Duality between k-essence and Rastall gravity

The k-essence theory with a power-law function of $(\partial\phi)^2$ and Rastall's non-conservative theory of gravity with a scalar field are shown to have the same solutions for the metric under the assumption that both the metric and the scalar fields depend on a single coordinate. This equivalence (called k-R duality) holds for static configurations with various symmetries (spherical, plane, cylindrical, etc.) and all homogeneous cosmologies. In the presence of matter, Rastall's theory requires additional assumptions on how the stress-energy tensor non-conservation is distributed between different contributions. Two versions of such non-conservation are considered in the case of isotropic spatially flat cosmological models with a perfect fluid: one (R1) in which there is no coupling between the scalar field and the fluid, and another (R2) in which the fluid separately obeys the usual conservation law. In version R1 it is shown that k-R duality holds not only for the cosmological models themselves but also for their adiabatic perturbations. In version R2, among other results, a particular model is singled out that reproduces the same cosmological expansion history as the standard $\Lambda$CDM model but predicts different behaviors of small fluctuations in the k-essence and Rastall frameworks.Comment: 10 pages, no figures. Two references adde

A note on non-vanishing divergence of the stress-energy tensor in theories of gravity

In this paper we investigate three theories characterised by non-vanishing divergence of the stress-energy tensor, namely $f(R,\mathcal L_M)$, $f(R,T)$, and Rastall theory. We show that it is not possible to obtain the third from the first two, unless in some very specific case. Nonetheless, we show that in the framework of cosmology in the $f(R,T)$ theory, a result similar to that found in the Rastall one is reproduced, namely that the dynamics of the $\Lambda$CDM model of standard cosmology can be exactly mimicked, even though the dark energy component is able to cluster.Comment: 6 page

Duality between k-essence and Rastall gravity

The k-essence theory with a power-law function of (partial phi )^2( 02\u3d5) 2 and Rastall\u2019s non-conservative theory of gravity with a scalar field are shown to have the same solutions for the metric under the assumption that both the metric and the scalar fields depend on a single coordinate. This equivalence (called k\u2013R duality) holds for static configurations with various symmetries (spherical, plane, cylindrical, etc.) and all homogeneous cosmologies. In the presence of matter, Rastall\u2019s theory requires additional assumptions on how the stress-energy tensor non-conservation is distributed between different contributions. Two versions of such non-conservation are considered in the case of isotropic spatially flat cosmological models with a perfect fluid: one (R1) in which there is no coupling between the scalar field and the fluid, and another (R2) in which the fluid separately obeys the usual conservation law. In version R1 it is shown that k\u2013R duality holds not only for the cosmological models themselves but also for their adiabatic perturbations. In version R2, among other results, a particular model is singled out that reproduces the same cosmological expansion history as the standard Lambda\u39b CDM model but predicts different behaviors of small fluctuations in the k-essence and Rastall frameworks

Mercury adsorption on natural and organofunctionalized smectites - thermodynamics of cation removal

A natural smectite clay sample from Piauí State, Brazil, was organofunctionalized with 3-mercaptopropyltrimethoxysilane and 3-aminopropyltriethoxysilane silyating agents. The basal spacing of 0.99 nm and surface area of 48 m² g-1 for natural clay increased to 1.84 and 2.01 nm, and 781 and 795 m² g-1 for modified clays, respectively. The natural and chemically immobilized clay samples adsorb mercury cations from aqueous solutions at pH 3.0 at 298 ± 1 K. The Langmuir, Redlich-Peterson and Toth adsorption isotherm models were applied to fit the experimental data with a nonlinear approach. From the cation/basic center interactions for each smectite at the solid-liquid interface, by using calorimetry methodology, the equilibrium constant and exothermic thermal effects were obtained. By considering the net interactive number of moles for each cation and the equilibrium constant, the enthalpy, intHº (-11.98 to -13.93 kJ mol-1) and negative free Gibbs energy, intGº (-22.4 ± 0.1 to -23.9 ± 0.1 kJ mol-1) were calculated. These values enabled the determination of positive entropy, intSº (51 ± 01 to 55 ± 2 J K-1 mol-1). The cation-basic center interactions are spontaneous in nature as demonstrated from favorable enthalpic and entropic results. Natural and anchored smectites have the ability to complex mercury, acting as useful materials for removal of this hazardous metal from an ecosystem.Uma amostra natural de esmectita oriunda do estado do Piauí, Brasil, foi organofuncionalizada com 3-mercaptopropiltrimethoxissilano e 3-aminopropiltriethoxissilano. O espaçamento basal da argila natural é de 0,99 nm e área superficial 48 m² g-1. Houve um aumento no espaçamento basal para 1,84 e 2,01 nm e o aumento da área específica para 781 e 795 m² g-1 para as argilas quimicamente modificadas, respectivamente. A argila natural e a argila quimicamente modificada adsorveram cátions mercúrio em solução aquosa em pH 3,0 e 298 ± 1 K. Os modelos de isotermas de adsorção de Langmuir, Redlich-Peterson e Toth foram aplicados para ajuste dos dados experimentais com aproximação não linear. Para as interações cátion/centros básicos para cada esmectita na interface sólido/líquido foi utilizada metodologia calorimétrica e foram obtidas as constantes de equilíbrio e os efeitos térmicos exotérmicos. Considerando o número interativo de moles para cada cátion e as constantes de equilíbrio, a entalpia, intHº (-11,98 a -13,93 kJ mol-1) e a energia livre de Gibbs negativa, intGº (-22,4 ± 0,1 a -23,9 ± 0,1 kJ mol-1) foram calculadas, o que permitiram a determinação da entropia positiva intSº (51 ± 01 a 55 ± 2 J K-1 mol-1). As interações cátion/centros básicos são de natureza espontânea como demonstram os valores de energia livre de Gibbs, dando o conjunto de dados favoráveis como expressam a entalpia exotérmica e a entropia positiva, mostrando que a esmectita natural e as quimicamente modificadas têm habilidade em complexar mercúrio. Logo, esses materiais são úteis na remoção de mercúrio em um ecossistema.594603Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Mercury adsorption on natural and organofunctionalized smectites - thermodynamics of cation removal

A natural smectite clay sample from Piauí State, Brazil, was organofunctionalized with 3-mercaptopropyltrimethoxysilane and 3-aminopropyltriethoxysilane silyating agents. The basal spacing of 0.99 nm and surface area of 48 m² g-1 for natural clay increased to 1.84 and 2.01 nm, and 781 and 795 m² g-1 for modified clays, respectively. The natural and chemically immobilized clay samples adsorb mercury cations from aqueous solutions at pH 3.0 at 298 ± 1 K. The Langmuir, Redlich-Peterson and Toth adsorption isotherm models were applied to fit the experimental data with a nonlinear approach. From the cation/basic center interactions for each smectite at the solid-liquid interface, by using calorimetry methodology, the equilibrium constant and exothermic thermal effects were obtained. By considering the net interactive number of moles for each cation and the equilibrium constant, the enthalpy, "intHº (-11.98 to -13.93 kJ mol-1) and negative free Gibbs energy, "intGº (-22.4 ± 0.1 to -23.9 ± 0.1 kJ mol-1) were calculated. These values enabled the determination of positive entropy, "intSº (51 ± 01 to 55 ± 2 J K-1 mol-1). The cation-basic center interactions are spontaneous in nature as demonstrated from favorable enthalpic and entropic results. Natural and anchored smectites have the ability to complex mercury, acting as useful materials for removal of this hazardous metal from an ecosystem

Autonomous driving of trucks in off-road environment

Off-road driving operations can be a challenging environment for human conductors as they are subject to accidents, repetitive and tedious tasks, strong vibrations, which may affect their health in the long term. Therefore, they can benefit from a successful implementation of autonomous vehicle technology, improving safety, reducing labor costs and fuel consumption, and increasing operational efficiency. The main contribution of this paper is the experimental validation of a path tracking control strategy, composed of longitudinal and lateral controllers, on an off-road scenario with a fully-loaded heavy-duty truck. The longitudinal control strategy relies on a Non-Linear Model Predictive Controller (NMPC), which considers the path geometry and simplified vehicle dynamics to compute a smooth and comfortable input velocity, without violating the imposed constraints. The lateral controller is based on a Robust Linear Quadratic Regulator (RLQR), which considers a vehicle model subject to parametric uncertainties to minimize its lateral displacement and heading error, as well as ensure stability. Experiments were carried out using a fully-loaded vehicle on unpaved roads in an open-pit mine. The truck followed the reference path within the imposed constraints, showing robustness and driving smoothness.Comment: Paper accepted at Journal of Control, Automation and Electrical System

A CARTOGRAFIA DOS MUSEUS COM ACERVOS DA DIÁSPORA AFRICANA NO BRASIL & A GEOPOLÍTICA DA EXCLUSÃO SECULAR

Estabelecer e reconhecer outras perspectivas para A compreensão dos séculos de tráfico, da escravidão e da diáspora africana como elementos formadores da configuração do mundo contemporâneo constituem pressupostos básicos para traçar um contexto mais adequado referente ao papel das culturas de matriz africana na formação dos territórios e dos povos em praticamente todos os continentes. Não podemos perder de vista que entre os principais entraves ao desempenho das populações de ascendência na África na sociedade dominante, se destaca a inferiorização destas em todos os seguimentos, sobretudo na escola, nas representações sociais e na ocupação territorial. Esta invisibilidade secular sistêmica que ignoram os povos e a territorialidade constituída tem como "pano de fundo" não oferecer modelos relevantes que ajudem a construir uma auto-imagem positiva, nem dar referência a sua verdadeira geografia e sua história no processo diaspórico secular