Doutorado em Física
URI Permanente para esta coleção
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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- ItemAbordagem não-conservativa da teoria unimodular:aplicação a cenários cosmológicos(Universidade Federal do Espírito Santo, 2025-03-21) Alvarenga, Marcelo Henrique de; Fabris, Júlio César; https://orcid.org/0000-0001-8880-107X; http://lattes.cnpq.br/5193649615872035; https://orcid.org/0000-0002-0949-7936; http://lattes.cnpq.br/4549393780405762; Velten, Hermano Endlich Schneider; https://orcid.org/0000-0002-5155-7998; http://lattes.cnpq.br/0282590467459210; Piattella, Oliver Fabio; https://orcid.org/0000-0003-4558-0574; http://lattes.cnpq.br/5707156831919279; Vera, José Alberto Casto Nogales; https://orcid.org/0000-0003-0146-1063; http://lattes.cnpq.br/7972689654356212; Brito, Francisco de Assis de; https://orcid.org/0000-0001-9465-6868; http://lattes.cnpq.br/4294161599213457; Rodrigues, Davi Cabral; https://orcid.org/0000-0003-1683-5443; http://lattes.cnpq.br/5465449494182034The unimodular theory is one of the simplest modification of the theory of General Relativity (GR). According to the set of symmetries present in Unimodular Gravity (UG), it is invariant to a subclass of diffeomorphism transformations, transverse diffeomorphism (Tdiff), which pre serves the determinant of the metric tensor. This characteristic leads to the field equations in GU being trace-free. A direct consequence, which differs from GR, is that the Bianchi identities no longer lead directly to the conservation of the energy-momentum tensor, that is, the general law of conservation is an imposition made separately on the structure of the field equations in UG. In fact, if the imposition is made, the resulting equations are GR+Λ, however, the cosmological constant appears as an integration constant. This fact leads to many discussions about the equivalence between theories. In this work we explore the issue of imposing the conservation of the energy-momentum tensor as a necessary condition to recover the equivalence between UG and GR+Λ. Conservation law is a matter of choice and we chose to maintain the nonconserva tive nature. We study the consequences of this non-imposition in cosmological scenarios. We explore cosmological evolution and show that there is a viable cosmological model that transi tions from a radiative phase to an accelerated de Sitter-type expansion. Furthermore, we also analyze cosmological perturbations in non-conservative Unimodular Gravity (NUG). We show that, unlike the usual unimodular theory, in NUG we can use the synchronous gauge condition and analyze both scalar and tensor modes. This leads to interesting signatures that differ from RG. We also study scalar perturbations in the gauge invariant formalism; in vacuum solutions and by imposing the conservation of the energy-momentum tensor, we recover the same equations as in GR. But, when we add matter fields, the equations are different and we end up in an underdetermined system. We also propose a study within the cosmological context in NUG considering the dark energy component as holographic, which led us to construct a viable back ground cosmological model. According to the analysis of cosmological perturbations in both cases, the equivalence between UG and GR seems to be incomplete.
- ItemPropriedades eletrônicas e magnéticas de nanoflakes triangulares(Universidade Federal do Espírito Santo, 2025-03-17) Fiorini Filho, Luciano; Pansini, Fernando Néspoli Nassar; https://orcid.org/0000-0001-8984-686X; http://lattes.cnpq.br/7331959117489023; https://orcid.org/0000-0002-4190-3674; http://lattes.cnpq.br/2172049280967757; Amorim, Rodrigo Garcia; https://orcid.org/0000-0001-9611-8772; http://lattes.cnpq.br/0616474769970457; Batista, Ronaldo Junio Campos; https://orcid.org/0000-0002-7471-4968; http://lattes.cnpq.br/4374918656241879; Scopel, Wanderlã Luis; https://orcid.org/0000-0002-2091-8121; http://lattes.cnpq.br/1465127043013658; Mota, Vinícius Cândido; https://orcid.org/0000-0001-8368-0803; http://lattes.cnpq.br/4038237972209273The scientific interest in finite triangular-shaped systems formed purely by carbon atoms (triangulenes or n-GRt) has been increasing since their theoretical con ception in the 1950s, gaining even more significance as such systems are synthesized and theorized as potential candidates for nanoelectronic devices. With this in mind, we employed the methodological tools of density functional theory (DFT), combined with the B3LYP exchange-correlation functional, to electronically characterize both triangular graphene systems and similarly shaped systems composed of silicon carbide (n-SiCt), a composition that shares some properties with n-GRt systems. These types of systems, in their ground state, exhibit a non-trivial magnetic moment, characterizing them as ferrimagnetic systems. caused by the imbalance between atomic sublattices that naturally occurs when the system has a triangular shape with zig-zag edges, as predicted by Lieb’s theorem. In this work, two methods for manipulating the total spin state of these systems will be presented. These methods include the application of electric and magnetic fields, as well as the adsorption of hydrogen atoms onto the flake to capture one of the unpaired electrons
- ItemA dinâmica cosmológica do Modelo de Kantowski-Sach(Universidade Federal do Espírito Santo, 2025-06-13) Silva, Breno Barreto da; Gonçalves, Sergio Vitorino de Borba; https://orcid.org/0000-0002-8570-9750; https://lattes.cnpq.br/4992784379693871; https://orcid.org/0000-0001-7346-0129; https://lattes.cnpq.br/8497753547288933; Spalenza, Wesley; https://orcid.org/0000-0001-9644-3938; https://lattes.cnpq.br/2687428810786056; Monerat, Germano Amaral; https://orcid.org/0000-0003-2536-1171; https://lattes.cnpq.br/5031014907752547; Belich Junior, Humberto; https://orcid.org/0000-0002-8795-1735; http://lattes.cnpq.br/; Alvarenga, Flávio Gimenes; https://orcid.org/0000-0002-7579-9561; https://lattes.cnpq.br/7169430092692431In this thesis, we investigate the application of the homogeneous and anisotropic Kantowski-Sachs metric, characterized by two scale factors, in the construction of cosmological models alternative to the standard isotropic paradigm. To this end, we begin with a comprehensive review of the fundamentals of general relativity, relativistic hydrodynamics, and the Raychaudhuri equation, as well as an overview of the standard cosmological model, gathering the necessary elements for a consistent analysis of anisotropic scenarios. Initially, we revisit the original calculations of the Kantowski Sachs model, proposing a new graphical and interpretative approach to its dynamics. Subsequently, as an original contribution, we introduce a relation between the scale factors of the metric and obtain an exact solution of Einstein’s field equations, considering a general expression for the universe’s matter content, including the presence of a scalar f ield. We find that the presence of the scalar field leads to a significant decrease in energy density during the early stages, in a manner analogous to the inflationary process. Wealso determine the kinematic parameters associated with the model, such as the scalar expansion Θ, the shear σ, and the term RµνUµUν, related to the acceleration of the universe’s expansion. Finally, we analyze the evolutionary dynamics of the model through the Hubble, density, and deceleration parameters, aiming to understand the influence of anisotropy in a cosmological scenario with accelerated expansion.
- ItemElectrical identification of SF6 breakdown by-products using 2D carbon allotrope nanodevices(Universidade Federal do Espírito Santo, 2025-10-16) Spalenza, Pedro Elias Priori; Scopel, Wanderlã Luis; https://orcid.org/0000-0002-2091-8121; http://lattes.cnpq.br/1465127043013658; https://orcid.org/0000-0003-1476-4645; http://lattes.cnpq.br/7527588660443784; Souza, José Eduardo Padilha de; https://orcid.org/0000-0002-4299-2808; http://lattes.cnpq.br/; Rodrigues, Débora Carvalho de Melo ; https://orcid.org/0000-0003-2495-2463; http://lattes.cnpq.br/4077880075640475; Lima, Filipe Camargo Dalmatti Alves; https://orcid.org/0000-0001-7062-5450; http://lattes.cnpq.br/9691181918031689; Nascimento, Valberto Pedruzzi ; https://orcid.org/0000-0002-9543-5335; https://orcid.org/0000-0002-9543-5335; http://lattes.cnpq.br/9908042258225541Sulfur hexafluoride (SF6) is widely employed as an insulating gas in the power industry due to its exceptional dielectric properties. However, it inevitably decomposes into hazardous by-products during prolonged operation. Detecting these decomposition products is crucial for assessing equipment health and preventing insulation failures. Two-dimensional (2D) carbon-based materials have recently emerged as promising platforms for gas sensing. Nonetheless, their inherently weak van der Waals interactions with SF6 by-products often require surface functionalization, potentially compromising device reusability. Here, we propose four pristine 2D carbon allotropes- Net-graphene, Graphene+, T-graphene, and Biphenylene- as field-effect nanosensors for SF6 decomposition products. Using density functional theory combined with non-equilibrium Green’s function calculations, we examined the physisorption of H2S, SO2, SO2F2, and SOF2 on these materials. Although adsorption is dominated by van der Waals forces, an appropriate gate voltage shifts the chemical potential into sensitive regions of the transmission spectrum, enabling both detection and unambiguous identification of target molecules. In particular, a Net-graphene device can distinguish SO2 and H2S with high specificity, negligible cross-selectivity to O2 and H2O, and ultrafast recovery times. Moreover, Graphene+ uniquely detects both SO2 and SOF2 at a single gate voltage. Overall, the combination of intrinsic stability, low-power operation, rapid recovery, high sensitivity, and strong selectivity positions Net-graphene and Graphene+ as leading candidates for real-time, field-effect-based monitoring of SF6 decomposition products in power-industry applications.
- ItemEfeitos da violação da simetria de Lorentz em plasmas confinados por campos magnéticos(Universidade Federal do Espírito Santo, 2025-05-09) Soares, Diego Novaes; Spalenza, Wesley; https://orcid.org/0000-0001-9644-3938; http://lattes.cnpq.br/2687428810786056; Belich Junior, Humberto; https://orcid.org/0000-0002-8795-1735; http://lattes.cnpq.br/3879935393431243; https://orcid.org/0000-0002-7775-1908; http://lattes.cnpq.br/0840099631239811; Nogueira, Álvaro Luis Martins de Almeida; https://orcid.org/0009-0004-0736-9270; http://lattes.cnpq.br/1355329435993096; Melo, João Pacheco Bicudo Cabral de; https://orcid.org/; http://lattes.cnpq.br/0666138903452463; Braga, Filipe Leoncio; https://orcid.org/0000-0002-8571-9975; http://lattes.cnpq.br/0333646264188181; Mota, Vinícius Cândido; https://orcid.org/0000-0001-8368-0803; http://lattes.cnpq.br/4038237972209273; Paz, Wendel Silva; https://orcid.org/0000-0001-5737-0633; http://lattes.cnpq.br/8332147920469110Inspired by extensions of the Standard Model, we investigate the effects of space-time anisotropies arising from Lorentz Symmetry Violation (LSV) in a plasma column con f inement configuration. As proposed by Carroll, Field, and Jackiw, electrodynamics in an LSV scenario can be analyzed through the action of a background vector field, which couples to the electromagnetic field and modifies its classical behavior. In this context, the presence of such a background vector field influences the intensities of electromagnetic fields and particle densities. By varying its order of magnitude, its contribution to the classical model becomes evident, altering the intensity of elec tromagnetic fields and the distribution of charged particles, such as electron and ion densities in the plasma