Teorias f(R) de gravidade na formulação de Palatini

In this dissertation, after a brief review on the Einstein s General Relativity Theory and its application to the Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological models, we present and discuss the alternative theories of gravity dubbed f(R) gravity. These theories come about when one substitute in the Einstein-Hilbert action the Ricci curvature R by some well behaved nonlinear function f(R). They provide an alternative way to explain the current cosmic acceleration with no need of invoking neither a dark energy component, nor the existence of extra spatial dimensions. In dealing with f(R) gravity, two different variational approaches may be followed, namely the metric and the Palatini formalisms, which lead to very different equations of motion. We briefly describe the metric formalism and then concentrate on the Palatini variational approach to the gravity action. We make a systematic and detailed derivation of the field equations for Palatini f(R) gravity, which generalize the Einsteins equations of General Relativity, and obtain also the generalized Friedmann equations, which can be used for cosmological tests. As an example, using recent compilations of type Ia Supernovae observations, we show how the f(R) = R − fi/Rn class of gravity theories explain the recent observed acceleration of the universe by placing reasonable constraints on the free parameters fi and n. We also examine the question as to whether Palatini f(R) gravity theories permit space-times in which causality, a fundamental issue in any physical theory [22], is violated. As is well known, in General Relativity there are solutions to the viii field equations that have causal anomalies in the form of closed time-like curves, the renowned Gödel model being the best known example of such a solution. Here we show that every perfect-fluid Gödel-type solution of Palatini f(R) gravity with density and pressure p that satisfy the weak energy condition + p 0 is necessarily isometric to the Gödel geometry, demonstrating, therefore, that these theories present causal anomalies in the form of closed time-like curves. This result extends a theorem on Gödel-type models to the framework of Palatini f(R) gravity theory. We derive an expression for a critical radius rc (beyond which causality is violated) for an arbitrary Palatini f(R) theory. The expression makes apparent that the violation of causality depends on the form of f(R) and on the matter content components. We concretely examine the Gödel-type perfect-fluid solutions in the f(R) = R−fi/Rn class of Palatini gravity theories, and show that for positive matter density and for fi and n in the range permitted by the observations, these theories do not admit the Gödel geometry as a perfect-fluid solution of its field equations. In this sense, f(R) gravity theory remedies the causal pathology in the form of closed timelike curves which is allowed in General Relativity. We also examine the violation of causality of Gödel-type by considering a single scalar field as the matter content. For this source, we show that Palatini f(R) gravity gives rise to a unique Gödeltype solution with no violation of causality. Finally, we show that by combining a perfect fluid plus a scalar field as sources of Gödel-type geometries, we obtain both solutions in the form of closed time-like curves, as well as solutions with no violation of causality

Propriedades críticas do processo epidêmico difusivo com interação de Lévy

The diffusive epidemic process (PED) is a nonequilibrium stochastic model which, exhibits a phase trnasition to an absorbing state. In the model, healthy (A) and sick (B) individuals diffuse on a lattice with diffusion constants DA and DB, respectively. According to a Wilson renormalization calculation, the system presents a first-order phase transition, for the case DA > DB. Several researches performed simulation works for test this is conjecture, but it was not possible to observe this first-order phase transition. The explanation given was that we needed to perform simulation to higher dimensions. In this work had the motivation to investigate the critical behavior of a diffusive epidemic propagation with Lévy interaction(PEDL), in one-dimension. The Lévy distribution has the interaction of diffusion of all sizes taking the one-dimensional system for a higher-dimensional. We try to explain this is controversy that remains unresolved, for the case DA > DB. For this work, we use the Monte Carlo Method with resuscitation. This is method is to add a sick individual in the system when the order parameter (sick density) go to zero. We apply a finite size scalling for estimates the critical point and the exponent critical =, e z, for the case DA > DB

Trabalho e formação dos educadores de creche em Botucatu: reflexões críticas

Considerando a recente preocupação de estabelecer programas de formação em serviço para educadores de creche, estudamos oito creches municipais de Botucatu (SP). O objetivo foi conhecer as condições de trabalho e de formação dos educadores com base em dados que permitissem avaliar os procedimentos de educação inicial e continuada a que foram submetidos, as concepções subjacentes à sua prática profissional, suas expectativas sobre os programas de formação em serviço, assim como as efetivas necessidades a que esses programas precisam responder em vista dos parâmetros de qualidade estabelecidos para a educação infantil. A partir dos resultados obtidos, traçamos um panorama e esboçamos sugestões que possam subsidiar uma proposta de formação inicial e continuada para esses educadores, valendo-nos de algumas contribuições da teoria histórico-cultural enriquecidas com reflexões críticas e recentes na área, e do contraponto com as propostas defendidas por documentos oficiais em vigor propalados nacionalmente.

Imigração e teorias antropólogicas no Brasil (1910-1920)

Brazil takes pride in its alleged lack of racial discrimination. These idealized racial relations are a construction of enlightened elites. This article analyzes one of the main cultural publications in the country in order to establish how European anthropological theories were interpreted by Brazilian intelectuals. In the reappraisal of the country proposed in the journal, the ethnic question was intensely discussed. A whitening of the population was generally perceived as a sort of magic solution to the contradictions in a multiracial, heterogeneous and rigidly hierarchic society. This natural process might be accelerated by an inflow of European immigration. The many expectations and tensions surrounding immigration were expressed in the construction of categories of desirable and undesirable immigrants. Thereof an ideal white country emerged, far away from the myth of racial democracy, which has not materialized in Brazilian society today.

Observatório da habitação da cidade de São Paulo: caracterização, processos e situações críticas de encaminhamento

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Observatorio de la vivienda en la ciudad de São Paulo: caracterización, procesos y situaciones críticas en su ejecución

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Desarrollo y educación en América Latina: borrador para críticas y comentarios

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Críticas de las teorías y la política burguesas de la población

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La urbanización en América Latina: 1950-1970; patrones y áreas críticas

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Las teorias de la poblacion de John Maynard Keynes y el concepto de optimo""

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Teorias y politicas de poblacion

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Virtudes y limitaciones de los mapas censales de carencias críticas

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Los censos de población y vivienda: críticas y sugerencias

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Información de los censos demográficos del Brasil sobre migraciones internas: críticas y sugerencias para el análisis

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Dinámica y estructura del proceso de asentamiento humano en América Latina y el Caribe: principales áreas críticas = Dynamics and structure of the human settlement process in Latin America and the Caribbean: main critical areas

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