Dissertações em Física (Mestrado) - PPGF/ICEN
URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2340
O Mestrado Acadêmico iniciou-se em 2003 e pertence ao Programa de Pós-Graduação em Física (PPGF) do Instituto de Ciências Exatas e Naturais (ICEN) da Universidade Federal do Pará (UFPA).
Navegar
Navegando Dissertações em Física (Mestrado) - PPGF/ICEN por CNPq "CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA::FISICA DA MATERIA CONDENSADA"
Agora exibindo 1 - 9 de 9
- Resultados por página
- Opções de Ordenação
Item Acesso aberto (Open Access) Análise da potencialidade a condução do BDT através da densidade eletrônica de estados via tight binding e desenvolvimento de software (B3J)(Universidade Federal do Pará, 2007) GUIMARÃES, Jeconias Rocha; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899In this work we studied the potentiality of the polymer BDT (1,3-benzodithiole 4Hciclopenta[2,1-b:3,4b’]) to become a conducting polymer. Ground state conformations and the electronic structure have been calculated through quantum chemical methods in order to obtain the density of electronic states. The presence of several types of conformational defects and the variation of doping level has been considered. One of the most used theories to study the doping effects on conjugated polymers is the Huckel method. It is based on the separability of the sigma and pi bonds of planar molecules. BDT oligomers are not planar molecules and an extended Huckel method that includes all the atomic valence functions has been used. An original computation code, the B3J program, has been developed for this purpose. Simulations of the absorption spectrum in the UV-visible-near IR region have seen performed as well. Program B3J calculates the density of states of polymeric systems. The band structure of BDT was obtained with this software. We calculated the density of states of the neutral system and doped systems including several doping levels and both random and uniform distribution of defects. The square of the coefficients expansion of the wave function was obtained for polymers including up to 20 monomers. For these calculations we used geometries calculated by AM1 and PM3 quantum chemical methods. Finally, we studied the asymmetry of the charge separation induced by the presence of an external static electrical field in BDT oligomers suitably substituted by electron acceptor/donor species. The results are consistent with a transistor-like behavior of neutral and charged molecules.Item Acesso aberto (Open Access) Difração de policristais e difração múltipla de raios X para o estudo da influência dos íons Mn+2, Mg+2 e Cu+2 nas estruturas cristalinas da L asparagina monohidratada e do sulfato de níquel hexahidratado(Universidade Federal do Pará, 2012) MELO, Geraldo Souza de; REMÉDIOS, Cláudio Márcio Rocha; http://lattes.cnpq.br/7146076994037490In this work we accomplished a study about the influence of doping Mn+2, Mg+2 and Cu+2 in the crystal structures of crystals of nickel sulfate hexahydrate (NSH) and L Asparagine Monohydrate (LAM). The introduction of dopants in a crystal lattice must change its physical properties or growth habit. These changes must promote the technological applications of these crystals in many areas like medicine, agriculture, optics and electronics. The NSH crystals were grown by the slow evaporation method of the solvent and doped with ions of Mn+2 and Mg+2, resulting in crystals of good quality. We measures method of X-ray diffraction of the pure crystals and polycrystalline doped and from the results obtained we refinements, using the method of Rietiveld where was observed that the same crystal structure doped showed the same tetragonal and space group that the pure crystal, having a little change in their lattice parameters and volume of its unit cells. We observed that the introduction of dopants caused changes in the lengths of the links and the angles between the nickel and oxygen atoms, this may explain why the temperature of dehydration crystals NSH:Mn and NSH:Mg is bigger than that of pure NSH. We use the X-ray Diffraction Multiple technique with synchrotron radiation in differents energies on the workstation XRD1, of the National Synchrotron Light Laboratory (LNLS) in order to identify possible changes in the structures of doped crystals of nickel sulphate and L Asparagine. The Renninger diagrams show changes in the intensity, profile and position of the secondary peaks of doped crystals caused by the introduction of dopants. The crystals were grown L Asparagine monohydrate by the method of slow solvent evaporation, and doped with ions of Cu+2. The diffraction measurements showed that the doped crystal has the same orthorhombic structure that the pure crystal. Our results indicate that the incorporation mechanisms of the Cu+2 ions in the crystal lattice of Asparagine Monohydrate L occur in interstitial form. Changes were detected in intensity as well as in the positions and profile diagrams Renninger secondary peaks in the crystal doped.Item Acesso aberto (Open Access) Difração de raios X em minerais de bauxita e análise através de refinamento pelo método de Rietveld(Universidade Federal do Pará, 2011) ERDÓCIA, Félix Anderson Barros; REMÉDIOS, Cláudio Márcio Rocha; http://lattes.cnpq.br/7146076994037490The aluminum metal is obtained from bauxite ore, great industrial importance, consisting of one or more types of aluminum hydroxide plus a mixture of compounds containing silica, iron oxide, titania and aluminosilicates. Because of the variation in the relative concentration of these components in different samples of bauxite, the qualitative and quantitative mineralogy of the ore, has great importance with regard to its technological application, since this is directly related to the content of these components. This work was applied in eight samples of bauxite, extracted from a mine in Paragominas, the process of refining the spectra of X-ray diffraction using the Rietveld method, which were identified and quantified the crystalline phases: gibbsite, kaolinite, goehtita, anatase, quartz and hematite. Carried the refinements of the samples, we found that all had high levels of Gibbsite and Goethite low which gives an excellent type of bauxite to be used in extraction of alumina.Item Acesso aberto (Open Access) Espectrometria Raman, UV, DOS e Circular Dicroísmo de alcalóides do cigarro(Universidade Federal do Pará, 2011-02-28) GUEDES, Alberto Monteiro; CHAVES NETO, Antonio Maia de Jesus; http://lattes.cnpq.br/3507474637884699This work is about spectroscopic analysis of some molecular structures present in tobacco (Nicotiana glauca), the base for cigarette, and their interactions with the DNA molecule. According to its importance, among the variety present in the cigarette, the molecules studied were derived from nicotinic acid, nicotinic acid (niacin / vitamin B3), nicotinamide, trigonelline, nicotine, nornicotine and anabasine. The optimizations of these structures were initially obtained in the Hyperchem 7.5 computational software based on the theory of molecular mechanics. Then, they were optimized using the method Density Functional Theory, on the basis B3LYP/ 6-311 + + G (d, p), simulated in software Gaussian 03. Once the optimized structures, we obtained the UV absorption, Raman, Infrared, Circular Dichroism and Density of States spectra using Time-Dependent Density Functional Theory also simulated the in the same software. At the end of this process was also simulated, via molecular mechanics, the interactions of these structures with the DNA molecule in order to verify the potential carcinogenic or not these substances.Item Acesso aberto (Open Access) Estudo de nanofios de Au e dendrímeros(Universidade Federal do Pará, 2010-01-12) COSTA, José Francisco da Silva; CHAVES NETO, Antonio Maia de Jesus; http://lattes.cnpq.br/3507474637884699First part of this work is about the classical molecular dynamics simulation of the interaction of matrix systems of parallel nanowires of Au as a function of time. The results find the time of collision between the wires of the array. The second part of this work is using classical molecular dynamics simulation for five generations of PAMAM dendrimers, each interacting individually with a carbon nanotube as a function of time resulting in a molecular motor. Furthermore, it were calculated the absorption spectra of this system and it was found that they could be nanomotors controlled by light. For all these systems were calculated kinetic energy, potential, speed, thermodynamic properties as molar entropy variation, molar heat capacity and temperature in situ. These quantities provide us with valuable information about the behavior of these systems.Item Acesso aberto (Open Access) Medidas de espectroscopia Raman em cristais KDP e Nanotubos de Carbono: implementação da técnica(Universidade Federal do Pará, 2008-08-29) FERREIRA, Marcel Luiz Rodrigues; REMÉDIOS, Cláudio Márcio Rocha; http://lattes.cnpq.br/7146076994037490; MOREIRA, Sanclayton Geraldo Carneiro; http://lattes.cnpq.br/7312223977002681Currently, physicist have developed new techniques for characterization materials, mainly in the field of new materials that are being produced from existing materials such as glass, ceramics, polymers, semiconductor and superconductor materials, magnetic materials, etc. In that line, the Group of Physic of materials of Amazon has acquired new techniques for material characterization and this work is the beginning of the implantation of Raman spectroscopy technique. In this work, we used sample of KH2PO4 crystals (KDP) and carbon single wall nanotube (SWNT). The KDP was chosen because their spectra are well-known and their preparation quite simple. The KDP pure or doped is still researched due have a ferroelectric transition and their several applications in laser, sensors, second and third harmonic generation. SWNT was used in this work because are materials of great scientific and technological interest with applications in nanotechnology such as transistor, diode. KDP samples were submitted uniaxial pressure and high temperatures to investigated possible phase transition. Both decomposition and phase transition was observed through Raman spectra of KDP. In the SWNT Raman spectra was identified well known D and G bands. The results support implantation of Raman spectroscopy in the Laboratory of spectroscopy of UFPA.Item Acesso aberto (Open Access) Medidas de não-linearidades utilizando a técnica de varredura-Z aplicada a mistura ácido oleico e beta-caroteno(Universidade Federal do Pará, 2011) SILVA, Kleber José Rosario da; MOREIRA, Sanclayton Geraldo Carneiro; http://lattes.cnpq.br/7312223977002681We use the Z-scan technique to determine the nonlinear optical parameter (nonlinear refraction index) from oleic acid and beta-carotene diluted in oleic acid. The concentrations of the studied mixture were as the following: 0, 5.6, 11.3, 22.5, 30, 45 and 60 μg/ml. The nonlinear refraction index were evaluated considering the experimental data and Sheik-Bahae theory. The pure oleic acid and the solution of oleic acid with beta-carotene (60 μg/ml) presented nonlinear absorption and its coefficient were calculated. We obtain too nonlinear refraction index for some Amazon vegetable oils.Item Acesso aberto (Open Access) Métodos teóricos na investigação da estrutura eletrônica do resveratrol e derivados(Universidade Federal do Pará, 2004-09) COSTA, Sheila Cristina dos Santos; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899In this work we report na ab initio, density functional and a semiempirical investigation of the ground and vertical excited states and of the spectroscopic properties of resveratrol, a phytoalexin with known antioxidative properties, and of structurally related derivatives as piceatannol, paravinylphenylphenol and resveratrol-dihydroxyl_N (N=1,2 and 3). The results of the simulation of bond length resulting from the photoexcitation and of the corresponding theoretical spectra gives us new insight of how chemical modifications of these molecules could affect the possible physiological properties of resveratrol. Also we report new molecules (piceatannol and resveratrol-dihydroxyl_3) as antioxidative properties by the analysis of molecular parameters and electronic properties.Item Acesso aberto (Open Access) Propriedades dielétricas e térmicas das blendas de poliestireno com ácido oléico e poliestireno com betacaroteno(Universidade Federal do Pará, 2008-08-29) BELO, Ezequiel de Andrade; REMÉDIOS, Cláudio Márcio Rocha; http://lattes.cnpq.br/7146076994037490; MOREIRA, Sanclayton Geraldo Carneiro; http://lattes.cnpq.br/7312223977002681The thermal, dielectrics and optics properties of vegetable oils have been studied by Amazonian Materials Physic Group since 1996 in the Department of Physic of UFPA. Recently collaboration with Physical-chemistry of polymer Laboratory in the Chemistry Institute of UnB allowed studying these oils and its components as polymeric blends. In this work, we search to contribute for this study and we explore thermal and dielectric properties as temperature dependence of blends: Polystyrene (PS) modified with Oleic Acid (OA) and polystyrene modified with Beta-Carotene (BC). We performed dielectric constant and thermal diffusivity measurements resorting Capacitance Bridge and photopyroelectric technical, respectively. We estimate moment of dipole for PS/OA blend in the Debye, Onsager and Kirkwood theoretical models and fitting linear regression of experimental data. The results show the phase transition of OA persists in the blend and it is displacement for high temperature.