https://tedebc.ufma.br/jspui/handle/tede/706 2026-09-15T09:24:55Z https://tedebc.ufma.br/jspui/handle/tede/7227 Título: Plasmas quirais com aplicações em efeitos ópticos, conversão áxion-fóton e em cenários astrofísicos Autor: RIBEIRO, Filipe dos Santos Primeiro orientador: FERREIRA JUNIOR, Manoel Messias Abstract: In this work, we discuss the propagation of electromagnetic waves in cold chiral plasmas within the framework of the Maxwell-Carroll-Field-Jackiw (MCFJ) theory and bi-isotropic constitutive relations. We initiate by reviewing the essential aspects of electromagnetic wave propagation in plasmas, analyzing dispersion relations, refractive indices, propagation modes, birefringence effects, and low-frequency he- licon modes. Next, we revisit fundamental aspects of chiral media, whose properties are effectively ruled by axion electrodynamics, which is also connected to Carroll-Field-Jackiw (CFJ) electrodynamics. Dis- crete symmetries and the corresponding equations of motion associated with these theories are also exa- mined. We then analyze wave propagation parallel to an external magnetic field, considering the timelike and spacelike components of the CFJ term, which play the role of anomalous chiral conductivities. Modi- fied electromagnetic modes and refractive indices are derived and associated with right- and left-handed circularly polarized waves. For each refractive index, propagation and absorption regions are illustrated for selected parameter values. In the low-frequency regime, modified helicon modes with right- and left- handed circular polarizations are obtained, exhibiting behaviors distinct from the conventional helicon. Optical properties are further investigated through the rotatory power (RP) and the dichroism coeffici- ent. A reversal of the RP sign is observed, an uncommon feature in magnetized plasmas but previously reported in rotating systems. The same analysis is performed for plasmas described by bi-isotropic cons- titutive relations, where the emergence of a double RP reversal is highlighted. Data from dispersion and birefringence measurements of radio signals emitted by pulsars and Fast-Radio-Bursts (FRBs) are used to impose constraints on the chiral parameters. These constraints are tabulated and compared with previ- ously established results in the literature. Chiral effects in rotating plasmas are also analyzed, particularly birefringence, for which a reversal of PR is again observed. Finally, photon-axion conversion in a chiral plasma is proposed and investigated, highlighting the selectivity of the chiral medium toward photons with a specific circular polarization and enabling resonant conversion between axions and either RCP or LCP photons. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese 2026-08-25T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/7146 Título: Propriedades estruturais, eletrônicas e energéticas de pesticidas interagindo com nanotubos de nitreto de gálio Autor: LIRA JUNIOR, Paulo Brito Oliveira Primeiro orientador: GUERINI, Silvete Coradi Abstract: The structural, electronic and energetic properties of single-walled (10, 0) GaN nanotube (GaNNT) interacting with the pesticides acephate and glyphosate, in different configurations, were investigated through first-principles calculations based on density functional theory ( DFT) broke in the SIESTA computer program, to verify the use of GaNNT as a filter or sensor for pesticides. The calculation results indicate that acephate and glyphosate can be adsorbed on the GaNNT wall through electrostatic interaction. The results also show that acephate and glyphosate change the properties of the nanotube when they interact with it. The band structure for GaNNT was pure modified with the adsorption of acephate and glyphosate by the appearance of localized levels, as well as the reduction of the energy gap. The binding energy shows that the interaction of acephate and glyphosate with GaNNT occurs via a chemical process. Our results also indicate that GaNNT is a promising material for detecting and removing pesticides from the environment. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação 2024-09-26T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/7000 Título: Propriedades estruturais, vibracionais e elétricas das manganitas ortorrômbica eumno3 e hexagonal ErMnO3 Autor: CORREA, Adriano Primeiro orientador: SANTOS, Clenilton Costa dos Abstract: We investigated the structural, magnetic and vibrational properties of orthorhombic EuMnO3 and hexagonal ErMnO3 manganites using X-Ray Diffraction (XRD), Magnetometry, Raman spectroscopy and Dielectric spectroscopy. The structural and vibrational data obtained respectively via X-ray and Raman diffraction are consistent with the Pnma space group orthorhombic symmetries (D2h 16-62) and the P63cm space group hexagonal symmetries (C6υ 3-185)) for the EuMnO3 and ErMnO3 manganites, respectively. X-ray diffraction data as a function of temperature for both manganites show that there are deviations in the monatomic behavior of both lattice parameters and interatomic distances, unprecedented information for both manganites, since structural data as a function of temperature are scarce for these manganites, which allowed us to analyze in more detail the cause of the strong renormalizations of phonon frequencies and evidence of isostructural transitions. In addition, our XRD results for the EuMnO3 manganite give indications of the orbital ordering of the lattice associated with the Jahn-Teller distortion and we also observed, from the structural data, behaviors consistent with the magnetic ordering of the Mn spins in the ac plane, a result that is very interesting since the literature reports difficulty in obtaining the orientation of the spins for EuMnO3. Regarding the ErMnO3 manganite, we observed evidence of the participation of the Mn3+(site 6c) and Er3+(site 4b) spin networks, contrary to what is reported for the hexagonal manganites ReMnO3 (Re = Y, Dy, Ho, Tm, Yb and Lu) that indicate only the participation of the spin network of Mn3+ (site 6c) for the magnetic symmetry. In addition, we observed evidence of the occurrence of isostructural transitions involving the Er3+ spin network occurring from the Γ2Er configuration to the Γ4Er. The dielectric measurements data for the polycrystalline ErMnO3 manganite allowed us to investigate in more detail the contributions of grains and grain boundaries to the electrical conductivity, important results since the few existing results in the literature are concentrated in monocrystalline samples. In addition, the dielectric measurements showed anomalies in the dielectric constant in the vicinity of the magnetic region, these anomalies, together with magnetometry results, suggest the existence of magnetoelectric coupling for ErMnO3. Finally, we show evidence of a coupling between multi-order parameters and their interaction with the magnetoelectric effect in h-ErMnO3. A high magnetostriction response is evidenced by the Einstein-Grüneisen model. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese 2024-07-12T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/6868 Título: Determinação da estrutura cristalina do novo complexo de L-Glutamina com Ni(II): um estudo de difração de raios X em policristais auxiliado por análise térmica, vibracional e cálculos DFT Autor: OLIVEIRA, Wesley Kardex Cordeiro de Primeiro orientador: MENEZES, Alan Silva de Abstract: In this work, the determination of the crystal structure of the L-glutamine-nickel complex through X-ray diffraction in polycrystals was carried out and aided by thermal and vibrational analysis and DFT calculations. This material was synthesized in the proportion of 2 mols of L-glutamine and 1 mol of nickel, which grew in the form of polycrystalline spheres. These spheres were ground and subjected to X-ray diffraction measurements in polycrystals. After a search at the Cambridge Crystallographic Data Center (CCDC) for materials that had a crystal structure that matched the diffraction pattern of the complex studied in this work, it was found that the available X-ray diffraction patterns did not match the pattern of the complex. glutamine with nickel. Therefore, a new material had been obtained and therefore its crystal structure had to be determined. From the thermogravimetric analysis, a loss of mass around 160 ◦C was observed, equivalent to the mass of two water molecules, which were coordinated to the metal. Thus, it was considered that the chemical formula of this new complex is: Ni(L-glutamine)2(H2O)2. DFT calculations were performed with the aim of generating an initial molecule to resolve the structure of this crystal. Initially, the analysis of five molecules of the complex was established, arranged with two molecules of glutamine and water linked to the nickel atom. These structures were optimized with the hybrid functional B3LYP with the base function def2-tzvp for the nickel atom and 6-311++G(d,p) for the other atoms, and relaxed scan calculations were performed. in order to build the potential energy surfaces, and identify the most stable structure. With the measurement of X-ray diffraction in polycrystals and with the possible configurations of the optimized molecules, the resolution of the crystal structure Ni(L-glutamine)2(H2O)2 was performed using the Simulated Annealing method. This compound crystallized in a triclinic system with space group P-1, with unit cell parameters a = 5.1308(2) Å, b = 10.6038(9) Å, c = 14.2084(14) Å, α = 104.325 ◦ , β = 96.652 ◦ , γ = 91.433 ◦ and V = 742.79(11) Å 3 . The crystal structure of Ni(L-glutamine)2(H2O)2 consists of two molecules per unit cell (Z = 2), accommodating one molecule in the asymmetric unit (Z’ = 1). The Rietveld method was used to refine the crystal structure and the fit quality indicators were: Rp = 3.53 %, Rwp = 4.77 % and the RBragg = 1.07 %. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação 2021-08-13T00:00:00Z