the CoRoT and Kepler space telescope observed  Thousand of stars (163 thousands for CoRoT and 400 thousand for Kepler) with an unprecedented richness and precision providing an opportunity to study the rotation and variability of solar-type stars (F, G and K) based on light curves . Light curves of those solar-type stars often show fluctuations due to rotational modulation by magnetic features (starspots and faculae) on stellar surfaces, and this is also dependent of the magnetic cycle period. In this Thesis, we are presenting rotation period measurements of a large sample of field stars in the solar neighbourhood, observed by CoRoT  and KEPLER satellites.  Rotation periods was measured from an unified technique  analysis composed by autocorrelation function, Lomb Scargle periodogram  and wavelet.  We also identified a sample of solar twins and analogs observed by the Kepler mission from which we determined their evolutionary status, rotation period and age from gyrochronology.  For the rotation activity we used a proxy based on the light curve modulation.  To interpret our results concerning the rotation measurements, based on solar physics, we compared the temporal variability of total solar irradiance (TSI) and the solar rotation period along a solar cycle. We used this interpretation with the variability of the CoRoT and Kepler light curves  to undertand  the connection of  the structures responsible for the intrinsic evolution and the light curve  modulation, as well as to determine the impact of the solar cycle on the measurements of the rotation period for F, G and K type stars.

12
  • HUMBERTO SCALCO GIMENES
  • LambdaCDM Model with dissipative nonextensive dark matter

  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • FABIO CABRAL CARVALHO
  • JOAO MEDEIROS DE ARAUJO
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MATTHIEU SEBASTIEN CASTRO
  • Maria Aldinez Dantas
  • RAIMUNDO SILVA JUNIOR
  • Data: 27-dic-2017


  • Resumen Espectáculo
  • Many models in cosmology typically assume the standard bulk viscosity. On this thesis, we study an alternative interpretation for the origin of the bulk viscosity. Using nonadditive statistics proposed by Tsallis, we propose a bulk viscosity component that can only exist by a nonextensive effect through the nonextensive/dissipative correspondence (NexDC). We consider the LambdaCDM model for a flat universe with a dissipative nonextensive viscous dark matter component, following the Eckart theory of bulk viscosity, without any perturbative approach. In order to analyse cosmological constraints, we use one of the most recent observations of Type Ia Supernova, baryon acoustic oscillations and cosmic microwave background data. It's shown that only exists viscous effect in 2 sigma confidence level scenarios.

2016
Disertaciones
1
  • IVANDSON PRAEIRO DE SOUSA
  • Dimer models in mixed planar lattices

  • Líder : FRANCISCO ALEXANDRE DA COSTA
  • MIEMBROS DE LA BANCA :
  • FRANCISCO ALEXANDRE DA COSTA
  • JOAO MEDEIROS DE ARAUJO
  • IDALMIR DE SOUZA QUEIROZ JÚNIOR
  • Data: 29-feb-2016


  • Resumen Espectáculo
  • In this study we present solutions for dimer models in mixed planar lattices, obtained from
    combinatorial method. In this method the partition function is obtained from the pfaffian
    associated with the problem. Particularly, in the thermodynamic limit, the free energy
    densities for 4-6, 3-6 and 3-4 lattices were determined. Besides the determination of the
    free energy for each case, we also computed the molecular freedom and the density of
    entropy in the high temperature limit. We considered three types of distinct 4-6 lattices,
    in which two of them exhibit phase transition. We also discuss the solutions for two types
    of 3-6 lattices which exhibit critical behavior similar to the 4-6 lattices cases discussed in
    the present work. The 3-4 lattice is geometrically similar to the triangular lattice problem,
    but presents distinct critical behavior. In all cases, we study numerically the behavior
    of free energy density as well as the behavior of its first derivatives, in order to better
    understand the thermodynamic behavior of the corresponding system. We also revise
    some results already presented in literature for the square, hexagonal, triangular and the
    mixed 4-8 lattices, treated by the pfaffian combinatorial approach.

2
  • ÍCARO KENNEDY FRANCELINO MOURA
  • Testes cosmológicos aplicados a modelos de energia escura

  • Líder : NILZA PIRES
  • MIEMBROS DE LA BANCA :
  • NILZA PIRES
  • RAIMUNDO SILVA JUNIOR
  • Maria Aldinez Dantas
  • Data: 02-mar-2016


  • Resumen Espectáculo
  • Grandes esforços observacionais têm sido direcionados para investigar a natureza da chamada energia escura. Nesta dissertação derivamos vínculos sobre modelos de energia escura utilizando três diferentes observáveis: medidas da taxa de expansão H(z) (compiladas por Meng et al. em 2015);  módulo de distância de 580 Supernovas do Tipo Ia  (catálogo Union Compilation 2.1, 2011); e as observações do pico de oscilação de bárions (BAO) e a radiação cósmica de fundo (CMB) utilizando a chamada razão CMB/BAO, que relaciona 6 picos de BAO  (um pico determinado através dos dados do Survey 6dFGS, dois através do SDSS e três através do WiggleZ). A análise estatística utilizada foi o método do χ2 mínimo (marginalizado ou minimizado sobre h sempre que possível) para vincular os parâmetro cosmológicos: Ωm, ΩΛ, ω e δω0. Esses testes foram aplicados em duas parametrizações do parâmetro ω da equação de estado da energia escura, p=ωρ (aqui, p é a pressão e ρ é a densidade de energia da componente). Numa,  ω é considerado constante e menor que -1/3, conhecido como modelo XCDM; na outra parametrização, o parâmetro da equação de estado varia com o redshift, no qual o chamamos de Modelo GS. Esta última parametrização é baseada em argumentos que surgem da teoria da inflação cosmológica. Para efeitos de comparação também foi feita a análise do modelo ΛCDM. A comparação dos modelos cosmológicos com as diferentes observações leva a diferentes melhores ajustes. Assim, para classificar a viabilidade observacional dos diferentes modelos teóricos, utilizamos dois critérios de informação, ou seja, o critério de informação bayesiana (BIC) e o critério de informação Akaike (AIC). A ferramenta matriz de Fisher foi incorporada aos nossos testes para nos fornecer a incerteza dos parâmetros de cada modelo teórico. Verificamos que a complementariedade dos testes é necessária para não termos espaços paramétricos degenerados. Fazendo o processo de minimização encontramos, dentro da região de 1σ (68%), que para o Modelo XCDM os melhores ajustes dos parâmetros são Ωm=0,28±0,012 e ωX=-1,01±0,052. Enquanto que para o Modelo GS os melhores ajustes são Ωm=0,28±0,011 e δω0=0,00±0,059. E realizando uma marginalização encontramos, dentro da região de 1σ (68%), que para o Modelo XCDM os melhores ajustes dos parâmetros são Ωm=0,28±0,012 e ωX=-1,01±0,052. Enquanto que para o Modelo GS os melhores ajustes são Ωm=0,28±0,011 e δω0=0,00±0,059.

3
  • ISAAC DE MACÊDO FÉLIX
  • Transporte térmico em nanofitas de grafeno-nitreto de boro

  • Líder : LUIZ FELIPE CAVALCANTI PEREIRA
  • MIEMBROS DE LA BANCA :
  • ANDERSON LUIZ DA ROCHA BARBOSA
  • CLAUDIONOR GOMES BEZERRA
  • LUIZ FELIPE CAVALCANTI PEREIRA
  • SERGIO ANDRÉ FONTES AZEVEDO
  • Data: 29-mar-2016


  • Resumen Espectáculo
  • A capacidade de manipular propriedades térmicas de super-redes pode ajudar na descoberta de materiais mais promissores para aplicações na nanotecnologia. Por meio de simulações de dinâmica molecular de não-equilíbrio, investigamos o transporte térmico em nanofitas BNC, revezando periodicamente quantidades equivalentes de grafeno e nitreto de boro ao longo do seu comprimento, nomeando de período de rede o tamanho de cada par de domínio (grafeno-nitreto de boro). Este trabalho revela que a condutividade térmica nessa super-rede varia não-monotonicamente com o períodos de rede, podendo dessa forma ser controlada de acordo com os domínios de grafeno e nitreto de boro. Isso possibilita identificar o período de rede que fornece a menor condução de calor nessa super-rede. Nesse sentido, para nanofitas com período de rede de 3,43 nm, registramos uma condutividade térmica de ~ 89 W/m·K. Este valor é muito menor do que o encontrado para grafeno e nitreto de boro isolados. O transporte térmico em nanofitas BNC é dominado por vibrações na sua rede cristalina (fônons). Associamos o comportamento não-monotônico da condutividade térmica dessa super-rede com o transporte térmico de fônons coerentes e incoerentes. Por meio da densidade de estados vibracionais (VDOS) e da dispersão de fônons, analisamos seu espectro vibracional.

4
  • REBECCA DE MOURA BRAZ DINIZ
  • Caminhantes Aleatórios Com Perfil de Memória Binomial

  • Líder : JOAO MEDEIROS DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • JOAO MEDEIROS DE ARAUJO
  • ANANIAS MONTEIRO MARIZ
  • FRANCISCO ALEXANDRE DA COSTA
  • GISLENE MICARLA BORGES DE LIMA
  • Data: 27-may-2016


  • Resumen Espectáculo
  • Grande tem sido o interesse nas difusões anômalas, pois se apresentam nas mais diversas áreas do conhecimento. A introdução de perfil de memória no caminhante aleatório torna-o numa dinâmica estocástica não-markoviana, cujas correlações criam superdifusão, persistencia e log-periodicidade. Apresentamos uma revisão da literatura sobre os perfis de memória e introduzimos nosso modelo. O modelo de memória binomial pode selecionar diferentes regiões de perda de memória, desde a inicial até a recente. Dessa forma, investigamos o impacto da posição da perda de memória no comportamento superdifusivo do caminhante aleatório e unificamos muitos dos resultados da literatura. Obtivemos que memórias iniciais geram maior superdifusão medidas pelo coeficiente de Hurst, enquanto que memórias recentes tendem a diminuir a superdifusão, tornando mais caminhantes adeptos da difusão normal. Também investigamos o regime de memória curta inicial, com largura tendendo a zero.  Observamos log-periodicidade para alguns caminhantes sugerindo regimes diferentes de comportamento log-periodico, incluindo aqueles considerados de difusão normal. Uma particularidade do modelo binomial são os resutados extremamente simétricos para o diagrama Hxr.

5
  • CARLOS AUGUSTO PITOMBEIRA VIANA
  • Processos Não-Randômicos Associados ao Aquecimento do Disco Galático.

  • Líder : DANIEL BRITO DE FREITAS
  • MIEMBROS DE LA BANCA :
  • DANIEL BRITO DE FREITAS
  • BRUNO LEONARDO CANTO MARTINS
  • JOSÉ RONALDO PEREIRA DA SILVA
  • Data: 30-may-2016


  • Resumen Espectáculo

  • Neste trabalho, analisamos os mecanismos que regem os processos que governam o aquecimento do disco galáctico através da dinâmica das velocidades espaciais U, V e W extraídas do Catálogo Genebra-Copenhagen. Nós partimos da premissa, até então aceita a priori, de que os processos que atuam no disco galáctico são de natureza aleatória e responsáveis por um aquecimento puro revelado pela componente W. Em seguida, nós utilizamos um modelo baseado na Mecânica Estatística Não-Extensiva onde derivamos as funções de distribuição de probabilidade que quantificam o afastamento da Gaussianidade dado o perfil da cauda da distribuição mensurado pelo índice entrópico q. Nossos resultados revelam que a aleatoriedade ocorre apenas em regiões limitadas de idade independente da velocidade espacial e faixa espectral, contrariando assim a premissa acima destacada. Além disso, utilizando as distribuições do tipo não-Gaussianas para descrever o comportamento das velocidades U, V e W, nós encontramos que o aumento da dispersão da velocidade, sigma, com a idade das estrelas segue uma lei do tipo lei de potência, indicando que existe um desencadeamento do tipo avalanche ocorrendo em diferentes escalas. Finalmente, nossos resultados colocam um novo olhar nessa questão e abre um caminho para o estudo das componentes cinemáticas Galácticas pela ótica de modelos estatísticos mais robustos que levam em conta os efeitos de não-gaussianidade e não-linearidade.

6
  • ZAIRA BRUNA BORGES DE OLIVEIRA
  • Relativistic kinetic theory: non-extensive effects on the H-Theorem
  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • RAIMUNDO SILVA JUNIOR
  • EDÉSIO MIGUEL BARBOZA JÚNIOR
  • JAILSON SOUZA DE ALCANIZ
  • Data: 03-jun-2016


  • Resumen Espectáculo
  • The relativistic H-theorem, including non-extensive effects, was calculated using the q-calculation.
     The hypothesis of molecular chaos was generalized in order to introduce strong statistical
     correlations between the functions of relativistic distributions. The positivity of the entropy 
    source leads to a thermodynamic bond on the entropy parameter, q Є [0.2]. It has also been 
    proved that states of collisional equilibrium (term of the null entropy source) are described by a 
    law of relativistic power that extends the exponential distribution of Juttner, which reduces, in 
    the classical domain, the power law function of Tsallis. All results provide the standard results 
    at the extensive limit (q = 1), thus showing that Tsallis's formalism is compatible with the
     issues addressed in special relativity theory.
     
     
     
7
  • MÁRCIO ASSUNÇÃO TEIXEIRA
  • Ferramentas da Astroestatística para o estudo da velocidade radial estelar

  • Líder : DANIEL BRITO DE FREITAS
  • MIEMBROS DE LA BANCA :
  • DANIEL BRITO DE FREITAS
  • BRUNO LEONARDO CANTO MARTINS
  • JOSÉ RONALDO PEREIRA DA SILVA
  • Data: 18-jul-2016


  • Resumen Espectáculo
  • A velocidade radial estelar tem sido usada desde as descobertas dos primeiros exoplanetas. Esse método tem se mostrado bem sucedido na obtenção dos parâmetros orbitais dos exoplanetas, como, por exemplo, a excentricidade da órbita, o período de translação, a massa do planeta, a distância do periastro, entre outros. A análise dos dados de velocidade radial contém vários problemas, devido a sua função matemática ser altamente não-linear e multimodal. Para a inferência desses parâmetros, métodos estatísticos robustos são necessários na análise dos dados.


    Nesse trabalho, desenvolvemos algoritmos que nos permite realizar inferências estatísticas. Os métodos de inferência utilizados são o método do 2 mínimo, o método de Monte Carlo via cadeia de Markov e o Nested Sampling. Estudamos cada um dos métodos, simulando dados, com adição de ruído, e aplicando-os em dois casos: na equação linear e para funções senoidais. Por último, aplicamos os métodos estatísticos para o caso da velocidade radial estelar, fazendo uso de dados da estrela HD 187085, com o objetivo de determinar a eficácia de tais métodos, comparando os resultados com os obtidos na literatura.

8
  • EVERSON FRAZÃO DA SILVA
  • Study of Photonic Quasicrystals of Fibonacci, Octonacci and Dodecanacci with Graphenes

  • Líder : MANOEL SILVA DE VASCONCELOS
  • MIEMBROS DE LA BANCA :
  • MANOEL SILVA DE VASCONCELOS
  • DORY HELIO AIRES DE LIMA ANSELMO
  • CARLOS HUMBERTO OLIVEIRA COSTA
  • Data: 26-oct-2016


  • Resumen Espectáculo
  • The richness of optical and electronic properties of graphene has attracted enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and stability. Until recently, the main focus has been on fundamental physics and the physics of electronic devices. However, we believe that the full potential of graphene is in photonics and optoelectronic, where the combination of their optical and electronic properties are unique and can be fully exploited even in the absence of an electronic "band gap". In this master thesis we studied the optical transmissivity spectra in periodic dielectric multilayer (photonic crystals) and multilayers who obey quasiperiodic sequences (photonic quasicrystals) composed of graphene and compare our results with the same structures without graphene. Thus, first we calculate the transmittance spectrum photonic crystal formed by alternating layers of dielectric permittivities with  and B, for comparative purposes. In the second stage, we have introduced between the dielectric monolayers a monolayer of graphene. Then we study the photonic Fibonacci’s quasicrystals, with and without graphene entres the dielectric layers, which can be generated by a recurrence relation of the type: Sj + 1 = Sj Sj-1 where S0 = B and S1 = A. In both cases we use the transfer-matrix technique to obtain the transmittance spectra. We have also studied a generalization of the Fibonacci quasicrystal structure called “Octonacci”, where the n-th stage of these multilayer structure (Sn) is given by the recurrence rule: Sn = Sn-1 Sn-2Sn-1, with n>2 to S1=A and S2=B. Finally, for completeness, we study the further generalization of the Fibonacci sequence called Dodecanacci, which can be generated starting from the inflation rule: A-> AABAA and B-> AB. Our results show that all the optical spectra are affected and their "band gap", and slightly translated to high frequencies. We also show that the properties of fractality and self-similarity of the spectra are maintained to high frequencies. Our results show a good insight into new devices that use the quasiperiodic multilayer instead of the well known Bragg reflectors.

9
  • MILTON GOMES DE SOUZA NETTO
  • Astrophysics noise's classification in the presence of a planetary transit

  • Líder : DANIEL BRITO DE FREITAS
  • MIEMBROS DE LA BANCA :
  • DANIEL BRITO DE FREITAS
  • JOSE RENAN DE MEDEIROS
  • MARIA LIDUINA DAS CHAGAS
  • Data: 28-oct-2016


  • Resumen Espectáculo
  • Motivated by the growing number of missions and data in the exoplanet field and the shortage of mathematical models that use non-Gaussian and correlated noise in the photometry data, we analyze the change of the statistical parameter Hurst exponent, H, in time series of a variety types of astrophysical noise with and without the presence of a planetary transit. In addition, we determined the value of the Hurst exponent for two light curves from the public database of the CoRoT mission. To estimate the value of H we used two methods, the rescaled range analysis R/S and the fast Fourier transform, fft. To do this, we developed an astrophysical noise simulator, generating time series of several types of noises and estimate the value of H for all of time series. After, we generated a synthetic planetary transit and insert in the noise background and then recalculate the value of H. We note that the presence of planetary transit change significantly the value of the Hurst exponent, and the method of R/S analysis is more suitable than the Fourier Transform. We have found that the Hurst exponent can be a powerful discriminant to distinguish time series with different kind of variability, in particular the distinction between time series presenting a planetary transit. We also have estimated the Hurst exponent for 30 stars from public database of Kepler mission and relate to the orbital period of planets present in these systems.

10
  • RAFAEL RAMON FERREIRA
  • A quantitative and qualitatively study of the star HD 43587 based on CoRoT Mission data and spectroscopy

  • Líder : MATTHIEU SEBASTIEN CASTRO
  • MIEMBROS DE LA BANCA :
  • MATTHIEU SEBASTIEN CASTRO
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • GUSTAVO ANDRES GUERRERO ERASO
  • Data: 04-nov-2016


  • Resumen Espectáculo
  • Among several aspects related to the Sun's activity history, the extended period of the Sun's evolution with a low chromospheric activity level and a low quantity of observed sunspots compared with other epochs, known as Maunder Minimum, remains as a puzzle for the stellar evolution theory.  In this work we study HD 43587 a solar analog star that is a seismic primary target from the CoRoT mission and presents measurements of activity index along 50 yrs by the Mount Wilson program and outher spectroscopic measurements.  Based on the similarity of HD 43587 with the Sun and by using observations collected by the CoRoT satellite as well as data from the literature, our preliminary analysis (Lithium abundance and chromosferic activity) confirms the evolutionary status of HD 43587. The CoRoT light curve indicates also a flat activity profile, that is a indicative of very low chromospheric activity. All this measurements and analysis make this star an excellent Maunder minimum candidate.

Tesis
1
  • DANILO OLIVEIRA PEDREIRA
  • Estudo teórico das propriedades eletrônicas e termodinâmicas de nanofitas quasiperiódicas BCN

  • Líder : CLAUDIONOR GOMES BEZERRA
  • MIEMBROS DE LA BANCA :
  • CLAUDIONOR GOMES BEZERRA
  • CARLOS CHESMAN DE ARAUJO FEITOSA
  • LUIZ FELIPE CAVALCANTI PEREIRA
  • CLÁUDIO BENEDITO SILVA FURTADO
  • SERGIO ANDRÉ FONTES AZEVEDO
  • Data: 19-feb-2016


  • Resumen Espectáculo
  • Materiais em nanoescala compostos por átomos de boro, carbono e nitrogênio apresentam propriedades únicas e podem ser úteis no desenvolvimento de novas tecnologias. Nesta tese, investigamos algumas propriedades de nanofitas BCN com arranjo quasiperiódico dado por uma sequência Fibonacci. Analisamos propriedades como: estabilidade estrutural, densidade eletrônica de estados, calor específico eletrônico, estrutura de bandas e gap de energia. Realizamos cálculos de primeiros princípios baseados na teoria do funcional da densidade implementado como no código SIESTA. Os resultados mostraram que nanofitas com maior geração Fibonacci tendem a apresentar um valor fixo para a energia de formação. A densidade eletrônica de estados foi utilizada para calcular o calor específico. Encontramos um comportamento oscilatório do calor específico eletrônico, para o regime de baixas temperaturas. Analisamos a estrutura de bandas para determinar o gap de energia. O gap de energia apresenta oscilações como função do índice n da geração Fibonacci. Nosso trabalho sugere que uma escolha apropriada dos blocos de construção da sequência quasiperiódica do material pode levar a um controle do gap de energia para nanofitas quasiperiódicas.

2
  • KLAYDSON REINALDO CELINO
  • Anisotropia magnética em nanofilmes com assimetria cristalográfica

  • Líder : CLAUDIONOR GOMES BEZERRA
  • MIEMBROS DE LA BANCA :
  • CLAUDIONOR GOMES BEZERRA
  • CARLOS CHESMAN DE ARAUJO FEITOSA
  • DORY HELIO AIRES DE LIMA ANSELMO
  • CARLOS HUMBERTO OLIVEIRA COSTA
  • RAIMUNDO NOGUEIRA DA COSTA FILHO
  • Data: 26-feb-2016


  • Resumen Espectáculo
  • Esta Tese compreende um estudo teórico sobre a influência da anisotropia magnetocristalina nas propriedades magnéticas estáticas e dinâmicas de filmes finos: monocamadas e tricamadas acopladas através dos campos de troca bilinear e biquadrático, para situações nas quais os sistemas são crescidos em direções não usuais [hkl] de baixa simetria. Usando uma teoria baseada em um modelo fenomenológico realístico para descrever sistemas magnéticos nanométricos, consideramos a energia magnética livre total incluindo a interação Zeeman, anisotropias magnetocristalinas cúbica e uniaxial, anisotropias desmagnetizante e de superfície, bem como os termos de troca. Os cálculos numéricos são conduzidos através da minimização da energia magnética total a partir da determinação das configurações estáticas de equilíbrio. Consideramos parâmetros experimentais da literatura para ilustrar nossos resultados em sistemas tipo Fe/Cr/Fe. Em particular, um total de seis diferentes cenários magnéticos é analisado para três grupos de campos de troca e as direções de crescimento de baixa simetria [211] e [321]. Após minimizarmos numericamente a energia total, utilizamos as configurações de equilíbrio para obter curvas de magnetização e de magnetoresistência com as respectivas fases magnéticas e os campos críticos de transições de fases. Estes resultados também são usados para a determinação da fronteira de ocorrência dos estados saturados. Dentro do contexto das ondas de spin, resolvemos a equação de movimento para estes sistemas a fim de encontrarmos as respectivas relações de dispersão associadas. Os resultados mostram curvas de magnetização e magnetoresistência similares em ambos os cenários [211] e [321], com comportamento de transição magnética equivalente. No entanto, a combinação entre simetrias peculiares e a influência da energia de troca resulta em propriedades cativantes, incluindo a geração de estados magnéticos dependentes da direção de crescimento e aumento de incompatibilidade entre valores de campo de saturação da magnetização e magnetoresistência para eixos anisotrópicos cúbicos intermediários, particularmente no regime onde os campos de troca bilinear e biquadrático são comparáveis. As relações de dispersão e os resultados estáticos são coerentes, com as fases magnéticas também presentes em ambos os modos acústico e óptico. Excitações de Goldstone são observadas particularmente nos eixos anisotrópicos cúbicos intermediários, um efeito relacionado às transições de segunda ordem e à quebra espontânea de simetria imposta pela combinação entre o acoplamento biquadrático e as anisotropias cúbica e uniaxial.

3
  • FRANCISCO CESAR DE MEDEIROS FILHO
  • Influência da interação dipolar nas fases magnéticas de nanopartículas esféricas com estrutura núcleo@camada.

  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ARTUR DA SILVA CARRICO
  • JOSE HUMBERTO DE ARAUJO
  • SUZANA NOBREGA DE MEDEIROS
  • IDALMIR DE SOUZA QUEIROZ JÚNIOR
  • VAMBERTO DIAS DE MELLO
  • Data: 29-feb-2016


  • Resumen Espectáculo
  • As nanopartículas tipo núcleo@camada tem despertado a atenção de vários pesquisadores

    devido a grande aplicabilidade que estas oferecem. A possibilidade de combinar diferentes funcionalidades de materiais magnéticos as torna peça chave em várias áreas. Como exemplo disso, existem as mídias de gravação em que a anisotropia eficaz da nanopartículas é reduzida acoplando um material magneticamente duro a um com baixa anisotropia. Nos sistemas biomédicos, a conversão de energia eletromagnética em calor tem se tornado uma poderosa técnica de caráter não invasivo para aplicações biotecnológicas, tais como vetorização e liberação controlada de fármacos no tratamento de doenças. Além disso, esse tipo de nanoestrutura destaca-se em sensores magnéticos, desenvolvimento de novos medicamentos e ímãs permanentes. As nanopartículas magnéticas tipo núcleo@camada são controladas por meio de propriedades intrínsecas dos materiais do núcleo e da casca bem como das interações entre eles, além dos efeitos de tamanho e geometria. Assim, foi desenvolvido nesta tese um estudo teórico acerca da contribuição da interação dipolar entre materiais de propriedades magnéticas diferentes em nanopartículas núcleo@camada convencionais de geometria esférica. Os materiais analisados foram a CoFe2O4, MnFe2O4 e CoFe2 em várias combinações e tamanhos. Os resultados apontam que o impacto do campo dipolar do núcleo sobre a camada, faz com que a esta reverta sua magnetização precocemente, antes do núcleo, em nanopartículas de CoFe2O4 (22nm)@ CoFe2 (2nm), causando com isso, uma diminuição no campo coercivo de 65% em comparação com as nanopartículas simples de CoFe2O4 (HC=13.6 KOe) de mesmo diâmetro. O formato da curva de magnetização é altamente influenciada pelos parâmetros já citados. A alta anisotropia do núcleo em nanopartículas convencionais torna-o uma fonte de campo dipolar estável sobre a camada, que varia numa escala de comprimento da ordem do raio deste núcleo. Além disso, o impacto do campo dipolar é reforçado pelas restrições geométricas e pelas propriedades magnéticas de ambos os materiais. Em sistemas com núcleo revestido com uma fina camada de espessura inferior ao comprimento de troca, a interação da interface pode prender a reversão da camada, ocorrendo assim, uma reversão uniforme da magnetização. Contudo esse efeito só é pertinente nos sistemas em que os efeitos do campo dipolar são fracos comparados com a interação de troca.

4
  • ELIÂNGELA PAULINO BENTO

  • Generalized entropies: thermodynamic bonds of the third law.

  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • RAIMUNDO SILVA JUNIOR
  • JOAO MEDEIROS DE ARAUJO
  • MADRAS VISWANATHAN GANDHI MOHAN
  • FERNANDO DANTAS NOBRE
  • MARCOS GOMES ELEUTERIO DA LUZ
  • Data: 22-abr-2016


  • Resumen Espectáculo
  • Based on the third law of thermodynamics, we question 
    whether generalized entropies satisfy this fundamental property. 
    In general terms, the third Law states that, for systems with fundamental
     states not degenerate in equilibrium, The entropy approaches zero as the 
    temperature (in absolute scale) is also Approaches zero. However, the entropy
     can disappear only with the temperature in the Absolute zero. In this context, we 
    propose a direct analytical procedure to test whether Generalized entropy satisfies 
    the third law, assuming only a general form of Entropy S and energy U of an arbitrary 
    classical N-level system. Mathematically, The method depends on the exact calculation 
    of the parameter β = dS / dU in terms of the probabilities of microstates pi. Finally, we 
    determine the relation between the Entropy S → 0 (or, more generally, S → Smin) and 
    the minimum temperature limit β → ∞. THE Comparison, we apply the Boltzmann-Gibbs 
    entropy method (model Standard), Kaniadakis and Tsallis (generalized models). For 
    the last two, we illustrate the Power of the method by calculating the intervals of the 
    entropic parameters in which the entropy Satisfies the third law. The results obtained
     showed that, for the κ-entropy, the values Usually assigned to the parameter κ satisfy 
    the third law (-1 <κ <1). However, For q-entropy the same does not occur. We have 
    shown that q-entropy can disappear Temperatures of zero for certain values of q. As a 
    concrete example, we consider the one-dimensional Ising model with interactions of first
     neighbors, which Is one of the most important models in all physics. Classically, the Ising
     model is Resolved through the canonical ensemble, 
    but it can also be solved through Of generalized ensembles.
5
  • THIAGO RAFAEL DA SILVA MOURA
  • Transiente superdifusivo em caminhadas aleatórias com perfil de memória q-exponencial

  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • EDEMERSON SOLANO BATISTA DE MORAIS
  • JOSÉ CARLOS CRESSONI
  • LUCIANO RODRIGUES DA SILVA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • UMBERTO LAINO FULCO
  • Data: 02-may-2016


  • Resumen Espectáculo
  • Propomos nesta pesquisa um modelo de caminhada aleatória com perfil de decaimento q-exponencial. A função q-exponencial é uma generalização da função exponencial ordinária. No limite q→1, a função q-exponencial torna-se a função exponencial ordinária. Nosso modelo apresenta um comportamento difusivo Markoviano, onde se sabe que o Teorema Central do Limite proibe superdifusão neste caso. Apesar de neste problema não ser esperado o surgimento de uma transição superdifusiva no limite assintótico conseguimos observar tais transições para caminhadas de tamanho finito.

6
  • THARCISYO SA E SOUSA DUARTE
  • Espectropolarimetria e espectroscopia de alta resolução para estrelas análogas e gêmeas solares

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • JEFFERSON SOARES DA COSTA
  • GABRIEL ARMANDO PELLEGATTI FRANCO
  • GUSTAVO FREDERICO PORTO DE MELLO
  • Data: 20-may-2016


  • Resumen Espectáculo
  • The interest in studying the objects similar to the Sun, stars labeled as solar-type stars,
    analogs and solar twins, brings in its essence an attempt to find out another reference
    star and, furthermore, provides an investigation of evolutionary dynamic of our star as
    a function of various parameters. For this, we used three distinct samples of observable
    data, 170 solar-type stars from BCool catalog and observed with spectropolarimeters
    ESPaDOnS e NARVAL, 88 solar-twin stars of HARPS surveys, and 20 solar-analog stars
    from Kepler.
    From these data, we have investigated mainly the correlation among the rotation
    period, lithium abundance and stellar age. For the BCool stars and solar-twin from
    HARPS, we have used the rotation period determined through of chromospheric activity,
    in the case of Kepler solar analogs, the rotation period it is derived from photometric
    modulation. The lithium abundance for most of the solar-type and solar-twin stars have
    been collected from literature, while for the solar analogs, the lithium abundance were
    determined in the LTE regime using Kurucz atmospheric models and the MOOG code.
    For stellar age, we have used the gyrochronology method, which was calibrated using the
    Sun and a selection of open clusters, to redetermine them and comparing them with those
    derived from standard isochronal.
    Our results indicate that exist a decay law for the rotation period as a function of
    lithium abundance. This correlation becomes more clear for the solar-analog and solar-
    twin stars, even the rotation period being determined through distinct mechanisms for
    each case. For stellar ages, measured from standard isochronal and gyrochronology, we
    realized that they diverge considerably when the stars are older than the Sun. This result
    v
    has also been investigated by van Saders et al. (2016) and reflect our limitation about the
    stellar evolution and mixing mechanisms.
    Our work has resulted in five publications in indexed journals, two already in print
    format, one recently submitted and other in final stage of conclusion.

7
  • LEONARDO LINHARES OLIVEIRA
  • Core-Shell Magnetic Nanostructure: A Study of Impact of Dipolar Field

  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ARTUR DA SILVA CARRICO
  • CARLOS CHESMAN DE ARAUJO FEITOSA
  • SUZANA NOBREGA DE MEDEIROS
  • ANA LUCIA DANTAS
  • GUSTAVO DE OLIVEIRA GURGEL REBOUCAS
  • VAMBERTO DIAS DE MELLO
  • Data: 23-jun-2016


  • Resumen Espectáculo
  • Bi-magnetic anoparticles has been shown promises in several tachnological applications, such that permanent magnets, microwave generators devices, nanooscilators and magnetic record system for example. We presents a theoretical study about bi-magnetic core@shell nanoparticles consisting of high and low anisotropy ferromagnetic materials. The present work has analyzed nanoparticles with spherical and cylindrical geometries. Spherical particles can be employed as building block for high performance magnets,
    because can presents a expensive improvement in high energy product, (BH)max, of the system. The (BH)max is a key parameter,  because it’s indicate if a material is good to permanent magnets. Our results show that (BH)maxcan be improved significantly, a particle
    of SmCo5 with 3.5 nm recovered by iron shell with 2.5 nm thickness can presents (BH)max thereabout 4 times great then uncovered  particle. In other way, a core of the same material, with major diameter s relative thick shell there is a reduction in (BH)max that unfeasible
    their use in production of permanent magnets. We discuss in the present work the behavior of energy product these systems. Nanostructures with cylindrical geometries presents several applications, such that nano-oscillators and magnetic memory. In this way, know the magnetic profile and behavior of magnetization in demagnetizing process is relevant. A permalloy cylinder can, with 57.0 nm diameter and 21.0 nm height, presents along your magnetization curve, a vortex state. The inhibition of this state is relevant for some applications and can be reached with a presence of an external ring with elevated magnetic moment material. In the same way, can present vortex in magnetization curve by magnetic ring presence. We study further the magnetic states existing in magnetic ring
    due to magnetic dipolar interaction with a core.

8
  • GISLANA PEREIRA DE OLIVEIRA
  • Exoplanets in open star clusters: Stellar characterization.

  • Líder : BRUNO LEONARDO CANTO MARTINS
  • MIEMBROS DE LA BANCA :
  • ANTONIO CARLOS DA SILVA MIRANDA
  • BRUNO LEONARDO CANTO MARTINS
  • CRISTIAN ANDRES CORTES ANGEL
  • DANIEL BRITO DE FREITAS
  • JOSE RENAN DE MEDEIROS
  • Data: 14-jul-2016


  • Resumen Espectáculo
  • After the pioneering discovery of a giant planet orbiting 51 Peg by Mayor $\&$ Queloz (1995), about two decades ago, the literature reports the discovery of more than 3434 confirmed planets (exoplanet.eu), in about 2568 planetary systems. Solar mass main sequence field stars host the vast majority of these exoplanets. The observation of these stars offers several advantages, including brightness and a large variety of stellar characteristics, such as mass, age, chemical composition and evolutionary status. However, the widely differing characteristics of field stars also represents a drawback for our capability to derive precise conclusions to very basic questions, including the role of stellar environment on planet formation. There is no clear answer for the fact that main-sequence stars hosting giant planets are metal rich (Gonzalez 1997; Santos et al. 2004), while evolved stars hosting giant planets are not (Pasquini et al. 2007). Indeed, different phenomena have been proposed to explain this discrepancy in metallicity, including stellar pollution acting on main-sequence stars (Laughlin $\&$ Adams 1997, e.g.), a planet formation mechanism favouring the birth of planets around metal rich stars (Pollack al. 1996) and the stellar environment (Haywood 2009). The observation of stars in open cluster offers the possibility to strictly control the stellar characteristics, because each cluster represents a homogeneous set of stars. Besides, open cluster stars were formed at the same time and in the same circumstances and thus are expected to have the same age, metallicity, and galactocentric distance. From the work of Mermilliod $\&$ Mayor 2008 we choose clusters harbouring giants stars to be included in our survey. We used the WEBDA cluster database (Mermilliod 1995) to get information about our sample. The main criteria we focused on were the age of the cluster (between 0.02 and a few Gyr, with TO masses $>$ 1,5 M$_{\bigodot}$) and the magnitude of its giant stars (brighter than V = 13.5). Then we rejected stars with colour index (B - V) larger than 1.4, because cool, bright giants are known to be RV unstable. The observations were performed using HARPS (Mayor et al. 2003), the planet hunter at the ESO 3.6 m telescope. In high accuracy mode (HAM), it has an aperture on the sky of one arcsecond, and a resolving power of 115000. The spectral range covered is 380 - 680 nm. Our spectral analysis is based on the MARCS models of atmospheres and Turbospectrum spectroscopic tool. We determined stellar parameters and metallicity from LTE analysis of Fe I and Fe II lines. Once we get the high resolution and high S/N spectra, we also computed Li abundances that was obtained using the line at 6707.78 {\AA}, Si I, Na I, Mg I, Al I, Ca I, Ti I, Co I, Ni I, Zr I, La II and Cr I. We presented a spectroscopic characterisation of 42 giants, in 12 open clusters, using high resolution spectroscopy. All these clusters are part of a survey for giant planets orbiting intermediate-mass giant stars and the results show that all the clusters studied have $[Fe/H]$ values close to solar, results that agree with the literature with a small dispersion. These abundances will enable us to perform a comparative analysis of the abundances of stars with and without planets, from which it will be possible to detect differences, anomalies and determine the level of planet-star interactions. The goal of this campaign is to study the formation of giant planets in OCs to understand whether a different environment might affect the planet formation process, the frequency, and the evolution of planetary systems with respect to field stars. In addition, searching for planets in OCs enables us to study the dependency of planet formation on stellar mass and to compare the chemical composition of stars with and without planets in detail.

9
  • EDIMILSON FÉLIX DA SILVA
  • Quasi-static and dynamic magnetic properties of biphase ferromagnetic films

  • Líder : FELIPE BOHN
  • MIEMBROS DE LA BANCA :
  • FELIPE BOHN
  • LUIZ FELIPE CAVALCANTI PEREIRA
  • MARCIO ASSOLIN CORREA
  • ANTONIO AZEVEDO DA COSTA
  • RUBEM LUÍS SOMMER
  • Data: 12-ago-2016


  • Resumen Espectáculo
  • The magnetoimpedance effect appears as one of the most versatile tools to investigate nanostructured magnetic materials, revealing its magnetic properties in different frequency ranges and magnetic field values, even at unsaturated states. In recent decades, great attention has been given to this effect due to their contribution to the understanding of the physics associated to the magnetization dynamics and to the possibility of application of magnetic materials as probe element in sensor devices for low-field detection. Although soft magnetic materials are highly sensitive to small variations in low magnetic fields, many of them have essentially a nonlinear magnetoimpedance behavior in magnetic fields near zero, which prevents a simple straightforward derivation of an appropriate signal for sensors applications. To improve the linear features of the magnetoimpedance response, several studies have been carried out considering different magnetic systems, including wires, ribbons and amorphous multilayered films with \textit{exchange bias}. Recently, it has been shown that materials exhibiting asymmetric magnetoimpedance, characterized by a linear response close to zero magnetic field, appear as a promising alternative for applications, opening the possibility to use such materials in auto-biased linear magnetic field sensors. In these materials, asymmetric effects are obtained by inducing asymmetric static magnetic configuration, usually done by magnetostatic interactions, exchange bias, or by modifying the orientation of the external magnetic field and magnetic anisotropy.

    In this work, we investigate the structural properties, quasi-static magnetic properties, and the magnetization dynamics and magnetoimpedance effect in biphase ferromagnetic films and multilayers, with structures NiFe/NM/Co, where NM is a non-magnetic metallic spacer. Considering the results, these films present biphase magnetic behavior and asymmetric magnetoimpedance effect. We observe that the magnetoimpedance response is dependent on the thickness of the non-magnetic spacer material, explore the possibility of tuning the linear region of the magnetoimpedance curves around zero magnetic field by varying the thickness of the spacer and probe current frequency, and optimize the sensitivy by considering multilayered films. We discuss the experimental results in terms of the different mechanisms governing the magnetization dynamics at distinct frequency ranges, quasi-static magnetic properties, thickness of the spacer, and the kind of the magnetic interaction between the ferromagnetic layers. The results place films with biphase magnetic behavior exhibiting asymmetric magnetoimpedance effect as very attractive candidates for application as probe element in the development of auto-biased linear magnetic field sensors.

10
  • MATEUS BRUNO BARBOSA
  • Lévy Walk Analysis in 2D curved trajectories

  • Líder : MADRAS VISWANATHAN GANDHI MOHAN
  • MIEMBROS DE LA BANCA :
  • MADRAS VISWANATHAN GANDHI MOHAN
  • JOAO MEDEIROS DE ARAUJO
  • LUCIANO RODRIGUES DA SILVA
  • ERNESTO CARNEIRO PESSOA RAPOSO
  • MARCOS GOMES ELEUTERIO DA LUZ
  • RAPHAEL MATOZO TROMER
  • Data: 06-oct-2016


  • Resumen Espectáculo
  • A crucial problem in the study of anomalous diffusion and transport refers to adequate analysis of trajectory data. The analysis and inference of Lévy walk model from empirical or simulated trajectories of particles in two and three-dimensions (2D and 3D) is much more hard than in 1D because path curvature is nonexistent in 1D but pretty common in higher dimensions. Lately, a new method to detect Lévy walks, which considers 1D projections of 2D or 3D trajectory data, has been proposed by Humphries et al. The main idea of this method is to explore the fact that a 1D projection of a high-dimensional Lévy walk is itself a Lévy walk. In this work, we ask whether or not this projection method is capable enough to clearly distinguish a 2D Lévy walk with curvature from a simple Markovian correlated random walk. We focus this work in challenging case in which both 2D walks have the same probability density functions (pdf) of step sizes as well as of turning angles between succesive steps. Our approach extends the original projection the original projection method by introducing a rescaling of the projected data. After a projection and coarse graining, the renormalized pdf for the travel distances between successive turnings is seen to possess a fat tail when there is an underlying Lévy process. We exploit this effect to infer a Lévy walk process in the original high-dimensional curved trajectory. In contrast, there is no fat tail when a (Markovian) is analyzed. We show that this procedure works very well in clearly identifying a Lévy walk even when there is noise from curvature. The present protocol may be useful in realistic contexts involving ongoing debates on the presence (or not) of Lévy walks related to animal movement on land (2D) and air and oceans (3D).

11
  • EDI ROZEMBERGH BRASILEIRO DA SILVA BRANDÃO
  • ESPECTRO DE TRANSMISSÃO ÓPTICAS E POLARITONS EM QUASI-CRISTAIS DE OCTONACCI

  • Líder : MANOEL SILVA DE VASCONCELOS
  • MIEMBROS DE LA BANCA :
  • MANOEL SILVA DE VASCONCELOS
  • DORY HELIO AIRES DE LIMA ANSELMO
  • EUDENILSON LINS DE ALBUQUERQUE
  • CARLOS ALEXANDRE AMARAL ARAUJO
  • PAULO WILSON MAURIZ
  • Data: 20-oct-2016


  • Resumen Espectáculo
  • Abstract:
    In this work, we present a theoretical study of the propagation of electromagnetic waves in multilayer structures termed Photonic Crystals. Within this scope, this work has three strands. In the first part, we study theoretically the transmission spectra in one-dimensional photonic quasi-crystals, made up of SiO2 (A) and TiO2 (B), materials, organized following the Octonacci sequence, where the nth-stage of the multilayer Sn is given by the rule Sn=Sn-1Sn-2Sn-1, for n ≥ 3 and with S1=A e S2=B. The expression for transmittance was obtained by employing a theoretical calculation based on the transfer-matrix method. For normally incident waves, we observe that, for a same generation, the transmission spectra for transverse electric (TE) and transverse magnetic (TM) waves are equal, at least qualitatively, and they present a scaling property where a self-similar behavior is obtained, as an evidence that these spectra are fractals. The spectra show regions where the omnidirectional band gaps emerges for specific generations of Octonacci photonic structure, except to TM waves. For TE waves, we note that all of them have almost the same width, for different generations. We also report the localization of modes as a consequence of the quasi-periodicity of the heterostructure.

    In the second part, we investigate the optical transmission spectra for s and p-polarized (TE) waves in one-dimensional photonic quasi-crystals on a quasi-periodic multilayer structure made up by alternate layers of SiO2 and metamaterials, organized by following the Octonacci sequence. Maxwell's equations and the transfer-matrix technique are used to derive the transmission spectra for the propagation of normaly and obliquely incident electromagnetic fields. We assume Drude-Lorentz-type dispersive response for the dielectric permittivity and magnetic permeability of the metamaterials. For normally incident waves, we observe that the spectra does not have self-similar behavior or mirror symmetry and it also features the absence of optical band gap. We also show the appearance of the complete band gaps and pseudo reflectors Bragg (or Bragg mirrors).

    In the third and final part, we studied the propagation of plasmons polariton in systems formed by periodic multilayer and quasi-periodic organized in accordance to the Octonacci sequence from the behavior description of their modes of volume and surface in their individual constituents. Through analytical and computational numerical calculation, initially we get the frequency spectra of plasmon polariton these superstructures. Subsequently, we investigated the quasi-periodicity changes its band structure in relation to the periodic case, inducing their spectra to a self-similar way, characterizing its fractality/multifractality.

12
  • MACKSON MATHEUS FRANÇA NEPOMUCENO
  • Fractal and multifractal analysis of gravitational-wave GW150914 detected by LIGO.

  • Líder : DANIEL BRITO DE FREITAS
  • MIEMBROS DE LA BANCA :
  • DANIEL BRITO DE FREITAS
  • JOSE RENAN DE MEDEIROS
  • MADRAS VISWANATHAN GANDHI MOHAN
  • ODYLIO DENYS DE AGUIAR
  • RODRIGO FERNANDES LIRA DE HOLANDA
  • Data: 12-dic-2016


  • Resumen Espectáculo
  • Data of the recent discovery of gravitational waves detected by Advanced Laser Interferometer
    Gravitational Wave Observatory-LIGO were used in application of multifractal
    analysis formalism. A time-series derived by strain measurement caused by gravitational
    wave GW150914 was mounted. Detrended moving average method for multifractals,
    named MFDMA, was used for analisys of such data. Shuffling and Surrogate procedures
    was used for determinate sources of multifractality on the time series. Results indicate
    two regimes of multifractality in time-series from GW150914. The instant that defines the
    separation of these regimes may be interprated like the black holes merger time interval.

13
  • SAMURAÍ GOMES DE AGUIAR BRITO
  • Role of dimensionality in complex networks: Connections with nonextensive statistical mechanics

  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • ANANIAS MONTEIRO MARIZ
  • CONSTANTINO TSALLIS
  • EVALDO MENDONÇA FLEURY CURADO
  • LIACIR DOS SANTOS LUCENA
  • LUCIANO RODRIGUES DA SILVA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • Data: 13-dic-2016


  • Resumen Espectáculo
  • Studies in complex networks are quite current and promote the integration of several areas of knowledge. Has been verified in previous research that the nonextensive statistical mechanics is the more suitable approach to describe the complex networks when there is long-range interactions between your constituents. At the thermodynamic limit the degree distribution is of the form P(k) ∝ e^(k/κ), where e_q is the q-exponential defined by e^z  ≡ [1 + (1 - q)z]^(1/(1-q) ) which optimizes the non-additive entropy S_q (when q→1, the Boltzmann-Gibbs entropy is recovered). In this thesis we have introduced a study of the d-dimensional geographic networks (Natal Model) which grow with preferential attachment involving Euclidean distance by introducing the term r^(-α_A )  (α_A  ≥ 0) into the preferential attachment rule. Given the connection between complex networks and the q-statistic, we numerically verified (for d = 1,2,3 e 4) that the degree distributions exhibit, for both q and κ, universal dependencies with respect to the variable α_A/d. In addition, the limit q = 1 is quickly reached when α_A/d → ∞. We also verified that other properties of the network also have universal dependencies with respect to α_A/d, such as: shortest path length ⟨l⟩, dynamic exponent β (from connectivity time evolution of the sites) and the entropy S_q of the degree distribution.

14
  • NYLADIH THEODORY CLEMENTE MATTOS DE SOUZA
  • Non-Conventional Description of Generalized Cantor Fractals and Chromosomal Sequences of Human DNA in the Kaniadakis Formalism

  • Líder : DORY HELIO AIRES DE LIMA ANSELMO
  • MIEMBROS DE LA BANCA :
  • DORY HELIO AIRES DE LIMA ANSELMO
  • MANOEL SILVA DE VASCONCELOS
  • NILSON SENA DE ALMEIDA
  • RAIMUNDO SILVA JUNIOR
  • VAMBERTO DIAS DE MELLO
  • Data: 16-dic-2016


  • Resumen Espectáculo
  • In the present work, we present a statistical analysis, via theory of information in the context of the Kaniadakis generalized statistics, of generalized Cantor sets (type d-(m, r)) and the Y chromosome of human DNA. The objectives of our study are to determine, through -entropy (which is suitable for systems with long-range correlations), the laws of scale, self-similar behaviors and characteristical fractal dimensions of these two systems: one deterministic, and the other found in nature. For the generalized Cantor set, we determine analytically and numerically the values of  that make the entropy linear with the system size, obtaining a relation between  (the deformation parameter), the fractal dimension (df) and the support dimension (d). Using the concept of blocks, we show that for arbitrary intervals of L (system size), and s (size of the information block), the -entropy exhibits self-similar behavior, as well as a power law-like behavior with respect to s. In the entropy analysis of the Y chromosome we observed that, regardless of the value of , the Kaniadakis entropy, when presented as a function of the size of the system, presents in general (but not always) three regimes: one oscillatory, one monotonically linear, and another of saturation. The latter is a result of the fact that the entropy is extensive, and the system is finite. The second regime, in turn, denotes an apparent internal order. However, in this case it was not possible to observe a self-similar behavior. Our analysis was restricted to the coding part of the Y chromosome, where we have neglected the noncoding parts.

15
  • KELDER CAVALCANTI DE VASCONCELOS
  • Effects of non-linear electrodynamics on radiation propagation around charged compact object

  • Líder : LEO GOUVEA MEDEIROS
  • MIEMBROS DE LA BANCA :
  • CARLOS AUGUSTO ROMERO FILHO
  • JANILO SANTOS
  • LEO GOUVEA MEDEIROS
  • PEDRO JOSÉ POMPEIA
  • RAIMUNDO SILVA JUNIOR
  • Data: 19-dic-2016


  • Resumen Espectáculo
  • : In this thesis, the propagation of non-linear electromagnetic waves is careful analyzed on a curved spacetime created by spherically symmetric mass and charge distribution. Using certain approximations we verified the existence of electromagnetic self-interaction between the background electrostatic field and the radiation that propagating in it, and we adopted for this analysis an approach known as effective metric. We observe that the effective metric does not generate effective events horizons, but the non linearities changes the event horizons usual positions of Reissner-Nordström black holes. In linear approximation, we compute how the self-interaction affects the geodesic deviation and the redshift of photons propagating near this massive charged object. Using the Euler-Heisenberg effective Lagrangian, we estimate the contribution of these self-interactions in the geometrical reshift near extremal compact objects.

2015
Disertaciones
1
  • JADSON TADEU SOUZA DANTAS
  • Magnetic States in Elliptical Iron Nanostructures in Remanence
  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ARTUR DA SILVA CARRICO
  • JOSE HUMBERTO DE ARAUJO
  • IDALMIR DE SOUZA QUEIROZ JÚNIOR
  • Data: 19-feb-2015


  • Resumen Espectáculo
  • Submicron ferromagnetic (F) nanostructures are of interest as they are essential
     parts of modern magnetoelectronic devices. The states or magnetic phases of
     this system along the magnetization curve or polarized electric current effect 
    are functions of the particle size as well as the intrinsic parameters of the ferromagnet.
    We investigated the magnetic phases of Fe elliptic nanoelements along the magnetization curve,
     from their positive saturation field to zero field, using a self-consistent micromagnetic model
     that allows to represent dipole effects of the system geometry, as well as the other parameters
     Intrinsic properties of the nanoelement. We studied the magnetic states of isolated and coupled 25nm 
    thick elliptic iron nanoparticles, with a smaller diameter between 100nm to 200nm and the largest 
    diameter ranging from 300nm to 500nm. In the case of coupled structures the spacer is
     non-magnetic and has a thickness of 25nm. The anisotropy axis is in the direction of the minor
     radius of the ellipse, and the outer field can be applied either in the direction of the minor
     axis or in the direction of the major axis. This field preparation route results in different
     remanence magnetic states for nanoelements of the same size. We identify magnetic states 
    as a function of the lateral dimensions of the ellipse. We find a diversity of states: uniform states, 
    single vortex, double vortices, with opposite and equal chiralities and polarities, and states with three
     vortices in the same structure. We show that the preparation route and coupling are very important factors
     for the remaining state of these structures.
2
  • RAFAELA MEDEIROS DE SOUZA
  • "Estudo da Densidade de Corrente Crítica para Reversão da Magnetização de Nanoelementos Ferromagnéticos"

  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ARTUR DA SILVA CARRICO
  • SUZANA NOBREGA DE MEDEIROS
  • ANA LUCIA DANTAS
  • Data: 16-mar-2015


  • Resumen Espectáculo
  • A descoberta de que uma corrente elétrica é capaz de exercer um torque em um material ferromagnético, através da transferência de momento angular de spin, pode proporcionar o desenvolvimento de novos dispositivos tecnológicos que armazenam informação a partir da direção da magnetização. A redução da densidade de corrente para reversão da magnetização é primordial para potenciais aplicações em células de memórias magnéticas de acesso aleatório não voláteis (MRAM). Apresentamos uma investigação teórica dos efeitos de forma e do campo de dipolar na densidade de corrente crítica para reversão da magnetização, via torque por transferência de spin (STT), em nanoelementos ferromagnéticos. O sistema nanoestruturado consiste em uma camada de referência, na qual a corrente será polarizada em spin, e uma camada livre de reversão da magnetização. Observamos consideráveis variações na densidade de corrente crítica em função da espessura (t = 1.0nm, 1.5nm, 2.0nm e 2.5nm) e da geometria do nanoelemento (circular e elíptico), do tipo de material que compõe a camada livre do sistema (Ferro e Permalloy) e de acordo com a orientação da magnetização e da polarização em spin com o eixo maior. Mostramos que a densidade de corrente crítica pode ser reduzida em cerca de 50 % diminuindo a espessura da camada livre de Fe e em 75% ao modificar a magnetização de saturação de nanoelementos circulares com 2.5nm de espessura.    Observamos, ainda, uma redução de até 90 % na densidade de corrente de reversão para nanoelementos ultrafinos magnetizados ao longo da direção do eixo menor, usando a polarização no plano paralela à magnetização.

     

3
  • RODRIGO DA SILVA SOBRINHO
  • Efeitos do Freio Magnético Sobre a Distribuição da Rotação Estelar

  • Líder : DANIEL BRITO DE FREITAS
  • MIEMBROS DE LA BANCA :
  • DANIEL BRITO DE FREITAS
  • JOSE RENAN DE MEDEIROS
  • JOSÉ RONALDO PEREIRA DA SILVA
  • Data: 21-may-2015


  • Resumen Espectáculo
  • O pioneiro trabalho proposto por Skumanich (1972) mostrou que a velocidade de rotação projetada média <v sini> para estrelas do tipo solar, obedece uma lei de decrescimento no tempo dado por t-1/2, onde t é a idade da estrela. Essa relação é consistente com as teorias de perda de momentum angular através do vento estelar ionizado, que por sua vez está acoplado à estrela pelo seu campo magnético. Vários autores (e.g.: Silva et al. 2013 e de Freitas et al. 2014) analisaram as possíveis correlações entre o decaimento rotacional e o perfil da distribuição de velocidade. Esses autores chegaram a uma simples relação heurística, mas não construíram uma passagem direta entre o expoente do decaimento rotacional (j) e o expoente da distribuição rotacional (q). Todo esse cenário teórico foi proposto usando uma eficiente e robusta mecânica estatística bem conhecida como mecânica estatística não-extensiva. A presente dissertação propõe efetivamente, fechar essa questão elaborando um caminho teórico para modificar as distribuições q-Maxwellianas em q-Maxwellianas com vínculos físicos extraídos da teoria do freio magnético. Para testar nossas distribuições, usamos um pacote de dados do catálogo de Geneva-Copenhagem Survey com aproximadamente 6000 estrelas F e G limitadas em idade. Como resultado, obtivemos que os expoentes da lei de decaimento e da distribuição seguem uma relação similar àquela proposta por Silva et al. (2013).

     

     

     

4
  • WILLIAM JOUSE COSTA DA SILVA
  • Interação no Setor Escuro: Uma Análise Termodinâmica

  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • RAIMUNDO SILVA JUNIOR
  • NILZA PIRES
  • Maria Aldinez Dantas
  • Data: 31-ago-2015


  • Resumen Espectáculo
  • Nesse trabalho, investigamos uma abordagem geral para o modelo de interação entre as componentes do setor escuro do Universo usando argumentos termodinâmicos amplamente conhecidos, ou seja, a positividade da entropia mais a segunda lei da termodinâmica. Neste sentido, apresentamos alguns vínculos termodinâmicos no parâmetro da equação de estado (EoS) variável do tipo  =  relacionado com a energia escura e que interage com a matéria escura, isto é, consideramos uma interação fenomenológica entre a matéria escura fria e a energia escura como uma função do fator de escala cósmico. Essa abordagem generaliza alguns modelos propostos na literatura: representa um modelo sem interação, enquanto que   conduz ao modelo de interação constante entre as componentes escura do Universo.  Por outro lado,   e  proporciona uma análise termodinâmica para a energia escura que exclui a chamada cosmologia fantasma. Além disso, também discutimos algumas consequências cosmológicas desta abordagem geral, comparando nossos resultados com os propostos usando a EoS constante, isto é, ω(a)→ ω_0 e ϵ(a)→ ϵ(a).

     

5
  • ÂNGELA MARTA DA SILVA
  • Produção e Caracterização Magnética Estática e Dinâmica de Camada Simples e Multicamada de Co2FeAl Crescidos em Substratos Amorfos.

  • Líder : MARCIO ASSOLIN CORREA
  • MIEMBROS DE LA BANCA :
  • FELIPE BOHN
  • MARCIO ASSOLIN CORREA
  • RICARDO BARRETO DA SILVA
  • Data: 08-sep-2015


  • Resumen Espectáculo
  •  

    Neste trabalho foram produzidas e estudadas ligas de CFA, do tipo full-Heusler, onde obtivemos resultados de filmes finos simples de Co2FeAl (CFA) e multicamadas de CFA/Ag/CFA, produzidas por magnetron Sputtering em substratos amorfos (vidro), enfatizando o estudo de suas propriedades estruturais, magnéticas quasi-estáticas e dinâmicas. Através da análise de raios-X verificou-se a formação da estrutura cristalina do CFA, obtendo a fase A2 (desordenada estruturalmente,  onde os átomos encontram-se distribuídos aleatoriamente) e a fase B2 (estrutura semi-ordenada). As medidas revelaram um comportamento magnético quasi-estático que para camadas simples de MGO/CFA apresentam clara anisotropia do tipo uniaxial, enquanto para a camada simples e multicamada de CFA apresentam anisotropia uniaxial induzida no plano. Medidas de magnetoimpedância (MI) são realizadas numa vasta gama de frequências variando de 1.0 GHz a 3.0 GHz e variando o ângulo entre o campo magnético externo e a corrente de sonda com relação aos eixos de anisotropias. As curvas de MI apresentam comportamento típico verificada para amostra anisotrópica, com estrutura simples e de duplo pico de acordo com as frequências e ângulos como esperado.

     

     

     

     

     

     

     

      

     

6
  • DANIELLY FREIRE DA SILVA
  • Busca por Excesso no Infravermelho Médio em Estrelas Evoluídas com Fotometria WISE E 2MASS

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • JOSE RENAN DE MEDEIROS
  • BRUNO LEONARDO CANTO MARTINS
  • ANTONIO CARLOS DA SILVA MIRANDA
  • Data: 11-sep-2015


  • Resumen Espectáculo
  • Busca por Excesso no Infravermelho Médio em Estrelas Evoluídas com Fotometria WISE E 2MASSBusca por Excesso no Infravermelho Médio em Estrelas Evoluídas com Fotometria WISE E 2MASSDiscos de detritos são comumente detectados orbitando estrelas da sequência principal, mas pouco se sabe sobre seu destino quando as estrelas evoluem ao longo dos estágios subgigante e gigantes. Jones (2008) encontrou fortes evidências sobre a presença de excesso de IR médio em estrelas do tipo G e K e classe de luminosidade III, utilizando dados fotométricos dos catálogos Two-Micron All Sky-Survey (2MASS) e WISE. Embora a origem desses excessos permanece incerto, é plausível que eles surgem a partir de discos de detritos em torno destas estrelas.

    O presente estudo traz uma pesquisa inédita na busca de excesso de IR médio em estrelas evoluídas simples e binárias do tipo espectral F, G e K das classes de luminosidade IV, III, II e Ib. Para este estudo, utilizamos dados fotométricos do WISE e 2MASS para uma amostra de 3000 estrelas evoluídas, com magnitude visual até 6,5. Como principais resultados, verificou-se que a frequência de estrelas evoluídas mostrando excesso de IR médio e aumentos excessivos das classes de luminosidade IV e III para as classes de luminosidade II e Ib. Além disso, não existe uma clara diferença entre a presença de excesso de IV em sistemas binários e único para todas as classes de luminosidade analisados.

     

     

     



     

7
  • NAGILSON MENDES DE SOUSA
  • Síntese e Catacterização de Nanopartículas Magnéticas de Co e Ni Com Aplicação em Magnetohipertermia

  • Líder : MARCO ANTONIO MORALES TORRES
  • MIEMBROS DE LA BANCA :
  • JOÃO MARIA SOARES
  • MARCO ANTONIO MORALES TORRES
  • SUZANA NOBREGA DE MEDEIROS
  • Data: 14-sep-2015


  • Resumen Espectáculo
  • Nanopartículas (Nps) são importantes no desenvolvimento de novas aplicações tecnológicas. Nanopartículas magnéticas metálicas tais como Níquel e Cobalto surgem como objetos promissores devido as suas aplicabilidades em várias áreas da ciência e tecnologia. No presente trabalho apresentamos um estudo sobre o método de síntese, caracterização estrutural e magnética em nanopartículas de Co e Ni. As amostras foram preparadas pelo método Sol-Gel e formadas no polímero quitosana, a redução ocorreu em ausência de Hidrogênio. A estrutura cristalina do Co e Ni  são cúbicas de face centrada e seus diâmetros variaram de 19-50nm e 7-77nm, respectivamente. As superfícies das nanopartículas foram naturalmente passivadas com seus monóxidos apresentando estabilidade química por longos intervalos de tempo. A estrutura formada é do tipo núcleo/casca, o que favoreceu as interações de exchange bias entre o núcleo ferromagnético (FM) e a casca antiferromagnética (AFM). As condições de síntese foram otimizadas para obter principalmente a fase FM. Ambas NPs foram submetidas à ação de um campo magnético AC e houve aquecimento rápido atingindo temperaturas entre 80-140 °C em intervalos de tempo de até 5 min. As amostras dispersadas em um fluído, atingiram valores de 40- 59°C de aquecimento em até 12 minutos, possibilitando possíveis aplicações em hipertermia magnética. As ligas metálicas destes materiais como Ni-Co, Ni-Fe e Fe-Co estão sendo preparadas em nosso grupo e possibilitarão novos estudos e aplicações.

8
  • NATHALIA MATTOS NOVAES DA ROCHA
  • Análise Wavelet da Variabilidade do Quasar 3C 273

  • Líder : BRUNO LEONARDO CANTO MARTINS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • JOSE RENAN DE MEDEIROS
  • Maria Aldinez Dantas
  • Data: 14-sep-2015


  • Resumen Espectáculo
  •  

    Descoberto em 1963, 3C 273 foi o segundo quasar identificado e catalogado no Terceiro Catálogo de Cambridge para rádio fontes, e o primeiro para o qual as linhas de emissão foram identificadas com uma sequência de hidrogênio desviada para o vermelho. Ele é o quasar mais brilhante da esfera celeste, o mais estudado, analisado, e com uma resultante abundância de dados disponíveis em uma vasta literatura. A análise precisa dos desvios das linhas espectrais de quasares, fornece informação suficiente para pôr em prova a variação das constantes fundamentais da natureza e similarmente da taxa de expansão do universo. A análise da variabilidade das curvas de luz desses corpos, e a consequente precisão das suas periodicidades, é de suma importância pois proporciona uma eficácia nas observações deles, possibilita uma maior compreensão dos seus fenômenos físicos, e torna factível a realização de observações espectrais em datas mais exatas (momentos nos quais suas curvas de luz apresentam picos acentuados e, por conseguinte, espectros mais ricos em informação). Na presente dissertação, vinte e oito curvas de luz do quasar 3C 273 são estudadas, abrangendo todas as faixas do espectro eletromagnético (da emissão rádio aos raios gama), totalizando na análise de quatro curvas de luz para cada faixa. Aplicamos o método da Transformada Wavelet Contínua do tipo Morlet de ordem w = 06 e obtivemos resultados precisos e coerentes com a literatura.

9
  • SUZIERLY ROQUE DE LIRA ARAUJO
  • Análise Wavelet em Curvas de Luz de Sistemas Binários da Missão Espacial CoRoT

     

     

     

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • JOSE RENAN DE MEDEIROS
  • BRUNO LEONARDO CANTO MARTINS
  • BRAULIO BATISTA SOARES
  • Data: 16-sep-2015


  • Resumen Espectáculo
  • Os sistemas binários constituem ambientes fundamentais para conhecermos as propriedades fundamentais das estrelas. Neste trabalho, analisamos 99 sistemas binários identificados pela missão espacial CoRoT. A partir do estudo dos diagramas de fase destes sistemas, nossa amostra é dividida em três grupos: aquele cujos sistemas são caracterizados pela variabilidade relativa aos eclipses binários; aquele no qual observamos componentes com fortes modulações, provavelmente associadas à presença de manchas escuras na superfície da estrela; e aquele constituído de sistemas com variabilidade associada à expansão e contração das camadas superficiais.

    Para as estrelas que apresentam eclipses binários em suas curvas de luz, utilizamos diagramas de fase a fim de estimar a classificação desses sistemas quanto à sua morfologia, com base no estudo das superfícies equipotenciais. Neste contexto, para determinar o período de rotação, identificar a presença de regiões ativas, investigar a possibilidade dos sistemas apresentarem rotação diferencial e analisar as pulsações estelares utilizamos o procedimento wavelet.

    A transformada wavelet tem sido utilizada como uma ferramenta poderosa no tratamento de um amplo número de problemas em Astrofísica. Através desta transformada, pode-se realizar uma análise em tempo-frequência de curvas de luz rica em detalhes que contribuem significativamente para o estudo de fenômenos associados com a rotação, a atividade magnética e as pulsações estelares. Neste trabalho, aplicamos a wavelet Morlet de 6ª ordem, que oferece uma alta resolução em tempo e frequência e obtemos os espectros de potência wavelet local (interpretado com a distribuição de energia do sinal) e global (integração temporal do mapa local). Utilizando a análise wavelet, identificamos as periodicidades relacionadas a treze sistemas com modulação rotacional, além da assinatura de padrão de batimento no mapa wavelet local de cinco variáveis pulsantes ao longo de toda a janela temporal.

10
  • JOSE EDVALDO DE LIMA JUNIOR
  • Analise do Excesso de Infravermelho de Estrelas Evoluídas Observadas pelo Satelite Kepler

  • Líder : BRUNO LEONARDO CANTO MARTINS
  • MIEMBROS DE LA BANCA :
  • ANTONIO CARLOS DA SILVA MIRANDA
  • BRUNO LEONARDO CANTO MARTINS
  • JOSE RENAN DE MEDEIROS
  • Data: 21-dic-2015


  • Resumen Espectáculo
  • Este trabalho tem como foco principal a análise do infravermelho das 1916 estrelas gigantes vermelhas do catálogo de Pinsonneault. Para realizar tal análise nos utilizamos da avaliação do diagrama cor-cor como primeiro critério de seleção para a procura de estrelas com excesso de infravermelho, das quais 47 estrelas foram selecionadas, depois analisamos as distribuições espectrais de energia ou SED onde 29 estrelas foram selecionadas e para confirmação do excesso de infravermelho, passamos pela inspeção visual, onde das 29 estrelas apenas uma não apresentou contaminação por background de galáxias ou por uma estrela próxima. Na inspeção visual, e nas SEDS analisamos o excesso nas bandas W1, W2 e principalmente nas bandas W3 e W4 do satélite WISE. Por fim calculamos a temperatura dessa poeira em aproximadamente 200K.

     

11
  • LUCIANO LUIZ ALENCAR DE OLIVEIRA
  • “Sobre o Comportamento Rotacional das Estrelas Evoluídas de Classe de Luminosidade IV, III, II E Ib.

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • JOSE RENAN DE MEDEIROS
  • BRUNO LEONARDO CANTO MARTINS
  • ANTONIO CARLOS DA SILVA MIRANDA
  • Data: 21-dic-2015


  • Resumen Espectáculo
  • A rotação é um dos mais importantes observáveis em astronomia estelar, conduz a formação e evolução das estrelas. De fato, a principal meta desafiadora no estudo da rotação estelar é a compreensão da história do momento angular, uma vez que as estrelas evoluem ao longo do diagrama HR, bem como o papel da rotação em diferentes fenômenos dinâmicos, incluindo a atividade magnética estelar, processos de acreção e coalescência. O presente trabalho traz a análise sem precedentes da rotação ao longo do diagrama HR, com base em uma amostra completa de estrelas evoluídas de classe de luminosidade Ib, II, III e IV, respectivamente as supergigantes Ib, gigantes brilhantes, gigantes e subgigantes. Para o estudo rotacional, nós usamos a velocidade de rotação projetada, v sem i, calculada a partir de observações feita com o espectrômetro CORAVEL (Baranne et al. 1979) e apresentadas em diferentes catálogos (De Medeiros e Mayor (1999); De Medeiros et al. (2002) e De Medeiros et al. (2014)). Pela primeira vez um estudo da evolução da rotação é apresentada por estrelas individuais e múltiplas. Confirmamos que a rotação de estrelas individuais diminui acentuadamente a partir de tipo espectral F e G, dependendo da classe de luminosidade e da massa estelar. A partir das regiões espectrais G e K, a rotação diminui para todas as classes de luminosidade. O presente estudo revela também o aumento da rotação estelar devido a sincronização, resultado dos efeitos de marés, em sistemas binários com componentes evoluídas. Para todas as classes de luminosidade analisada detectamos rotação nas regiões espectrais F, G e K com valores de até 70 km/s.

Tesis
1
  • THIAGO BRUNO RAFAEL DE FREITAS OLIVEIRA
  • “Teorias f(R) de Gravidade na Formulação de Palatini e no Formalismo Métrico”

  • Líder : JANILO SANTOS
  • MIEMBROS DE LA BANCA :
  • JANILO SANTOS
  • Maria Aldinez Dantas
  • NILZA PIRES
  • RAIMUNDO SILVA JUNIOR
  • VALDIR BARBOSA BEZERRA
  • Data: 20-feb-2015


  • Resumen Espectáculo
  •           A observação atual da expansão acelerada do universo, bem como o tão conhecido problema da matéria escura em astrofísica, tem fornecido muitas discussões e algumas dúvidas sobre a bem testada teoria de gravitação de Einstein, conhecida como relatividade geral. Várias modificações, assim como teorias extendidas de gravidade, tem sido formuladas nos últimos 15 anos, e alguns autores tem feito surgir uma nova roupagem. Nesta tese, apresentamos e discutimos, em uma classe de gravidade extendida, a teoria alternativa conhecida como gravidade f(R). Essas teorias surgem quando substituímos na ação de Einstein-Hilbert o escalar de curvatura R por alguma bem comportada função não linear f(R). Elas fornecem uma maneira alternativa para explicar a aceleração cósmica atual sem necessitar invocar qualquer componente de energia escura ou a existência de dimensões espaciais extras. Ao lidar com gravidade f(R), duas diferentes abordagens variacionais podem ser seguidas, a saber, o formalismo métrico e o de Palatini. Na abordagem métrica, as conexões são assumidas, desde o princípio, como sendo as conexões de Levi-Civita e variação da ação é feita com respeito à métrica apenas, enquanto que na abordagem de Palatini a métrica e as conexões são tratadas como campos independentes e a variação da ação é feita com respeito a ambos. Apesar de fornecer as mesmas equações para a ação de Einstein-Hilbert, para um termo geral não-linear f(R) na ação, dão origem a equações de movimento muito diferentes. Para os dois formalismos, fizemos uma sistemática e detalhada derivação das equações de campo, com generalização das equações de Einstein da relatividade geral e examinamos a conservação covariante destas equações. Nessa consideração, detectamos e chamamos atenção para a conservação covariante das equações de Palatini para a gravidade f(R), que, em nosso ponto de vista, merece um pouco mais de debate sobre a relevância física dos aspectos conformes da abordagem de Palatini.

              Afim de lançar algum luz sobre o debate do papel da gravidade f(R), examinamos também a questão de como essas teorias permitem espaços-tempos na qual a causalidade, um resultado fundamental em qualquer teoria física, é violada. No âmbito da gravidade f(R), a estrutura causal do espaço-tempo quadridimensional tem, localmente, a mesma natureza qualitativa como o espaço-tempo plano da relatividade especial: a causalidade é permitida localmente. A questão não-local, entretanto, e deixada em aberto, e a violação de causalidade pode ocorrer. Como bem se sabe, na relatividade geral existem soluções para as equações de campo que tem anomalias causais na forma de curvas de tipo-tempo fechadas, o renomado modelo de Gödel sendo o exemplo mais conhecido de uma solução deste tipo. Aqui mostramos que para a gravidade f(R) satisfazendo a condição df/dR>0, independentemente de ser formulada no formalismo métrico ou de Palatini, cada solução do tipo-Gödel para um fluido perfeito com densidade ρ e pressão p que satisfaz a condição de energia forte (ρ + p  0) é necessariamente isométrica à geometria de Gödel. Isso demonstra que essas teorias apresentam anomalias causais na forma de curvas tipo-tempo fechadas. Nós também derivamos uma expressão para o raio crítico rc, além do qual a causalidade é violada, para uma teoria f(R) de gravidade arbitrária de Palatini assim como métrica. As expressões tornam evidente que a violação da causalidade depende da forma de f(R) e dos componentes de matéria. Como um exemplo, examinamos a solução tipo-Gödel de fluido perfeito na classe f(R) = R - β/Rn de teorias de gravidade de Palatini, e mostramos que para a densidade de matéria positiva e para β e n no intervalo permitido pelas observações, essas teorias não admitem a geometria de Gödel como solução para um fluido perfeito de suas equações. Nós também examinamos a violação de causalidade do tipo-Gödel considerando um campo escalar como conteúdo material. Para essa fonte, mostramos que a gravidade f(R) de Palatini dá surgimento a uma única solução do tipo-Gödel sem nenhuma violação de causalidade. Finalmente mostramos pela combinação de um fluido perfeito com um campo escalar como fontes da geometria do tipo-Gödel, obtemos tanto soluções na forma de curvas do tipo-tempo fechadas como soluções sem nenhuma violação de causalidade. No formalismo métrico, pegamos outro exemplo, a gravidade f(R) = R - α R*ln(1+R/R*), que é livre de singularidades do escalar de Ricci e é cosmologicamente viável. Aqui também mostramos que combinando fluido perfeito com campo escalar como fontes da geometria de Gödel, essa classe de teorias acomoda tanto soluções causais e não-causais para a faixa de parâmetros permitidos cosmologicamente. Nossas conclusões é que a gravidade f(R) pode remediar a patologia causal na forma de curvas do tipo-tempo fechadas que são permitidas na relatividade geral.

2
  • VIVIAN MONTARDO ESCOBAR
  • Influência da desordem estrutural nas propriedades magnéticas de filmes finos de Co2FeAl

  • Líder : MARCIO ASSOLIN CORREA
  • MIEMBROS DE LA BANCA :
  • MARCIO ASSOLIN CORREA
  • CARLOS CHESMAN DE ARAUJO FEITOSA
  • FELIPE BOHN
  • LUIZ FERNANDO SCHELP
  • RUBEM LUÍS SOMMER
  • Data: 27-mar-2015


  • Resumen Espectáculo
  • Filmes finos de Co2FeAl (CFA) e tricamadas CFA/Ag/CFA, produzidos por magnetron sputtering em substrato de vidro e MgO (100), foram investigados segundo suas propriedades estruturais, magnéticas estáticas e dinâmicas. Na análise de difração de raios-X destaca-se a formação de estrutura cristalina cúbica com fase A2 (desordenada estruturalmente), onde os átomos se distribuem aleatoriamente na rede. As medidas de MI foram realizadas variando o ângulo de aplicação do campo magnético externo com relação a anisotropia induzida e a corrente de sonda, tais ângulos foram os mesmos utilizados nas medidas de VSM. As medidas de VSM revelam, em algumas amostras, a presença de um patamar ocasionado pela formação de sistema bifásico. Por esse motivo, os resultados apresentaram efeitos de magnetoimpedância assimétrica (AMI) em algumas faixas de frequência. Para filmes simples e tricamadas com espessura da camada magnética (500 nm), o efeito AMI é mais pronunciado. Com o aumento da espessura (1000 nm), apesar do comportamento bifásico permanecer, os efeitos assimétricos começam a diminuir. Portanto, foi estabelecida uma rota para produção de ligas de Heusler na forma de filmes finos, com baixo fator de amortecimento de Gilbert, nos quais o efeito de desordem estrutural proporcionou o estudo dos efeitos histeréticos e assimétricos de MI. 

3
  • MADSON RUBEM OLIVEIRA SILVA
  • Buraco Negros, Correspondência AdS/BCFT e Fluido/Gravitação

     

  • Líder : DMITRY MELNIKOV
  • MIEMBROS DE LA BANCA :
  • ALVARO FERRAZ FILHO
  • JANILO SANTOS
  • DMITRY MELNIKOV
  • PASQUALE SODANO
  • FRANCISCO DE ASSIS DE BRITO
  • RODOLFO ALVAN CASANA SIFUENTES
  • Data: 22-may-2015


  • Resumen Espectáculo
  • Resumo

    A equação de Einstein com constante cosmológica negativa gera um espaço-tempo (+ 1)-dimensões, que denominamos de espaço anti de Sitter, AdSd+1, que nos referimos de "bulk". O princípio holográfico afirma que a gravidade quântica sobre o AdSd+1 é codificada por uma teoria de contorno, uma CFTd. Por exemplo, uma teoria de cordas IIB sobre uma espaço-tempo assintoticamente AdS5 XS5 é dual a uma teoria de gauge de super Yang-Mills = 4 SYM no espaço-tempo de 4-dimensões. Outro exemplo é a relação entre a equação de Einstein no "bulk" e a equação hidrodinâmica descreve uma teoria efetiva no contorno, o qual denominamos de fluido/gravitação.

    Uma extensão da dualidade AdS/CFT foi proposta por Takayanagi que denominou de correspondência AdS/BCFT. O contorno do CFT extende-se para o "bulk" e restringe o AdSd+1. Quando impomos a condição de Neumann sobre a extensão do contorno obtemos uma equação de movimento dinâmica que determina a forma da extensão. Da perspectiva da correspondência fluido/gravitação o tensor energia-momento do fluido residindo no contorno será a fonte da geometria do "bulk". Ampliando a proposta de Takayanagi para correspondência fluido/gravitação estudaremos a consistência do AdS/BCFT a temperatura finita ou equivalentemente a geometria de BH no "bulk".

     

4
  • RONIVON LOURENÇO ENEIAS
  •  

    “Acoplamento BCS em um Líquido de Luttinger em uma Dimensão”

     

  • Líder : ALVARO FERRAZ FILHO
  • MIEMBROS DE LA BANCA :
  • ALVARO FERRAZ FILHO
  • DMITRY MELNIKOV
  • EBERTH DE AMEIDA CORREA
  • EDUARDO CANTERA MARINO
  • PASQUALE SODANO
  • Data: 07-jul-2015


  • Resumen Espectáculo
  •  

    Neste trabalho nos investigamos o efeito de um emparelhamento do tipo BCS para férmions livres sem spin, em 1 + 1 dimensões. Usando técnicas de bosonização testamos a existência de modos de quasipartículas no estado supercondutor resultante. Nós calculamos a função de Green de uma partícula isolada, a função de correlação de pares e a condutividade óptica e mostramos como elas diferem das funções análogas para quasipartículas convencionais. Nós compararmos os nossos resultados com os resultados experimentais relacionados aos supercondutores de alta temperatura e mostramos que eles se encaixam qualitativamente bem com os modos de quasipartículas observados nesses materiais.

     

5
  • PRISCILA VALDENIA DOS SANTOS
  • Título:  Efeitos de Campos Aleatórios no Modelo  Blume-Capel de Alcance Infinito

  • Líder : FRANCISCO ALEXANDRE DA COSTA
  • MIEMBROS DE LA BANCA :
  • FRANCISCO ALEXANDRE DA COSTA
  • FRANCISCO DE ASSIS DE BRITO
  • IDALMIR DE SOUZA QUEIROZ JÚNIOR
  • JOAO MEDEIROS DE ARAUJO
  • LUCIANO RODRIGUES DA SILVA
  • Data: 15-jul-2015


  • Resumen Espectáculo
  •  

    Neste trabalho investigamos o efeito dos campos aleatórios no modelo Blume-Capel com interações de longo alcance. O modelo é completamente solúvel no ensemble canônico, e sua densidade de energia livre nos leva a resultados correspondentes a uma  teoria de campo médio. São estudados os casos para spin S = 1 sob influência de desordem temperada na presença de: (i) um campo cristalino aleatório; (ii) de um campo magnético aleatório; (iii) e de ambos.  Para uma escolha adequada do campo aleatório, mostramos que o modelo apresenta uma variedade de comportamentos multicríticos, linhas de transição contínuas e de primeira ordem, além de fenômenos de re-entrância. Os diagramas de fases, obtidos a partir do cálculo da energia livre por spin, exibem diversas topologias em função do parâmetro  que mede o grau de desordem.

     

     

6
  • UBIRATAN CORREIA SILVA
  • “Produção e Estudo de Multicamadas Magnéticas em Substrato Flexível”

  • Líder : ALEXANDRE BARBOSA DE OLIVEIRA
  • MIEMBROS DE LA BANCA :
  • ALEXANDRE BARBOSA DE OLIVEIRA
  • CARLOS CHESMAN DE ARAUJO FEITOSA
  • CHARLIE SALVADOR GONCALVES
  • MARCO ANTONIO MORALES TORRES
  • THATYARA FREIRE DE SOUZA
  • Data: 28-ago-2015


  • Resumen Espectáculo
  • Multicamadas magnéticas são a base para a produção de dispositivos spintrônicos e ter o domínio na produção de tais multicamadas, é fundamental para obter avanços nesta área, e nos últimos anos está em destaque a produção de dispositivos spintrônicos orgânicos e flexíveis. Devido a essa tendência, o objetivo do presente trabalho é produzir multicamadas magnéticas depositadas em substrato flexível utilizando a técnica de Magnetron sputtering dc. Três conjuntos de amostras foram confeccionados. O primeiro conjunto, constituído de tricamadas do tipo CoFe/Cu(t)/CoFe com diferentes espessuras do espaçador metálico. O Segundo conjunto, composto por dois subgrupos de multicamadas CoFe/Cu com a presença do IrMn como buffer layer e na multicamada seguinte como cap layer. O terceiro conjunto, constituído por multicamadas não magnetoestritivas de Permalloy (Py/Ta e Py/Ag) sobre substrato de material flexível e de vidro. Para a investigação das propriedades magnéticas, foram realizadas medidas de magnetometria de amostra vibrante,  ressonância ferromagnética e magnetoimpedância (MI), todas as medidas executadas em temperatura ambiente e com campo magnético aplicado sempre no plano da amostra. Para a análise estrutural, a técnica de difração de raios-X foi usada. Os resultados das tricamadas mostraram um alto campo de anisotropia tipo uniaxial para a amostra com espaçador de 4,2 nm. Para a multicamada com a presença do IrMn como buffer layer, os resultados das propriedades magnéticas estáticas e dinâmicas apresentaram comportamento isotrópico. Para a multicamada com a presença do IrMn como cap layer, os resultados das propriedades magnéticas estáticas apresentaram o comportamento magnético de uma estrutura tipo válvula de spin. Entretanto houve uma divergência com resultados das medidas de ressonância ferromagnética, a qual foi justificada devido a contribuição dos grãos instáveis e estáveis para a anisotropia rodável e anisotropia de polarização (Exchange bias) na interface ferromagnética-antiferromagnética. Para a terceira série de amostras, os resultados apresentaram comportamentos semelhantes da MI. Para as multicamadas com espaçador de Ag para ambos os substratos e variação significativa nas amostras com o espaçador por Ta onde foi possível associar a variação na MI entre os substratos de vidro e flexível ao estresse compressivo na amostra de substrato flexível.

     

7
  • FRANCISCO JOSÉ PAZ CHINCHÓN
  • Sobre o Momentum Angular de Estrelas Kepler com Planetas

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • DANIEL BRITO DE FREITAS
  • EDUARDO JANOT PACHECO
  • JOSE RENAN DE MEDEIROS
  • MARCIO CATELAN
  • Data: 28-ago-2015


  • Resumen Espectáculo
  • No presente trabalho de tese apresentamos o estudo rotacional e de momentum angular para uma amostra de estrelas com planetas confirmados e candidatas a possuir companheiras planetárias (Objetos de Interesse Kepler), ambas pertencentes à missão Kepler. Para realizar estas estimativas, 3.807 estrelas foram analisadas conjuntamente mediante os métodos Lomb-Scargle e wavelet, definindo um alto grau de confiança quando os resultados concordavam dentro de um 10%. Para 540 estrelas conseguimos obter períodos rotacionais onde a significância dos métodos era maior a 99% e dentre elas 63 não possuíam medições na literatura até Fevereiro de 2015. De acordo com os valores de massa presentes na literatura, a amostra final de 131 estrelas com planetas confirmados e 409 estrelas candidatas está definida pelo intervalo de massas de 0,48 − 1,53 M⊙, que corres- ponde a tipos espectrais M até F tardio. Enquanto as relações de períodos, o conjunto de valores abrange o intervalo 2 − 89 d, possuindo um alto grau de concordância com a literatura e com predições teóricas. Com as estimativas do momentum angular chegamos a corroborar a relação com a massa estelar proposta por Kraft para estrelas de tipo espectral F e G, mas permanece o desafio de prolongar o estudo para massas menores onde a estrutura interna estelar é modificada e novos procedimentos devem ser utilizados. Adicionalmente ao estudo desta amostra principal, o conjunto total de estrelas da base Kepler foi analisada na busca de padrões de ruído. As metodologias, comparações com outras abordagens e detalhes da inspeção visual são aqui exibidos. Os resultados do conjunto de testes conduzidos (e.g., análise Bayesiana, testes não paramétricos) estão detalhados no texto. Os resultados de maior relevância foram publicados em nosso trabalho Paz-Chinchón et al. (2015).

     

     

     

     

8
  • KENNEDY LEITE AGRA
  •  

    Estudo da Dinâmica da Magnetização em Multicamadas Magnetostrictivas.

  • Líder : MARCIO ASSOLIN CORREA
  • MIEMBROS DE LA BANCA :
  • MARCIO ASSOLIN CORREA
  • CLAUDIONOR GOMES BEZERRA
  • SUZANA NOBREGA DE MEDEIROS
  • RICARDO BARRETO DA SILVA
  • ROBERTO LÁZARO RODRIGUEZ SUAREZ
  • Data: 10-sep-2015


  • Resumen Espectáculo
  •  

    Multicamadas magnéticas têm uma grande importância no desenvolvimento de elementos sensores baseados no efeito magnetoimpedância (MI). O advento de dispositivos usando substrato flexível orgânico têm aberto novas fronteiras para o desenvolvimento da tecnologia nas mais diversas áreas. Diante disso torna-se necessário a produção e estudo das propriedades magnéticas e mecânicas em filmes ferromagnéticos crescidos em substrato flexível. Neste trabalho, foram produzidas multicamadas ferromagnéticas de Py, Co e FeCuNbSiB em substratos flexível  e rígido, utilizando a técnica de magnetron sputtering. Na ocasião utilizou-se de uma metodologia para caracterizar as propriedades estruturais, magnéticas e mecânicas. Para isso foram utilizados os seguentes instrumentos de medida: difratômetro de Raios-X, magnetômetro de amostra vibrante, analisador de impedância, instrumentos de medida de dimensões e software de elementos finitos. Através de uma análise meticulosa, foi possível observar e correlacionar o comportamento do efeito MI com as propriedades magnéticas quase-estáticas, estruturais e mecânicas. Observando-se uma forte dependência da MI com a magnetostricção de saturação, quando são introduzidas anisotropias magnetoelásticas, através de tensões mecânicas. As propriedades magnéticas das multicamadas de Py mostram-se insensíveis as tensões aplicadas. Já, nas multicamadas ferromagnéticas de Co, teve como principal resultado, um aumento da dispersão de MI atrelado à elevação das tensões mecânicas. No caso, das multicamadas de FeCuNbSiB, a inversão do eixo de anisotropia é o resultado mais interessante, provocando modificações na configuração do efeito MI, trazendo informações muito ricas da dinâmica da magnetização, quando tensões mecânicas são aplicadas ao sistema.    

9
  • LINDON JOHNSON FREITAS RODRIGUES
  • Fases Magnéticas, Poláritons Magnéticos e Modos Magnetostáticos em Filmes e Cristais Magnônicos de Terras-Raras.

     

  • Líder : MANOEL SILVA DE VASCONCELOS
  • MIEMBROS DE LA BANCA :
  • MANOEL SILVA DE VASCONCELOS
  • DORY HELIO AIRES DE LIMA ANSELMO
  • EUDENILSON LINS DE ALBUQUERQUE
  • PAULO WILSON MAURIZ
  • VAMBERTO DIAS DE MELLO
  • Data: 10-sep-2015


  • Resumen Espectáculo
  • Neste trabalho, primeiramente abordamos o estudo das fases magnéticas em filmes finos e ultrafinos de Hólmio (Ho) no intervalo de temperatura entre            20K e 132 K, onde mostramos que o tamanho do filme, os efeitos de superfície e a aplicação do campo magnético externo alteram significativamente o diagrama de fases magnéticas de terra-rara. Também constatamos uma redução correspondente a intensidade do campo magnético externo necessário para saturar a magnetização e para filmes ultrafinos o estado helicoidal não irá se formar. Usamos o calor específico e a susceptibilidade magnética como ferramentas auxiliares para explorar e discutir a natureza das transições de fase na presença de campo magnético externo, temperatura e efeitos magnéticos externos. Neste caso a presença de um campo externo dá origem as fases magnéticas Fan e Spin slip. Em seguida, estudamos os poláritons magnéticos, que são excitações elementares em cristais, em multicamadas periódicas compostas do terra-rara Disprósio (Dy) e Fluoreto de zinco (ZnF2), que define um cristal magnônico. Na presença de um campo magnético externo e em uma determinada temperatura, os efeitos do comportamento efetivo dos poláritons magnéticos fazem surgir novos modos de superfície. Também, no estudo dos poláritons de volume, surge uma região de dispersão, que é bastante conhecida na literatura dos grafenos, como região de            “gap zero”. Apresentamos ainda um estudo dos modos magnetostáticos para complementar nossos resultados. Essas novas propriedades são explicadas pelo comportamento efetivo dos poláritons magnéticos em uma multicamada periódica. Usando o modelo do meio efetivo podemos explicar, por exemplo, o comportamento anômalo (hiperbólico) na relação de dispersão dos poláriotns magnéticos. Em suma, discutimos os resultados e apresentamos novas perspectivas para o estudo dos poláritons e modos magnetostáticos nessa nova área de pesquisa, chamada de cristais magnônicos.

     

10
  • CAIO FÁBIO TEIXEIRA CORREIA
  • Effects of Opacity on Interstellar Turbulence Study
  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • JOSE RENAN DE MEDEIROS
  • BRUNO LEONARDO CANTO MARTINS
  • DANIEL BRITO DE FREITAS
  • ANTONIO CARLOS DA SILVA MIRANDA
  • DIEGO FALCETA GONÇALVES
  • Data: 11-sep-2015


  • Resumen Espectáculo
  • In this work we study the 
    quality of Mach number
     estimation (MS) from 13
     CO line widths in interstellar 
    medium molecular clouds (MIE),
     taking into account effects of opacity and self absorption. To do
     so, we analyzed magnetohydrodynamic (MHD) simulations, including 
    post-processing to include the effects of radiative transfer on real-cloud radio 
    observations. We found a good agreement for the measured value of MS with 
    the true value, available through the simulations. However, we found that the
     widening of CO line widths due to opacity, in optically dense environments, 
    causes an overestimation of MS by a factor ≈ 1.16 - 1.3. We also found that this super estimate 

    has dependence on the magnetic field of the molecular cloud. The super-Alfvanic turbulence 
    (weak magnetic fields) will cause a further widening of the CO emission lines compared to
     the sub-Alfvanic turbulence (strong magnetic fields), for the full range of optical depths studied here. 
    These results have implications for the relationship between the standard deviation of the column
     density (σN / <N>) and the Cloud Mach MS number, obtained observationally. In addition to this,
     we investigated the ability of the Principal Component Analysis (PCA) technique to detect 
    variations of the power spectra of velocity in high optical depth regimes. To do so, we studied synthetic observations of CO in simulations of MHD media and Brownian fractal distribution. Our results indicate that PCA is capable of detecting changes in the power spectrum of the speed, even in high opacity regimes, and that this occurs because, in addition to the spectral information, this technique is sensitive to phase information, contrasting with other techniques based
     only In spectral information, which in turn saturates to a spectral index of β ~ -3 in optically dense media.
11
  • ANTÔNIO DGERSON PEREIRA DA COSTA
  • Infrared-medium in Binary Systems with Evolved Components
  • Líder : BRUNO LEONARDO CANTO MARTINS
  • MIEMBROS DE LA BANCA :
  • BRUNO LEONARDO CANTO MARTINS
  • DANIEL BRITO DE FREITAS
  • JOSE RENAN DE MEDEIROS
  • CRISTIAN ANDRES CORTES ANGEL
  • MARIA JAQUELINEVASCONCELOS
  • Data: 14-sep-2015


  • Resumen Espectáculo
  • In the present work, we studied the behavior of the infrared-medium emission,
     represented by the color indexes K - [22] and K - [12], obtained from the 
    magnitudes WISE and 2MASS, for a sample of 244 evolved class binary 
    systems Of luminosity III and spectral types F, G and K. In addition to 
    investigating this behavior in an evolutionary perspective, we also analyze 
    the relation between such infrared emission and the speed of rotation, 
    searching for correlations and tendencies between these parameters and 
    gravitational tides reflexes.   For a better understanding of the evolution 
    profile of the stars the HR diagram of the sample was constructed, along
     with evolutionary traces indicating a mass range of 0.6 to 7.0. We verified 
    in this diagram that, the emission and rotation distribution presented different behaviors. 
    While rotation exhibits a discontinuity due to the absence of synchronization in most stars, 
    color indices are scattered, with no dependence on mass or evolutionary stage.  
     We studied the behavior of the infrared emission in function of several parameters, 
    such as the speed of rotation, orbital period and eccentricity. Regarding the 
    rotation, we observed an inhibition of the infrared emission level for stars 
    with higher rotation, probably due to the dispersion of possible circumstellar 
    disks due to the action of stellar winds. This tendency is reinforced by the fact 

    that practically all stars with excess infrared confirmed by spectral energy
     distributions are low-rotation stars, that is, non-synchronized and non-circularized stars. 
    Despite this fact, for the infrared emission in general, no clear correlation was found 
    between such emission and the orbital parameters (orbital period and eccentricity), 
    suggesting at first that infrared emission is not influenced by the synchronization 
    processes and Circularization of binary systems. When applying the Kolomogorov-Smirnov
     test (KS test), we verified that the cumulative distributions of the indices Of color K - [22] 
    and K - [12] for stars (synchronized and non - synchronized) and (circularized and non - 
    circularized) do not present statistically significant differences.

     
12
  • ALINE AMABILE VIOL BARBOSA
  •  

    Entropia de Shannon e Propriedades Topológicas de Redes Funcionais do Cérebro Humano Sob Efeito de Ayahuasca

  • Líder : MADRAS VISWANATHAN GANDHI MOHAN
  • MIEMBROS DE LA BANCA :
  • ADRIANO MESQUITA ALENCAR
  • DRAULIO BARROS DE ARAUJO
  • FRANCISCO ALEXANDRE DA COSTA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MARCO ANTONIO ALVES DA SILVA
  • SIDARTA TOLLENDAL GOMES RIBEIRO
  • Data: 18-sep-2015


  • Resumen Espectáculo
  • O recente desenvolvimento do poder de processamento computacional vem trazendo para dentro do escopo da física e outras ciência exatas desafios até então considerados exclusivos de ciências qualitativas. Métodos e conceitos da Física têm contribuído para avanços em diversas áreas, dentre elas neurociência. Vimos na presente tese de doutorado estudar o comportamento do cérebro humano em estado alterado de consciência, a partir de mapas funcionais gerados por ressonância magnética funcional (fMRI, {\it functional Magnetic Ressonance}) usando ferramentas da física estatística e da teoria de redes complexas. Analisamos dados de fMRI do cérebro de sujeitos em estado de repouso em duas condições distintas: em estado natural e em estado alterado de consciência pela ingestão de uma infusão psicoativa, proveniente da cultura indígena amazônica, chamada Ayahuasca. Em linhas gerais fomos guiados por duas perguntas. O Ayahuasca causa diferenças nas redes funcionais do cérebro? Como quantificar essas diferenças? Inicialmente construímos redes complexas usando os dados de fMRI para mapear informações das redes funcionais do cérebro de cada sujeito em ambas condições. A seguir analisamos as propriedades estatísticas e topológicas dessas redes. Comparando as redes geradas a partir  dos dados adquiridos antes e depois da ingestão do Ayahuasca, detectamos duas mudanças importantes nas propriedades estatísticas e topológicas. Encontramos primeiramente um aumento na entropia de Shannon da distribuição de grau. Encontramos também uma segunda mudança importante: Uma variação na topologia que interfere nas eficiências das redes referentes ao estado alterado. Parte das mudanças nas eficiências de rede vão além do que pode ser explicado exclusivamente pelo aumento de entropia.  Interpretamos e discutimos esses dois resultados no contexto de neurociência. Comentamos também sobre a como a quantificação de  informações das redes funcionais pode ser melhorar nossa compreensão do funcionamento do cérebro humano e, consequentemente, contribuir para o  desenvolvimento de novas metodologias em diagnóstico e tratamento de distúrbios psiquiátricos ainda pouco compreendidos.

13
  • BRUNO FERREIRA AMORIM
  • “Síntese e Caracterização Estrutural e Magnética de Ferritas de Cobalto-Manganês”.

  • Líder : SUZANA NOBREGA DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • ANA LUCIA DANTAS
  • CLAUDIONOR GOMES BEZERRA
  • JOSE HUMBERTO DE ARAUJO
  • SUZANA NOBREGA DE MEDEIROS
  • VAMBERTO DIAS DE MELLO
  • Data: 07-dic-2015


  • Resumen Espectáculo
  • “Síntese e Caracterização Estrutural e Magnética de Ferritas de Cobalto-Manganês”.

14
  • NOELIA SOUZA DOS SANTOS
  • "O Problema da Matéria Escura e o Teorema do Virial na Teoria de Gravidade Eddington-Born-Infeld"

  • Líder : JANILO SANTOS
  • MIEMBROS DE LA BANCA :
  • JANILO SANTOS
  • LEO GOUVEA MEDEIROS
  • RAIMUNDO SILVA JUNIOR
  • CARLOS AUGUSTO ROMERO FILHO
  • VALDIR BARBOSA BEZERRA
  • Data: 18-dic-2015


  • Resumen Espectáculo
  • A matéria escura é uma quantidade fundamental da Cosmologia Moderna. A princípio, ela é necessária para explicar o processo de formação das estruturas no Universo, a curva de rotação das galáxias e a discrepância na massa dos aglomerados de galáxias. Entretanto, apesar de muitos esforços realizados, em ambos os aspectos, teórico e experimental, a natureza da matéria escura é ainda desconhecida, e a única evidência convincente de sua existência é gravitacional. Isso incita dúvidas sobre a existência da matéria escura, e por sua vez, sugere que a gravidade de Einstein precisa ser modificada em algumas escalas. Estudamos, neste trabalho, a possibilidade da gravidade modificada Eddington-Born-Infeld (EBI) fornecer uma explicação alternativa para a discrepância da massa dos aglomerados de galáxias. Para esse propósito, derivamos as equações de campo de Einstein modificadas, e obtemos suas soluções para um sistema esférico constituído de partículas idênticas acolisionais. Posteriormente, consideramos a equação de Boltzmann relativística acolisional, e usando algumas aproximações e suposições no regime de campo fraco, derivamos o teorema do virial generalizado, na gravidade EBI. Para compararmos as predições da gravidade EBI com os dados observacionais, estimamos a ordem de magnitude da massa geométrica de um aglomerado, e encontramos que é compatível com as observações. Por fim, considerando que a densidade das galáxias do aglomerado seja descrita por um perfil tipo lei de potência, derivamos o perfil de dispersão das velocidades das galáxias o qual pode ser usado para testar alguns aspectos da gravidade EBI.

15
  • TIAGO DE MEDEIROS VIEIRA
  • "Estudo da Transição de Fase da Percolação Através da Entropia da Informação"

  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • ANTONIO DE MACEDO FILHO
  • DANIEL JUDSON BEZERRA SOARES
  • JOAO MEDEIROS DE ARAUJO
  • LUCIANO RODRIGUES DA SILVA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • MAURICIO LOPES DE ALMEIDA
  • Data: 21-dic-2015


  • Resumen Espectáculo
  • Muitos sistemas físicos têm uma dinâmica que pode ser modelada através de processos de percolação. A percolação é utilizada para estudar desde a difusão de um fluido em um meio desordenado até a fragmentação de um rede de computadores causada por um ataque de hackers. Uma característica comum a todos esses sistemas nos quais a percolação pode se aplicar é a presença de dois regimes não-coexistentes associados a certas propriedades do sistema. Por exemplo: o meio desordenado pode permitir ou não a passagem do fluido de acordo com sua porosidade. A mudança de um regime para o outro caracteriza a transição de fase percolativa. A forma padrão de se analisar essa transição é através do chamado parâmetro de ordem, uma variável relacionada a alguma característica do sistema que apresenta valor zero em um dos regimes e valor diferente de zero no outro. A proposta apresentada na presente tese é que essa transição de fase pode ser avaliada sem o uso direto do parâmetro de ordem, sendo possível caracterizá-la através do uso da entropia de Shannon. Essa entropia é uma medida do grau de incerteza na informação codificada através de uma distribuição de probabilidades. A proposta é estudada no contexto da formação de aglomerados em grafos aleatórios, sendo aplicada tanto para a percolação clássica quanto para a percolação explosiva. Ela se baseia no cálculo da entropia da distribuição de probabilidades dos tamanhos dos aglomerados e os resultados obtidos mostram que o ponto crítico da transição está relacionado às derivadas da função entropia. Além disso, a diferença entre as naturezas suave e abrupta das transições clássica e explosiva, respectivamente, é reforçada ao se observar que a entropia tem valor máximo no ponto crítico da transição clássica, enquanto que essa correspondência não ocorre durante a transição explosiva. 

2014
Disertaciones
1
  • LEONARDO FABRICIO GOMES BATISTA
  • “Não-Extensividade no Contexto da Atividade Magnética Solar: O Problema da Assimetria Hemisférica”

  • Líder : DANIEL BRITO DE FREITAS
  • MIEMBROS DE LA BANCA :
  • DANIEL BRITO DE FREITAS
  • JOSE RENAN DE MEDEIROS
  • JOSÉ RONALDO PEREIRA DA SILVA
  • Data: 14-feb-2014


  • Resumen Espectáculo
  • Diversos indicadores de atividade solar, tais como número de manchas 
    solares, área das manchas e flares, sobre a fotosfera do Sol não são 
    distribuidos de forma simetrica. Este comportamento é também conhecido 
    como Assimetria Norte-Sul dos diferentes indices solares. Dentre as 
    diferentes conclusões obtidas por vários autores, nós podemos apontar 
    que a assimetria N-S é um fenômeno sistemático e real e não devido à 
    variabilidades aleatórias. No presente trabalho, as distribuições de 
    probabilidade dos dados provinentes do satélite Marshall Space Flight 
    Centre (MSFC) da NASA são investigadas usando uma ferramenta estátistica 
    originada da bem-conhecida Mecânica Estatística Não-Extensiva proposta 
    por C. Tsallis em 1988. Nós apresentamos nossos resultados e discutimos 
    suas implicações físicas com a ajuda do modelo teórico e observações. 
    Nossos resultados revelam que existe uma forte dependência entre o 
    parâmetro entrópico não-extensivo e a variabilidade de longo-termo 
    presente nos dados de área de manchas solares. Dentre os resultados mais 
    importantes, nós destacamos que a assimetria do índice $q$ revela o 
    domínio do hemisfério norte em relação ao sul. Este comportamento já foi 
    discutido e confirmado por vários autores, mas em nenhum momento eles 
    atribuiram tal comportamento à uma propriedade estatística do modelo. 
    Com isso, concluimos que tal parâmetro pode ser considerado como uma 
    medida eficiente para diagnosticar variações de longo-termo do dínamo 
    solar. Finalmente, nossa dissertação abre um novo caminho para 
    investigar séries temporais em Astrofísica pela ótica da não-extensividade.
2
  • GERDIVANE FERREIRA DUARTE
  • Física Estatística Aplicada a Sistemas Sociais Através do Estudo de Redes Complexas

  • Líder : LUCIANO RODRIGUES DA SILVA
  • MIEMBROS DE LA BANCA :
  • LUCIANO RODRIGUES DA SILVA
  • MADRAS VISWANATHAN GANDHI MOHAN
  • ANTONIO DE MACEDO FILHO
  • MAURICIO LOPES DE ALMEIDA
  • Data: 21-feb-2014


  • Resumen Espectáculo
  • Neste trabalho apresentamos um estudo das redes sociais baseado na análise dos nomes de famílias. Fazemos uma abordagem básica do formalismo matemático dos grafos e em seguida apresentamos os principais modelos teóricos para as Redes Complexas com o objetivo de fundamentar nossa análise das redes de sobrenomes. Estas, por sua vez, são trabalhadas de modo a extrairmos as principais grandezas, tais como coeficiente de agregação, menor caminho médio e distribuição de conectividades. Com base nestas grandezas, podemos afirmar que as redes de sobrenomes são um exemplo de rede complexa, exibindo características importantes como ligação preferencial e o caráter de mundo pequeno.

     

3
  • RICARDO BORGES DA COSTA
  • Magnetoresistência Perturbativa e Sua Aplicabilidade na Investigação de Bicamadas FM/AFM Acopladas    

  • Líder : ALEXANDRE BARBOSA DE OLIVEIRA
  • MIEMBROS DE LA BANCA :
  • ALEXANDRE BARBOSA DE OLIVEIRA
  • MARCIO ASSOLIN CORREA
  • ANTONIO AZEVEDO DA COSTA
  • Data: 28-feb-2014


  • Resumen Espectáculo
  • Este trabalho apresenta o estudo de propriedades magneticas de lmes nos com interface
    ferromagnetica/antiferromagnetica. Para interpretar e analisar os resultados experimentais
    foi usado um modelo fenomenologico baseado nos termos de energias livres. Os
    termos de energia relevantes para este modelo s~ao: energia Zeeman, energia de anisotropia
    uniaxial, energia de anisotropia unidirecional (Exchange Bias) e a energia de anisotropia
    rotatoria. Essas anisotropias s~ao abordadas por meio de uma nova tecnica experimental
    capaz de detectar propriedades magneticas de origem perturbativa. Trata-se de uma
    modi cac~ao da tecnica convencional da magnetoresist^encia de quatro pontas, batizada
    como magnetoresist^encia perturbativa (PMR). As quatro pontas s~ao xadas de maneira
    colinear sobre a amostra. O conjunto e submetido a ac~ao de dois campos magneticos,
    o campo
    !
    H (magnitude em torno de 1000 Oe) de natureza contnua (DC) e o campo
    alternado
    !
    hac (de baixa intensidade e frequ^encia em torno de 400 Hz) perturbando a
    magnetizac~ao do material. Os dois contatos externos s~ao usados para aplicar uma corrente
    eletrica contnua (poucos mA). Atraves de um ampli cador lock-in conectado aos
    dois contatos internos, mede-se a tens~ao cuja frequ^encia da parte oscilatoria e a mesma
    do campo magnetico
    !
    hac. A express~ao matematica que representa o sinal para esta medida
    foi demonstrada usando teoria perturbativa de func~oes, que consiste em expandir o
    sinal medido em serie de Taylor, tendo como variavel de expans~ao a perturbac~ao (hac).
    O comportamento do sinal em func~ao do campo magnetico H foi analisado e foram feitos
    ajustes numericos dos resultados experimentais recentes que mostram a validade do
    modelo fenomenologico proposto. Usando o modelo fenomenologico proposto foi possvel
    entender a relac~ao entre par^ametros retirados das medidas de PMR, os campos de anisotropias
    unidirecional (Exchange Bias) e a in u^encia da anisotropia rotatoria sobre a
    4
    curva de PMR. Nos calculos foram consideradas duas diferentes de nic~oes de anisotropia
    rotatoria: a de Stiles/McMichael e a de J. Geshev. Tambem foi realizada uma analise do
    sinal de PMR frente a variac~ao angular do campo magnetico, possibilitando a comparac~ao
    entre os dois modelos. Atraves desta abordagem teorico-experimental foi possvel mostrar
    como os campos de anisotropias unidirecional e rotatoria interferem nas propriedades do
    material, o que nos deu base para confrontar os resultados teoricos com os experimentais,
    obtidos pelo grupo atraves da tecnica de magnetoresist^encia perturbativa (PMR

4
  • WELLINGTON CANTANHEDE DOS SANTOS
  • “Síntese e Caracterização Estrutural, Magnética e Térmica da Hidroxiapatita Dopada com Ferro”

  • Líder : SUZANA NOBREGA DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • SUZANA NOBREGA DE MEDEIROS
  • FELIPE BOHN
  • ANA LUCIA DANTAS
  • Data: 14-mar-2014


  • Resumen Espectáculo
  • No presente trabalho foram sintetizados compósitos, a partir da moagem de alta
    energia dos precursores hidroxiapatita - HAp (Ca10(PO4)6(OH)2) e ferro metálico (α-Fe),
    com o intuito de serem utilizados em hipertermia magnética no tratamento do câncer. Os
    produtos da moagem foram caracterizados por difratometria de raios X (DRX),
    microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva (EDS),
    medidas de magnetização em função do campo aplicado e medidas de temperatura em
    função do campo alternado. Os DRX das amostras batidas de HAp/Fe revelaram somente a
    presença dos precursores. O MEV mostrou aglomerados com formatos irregulares. As
    curvas de magnetização obtidas apresentam casos típicos de comportamento
    ferromagnético fraco. Para as amostras batidas e submetidas a tratamento térmico as
    seguintes fases foram identificadas: HAp (Ca10(PO4)6(OH)2) , hematita (Fe2O3) e ferro
    fosfato tricálcio, FeTCP, Ca19Fe2 (PO4)14. Analisando os resultados de M x H, verificou-se
    uma redução na magnetização de saturação, tendo em vista que o Fe foi incorporado à
    HAp. As curvas de histerese, obtidas a 300 K, são características de amostras que possuem
    mais de uma fase. Em 77 K, o comportamento da curva de histerese é influenciado pela
    presença da hematita que é antiferromagnética. Já em T = 4,2K, é observado um
    comportamento ferromagnético fraco. Além disso, verifica-se o efeito de “exchange bias”.
    Os resultados obtidos das medidas de temperatura em função do campo alternado são
    promissores para aplicações em hipertermia magnética e outras aplicações biomédicas.

5
  • ANDRÉ LUIS BRITO QUERINO
  • Estudo Sobre a Detecção de Invariância de Escala Discreta em Sistemas com Criticalidade Auto-Organizada

  • Líder : JOAO MEDEIROS DE ARAUJO
  • MIEMBROS DE LA BANCA :
  • JOAO MEDEIROS DE ARAUJO
  • MADRAS VISWANATHAN GANDHI MOHAN
  • GISLENE MICARLA BORGES DE LIMA
  • Data: 20-mar-2014


  • Resumen Espectáculo
  • Recentemente, estudos têm mostrado evidências de comportamento log-periódico em sistemas não-hierárquicos. Um fato interessante é o surgimento de tais propriedades em ruptura e quebra de materiais complexos e falhas financeiras. Estes podem ser exemplos de sistemas com criticalidade auto-organizada (SOC). Neste trabalho estudamos a detecção de invariância de escala discreta ou log-periodicidade. Mostrando teoricamente a eficácia de métodos baseados na Transformada de Fourier para a detecção de log-periodicidade, não só com conhecimento prévio do ponto critico como também antes deste ponto. Especificamente, estudamos o mercado financeiro brasileiro com o objetivo de detectar a invariância de escala discreta no índice Bovespa (Bolsa de Valores de São Paulo). Algumas séries históricas foram selecionadas de períodos em 1999, 2001 e 2008. Relatamos evidência de detecção de possíveis log-periodicidade antes das quebras, mostrado sua aplicabilidade no estudo de sistemas com provável invariância de escala discreta, no caso das falhas financeiras, isso mostra uma evidencia da possibilidade de previsão da quebra.

6
  • PIERRE NIAU AKMANSOY
  • Termodinâmica de um gás de fótons no contexto de eletrodinâmicas não-lineares.

  • Líder : LEO GOUVEA MEDEIROS
  • MIEMBROS DE LA BANCA :
  • RAIMUNDO SILVA JUNIOR
  • LEO GOUVEA MEDEIROS
  • RODRIGO ROCHA CUZINATTO
  • Data: 31-mar-2014


  • Resumen Espectáculo
  • Existe uma série de motivos para se estudar extensões da eletrodinâmica de Maxwell (EDM) dentre os quais podemos citar: problema de divergência clássica para o potencial Coulombiano, vínculos experimentais sobre a massa do fóton, estudo clássico de efeitos de polarização do vácuo e alterações da eletrodinâmica no contexto de branas. Além disso, o próprio estudo de variações/extensões da eletrodinâmica nos ajuda a entender melhor a EDM.

    Dentre as várias extensões possíveis a classe de eletrodinâmicas mais conhecidas é aquela obtida a partir da Lagrangiana  onde  e . Extensões deste tipo resultam em modelos não-lineares e portanto são chamadas genericamente de modelos de eletrodinâmica não-linear (NLED). Uma das características mais interessantes nas NLED é o surgimento de relações de dispersão modificadas devido a interação da radiação com um campo eletromagnético de fundo. Este efeito foi primeiramente obtido em [1] e [2] e mais recentemente por [3].

    Neste trabalho, usamos o procedimento seguido em [2] para encontrar as relações de dispersão para o fóton. Assim, o campo eletromagnético  é separado em um campo eletromagnético forte de fundo  e uma perturbação fraca  que se propaga neste meio, ou seja . A partir deste procedimento chegamos a uma relação de dispersão para a radiação que depende do campo eletromagnético de fundo e da eletrodinâmica considerada. Neste contexto, ainda existe a possibilidade de, dependendo da forma da Lagrangiana, surgirem duas relações de dispersão que estão associadas à polarização da radiação. Este fenômeno é conhecido como birrefringência e irá alterar as propriedades termodinâmicas da radiação.

    Encontrada a relação de dispersão (ou relações de dispersão) entramos no processo estatístico que permite determinar as propriedades do gás de fóton. Por se tratar de fótons, usamos a estatística de Bose-Einstein para calcular a função de partição da radiação no contexto de uma NLED. Como mencionado acima, o efeito de birrefringência deve ser levado em conta neste cálculo. As propriedades termodinâmicas encontradas (pressão  e densidade de energia ) dependem do campo de fundo e da forma da Lagrangiana, porém a equação de estado da radiação ( ) não se altera. Finalmente, aplicamos o procedimento as NLED de Born-Infeld e Euler-Heisenberg e comparamos os resultados com a EDM.

    [1] Guy Boillat, J. Math. Phys. 11, 941 (1970).

    [2] Z. Bialynicka-Birula and I. Bialynicki-Birula, Phy. Rev. D 2, 2341 (1970).

    [3] Novello et al., Phys. Rev. D 61, 45001 (2000).

     

7
  • BRUNO LUSTOSA DE MOURA
  • O Enigmático Problema das Gigantes Ricas em Lítio e as Perspectivas com o Satélite Kepler

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • JOSÉ RONALDO PEREIRA DA SILVA
  • Data: 24-abr-2014


  • Resumen Espectáculo
  • O Lítio (Li) é um elemento químico com número atômico 3 e está entre os elementos mais leves conhecidos no Universo. De forma geral, o Li é encontrado na natureza sob a forma de dois isótopos estáveis, o  6Li e o 7Li . O isótopo 7Li é o mais dominante e responde por cerca de 93% do Li encontrado no Universo. Devido a suas características de fragilidade, este elemento é largamente utilizado na astrofísica, sobretudo no que diz respeito ao entendimento dos processos físicos que ocorrem desde o Big Bang, passando pela evolução química de Galáxias até as estrelas.

    Na nucleossíntese primordial no momento do Big Bang (BBN), os cálculos teóricos preveem uma produção de Li juntamente com os outros elementos leves tais como o deutério e o Berílio.  Para o Li a teoria do BBN revê uma abundância primordial de log n (Li) = 2.72 dex, numa escala logarítmica relativa ao H.  A abundância de Li encontrada nas estrelas pobres em metal, ou estrelas de pop II, é assim clamado como sendo a abundância de Li primordial e apresenta a medida de log n(Li) = 2.27 dex. Já no ISM (interestellar medium ou meio interestelar), que reflete o valor atual, a abundância de Li é de log n(Li) = 3.2 dex. Esta valor é de grande importância para a nossa compreensão da evolução química do Galáxia. Os processos responsáveis pelo aumento do valor primordial para o valor presente Li (ISM) não são claramente compreendidos nos dias de hoje.

    O fato é que existe uma contribuição real de Li provenientes das estrelas gigantes de pouca massa, e esta contribuição precisa ser bem estimada se quisermos entender a evolução química da nossa Galáxia.  O principal entrave desta sequência lógica, é o aparecimento de algumas estrelas gigantes de baixa massa, de tipos espectrais G e K cujo a atmosfera é altamente enriquecido com Li.  Tais valores elevados são exatamente ao contrário do que se poderia esperar como abundancia típica para as estrelas gigantes de baixa massa, onde envelopes convectivos passam por um aprofundamento em massa (dredge-up) no qual todo o Li deveria ser diluído e apresentar abundancias em torno de log n(Li) ~ 1,4, seguindo o modelo padrão de evolução estelar.

    Na literatura, encontram-se três sugestões que tentam reconciliar os valores da abundância de Li teórica e observada nestas gigantes ricas em Li, no entanto nenhum destes traz respostas conclusivas. No presente trabalho, propomos um estudo qualitativo do estado evolutivo das estrelas ricas em Li presentes na literatura.  Neste sentido foi coletado uma de estrelas ricas em Li da literatura juntamente com a recente descoberta da primeira estrela rica em Li observada pelo satélite Kepler. O objetivo principal deste trabalho é de promover uma sólida discursão sobre o estado evolutivo baseado nas características obtidas a parir da análise sísmica do objeto observado pelo satélite Kepler.  Utilizamos traçados evolutivos e simulações feitas com o código de síntese de população TRILEGAL com o intuito de avaliar tão preciso quanto possível o estado evolutivo e a estrutura interna deste grupo de estrelas. Os resultados apontam para um tempo característico muito curto, quando comparado com a escala evolutiva, referente ao enriquecimento destas estrelas.

8
  • FLÁVIO MAUX VIANNA DA SILVA
  • "Estudo do Fluxo de Neutrino Solar Com o Código Evolutivo de Toulouse - Geneva"

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • JOSÉ RONALDO PEREIRA DA SILVA
  • Data: 24-abr-2014


  • Resumen Espectáculo
  • O estudo do neutrino solar é muito importante para uma melhor compreensão sobre o conjunto de reações nucleares que ocorre no interior do Sol e nas estrelas do tipo solar.  O fluxo de neutrino também proporciona uma  melhor compreensão da estrutura estelar como um todo. Nesta dissertação, analisamos o fluxo de neutrinos em um modelo Solar com intuito de determinar e verificar a distribuição do fluxo do ponto de vista estatístico, uma vez que este fluxo depende das distribuições intrínsecas de velocidades das partículas no plasma estelar.  A principal ferramenta desta analise foi o código de evolução estelar Toulouse-Geneva  (Stellar Evolution Code, ou TGEC), o qual permite-nos obter os valores do fluxo de neutrino por reação e por camada  no  interior do Sol e  assim podemos comparar com os resultados observacionais para o fluxo de neutrino  detectado a partir de experimentos com base no (Homestake), (SAGE, Gallex/GNO) e água (SNO). Nosso resultado mostra a distribuição final para o fluxo de neutrinos e expõem as equações relacionadas com este fluxo e que estão presentes no TGEC.

     

9
  • JOSE CRISANTO DA COSTA NETO
  • Efeito Nernst Anômalo em Materiais com Anisotropia Magnetocristalina (110)

  • Líder : CARLOS CHESMAN DE ARAUJO FEITOSA
  • MIEMBROS DE LA BANCA :
  • CARLOS CHESMAN DE ARAUJO FEITOSA
  • CLAUDIONOR GOMES BEZERRA
  • EDSON PASSAMANI CAETANO
  • Data: 09-may-2014


  • Resumen Espectáculo
  • Quando um material ferromagnético é submetido a um gradiente de temperatura e a um campo magnético surge o chamado efeito Nernst-Anômalo, medido por uma voltagem na amostra magnética. Este efeito atualmente vem sendo investigado em materiais para aplicação em spintrônica e caloritrônica [24]. Atualmente os materiais chamados de Heusler, são os mais promissores para essa nova área de pesquisa. Neste trabalho investigamos as curvas de voltagem associadas ao efeito Nernst-Anômalo com anisotropia magneto-cristalina, voltagem versus campo magnético aplicado, e voltagem versus ângulo planar. Analisamos três tipos de anisotropia, anisotropia cúbica (100) que apresenta simetria C4 , anisotropia uniaxial que também possui simetria do tipo C4 e a anisotropia cúbica (110) que é C2. O objetivo foi comprovar que o uso da anisotropia cúbica (110) é equivalente a anisotropia (100) adicionada de uma uniaxial, especificamente, quando a constante de anisotropia uniaxial é considerada grande, cerca de 50% da constante da anisotropia cúbica (100) e o eixo fácil está a 90º do eixo fácil da (100). Os resultados demonstram essa total equivalência e produz uma nova interpretação com o uso da anisotropia cúbica (110).

10
  • ANNA CECÍLIA DANTAS DE MEDEIROS
  • "Anisotropia Magnética (110) em Nanofilmes de Permalloy Sobre MgO(100)"

  • Líder : CARLOS CHESMAN DE ARAUJO FEITOSA
  • MIEMBROS DE LA BANCA :
  • CARLOS CHESMAN DE ARAUJO FEITOSA
  • MARCIO ASSOLIN CORREA
  • FERNANDO PELEGRINI
  • Data: 30-may-2014


  • Resumen Espectáculo
  •  

                O estudo e obtenção de sistemas nanoestruturados compostos por materiais magnéticos tem se mostrado uma área de grande interesse científico e tecnológico. Materiais magnéticos macios, em especial, tem tido grande importância no desenvolvimento de dispositivos magnéticos. Entre esse tipo de materiais cabe-nos destacar o uso de ligas de Ni e Fe, conhecidas como Permalloy. Neste trabalho apresentamos resultados de medidas de caracterização estrutural e magnética em filmes nanométricos de Permalloy (Ni81Fe19), conhecido por ser um material com alta permeabilidade magnética, baixa coercividade e pequena anisotropia magneto-cristalina, depositado em substratos de MgO(100). A técnica de Magnetron Sputtering foi utilizada na obtenção das amostras com espessuras variando entre 9 – 150nm. As técnicas de Difratometria de Raios-X em alto e baixo ângulo foram empregadas para confirmar a orientação cristalográfica e espessura dos filmes. Com o intuito de investigar as propriedades magnéticas dos filmes foram usadas as técnicas de Magnetometria de Amostra Vibrante (VSM), Ressonância Ferromagnética Eletrônica (FMR) e Magnetoimpedância. As curvas de magnetização revelaram a presença de anisotropia para os filmes de Py/MgO(100), de onde verificou-se a ocorrência de três eixos distintos – um eixo-fácil para θH=0°, um eixo-duro para θH=45° e um eixo intermediário para θH=90°. Os resultados obtidos das técnicas de FMR e Magnetoimpedância confirmam que há também três eixos distintos, isto é, há uma simetria tipo C2. Propomos então, para esses resultados, a interpretação de que a anisotropia magnética do Py/MgO(100) seja do tipo C2 simples, isto é, uma anisotropia magnética cúbica tipo (110).

11
  • ANA KAROLLINA GOMES DE ARAUJO
  • Deposição de filmes magnéticos por gaiola catódica.

  • Líder : ARTUR DA SILVA CARRICO
  • MIEMBROS DE LA BANCA :
  • ARTUR DA SILVA CARRICO
  • SUZANA NOBREGA DE MEDEIROS
  • VAGNER EUSTÁQUIO DE CARVALHO
  • Data: 25-jul-2014


  • Resumen Espectáculo
  • Filmes de nitreto de ferro, com centenas de nanometros de espessura foram depositados pelo método de deposição/nitretação por Gaiola Catódica utilizando um plasma de N2/H2 sobre um substrato de vidro comum. A estrutura, morfologia da superfície e propriedades magnéticas foram investigadas com o uso de Difratometria de Raio-X (DRX), Microscopia de Força Atômica (MFA) e Magnetômetro de Amostra Vibrante (MAV). A DRX exibe a formação da fase γ’’FeN e mistura de fases ζFe2N + ɛFe3N. A magnetização de saturação e coercividade dos filmes de nitreto de ferro dependem da morfologia, composição, tamanho de grão e temperatura de tratamento. Com o aumento da temperatura de 250 para 350 ºC, a magnetização de saturação e a coercividade na direção paralela à superfície dos filmes também aumentam em proporção relativa. Isto pode ser atribuído aos tamanhos de grãos e às diferentes fases formadas, já que fases ricas em ferro como ɛFe3N surgem com frequência maior em temperaturas de tratamento mais elevadas. Neste estudo foi possível a deposição de filmes de boa adesão e boas propriedades magnéticas com grande aplicação em dispositivos magnéticos por um método novo e de baixo custo.

     

     

12
  • ED EK SOARES SILVA
  • Avaliando a distribuição de massa e a ocorrência de exoplanetas Jovianos nas estrelas subgigantes.

  • Líder : JOSE DIAS DO NASCIMENTO JUNIOR
  • MIEMBROS DE LA BANCA :
  • JOSE DIAS DO NASCIMENTO JUNIOR
  • MATTHIEU SEBASTIEN CASTRO
  • EDER MARTIOLI
  • Data: 12-sep-2014


  • Resumen Espectáculo
  • O estudo dos planetas extra solares tem sido um grande esforço da astronomia moderna. A velocidade radial é um dos métodos mais eficientes e por intermédio deste método foram descobertos muitos exoplanetas em torno de estrelas com uma distribuição de massa concentrada principalmente entre 0,7 e 1,3 massas solares (California and Carnegie Planet Search - CCPS; Valenti & Fischer 2005). Entre 2004 e 2010 Johnson et al. (2013) apresenta uma realidade diferente e a distribuição de massa das estrelas hospedeiras de exoplanetas mostra uma frequência acima do intevalo do resultado anterior, além de uma correlação entre a massa estelar e a ocorrência de planetas Jovianos. A divergência das massa das estrelas subgigantes levanta a possibilidade de que as medidas da massa das subgigantes tenham sido superestimadas, causando um erro sistemático. No presente estudo, analisamos este problema a partir do uso de um modelo de síntese populacional estelar. Este modelo reproduz a distribuição de estrelas em todo o céu e gera a distribuição sintética das massas estelares, que por sua vez pode ser comparada com as massas produzidas pelos estudos anteriores para as subgigantes com exoplanetas. Nossa análise resulta no entendimento que esta discrepância é proveniente de um efeitos de seleção na amostra e isto apresenta um impacto na determinação da ocorrência de exoplanetas Jovianos em torno das estrelas subgigantes.

Tesis
1
  • PEDRO DA CUNHA FERREIRA
  • "Estudo da Interação no Setor Escuro Através do Parâmetro de Hubble",

  • Líder : JOEL CAMARA DE CARVALHO FILHO
  • MIEMBROS DE LA BANCA :
  • JAILSON SOUZA DE ALCANIZ
  • JANILO SANTOS
  • JOEL CAMARA DE CARVALHO FILHO
  • JOSE ADEMIR SALES DE LIMA
  • NILZA PIRES
  • Data: 13-feb-2014


  • Resumen Espectáculo
  • Uma abordagem possível para o problema da coincidência cosmológica é permitir que a matéria escura e a energia escura interajam uma com a outra também de forma não gravitacional. Nesta tese são consideradas duas classes gerais para tal interação, caracterizadas por um parâmetro de interação constante ( e ), e a sua capacidade de solucionar o problema da coincidência é avaliada. Em seguida, é determinada a precisão média necessária para distinguir modelos cosmológicos com interação do modelo padrão CDM a partir de dados da taxa de expansão cósmica . Esta análise é realizada em dois níveis: por meio de simulações de Monte Carlo baseadas em modelos com interação, em que amostras de  com diferentes precisões são geradas, e através de um método semi-analítico que calcula a propagação de erros dos parâmetros  e  em função do erro em . Mostra-se que a abordagem semi-analítica concorda com as simulações e que para detectar uma interação usando somente dados de  estes devem atingir uma precisão melhor do que 1% se o parâmetro  for da ordem daquele indicado pelas determinações mais recentes (). Isso significa que, dentre os projetos observacionais planejados/futuros, o Wide Field Infrared Survey Telescope tem a melhor chance de detectar uma interação, embora a um nível de significância baixo. Para determinar de forma mais segura a existência de uma interação seria preciso combinar os dados da expansão com outros observáveis.

2
  • MARIA LIDUINA DAS CHAGAS
  • Rotação Diferencial em Estrelas do Tipo Solar.

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • JOSE RENAN DE MEDEIROS
  • BRUNO LEONARDO CANTO MARTINS
  • DANIEL BRITO DE FREITAS
  • ADRIANA BENETTI MARQUES VALIO
  • EDUARDO JANOT PACHECO
  • Data: 07-abr-2014


  • Resumen Espectáculo
  •      A rotação diferencial superficial é um importante parâmetro para a compreensão do dínamo hidromagnético estelar, instabilidades e processos de transportes no interior estelar, bem como fornece subsídios para um melhor tratamento das marés em binárias próximas e sistemas estrela-planeta. As missões espaciais MOST, CoRoT e Kepler têm fornecido uma grande e homogênea quantidade de dados. O que permite, pela primeira vez, o estudo da rotação diferencial em amostras estatisticamente robustas cobrindo quase todos os estágios da evolução estelar. Nesta tese, nós desenvolvemos e apresentamos um método para medir o limite inferior para a amplitude da rotação diferencial a partir de séries fotométricas igualmente espaçadas, tais como aquelas obtidas pelas missões espaciais supracitadas. O modelo foi concebido para ser aplicado em estrelas do tipo solar cuja modulação ótica é dominada pelo efeito das manchas estelares. As estrelas são selecionadas a partir de uma auto-correlação das séries temporais, o que permite uma determinação precisa dos períodos de rotação das manchas. Um modelo simples de mancha é aplicado juntamente com critérios de informação bayesiana para selecionar, preliminarmente, os intervalos das séries temporais que mostram evidências de rotação diferencial com manchas de área quase constante. A significância da rotação diferencial detectada e as medidas de sua amplitude e incertezas são obtidas por análise a posteriori bayesiana, em uma aproximação Monte Carlo via cadeias de Markov (MCMC). Aplicamos nosso método para o Sol e outras oito estrelas para as quais a modelagem de manchas foi anteriormente realizada. Obtivemos então a rotação diferencial e comparamos os resultados obtidos pelo nosso método com aqueles já conhecidos na literatura. Entre os principais resultados deste trabalho, encontramos que auto-correlação é um método simples e eficaz para seleção de estrelas com um sinal rotacional coerente, pré-requisito para uma medida de rotação diferencial por meio de modelagem de manchas. Para uma análise adequada de MCMC é necessário levar em consideração a forte correlação entre diferentes parâmetros existentes na modelagem de manchas. Para a estrela hospedeira de planeta Kepler-30, encontramos um baixo limite para uma amplitude relativa de rotação diferencial. Também, confirmamos ainda que o nosso modelo não é adequado para medir a rotação diferencial do Sol como uma estrela, na banda ótica, devido à rápida evolução de suas regiões fotosféricas ativas. Em geral, o nosso modelo funciona bem em comparação com os mais sofisticados procedimentos até agora utilizados no estudo da rotação diferencial estelar.

3
  • RÍZIA RODRIGUES DA SILVA
  • Rotação e processos de acreção e coalescência em sistemas planetários e sistemas binários.

  • Líder : JOSE RENAN DE MEDEIROS
  • MIEMBROS DE LA BANCA :
  • ANTONIO CARLOS DA SILVA MIRANDA
  • BRUNO LEONARDO CANTO MARTINS
  • CARLOS ALBERTO TORRES
  • DANIEL BRITO DE FREITAS
  • JOSE RENAN DE MEDEIROS
  • Data: 08-abr-2014


  • Resumen Espectáculo
  • Resumo

     

     

     

    A descoberta de estrelas gigantes nas regiões espectrais G e K, apresentando rotação de moderada a rápida e um comportamento simples, ou seja com velocidade radial constante, representa hoje um importante tópico de estudos em Astrofísica Estelar. Na realidade, tal rotação anômala viola claramente as predições teóricas sobre a evolução da rotação estelar, uma vez que em estágios avançados da evolução espera-se que as estrelas simples apresentem essencialmente baixos valores de rotação, devido à própria expansão evolucionária. Tal propriedade é bem estabelecida do ponto de vista observacional, com diferentes estudos mostrando que para as estrelas gigantes simples de tipos espectrais G e K os valores da rotação são tipicamente menores do que 5kms-1. Esta Tese busca uma contribuição efetiva para a solução do paradigma acima descrito, tendo como objetivo a busca por estrelas simples de tipos espectrais G e K com rotação anômala, ou seja rotação de moderada a rápida, em outras classes de luminosidade. Neste contexto, analisamos uma amostra composta por 2010 estrelas aparentemente simples, de classes de luminosidade IV, III, II e Ib, com tipos espectrais G e K, com medidas de velocidade de rotação projetada v sin i e velocidade radial obtidas a partir de observações realizadas pelo espectrômetro CORAVEL. Como primeiro resultado de impacto descobrimos a presença de rotações anômalas também em estrelas subgigantes, gigantes brilhantes e supergigantes, ou seja estrelas de classes de luminosidade IV, II e Ib, em contraste com estudos anteriores que haviam reportado rotações anômalas apenas entre as gigantes clássicas de classe de luminosidade III. Tal aspecto se reveste de grande relevância, pois nos permite analisar a presença de rotações anômalas em diferentes intervalos de massa estelar, uma vez que as classes de luminosidade aqui consideradas cobrem um intervalo em massa compreendido entre 0,80 e 20Msolar, aproximadamente. No total, foram descobertas 1 subgigante, 11 gigantes, 3 gigantes brilhantes e 6 supergigantes Ib, nas regiões espectrais G e K, apresentando valores de v sin i≥10kms-1 e comportamento simples. Este total de 21 estrelas corresponde a uma frequência de 1,04% de estrelas evoluídas simples com rotações anômalas, entre as estrelas G e K das referidas classes de luminosidades, listadas no Bright Star Catalog, que é completo até magnitude visual 6.3.

    Face a estas novas descobertas, com base em uma amostra completa em magnitude visual, como aquela do Bright Star Catalog, realizamos uma análise estatística comparativa usando o teste Kolmogorov- Smirnov, de onde concluímos que as distribuições  da velocidade rotacional, v sin i, para estrelas com rotações anômalas nas classes de luminosidade III e II, são similares às distribuições de v sin i para sistemas binários espectroscópicos com componentes evoluídas do mesmo tipo espectral e classe de luminosidade. Tal resultado indica que o processo de coalescência entre estrelas de um sistema binário pode ser um possível mecanismo para explicar o excesso de rotação observado em estrelas anômalas, pelo menos entre as gigantes e gigantes brilhantes, onde o excesso de rotação estaria associado à transferência de momentum angular para a estrela resultante da fusão. Outro resultado relevante da presente Tese, diz respeito ao comportamento do fluxo de emissão em infravermelho na maioria das estrelas com rotação anômala aqui estudadas, onde 12 estrelas da amostra tendem a apresentar um excesso no IR, quando comparadas com estrelas simples com baixas rotações, dentro da respectiva classe de luminosidade. Tal propriedade representa um vínculo adicional na busca dos mecanismos físicos responsáveis pela rotação anômala observada, uma vez que estudos teóricos recentes mostram que a acreção de objetos de massa sub-estelar, tal como planetas gigantes e anãs marrons, por uma estrela pode elevar significativamente a rotação da estrela acretora e produzir um disco de poeira em torno desta. Este último resultado parece apontar nessa direção, uma vez que não é esperado que discos de poeira surgidos durante o estágio de formação estelar possam sobreviver até os estágios da subgigantes, gigantes e supergigantes Ib. Em síntese, nesta Tese, além da descoberta de estrelas simples G e K com rotações anomalamente elevadas em relação àquilo previsto pela teoria de evolução estelar, nas classes de luminosidade IV, II e Ib, apresentamos também a frequência dessas estrelas numa amostra completa até pelo menos magnitude visual 6.3. Apresentamos, ainda, sólidas evidências de que processos de coalescência em sistemas binários estelares e processos de acreção de anãs marrons ou planetas gigantes por estrelas podem atuar como mecanismos responsáveis pelo referido fenômeno de rotações anômalas em estrelas simples evoluídas.

     

4
  • HEYDSON HENRIQUE BRITO DA SILVA
  • SETOR ESCURO DO UNIVERSO: UMA ANÁLISE TERMODINÂMICA

  • Líder : RAIMUNDO SILVA JUNIOR
  • MIEMBROS DE LA BANCA :
  • FRANCISCO DE ASSIS DE BRITO
  • JAILSON SOUZA DE ALCANIZ
  • JANILO SANTOS
  • MADRAS VISWANATHAN GANDHI MOHAN
  • RAIMUNDO SILVA JUNIOR
  • Data: 16-abr-2014


  • Resumen Espectáculo
  •  

     

    O setor escuro é um dos grandes mistérios da cosmologia moderna e a compreensão da sua natureza deve introduzir novas concepç&o