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http://repositorio.ufpa.br/jspui/handle/2011/2338
2019-03-25T03:58:59ZDifração 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
http://repositorio.ufpa.br/jspui/handle/2011/5085
Title: 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
Authors: MELO, Geraldo Souza de
First Advisor: REMÉDIOS, Cláudio Márcio Rocha
Abstract: In 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.
Publisher: Universidade Federal do Pará
Type: Dissertação2012-01-01T00:00:00ZPotenciais pseudo-newtonianos e a radiação escalar emitida por uma fonte girando ao redor de um objeto estelar
http://repositorio.ufpa.br/jspui/handle/2011/5084
Title: Potenciais pseudo-newtonianos e a radiação escalar emitida por uma fonte girando ao redor de um objeto estelar
Authors: CRUZ FILHO, Jaime Luis Cardoso da
First Advisor: CRISPINO, Luís Carlos Bassalo
Abstract: We use the pseudo-newtonian potentials proposed by Paczynski and Wiita, Nowak
and Wagoner and Artemova et al. to calculate the scalar radiation emitted by a source in
uniform circular motion around a stellar object. We compare the results obtained in this
approach with the results obtained via quantum eld theory in Schwarzschild spacetime.
We find that, up to the marginally stable circular orbit (R = 6M) the potential that
better reproduces the Schwarzschild result is the Nowak and Wagoner one. Between this
orbit and the last unstable circular orbit (R = 3M) neither one of the pseudo-newtonian
potentials produce satisfactory results, and the newtonian potential turns out to be the
best approximation. The Paczy nski and Wiita potential, the most used in the literature
to analyze accretion disks, generates the less satisfactory results for this situation.
Publisher: Universidade Federal do Pará
Type: Dissertação2010-01-01T00:00:00ZInvestigação da transição isolante-metal do CDM via algoritmos computacionais e estudo de nano-dispositivos orgânicos
http://repositorio.ufpa.br/jspui/handle/2011/5083
Title: Investigação da transição isolante-metal do CDM via algoritmos computacionais e estudo de nano-dispositivos orgânicos
Authors: AMAZONAS, Járlesson Gama
First Advisor: DEL NERO, Jordan
Abstract: We present in this work a theoretical study on conjugated organic polymers. These
systems, in general semiconductors or insulators, when doped, show an increase in electrical conductivity. Under action of electric field, small oligomers can present a similar behavior to of usual devices, but with innumerable advantages as, for example, size extremely reduced (some nanometers). In the first chapter we will make a brief introduction on organic polymers conjugated showing some experimental results for 4-dicianometileno-4,4-ciclopenta polymer [2,1-b: 3,4b'] ditiofeno - CDM, that is the central object of study. Chapter 2 deals
with the used quantum methods. We will cite the Hartre-Fock (HF) approximation and its semiempirical derivations. The Configuration Interaction (CI) method and the Density Functional Theory (DFT) also will be treated in this chapter. Chapter 3 is dedicated to
describe the characteristics of some usual devices as diodes and transistors. We will still cite some extremely small electronic devices. Chapter 4 describes our results and quarrels
about the possibility the of the transistion insulator-metal in CDM when doped. We got the
characterization optics of oligomers of CDM with null charge and in the presence of defects
of the type bipolaron. From the Hartree-Fock level we calculate the Structure of Bands and
the Density of States (DOS) for the PCDM in the neutral and doped state. The calculation
of the DOS and the Dispersion had been carried through computational programs
developed here in the Group GFMA. We still present in this chapter the theoretical
absorption spectra for oligomers of CDM with geometry fully optimized by DFT. In chapter 5 we have the relative results to the analysis of nanodevice based on tetramers of CDM with and without charge. The curves of the charge displacement versus voltage present characteristics of curves of usual devices. We also analyze the theoretical absorption spectra of the nanodevice for values of null tension and in points of current saturation.
Publisher: Universidade Federal do Pará
Type: Dissertação2007-01-01T00:00:00ZPropriedades magnéticas de nanoestruturas adsorvidas em superfícies metálicas
http://repositorio.ufpa.br/jspui/handle/2011/5081
Title: Propriedades magnéticas de nanoestruturas adsorvidas em superfícies metálicas
Authors: BEZERRA NETO, Manoel Maria
First Advisor: KLAUTAU, Ângela Burlamaqui
Abstract: We use the first principles RS-LMTO-ASA (Real Space - Linear Muffin-Tin Orbital - Atomic Sphere
Approximation) method, based on the Density Functional Theory and implemented to calculate noncollinear
magnetic structures, to investigate the magnetic properties of nanostructures adsorbed on
metallic surfaces. We have considered different geometries and sizes such as adatoms, dimers, trimers,
nanowires, and nanostructures with triangular geometry of Fe, Fe-Co and Fe-Pt on Pt(111), as well as
Mn nanostructures on Ag(111) surface. The Fe-Co nanowires adsorbed on Pt(111) are found to order ferromagnetically
regardless of the nanowire size. We find enhanced spin and orbital moments at Fe and Co
sites compared to what is found in bulk, which is attributed to the reduced coordination number presented
at the surface. We also analyzed how these moments vary as a function of the concentration of these
elements at the nanowires. For systems composed by Fe-Pt nanowires adsorbed on Pt(111), our results
show that it is possible to tune the exchange interaction between magnetic adatoms (Fe) by introducing
a different number of Pt atoms to link them. For instance, the exchange interaction between Fe adatoms
can be considerably increased by introducing Pt chains to link them. Moreover, either a ferromagnetic
or an antiferromagnetic configuration between magnetic adatoms (Fe) can be stabilized depending on
the Pt spacer thickness. Furthermore, even a non-collinear magnetic ordering can be obtained tuned by
Pt-mediated atoms. For Mn clusters on Ag(111), the exchange interactions between Mn sites depend not
only on the distance between the atoms, but also on the coordination number of each site. Therefore, the
non-collinear ordering in these nanostructures is caused not only if antiferromagnetism is frustrated by
the cluster geometry, but also by the competition between short and long range exchange interactions.
The results obtained are in general in good agreement with experiment and other calculations, when
available in the literature.
Publisher: Universidade Federal do Pará
Type: Dissertação2011-01-01T00:00:00Z