Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1980. / Vita. Grant no.: OCE 73-01384. Includes bibliographical references (leaves 203-209).

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 204-215).

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Supervised by Carl Wunsch. Vita. Includes bibliographical references (leaves 203-209).

Thesis (M.A.)--York University, 2005. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 128-133). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url%5Fver=Z39.88-2004&res%5Fdat=xri:pqdiss &rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR11747

Research into the mechanisms responsible for the lasting, cyclic activity at Masaya volcano can lead to a better understanding of persistently degassing volcanoes. This study is greatly enhanced by the integration of dynamic micro-gravity, deformation and gas flux measurements. The acquisition of extended temporal and spatial geophysical data will also allow for the development of robust models for the dynamics of magmatic systems. Masaya volcano, Nicaragua, is one of the most active systems in Central America, making it an excellent natural laboratory for this study. It is noted for repeated episodes of lava lake formation, strong degassing and subsequent quiescence. Ground-based geophysical measurements show two episodes of similar magnitude gravity decreases in 1993-1994 and 1997-1999, separated by a period of minor gravity increase. A major increase in S02 gas flux from 1997-1999 correlates well with the most recent episode of gravity decrease. The gravity changes are not accompanied by deformation in the summit areas and are interpreted in terms of sub-surface density changes. The persistent degassing at Masaya suggests that up to -15 krrr' of magma may have degassed over the last 150 years, only a minute fraction of which has been erupted. Furthermore, thermal flux calculations suggest that 0.5 krrr' of magma (the estimated volume of the shallow reservoir) would cool from liquidus to just above solidus temperatures in only 5 years. The high rates of degassing and cooling at open-system volcanoes such as Masaya raise questions as to the ultimate fate of this degassed and cooled magma. A number of models have been proposed to explain this, but the most likely mechanism to explain persistent activity at Masaya and other similar volcanoes is convective removal of cooled and degassed magma and subsequent recharge by volatile-rich magma from depth. Another fundamental question in modem volcanology concerns the manner in which a volcanic eruption is triggered; the intrusion of fresh magma into a reservoir is thought to be a key component. The amount by which previously ponded reservoir magma interacts with a newly intruded magma will determine the nature and rate of eruption as well as the chemistry of erupted lavas and shallow dykes. The physics of this interaction can be investigated through a conventional monitoring procedure that incorporates the Mogi model relating ground deformation (~) to changes in volume of a magma reservoir. Gravity changes (.1.g)combined with ground deformation provides information on magma reservoir mass changes. Models developed here predict how, during inflation, the observed .1.gI~ gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity.

General Relativity (GR) is one theory amongst a wider range of plausible descriptions of the Universe. The aim of this thesis is to examine the behaviour of so-called screened theories, which are designed to avoid local tests of modified gravity (MG). We establish that these theories may be treated in a unified manner in the context of halo formation. A prerequisite for this is the clarification that the quasi-static approximation can be applied in cosmologically-plausible scenarios. Amongst the plethora of MG theories, we select three, each of which exhibit a different form of screening. This describes a self-concealing property whereby each theory behaves like GR in the conditions of the local Universe. Only at regions of high energy density (chameleon), large coupling to matter (symmetron) or large derivatives of the scalar field (Vainshtein) does their modified behaviour emerge. We examine f(R), symmetron and DGP gravity in the context of non-linear gravitational collapse for the remainder of the thesis. Relativistic scalar fields are ubiquitous in our modern understanding of structure formation. They arise as candidates for dark energy and are at the heart of many modified theories of gravity. While there has been tremendous progress in calculating their effects on large scales there are still open questions on how to best quantify their effects on smaller scales where non-linear collapse becomes important. In these regimes, it has become the norm to use the quasi-static approximation in which the time evolution of perturbations in the scalar fields are discarded, akin to what is done in the context of non-relativistic fields in cosmology and the corresponding Newtonian limit. We show that considerable care must be taken in this regime by studying linearly perturbed scalar field cosmologies and quantifying the error that arise from taking the quasi-static limit. We focus on f(R) and chameleon models to assess the impact of the quasi-static approximation and discuss how it might affect studying the non-linear growth of structure in N-body numerical simulations. The halo mass function (HMF) n(M) dM is the number of haloes with mass in the range [ M, M+dM ] per unit volume. It has two remarkable properties which render it a useful probe of extensions to general relativity (GR). On the one hand, it is (nearly-)universal, in the sense that it can be written in a form (f(v) which is (practically) insensitive to changes in redshift and cosmological parameters and redshift. We develop a method to generalise fitting functions derived in GR to a variety of screened MG theories, in order to examine whether they are universal in the sense of being insensitive to MG. On the other hand, the HMF is sensitive to both the expansion history of the universe and the non-linear behaviour of spherical collapse via the critical density parameter and the matter power spectrum via the halo resolution. This greatly complicates the theoretical framework required to calculate the HMF, particularly given the sensitivity of chameleon MG to the surrounding environment. We explore a variety of new and existing methods to do so. Finally we re-calibrate the MG halo mass functions with the same rigour as has been done in GR. An important indicator of modified gravity is the effect of the local environment on halo properties. This paper examines the influence of the local tidal structure on the halo mass function, the halo orientation, spin and the concentration-mass relation. We generalise the excursion set formalism to produce a halo mass function conditional on large-scale structure. Our model agrees well with simulations on large scales at which the density field is linear or weakly non-linear. Beyond this, our principal result is that f(R does affect halo abundances, the halo spin parameter and the concentration-mass relationship in an environment-independent way, whereas we find no appreciable deviation from LCDM for the mass function with fixed environment density, nor the alignment of the orientation and spin vectors of the halo to the eigenvectors of the local cosmic web. There is a general trend for greater deviation from LCDM in under-dense environments and for high-mass haloes, as expected from chameleon screening. Given the broad spectrum of MG theories, it is important to design new probes of MG. Despite the fact that we examine only three theories of MG, the techniques and methodology developed in this thesis can be applied to a wide variety of theories and can be extended to improve the results in this work.

The project concerns the study of the interplay among quantum mechanics, statistical mechanics and thermodynamics, in isolated quantum systems. The goal of this research is to improve our understanding of the concept of thermal equilibrium in quantum systems. First, I investigated the role played by observables and measurements in the emergence of thermal behaviour. This led to a new notion of thermal equilibrium which is specific for a given observable, rather than for the whole state of the system. The equilibrium picture that emerges is a generalization of statistical mechanics in which we are not interested in the state of the system but only in the outcome of the measurement process. I investigated how this picture relates to one of the most promising approaches for the emergence of thermal behaviour in quantum systems: the Eigenstate Thermalization Hypothesis. Then, I applied the results to study the equilibrium properties of peculiar quantum systems, which are known to escape thermalization: the many-body localised systems. Despite the localization phenomenon, which prevents thermalization of subsystems, I was able to show that we can still use the predictions of statistical mechanics to describe the equilibrium of some observables. Moreover, the intuition developed in the process led me to propose an experimentally accessible way to unravel the interacting nature of many-body localised systems. Then, I exploited the "Concentration of Measure" and the related "Typicality Arguments" to study the macroscopic properties of the basis states in a tentative theory of quantum gravity: Loop Quantum Gravity. These techniques were previously used to explain why the thermal behaviour in quantum systems is such an ubiquitous phenomenon at the macroscopic scale. I focused on the local properties, their thermodynamic behaviour and interplay with the semiclassical limit. The ultimate goal of this line of research is to give a quantum description of a black hole which is consistent with the expected semiclassical behaviour. This was motivated by the necessity to understand, from a quantum gravity perspective, how and why an horizon exhibits thermal properties.

TAHIM, Makarius Oliveira. Aspectos clássicos de gravitação topológica e dimensões extras. 2008. 115 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2008. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-22T20:22:11Z No. of bitstreams: 1 2008_tese_motahim.pdf: 525141 bytes, checksum: f66f89fe8740ec135888fd7be2a867ef (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-05-22T20:24:36Z (GMT) No. of bitstreams: 1 2008_tese_motahim.pdf: 525141 bytes, checksum: f66f89fe8740ec135888fd7be2a867ef (MD5) / Made available in DSpace on 2015-05-22T20:24:36Z (GMT). No. of bitstreams: 1 2008_tese_motahim.pdf: 525141 bytes, checksum: f66f89fe8740ec135888fd7be2a867ef (MD5) Previous issue date: 2008 / Nesta tese abordamos alguns aspectos relacionados com teorias de Gravidade. Essencialmente existem duas partes principais neste trabalho: 1) mecanismos de localização de campos em membranas e 2) nova interpretação para a teoria de gravitação. No que concerne aos mecanismos de localização de campos em membranas dois assuntos são colocados: a construção de modelos de gravidade topológica no contexto de teorias contendo membranas e localização de campos de gauge tensoriais em membranas finas (o denominado campo de Kalb-Ramond). No primeiro destes assuntos, a questão importante é a tentativa de se obter resultados semelhantes aqueles provindos do modelo de Randall-Sundrum, isto é, a solução do problema de hierarquia e localização do campo gravitacional na membrana. No entanto, o caminho escolhido está associado com modelos de gravitação topológica, modelos estes onde a métrica do espaço-tempo não é a quantidade fundamental da teoria. Existe na literatura uma corrente de pensamento baseada em um formalismo de quantização de gravidade que necessita do ponto de vista onde a mesma pode ser tratada por meio de uma teoria topológica de campos vinculada. Portanto, perguntar da validade dos resultados de Randall-Sundrum no contexto de gravidade topológica pode servir de teste para se construir resultados estritamente quânticos. Neste sentido, fazemos uma análise primeiramente clássica de modelos possíveis, discutindo diversos aspectos (quebras de simetrias, simetrias de gauge, etc.). Primeiramente mostramos que se pode obter de fato, no contexto acima citado, equações semelhantes àquelas obtidas nos modelos de Randall-Sundrum para explicar a existência da hierarquia entre as massas dos bósons de Higgs. No entanto, não se faz uma análise detalhada de como deve ser descrita gravidade em D=5. Nesta linha de raciocínio, construímos vários modelos com forma matemática semelhante a modelos de gravidade topológica (modelos equivalentes), tentando fazer a "localização" sobre as membranas de modo a linkar estes resultados ao primeiro citado logo acima. Por último, construímos efetivamente gravidade topológica em membranas nos moldes de modelos de gravidade topológica, fazendo a análise dos vínculos no espaço-tempo ortogonal à membrana. No segundo assunto, estudamos modelos de campos escalares que suportam defeitos tipo kink embutidos em espaço-tempo D=5. Tais modelos podem ser utilizados para se simular membranas finas. Neste caso analisamos a localização de campos de gauge tensoriais, principalmente o campo de Kalb-Ramond, no background de várias geometrias que não apresentam singularidades, como no caso do modelo de Randall-Sundrum. O resultado é que o modo-zero do campo de Kalb-Ramond pode ser localizado somente em background gravitacional onde o dilaton tem papel importante. A segunda parte da tese é um pouco mais especulativa. Trata de uma nova abordagem de interpretação da gravitação. A idéia, em suma, é comparar o próprio espaço-tempo a um sólido deformável. Neste sentido, busca-se identificar quem são os componentes microscópicos do sólido do espaço-tempo, em analogia com os sólidos cristalinos reais, os quais são compostos por uma rede contendo uma miríade de átomos e moléculas. Para tal empresa, a equação de Landau-Raychaudhuri tem papel importante. No total, discutem-se três sinais apontando para esta idéia: a) as deformações do volume do espaço-tempo, b) a origem elástica da ação de Einstein-Hilbert e c) a relação entre a Lei de Hooke da Elasticidade e a equação de Einstein da gravitação. A idéia principal é que as equações de Einstein parecem "emergir", sendo bastante naturais neste contexto.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O aumento do comércio intra-regional é um dos objetivos da União das Nações Sul-Americanas (UNASUL). O crescimento do comércio pressupõe, entretanto uma infra-estrutura adequada na região. O objetivo da presente dissertação de mestrado é o de avaliar os efeitos do estoque de infra-estrutura nos fluxos de comércio dos dez principais países da América do Sul. O modelo gravitacional foi escolhido como metodologia empírica, sendo testada uma especificação. Os resultados confirmam a hipóteses da importância da infra-estrutura para o aumento do comércio intra-regional. Logo, o projeto IIRSA (Iniciativa para a Integração da Infra-Estrutura Regional Sul-Americana) é um instrumento importante para a integração sul-americana. / The growth of intra-regional trade is one of the aims of UNASUL (South American United Nations). Nevertheless, the increase of the trade between the South America countries depends upon a good infrastructure of the region. The aim of this dissertation is to evaluate the effects of the infrastructure stock upon the trade flows of the ten main South American countries. The gravity model has been chosen to evaluate issue. One specification of the model have been applied. The results confirm the hypothesis about the relevance of the infrastructure for the increase is an important vehicle for the South American integration.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo nesta dissertação consiste em verificar se o crescimento das exportações de produtos manufaturados chineses afetou negativamente o desempenho das exportações desses produtos dos países da América Latina, no período de 1995-2005. As exportações chinesas são consideradas em conjunto com as de Hong Kong, tendo em vista que esse país é considerado um centro de re-exportação da China. Para tal, foi estimada uma equação gravitacional ampliada para as exportações dos países latino americanos destinadas a outros mercados, incluindo como variável explicativa as exportações da China para esses destinos. O resultado obtido com a aplicação de variáveis instrumentais em dois estágios mostrou que um aumento de 1% nas exportações chinesas para esses mercados reduz as vendas externas dos países latino americanos em 0,3%. No entanto, como os instrumentos disponíveis não variam com o tempo, não foi possível utilizar o método de efeito fixo que evita o viés decorrente da omissão de varáveis que captam as características específicas dos países, as quais podem influenciar o volume de comércio. Portanto, o resultado não foi conclusivo. / The objective in this investigation consists in verify if the growth of the Chinese manufactured goods negatively affected the performance from the exports of this products from the Latin America countries, in the period 1995-2005. The Chinese exports are considerate in set with the ones of Hong Kong, since this country is considered a center of re-exportation from China. For such, was esteem a gravity equation augmented to the exportations from the Latin America countries destined to other markets, including as explicative variable the exportations from China to these destinies. The result obtained with the application of instrumental variables in two stage showed that an increase of 1% on the Chinese exports to these markets reduces the external sales from the Latin America countries in 0,3%. However, since the instruments available no change over time, it was not possible to use the method of fixed effect that avoid the bias occurred from the omission of variables, that can influence the trade volume. Thus, the result was not conclusive.