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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- 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
- ItemEstudo teórico de propriedades eletrônicas e ópticas de heteroestruturas de van der Waals(Universidade Federal do Espírito Santo, 2025-03-10) Pedrosa, Renan Narciso; Scopel, Wanderlã Luis ; https://orcid.org/0000-0002-2091-8121; http://lattes.cnpq.br/1465127043013658; https://orcid.org/0000-0001-7966-4747; http://lattes.cnpq.br/2460667257000010; Miwa, Roberto Hiroki ; https://orcid.org/0000-0002-1237-1525; http://lattes.cnpq.br/8391413167385647; Freitas, Jair Carlos Checon de ; https://orcid.org/0000-0002-4474-2474; http://lattes.cnpq.br/3074997830683878; Nascimento, Valberto Pedruzzi ; https://orcid.org/0000-0002-9543-5335; http://lattes.cnpq.br/9908042258225541; Menezes, Marcos Gonçalves de ; https://orcid.org/0000-0001-8143-0181; http://lattes.cnpq.br/5945425658332294In this work, we examine the energetic, structural, electronic and optical properties of van der Waals heterostructures, based on first-principles calculations. The investigated interfaces were: (i) silicene/WSSe (metal-semiconductor) interface and (ii) MoSe2/WSSe (semiconductor-semiconductor). For cases (i) and (ii), the results indicate that the formation of the interface is driven by an exothermic process, where a charge transfer from silicene (WSSe) to WSSe (MoSe2) occurs, respectively. Furthermore, the results of the electronic properties show that, for cases (i) and (ii), the formation presents type-I and type-II band alignment characteristics, respectively. The optical properties obtained from the solution of the Bethe-Salpeter equation indicate, for case (i), that the power conversion efficiency of the heterostructure is 2.42 times higher than that of the WSSe (Janus) monolayer. On the other hand, for the MoSe2/WSSe heterobilayer, the lowest-energy excitonic states were verified. The results reveal that the first dipole-allowed state has an interlayer character with a transition rate ∼ 616 times lower than that of the intralayer ones. Consequently, this small transition rate implies a longer radiative lifetime of up to three orders of magnitude higher than that of the lowest-energy intralayer exciton. These findings emphasize that the formation of Janus-based heterobilayers presents a considerable improvement in optical properties compared to monolayers, which indicates their potential for application in optoelectronic devices
- ItemEstabilidade De Buracos Negros Dilatônicos(Universidade Federal do Espírito Santo, 2024-03-22) Martins, Ébano Vitor Lopes; Richarte, Martín Gustavo ; https://orcid.org/0000-0002-7157-9828; http://lattes.cnpq.br/2262133622995187; Fabris, Júlio César ; https://orcid.org/0000-0001-8880-107X; http://lattes.cnpq.br/5193649615872035; https://orcid.org/0000-0003-0731-4427; http://lattes.cnpq.br/7267903635440390; Saa, Alberto Vazquez; https://orcid.org/0000-0003-1520-4076; http://lattes.cnpq.br/0039310040138543; Falciano, Felipe Tovar; https://orcid.org/0000-0003-2263-1252; http://lattes.cnpq.br/7214193952056222; Coelho, Jaziel Goulart; https://orcid.org/0000-0001-9386-1042; http://lattes.cnpq.br/0298932683600051; Sotkov, Galen Mihaylov ; https://orcid.org/0000-0002-7276-016X; http://lattes.cnpq.br/6372536076880230This thesis focuses on the stability analysis of static black holes within the framework of the Einstein-Maxwell-dilaton (EMd) theory. Our investigation involves deriving master equations that govern perturbations, encompassing different modes of odd and even parity. We establish criteria for assessing the stability of black holes using the theory of self-adjoint operators. Furthermore, we extend our analysis through the implementation of numerical simulations aimed at obtaining the temporal evolution of equations governing perturbations, thereby corroborating our analysis based on the theory of self-adjoint operators. We explore the superradiant instability, demonstrating that the unstable modes lead to instability if there is a potential well outside the horizon where these modes remain confined.
- ItemTécnicas de RMN de Baixo Campo Aplicadas ao Estudo de Café e Propriedades Petrofísicas em Meios Porosos(Universidade Federal do Espírito Santo, 2024-03-12) Muniz, Rafael Oliari; Alfonso, Jorge Luis González; https://orcid.org/0000-0001-5841-8731; http://lattes.cnpq.br/9030024304752445; Freitas, Jair Carlos Checon de; https://orcid.org/0000-0002-4474-2474; http://lattes.cnpq.br/3074997830683878; https://orcid.org/0009-0009-9526-7026; http://lattes.cnpq.br/3488772005733003; Bonagamba, Tito José; https://orcid.org/0000-0001-8894-9170; http://lattes.cnpq.br/2090018228785477; Sarthour Junior, Roberto Silva; https://orcid.org/0000-0003-3573-8593; http://lattes.cnpq.br/1417657874331629; Castro, Eustáquio Vinicius Ribeiro de; https://orcid.org/0000-0002-7888-8076; http://lattes.cnpq.br/1055263403980509; Scopel, Wanderlã Luis; https://orcid.org/0000-0002-2091-8121; http://lattes.cnpq.br/1465127043013658This thesis reports the use of low-field nuclear magnetic resonance technique (LF-NMR) for the study of two works. The first work uses 1H LF-NMR relaxometry to detect concentrations in coffee samples of the Arabica and Robusta varieties. For this purpose, roasted and ground coffee samples from different Brazilian states' producing farms were used and categorized into two groups: pure samples (for both varieties) and blends (mixtures with different proportions of both varieties). As the method detects preferentially the NMR signals due to phases with high molecular mobility, which exhibit longer 𝑇𝑇2 values, the difference in the oil contents associated with Arabica and Robusta coffee was the key factor responsible for the detection of the contributions due to each variety. The calculations of relative hydrogen index (RHI) revealed a direct relationship between RHI values and the Arabica content in the blends; for the pure samples, higher RHI values were obtained for Arabica coffee samples from different origins, when compared to the values for all samples of the Robusta variety. The second work reports the use of a random walk-based algorithm to perform computational simulations reproducing experiments using the Carr-Purcell-Meiboom-Gill (CPMG) sequence. These simulations were applied to digital porous structures formed from the packing of interpenetrating spheres. Simulations are reported investigating the influences on magnetic relaxation curves of parameters such as porosity, relaxivity, temperature, Diffusion coefficient of the fluid filling the pore and magnetic susceptibility of the solid part of the rock. The results show that it is possible to capture, qualitatively, the main aspects observed in transverse magnetization relaxation experiments performed in porous media such as natural rocks. In particular, it is demonstrated that the presence of magnetic inhomogeneities is a decisive factor that must be considered when analyzing data regarding the temperature dependence of the relaxation rate.