Charged quark stars in metric f(R)f(R) gravity

We provide the modified TOV equations for the hydrostatic equilibrium of charged compact stars within the metric $f(R)$ gravitational background. We adopt the MIT bag model EoS for the dense matter and assume a charge distribution where the electric charge density $\rho_{\rm ch}$ is proportional to the standard energy density $\rho$. Using the Starobinsky model, we explore the role of the $\alpha R^2$ term, where $\alpha$ is a free constant and $R$ the Ricci scalar, on the global properties of charged stars such as radius, mass and total charge. We present the dependence of the structure of the star for several values of $\alpha$ and for different values of the constant parameter $\beta\equiv \rho_{\rm ch}/\rho$. Remarkably, we find that the radius decreases with respect to its GR value for low central densities, while the opposite occurs in the high-central-density region. The mass measured at the surface always decreases and the maximum-total charge undergoes a substantial increase as the parameter $\alpha$ increases. We also illustrate the variations of the asymptotic mass as a consequence of the electric charge and the extra quadratic term.Comment: 11 pages, 7 figures. To appear in JCA

Compact stars in scalar-tensor theories with a single-well potential and the corresponding f(R)f(R) theory

The macroscopic properties of compact stars in modified gravity theories can be significantly different from the general relativistic (GR) predictions. Within the gravitational context of scalar-tensor theories, with a scalar field $\phi$ and coupling function $\Phi(\phi)= \exp[2\phi/\sqrt{3}]$, we investigate the hydrostatic equilibrium structure of neutron stars for the simple potential $V(\phi)= \omega\phi^2/2$ defined in the Einstein frame (EF). From the scalar field in the EF, we also interpret such theories as $f(R)$ gravity in the corresponding Jordan frame (JF). The mass-radius relations, proper mass, and binding energy are obtained for a polytropic equation of state (EoS) in the JF. Our results reveal that the maximum-mass values increase substantially as $\omega$ gets smaller, while the radius and mass decrease in the low-central-density region as we move further away from the pure GR scenario. Furthermore, a cusp is formed when the binding energy is plotted as a function of the proper mass, which indicates the appearance of instability. Specifically, we find that the central-density value where the binding energy is a minimum corresponds precisely to $dM/d\rho_c^J = 0$ on the $M(\rho_c^J)$-curve.Comment: 9 pages, 6 figures. Accepted for publication in Physics of the Dark Univers

Distribution of the potassium concentration in soil with lysimeters cultivated with peanut

A aplicação de fertilizantes na agricultura pode provocar uma dinâmica de solutos no solo abaixo da zona radicular, podendo, além de provocar prejuízos econômicos, contaminar águas subterrâneas. O presente trabalho teve como objetivo acompanhar o processo de deslocamento do íon potássio (K+) em lisímetros preenchidos com solo de textura arenosa e cultivado com amendoim (Arachis hypogaea L.), sob diferentes condições de atenuação da densidade de fluxo radiante, como a utilização de filmes plásticos com diferentes espessuras (100 e 150 micras). O deslocamento do íon potássio (K+) foi monitorado por extratores de solução instalados em diferentes profundidades (15 e 25 cm), e o manejo da fertirrigação foi realizado com a utilização de tensiômetros. Concluiu-se que a baixa radiação solar incidente nos dois ambientes com coberturas plásticas afetou negativamente a produtividade do amendoim; o período em que o amendoim demanda maior quantidade de potássio ocorre dos 30 aos 55 dias após a semeadura; as plantas de amendoim não apresentaram deficiência nutricional com menor lixiviação de K+ para as camadas mais profundas do solo; nos lisímetros com cobertura plástica de 100 e 150 micras, ocorreu maior concentração de K+ na superfície do solo.The application of fertilizers in agriculture produce some solute displacement below the root zone and this situation has provoked great impacts, besides the economic damages, causing groundwater contamination. The present work has as the objective of monitoring the displacement process of the potassium (K+) in lysimeters filled with soil, sandy texture and cultivated with peanuts (Arachis hypogaea L.) under different conditions of reducing solar radiation by using plastic films with different thickness (100 and 150 µ). The potassium displacement was monitored by soil solution extractors installed in different depths (15 and 25 cm) and the fertigation management was accomplished by tensiometers. It was concluded that low incident solar radiation in the two environments with plastic coverings negatively affected peanut's yield; the period that the peanut demands larger amount of potassium happens from 30 to 55 days after sowing; peanut plants did not present nutritional deficiency with a smaller leaching of K+ for the deepest layers of soil; in the lysimeters with plastic covering of 100 and 150 micras occurred a larger concentration of K+ in the soil surface.CNP

A estrutura a termo de taxas de juros no Brasil: modelos, estimação e testes

In this paper, we propose a methodology for the construction of the risk-free interest rate term structure in Brazil, using the Svensson model for interpolation and extrapolation of the interest rate curves, and genetic algorithms, in complement to traditional algorithms of nonlinear optimization, for estimation of model parameters. The objective is to contribute to the Brazilian insurance market, so that insurance ces can appropriately measure their long-term obligations discounting cash flows in a manner that is consistent and coherent, considering the adoption of international standards of solvency supervision and financial reporting by the Superintendência de Seguros Privados (SUSEP). We present the results found in modeling the term structure of a number of interest rate curves in Brazil.Neste artigo, propomos uma metodologia para a construção da estrutura a termo da taxa de juros livre de risco no Brasil, usando o modelo de Svensson para interpolação e extrapolação das curvas de juros e algoritmos genéticos, em complemento aos algoritmos tradicionais de otimização não linear, para a estimação dos parâmetros do modelo. O objetivo é contribuir para que o mercado segurador brasileiro mensure suas obrigações descontando seus fluxos de caixa de maneira consistente e coerente, considerando a adoção, pela Superintendência de Seguros Privados (SU-SEP), de padrões internacionais de supervisão de solvência e de reporte financeiro. Ao longo do artigo, apresentamos os resultados encontrados na modelagem das estruturas a termo de diferentes curvas de juros no Brasil

The Role of Oxidative Stress and Lipid Peroxidation in Ventricular Remodeling Induced by Tobacco Smoke Exposure after Myocardial Infarction

OBJECTIVE: To evaluate the roles of oxidative stress and lipid peroxidation in the ventricular remodeling that is induced by tobacco smoke exposure after myocardial infarction.METHODS: After induced myocardial infarction, rats were allocated into two groups: C (control, n=25) and ETS (exposed to tobacco smoke, n=24). After 6 months, survivors were submitted to echocardiogram and biochemical analyses.RESULTS: Rats in the ETS group showed higher diastolic (C = 1.52 +/- 0.4 mm(2), ETS = 1.95 +/- 0.4 mm(2); p=0.032) and systolic (C = 1.03 +/- 0.3, ETS = 1.36 +/- 0.4 mm(2)/g; p=0.049) ventricular areas, adjusted for body weight. The fractional area change was smaller in the ETS group (C = 30.3 +/- 10.1 %, ETS = 19.2 +/- 11.1 %; p=0.024) and E/A ratios were higher in ETS animals (C = 2.3 +/- 2.2, ETS = 5.1 +/- 2.5; p=0.037). ETS was also associated with a higher water percentage in the lung (C = 4.8 (4.3-4.8), ETS = 5.5 (5.3-5.6); p=0.013) as well as higher cardiac levels of reduced glutathione (C = 20.7 +/- 7.6 nmol/mg of protein, ETS = 40.7 +/- 12.7 nmol/mg of protein; p=0.037) and oxidized glutathione (C = 0.3 +/- 0.1 nmol/g of protein, ETS = 0.9 +/- 0.3 nmol/g of protein; p=0.008). No differences were observed in lipid hydroperoxide levels (C = 0.4 +/- 0.2 nmol/mg of tissue, ETS = 0.1 +/- 0.1 nmol/mg of tissue; p=0.08).CONCLUSION: In animals exposed to tobacco smoke, oxidative stress is associated with the intensification of ventricular re-remodeling after myocardial infarction