Dissertations/Thesis

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2024
Dissertations
1
  • RANULFO DA SILVA DIAS
  • Advances in the treatment of Glioblastoma Multiforme via Tumor Treating Fields: development of an optimized simulation database using SimNIBS

  • Advisor : ALAN BENDASOLI PAVAN
  • COMMITTEE MEMBERS :
  • ADHIMAR FLAVIO OLIVEIRA
  • ALAN BENDASOLI PAVAN
  • MÁRIO VICENTE CAMPOS GUIMARÃES
  • RENATA FERRANTI LEONI
  • Data: Feb 8, 2024


  • Show Abstract
  • The Glioblastoma Multiforme (GBM) is an aggressive brain cancer with a low survival rate. Non-invasive brain stimulation is a promising approach for treating GBM, but there is still much to be learned about its effectiveness and safety.

    Based on research from the early 2000s on the application of electromagnetic fields in the treatment of GBM, this dissertation proposes the development of an optimized database of simulations using SimNIBS. SimNIBS was designed to simulate electrical stimulation in the brain and can generate simulations using code in the Python language.

    The research explored the effectiveness of Transcranial Electrical Direct Current Stimulation (tDCS) and Alternating Current Stimulation (tACS), the latter focused on the treatment of GBM. The results highlight the influence of electrode configuration on the distribution of electrical stimulation and the penetration of the electric field into brain tissue. The data obtained indicates the need for adjustments in the current applied in tDCS and recommends specific electrode configurations to optimize GBM treatment.

    Ultimately, this analysis is expected to contribute to a better understanding of neuromodulation in the context of GBM. The results suggest that tACS may be an effective option for treating GBM, but additional research is needed to validate the results and determine the long-term safety of the therapy.

2
  • Ricardo Alexandre Fernandes Filho
  • Modified Theories of Gravity: The Horndeski Models

  • Advisor : EDUARDO HENRIQUE SILVA BITTENCOURT
  • COMMITTEE MEMBERS :
  • EDUARDO HENRIQUE SILVA BITTENCOURT
  • FRANCESCO BAJARDI
  • SALVATORE CAPOZZIELLO
  • VITORIO ALBERTO DE LORENCI
  • Data: Feb 16, 2024


  • Show Abstract
  • In this thesis, a qualitative analysis is proposed on how theories related to gravity have
    changed over time until reaching the well-known modified theories of gravitation, demon-
    strating the power they hold. The aim is to serve as an entry point to the subject and
    provide a basis for more complex works in the future. Starting with the understanding of
    gravity and progressing to Albert Einstein’s groundbreaking theory of General Relativity,
    which explained some aspects not addressed by Newtonian theory but still left unexplained
    observations on large scales. After Einstein, efforts have been mostly focused on construct-
    ing extensions of General Relativity, paving the way for the well-known modified theories
    of gravitation. These theories manifest in various forms in the literature, but here the
    focus will be on those constructed by the inclusion of a scalar field into the theory, giving
    rise to the so called scalar-tensor theories. Among the modified scalar-tensor theories, the
    discussion will be restricted to those that preserve second-order equations of motion, with
    the most general known as the Horndeski theory, which will be the main theory addressed
    here. After dissecting the Horndeski theory, we analyze its equations of motion and apply
    the latter to certain cases of interest. The general aspect of the Horndeski theory will
    also be exploited to derive, from it, already known theories, such as Brans-Dicke, Cubic
    Galileon, and 𝑓 (𝑅) models. The final part of the work will be dedicated to delving into
    quantum cosmology using the Horndeski theory.

3
  • Thales Willian Cruz
  • Analog models for light propagation in nonlinear theories of electromagnetism

  • Advisor : VITORIO ALBERTO DE LORENCI
  • COMMITTEE MEMBERS :
  • ANNIBAL DIAS DE FIGUEIREDO NETO
  • CAIO CESAR HOLANDA RIBEIRO
  • EDUARDO HENRIQUE SILVA BITTENCOURT
  • VITORIO ALBERTO DE LORENCI
  • Data: Mar 8, 2024


  • Show Abstract
  • This work aims at studying analogous models for the propagation of light in nonlinear theories of electromagnetism. To do this, we first calculate the equations of motion and the momentum-energy tensor of an arbitrary theory dependent on the two electromagnetism invariants, F and G, in both tensorial and vector formalisms. Then, we demonstrate, through two different methods, how to obtain the dispersion relation of electromagnetic waves for these theories. We also calculate the phase velocity, group velocity and refractive index for such theories. We apply the results to the Born-Infeld and Euler-Heisenberg theories. Additionally, we find the phase velocity of a wave in a material medium exhibiting Pockels and Kerr effects. We then propose a formal analogy between the effective metric of the nonlinear theory and the effective metric of the material medium. Furthermore, we show that we can obtain the same analogous result by relating the change in the value of the refractive index due to the presence of electromagnetic fields in both nonlinear theories with the change in the refractive index in the material medium due to the presence of electromagnetic fields. Finally, we apply the obtained results in the construction of analogous models based on Germanium and Silicon.

2023
Dissertations
1
  • LUIS FERNANDO TEMOCHE HURTADO
  • Asymptotic symmetries and infrared phenomena in gauge theories and gravity

  • Advisor : ALEXIS ROA AGUIRRE
  • COMMITTEE MEMBERS :
  • ALEXIS ROA AGUIRRE
  • BRUCE LEHMANN SÁNCHEZ VEGA
  • EDUARDO HENRIQUE SILVA BITTENCOURT
  • Data: Feb 23, 2023


  • Show Abstract
  • The objective of the following dissertation is to present the existent connection in the infrared regime behavior of both gauge theories and gravity. The first element in this picture analysis is the study of soft theorems, originally developed by Weinberg [1][2]. In a general sense, scattering processes are governed through constraints that control the way soft particles are produced. The second one shall be the asymptotic spacetime symmetries developed by Bondi, van der Burg, Metzner and Sachs [3] [4] of asymptotically flat spacetimes. They lead to the appearance of conserved charges associated to the behavior of the fields at null infinities. The third but not least, the existence of memory effects, like the ones studied by Christodolou [5][6] and Thorne [7] in the infrared limit. Again, in simple terms, they refer to the surgence of perturbations in the fabric of spacetime due to its propagation, leading to field shifts. We explore the connection in terms of the application of Fourier transforms and Ward identities. For simplicity we focus on the case of Quantum Electrodynamics and Quantum Gravity.

2
  • ADALBERTO RAFAEL DA CUNHA SILVA
  • Revisiting the Abundance Gradient Milky Way disk

  • Advisor : OSCAR CAVICHIA DE MORAES
  • COMMITTEE MEMBERS :
  • HEKTOR STHENOS ALVES MONTEIRO
  • MAXIMILIANO LUIS FAUNDEZ ABANS
  • OSCAR CAVICHIA DE MORAES
  • Data: Jun 16, 2023


  • Show Abstract
  • Planetary nebulae have been used extensively to study the chemical evolution of the Milky Way. They are originated by stars of medium and low mass (0.8~M⊙ to 8~M⊙) that have their outermost layers ejected, and the ejected material continues to be ionized by the white dwarf. There are countless works where the radial gradients of chemical abundances of the Milky Way were obtained from the NPs. Some works report that the oxygen gradient has deviations from a simple linear fit, but this gradient discontinuity is not a consensus in the literature. This apparent disagreement stems from the uncertainties involved in determining key quantities to obtain the gradient: chemical abundances and distances. In this work, we have a sample of 347 PNs with known chemical abundances, used for the construction of the radial abundance gradient of the Milky Way disk, from galactocentric distances obtained from the Gaia mission and statistical methods, where a physical property , like the diameter for example, is used to obtain the distances of the NPs, allowing a more accurate obtainment of the radial gradient of abundances of the Milky Way disk.

3
  • WALISON YAN APARECIDO DA SILVA
  • COUPLING FOR THE SCALAR FIELD OF TYPE CURRENT ALONG A BORDER

  • Advisor : FABRICIO AUGUSTO BARONE RANGEL
  • COMMITTEE MEMBERS :
  • FABRICIO AUGUSTO BARONE RANGEL
  • GABRIEL FLORES HIDALGO
  • HELDER LUIZ DE OLIVEIRA
  • LUIZ HENRIQUE DE CAMPOS BORGES
  • Data: Jun 30, 2023


  • Show Abstract
  • In this Dissertation we initially make a brief study on the complex scalar field under the action of an external potential of the Dirac delta type concentrated along a plane. We consider the complex field with mass and make an approach with the structured field in its matrix form. For this case, we obtain Green's function and the interaction between the potential and a source for the field, which plays the role of what would become a charge in electromagnetism. The obtained results are not original, but they serve to introduce the reader to the study of fields under the action of external potentials of the Dirac delta type (main subject of the Dissertation) and the approach of the complex scalar field in its matrix form. This approach is used in the rest of the work. Later we present a study on the complex scalar field interacting with an external potential, in a current-type coupling. We study the interaction that arises between the potential and stationary point sources for the scalar field. These are original results, as far as we know, and they present very interesting characteristics, not yet observed in any other model of the type in the literature. One of the reasons for this stems from the fact that the considered coupling is not isotropic, with a distinction between the two sides of the plane where the potential is concentrated. In addition to the description of condensed matter systems, where scalar field models are often used, we believe that the results obtained may also be useful in the study of MIT-type models for bosonic fields, where not the field but its associated current is confined. Some aspects of the model still need to be explored. We hope soon to obtain additional results from those presented in this text and present them all in the form of a scientific article to be submitted for publication.

4
  • MARCOS PAULO CYRILLO DA SILVA
  • Deposition and characterization of thin films of TiO2 doped with Ag via the sol-gel method

  • Advisor : DANILO ROQUE HUANCA
  • COMMITTEE MEMBERS :
  • ADHIMAR FLAVIO OLIVEIRA
  • DANILO ROQUE HUANCA
  • SUELEN DE CASTRO
  • WAGNER SOUZA MACHADO
  • Data: Jul 3, 2023


  • Show Abstract
  • Titanium dioxide (TiO2) is a highly investigated semiconductor material renowned for its exceptional optical and catalytic properties, making it an ideal candidate for various applications, including sensors, antibacterial coatings, and photovoltaic cells. In this study, it was investigated the effect of silver (Ag) doping on the optical and electrical characteristics of thin film layers composed of TiO2 deposited on glass, indium tin oxide (ITO), as well as p-type and n-type crystalline silicon substrates. This doping process led to the formation of heterostructures exhibiting electrical behavior like the junction diodes, with the specific characteristics strongly dependent on the concentration of Ag used as a dopant. The deposition of these films was accomplished through the reverse micelle sol-gel method. For this purpose, a solution was prepared by combining titanium tetrabutoxide, xylene, and Triton X-100. To introduce Ag as a dopant, silver nitrate (AgNO3) was incorporated into the solution at concentrations of 0.1%, 0.5%, and 1%. The optical analysis of the TiO2 sol-gel solution through absorbance measurements in the ultraviolet (UV) region, it was observed that the inclusion of Ag resulted in a decrease in the material's band gap. The band gap values ranged from (3.4 ± 0.2) to (1.88 ± 0.02) eV, indicating a significant reduction caused by the presence of Ag. Additionally, the inclusion of Ag facilitated the formation of silver nanoparticles within the films. These nanoparticles exhibited an effective diameter ranging from 30 to 34 nm, and their concentration varied from 0.44x10^12 to 1.33x10^12 particles/ml insofar the concentration of AgNO3 increased from 0% to 1.0%, respectively. Prior to the deposition of the films, thorough substrate preparation was conducted. The substrates underwent a cleaning process involving an aqueous solution of sulfuric acid, followed by a brief immersion in hydrofluoric acid. In the case of silicon substrates, an ammonium-based aqueous solution was employed to eliminate organic contaminants. Subsequently, the silicon substrates were subjected to thermal oxidation at 900 ºC. The deposited films underwent a similar treatment, with sintering temperatures set at 450 ºC and 550 ºC. The optical characterization of these films, conducted through UV absorbance measurements, revealed variations in the optical band gap depending on the type of transition. For an indirect transition, the band gap ranged from 2.8 to 3.6 eV, while for a direct transition, it fell between 3.5 and 3.9 eV. Notably, the size of the nanoparticles displayed a similar trend to that observed in the sol-gel solution. Furthermore, the size variation of nanoparticles influenced the band gap in a manner consistent with the aforementioned observations. Chemical analysis utilizing techniques such as infrared spectrometry (FTIR), X-ray diffraction (XRD), and X-ray energy dispersion spectroscopy (EDS) was performed to examine the films following sintering. The results indicated that the films primarily consisted of the anatase phase. Morphological characterization further revealed the formation of films with an average thickness of 1 µm, along with particles measuring up to 10 µm in size, in addition to the nanometric-sized particles of the sol-gel solution of TiO2. On the other side, the electrical characterization results revealed interesting findings regarding the impact of silver doping on the properties of the TiO2 matrix. When silver is introduced as a dopant, it supplies electrons to the TiO2 matrix. In the case of n-type silicon substrate, it enhances conductivity and reduces electrical resistance. Conversely, an opposite behavior is observed for the ITO substrate. However, a distinct behavior is observed in the heterostructures formed by TiO2/p-type silicon. In this case, the introduction of silver causes the recombination of electrons provided by silver with holes in the p-type silicon, resulting in an opposite effect. As a result, the electrical resistance increases in the TiO2/p-type silicon heterostructures. The doping-induced changes are further elucidated by Mott-Schottky analysis. Consistent with our previous observations, the concentration of electrons in the TiO2/n-type silicon junction increases due to doping, while it decreases when the substrate is p-type silicon. This behavior is captured by the Mott-Schottky analysis, which provides valuable insights into the changes in electron concentration at the junction interfaces. Lastly, regardless of the substrate used for TiO2 deposition, the presence of silver as a dopant leads to an increase in the height of the Schottky barrier associated with the junctions of the device, indicating a significant influence on the overall electronic properties.

5
  • NEIL LIZANDER GOYZUETA PALOMINO
  • Analysis of the characteristics of the evolution of matter fields in symmetrically spherical spacetimes

  • Advisor : ALAN BENDASOLI PAVAN
  • COMMITTEE MEMBERS :
  • JEFERSON DE OLIVEIRA
  • ALAN BENDASOLI PAVAN
  • CARLOS MOLINA MENDES
  • RODRIGO SILVA LIMA
  • Data: Aug 28, 2023


  • Show Abstract
  • The main properties of the dynamics of matter fields in spherically symmetric spacetimes have been analyzed in this work,to do this, we take into account the metric for the different space-times, which will be encoded in the line element (space-time interval). Special attention was paid to the scalar field evolving around of black holes spacetimes. Some features of test field evolution, such as tortoise coordinate, effective potential, physical boundary conditions and oscillation modes were explored and discussed considering the asymptotic behavior of spacetimes being (AdS, Minkowski, dS). The normal and quasinormal frequencies of oscillation of the scalar field were calculated exactly for AdS, dS, Minkowski and BTZ black hole spacetimes, for which we use special functions that are solutions of known differential equations (Bessel, Hypergeometric). We also numerically calculate the quasinormal modes for the Schwarzschild and Schwarzschild-AdS spacetimes, using the spectral methods of series solutions (Frobenius and Bernstein).

2022
Dissertations
1
  • ALAN DE GOIS CESAR
  • Analysis of a gravitational collapse in a closed universe model dominated by a scalar field

  • Advisor : EDUARDO HENRIQUE SILVA BITTENCOURT
  • COMMITTEE MEMBERS :
  • EDUARDO HENRIQUE SILVA BITTENCOURT
  • GRASIELE BATISTA DOS SANTOS
  • JONAS PEDRO PEREIRA
  • MARIO NOVELLO
  • VITORIO ALBERTO DE LORENCI
  • Data: Mar 3, 2022


  • Show Abstract
  • A gravitational collapse model is constructed by analyzing the evolution of a hypersurface that separates two regions of a manifold. A Vaidya type metric is used for the exterior region and for the interior region the Friedmann-Lemaître-Robertson-Walker (FLRW) type of metric is taken, which are glued using the Darmois matching conditions. Initially, the source of the curvature in the interior region is a scalar field non-minimally coupled to the geometry, in such a way to produce a bouncing model that does not violate the null energy condition, however it is obtained that this condition limits the model to the minimun coupling situation. With this aim, it is made a power series approximation of the system of equations formed by the Einstein field equations and the equation of the scalar field close to the bounce. The results obtained for the coefficients and the validity of the approximation itself reinforce the need for a positive spatial tri-curvature, whose value is defined in the validity intervals obtained during the analysis of the parameters. Initial conditions that characterize the collapse are also determined and conditions that allow the identification of its final stage are studied, which may in the emission of the entirety of the object mass as eletromagnetic radiation, that is, an evaporation, It is also possible to obtain a singular model or even a bounce of the object itself.

2
  • ISABELA FRANCO COSTA
  • Shubnikov-de Haas oscillations in nanostructures based in narrow gap semiconductors

  • Advisor : MARCELOS LIMA PERES
  • COMMITTEE MEMBERS :
  • ADHIMAR FLAVIO OLIVEIRA
  • MARCELOS LIMA PERES
  • VALMIR ANTONIO CHITTA
  • Data: Apr 5, 2022


  • Show Abstract
  • In this work, magneto transport properties were investigated in quantum well structures of PbTe, doped with BaF2, and a heterostructure of SnTe/Sn(1-x)EuxTe. Both structures were grown by the molecular beam epitaxy (MBE) technique by the Associated Laboratory of Sensors and Materials of the National Institute for Space Research - LAS/INPE in the city of São José dos Campos (SP), in order to develop semiconductors with high crystallinity. These structures are p-type and have thicknesses given by 10 nm of the well and 5 μm of the film. The measurements performed considered two lighting conditions, with infrared light (IR) (940 nm wavelength) and dark, for temperatures ranging from 300 K to 1.9 K and with an applied magnetic field of up to 9 T perpendicular to the surface. In the discussions of the magnetoresistance curves, the oscillatory components of the Shubnikov-de Haas effect were analyzed in order to identify the origin of the beating pattern, considering the occurrence of the Rashba effect due to spin-orbit interactions and symmetry properties of the system. For this purpose, effective masses, concentration and electron mobility of carriers were calculated, in addition to Landé's 𝑔-factors, to investigate anisotropy of the system. In the analysis of the magneto transport measurements for the PbTe:BaF2 quantum well, the transport by multivalleys was confirmed, that is, with a contribution to the electronic transport through the longitudinal and oblique valleys of the Fermi surface, through the calculation of the confinement energies of the valleys inside from the well. While for the heterostructure the transport occurred only through the longitudinal valley. For these samples, the effects that contributed to the generation of oscillatory components of the Shubnikov-de Haas effect were also verified. In this case, for PbTe:BaF2 the calculation of the Rashba energy of 8.4 𝑚𝑒𝑉 explained longitudinal valley splitting and the occurrence of frequencies 𝛼 and 𝛽. For the heterostructure, this Rashba splitting energy corresponded to a small value of 0.17 𝑚𝑒𝑉, calculated from values of frequencies of Shubnikov-de Haas oscillations extracted from the Lifshitz-Kosevich (LK) fit. From this same fit, transport by bulk states in the heterostructure was confirmed, although SnTe is a crystalline topological insulator and in the theory of topological insulators, transport by surface states (TSS) is expected.

3
  • CARLA RIBEIRO RODRIGUES DA ROCHA
  • Compton Scattering in the QED with break of Lorentz Symmetry

  • Advisor : GABRIEL FLORES HIDALGO
  • COMMITTEE MEMBERS :
  • ALEXIS ROA AGUIRRE
  • GABRIEL FLORES HIDALGO
  • RODOLFO ALVAN CASANA SIFUENTES
  • Data: Jun 30, 2022


  • Show Abstract
  • After a review of Quantum Electrodynamics and the calculation in detail of the cross section associated with the Compton scattering effect, in this dissertation, we present the calculations of the Compton scattering cross section in a Quantum Electrodynamics model with a term that breaks Lorentz symmetry. In the model under study, we consider a Lorentz symmetry violation term that modifies the vertex of the theory leaving the propagators unchanged.

4
  • ANDERSON SILVA DE ALMEIDA
  • Mass determination of open clusters utilizing data from the EDR3 catalogue

  • Advisor : HEKTOR STHENOS ALVES MONTEIRO
  • COMMITTEE MEMBERS :
  • JACQUES RAYMOND DANIEL LEPINE
  • HEKTOR STHENOS ALVES MONTEIRO
  • OSCAR CAVICHIA DE MORAES
  • Data: Jul 29, 2022


  • Show Abstract
  • With the publication of the Gaia catalogue, and with the existence of automated isochrone fitting methods, the study of open clusters has undergone major advances in recent years. Its fundamental parameters have been, consequently, getting estimated in a larger scale and with better precision. However, important parameters such as the total masses of these objects, the details about populations of individual stars and of binary stars, and the existence of mass segregation are not adequately studied. Within this context, in this work we introduce a new method to determinate individual masses, including of binary stars. This method allows us to study the total mass of open clusters, as well as to study details of binary populations through their mass functions. To validate the method and its efficiency, we used synthetic clusters with predetermined parameters. With the validated method, we applied the procedure to clusters from a recent catalogue of fundamental parameters by our group, obtained from GAIA Early Data Release 3 (EDR 3). The main results include the obtaining of the detailed mass function for the populations of individual, primary, and secondary stars, in addition to the total masses for 895 clusters. We also show the relation between the total masses and other fundamental parameters, discussing its dynamic implications.

5
  • LUCAS TOBIAS DE PAULA
  • Analogue models of classical and semiclassical gravity

  • Advisor : VITORIO ALBERTO DE LORENCI
  • COMMITTEE MEMBERS :
  • ALESSANDRO FABBRI
  • CAIO CESAR HOLANDA RIBEIRO
  • EDUARDO HENRIQUE SILVA BITTENCOURT
  • VITORIO ALBERTO DE LORENCI
  • Data: Aug 2, 2022


  • Show Abstract
  • Formal analogies between gravitational and acoustic or optical phenomena have been a subject of study for over a century, leading to interesting scenarios for testing kinematic aspects of general relativity in terrestrial laboratories. Here, some aspects about analog models of gravity obtained from the description of these two different kind of systems are analysed. First, light propagation in linear magnetoeletric media is examined. In particular, it is shown that this effect produces mixed time-space terms in the effective metric that depend only on the antisymmetric part of the generally non-symmetric magnetoelectric coefficient. Furthermore, the dispersion relation related to the linear effect motivates the analysis of an idealised exact model presenting an analog event horizon. Then, a short discussion comparing different ways of constructing analog models is provided. Subsequently, motivated by the results obtained in the optical context, we make a bibliographic review about those analog models obtained from moving media, establishing an equivalence between the propagation of acoustic perturbations in such a background and the propagation of free scalar fields near a Schwarschild black hole. This last aspect drives us to analyse the particle production in this scenario, a result that was first addressed by Stephen Hawking, which yields to the the description of the so called Hawking radiation. When treating a non-stationary spacetime, particularly those presenting a gravitational collapse, we can extend the description of quantum fields to curved spacetimes by splitting the metric into two asymptotically stationary regions, with that we show that the presence of the horizon is fundamental for the creation of particles. Finally, it is also shown that the thermal distribution of this particle emission is identical to the Planck distribution for bosons, and because of that the Hawking temperature appears to be very small when we consider astrophysical scenarios.

6
  • JACKELYNE LISSET MEDINA VILLANUEVA
  • Porous silicon photonic crystals: Surface passivation and etch-stop effect on the optical response

  • Advisor : DANILO ROQUE HUANCA
  • COMMITTEE MEMBERS :
  • ADHIMAR FLAVIO OLIVEIRA
  • DANILO ROQUE HUANCA
  • ROBERTO SHIGUERU NOBUYASU JUNIOR
  • SEBASTIAO GOMES DOS SANTOS FILHO
  • Data: Dec 16, 2022


  • Show Abstract
  • The aim of this study was to investigate the influence of the etch-stop time on the structural and optical properties of multilayer structures and their passivation to avoid aging effects. Structural analysis by scanning electron microscopy (SEM) and the optical reflectance data fitting procedure have shown that the inclusion of a pause during the growth of the porous matrix promotes the formation of thicker layers (2638 nm, for 10 s of pause), compared with the layer with low porosity without pause (2584 nm). Similar behavior was observed for high porosity layers changing from 4500 to 4780 nm. This trend was also observed for multilayer structures. As for porosity, an opposite behavior was observed, decreasing in about 9.5% and 6.5% with increasing etch stop time for single layers with low and high porosity, respectively. This phenomenon was attributed to the recovery of hydrofluoric acid consumed during pore formation at the electrolyte-silicon interface. To obtain 1D photonic crystals (1D-PC) of porous silicon with optical responses close to those projected, this phenomenon must be taken into account in device development. The fabrication of 1D-PC with a sequence starting with a layer with high porosity and others where the first upper layer has low porosity proves that the increasing effect of thickness and the decrease of porosity does not depend on the stacking order. However, the thermal treatment made in air environment shows significant changes in the optical response after the oxidation at 400°C. Since the oxidation of porous silicon depends on the characteristics of the porous matrix, it is concluded that the etch-stop promotes the formation of high and low porosity layers with different microstructures, so that after thermal annealing at 1000°C in devices with the first upper layer with high porosity, the main photonic band gap (PBG) is destroyed, i.e., the optical thickness of the high and low porosity layers no longer obeys Bragg’s law due to the contraction-expansion effect of the low and high porosity layers. Three different materials were used for surface passivation: thermal silicon oxide (SiO2), gold (Au), and titanium oxide (TiO2). Despite the passivation layer, the presence of these elements resulted in a blue shift of the PBG. However, in the case of the deposited TiO2, some samples showed a red shift, while in others the PBG is not changed. The red shift was associated with the presence of xylene in the sol-gel TiO2 within the pores. Unaltered PBG was associated with the formation of a thin pore-sealing TiO2 sol-gel layer. After thermal treatment, the typical blue shift was observed. Despite the passivation material, fast Fourier infrared spectroscopy (FTIR) reveals the presence of SiO2 in addition to the Au or TiO2 phases. Energy dispersive X-ray spectroscopy analysis (EDS) showed that Au and TiO2 were deposited in a deep concentration gradient, but with a homogeneous distribution along the sample surface. X-ray diffraction (XRD) showed that after thermal treatment at 450°C, the rutile and anatase phases coexist, with the latter predominating. The stability of the optical properties after passivation was confirmed by measurements of the samples after 20 and 36 weeks of storage. No spectral changes were observed in the PBG position.

7
  • JOAQUÍN EDUARDO LLANOS SALAZAR
  • Scalar Fields Gravitational Collapse Analysis

  • Advisor : ALAN BENDASOLI PAVAN
  • COMMITTEE MEMBERS :
  • ALAN BENDASOLI PAVAN
  • BERTHA CUADROS-MELGAR
  • EDUARDO HENRIQUE SILVA BITTENCOURT
  • LEONARDO WERNECK DE AVELLAR
  • Data: Dec 16, 2022


  • Show Abstract
  • One of the posible explanations for the accelerated expansion of the universe is the existence of dark energy. Different mathematical models have been proposed for it, among those models the simplest one uses scalar fields with different effective potentials. A possible model is the phantom scalar field which has an equation of state with negative pressure. Therefore, understanding how the gravitational evolution of that field is dictated is something of interest for Cosmology and Astrophysics. In this work, we analysed the collapse of both the conventional scalar field and the phantom scalar field. The time evolution of the fields was carried out with the SFcollapse1D code, in which it is possible to evaluate black hole formation or dispersion of such fields. The critical value η* for black hole formation from conventional scalar fields was obtained as in the literature, nevertheless, in the case of phantom scalar field only dispertion was obtained. This behavior seems to agree with the fact that the phantom scalar field has an expansive characteristic.

2021
Dissertations
1
  • Edson da Silva Souza
  • Topological Defects in Field Theories

  • Advisor : ALEXIS ROA AGUIRRE
  • COMMITTEE MEMBERS :
  • ALEXIS ROA AGUIRRE
  • DIONISIO BAZEIA FILHO
  • FABRICIO AUGUSTO BARONE RANGEL
  • GABRIEL LUCHINI MARTINS
  • Data: Feb 22, 2021


  • Show Abstract
  • In this work we propose the development of new models of two and three fields coupled scalar real supporting BPS solutions (Bogomolnyi-Prasad-Sommerfield). For this purpose, we will use the recently proposed method, known as the extension method. In particular, we will explicitly construct new models of two and three coupled scalar fields, and also we will study the linear stability of their respective BPS solutions.

2
  • GABRIEL RIBEIRO FERREIRA LOPES
  • Investigation of the photoconductivity effect in SnTe/PbEuTe quantum wells

  • Advisor : MARCELOS LIMA PERES
  • COMMITTEE MEMBERS :
  • ADHIMAR FLAVIO OLIVEIRA
  • HUGO BONETTE DE CARVALHO
  • MARCELOS LIMA PERES
  • SUELEN DE CASTRO
  • Data: Dec 13, 2021


  • Show Abstract
  • In this work, we study the photoconductivity effect in p-type IV-VI semiconductors
    SnTe/Pb0,9Eu0,1Te. The samples were grown using molecular beam epitaxy, resulting
    in high quality 30 nm-wide structures. Photoconductivity measurements are made for
    temperatures below 200 K, with radiation varying from infrared (IR, 940 nm) to ultraviolet
    (UV, 398 nm) wavelengths. A positive photoresponse is observed for temperatures greater
    than 10 K, with persistent photoconductivity when the light is turned off. Analysis of
    the photoconductivity decay curves showed that defect states are present in the energy
    band structure of SnTe, and that different defects are activated, as functions of the
    radiation energy. For temperatures below 10 K, a transition from positive to negative
    photoconductivity is observed when the sample is illuminated by UV light. To explain the
    negative effect, Hall measurements were made in order to obtain the carrier concentration
    and mobility under light and dark conditions, comparing the variation of these parameters
    using UV radiation. With this information, the negative photoconductivity effect is
    explained with a classical transport model that predicts the transition for temperatures
    below 4 K. Magnetoresistance measurements showed that there is no contribution of the
    topological surface states for the electrical transport under illumination. In a second sample, photoconductivity measurements were conducted for lights ranging from IR, through visible to UV, in order to verify the dependence of negative photoconductivity on radiation energy. It was observed that the negative effect indeed manifests only for radiations with energies greater than 2 eV, starting with yellow. This leads to the conclusion that the negative photoconductivity is originated from the energy bands above 2 eV.

2020
Dissertations
1
  • Rosimara Passos Toledo
  • Physical properties of porous silicon layers with Erbium-doped in PANI deposition.

  • Advisor : ADHIMAR FLAVIO OLIVEIRA
  • COMMITTEE MEMBERS :
  • ADHIMAR FLAVIO OLIVEIRA
  • DANILO ROQUE HUANCA
  • MARIA ELENA LEYVA GONZALEZ
  • SEBASTIAO GOMES DOS SANTOS FILHO
  • Data: Feb 17, 2020


  • Show Abstract
  • P-type silicon was used for the formation of macroporous silicon (MPS) by electrochemical corrosion in HF: DMF solution, 1: 9 in volume. Then, these structures were passivated by depositing a polyaniline layer (PANI) using the cyclic voltammetry method, a method that was also used for doping the PANI layer with small concentrations of erbium (Er), in millimolar order (mM). The structural analysis by scanning electron microscopy (SEM) showed that the pores are formed randomly throughout the porous region, with a diameter varying between 0.3 and 1.3 𝜇m. The Spectrometry analysis X-rays by energy dispersion (EDS) reveals that the PANI was deposited along the pore walls, with a higher concentration in the regions closest to the surface of the porous layer. Rutherford backscattering spectrometry (RBS) shows that Er has been diffusing through the PANI layer, but with greater concentration at the superficial region. These two techniques showed the presence of oxygen that is associated with the formation of silicon oxide (SiO2), confirmed using Fourier-transform infrared spectroscopy (FTIR), where the presence of functional groups associated with O-Si-O bonds. In samples doped with Er, both FTIR and Raman spectroscopy showed that Er creates additional functional groups that, according to X-ray diffraction (XRD), reduce the crystallinity of PANI and with that decrease the conductivity. The electrical characterization confirms, not only the decrease in the conductivity of the PANI but also the decrease in the current that passes through the MPS/PANI junction, this is associated with the increase in the amount of SiO2 within the porous structure. This effect was partially recovered by the inclusion of Er, possibly due to its effect of reducing the width of the space charge region, as well as the effect of Er present in the MPS/PANI interface through the modification of the work function or the increase of surface states. This effect was confirmed by the reflectance in the UV-VIS region, which shows a decrease in indirect transfer energy.

2
  • Everson Henrique Rodrigues
  • Lee-Wick field in presence of semi-transparent boundaries

  • Advisor : FABRICIO AUGUSTO BARONE RANGEL
  • COMMITTEE MEMBERS :
  • ALEXIS ROA AGUIRRE
  • ANDERSON ANTUNES NOGUEIRA
  • FABRICIO AUGUSTO BARONE RANGEL
  • LUIZ HENRIQUE DE CAMPOS BORGES
  • Data: Feb 19, 2020


  • Show Abstract
  • In this study, we do a review about the Lee-Wick vetorial field, where is showed that if there is an interaction between point-like charge and a perfectly conductive plane plate. It is shown that interaction propagator can not be obtained by a simple sum of propagators for Proca and Maxwell fields. We analyze for the scalar field, achieving analytically the propagator and numerically the energy and force. It is analyzed the interaction between charge and plate in Lee-Wickfield. Forbothcases, theinteractionforceshowsextremapointsforfinitevaluesofthe Lagrangian coupling parameters. The analysis of extrema cases shows that these parameters generate consistent results previously obtained.

3
  • MARCOS FELIPE FARIA TERRA SIQUEIRA
  • Atmospheric Characterization of Hot-Jupiters like Exoplanets Through Transit's Differencial Spectrophotometry

  • Advisor : OSCAR CAVICHIA DE MORAES
  • COMMITTEE MEMBERS :
  • ALAN BENDASOLI PAVAN
  • FRANCISCO JOSÉ JABLONSKI
  • GABRIEL RODRIGUES HICKEL
  • OSCAR CAVICHIA DE MORAES
  • Data: Mar 5, 2020


  • Show Abstract
  • Differential spectrophotometry of transiting Hot-Júpiters has shown to be a promising technique to characterize the upper atmosphere of these planets, without the necessity of spatially resolving it from its host star. The enhancement of this technique in the last decade allowed the achievement of transmission spectra in smaller telescopes, like the NOT 2.4m. Motivated by these results, this work aims to test the viability of characterizing exoplanetary atmospheres applying this technique in the 1.6m Perkin Elmer telescope, based in observations performed in OPD-LNA. The light curves obtained for the monitored objects showed a dispersion in the order of the transit depth, possibly generated by the oscillation of the objects in the slit together with unfavorable nights. Through the combination of the acquired spectra, it was possible to generate the transmission spectrum of the WASP-87b. The atmospheric models adjusted to the data indicate an oxygen-rich atmosphere (C/O < 1), with strong haze and evidence of TiO and VO absorber structures, which at temperatures above 2000K, suppress the Na and K absorption lines. This individual result is not enough to confirm the effectiveness of the method, and new observations must be made in order to better understand systemic errors and restrict the limits of its applicability.

4
  • CELSO HENRIQUE CORREA CARVALHO
  • Spectroscopic and Abundance Analysis of Planetary Nebula NGC 6445.

  • Advisor : HEKTOR STHENOS ALVES MONTEIRO
  • COMMITTEE MEMBERS :
  • HEKTOR STHENOS ALVES MONTEIRO
  • ISABEL REGINA GUERRA ALEMAN
  • OSCAR CAVICHIA DE MORAES
  • PAULO JAKSON ASSUNÇÃO LAGO
  • Data: Mar 6, 2020


  • Show Abstract
  • NGC 6445 is a planetary nebula that has been the target of only a few specific studies. In this work, our aim is to complement the studies carried out until now, analyzing the spatial distribution of the optical emission of several atomic lines from this nebula. With this purpose, the central part of the nebula was mapped with multiple optical spectra obtained with the use of narrow slits in different positions of the nebula. The observations were made with the Cassegrain spectrograph attached to the 1.6 m telescope at the Pico dos Dias Observatory. With this data, we obtained the traditional integrated spectrum and the spatially resolved spectrum. With these data, we studied not only of the average physical and chemical properties of this object, but also their two dimensional distribution.

5
  • Daniel da Cruz Alves
  • Investigation of the photoconduction effect in p-type PbTe quantum wells.

  • Advisor : MARCELOS LIMA PERES
  • COMMITTEE MEMBERS :
  • MARCELOS LIMA PERES
  • PAULO HENRIQUE DE OLIVEIRA RAPPL
  • SANDRA NAKAMATSU
  • Data: Mar 13, 2020


  • Show Abstract
  • In this work, a study of the photoconductivity effect was carried out on two PbTe single quantum well samples, p-type, 10 and 20 nm grown on a BaF2 substrate. Photoconduction measurements were carried out in a temperature range of 300 - 1.9 K and under the illumination of an infrared (IR) emitter LED. The samples presented positive photoconductivity and a persistent effect at low temperatures. The effect of persistent photoconductivity was associated with the presence of defect levels within the well band structure. Adjustments from the decay curves were performed to obtain the recombination times for the two studied quantum wells and, thus, to obtain the positions of the defect levels responsible for the persistence effect. The recombination times for each sample were obtained, indicating that more than one defect level influences the electrical transport of the carriers. In the 10 nm-thick well, the defect level is activated at 20 K and is responsible for the persistence in the photoconductivity of the sample that arises from that temperature. However, the 10 nm well showed a larger photoresponse for T = 10 K than for T = 4.2 K, a behavior that was not expected. For the 20 nm well, the defect level starts to have an influence from 45 K and thus the persistence effect is evident from that temperature. Hall Effect measurements were also performed to help understand the IR radiation influence on electrical transport. For the 10 nm-thick sample, the measurements indicated that illumination increases the concentration of carriers and, for a given temperature region, an increase in carrier mobility. The change in the behavior of the mobility and concentration of carriers reveals, defect level influence found in the sample. The increase in mobility explains the fact that the variation in the photoconduction amplitude in 10 K is greater than in 4.2 K. For the 20 nm well, the illumination causes an increase in the concentration of carriers and a decrease in mobility from 30 K, showing that the defect levels influence the sample photoconduction curves. The saturation presented by the mobility curve helps to understand the similarity between the photoconduction amplitudes for 10 K and 4.2 K for the 20 nm well.

6
  • ELIANE APARECIDA MORAIS
  • Investigation of electrical properties p-type in PbTe quantum wells

  • Advisor : MARCELOS LIMA PERES
  • COMMITTEE MEMBERS :
  • HORÁCIO WAGNER LEITE ALVES
  • MARCELOS LIMA PERES
  • ROBERTO SHIGUERU NOBUYASU JUNIOR
  • Data: Jul 23, 2020


  • Show Abstract
  • In this work, the properties of electric transport and the Rashba effect were investigated in p type PbTe / Pb0.9Eu0.1Te quantum wells, with and without BaF2 doping, with 10nm thickness. The measurements were carried out in the temperature range from 1.9K to 40K, using a blue LED with a wavelength of 460 nm and intensity of 276 mW / m². In magnetoresistance measurements for the doped sample, with and without illumination, we observed that for values below B ~ 4 T there are no significant oscillations at any measured temperature, but above B ~ 4 T there are oscillations at lower temperatures in the range of 1.9 K at 10K and for temperatures above 15 K the oscillations become evident in B ~ 7 T. The concentration of carriers and their mobility were also analyzed for the sample at temperature of 4.2 K, which showed a minimal decrease in the concentration of carriers and an increase in mobility when illuminated. The magnetoresistance measurements for the doped sample, with and without illumination, showed oscillations from B ~ 4 T for temperatures in the range of 1.9 K to 15 K and for temperatures above 20 K the oscillations are very discrete above B ~ 7 T. Without light, the oscillations of the undoped sample are composed of two oscillatory components and when illuminated, they are composed of three components with very different frequencies. At temperature of 6 K, the non-doped sample showed an increase in the concentration of carriers and a decrease in mobility when illuminated. The effective cyclotronic masses and the Landé g factor were also obtained for the samples. The analysis of the frequencies found indicates the Rashba effect (or SO). The doped sample showed splitting Rashba of ellipsoids than the non-doped sample, reaching 50%. The energy of Rashba found for the doped sample was 13 meV.

7
  • Diego Renan da Silva
  • Optical analogue models for black holes and wormholes

  • Advisor : RENATO KLIPPERT BARCELLOS
  • COMMITTEE MEMBERS :
  • DANTE DONIZETI PEREIRA
  • EDUARDO HENRIQUE SILVA BITTENCOURT
  • RENATO KLIPPERT BARCELLOS
  • RODRIGO LIPPARELLI FERNANDEZ
  • Data: Jul 30, 2020


  • Show Abstract
  • This work aims to present and discuss the optical analogue models used to study gravitational systems using condensed matter systems. The whole mathematical theory behind the construction of an analogue optical model and the explicit presentation of two analogue models are provided: Schwarzschild black hole and Morris-Thorne wormhole. A parametrization of such models is proposed in order to unify them through a free real parameter that generates a family of new models, and open the possibility that some of theses new models could actually be analogue models.

8
  • Bárbara Luiza de Miranda Marques
  • Study of planetary nebulae observed with integral field spectroscopy

  • Advisor : HEKTOR STHENOS ALVES MONTEIRO
  • COMMITTEE MEMBERS :
  • ALBERTO RODRÍGUEZ ARDILA
  • HEKTOR STHENOS ALVES MONTEIRO
  • ISABEL REGINA GUERRA ALEMAN
  • STAVROS AKRAS
  • Data: Aug 10, 2020


  • Show Abstract
  • In this work, four planetary nebulae (PNe) were studied through the analysis of integral field spectroscopy (IFS) data, obtained in one of the four telescopes that form the Very Large Telescope (VLT, European Southern Observatory, Chile). These objects were selected from an original sample of 16 observed PNe, based on the quality and completeness of the data necessary to determine their physical conditions and abundances. These four PNe had never been studied with IFS, a technique that allows obtaining spectral information spatially resolved. The origin of the diversity of PNe morphologies is not yet fully understood, being an important research front in this field. From this data we can investigate the morphological characteristics shown by the emission of different species and ions, in addition to physical and chemical parameters of these objects. Of the four PNe selected, He 2-108 was the focus of this work, as their observations showed several interesting characteristics. For this object, we made a detailed study, including the determination of line intensity maps and, from these, we determined gas temperature and density maps. Chemical abundances were calculated from the integrated spectrum, leading to an ADF(N/H) = 55. The analysis of the central region’s spectrum indicates that the central star still produces an intense wind that affects the emission of the most central region of the PN. The presence of that wind is an evidence of its very young evolutionary stage. The first results of the similar analysis made for the PNe He 2-117, He 2-434 and IC 4191 are also presented. The integrated spectra and the first flux maps of these objects were obtained.

9
  • MONIQUE MARQUES DE BRITO
  • A spectrophotometric study of planetary nebulae and HII regions in the M83 galaxy

  • Advisor : OSCAR CAVICHIA DE MORAES
  • COMMITTEE MEMBERS :
  • ANGELA CRISTINA KRABBE
  • HEKTOR STHENOS ALVES MONTEIRO
  • OSCAR CAVICHIA DE MORAES
  • Data: Aug 24, 2020


  • Show Abstract
  • Planetary nebulae (PNe) and HII regions represent important tools with regard to determining chemical abundances and exploring radial abundance gradients in spiral galaxies. Both objects configure stellar populations with different ages, so the determination of their abundances allows to study the chemical composition of galaxies at different times of their evolution. In this work we aimed to determine the chemical abundances of the populations of PNe and HII regions in the barred spiral galaxy M83. Our data is made up of objects that are candidates for PNe and HII regions in M83 observed with the Gemini South telescope, which have not yet calculated chemical abundances. We obtained, for the first time, abundances by the direct method for two PNe of the galaxy M83. For ten HII regions in our sample, different statistical methods and calibrations were adopted to derive their abundances; and for only one of these HII regions, abundance was also obtained by the direct method. With the abundance of the two PNe it was possible, with the help of data from models of stellar evolution, to estimate the masses of their progenitor stars. The abundances calculated for the HII regions allowed us to explore the radial gradients of oxygen abundance. Our results show that the radial gradients differ according to the method adopted, both in height and inclination. The abundances of the two PNe, compared to the abundances of the HII regions by different methods, are lower. This result strengthens the hypothesis that a possible chemical enrichment happened in the barred spiral galaxy M83.

10
  • Leandro Santana
  • An analysis of the Penrose Singularity Theorem under the action of misshapen transformations

  • Advisor : EDUARDO HENRIQUE SILVA BITTENCOURT
  • COMMITTEE MEMBERS :
  • CARLOS AUGUSTO ROMERO FILHO
  • GABRIEL GUIMARÃES CARVALHO
  • BRAULIO AUGUSTO GARCIA
  • EDUARDO HENRIQUE SILVA BITTENCOURT
  • IARLEY PEREIRA LOBO
  • Data: Aug 26, 2020


  • Show Abstract
  • In this dissertation, after a brief review of the elements present in differential geometry, we present Penrose's Singularity Theorem (1965) and rewrite it from the perspective of disformal transformations. Without intending to use a complete and sophisticated mathematical apparatus, we are going to present an outline of the proof of the Singularity Theorem and a brief alternative to it. Then, separating the disformal transformations into two complementary classes, more specifically the conformal case and the Kerr-Schild type transformations, we will present an analysis of the Singularity Theorem according to these transformations. Finally, we were able to make an analysis of space-times that relate through the disformal transformations and thus describe the hypotheses necessary for the addition or removal of singularities.

11
  • Alexsandre Leite Ferreira Junior
  • Fluctuations of a massive scalar field: Temperature and boundary.

  • Advisor : VITORIO ALBERTO DE LORENCI
  • COMMITTEE MEMBERS :
  • LAWRENCE HOWARD FORD
  • LEANDRO GUSTAVO GOMES
  • VITORIO ALBERTO DE LORENCI
  • Data: Aug 31, 2020


  • Show Abstract
  • It is well established that a change in the physical state of a quantum field induces dispersions on the velocity of a interacting non-relativistic test particle. Here such a interacting model is addressed with a finite transition time between states of the field. Underlining that such induced stochastic motion is different from an usual Brownian motion, as, at late times, the dispersions are bounded and do not depend on the interaction time, without the need for a dissipative force. Further, we study the case for a massive scalar field at finite temperatures, thus generalizing previous investigation in [1]. The results presented here show subvacuum effects even at finite temperature. Nonetheless, novel effects are also unveiled, as a detailed description of the thermal contribution highlights their discrepancy to the usual Brownian motion and stresses the opposing character of mass and temperature. The presence of the field mass weakens thermal contributions and temperature hides the characteristic oscillatory pattern of massive fields. Such interplay is even more relevant in the presence of a boundary, when investigating the distance behavior of the dispersions and the vacuum versus thermal dominance near the wall. As for higher masses the vacuum term dominates for larger distances, being able also to create and interchange in such dominance as the wall is approached.

12
  • PATRICIA MARIA DOS SANTOS
  • Studies of Spatial Variation of Abundances: The Case of the Menzel Planetary Nebula 1

  • Advisor : HEKTOR STHENOS ALVES MONTEIRO
  • COMMITTEE MEMBERS :
  • ALAN BENDASOLI PAVAN
  • HEKTOR STHENOS ALVES MONTEIRO
  • PAULO JAKSON ASSUNÇÃO LAGO
  • Data: Oct 15, 2020


  • Show Abstract
  • Planetary Nebulae (PNe) are objects of very complex morphologies and the details of their spatial structure formation are still object of investigation. There are few works that take into account the three-dimensional character of objects. In addition to the spherical structure, the older models also assume that the abundance of elements is uniform throughout the PNe. Just few studies explore the hypothesis that there are variations in abundances. In this work, we present a model for the planetary nebula Menzel 1 made with the code MOCASSIN. Its bipolar structure and homogeneous abundances were taken into account in order to analyze how they can influence the results obtained. We show that the results obtained with the updated model lead to significantly different values when compared to previous models for the same object. We discuss the influence of atomic data and the detailed treatment of diffuse radiation on the discrepancies found. With the NEAT code, integrated and bidimensional abundances were determined from the flux maps derived from the model. The abundance maps show discrepancies with respect to the initial parameters of the model. We conclude that the empirical method creates non-real variations since this method does not take into account the three-dimensional complexity of the object's structure.

13
  • Rodrigo Galhardo Rana
  • Contours and defects in conformal field theories

  • Advisor : GABRIEL FLORES HIDALGO
  • COMMITTEE MEMBERS :
  • FRANCESCO TOPPAN
  • ALEXIS ROA AGUIRRE
  • GABRIEL FLORES HIDALGO
  • LEANDRO GUSTAVO GOMES
  • Data: Dec 16, 2020


  • Show Abstract
  • In this work we study the main properties and algebraic structures of the conformal field theories. In particular, we consider classical and quantum field theories for free bosonic and fermionic systems with differents boundary conditions. In addition, we study the classical and quantum aspects considering defects and the permutation of branes in the Liouville theory.

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