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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A energia de Casimir e a energia de transição de fase Ferromagnética em Duplas Perovskquitas
(Universidade Federal do Espírito Santo, 2017-05-26) Rocha, Jefferson Rodrigues; Orlando, Marcos Tadeu D’Azeredo; Orlando, Marcos Tadeu DAzeredo; Nogueira, José Alexandre; Batista, Antonio Brasil; Soares, Jacyra Ramos; Orlando, Marcos Tadeu D’Azeredo; Justo Filho, João Francisco
This thesis is based on Bordag’s theory of Casimir energy. This proposal relates the Casimir energy between conductor plasma planes and the thermal energy in the transition in double ferromagnetic conductive perovskites. Using this association it was possible to calculate the critical temperature of Curie ???? relating the fraction of the energy between these materials and the parameters of Sommerfeld ?? of each compound. To evaluate experimentally our proposal we considered the transition temperatures ???? and the parameters of 3 samples: ????2??????????6,????2?? ????????6 e ????2?? ????????6.We have found that for these samples the distance ?? between the conducting planes is associated with the Curie temperature Tc. Our proposal for the calculation of ???? is consistent with the values found in the literature for samples with these characteristics (ferrometal and conductive). Based on our theory we proposed the preparation of a new sample that presented a parameter ?? similar to that of the sample ????2??????????6 thus generating a Curie temperature ???? ˜ 635??,namely:????1.8??0.2??????????6. This new compound is a double perovskite with ferromagnetic metallic characteristics and octahedral geometry formed by planes containing ??????6 and presenting ?? ?? = 635??.
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.
Abordagem relativística para o átomo de hidrogênio em um cenário de comprimento mínimo introduzido pela álgebra Lorentz-covariante de Quesne-Tkachuk
(Universidade Federal do Espírito Santo, 2013-11-29) Francisco, Ronald Oliveira; Fabris, Júlio César; Nogueira, José Alexandre; Helayel Neto, José Abdalla; Bazeia Filho, Dionisio; Rodrigues, Davi Cabral
One of the reasons for gravity can not be included in the standard model is its non-renormalizability. Almost all the proposals for the quantization of gravity leads to existence of a minimal length which acts as a natural regulator. That effect suggests a generalized uncertaintly relations between position and momentum operators what results in a modified commutation relation between these operators, and thus changing the whole structure of quantum mechanics. In this work we calculate the magnitude of this minimum length through the energy of the ground state of the hydrogen atom in Dirac’s theory, based on the Quesne-Tkachuck commutation relation. Comparing with experimental data, we obtained the value of the minimum length is orders of magnitude less than or equal to 10-20m
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
Bases gaussianas geradas com os métodos Monte Carlo Simulated Annealing e Particle Swarm Optimization.
(Universidade Federal do Espírito Santo, 2017-10-03) Reis, Thiago Mello dos; Alfonso, Jorge Luis Gonzalez; Caetano, Edson Passamani; Continentino, Mucio Amado; Nascimento, Valberto Pedruzzi; Macedo, Waldemar Augusto de Almeida
The Monte Carlo Simulated Annealing and Particle Swarm Optimization methods were used to generate adapted Gaussian basis set for the atoms from H to Ar, in the ground state. A study about the e ciency and the reliability of each method was performed. In order to check the reliability of the proposed methods, we perform an speci c study considering a training set of 15 atoms, namely: N, Mg, Al, Cl, T i, N i, Br, Sr, Ru, P d, Sb, Cs, Ir, Tl, At. First of all, the Improved Generator Coordinate Hartree-Fock Method was applied to generate adapted basis which was used as start point to generate new Gaussian basis sets. After that, the Monte Carlo Simulated Annealing and Particle Swarm Optimization methods were developed from parallel studies, however following the same procedure so as we could have the possibility to compare them. Previously applying of the developed methods we perform some calibrations in order to de ne the values of the parameters of the algorithms; we perform studies about annealing schedules (for the Monte Carlo Simulated Annealing method), the total of swarm's particle (for the Particle Swarm Optimization method), and the total of steps for each algorithm. After the calibration procedure, both methods were applied, with the variational principle, to the Hartree-Fock wave function to give us the fully optimized Gaussian basis sets. Next, the basis sets were contracted by considering the lowest total energy loss, prioritizing the contraction of the most internal exponents. The last two steps of our procedure were the addition of polarized and di use functions, respectively. These procedures were performed by using the methods which we developed in this work through calculations to the MP2 level. The basis sets that have been generated in this work were used in some atomic and molecular calculations; we compare such results with relevant results from literature. We veri ed that, if we consider the same computational e ciency for both Monte Carlo Simulated Annealing and Particle Swarm Optimization methods, there is a vi small di erence between them as regards the accuracy, so that by using the Monte Carlo Simulated Annealing method we obtain best results. When we compare the results of this work with those from literature we note similar results for the properties that were studied, however the proposed methods in this work are more e cient, and we can de ne a single total numbers of steps for the algorithms even though we are treating with di erent atomic systems. In addition, we verify that the proposed methods in this work are more accurate than other similar methods presented in the literature, in the task of nding the global minima of the uncontracted basis sets to HF level of theory. It will be necessary to perform additional studies to check the real relationship between the accuracy of the methods. We do not verify the in uence of several parameters of the Particle Swarm Optimization algorithm in this work. The fact that the developed methods in this work have been constructed through Double Zeta basis does not prevent them to be used for larger basis sets, the two methods are able to be applied to generate Gaussian basis sets in the atomic environment for Gaussian basis sets with di erent qualities
Bases gaussianas geradas em ambientes atômico e molecular
(Universidade Federal do Espírito Santo, 2014-09-19) Arruda, Priscilla Mendes; Canal Neto, Antônio; Jorge, Francisco Elias; Freitas, Jair Carlos Checon de; Poveda Calviño, Luis Argel; Campos, Cesar Turczyn
A Gaussian basis set of small size for the atoms from H through Ar was constructed from a single sequence of exponents of 19 Gaussian functions, based on the generator coordinate Hartree-Fock method. For each atom studied a segmented contraction scheme was proposed and polarization functions and di use functions were added. Applications of the new contracted and uncontracted basis sets for the the calculation of the equilibrium geometries and electric properties (electric dipole moments and polarizabilities) of various molecular systems were performed and comparisons were made between theoretical and experimental results. The universal Gaussian basis sets presented in this work (with and without contraction) are competitive when compared to adapted basis sets of similar size. The Monte Carlo simulated annealing method was adapted to optimize correlated Gaussian-type functions in non-relativistic molecular environments. Starting from an atom-centered atomic Gaussian basis set, the uncontracted functions were reoptimized in the molecular environments corresponding to the BF, CN -, CO, CO2, CS, H2O, N2 and NO+ systems. These new molecule-optimized basis sets, called hybrid-basis sets HXZP (X = D, T, Q, and 5), were used to calculate total energies, harmonic vibrational frequencies, equilibrium geometries, electric dipole moments, and polarizabilities, at correlated level of theory. The present methodology is a simple and e ective way to improve molecular correlated wave functions, without the need to enlarge the molecular basis set. This methodology was employed to generate hierarchical sequences of molecular basis sets with increasing size, which we used to obtain complete basis set limits. xv xvi Additionally, the Monte Carlo simulated annealing method was employed to generate a hierarchical sequence of molecule-optimized basis set to CN -, CO, CO2, CS, H2O, N2 and NO+ systems. In these basis sets, all exponents were optimized in the molecular environment. Contraction schemes were proposed to each studied system, resulting in a nal molecular basis set, which we called MXZP (X = D, T, and Q). We used this hierarchical sequence of basis set to calculate total energies, harmonic vibrational frequencies, equilibrium geometries, electric dipole moments, and polarizabilities, at correlated level of theory. Also, we used that hierarchical sequences of molecular basis sets to obtain complete basis set limits. We veri ed, for the studied systems, that the MXZP basis sets produced more suitable molecular properties than the corresponding HXZP basis sets
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.
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
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
Conjuntos de bases gaussianas de qualidade quádrupla zeta de valência para os átomos de Rb até Xe
(Universidade Federal do Espírito Santo, 2013-04-25) Ceolin, Geovane de Araujo; Jorge, Francisco Elias; Muniz, Eduardo Perini; Georg, Herbert de Castro; Pires, José Maria; Lopes, Juliana Fedoce; Suave, Rogério Netto
All-electron segmented contracted quadruple zeta valence plus polarization function (QZP) basis sets for the elements Rb-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 original QZP basis set, i.e., the values of the contraction coefficients were reoptimized using the relativistic DKH Hamiltonian. This extends earlier works on segmented contracted QZ basis set for atoms H-Kr. At the Coupled Cluster level of theory, the convergence of atomic ionization energy as well as 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. Augmented Gaussian basis set of quadruple zeta valence quality plus polarization functions for the atoms Rb and from Y to Xe is presented. It was were constructed from the all-electron unaugmented set by addition of diffuse functions (s, p, d, f, g, and h symmetries) that were optimized for the anion ground states. From this set, Hartree-Fock, second-order Mfller-Plesset perturbation theory, and density functional theory electric dipole moment and polarizabilities for a sample of molecules as well as for Agn (n = 4) clusters were calculated and compared with theoretical and experimental values available in the literature
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
Conjuntos de bases gaussianas segmentados para todos os elétrons para os elementos de Cs até Rn e de Th até Lr.
(Universidade Federal do Espírito Santo, 2017-02-06) Martins, Lucas Sousa Carvalho; Jorge, Francisco Elias; Morgon, Nelson Henrique; Canal Neto, Antônio; Freitas, Jair Carlos Checon de; Machado, Luiz Carlos
All-electron contracted Gaussian basis set of triple zeta valence quality plus polarization functions (TZP) for the elements Cs, Ba, La, and from Hf to Rn is presented. Douglas-Kroll-Hess (DKH) basis set for fifth-row elements is also reported. We have recontracted the original TZP basis set, i.e., the values of the contraction coefficients are re-optimized using the second-order DKH Hamiltonian. By addition of diffuse functions (s, p, d, f, and g symmetries), which are optimized for the anion ground states, an augmented TZP basis set is constructed. Using the Becke 3-parameter (exchange) and the Lee, Yang and Parr (correlation) functional (B3LYP), the performance of the TZP-DKH basis set is assessed for predicting atomic ionization energy as well as spectroscopy constants of some compounds. Segmented all-electron basis sets of valence double zeta quality plus polarization functions (DZP) for the elements from Ce to Lu are also generated to be used with the non-relativistic and DKH Hamiltonians. At the B3LYP level, the DZP-DKH atomic ionization energies and equilibrium bond lengths and atomization energies of the lanthanide trifluorides are evaluated and compared with benchmark theoretical and experimental data reported in the literature. Finally, for the actinides, two segmented all-electron basis sets of valence double zeta quality plus polarization functions (DZP) are developed. One of them must be used along with the non-relativistic Hamiltonian, whereas the other with the DKH one. For the actinide trichlorides, geometric parameters, atomic charges of the actinides, and populations for the actinide valence orbitals are calculated using the B3LYP functional in conjunction with the DZP-DKH basis set. For UCl3 and UF3, dissociation energies are also reported.Comparison with benchmark theoretical and experimental values found in the literature is carried out. It is verified that the performance of the relativistic compact size basis sets generated in this work are regular, efficient, and reliable. They will be extremely helpful on molecular property calculations that need explicitly to consider the core electrons.
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
Correlação entre a massa efetiva (𝑚*), 𝜆ab E 𝑇C de cupratos supercondutores em um cenário de energia de Casimir.
(Universidade Federal do Espírito Santo, 2018-05-17) Rouver, Anderson do Nascimento; Orlando, Marcos Tadeu D'Azeredo; Nogueira, José Alexandre; Rodrigues, Davi Cabral; Scandian, Cherlio; Justo, João Francisco; Martinelli, Antonio Eduardo; Muccillo, Eliana Navarro dos Santos
The Casimir effect was discovered in 1948 and its relevance was recently pointed out in studies on materials such as graphene and high-temperature superconducting cuprates. The relationship between Casimir energy and the energy of a superconducting condensate with anisotropy characterized by high bidimensionality has already been discussed in certain theoretical scenarios. This work describes the relationship between the effective mass of the charge carriers (??* = ??????, whete ???? is the mass of the electron) and the macroscopic parameters characteristic of several families of high critical temperature (????) superconducting cuprates (Cu-HTSC) that have copper and oxygen superconducting planes (Cu-O). It has been found that there is an expression that correlates the effective mass, the London penetration length in the plane ??????, the critical temperature ???? and the distance ?? between the equivalent superconducting planes of Cu-HTSC, showing an asymptotic behavior of ?? as a function of ???? and the line describing the optimal value of ?? ? 2 ( ??* ? 2????). This indicates that a nonadiabatic region exists, which implies a carrier-lattice interaction and where the critical temperature may have its highest value in Cu-HTSC.
Cosmologia com interação no setor escuro do Universo.
(Universidade Federal do Espírito Santo, 2017-10-25) Marttens, Rodrigo Fernando Lugon Cornejo von; Casarini, Luciano; Zimdahl, Winfried Ernst Wilhelm; Kremer,Gilberto Medeiros; Velten, Hermano Endlich Schneider; Piattella, Oliver Fabio; Ramos, Rudnei de Oliveira; Marra, Valerio; Ricaldi, Wiliam Santiago Hipolito
According to our understanding of the universe, dark matter and dark energy are the dominant components in the dynamics of the current universe, while baryons and radiation contribute only a small fraction of less than 5 % of the cosmic energy. Although this dark sector is important to describe a series of phenomena that are currently observed, its nature is still one of the greatest mysteries of cosmology. In this work we consider the study of models that, unlike the standard model, present a non-gravitational interaction between dark matter and dark energy. Initially, this interaction is parameterized in a general way that depends on an arbitrary function of the ratio between the energy densities of dark matter and dark energy. It is possible to show that in cases where this ratio depends exclusively on the scale factor, this model can be identified with a unified description of the dark sector. Since this general parameterization has no analytical solution, some specific cases of this class of models are chosen to perform a statistical analysis of parameter selection. This statistical analysis is done using the CLASS cosmological code (modified for each model) combined with the statistical code MontePython. This observational test is done by analyzing the data of H0, SNe Ia (JLA) and Planck TT. The purpose of this analysis is to verify how each observational datasets constraints an interaction in the dark sector in counterpart of the ?CDM model, and if there is a concordance between the background results (H0, SNe Ia and BAO) and the results at the linear level (Planck TT).
Cosmologia quântica em teorias escalares-tensoriais: aspectos físicos e matemáticos.
(Universidade Federal do Espírito Santo, 2017-09-21) Almeida, Carla Rodrigues; Fabris, Júlio César; Rodrigues, Davi Cabral; Batista, Antonio Brasil; Nogueira, José Alexandre; Piattella, Oliver Fabio; Pinto Neto, Nelson; Perez Bergliaffa, Santiago Esteban
The proposal of this work is to study the mathematical and physical aspects of the canonical quantization of scalar-tensor theories, Brans-Dicke Theory in particular, using a perfect fluid as the universe’s matter component, inserted by Schutz’s formalism. We do a thorough analysis of the self-adjointness of the effective energy operator obtained in the quantization of theory. Such quantization is made through the Wheeler-DeWitt equation, the energy constraint from the Hamiltonian description of General Relativity, to obtain a Schr¨odinger-like equation, taking the temporal parameter to be given by the fluid that permeates the universe. Also, we present the quantization of the K-essence Theory, for a particular limit which we recover a perfect fluid behavior from General Relativity by Schutz. We also introduce the notion of affine quantization as an alternative to the canonical method, and present the mathematical concepts needed for the theory. We apply this method in a cosmological example, of a universe filled with dust. Also, we do a qualitative semiclassical analysis of the Brans-Dicke Theory.
Criação de partículas em modelos cosmológicos
(Universidade Federal do Espírito Santo, 2010-09-24) Houndjo, Stéphane Jonas Mahouton; Fabris, Júlio César; Batista, Antonio Brasil; Alvarenga, Flavio Gimenes; Chapiro, Ilia; Pinto Neto, Nelson; Piguet, Olivier; Silva, Saulo Carneiro de Souza
We investigate particle production in an expanding universe dominated by a perfect fluid with the equation of state p = a?. The particle production rate, using the Bogoliubov coefficients, is determined exactly for any value of a in the case of a flat universe. When the strong enegy condition is satisfied, the particle production rate decreases with time; the opposite occurs when the strong energy condition is violated. In the phantom case, the particle production rate diverges at finite time for each mode represented by a wavenumber k. In a first step, in order to compute the energy density associated with the produced particles, we use a cut-off in the Planck scale and find that it tends to zero as the big rip is approached. We conclude that quantum effects due to particle creation are not able to prevent the big rip. In the second step, in order to perform a deep analysis of the quantum effects, we use the n-wave regularization technique for calculating the quantum energy density and find that it becomes the dominant component of the universe near the big rip. We conclude in this case that quantum effects can prevent the occurrence of the big rip. We also investigate the effects of quantum particle production on a classical sudden singularity occurring at finite time in a Friedmann universe. We use an exact solution to describe an initially radiation-dominated universe that evolves into a sudden singularity at finite time. We calculate the density of the created particles exactly and find that it is generally much smaller than the classical background density and pressure which produce the sudden singularity. We conclude that, in the example studied, quantum particle production does not avoid nor modify of the sudden future singularity
Detecção e identificação elétrica dos nucleotídeos do DNA via nanoporo híbrido de grafeno e nitreto de boro hexagonal: um estudo teórico.
(Universidade Federal do Espírito Santo, 2017-09-15) Souza, Fábio Arthur Leão de; Scopel, Wanderlã Luis; Canal Neto, Antônio; Freitas, Jair Carlos Checon de; Campos, César Turczyn; Amorim, Rodrigo Garcia; Silva, Edison Zacarias da
In this thesis work, a novel architecture of solid-state nanopore in a hybrid two-dimensional (2D) material for detection and identification of biomolecules is proposed. The system is composed of a zigzag graphene nanoroad embedded in hexagonal boron nitride (h-BN). A theoretical study based on ab-initio calculations was carried out to assess its energetic stability, structural, electronic and transport properties. Our results indicate the capability of controlling by gate voltage the current pathways through the conducting graphene strip. Then, motivated by the recently developed electrochemical reaction (ECR) technique for fabricating nanopores in a highly controlled manner in 2D materials, and aiming to evaluate the possibility of drilling pores in the hybrid material, vacancy defect formation energies of carbon, boron and nitrogen were evaluated throughout different regions of the system. As a result, our findings suggest that it would be possible to drill a pore in graphene nanoroad from a carbon vacancy in the graphene/h-BN interface, keeping just a carbon chain between the pore and h-BN domain in the opposite interface. Accordingly, a pore of approximately 12.5Å in diameter with aforementioned characteristics was built. Therefore, to develop and assess the feasibility of such proposed device to act as nanosensor, a combination of density functional theory with non-equilibrium Green’s function methods were employed. Hence, investigations on how each nucleotide that forms DNA should modulate the local current at the nanopore device were performed, where four nucleotides were tested: deoxyadenosine monophosphate (dAMP), deoxyguanosine monophosphate (dGMP), deoxycytidine monophosphate (dCMP), and deoxythymidine monophosphate (dTMP). Analyses of the pore+nucleotide zero-bias transmission functions have revealed that it should be in principle possible to distinguish between all four nucleotides inside the nanopore setup, which should occur in practice by their sensitivity fingerprints in real-time conductance measurements. Furthermore, it was demonstrated that the mechanism of detection of the referred hypothetical sensor is governed by modulation of the conductance of the carbon chain running along the graphene/h-BN interface due to local dipole moments of the target molecule.
Determinação da rede magnética da perovskista dupla Ca2MnReO6 através de difração de neutrons.
(Universidade Federal do Espírito Santo, 2018-08-23) Cavichini, Arthur SantAna; Orlando, Marcos Tadeu D'Azeredo; Martinelli, Antonio Eduardo; Muccillo, Eliana Navarro dos Santos; Alves, Haimon Diniz Lopes; Fantini, Márcia Carvalho de Abreu
This work investigated the magnetic structure of the double perovskite Ca2MnReO6 by powder neutron diffraction. Up to the present work, there were no conclusive studies about its magnetic structure. In order to clarify this structure, polycrystalline samples of this compound were produced in sufficient quantities to perform neutron diffraction studies. About 10 g of the compound were synthesized in batches by solid state reaction in a vacuum-sealed quartz tube. X-ray diffraction measurements showed crystallinity and quality of the batches. The dc magnetization with ?? = 0.1 T showed a paramagnetic transition at ?? = 121 K, a magnetic frustration on the ZFC magnetization curve and a significant magnetization of ?? ~ 0.5????/f.u in FC. The fit of the Curie-Weiss Law in the paramagnetic region in ?? -1 resulted in a ?????? = 70 K, indicating a predominance of ferromagnetic interactions in the lattice. ZFC magnetic hysteresis at ?? = 10 K showed that the compound exhibits a hard magnetic behavior and an ???? = 4 T, indicating a magnetocrystalline coupling. Rietveld refinement of the cold neutron diffraction spectra as a function of temperature revealed that between 75 K-120 K there is an anomalous expansion of the ?? axis and a large contraction of the ?? parameter with the cooling, which may be related to the magnetocrystalline coupling. The evolution of the total moments as a function of the temperature show that their values arrive at zero near ????, and that a above ?? = 80 K there is an increase of the ferromagnetic component of Mn. Rietveld refinement of the thermal neutron diffraction spectra showed no structural phase transition of the compound as a function of temperature. As a conclusion of this work, it has been determined of unpublished form that the magnetic group ??21/?? describes the magnetic structure of the compound Ca2MnReO6. Such a conclusion was based on a detailed crystallographic analysis of the purely magnetic peaks of the cold neutron diffraction spectra at ?? = 2 K and using the propagation vector ??? = (0,0,0). Moreover, it was found that the Mn and Re magnetic sub-lattice present an A-AFM type ordering, with magnetic vectors [2.41(3), ±0.8(3), 3.53(3)] and [-0.16(4), 0.15(4)], respectively. It was also found that the magnetic vector of Re makes an angle of 100° with respect to the magnetic vector of Mn in even ??, revealing an orthogonality relationship between them. The orthogonal magnetic coupling between the moments of Mn and Re indicates the predominance of an antisymmetric exchange interaction (Dzyaloshinskii-Moriya) in comparison to a symmetric exchange interactions (Heisenberg). This coupling characterizes the compound as a spin-orbit-assisted Mott insulator, similar to that observed in Iridates.
Dualidade de Fator de Escala e Cosmologias Pre-Big-Bang.
(Universidade Federal do Espírito Santo, 2017-09-20) Lima, Andre Luiz Alves; Sotkov, Galen Mihaylov; Rodrigues, Davi Cabral; Nastase, Horatiu Stefan; Pereira, José Geraldo; Pereira, José Geraldo; Fabris, Júlio César; Silva, Ulysses Camara da
This thesis is an investigation of cosmological models dual under an inversion of the scale factor in conformal time, in Einstein gravity. The Scale Factor Duality in conformal time (SFD) acts as a map between high and small energy, and between accelerated and decelerated evolutions of the universe. Used as a symmetry principle, the SFD selects models with two phases of acceleration of the scale factor, symmetric by reflection over the point when acceleration vanishes. We derive a class of such models, corresponding to a modified Chaplygin gas, which might be used as a toy model in more than one phenomenological regime, e.g. a hilltop inflationary phase or a quintessence model. In Einstein gravity, SFD is analogous to a well known duality in dilatonic gravity, in which the inversion of the scale factor in the string frame, along with an appropriate transformation of the dilaton, is a symmetry of the gravidilatonic equations for a restricted class of potentials. Although it is a symmetry of the Friedmann equations in the Einstein frame, dual solutions obtained with the SFD, for any potential, may be mapped to the string frame, providing transformations which relate small and large values of the (string-frame) scale factor. Gravidilatonic duality gives rise to the so-called Pre-Big-Bang Scenario of string cosmology. Analogously, a universe obtained by the SFD may be interpreted as being “before” the big-bang of its dual, in Einstein gravity. We concentrate in the analysis of such pre-big-bang universes which are eternally expanding (in contrast with bouncing models), and their final, accelerated phase plays the rˆole of an inflationary phase previous to the big-bang of the ensuing decelerated universe. This idea is reminiscent of a ‘Conformal Cyclic Cosmology’. The transition across the singularity requires a conformal identification; we address this issue by making use of the dS/CFT correspondence and the holographic renormalization group.

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