Stellar equilibrium configurations of white dwarfs in the f(R,T)f(R,T) gravity

In this work we investigate the equilibrium configurations of white dwarfs in a modified gravity theory, na\-mely, $f(R,T)$ gravity, for which $R$ and $T$ stand for the Ricci scalar and trace of the energy-momentum tensor, respectively. Considering the functional form $f(R,T)=R+2\lambda T$, with $\lambda$ being a constant, we obtain the hydrostatic equilibrium equation for the theory. Some physical properties of white dwarfs, such as: mass, radius, pressure and energy density, as well as their dependence on the parameter $\lambda$ are derived. More massive and larger white dwarfs are found for negative values of $\lambda$ when it decreases. The equilibrium configurations predict a maximum mass limit for white dwarfs slightly above the Chandrasekhar limit, with larger radii and lower central densities when compared to standard gravity outcomes. The most important effect of $f(R,T)$ theory for massive white dwarfs is the increase of the radius in comparison with GR and also $f(R)$ results. By comparing our results with some observational data of massive white dwarfs we also find a lower limit for $\lambda$, namely, $\lambda >- 3\times 10^{-4}$.Comment: To be published in EPJ

Anticarsia gemmatalis Hübner, 1818 (Lepidoptera: Noctuidae) biologia, amostragem e métodos de controle.

A lagarta da soja, Anticarsia gemmatalis Hübner, 1818 (Lepidoptera: Noctuidae) é a principal desfolhadora da soja no Brasil, sendo encontrada em todos os locais de produção, representando um risco à produção e à qualidade dos cultivos brasileiros (GAZZONI e YORINIORI, 1995; MOSCARDI e SOUZA, 2002). Este inseto causa grandes danos à lavoura de soja, que vão desde o desfolhamento até a destruição completa da planta. A lagarta da soja é um inseto mastigador e se alimenta de folhas jovens. Quando a folhagem é removida, ataca outras partes da planta, como pecíolos e a haste. O desfolhamento compromete o enchimento das vagens, devido à diminuição da área foliar responsável pela fotossíntese, com conseqüente redução da produção de grãos. Quando se alimentam, além de remover os tecidos vegetais, que contem nutrientes, as lagartas injetam toxinas nas plantas (SILVA et al., 2002). Existem, também, outras culturas em que a lagarta da soja causa prejuízos como cultura da alfafa, do amendoim, do arroz, da ervilha, do feijão, do feijão-vagem e do trigo, atacando durante a fase vegetativa e, em alguns casos, até no período da floração (PRATISSOLI, 2002). A lagarta da soja costuma atacar as lavouras nas regiões setentrionais e a partir de janeiro no extremo sul do País e chega a ocasionar 100% de destruição foliar (HOFFMANN et al., 1979; GAZZONI e YORINIORI, 1995), sendo, portanto, de grande importância conhecer o comportamento desta praga e os métodos utilizados para o seu controle.bitstream/CENARGEN/27983/1/doc196.pd

Nematic liquid crystal dynamics under applied electric fields

In this paper we investigate the dynamics of liquid crystal textures in a two-dimensional nematic under applied electric fields, using numerical simulations performed using a publicly available LIquid CRystal Algorithm (LICRA) developed by the authors. We consider both positive and negative dielectric anisotropies and two different possibilities for the orientation of the electric field (parallel and perpendicular to the two-dimensional lattice). We determine the effect of an applied electric field pulse on the evolution of the characteristic length scale and other properties of the liquid crystal texture network. In particular, we show that different types of defects are produced after the electric field is switched on, depending on the orientation of the electric field and the sign of the dielectric anisotropy.Comment: 7 pages, 12 figure

Electrostatic self-force in (2+1)-dimensional cosmological gravity

Point sources in (2+1)-dimensional gravity are conical singularities that modify the global curvature of the space giving rise to self-interaction effects on classical fields. In this work we study the electrostatic self-interaction of a point charge in the presence of point masses in (2+1)-dimensional gravity with a cosmological constant.Comment: 9 pages, Late