Doutorado em Física

URI Permanente para esta coleção

http://repositorio.ufes.br/handle/10/17493

Nível: Doutorado
Ano de início: 2003
Conceito atual na CAPES: 4
Ato normativo: Parecer CES/CNE nº 487/2018, homologado pela Port. MEC 609, publicado no DOU em 18/03/2019.
Periodicidade de seleção: Semestral
Área(s) de concentração: Física
Url do curso: https://fisica.ufes.br/pt-br/pos-graduacao/PPGFis/detalhes-do-curso?id=1509

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Produção e cinética de formação de nanoestruturas de α-Fe em ligas do tipo Nanoperm ativadas mecanicamente
(Universidade Federal do Espírito Santo, 2008-03-28) Pereira, Rodrigo Dias; Caetano, Edson Passamani; Nascimento, Valberto Pedruzzi; Fernandes, Antonio Alberto Ribeiro; Biondo Filho, Armando; Caetano, Edson Passamani; Ardisson, José Domingos; Biasi, Ronaldo Sergio de
Nanostructured Fe84M9Cu1B6 alloys were produced by mechanosynthesis, using two different procedures (Serie I – sequential mixture of elemental powder or Serie II – mixture of all elemental powder). The amorphous phase type FeMCuB was dominantly obtained for the first procedure (Serie I), in the contrary, a-Fe(M) nanograins dispersed in an FeMCuB amorphous matrix were spontaneously produced by mechanosynthesis in samples of the serie II. The nanocrystalline material also was activated in the serie I using a temperature controlled annealing.The a-Fe (M) nanograins in both series I and II have sizes of grains, obtained by the Scherrer expression, of about 8 to 10 nm. Using the technique of exploratory differential calorimetry different aspects were studied: the kinetics of the processes of (I) the structural relaxation of the amorphous matrix produced by milling and of (ii) the amorphous to crystalline transformation of the amorphous phase and, (iii) the full crystallization of the materials produced by mechanosynthesis. The structural relaxation of the as-produced materials occurs around 500 K, independently of the refractory element (M), but its activation energy is in a range between 30 and 100 kJ /mol, which depends on the procedure (Series I or Series II) and also on the element refractory M (Zr, V, Nb). Considering, for example, the Fe84Zr9Cu1B6 alloy produced in the procedures of the series I and II, a reduction in the value of the peak temperature of the relaxation of approximately 3% was verified, but the energies of activation of the materials prepared in Series I and II are substantially different, respectively 96 and 31 kJ / mole for the Series I and II. The process of crystallization occurs in the range of temperature of 730 to 750 K for the first stage and with activation energy between 55 and 160 kJ /mol, while the second stage of IXcrystallization occurs between 636 and 939 K and with an activation energy between 105 and 330 kJ /mol, depending on the refractory element and the type of procedure for preparing the sample (Series I and Series II). The crystallization temperatures and activation energies, associated with the first and second crystallization stages, were found to be much lower for the milled alloys compared to corresponding melt-spun alloys, an effect associated with a larger number of defects induced by the mechanosynthesis process. Mössbauer spectroscopy was the technique used for a description of the microstructure of materials produced in series I and II. Three different regions were observed. The amorphous phases of the FeMCuB were characterized by containing distributions of magnetic fields with hyperfine peak around 20 T. Within the amorphous phases of the different matrixes, it was possible in some cases to determine regions rich and poor in Fe. Moreover the grain core of the a-Fe(M) nanograins have hyperfine magnetic fields around 33 T , While the atoms of Fe on the surfaces of the a-Fe (M) nanograins have a contribution in the distribution of hyperfine magnetic fields around 31 T. The hyperfine and magnetic properties of the amorphous Fe84M9Cu1B6 alloys produced in this thesis were comparable to those found in melt-spun alloys with similar composition.
Quantização do modelo de Jackiw-Teitelboim no gauge temporal via o formalismo de laços
(Universidade Federal do Espírito Santo, 2009-06-30) Lourenço, José André; Constantinidis, Clisthenis Ponce; Piguet, Olivier; Franco, Daniel Heber Theodoro; Alvarenga, Flavio Gimenes; Sotkov, Galen Mihaylov; Pinto Neto, Nelson; Constantinidis, Clisthenis Ponce; Piguet, Olivier
In this work we study the Jackiw-Teitelboim model (JT model), as a model that has the structure of a topological theory of the BF type. In two dimensional space-time, gravitation can be seen as a gauge theory characterized by the Poincaré group ISO(1, 1). As this group, doesn't admit an invariant and nondegenerate quadratic form, the JT model is based on the (Anti)- de Sitter group (A)dS , the group SO(2, 1), which contains the Lorentz group as a subgroup and corresponds to a gravitation theory with a cosmological constant. We see then, that the (A)dS group, taken as a gauge group, contains naturally the di eomorphism symmetry. In this line we investigate the canonical formulation of the JT model in order to quantize it through the formalism of loop quantum gravity (LQG). Following Dirac's program of canonical quantization applied to the loop formalism, we obtain a quantum con guration space starting from the Bohr compacti cation of the real line, we build the respective kinematic Hilbert space and we de ne in a consistent way the volume operator. Finally, we treat the dynamics of the model at the quantum level through the implementation of the constraints originating from the classical theory of the JT model in the temporal gauge in an appropriate Hilbert space.
Conjuntos de bases gaussianas correlacionados não relativístico e relativístico : aplicação em cálculos de constantes espectroscópicas e de propriedades elétricas e magnéticas moleculares
(Universidade Federal do Espírito Santo, 2009-12-18) Camiletti, Giuseppi Gava; Jorge, Francisco Elias; Canal Neto, Antônio; Machado, Antonio Eduardo da Hora; Silva Filho, Eloi Alves da; Guimarães, Freddy Fernandes; Morigaki, Milton Koiti
Contracted basis set of double zeta (DZ) quality for the atoms from K to Kr is presented. It was determined from fully-optimized basis set of primitive Gaussian-type functions generated in atomic Hartree-Fock calculations. Sets of Gaussian polarization functions optimized at the Mfller-Plesset second-order level were added to the DZ basis set. This extends earlier work on segmented contracted DZ basis set for atoms H-Ar. From this set, using the BP86 non-hybrid and B3LYP hybrid functionals, dissociation energy, geometric parameters, harmonic vibrational frequency, and electric dipole moment of a set of molecules were calculated and compared with results obtained with other basis sets and with experimental data reported in the literature. In addition, 57Fe and 77Se nuclear magnetic resonance chemical shifts in Fe(C5H5)2, H2Se, and CSe2 were calculated using density functional theory and gauge-including atomic orbitals and, then, compared with theoretical and experimental values previously published in the literature. Except for chemical shift, one verifies that our results give the best agreement with experimental and benchmark values. Augmented Gaussian basis sets of double and triple zeta valence qualities plus polarization functions for the atoms K and from Sc to Zn are also presented. They were generated from the all-electron unaugmented sets by addition of diffuse functions (s, p, d, f, and g symmetries), that were optimized for the anion ground states. From these sets, HartreeFock, second-order Mfller-Plesset perturbation theory, and density functional theory electric dipole moment and dipole polarizability calculations for a sample of molecules were carried out. Finally, Douglas-Kroll-Hess (DKH) contracted Gaussian basis sets of double, triple, and quadruple zeta valence qualities plus polarization functions (XZP, X=D, T, and Q, respectively) for the atoms H, Li, Be, Na, and Mg and DZP and TZP for K-Zn are presented. xv They have been determined from the corresponding non-relativistic basis sets generated previously by Jorge et al. We have recontracted the original XZP basis sets, i.e., the values of the contraction coefficients were reoptimized using the relativistic DKH Hamiltonian. The scalar relativistic effect at the coupled-cluster level of theory on the ionization energy of some atoms and dissociation energy and geometric parameters for a sample of molecules is discussed. All results obtained in this work were compared with theoretical and experimental values available in the literature
Análise perturbativa em modelos cosmológicos fantasmas
(Universidade Federal do Espírito Santo, 2010-02-19) Jardim, Deborah Faragó; Fabris, Júlio César; Tonini, Eduardo Valentino; Dito, Giuseppe; Silva, Saulo Carneiro de Souza; Gonçalves, Sergio Vitorino de Borba; Zimdahl, Winfried Ernst Wilhelm
Dark energy models have became extensively studied in recent years. Earlier proposals have emerged this century to describe the Universe by means of a fluid whose equation of state was breaking with the paradigm imposed by the standard cosmology. Fluid of this kind require to violate some energy conditions and have a very peculiar behavior, denominated for this reason "phantom fluid". This work investigates the structures formation through the study of cosmological perturbations in Universe which scenario is the phantom cosmology. They have proposed two models, the first them by solving the perturbed equations for scalar modes, using a hydrodynamic and fields representation for the fluid and then making the asymptotic behavior analysis. The second model is a composite of two fluids, one component of pressureless matter and another with negative pressure, represented by a self-interacting scalar field . In this case, the solution was obtained by numerical calculation. Results were confronted with the observational data and it showed models phantom of this nature are quite possible and its open a new window of research
Buracos negros fantasmas.
(Universidade Federal do Espírito Santo, 2010-04-23) Rodrigues, Manuel Eleuterio; Fabris, Júlio César; Alvarenga, Flávio Gimenes; Mello, Eugênio Ramos Bezerra de; Piguet, Olivier; Sotomayor, Patrício Anibal Letelier
We obtain the general solution of the Einstein-(anti) Maxwell-(anti) Dilaton (EMD)theory for a static, spherically symmetric spacetime in four dimensions. In the phantom(anti) cases, we obtain new solutions with non-degenerate horizon and make the analysis oftheir causal structures. The causal structures of some solutions are exotics, some of themcan not be described in two-dimensional usual Penrose diagrams. We obtain also, usingthe method of Sigma model, new stationary solutions with axial symmetry, for Einstein-anti-Maxwell-Dilaton (E ¯MD) and Einstein-anti-Maxwell-Dilaton-Axion (E ¯MDA) theory.We analyse the causal structure of these new solutions.
Modelo para análise de tensões principais biaxiais e triaxiais em materiais ortotrópicos através de medidas de difração de raios-x
(Universidade Federal do Espírito Santo, 2010-07-08) Santos, Edson Mascarenhas; Orlando, Marcos Tadeu D'Azeredo; Garcia, Flávio; Belich Junior, Humberto; Rossi, Jesualdo Luiz; Fabris, Júlio César; Macêdo, Marcelo Camargo Severo de; Santos, Marco Antonio dos
In this work it was developed expressions for the calculation of biaxial and triaxial principals stresses in polycrystalline anisotropic materials. Taken into account these mathematic expressions was possible to determine the elastic constants using the Theory of Elasticity Continuum for small deformations. The constitutive relation between strain and stress must be considered orthotropic, obeying the generalized Hooke's law. One technique that can be applied to obtain the stresses and elastic constants was the X-ray diffraction, because the experimental conditions are similar to the assumptions of the model, ie, measure small deformations compared the sample sizes and magnitude of stress is involved in the elastic range. Therefore, based on the equations obtained, here it is possible to use the technique of x-ray diffraction sin2 ? for materials with texture or anisotropic, determining, rst, a characterization of the texture through the pole gures in order to determine possible angles ?, which can be used in our equation. Next, it was determined the deformation for each diffraction peak with the angles ? obtained from the pole gures. As considering the elastic constants of the material knowledge, our can use equation to calculate the residual stress in a material. We presented a test of the consistency of our equations by comparing with the equations in the literature for isotropic materials, moreover we applied the model to biaxial principal stress, using experimental data from the work of D. Faurie et al, in order to be possible to compare the elastic constants obtained with the study reported.
Modelos de Matéria e Energia Escuras Alternativos ao Cenário Padrão
(Universidade Federal do Espírito Santo, 2010-07-23) Batista, Carlos Eduardo Magalhães; Fabris, Júlio César; Chapiro, Ilia; Helayel Neto, José Abdalla; Lima, José Ademir Sales de; Piattella, Oliver Fabio; Ricaldi, Wiliam Santiago Hipolito
In this tese we investigate the behavior of TeVeS when the the ratio between the enegy densities ?2 and ?1 is constant in the Einstein frame, where ?2+?1 = ?ef is the energy density efective in the Einstein frame. We have verified TeVeS can geometrize the dark matter in the physical frame, eliminating the dark matter. Then we used a similar procedure in the case of scalar-tensor theories, preserving the ratio constant between the matter energy density and the field energy density in the Einstein frame. The result predict the existence of geometrized dark energy , then it is not necessary a new kind of energy filling the universe to describe the universe acelaration. The third part deal with the possibility of negative energy density filling the universe. Our model with cosmological constant and sclar field is compared with supernovas types Ia and to the 2dFGRS data. The result show that it is possilble to exist negative energy density for the scalar field as well as for the cosmological constant, but it does not allow negative energy density for the matter.
Conjunto de bases gaussianas de qualidade dupla zeta para os átomos de Rb até Xe
(Universidade Federal do Espírito Santo, 2010-09-28) Barros, Cezar Laurence; Canal Neto, Antônio; Jorge, Francisco Elias; Lima, Denise da Costa Assafrão de; Pires, José Maria; Castro, Marco Antônio de; Fonseca, Tertius Lima
All-electron contracted Gaussian basis set of double zeta valence quality plus polarization functions (DZP) for the atoms from Rb to Xe is presented. This set was augmented by addition of diffuse functions (s, p, d, and f symmetries) that were optimized for the anion ground states and that are critical for an accurate description of electron affinity, polarizabilities, optical rotation, and hydrogen bonding. Besides, Douglas-Kroll-Hess (DKH) basis set for fourth-row elements is reported. We have recontracted the original DZP basis set, i.e., the values of the contraction coefficients were re-optimized using the relativistic DKH Hamiltonian. This extends earlier works on segmented contracted DZ basis set for atoms HKr. Our sets along with ab initio methods and density functional theory were used to calculate ionization energies of some atoms and spectroscopic constants and static electric properties of a sample of molecules and, then, comparison with results obtained with other basis sets and with experimental data reported in the literature was done. One verifies that our results give good agreement with experimental and benchmark values
Magnetismo de ferritas nanoestruturadas preparadas por mecanossíntese e Sol-Gel Protéico
(Universidade Federal do Espírito Santo, 2011-01-21) Segatto, Breno Rodrigues; Caetano, Edson Passamani; Larica, Carlos; Proveti, José Rafael Cápua; Paniago, Roberto Magalhães; Ardisson, José Domingos
Magnetic properties of nanocrystalline AFe2O4 (A = Ni, Zn and Co) spinel-like mechanically processed and also of the nanocrystalline NiFe2O4 ferrite prepared by sol-gel technique have systematically been studied using temperature dependent from zero-field 57Fe Mössbauer spectrometry and magnetization measurements, while the crystal structures were investigated by X-ray difraction. Specifically, for the NiFe2O4mechanically processed in-field 57Fe Mössbauer spectrometry has also been performed. For the nanocrystalline ferrite mechanically processed with spinel-like, the hyperfine structure studied by Mössbauer spectroscopy allows us to distinguish two main magnetic contributions: one attributed to the crystalline grain core (n-G), which has magnetic properties similar to the bulk AFe2O4 (A = Ni, Zn and Co) spinel-like structure (n-AFe2O4) and the other one due to the disordered grain boundary region (GB), which presents topological and chemical disorder features (d-AFe2O4). Mössbauer spectrometry determines a large fraction for the d-AFe2O4 region of the nanocrystalline AFe2O4 ferrite milled for long times (longer than 80 hours). Under applied magnetic field, from Mössbauer it is determined that the n-NiFe2O4 spins are canted with angle dependent on the applied field magnitude, whereas a speromagnet-like structure is suggested for the d-NiFe2O4 with 63% of the Mossbauer spectra area. Mossbauer data for the nanocrystalline NiFe2O4 also show that even under 12 T no magnetic saturation is observed for the two magnetic phases (n-NiFe2O4 and d-NiFe2O4). In general, hysteresis loops for the AFe2O4 (A = Ni, Zn and Co), obtained in field cooling protocol and recorded for scan field (maximum field of 7 T), are shifted in both field and magnetization axes, for temperatures below about 50 K. It has also been shown that the spin configuration of the spin-glass-like phase of the NiFe2O4 ferrite is strongly modified by the consecutive field cycles, consequently the n-NiFe2O4/d- XIII NiFe2O4 magnetic interaction is also affected in this process. One has to emphasize that the mechanically processed ZnFe2O4 ferrite has an inverse spinel-like structure with a magnetic ordering temperature (above 40 K) higher than that of the equivalent bulk ferrite (11 K). On the other hand, it is shown in this work that the NiFe2O4nanocrysalline ferrite, prepared by sol-gel method, has no hysteresis loop shift effects, after field cooling protocol, and, at the same time, the hysteresis loops do not saturate. The apparent absence of horizontal loop shift effect (exchange bias) is explained by the fact that in the sol-gel method the crystalline grains are big (~19 nm) and consequently the exchange bias field goes to zero due to the fact that the HEBa 1/tFI, where the tFIparameter is the ferrimagnetic thickness assumed to be the grain size. Comparing the magnetic results obtained for the nanocrystalline NiFe2O4 ferrites prepared by high energy milling and sol-gel methods, it can be concluded that the hysteresis loop shifts are extremely dependent on the high magnetic anisotropy of the d-AFe2O4 (A = Ni and Zn) phase. Therefore, the loop shift effects are due the exchange bias field at the d-AFe2O4/n-AFe2O4 interfaces and also from the spin freezing effect caused by cooling the spin-glass-like phase under applied magnetic field.
Simulação Numérica de Experimentos de Ressonância Magnética de Núcleos Quadrupolares com Aplicações em Computação Quântica
(Universidade Federal do Espírito Santo, 2011-05-13) Possa, Denimar; Freitas, Jair Carlos Checon de; Oliveira Junior, Ivan dos Santos Oliveira; Bonagamba, Tito José; Canal Neto, Antônio; Nogueira, José Alexandre; Suave Netto, Rogério
Nuclear magnetic resonance (NMR) at high magnetic field is oneof the most viabletools for implementing small-scale quantum computation. This fact motivates the studyof other magnetic resonance techniques for similar purposes. In this work we show, byextensively using numerical simulations, how nuclear quadrupole resonance (NQR) atzero external magnetic field can be used to perform basic quantum computing tasks.Specifically, concrete proposals to represent 2 and 3 q-bit states are presented, obtainedin systems of nuclei with spin 3/2 and 7/2, respectively, subjected to a pure quadrupolecoupling to an axially symmetric electric field gradient. Inthe spin 3/2 case, a methodfor quantum state tomography is also described, involving the use of two crossed coilsfor signal detection. Due to the similarity between the NMR and NQR techniques,many procedures used for obtaining pseudopure states and creating logic gates bearresemblance to those commonly used in NMR. However, NQR has some specific featureswhich provide important differences with regard to NMR, especially with respect to thedesign of the radiofrequency (RF) pulses responsible for handling the system. The useof circularly polarized pulses provides a mechanism of selective excitation in NQR withno counterpart in high-field NMR; these selective pulses are much shorter than the longselective pulses normally used in NMR, which is an advantage in terms of computationaltime and also considering the existence of decoherence effects. Another advantage ofNQR compared to high-field NMR is the relatively low cost of NQR spectrometers,which do not require the use of superconducting magnets. A second aim of this workis the development of a computational program for the numerical simulation of generalmagnetic resonance experiments involving quadrupolar nuclei in crystals, without anyrestriction as to the relative magnitude of the Zeeman and quadrupole interactions. Thisallows us to address, within the same theoretical framework, high-field NMR as well aspure NQR experiments, also including intermediate cases inwhich the interactions havecomparable magnitudes. The program, which was developed using the Mathematicapackage, makes use of the interaction picture to compute thetime evolution of the densityoperator under the effects of the relevant nuclear spin interactions and RF pulses. Someconditions specifically required for quantum computing applications are implemented inthe program, such as the possibility of use of elliptically polarized radiofrequency and theinclusion of zero- and first-order terms in the average Hamiltonian expansion. A numberof examples dealing with simple NQR and quadrupole-perturbed NMR experiments arepresented, along with the proposal of experiments to createquantum pseudopure statesand logic gates using pure NQR.
Quando Gravitação e Cosmologia Destoam do Padrão : Testando MOND e modelos de unificação do setor escuro
(Universidade Federal do Espírito Santo, 2011-11-25) Velten, Hermano Endlich Schneider; Zimdahl, Winfried; Fabris, Júlio César; Rodrigues, Davi Cabral; Waga, Ioav; Belich Junior, Humberto; Silva, Saulo Carneiro de Souza; Ricaldi, Wiliam Santiago Hipolito; Zimdahl, Winfried Ernst Wilhelm
The aim of this thesis is to investigate alternative ideas for the standard cosmology (here,denoted by the?CDM model). The two main ingredients of such standard description ofthe cosmic medium are cold dark matter (CDM) and dark energy (DE), which together formthe dark sector. We start our discussion with an alternative description of the dark matterphenomena. We aply the Modified Newtonian Dynamics (MOND) to the COMA galaxy clusterin order to explain the large mass to light ratio of such system. This corresponds to the“astrophysical part” of this work. At the end of chapter 3 we state that dark matter is afundamental component of the cosmic energy budget. Then, it occurs a transition into thethesis. Chapters 5, 6 and 7 (the “cosmological part”) are devoted to unified models for the darksector. In some sense, we are dealing now with alternatives to thedark energy phenomena. Inthis unification scenario, DM and DE are different manifestations of a single dark component.The Chaplygin gas and the bulk viscous fluid realize this idea. The homogeneous and isotropicbackground dynamics of these candidates is well compatible with the data (in particular, weuse Supernovae, Gamma Ray-Bursts, indirectH(z)measurements). However, we discuss indetail de differences between the perturbative dynamics of theChaplygin (adiabatic) modeland the bulk viscous (nonadiabatic) one. At the perturbative level our cosmological probesare the matter power spectrum and the integrated Sachs-Wolfe effect. There appears somepathologies with these alternative components what bring our attentions back to the standardcosmology. Within the?CDM conception for the Universe we relax the assuption that CDMis a ideal fluid make it “more real” by adding to its energy momentumtensor a dissipativecomponent (given by the bulk viscous pressure). This gives rise to the?vCDM model studiedin chapter 7. We find that the current cosmological data allows CDM to have a viscosity of=109Pa.seg. In some sense, we hope that this result could mean a new prediction to be testedin the future CDM laboratories.
Fluidos em Espaços Não-Comutativos
(Universidade Federal do Espírito Santo, 2011-12-27) Holender, Luiz; Santos, Marco Antonio dos; Orlando, Marcos Tadeu D’Azeredo; Passos, Carlos Augusto Cardoso; Justo Filho, João Francisco; Helayel Neto, José Abdalla
In this work, we present the results of our research on the generalization of the relativistic fluids in the K¨ahler parametrization to noncommutative spaces by applying methods of field theory. Our proposal can be applied to a large class of fluid models parametrized by two arbitrary smooth functions that generalize the K¨ahler potential on the surface of complex potencials of fluids and the parameter function of the state equation, respectively. We determine the constraints that the degress of freedom of the fluid should satisfy in order to have the fundamental symmetries of the noncommutative geometry and calculate the physical quantities of the noncommutative fluid.
Modelos cosmológicos na teoria de Rastall
(Universidade Federal do Espírito Santo, 2012-03-29) Mahamadou, Hamani Daouda; Piattella, Oliver Fabio; Fabris, Júlio César; Fernandes, Antonio Alberto Ribeiro; Mello, Eugênio Ramos Bezerra de; Zimdahl, Winfried Ernst Wilhelm
Rastall's theory is a modification of the general theory of relativity that leads to an expression different from the usual for the law of conservation in the field of matter. Recently it has been argued that such a theory may have applications to the problem of energy, since a fluid without pressure can lead to the acceleration of the universe. In this work, we confront Rastall's theory with the power spectrum data. The results indicate a configuration that essentially reduces Rastall's theory to general relativity, unless the unusual conservation law refers to a scalar field, a situation where other configurations would eventually be possible. A unification of energy dark and dark matter, is obtained if a wide field of non-canonical interaction, inspired by Rastall's theory of gravity, is imposed. In this case, agreement with the background tests and with the power spectrum is possible. We investigated the evolution of the gravitational potential in Rastall's scalar field theory. For a single component model, the perturbation theory, in Newtonian caliber, is consistent only for ? = 1, which is the limit of general relativity. On the other hand, it is possible to have a consistent model with ? 6 = 1 when another component, in the form of a perfect fluid, is introduced. We introduced in this theory a model of two fluids, one of the components representing the energy of the vacuum and the other the matter without pressure (for example, baryons plus matter is cold). The cosmological scenario is the same as for the ?CDM model, at the bottom and at the linear perturbative level, with the exception of one aspect: now the energy can be agglomerated. We hope that this may lead to the possibility of distinguishing the Rastall model from the ?CDM at a non-linear disturbing level
Extensão supersimétrica do modelo BF bisimensional e a quantização de laços
(Universidade Federal do Espírito Santo, 2012-03-30) Bautista, Luis Ivan Morales; Constantinidis, Clisthenis Ponce; Piguet, Olivier; Franco, Daniel Heber Theodoro; Gomes, José Francisco; Fabris, Júlio César
One of the main challenges in theoretical physics over the last fifty years has been to reconcile Quantum Mechanics with General Relativity into a theory of Quantum Gravity. Theory that has not yet been found, in a concrete way, due to its complexity, specially when we deal with gravity-matter systems, and lack of technologies that may give us experimental evidences. But, there are many theoretical models which try to explain this theory, among of them we have Loop Quantum Gravity. In order to understand and simplify the difficulties of of Loop Quantum Gravity theory in 3 +1 dimensions, we study models in lower dimensions. Starting from a topological BF model, discussed in this thesis gravity-matter systems of two-dimensional space-time, by means of supersymmetric extensions N = 1. We discuss two models: 1.) In the first model, the gauge group of the theory is given by the super-(anti-) de Sitter, S(A)dS, supergroup, that is a supersymmetric extension N = 1 of the (A)dS gauge group, which have three bosonic generator and two fermionic generators. 2.) In the second model, we couple topological matter, being guided by the existence of a rigid supersymmetry (especifically we study the Euclidean gravity with positive cosmological constant), where the fields content is of the theory is expressed in terms of superfields, with the gauge group being a "supersymmetrization"of SU(2). In this particular case we quantize the model by extending techniques well used in Loop Quantum Gravity. In both cases, we discuss the canonical structure of the model, we show that the Hamiltonian of the theory is completely constrained, we also construct gauge invariant quantities (Dirac observables)
A Quantização da Gravitação em 3D com Constante Cosmológica Positiva
(Universidade Federal do Espírito Santo, 2012-07-31) Almaraz, Zui Agustin Oporto; Constantinidis, Clisthenis Ponce; Piguet, Olivier; Vanzella, Daniel Augusto Turolla; Ribeiro, Maria Cristina Batoni Abdalla; Alvarenga, Flávio Gimenes; Gomes, Jose Francisco; Gonçalves, Sergio Vitorino de Borba
It was shown by Bonzom and Livine that 2+1 gravity with cosmological constant contains an ambiguity that depends on a Barbero–Immirzi-like parameter ? known from 4D gravity. Based on this fact, we showed that, for the ? > 0 case, the Lorentzian theory can be partially reduced, thanks to a suitable gauge fixing, to a Chern–Simons theory with compact gauge group SU(2). Then we revised already known loop quantization of Chern–Simons theory for the case of a space with the topology of a cylinder. Finally we construct a quantum observable which, despite having a not trivial spectrum at the quantum level, it corresponds to a classical quantity identically null.
Os efeitos das condições de contorno na eletrodinâmica escalar e o efeito Casimir para N regiões de largura finita e diferentes potenciais
(Universidade Federal do Espírito Santo, 2012-10-26) Dilem, Bernardo Brunoro; Nogueira, José Alexandre; Orlando, Marcos Tadeu D'Azeredo; Justo Filho, João Francisco; Gonçalves, Sergio Vitorino de Borba; Salcedo, Walter Jaimes; Zimdahl, Winfried Ernst Wilhelm
The present work can be divided into two main parts: the former, Chapter 3, we have investigated in what conditions the imposition of homogeneous Neumann boundary conditions on two infinite parallel plane surfaces separated by a distance a, could inhibit the spontaneous symmetry breaking in Coleman-Weinberg mechanism for the scalar electrodynamics. In the work of reference [1], this objective has been achieved through an expansion of the effective potential in powers of a?, where ? 2 represents the quadratic terms in the scalar field, from which the critical points ??c? of Vef (maximum and minimum) were found. That approach is tedious and complex, and require careful analyse. In this work, without resorting to any expansion of the effective potential, we have showed in a very simple way that, if a ˜ e 2M-1 ? (where e is the charge of the scalar field and M? its mass generated by Coleman-Weinberg mechanism), ??c? = 0 is the minimum point of Vef and that, therefore, the spontaneous symmetry breaking is inhibited. In the second part, Chapter 6, we have developed a more general proposal to deal with the Casimir effect. As a prototype we have used the real scalar field interacting with N regions of different potentials – represented by step functions – in (n+1) dimensions. As result we have obtained expressions which permit us to calculate, through the momentumenergy tensor, the energy and the force of Casimir for any number of barriers or regions of different constant potentials, consequently it is applicable to very different cases. In the Chapter 7 and 8 we have investigated some possibilities, alternating our original propose of different finite regions and the extreme case of barriers represented by delta Dirac functions. We have also shown that, in the limit of strong coupling, our results recover the famous L¨ucher et al. result, as it was expected
Conjuntos de bases gaussianas: aplicações em cálculos de constantes espectroscópicas e rotação ótica
(Universidade Federal do Espírito Santo, 2012-12-14) Campos, Cesar Turczyn; Jorge, Francisco Elias; Schneider, Edgar; Pires, José Maria; Freitas, Luiz Carlos Gomide; Morigaki, Milton Koiti
Segmented all-electron contracted sextuple zeta valence plus polarization function (6ZP) basis sets for the elements from H to Ar were constructed to be used in conjunction with the nonrelativistic and Douglas-Kroll-Hess (DKH) Hamiltonians. The scalar relativistic effect at the coupled cluster (CC) level of theory on atomization energy for a sample of molecules was discussed. Additional improvements in the atomization energies were achieved by applying corrections due to core/valence correlation, atomic spin-orbit effects, and addition of tight d and f functions on second-row elements. This leads to estimates for the heat of formation of gaseous boron and carbon tetrafluoride. With the purpose to have a better description of some molecular properties, the non relativistic and relativistic segmented all-electron contracted double, triple, quadruple, quintuple, and sextuple zeta valence plus polarization function (XZP and XZP-DKH, X= D, T, Q, 5, and 6) basis sets for the elements from H to Ar were augmented with high-exponent d “inner polarization functions”, which were optimized in the molecular environment at the M?ller-Plesset secondorder level. At the CC level of theory, the effect of including tight d functions in these elements was found to be essential to improve the agreement between theoretical and experimental zero-point vibrational energy (ZPVE) and atomization energy. For all molecules studied, the ZPVE errors are always smaller than 0.5%. Additional improvements in the atomization energies were achieved by applying corrections due to core/valence correlation and atomic spin-orbit effects. This leads to estimates for the atomization energies of various compounds in gaseous phase. The largest error (1.2 kcal/mol) occurs for SiH4. Finally, using the hierarchical sequence of augmented XZP (AXZP, X = D, T, and Q) for the atoms from H to Ar in conjunction with the B3LYP, PBE1PBE, M06, and M06-2X functionals, a systematic study of Gaussian basis set convergence on frequency dependent optical rotation ([?]?) calculations of thirteen rigid chiral molecules at their equilibrium geometries were xvii reported. By direct calculations or by fitting the directly calculated values through one extrapolation scheme, estimates of complete basis set limits were obtained. These limits can be used as reference values to calibrate further density functional theory calculations
Relação entre o transporte elétrico e a estrutura de poros no sistema YBa2Cu3O7
(Universidade Federal do Espírito Santo, 2013-01-29) Piumbini, Cleiton Kenup; Alfonso, Jorge Luis Gonzalez; Cunha, Alfredo Gonçalves; Rodrigues Junior, Durval; Ferreira, Letície Mendonça; Freitas, Jair Carlos Checon; Caetano, Edson Passamani
The principal objective of this thesis is the study of the relationship between the transport critical current density and the pore structure in YBa2Cu3O7-y bulk samples. In order to perform the experimental work samples of two different systems were prepared. The first sintered system was (YBa2Cu3O7-y)1-x(Sb2O3)xwhile the second one was obtained through the use of different sintering conditions. The samples were characterized through X-ray, magnetic and transport critical current density measurements, besides N2 sorption analysis. In both systems, the doping and the different sintering conditions modified the pore structure of the samples. For the (YBa2Cu3O7-y)1-x(Sb2O3)x system the transport critical current density did not depend on the pore structure, while in the second system this parameter showed a strong correlation with the principal features of the pore structure. In order to better understand the correlation between the electric transport and the structural properties of the specimens, it was developed a computational simulation aiming to incorporate the principal elements of the granular structure of ceramic samples. To this end, the granular simulated granular structure was obtained by a tessellation of the space through the Voronoi technique. The results of computer simulations show that it is possible to capture the dependence of the critical current density of transport with the relevant quantities to different systems studied in this thesis. Finally, this work shows the importance of controlling the pore structure in order to optimize the electrical properties of ceramic superconductors cuprates, which is transcendent to possible technological applications of these systems.
Conjuntos de bases gaussianas para K até Kr e para Pt: aplicações em cálculos de propriedades moleculares
(Universidade Federal do Espírito Santo, 2013-03-04) Berredo, Ricardo Coelho de; Jorge, Francisco Elias; Canal Neto, Antônio; Lima, Denise da Costa Assafrão de; Santos, Hélio Ferreira dos; Mohallem, José Rachid
All-electron segmented contracted quadruple zeta valence plus polarization function (QZP) basis sets for the elements from K to Xe were constructed to be used in conjunction with the non-relativistic and Douglas-Kroll-Hess (DKH) Hamiltonians. The QZP-DKH set is obtained from the corresponding original QZP basis set, i.e., the values of the contraction coefficients were re-optimized using the relativistic DKH Hamiltonian. This extends earlier works on segmented contracted QZ basis set for atoms H–Ar. At the Coupled-Cluster level of theory, the convergence of atomic ionization energy as well as of molecular spectroscopic constants as a function of basis set size is examined. Additional improvements on spectroscopic constants were achieved by applying corrections due to core-valence correlation and spin-orbit effects. This leads to estimates for the spectroscopic constants of various diatomics in gaseous phase. One verifies that the experimental and benchmark theoretical bond lengths, dissociation energies, and harmonic vibrational frequencies can be reproduced well with the QZP-DKH set. Segmented all-electron contracted double zeta valence plus polarization function (DZP) basis sets for the Pt element were constructed for use along with the non-relativistic and DKH Hamiltonians. The DZP-DKH set is loosely contracted and thus offer computational advantages compared to the generally contracted relativistic basis sets, while their sufficiently small size allows it to be used in place of effective core potentials (ECP) for routine studies of molecules. Using the one-parameter hybrid functional mPW1PW, the performance of the basis sets is assessed for predicting the molecular structures and atomic charges of platinum(II) antitumor drugs, cisplatin and carboplatin. These results can be used as reference values to calibrate further ECP calculations. Despite their compact size, the DZP sets demonstrate consistent, efficient, and reliable performance and will be especially useful in calculations of molecular properties that require explicit treatment of the core electrons. With the purpose of having a better description of electron affinity, polarizabities, and hydrogen bonding, the DZP set was augmented with diffuse (s, p, and d symmetries) and polarization (f symmetry) functions that were optimized for the anion at the Hartree-Fock and Møller-Plesset second-order levels, respectively. From optimized relativistic geometries and using non-hybrid and hybrid functionals, the performance of the augmented DZP (ADZP) set is assessed for predicting static electric dipole moment and polarizability of PtH, PtH2, and antitumor drugs (cisplatin and carboplatin). Despite its compact size, the ADZP set demonstrates consistent, efficient, and reliable performance. ADZP electric property calculations showed to be as fast as those that use augmented ECP basis sets
Transições de Fase nas Teorias Holográficas sem Supersimetria
(Universidade Federal do Espírito Santo, 2013-03-14) Silva, Ulysses Camara da; Sotkov, Galen Mihaylov; Lourenço, José André; Gomes, José Francisco; Pereira, Rodrigo Gonçalves; Braga, Nelson Ricardo de Freitas
According to the gauge/gravity correspondence rules, the holographic description of certainstrongly coupledQF Td-1at infinite volume and zero temperature is based on the particularflat Domain Walls (DW’s) solutions of their duald-dimensional Gravity models. The mainproblem addressed in the present thesis concerns the systematic application of the Gauss-Bonnet (GB) and cubic Quasi-Topological Gravity (QTG) DW’s to the investigation of theRenormalization Group (RG) properties and of the phase structure of theirQF Td-1’s duals.It represents an off-critical extension of the recent holographic studies of a family ofa!=cCF Td-1’s with non-vanishing energy flux parametert4.We derive a BPS-like first order system of equations for a family of flat static DW’s for the GBand cubic QTG extensions of Einstein Gravity coupled to massive scalar self-interacting matter,by introducing an appropriate matter superpotential. The knowledge of such DW’s solutions,allows us to construct the exactQF T’s beta-functions, as well as of the trace anomaliesa(l)andc(l), in terms of the corresponding superpotentials. As a consequence, we are ableto determine the complete set ofCF T'sdata characterizing the universality classes of theUV and IR critical points and to follow the particular RG evolution of this data. We furtheranalyse the dependence of the critical properties of such dualQF T’s on the values of thegravitational GB’s and QT couplings and on the shape of the considered superpotentials. Forodd values ofd, the explicit form of the “a- andc-central charges”, as functions of the runningcoupling constant, enable us to establish the conditions under which thea&c-Theorems fortheir decreasing are valid. The restrictions imposed on the massless Holographic RG flows bythe requirements of the positivity of the energy fluxes are also derived. Few specific polinomialsuperpotentials are studied in detail.They provide examples of unitary dualQF T’s having c!=acritical points representing second or infinite order phase transitions. Depending onthe range of the values of the coupling constant, they exhibit massive and massless phases,described by a chain of distinct DW’s solutions sharing common boundaries.We have also found an extension of the superpotential method for GB’s and cubic Quasi-Topological Gravity coupled to an arbitrary number of interacting scalar fields. For appropriatechoices of the matter superpotentials, theirphase diagrams turn out to have the well knownBerezinski-Kosterletz-Thouless form, with aline of second order phase transitions at weakcoupling and specific infinite order massless-to-massive phase transitions in the cross-overregion.The aim of the present research is to provide more arguments in favour of the conjecturethat by holographic calculations based ond=5GB and cubic QT Gravity models one canreproduce the strong coupling limits of certain unitary (non-supersymmetric)QF T4’s, whosemassive and massless phases exhibit “phenomenologically reasonable” off-critical features.

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