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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- 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.
- ItemEstudo sobre os efeitos biológicos da radiação gama da praia de Meaípe na cidade de Guarapari-ES(Universidade Federal do Espírito Santo, 2023-07-13) Zordan, Alan Bragança; Orlando, Marcos Tadeu D Azeredo; https://orcid.org/0000000283876504; http://lattes.cnpq.br/3562894103432242; https://orcid.org/; http://lattes.cnpq.br/; Guimaraes, Marco Cesar Cunegundes; https://orcid.org/0000000321460180; http://lattes.cnpq.br/0261991057482057; Prado, Adilson Ribeiro; https://orcid.org/; http://lattes.cnpq.br/3085491325255749; Pansini, Fernando Nespoli Nassar; https://orcid.org/0000-0001-8984-686X; http://lattes.cnpq.br/7331959117489023; Buffon, Luiz Otavio; Sepulveda, Alex Arbey LoperaMonazite sand deposits along certain beaches in Brazil have average external radiation levels of up to 20 µGy h -1 . However, there is a considerable gap in the literature regarding the effects of these low levels of natural radiation on biological systems. Samples of monazite-rich sand from Meaípe beach in southeastern Brazil were collected and analyzed by X-ray fluorescence, X-ray diffraction, and magnetic susceptibility. The natural terrestrial radiation from the beach sand showed positive correlation with the elements Th and Y, which are closely associated with Ce, Nd, Ca and P, suggesting that this grouping is mainly associated with the local natural radiation. The highest doses of gamma radiation are associated with the particle size fraction between 100 and 200 μm, and, the radioactive isotopes are present in the yellow fraction of the sand, which corresponds to approximately 14% by mass of each sample of the collected sands. It was observed that the samples collected during 12 months do not have a homogeneous composition, as they suffer changes in their composition coming from spatial variations, probably associated with the hydrogeological flows of the beach. A physical simulator of natural radiation with physicochemical parameters similar to the real beach conditions with monazite sand was built, to evaluate the biological effects of gamma radiation on E. coli, S. aureus and Chlorella sp., as study models. E. coli exposed to gamma radiation from the simulator for 1 day showed a 23.8% reduction in growth. S. aureus exposed to gamma radiation from the simulator for 1 day showed a reduction of 18.4% in growth. Electronic microscopy images showed morphological alterations in both microorganisms. Chlorella sp. exposed to gamma radiation from the simulator for 10 days showed a significant reduction of 30.16% in growth, increase of 10.85% in generation time, reduction of 7.61% in total protein content, increase of 15.61% in total lipid content, 6.74% increase in total antioxidant activity and 34.64% increase in autofluorescence. Characterization by CHNS organic analyzer did not show significant differences in carbon, hydrogen, nitrogen and sulfur contents. The percentage of mass obtained by EDS spectra also showed no changes in intracellular levels of calcium, sodium and magnesium.
- ItemEspectroscopia e relaxometria de RMN aplicadas em estudos envolvendo a síntese de biodiesel por catálise heterogênea(Universidade Federal do Espírito Santo, 2023-03-28) Fernandez, Joycel Verde; Alfonso, Jorge Luis Gonzalez; https://orcid.org/0000-0001-5841-8731; http://lattes.cnpq.br/9030024304752445; https://orcid.org/000000022465811X; http://lattes.cnpq.br/9965613684540239; Novotny, Etelvino Henrique; https://orcid.org/0000-0001-9575-1779; http://lattes.cnpq.br/3604285557454730; Nascimento, Valberto Pedruzzi; https://orcid.org/0000000295435335; http://lattes.cnpq.br/9908042258225541; Santos, Reginaldo Bezerra dos; https://orcid.org/0000-0003-2966-7231; http://lattes.cnpq.br/6265396050660132; Lopes, Thierry RamosThis work describes the use of NMR spectroscopy and relaxometry methods in research involving the synthesis of biodiesel from oils of vegetable origin. In the first part of the work, solid state 13C and 31P NMR methods were used to characterize biochars and ash from coffee husk, which were used as heterogeneous catalysts to produce biodiesel from the transesterification reaction between methanol and. commercial and fried soybeans oils. The results showed the presence of different inorganic compounds, mostly phases containing Ca and K, several carbonates, and specifically the compound K2Ca(CO3)2, which was identified in all catalysts. Biodiesel conversions obtained using the biochars samples had values above 66 % and for the activated biochar sample (PC700_CA) the value was 74 %. However, ash catalysts had conversions to biodiesel above 90 %. This effect was related to the high concentrations of K and Ca salts (fairchildite and buetschliite) in the ashes. Reuse tests conducted with the ash catalyst showed a significant reduction in efficiency after the second cycle, due to the partial removal of active phases containing mainly K. Calibration methods, using DTG and NMR-TD techniques, were constructed to quantify the biodiesel concentrations obtained by the catalysts. The efficiencies of the calibration methods showed better performances for the ash catalysts. In conclusion, coffee husk represents a cheap and viable source with regard to the preservation of the environment for the production of biodiesel via heterogeneous catalysis, without the need for chemical modifications. Such methods proved to be efficient for the quantification of biodiesel concentrations in liquid solutions, allowing the detection and quantification of contamination or adulteration of vegetable oil in biodiesel samples. These methods are recommended for use with other sources of oils.
- ItemProbabilidade de tunelamento quântico para o surgimento de um universo clássico preenchido com gás de Chaplygin e poeira(Universidade Federal do Espírito Santo, 2023-03-14) Rocha, Nathália Mattos Novaes da; Goncalves, Sergio Vitorino de Borba; https://orcid.org/0000000285709750; http://lattes.cnpq.br/4992784379693871; https://orcid.org/0000000345816364; http://lattes.cnpq.br/5376461651668363; Ribeiro, Andre Luis Batista; https://orcid.org/0000-0002-3813-2565; http://lattes.cnpq.br/3417734567782570; Alvarenga, Flávio Gimenes; http://lattes.cnpq.br/7169430092692431; Silva, Eduardo Vasquez Corrêa; https://orcid.org/0000-0003-3866-8105; http://lattes.cnpq.br/0541169610474136; Constantinidis, Clisthenis Ponce; http://lattes.cnpq.br/1328163673123152; Oliveira Neto, Gil deThe present work aims to analyze the quantum dynamics contained in the Planck era of the Universe, its emergence mechanism for the inflationary phase and its classical dynamics in a homogeneous and isotropic model, composed of a perfect fluid in the form of dust and a Chaplygin gas. The analysis was carried out through probabilistic calculations of quantum tunneling of a numerical model quantized by the Crank-Nicolson method, whose calculations were performed in terms of the model parameters. The results show a greater susceptibility for the classical emergence of a Universe filled with dust and Chaplygin gas, when compared to results found in the literature for a model in which the Universe is filled with Chaplygin gas and radiation.
- ItemEstudos teóricos dos efeitos de pressão nas propriedades magnéticas e eletrônicas do composto ferromagnético itinerante fraco Sc3In.(Universidade Federal do Espírito Santo, 2022-12-08) Santana, Deivid Wilson Oliveira; Scopel, Wanderla Luis; https://orcid.org/0000000220918121; http://lattes.cnpq.br/1465127043013658; https://orcid.org/; http://lattes.cnpq.br/; Nascimento, Valberto Pedruzzi; https://orcid.org/0000000295435335; http://lattes.cnpq.br/9908042258225541; Souza, Fabio Arthur Leao de; https://orcid.org/0000-0002-6158-7330; http://lattes.cnpq.br/1140962711692698; Garcia, Flavio; https://orcid.org/0000-0002-3150-3909; http://lattes.cnpq.br/3814399624794416Materials labeled as weak itinerant ferromagnetic, composed of non-magnetic elements, are rare and intriguing. Therefore, the study of this physical system represents a challenge in condensed matter physics. Their representatives are the compounds 𝑆𝑐3𝐼𝑛 and 𝑍𝑟𝑍𝑛2. In these systems, the unpaired electrons of the 3𝑑 bands play a major role in their magnetic properties. Experimental results show that the main magnetic characteristics of these compounds are the low magnetic moment and low critical Curie temperature (𝑇𝑐). In the case of 𝑆𝑐3𝐼𝑛, an increase in the magnetic properties of this compound was experimentally detected, such as the Curie temperature and magnetic moment when subjected to hydrostatic pressure. This behavior is anomalous to ferromagnet compounds and unraveling the mechanism that underlies this phenomenon is one of the topics addressed in this thesis work. Our approach will be theoretical, using first principles calculations through Density Functional Theory (DFT) to simulate the effects of applied pressures on the electronic structure, and study the electronic, magnetic and structural properties of 𝑆𝑐3𝐼𝑛 together with the Stoner's theory, corrected by Moriya's spin fluctuation renormalization theory. Theoretical calculations at ambient pressure confirm the role of electrons that occupy the 𝑑 − 𝑆𝑐 orbitals in the origin of the magnetic and electrical properties of this studied compound. Our results show the decrease in the magnetic moment of the scandium atom under hydrostatic pressure and in its density of unpolarized states for the 𝑑 − 𝑆𝑐 orbitals at Fermi energy. These results are combined with the theoretical Moriya-Kawabata model and experimental results to explain the dependence of 𝑇𝑐 with pressure application. In this sense, our results conclude that the increase in the Curie temperature, with the pressure dTc/dP , observed in experimental results, is related to the increase in the electron-electron exchange interaction 𝐼 between the conduction electrons that occupy the bands 𝑑 − 𝑆𝑐 of the compound 𝑆𝑐3𝐼𝑛.