Modeling the line variations from the wind-wind shock emissions of WR 30a

The study of Wolf-Rayet stars plays an important role in evolutionary theories of massive stars. Among these objects, ~ 20% are known to be in binary systems and can therefore be used for the mass determination of these stars. Most of these systems are not spatially resolved and spectral lines can be used to constrain the orbital parameters. However, part of the emission may originate in the interaction zone between the stellar winds, modifying the line profiles and thus challenging us to use different models to interpret them. In this work, we analyzed the HeII4686\AA + CIV4658\AA blended lines of WR30a (WO4+O5) assuming that part of the emission originate in the wind-wind interaction zone. In fact, this line presents a quiescent base profile, attributed to the WO wind, and a superposed excess, which varies with the orbital phase along the 4.6 day period. Under these assumptions, we were able to fit the excess spectral line profile and central velocity for all phases, except for the longest wavelengths, where a spectral line with constant velocity seems to be present. The fit parameters provide the eccentricity and inclination of the binary orbit, from which it is possible to constrain the stellar masses.Comment: accepted for publication in the MNRA

Comparação entre características agronômicas, culinárias e nutricionais em variedades de arroz branco e vermelho.

O arroz vermelho é cultivado por pequenos agricultores do Brasil, principalmente nos estados da Paraíba, Rio Grande do Norte e Pernambuco, em função de suas características diferenciadas em relação ao arroz branco, como sabor, textura e suposto valor nutricional. As variedades atualmente em uso foram selecionadas pelos próprios agricultores e, em geral, apresentam arquitetura de planta tradicional e baixa produtividade de grãos. O trabalho teve como objetivo comparar as principais características agronômicas, culinárias e nutricionais entre variedades de arroz branco e de arroz vermelho. A pesquisa de campo foi realizada na Embrapa Meio-Norte, em Teresina, no Piauí, e as análises de laboratório, na Embrapa Arroz e Feijão, em Santo Antônio de Goiás, no estado de Goiás. Foram avaliadas onze variedades de arroz branco e quatro de arroz vermelho, com ênfase em produtividade de grãos, teor de amilose, tempo de cocção e concentrações de ferro e zinco nas formas de consumo do arroz polido e integral. As variedades de arroz branco foram mais produtivas, apresentaram maiores teores de amilose e demandaram menos tempo para cozimento do que as variedades de arroz vermelho, todavia o arroz vermelho sobressaiu, na forma de grão polido, quanto aos teores dos micronutrientes ferro e zinco

Tailoring the thermal Casimir force with graphene

The Casimir interaction is omnipresent source of forces at small separations between bodies, which is difficult to change by varying external conditions. Here we show that graphene interacting with a metal can have the best known force contrast to the temperature and the Fermi level variations. In the distance range 50–300 nm the force is measurable and can vary a few times for graphene with a bandgap much larger than the temperature. In this distance range the main part of the force is due to the thermal fluctuations. We discuss also graphene on a dielectric membrane as a technologically robust configuration

Magneto-optical evidence of double exchange in a percolating lattice

Substituting $Eu$ by $Ca$ in ferromagnetic $EuB_6$ leads to a percolation limited magnetic ordering. We present and discuss magneto-optical data of the $Eu_{1-x}Ca_{x}B_6$ series, based on measurements of the reflectivity $R(\omega)$ from the far infrared up to the ultraviolet, as a function of temperature and magnetic field. Via the Kramers-Kronig transformation of $R(\omega)$ we extract the complete absorption spectra of samples with different values of $x$. The change of the spectral weight in the Drude component by increasing the magnetic field agrees with a scenario based on the double exchange model, and suggests a crossover from a ferromagnetic metal to a ferromagnetic Anderson insulator upon increasing $Ca$-content at low temperatures.Comment: 10 pages, 3 figure