Mestrado em Física

URI Permanente para esta coleção

http://repositorio.ufes.br/handle/10/17494

Nível: Mestrado Acadêmico
Ano de início: 1992
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=1508

Navegar

Agora exibindo 1 - 20 de 122

Uma revisão da gravitação bidimensional do ponto de vista da gravitação quântica de Loops
(Universidade Federal do Espírito Santo, 2007-06-28) Costa, Alex Rios; Piguet, Olivier; Constantinidis, Clisthenis Ponce; Alvarenga, Flavio Gimenes; Marchioro, Dáfni Fernanda Zenedin
We make an introductory study of the formalism of Loop Quantum Gravity. A brief review of the cononical formulation of General Relativity is performed, in order to motivate the introduction of the loop formalism. We show how it can be adapted to bidimensional gravity, more specifically to the Jackiw-Teitelboim model, for which we make a complete analisys of the canonical formulation using the first order formalism. We finally comment on how the quantization procedure could be implemented in this model
Correção logarítmica no potencial newtoniano e sua aplicação a galáxias espirais
(Universidade Federal do Espírito Santo, 2007-08-03) Campos, Juliano Pereira; Fabris, Júlio César; Sodré Júnior, Laerte; Gonçalves, Sérgio Vitorino de Borba
A well elaborated characterization of the masses of the galaxies is of basic importance to understand the formation and the evolution of the galaxies, as well as the Universe. The circular speed of the spiral galaxies is used to estimate the mass of the galaxies. The observacional data of the rotation curves exactly show that the circular speeds practically remain constant at large distances of the galactic center, where the influence of the luminous mass is very attenuated. With this observacional evidence, of originates one of the controvertial problems of astrophysics galactic and the extra-galactic: what it could cause this phenomenon? Some researchers try to solve the problem of the flattenning of the rotation curves adding one extra component of mass, the dark matter; other researchers consider a correction in the Newtonian gravitational potential. We present in this work, a logarithmic correction in the Newtonian gravitational potential as an alternative for the explanation of the problem of the flattenning of the rotation curves without the necessity to add dark matter. Moreover, the logarithmic structure of the correction opens possibility of connection with the theory of cosmic strings. Although the use of a simplified disk mass distribution, the obtained analytical results in the present work show to an excellent agreement with the observational data of the curves of rotation of the majority of analyzed galaxies LSB. These results stimulate to invest in the sophistication of the model
Confrontando cosmologias newtoniana e neo-newtoniana através do processo de formação de estruturas
(Universidade Federal do Espírito Santo, 2007-09-21) Velten, Hermano Endlich Schneider; Alvarenga, Flávio Gimenes; Gonçalves, Sérgio Vitorino de Borba; Silva, Saulo Carneiro de Souza
If we utilize the hidrodynamical equations in the study of the Universe we obtain a New-tonian cosmology. However, if we consider the effects of the inercial pressure and thedistinction between gravitacional mass and inercial mass it is possible to obtain a newset of hidrodynamical equations that we call neo-Newtoniancosmology. In this work westudy the aplicabillity of these two approach in structure formation theory throught amodel constituited by baryonic matter and Chaplygin gas. Weconfront the theoreticalpower spectrum of Newtonian cosmology and neo-Newtonian Cosmology with the 2dF-GRS observational data. The purpose of this analysis is to obtain the advantage of eachapproach. Moreover, we search the origin of the oscillations and divergences observed inthe Chaplygin gas power spectrum.
Estudo de efeitos dinâmicos até o início da fratura frágil
(Universidade Federal do Espírito Santo, 2007-10-29) Vassem Júnior, Arnobio Ignacio; Emmerich, Francisco Guilherme; Mendes Filho, Josué; Cunha, Alfredo Gonçalves; Alves, Klinger Marcos Barbosa
In this work it ismade the experimental study of dynamic effects to the beginning of the fragile fracture, being used anapparatus that simulates atwo-dimensional crys-tallinestructure, in the which is possible to accomplish reversible experiments of frac-ture. The apparatus reproduces atomistic characteristics and it is formed quadrupolar magnets in the roleof unitary cells. That experiment is important because the obser-vation in-locoof the area at the beginning of the fracture it is not trivial. With the ob-jective of analyzing the dynamic effects in full detail until the beginning of the rupture, a system of image observation was developed in which was possible to obtain digital recordings with rates of the order of hundreds of pictures persecond. During the ex-ecution of the experiments, they were applied mechanical disturbances to the sys-tem. Each disturbance generated a harmonic oscillation that was filmed with the de-veloped equipment. The videos were analyzedpicture bypicture and with these data,graphs of the oscillation widthin function of the time were tracedand were observed picks and valleysthat decline exponentially. Starting from these graphs they were obtained the oscillation frequencies for each configuration of applied tension. This way it was obtained the equivalent constant of spring of the system. A peculiar beha-vior was also observed where a transienthappens before the first valleyis obtained. The mounted equipment was shownefficient for the purpose that was idealized and also for other applications involving mechanical oscillations and fracture dynamics, as the propagation of cracks, in materials of module of elasticity relatively low as the employed solid in this work
A Influência da mecanossíntese na estabilização da fase tipo NaZn13 nos compostos [La0,95(RE)0,05]Fe11,4Si1,6 (RE = Y ou Gd)
(Universidade Federal do Espírito Santo, 2007-10-30) Alves, André Luíz; Proveti, José Rafael Cápua; Caetano, Edson Passamani; Nunes Filho, Evaristo; Sommer, Rubem Luis; Larica, Carlos
We have studied the stabilization of NaZn13 phase in the intermetallic compound of generic composition LaFe11,4sp1,6 (sp = Si, Al). This stabilization was investigated through the partial substitution of Fe by atoms of Al and Si, and trough the substitution of La by Y or Gd, which are rare earths elements with no orbital contribution to the magnetic moments. We have chosen to study the compounds with stoichiometry LaFe11,4sp1,6 (sp = Al, Si), with y = 0,88, for which compounds are metamagnetic. We firstly studied NaZn13 phase formation in some mixed compounds of composition LaFe11,4(AlxSi1-x)1,6 (0 less or equals x less or equals 1), prepared using an electric arc furnace. The compounds were characterized by Mössbauer Spectroscopy, X Rays Diffraction and Energy Dispersive X Ray Spectroscopy. Some compositions have a predominant NaZn13 phase, while in other regions the fraction of the NaZn13 phase is relative small due to the presence of other phases formed by segregation. We have also investigated the partial substitution of La atoms by atoms of Y and Gd, in the following compounds La1-x(RE)xFe11,4Si1,6 (RE = Gd or Y), with x= 5%. This substitution doesn t modify significantly the stabilization of the NaZn13 phase compared to the non-substituted compound and the fraction of the segregated a-Fe phase is maintained around 50%. We have used a new procedure using the mechanical alloying to prepare LaFe11,4Si1,6 compounds. It consists in submitting the melted sample to a 0.5 to 1 hour long high energy ball milling process and then in annealing the sample. The process induced a significant reduction of the rich-Fe phase formation compared to a conventional process. Therefore, the process allows to obtain samples with a higher fraction of the desired NaZn13 phase. Therefore, the process allows obtaining samples with a higher fraction of the desired NaZn13 phase
Efeitos das condições de contorno de Neumann na eletrodinâmica escalar
(Universidade Federal do Espírito Santo, 2008-02-21) Fagundes, Fábio Nascimento; Nogueira, José Alexandre; Belich Júnior, Humberto; Bayer, Valmecir Antonio dos Santos; Franco, Daniel Heber Theodoro
We consider the effects of homogeneous Neumann boundary conditions in the scalar electrodynamics with self-interaction. We have found if the length of the finite region is small enough the scalar field develops mass, even though spontaneous symmetry breaking is not induced. As a result the vector field does not develop mass. As byproduct we have gained the Casimir energy. We also show that the physical results (mass of the scalar field and vacuum energy density) are gauge-invariant
Influência da substituição de Mn por Fe sobre o efeito magnetocalórico inverso de ligas Heusler tipo Ni-Mn-Sn
(Universidade Federal do Espírito Santo, 2008-05-30) Xavier, Fábio; Larica, Carlos; Perlingeiro, Pedro Jorge Von Ranke; Caetano, Edson Passamani; Takeuchi, Armando Yoshihaki; Larica, Carlos
In this work, the magnetic entropy change was observedexperimentally inthe Heusler alloys Ni2(Mn1-xFex)Sn with x = (0; 0,25; 0,33; 0,50; 0,75)(series A)and type Ni2(Mn1-xFex)1,44Sn0,56with x = (0; 0,03; 0,07; 0,10; 0,15)(series B).The structural characterization of these alloys was carried by measurements ofX-Raydiffraction andElectronic Microscopy.The magnetocaloric properties had been quantified by magnetizationmeasurements in function of the temperature and applied magnetic field. The X-Ray diffraction patterns evidences a cubic phase type L21 for all samples at room temperature. The magnetization measurement for samples of series A,exhibitedaferromagnetic behavior.However, the increase of Fe concentrations in these samples resulted in a decrease of the Curietemperature (Tc) from 330 K to 290 K. The magnetization measurement for samples of series B, had demonstrated the presence of a structural phase transition until contents of 7% ofFe. The increase of iron content in these samples has resulted in an increase of the TCof 302 to 325 K and a reduction in the structural phase transition temperature of 290 to 160 K. Theinverse magnetocaloric effect was observed in samples of series Bwith structural transitionof type martensitic-austenitic. The magneticentropy change observed next to the structural transition temperatureswas of 10 J/kg.Kapproximately, inan applied magnetic field of 5 T.
Estudo do Modelo de Ginzburg-Landau e as Cerâmicas Supercondutoras
(Universidade Federal do Espírito Santo, 2008-06-05) Alves Junior, Leonidio Joaquim; Orlando, Marcos Tadeu D’Azevedo; Belich Junior, Humberto; Orlando, Marcos Tadeu D’Azevedo; Helayël Neto, José Abdalla; Nogueira, José Alexandre; Belich Junior, Humberto
In this dissertation we have worked out a study of thermodynamics described by the model of Ginzburg–Landau. We emphasized the points that always appear in the literature of superconducting temperature until 30 K. We analyzed the phase transitions that occur in the samples described by this model. It was also made a brief introduction to the properties of superconducting ceramics, taking the example of cuprates based on mercury (Hg - 1223). We noted that by spraying of the superconducting chip, appeared two different critical temperatures. We concluded the dissertation proposing an extension of the model Ginzburg - Landau describing this splitting of the critical temperature.
Estudos sobre o oxalato de cálcio dihidratado encontrado em pedras de rins
(Universidade Federal do Espírito Santo, 2008-09-30) Costa, Fanny Nascimento; Belich Junior, Humberto; Orlando, Marcos Tadeu DAzeredo; Passos, Carlos Augusto Cardoso; Correa, Hamilton Perez Soares; Pires, José Maria
Pirólise do pireno sob pressão com nitrogênio em temperaturas moderadas
(Universidade Federal do Espírito Santo, 2008-10-24) Vassem, Gilceia Libera Sarnaglia; Emmerich, Francisco Guilherme; Castro, Luiz Depine de; Freitas, Jair Carlos Checon de; Cunha, Alfredo Gonçalves; Emmerich, Francisco Guilherme
We made an study to help the understanding of the formation process ofpitches using a homogeneous compound, pyrene,whichis a polycyclic aromatic hydrocarbon constituted byfour benzene rings,meltingpointbetween145 and148 °C anda boilingpoint of 404 °C. The pyrene wassubmitted toheat treatmentsunder nitrogen atmospherein an experimentalset updeveloped at the Laboratory of Carbon MaterialsoftheFederal University of Espírito Santo. The heat treatments were performed at 400, 450 and 500 °C, with residence timeof 0, 1, 2, 4, 8 and 16 hours, under a final pressureof 6,9 MPa. The samples were characterized bythermogravimetry, differential scanning calorimetry, X-ray diffraction, solid-state 13C nuclear magnetic resonance spectroscopy,and scanning electron microscopy. We did not observe significant modifications of the samples heat treated at 400 and 450 °Cfor all studied residence times in relation to the original precursor. The samplesobtained at 500 °C suffered significant modifications from 4 hoursof residue time; the treatments for8 h and 16 h produced segregation, the samplesbeingdivided into two well-defined regions (A and B regions). The 500-8hBand 500-16hBsamples sufferedthe mostnoticeablemodifications in relation to the precursor. Theelementalanalysis and thermogravimetric results indicatedthat the 500-8hBsamplepresentedcharacteristics similar topitches, additionalstudieswillbenecessarytoverifyiftheanisotropiccarbonmaterialisreallyapitch. The elementalanalysis, X-ray diffraction and scanning electron microscopy resultsindicatedthat the 500-16hBsample presentedcharacteristicsof acoke. The X-ray diffraction patternsand NMR spectraresults of the 500-16hBsample indicate the formation of aromatic lamellae typicalof the turbostratic structure of grafitizable carbon materialswith a relatively hight value of Lcobtained at a low heat treatment temperature.
Caracterização Estrutural, Morfológica e Magnética da Dupla Perovsquita Ca2MnReO6.
(Universidade Federal do Espírito Santo, 2009-05-26) Souza, Danilo Oliveira de; Belich Junior, Humberto; Orlando, Marcos Tadeu D’Azeredo; Nogueira, José Alexandre; Mazzocchi, Vera Lúcia; Orlando, Marcos Tadeu D’Azeredo; Belich Junior, Humberto
Compounds with structure of ordered double perovskyte, A2B’B’’O6 (A being an alkaline-earth and B being a transition-metal in alternate sites) have attracted interest of the researches because their strong correlated structural and magnetic properties. Moreover, they are suitable candidates to produce devices with great application in spin-electronic, named “spintronics”. The special group of these compounds, the Re-based ordered double perovskites, i. e., the double perovskites where the B’’ sites are occupied by Re atoms, have been studied since 1961. However, it was only at the last decade, in spintronics framework, that these compounds have received a special attention. This work describes the synthesis and characterization of Ca2MnReO6 ordered double perovskyte. It does that by marking out sintered procedures and the structural and magnetic properties, which have been investigated by synchrotron x – ray powder diffraction, x – ray absorption spectroscopy and magnetic measurements. SEM images have shown homogeneity phase composition, the morphology and size of the ceramic grains. The Rietveld refinement has revealed a monophase compound and it was used to determinate the lattice parameters. The x – ray absorption spectroscopy agrees with the diffraction results and point to a formal (or effective) valence for Re atoms as +5,5. An interpretation of this result is that there exists a mixed valence for Re atoms, balanced by mixed valence of Mn atoms. The magnetic susceptibilities measurements were performed with temperature variation and have pointed a paramagnetic phase transition in 120 K with a spin glass type state below this value. An explanation for the magnetic result may be given with assumption of low contribution magnetic moment of Re atoms, or a nonexistent one.
O efeito da substituição parcial de Sn por metais 3d na transição de fase de primeira ordem de ligas Heusler NiMnSn.
(Universidade Federal do Espírito Santo, 2009-05-29) López Córdova, Cecilia; Caetano, Edson Passamani; Larica, Carlos; Proveti, José Rafael Cápua; Azevedo, Izabel Souza de; Caetano, Edson Passamani
Results reported in the literature show that the martensitic phase transformation (MFT) in the Ni50Mn25Sn25 Heusler alloy can be achieved when an excess of Mn atoms are in the Sn sites1 and the Mn partial substitution by Fe atoms in the martensitic Ni50Mn36Sn14 Heusler alloy results in a reduction of the MFT temperature, being this transformation absent for Fe concentration larger than 10 at. %.19 In this work, we prepared, by arc-melting furnace, two different series of samples, where we studied (i) the Fe localization and magnetism and also the origin of the reduction of the MFT observed after a partial substitution of Mn atoms by Fe in the martensitic Ni50Mn36Sn14 Heusler alloy (Series-A) and (ii) the possibility of MFT occurrence in the Ni50Mn25Sn25 Heusler alloy when Sn atoms are substituted either by Cr or by Fe (Series-B). We characterize our samples by magnetization, scanning electron microscopy and 57Fe Mössbauer spectroscopy. The results show that there is a solubility limit in all partial substitutions done in this work, i.e., Mn substituted by Fe and also Sn substituted either by Cr or by Fe; being the solubility limit more restricted in the Series-B case, since we observed segregated phases in all Series-B samples, even for very low substitution transition metal concentration (Cr or ). We conclude that this segregation effect, observed in both Series-A and B, is responsible for the absence of the MFT observed in our samples. Specially, in Series-B, Cr crystals, with polygonal shapes and sizes of about to , are formed during the phase segregation process in all Cr samples. Our results also allow us to estimate to be about 2% the solubility limit of 57Fe in Mn sites of the L21-structure of the martensitic Ni50Mn36Sn14 Heusler alloy. These 57Fe atoms are magnetic at 300K and have magnetic moment of.
Quantização de Laços no Modelo BF em 2+1 dimensões
(Universidade Federal do Espírito Santo, 2010-03-09) Mendonça, Diego Cézar Monteiro de; Constantinidis, Clisthenis Ponce; Piguet, Olivier; Alvarenga, Flávio Gimenes; Helayël Neto, José; Piguet, Olivier; Constantinidis, Clisthenis Ponce
The goal of this paper is to serve as an introductory text to the following topics: canonical quantization, loop quantization, and the BF model. To this end, we develop appropriate mathematical tools for treating a topological gauge theory of the general Yang-Mills type to formulate a covariant action and study its symmetries via the canonical Dirac quantization method, also known as the Hamiltonian bound method. This method is developed extensively, although it retains its introductory character, for the case of the 2+1 dimensional BF model, which we then quantize via bonds and find identifications of this whole process with the theory of general relativity expressed as a gauge theory. Finally, we will see how the quantum mechanics of these gauge theories develops by describing the basis for our state functions which is called the spin network, as well as the dynamics of these loop quantized theories which is described by the formalism of spin foams and also the calculation of some observables associated with our states.
O "V" de Gowin no laboratório estruturado de Física : um estudo exploratório em uma disciplina de Física Experimental da graduação em Física
(Universidade Federal do Espírito Santo, 2010-03-22) Maciel Junior, Paulo de Oliveira; Silva, Laércio Evandro Ferracioli da; Larica, Carlos; Alves, Klinger Marcos Barbosa; Gomes, Thiéberson da Silva
This exploratory study shows results on the investigation of the use of Gowin's Epistemological “V” in an Experimental Physics discipline in the Physics degree at the Federal University of Espírito Santo. For the development of this study, the implantation of the “V” by Gowin was structured in the Experimental Physics I discipline for the Educator / Degree and Researcher / Bachelor of the New Curriculum of the Physics Course at UFES. A script was used on the use of Gowin's "V" in Experimental Physics and the scripts of the experiments carried out in the discipline. The students produced a “V” by Gowin for each experiment, with the objective of explaining the structure of the experiment, that is, what are the Basic Research Questions related to the objectives of the experiment; what the Conceptual Domain consists of, that is, the Principles & Laws, the Hypotheses and the Concepts involved in the experience; what are the Events held to promote observations and data collection of the experiment; what is the Methodological Domain used, that is, what are the Records of Events, the necessary Transformations, the Results of these Transformations and the possible Interpretations from these Results; what are the Answers to the Basic Research Questions proposed and; what is the relevance of these Answers and of the entire experiment studied. To analyze the Gowin "V" s produced, evaluation criteria were used based on parameters that value the articulation of the "V" aspects. With the conclusion of the study, it was possible to analyze the skills and difficulties presented by the students with the implantation of Gowin's “V” in Experimental Physics. It was also possible to indicate contributions for the scripts delivered to students in the Experimental Physics discipline. And finally, an analysis was carried out on the evaluation criteria used in this study
Efeito da pressão em supercondutores de Hg-12(n-1)n e efeito Casimir na escala nanométrica.
(Universidade Federal do Espírito Santo, 2010-05-06) Rodrigues Junior, Valdi Antonio; Orlando, Marcos Tadeu D'Azevedo; Belich Junior, Humberto; Fabris, Júlio César; Ferraz Filho, Álvaro
In this work will be presented a description in wich Tc has a pressure-dependent behaviour in Hg-12(n-1)n superconductors, that takes into account the Casimir effect by considering the CuO2 conducting layers to act as plasma sheets. The Casimir energy arises from the parallel plasma sheets (Cu–O planes) whenever these are separated by distances on nanometer scale. The Tc pressure dependence in Hg12(n-1)n superconductors can be described by a pressure-induced charge transfer together with intrinsic terms that are associated with the Casimir energy. For Hg12(n-1)n samples with optimum oxygen content, the charge transfer term vanishes, leaving an explicit expression for the intrinsic term. By picking up realistic parameters and inserting them in the expression for the Tc pressure dependence, we have a good agreement with experimental intrinsic term data observed in the mercury family Hg-12(n-1)n superconductors.
Efeito Casimir em placas de plasma e a energia de condensação do supercondutor do tipo (Hg, Pb)Ba2-xSrxCa2Cu3O8+
(Universidade Federal do Espírito Santo, 2010-06-08) Amorim, Leandro Silva; Orlando, Marcos Tadeu D'Azeredo; Justo Filho, João Francisco; Nogueira, José Alexandre
In this work a study about the behavior of the critical temperature (Tc ) in ( ) 2- 2 3 8+d Hg,Pb Ba xSrxCa Cu O superconductors (Hg–1223) has been done. It is suggested that the condensation energy of the superconductor is due to Casimir energy of the CuO plans, considering these plans as thin plasma sheets. From this hypothesis one can relate de transition temperature dependence with some crystalline lattice variables, and universal constants as well, and among these variables, there is the effective mass correction parameter of the Cooper pairs. The desired goal here is to obtain an approximation of Tc for the family of the ceramics mentioned above in comparison to experimental data, and with arbitrary adjusted values of a , but in a concise and plausible way
Modelo acústico análogo ao buraco negro de Schwarzschild
(Universidade Federal do Espírito Santo, 2010-07-29) Toniato, Júnior Diniz; Gonçalves, Sérgio Vitorino de Borba; Monerat, Germano Amaral; Constantinidis, Clisthenis Ponce; Alvarenga, Flávio Gimenes
There isn t experimental evidences that can validate the results of black holes termodynamics. This because the radiation emitted by the black hole, predicted by theory, it is almost impossible to be detected due to its low value of magnitude. In the search for clues that could validate the existence of this radiation, the study of analog models to those objetcs has grown considerably in recent decades. They allow the idealization of experiments in labs that would be extremely complicate to be done directly with the gravitational systems. A fluid in moviment can act on the sound the same way that curved space-time can influence on light trajectory in the general relativity. So, one can describe the propagation these sound waves through an effective metric, under wich they will follow null geodesics. This thesis makes a review of these studies focusing in an analogy to Schwarzschild black hole using an acoustic system, showing its advantages and limitations when applied in the study of Hawking s theory
As supernovas tipo Ia e a cosmologia
(Universidade Federal do Espírito Santo, 2010-08-09) Oliveira, Paulo Louzada Castro de; Fabris, Júlio César; Ricaldi, William Santiago Hipolito; Alcaniz, Jailson Souza de
This dissertation is dedicated to the investigation on the nature of the dark matter and dark energy in the Universe through the technique that uses the observations of explosions os supernovae type Ia as indicators of distances, used at the end of the last century to detect the acelerated expansion of the Universe. Since then some projects dedicated to observation of supernovae where executed and published their results, which are used here to estimate parameters and compare cosmological models. The objective of this work is to study the power of the test based on the distances to supernovae and its response to different cosmological models and free parameters. To begin with we review the standard model of Cosmology and the evidences that suport the existance of dark matter and dark energy, followed by a study on the supernovae itself and its various observational and astrophysical aspects that allow the construction of the magnitude calibration techniques and the estimatives of its distances. Before moving on to the cosmological analyses we introduce the appropriate tool which is the bayesian statistics, studied here only in its basic tools and aplications. At last we aply these tools to the supernovae data sets available in the literature know as the Gold, SNLS, Essence and Constitution, to study some cosmological models, beginning with the concordance ?CDM model and the ?CDM parametrization that tests the supposition that ?X = -1 for the dark energy. After that we test two dynamical vaccum energy ?(t) models and a special case of the quartessence Generalized Chaplygin Gas model. The results show that when used alone the supernovae data sets leeds to quite less expressive results when compared to the literature where they are used together with other evidences. And also two of the data sets including the most up to date show unexpected irregularities that point to the existance of still uncontrolled effects on the magnitude calibration techniques. Both results show that the cosmological test based on supernovae data will go through another significant improvement on its quality in the near future.
Modelagem computacional da corrente crítica em supercondutores policristalinos do tipo HgRe-1223
(Universidade Federal do Espírito Santo, 2010-11-12) Bolzan, Marcio de Sousa; Orlando, Marcos Tadeu D'Azeredo; Passos, Carlos Augusto Cardoso; Rossi, Jesualdo Luiz
There are many applications of superconductors for use where it is important to know the behavior of critical current density as a function of magnetic field in the sample, for both it was developed and analyzed a model to describe such behavior in polycrystalline samples of high superconducting critical temperature. The idea was to capture all or part of this behavior as accurately as possible. The theory is based on assumptions that the grains that form polycrystalline superconducting samples are connected by Josephson junctions where it is observed macroscopic quantum interference effects between superconductors separated by a junction crossed by a tunneling current with a dependence on the flow of applied magnetic field, the Cooper pairs tunneling junctions with such a type Fraunhofer diffraction pattern so that the critical current in weak joints is influenced by the first application of magnetic field, thus in a certain field and temperature regime close to critical, critical current in the sample is given by the superposition of Josephson currents influenced by the field at each junction. Finally, the model was be adjusted with the aid of experimental data, the critical current density as a function of applied magnetic field, obtained from polycrystalline samples of superconducting ceramic HgRe-1223 with 5% oxygen doping
Gravitação quântica em laços : modelo de Chern-Simons e gravitação em 2+1 dimensões
(Universidade Federal do Espírito Santo, 2011-04-27) Barbosa, Rodrigo Martins de Siqueira; Piguet, Olivier; Constantinidis, Clisthenis Ponce; Gonçalves, Sergio Vitorino de Borba
The theory of Loop Quantum Gravity gives us an very interesting framework to handle the quantization of general gauge theories. On a work by Witten, 1989, it is proposed that General Relativity on 2+1 dimensions could be described as a gauge theory of a Chern-Simons action over a Poincar´e gauge group. The purpose of this work then is to make a possible quantum description of gravitation on 2+1 dimensions by the Chern-Simons model, and make a discussion about the observables of this model

Navegar

Navegando Mestrado em Física por Data de Publicação

Resultados por página

Opções de Ordenação