https://tedebc.ufma.br/jspui/handle/tede/707 2026-08-10T02:09:20Z 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/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 https://tedebc.ufma.br/jspui/handle/tede/6845 Título: Decaimento de fótons no modelo padrão estendido Autor: Ribeiro Júnior, Marcos Cezar Rios Primeiro orientador: SCHRECK,   Marco Abstract: The discovery of Lorentz symmetry was one of the great advances in modern physics. This symmetry has been increasingly confirmed by various experiments over the past few decades. Thus, a search for small deviations from this symmetry is a window to search for a new physics. The present work is dedicated to photon decay, in the context of the Standard-Model Extension (SME). To develop this subject matter, we initially carried out a literature survey on the Lorentz noninvariant extension of the Standard Model, the well-known SME. Next, we present the characteristics of the photon sector of the SME, such as the Lagrangian, the equation of motion and its solutions, as well as the conservation laws. Later, we discuss photon decay as a consequence of a violation of Lorentz symmetry. We analyze photon decay for a particular type of violation, known as isotropic. Such a violation is obtained from the CPT-even sector of the SME. Furthermore, we discuss some classical and quantum aspects of the isotropic sector of the modified electromagnetic theory and obtain a series of results related to the photon decay process. The fact that photon decay has not been observed in any experiment allows us to set limits on the isotropic coefficient. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação 2026-08-07T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/6786 Título: Espalhamento quântico não relativístico no espaço tempo de uma corda cósmica Autor: SOARES, José do Nascimento Linhares Primeiro orientador: SILVA, Edilberto Oliveira Abstract: In this work, we investigate nonrelativistic quantum scattering by a Coulomb potential in the spacetime of a cosmic string. We begin by reviewing the foundations of nonrelativistic quantum mechanics, with emphasis on the Schr¨odinger equation and its essential properties. We then develop the theory of quantum scattering, specializing the formalism to the Coulomb potential. The cosmic string is described by the line element ds2 = −dt2 +dr2 +r2dθ2 +α2r2sin2θdφ2, within which we formulate the Schr¨odinger equation and explicitly solve the problem for scat tering states. From these solutions, we determine the phase shift, the scattering amplitude, and the cross section, highlighting the modifications introduced by the topological defect. Mo reover, we show that the energy spectrum of bound states can be obtained from the poles of the scattering matrix, yielding energy levels corrected by the geometric parameter α. The results reveal that the topology associated with the cosmic string directly influences quantum observables, manifesting itself both in the asymptotic behavior of the scattered waves and in the geometric splitting of the energy levels of the hydrogen atom. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação 2020-03-16T00:00:00Z