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Dissertations |
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1
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Rosimara Passos Toledo
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Physical properties of porous silicon layers with Erbium-doped in PANI deposition.
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Advisor : ADHIMAR FLAVIO OLIVEIRA
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COMMITTEE MEMBERS :
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ADHIMAR FLAVIO OLIVEIRA
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DANILO ROQUE HUANCA
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MARIA ELENA LEYVA GONZALEZ
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SEBASTIAO GOMES DOS SANTOS FILHO
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Data: Feb 17, 2020
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Show Abstract
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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.
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2
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Everson Henrique Rodrigues
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Lee-Wick field in presence of semi-transparent boundaries
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Advisor : FABRICIO AUGUSTO BARONE RANGEL
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COMMITTEE MEMBERS :
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ALEXIS ROA AGUIRRE
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ANDERSON ANTUNES NOGUEIRA
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FABRICIO AUGUSTO BARONE RANGEL
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LUIZ HENRIQUE DE CAMPOS BORGES
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Data: Feb 19, 2020
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Show Abstract
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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.
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3
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MARCOS FELIPE FARIA TERRA SIQUEIRA
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Atmospheric Characterization of Hot-Jupiters like Exoplanets Through Transit's Differencial Spectrophotometry
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Advisor : OSCAR CAVICHIA DE MORAES
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COMMITTEE MEMBERS :
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ALAN BENDASOLI PAVAN
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FRANCISCO JOSÉ JABLONSKI
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GABRIEL RODRIGUES HICKEL
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OSCAR CAVICHIA DE MORAES
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Data: Mar 5, 2020
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Show Abstract
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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.
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4
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CELSO HENRIQUE CORREA CARVALHO
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Spectroscopic and Abundance Analysis of Planetary Nebula NGC 6445.
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Advisor : HEKTOR STHENOS ALVES MONTEIRO
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COMMITTEE MEMBERS :
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HEKTOR STHENOS ALVES MONTEIRO
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ISABEL REGINA GUERRA ALEMAN
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OSCAR CAVICHIA DE MORAES
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PAULO JAKSON ASSUNÇÃO LAGO
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Data: Mar 6, 2020
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Show Abstract
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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.
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5
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Daniel da Cruz Alves
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Investigation of the photoconduction effect in p-type PbTe quantum wells.
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Advisor : MARCELOS LIMA PERES
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COMMITTEE MEMBERS :
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MARCELOS LIMA PERES
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PAULO HENRIQUE DE OLIVEIRA RAPPL
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SANDRA NAKAMATSU
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Data: Mar 13, 2020
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Show Abstract
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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.
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6
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ELIANE APARECIDA MORAIS
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Investigation of electrical properties p-type in PbTe quantum wells
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Advisor : MARCELOS LIMA PERES
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COMMITTEE MEMBERS :
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HORÁCIO WAGNER LEITE ALVES
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MARCELOS LIMA PERES
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ROBERTO SHIGUERU NOBUYASU JUNIOR
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Data: Jul 23, 2020
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Show Abstract
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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.
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7
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Diego Renan da Silva
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Optical analogue models for black holes and wormholes
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Advisor : RENATO KLIPPERT BARCELLOS
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COMMITTEE MEMBERS :
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DANTE DONIZETI PEREIRA
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EDUARDO HENRIQUE SILVA BITTENCOURT
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RENATO KLIPPERT BARCELLOS
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RODRIGO LIPPARELLI FERNANDEZ
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Data: Jul 30, 2020
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Show Abstract
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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.
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8
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Bárbara Luiza de Miranda Marques
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Study of planetary nebulae observed with integral field spectroscopy
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Advisor : HEKTOR STHENOS ALVES MONTEIRO
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COMMITTEE MEMBERS :
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ALBERTO RODRÍGUEZ ARDILA
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HEKTOR STHENOS ALVES MONTEIRO
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ISABEL REGINA GUERRA ALEMAN
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STAVROS AKRAS
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Data: Aug 10, 2020
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Show Abstract
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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.
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9
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MONIQUE MARQUES DE BRITO
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A spectrophotometric study of planetary nebulae and HII regions in the M83 galaxy
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Advisor : OSCAR CAVICHIA DE MORAES
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COMMITTEE MEMBERS :
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ANGELA CRISTINA KRABBE
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HEKTOR STHENOS ALVES MONTEIRO
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OSCAR CAVICHIA DE MORAES
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Data: Aug 24, 2020
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Show Abstract
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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.
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10
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Leandro Santana
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An analysis of the Penrose Singularity Theorem under the action of misshapen transformations
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Advisor : EDUARDO HENRIQUE SILVA BITTENCOURT
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COMMITTEE MEMBERS :
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CARLOS AUGUSTO ROMERO FILHO
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GABRIEL GUIMARÃES CARVALHO
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BRAULIO AUGUSTO GARCIA
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EDUARDO HENRIQUE SILVA BITTENCOURT
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IARLEY PEREIRA LOBO
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Data: Aug 26, 2020
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Show Abstract
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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.
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11
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Alexsandre Leite Ferreira Junior
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Fluctuations of a massive scalar field: Temperature and boundary.
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Advisor : VITORIO ALBERTO DE LORENCI
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COMMITTEE MEMBERS :
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LAWRENCE HOWARD FORD
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LEANDRO GUSTAVO GOMES
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VITORIO ALBERTO DE LORENCI
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Data: Aug 31, 2020
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Show Abstract
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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.
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12
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PATRICIA MARIA DOS SANTOS
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Studies of Spatial Variation of Abundances: The Case of the Menzel Planetary Nebula 1
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Advisor : HEKTOR STHENOS ALVES MONTEIRO
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COMMITTEE MEMBERS :
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ALAN BENDASOLI PAVAN
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HEKTOR STHENOS ALVES MONTEIRO
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PAULO JAKSON ASSUNÇÃO LAGO
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Data: Oct 15, 2020
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Show Abstract
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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.
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13
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Rodrigo Galhardo Rana
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Contours and defects in conformal field theories
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Advisor : GABRIEL FLORES HIDALGO
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COMMITTEE MEMBERS :
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FRANCESCO TOPPAN
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ALEXIS ROA AGUIRRE
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GABRIEL FLORES HIDALGO
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LEANDRO GUSTAVO GOMES
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Data: Dec 16, 2020
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Show Abstract
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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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