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

Transporte eletrônico e propriedades termodinâmicas de nanobiomoléculas

We use a tight-binding formulation to investigate the transmissivity and the currentvoltage (I_V) characteristics of sequences of double-strand DNA molecules. In order to reveal the relevance of the underlying correlations in the nucleotides distribution, we compare theresults for the genomic DNA sequence with those of arti_cial sequences (the long-range correlated Fibonacci and RudinShapiro one) and a random sequence, which is a kind of prototype of a short-range correlated system. The random sequence is presented here with the same _rst neighbors pair correlations of the human DNA sequence. We found that the long-range character of the correlations is important to the transmissivity spectra, although the I_V curves seem to be mostly inuenced by the short-range correlations. We also analyze in this work the electronic and thermal properties along an _-helix sequence obtained from an _3 peptide which has the uni-dimensional sequence (Leu-Glu-Thr- Leu-Ala-Lys-Ala)3. An ab initio quantum chemical calculation procedure is used to obtain the highest occupied molecular orbital (HOMO) as well as their charge transfer integrals, when the _-helix sequence forms two di_erent variants with (the so-called 5Q variant) and without (the 7Q variant) _brous assemblies that can be observed by transmission electron microscopy. The di_erence between the two structures is that the 5Q (7Q) structure have Ala ! Gln substitution at the 5th (7th) position, respectively. We estimate theoretically the density of states as well as the electronic transmission spectra for the peptides using a tight-binding Hamiltonian model together with the Dyson's equation. Besides, we solve the time dependent Schrodinger equation to compute the spread of an initially localized wave-packet. We also compute the localization length in the _nite _-helix segment and the quantum especi_c heat. Keeping in mind that _brous protein can be associated with diseases, the important di_erences observed in the present vi electronic transport studies encourage us to suggest this method as a molecular diagnostic tool

Conducão eletrônica e propriedades termodinâmicas da molécula de DNA

In this thesis, we study the thermo-electronic properties of the DNA molecule. For this purpose, we used three types of models with the DNA, all assuming a at geometry (2D), each built by a sequence of quasiperiodic (Fibonacci and / or Rudin-Shapiro) and a sequence of natural DNA, part of the human chromosome Ch22. The first two models have two types of components that are the nitrogenous bases (guanine G, cytosine C, adenine A and thymine T) and a cluster sugar-phosphate (SP), while the third has only the nitrogenous bases. In the first model we calculate the density of states using the formalism of Dyson and transmittance for the time independent Schr odinger equation . In the second model we used the renormalizationprocedure for the profile of the transmittance and consequently the I (current) versus V (voltage). In the third model we calculate the density of states formalism by Dean and used the results together with the Fermi-Dirac statistics for the chemical potential and the quantum specific heat. Finally, we compare the physical properties found for the quasi-periodic sequences and those that use a portion of the genomic DNA sequence (Ch22).

Propiedades termodinámicas de sorción de agua de la pulpa de lulo en polvo con encapsulantes

Dados de umidade de equilíbrio de polpa de lulo em pó (PL) com e sem aditivos - 58% de maltodextrina (MD) ou 58% de goma Arábica (GA) - foram determinados nas temperaturas de 20, 30, 40 e 50 °C, utilizando-se o método estático gravimétrico numa faixa de atividade de água de 0,06 a 0,90. As isotermas apresentaram formato sigmoidal do tipo III e o modelo de Guggenhein-Anderson-de Boer (GAB) ajustou satisfatoriamente os dados experimentais de umidade de equilíbrio em função da atividade de água. A adição de encapsulantes afetou as isotermas de tal maneira que na mesma atividade de água, as amostras PL + GA y PL + MD apresentaram um menor conteúdo de umidade de equilíbrio e não foram afetadas pela variação de temperatura. Os calores isostéricos de sorção das polpas em pó com encapsulantes foram maiores (menos negativos) em relação à polpa de lulo em pó, sugerindo a existência de sítios polares mais ativos no produto sem adição de GA ou MD. Uma relação exponencial empírica foi utilizada para descrever a dependência do calor de sorção com o conteúdo de umidade do material.

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.

Efecto del método de secado en las propiedades termodinámicas de pulpa de mora en polvo

Three different types of maltodextrin encapsulated dehydrated blackberry fruit powders were obtained using vibrofluidized bed drying (VF), spray drying (SD), vacuum drying (VD), and freeze drying (FD). Moisture equilibrium data of blackberry pulp powders with 18% maltodextrin were determined at 20, 30, 40, and 50°C using the static gravimetric method for the water activity range of 0.06-0.90. Experimental equilibrium moisture content data versus water activity were fit to the Guggenheim-Anderson-de Boer (GAB) model. Agreement was found between experimental and calculated values. The isosteric heat of sorption of water was determined using the Clausius-Clapeyron equation from the equilibrium data; isosteric heats of sorption were found to increase with increasing temperature and could be adjusted by an exponential relationship. For freeze dried, vibrofluidized, and vacuum dried pulp powder samples, the isosteric heats of sorption were lower (more negative) than those calculated for spray dried samples. The enthalpy-entropy compensation theory was applied to sorption isotherms and plots of ΔH versus ΔS provided the isokinetic temperatures, indicating an enthalpy-controlled sorption process.

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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Planificacion de los asentamientos humanos en America Latina y el Caribe: teorias y metodologias; texto resumen

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Notas acerca de la familia y las teorias de la fecundidad

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Teorias de conta corrente: uma aplicação ao caso do Brasil nos anos noventa

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

O evolucionismo no ensino de Biologia: investigação das teorias de Lamarck e Darwin expostas nos livros didáticos de Biologia do Plano Nacional do Livro Didático do ensino médio - PNLEM

Pós-graduação em Educação - IBRC

Propriedades termodinâmicas de adsorção de água e cinética de secagem de subprodutos da industrialização de abacaxi (Ananás comosus L.): casca e cilindro central

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Um contraste entre as teorias cognitivas da consciência de Baars e Dennett: o espaço de trabalho global seria um teatro cartesiano?

Pós-graduação em Filosofia - FFC

Teorias duais massivas de spin-2 em D=2+1 via ação mestra e imersão de Noether

Pós-graduação em Física - FEG