Thin accretion disc with a corona in a central magnetic field

We study the steady-state structure of an accretion disc with a corona surrounding a central, rotating, magnetized star. We assume that the magneto-rotational instability is the dominant mechanism of angular momentum transport inside the disc and is responsible for producing magnetic tubes above the disc. In our model, a fraction of the dissipated energy inside the disc is transported to the corona via these magnetic tubes. This energy exchange from the disc to the corona which depends on the disc physical properties is modified because of the magnetic interaction between the stellar magnetic field and the accretion disc. According to our fully analytical solutions for such a system, the existence of a corona not only increases the surface density but reduces the temperature of the accretion disc. Also, the presence of a corona enhances the ratio of gas pressure to the total pressure. Our solutions show that when the strength of the magnetic field of the central neutron star is large or the star is rotating fast enough, profiles of the physical variables of the disc significantly modify due to the existence of a corona.Comment: Accepted for publication in Astrophysics & Space Scienc

Desempenho e qualidade dos ovos de poedeiras semipesadas alimentadas com dietas contendo óleos de soja e canola Performance and eggs quality in laying hens fed diets with soybean and canola oils

Objetivou-se analisar a influência da adição de níveis crescentes de óleo de soja e canola sobre os índices de desempenho e qualidade interna e externa dos ovos de poedeiras comerciais semipesadas da linhagem Bovans Goldline durante cinco períodos de 28 dias. Foram utilizadas 280 aves com 18 semanas de idade, em um delineamento inteiramente casualizado, com sete tratamentos em um esquema fatorial 2 × 3 + 1 (dois tipos de óleo e três níveis de óleo mais um testemunha adicional) com cinco repetições e oito aves por unidade experimental. Os níveis de óleo de soja e de canola não alteraram o consumo de ração, os pesos dos ovos, de albúmen, de gema e de casca, as porcentagens de albúmen, de gema e de casca e a gravidade específica dos ovos. Houve influência significativa da interação tipo × nível de óleo sobre a produção de ovos e a conversão por massa e por dúzia de ovos. Com o aumento do nível de óleo de soja, os resultados obtidos para estas variáveis melhoraram, entretanto, a conversão por massa de ovo piorou com o aumento dos níveis de óleo de canola. A adição de óleo de soja promoveu desempenho melhor que o obtido com óleo de canola.<br>The objective of this study was to evaluate the influence of soybean and canola oil added in crescent levels on production performance indexes and internal and external egg quality of brown commercial layers of the strain Bovans Goldline during five periods of 28 days. Two hundred and eighty hens with 18 weeks old were distributed in a completely randomized design, with seven diets in a 2 × 3 + 1 factorial arrangement (oil type and oil level, and an additional control), with 5 replicates of 8 hens per experimental unit. The soybean and canola oil levels did not affect the feed consumption; egg, albumen, yolk and shell weights; albumen, yolk and shell percentages, neither the specific gravity. There was an interaction between type and oils levels on egg production and mass conversion and per egg dozen. Better results for those characteristics were obtained as soybean oil increased. However, the egg mass conversion was negatively influenced by increase of canola oil. The addition of soybean oil promoted better performance as compared to canola oil