Thesis (doctoral)--Universität, Frankfurt (Main), 2004.

Thesis (Ph.D.)--Brown University, 2005. / Vita. Thesis advisor: Jimmie D. Doll. Includes bibliographical references (leaves 159-170). Also available online.

Thesis (Ph. D.)--Oregon Graduate Center, 1986.

In this paper we focus on the problem of estimating a boundeddensity using a finite combination of densities from a givenclass. We consider the Maximum Likelihood Procedure (MLE) and the greedy procedure described by Li and Barron. Approximation and estimation bounds are given for the above methods. We extend and improve upon the estimation results of Li and Barron, and in particular prove an $O(\frac{1}{\sqrt{n}})$ bound on the estimation error which does not depend on the number of densities in the estimated combination.

Thesis (Ph. D.)--University of Chicago, Committee on Human Nutrition and Nutritional Biology, March 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Oregon, 2000. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 159-176). Also available for download via the World Wide Web; free to University of Oregon users. Address:http://wwwlib.umi.com/cr/uoregon/fullcit?p9963443.

The present work was initially aimed at providing an explanation for some of the phenomena that occur in the ionosphere at sunrise. The approach that was taken was to determine the changes that take place on a theoretical model of the ionosphere and then to compare these with observations. A prerequisite for this approach was a theoretical model that would show, among other things, a bifurcation of the F layer during daytime without making unjustified arbitrary assumptions. The absence of such a model, particularly as far as non-equilibrium conditions are concerned, resulted in the present attempt to provide such a model for the F1 region.

A variety of modified minerals have been screened to determine their effectiveness as agents for the catalytic transformation of the thermally generated off gases arising from the pyrolysis of the polyolefinic plastic High Density Polyethylene (HDPE). This polymer has been shown to degrade through a series of known mechanisms to yield a hydrocarbon product mixture consisting of an homologous series of saturated and unsaturated hydrocarbons which include alk-1-enes, n-alkanes, alk-x-enes and a-w-dienes. Modification treatments have been wide ranging having included activation of the parent mineral by means of pillaring, ion exchange and acid activation. The activated products have been characterised by XRD, XRF, TGA and vibrational spectroscopy. Moreover, evolved gas analysis has been employed to perform catalytic screening runs on these modified minerals. In particular, attention has been paid to the activity of these materials in respect of the formation of potentially fuel applicable hydrocarbons, namely those exhibiting high octane ratings, including aromatics and branched aliphatics from the feedstock species present in the HDPE pyrolysate gas mixture. Pillared clays (PILC's) have proven ineffective in this role as a consequence of their poor reproducibility and lack of selectivity towards the formation of single ring aromatics. Likewise, ion exchange has been found to influence strongly the catalytic behaviour of previously acid activated clays, with autotransformed samples offering dehydrocyclisation (DHC) activity at levels significantly greater than seen with some ion exchanged samples, particularly protons. Acid activated metakaolinites have demonstrated poor selectivity in terms of aromatic formation, although total DHC activity is good. Metakaolin also gave rise to appreciable activity in respect of the formation of the single ring aromatics selected for monitoring in this work. Isomerisation activity was prevalent over these materials, but coking levels were high. Acid activated smectites represent the most suitable candidates to fulfil the role of single step fuel generation from the transformation of the gas stream resulting from HDPE pyrolysis. It has been found that careful control over the chemical and physical properties of acid activated clays can be achieved through consideration of the severity of the activation parameters chosen to induce modification. In addition, the nature of the activated product is strongly dependant on the nature of the base clay. In particular, acid activated beidellites have been shown to exhibit high levels of surface acidity as determined through the thermal desorption of cyclohexylamine. These materials consequently give rise to respectable activity and selectivity in terms of the formation of highly octane rated methyl substituted single ring aromatics, principally trimethylbenzene. In contrast, acid activated montmorillonites have been seen to offer lower levels of total surface acidity and have been shown to be active in promoting skeletal isomerisation reactions to yield branched aliphatics, again, highly octane rated. This activity variation has been attributed to the formation of highly Bronsted acidic silanol containing Surface Localised Acid Pools (SLAP's) on the exposed surfaces of the former as a consequence of the isomorphous substitution patterns observed in the tetrahedral sheets of beidellites.

Made available in DSpace on 2014-06-11T19:31:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-12-20Bitstream added on 2014-06-13T20:41:38Z : No. of bitstreams: 1 sanoja_a_dr_ift.pdf: 582908 bytes, checksum: 608a543719b2da86f0b937d5c00bfbba (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fazemos uma revisão do modelo cosmológico padrão, apresentando suas bases observacionais e mostrando os aspectos conceituais mais relevantes. Depois realizamos uma revisão da teoria de in ação, indicando as motivações conceituais que levaram à formulação da teoria, o mecanismo que faz possível a in ação cósmica e como esse processo resolve os problemas clássicos da cosmologia padrão. Após mostrar que a in ação é um mecanismo bem-sucedido para explicar a origem das perturbações de densidade primordiais, concentramo-nos em descrever a evolução das perturbações de densidade cosmológica, tanto na sua fase linear como não-linear. Além disso, mostramos como o campo de perturbações de densidade linear permite predizer estatisticamente a abundância e a distribuição das estruturas cósmicas. Posteriormente, consideramos a expansão acelerada do universo e discutimos os candidatos que têm sido propostos para tentar explicar a origem dessa aceleração, especialmente o candidato da energia escura, no qual nos detemos para revisar os modelos básicos propostos com respeito à sua natureza. Adicionalmente, mostramos como sua presença afeta a evolução das perturbações de densidade. Finalmente, baseandonos no modelo de Lemaître-Tolman-Bondi, fazemos uma generalização do modelo do colapso esférico para estudar a evolução não-linear de perturbações de densidade inhomogêneas, tanto em um universo Einstein-de Sitter como em um universo CDM / We present a review of the standard cosmological model, showing both its observational basis as well as the most revelant conceptual aspects. Subsequently, we give an overview of the in ation theory , pointing out the conceptual motivations that led to its formulation, the mechanism that allow the cosmic in ation and how that process resolves the classical problems of the standard cosmology. After showing that the in ation theory provides a successful mechanism to explain the origin of the primordial density perturbations, we focus on describing the evolution of the cosmological density perturbations, both in linear and nonlinear phase. On the other hand, we show how the linear density perturbation eld allows to predict statistically the abundance and distribution of the cosmic structures. Next, we consider the accelerated expansion of the universe and mention the candidates that have seen proposed to try to explain the origin of the acceleration; especially the dark energy candidate, in which we pause to examine the basic models proposed about its nature. Further, we expose how its presence a ects the evolution of the density perturbations. Finally, based on the Lemaître-Tolman-Bondi, we make a generalization of the spherical collapse model to study the evolution of inhomogeneous nonlinear density perturbations, both in an Einstein-de Sitter as CDM universe

D.Sc. / Please refer to full text to view abstract