Measuring stellar differential rotation with high-precision space-borne photometry

We introduce a method of measuring a lower limit to the amplitude of surface differential rotation from high-precision, evenly sampled photometric time series. It is applied to main-sequence late-type stars whose optical flux modulation is dominated by starspots. An autocorrelation of the time series was used to select stars that allow an accurate determination of starspot rotation periods. A simple two-spot model was applied together with a Bayesian information criterion to preliminarily select intervals of the time series showing evidence of differential rotation with starspots of almost constant area. Finally, the significance of the differential rotation detection and a measurement of its amplitude and uncertainty were obtained by an a posteriori Bayesian analysis based on a Monte Carlo Markov Chain approach. We applied our method to the Sun and eight other stars for which previous spot modelling had been performed to compare our results with previous ones. We find that autocorrelation is a simple method for selecting stars with a coherent rotational signal that is a prerequisite for successfully measuring differential rotation through spot modelling. For a proper Monte Carlo Markov Chain analysis, it is necessary to take the strong correlations among different parameters that exist in spot modelling into account. For the planet-hosting star Kepler-30, we derive a lower limit to the relative amplitude of the differential rotation of \Delta P / P = 0.0523 \pm 0.0016. We confirm that the Sun as a star in the optical passband is not suitable for measuring differential rotation owing to the rapid evolution of its photospheric active regions. In general, our method performs well in comparison to more sophisticated and time-consuming approaches.Comment: Accepted to Astronomy and Astrophysics, 15 pages, 13 figures, 4 tables and an Appendi

High coercivity induced by mechanical milling in cobalt ferrite powders

In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe2O4 treated by mechanical milling with different grinding balls. The cobalt ferrite nanoparticles were prepared using a simple hydrothermal method and annealed at 500oC. The non-milled sample presented coercivity of about 1.9 kOe, saturation magnetization of 69.5 emu/g, and a remanence ratio of 0.42. After milling, two samples attained coercivity of 4.2 and 4.1 kOe, and saturation magnetization of 67.0 and 71.4 emu/g respectively. The remanence ratio MR/MS for these samples increase to 0.49 and 0.51, respectively. To investigate the influence of the microstructure on the magnetic behavior of these samples, we used X-ray powder diffraction (XPD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The XPD analysis by the Williamson-Hall plot was used to estimate the average crystallite size and strain induced by mechanical milling in the samples

Sanitary analysis of asymptomatic and damaged grains of maize in Tocantins, Brazil.

In the climatic conditions of the state of Tocantins, fungi have been considered limiting factors to the production of maize (Zea mays), since they favor the pathogens development in all plant parts at different stages, including during the ripening and post-harvest of maize grains. The aim of this study was to identify and quantify the fungi present in asymptomatic and damaged grains of 11 maize cultivars. For sanitary analysis, the filter paper method (Blotter test) was used. In the study, 12 maize-grain-associated genres were found: Fusarium, Aspergillus, Penicillium, Cladosporium, Trichoderma, Bipolaris, Phoma, Curvularia, Rizhopus, Colletotrichum, Papularia, and Nigrospora. There was a little variation in the diversity of genres found in damaged and asymptomatic grains, taking into account the growing seasons. The highest incidence was observed of the Fusarium genus, followed by Cladosporium, Aspergillus and Penicillium, respectively, which were associated with all the evaluated cultivars grains. The cultivars showed low percentage of damaged grains in the evaluated conditions

Espermatogênese de tambaqui (Colossoma macropomum) criado em cativeiro.

No Amazonas, o constante aumento da pressão da pesca extrativista sobre os estoques de populações naturais de peixe, associado ao aumento da demanda pelo pescado, vêm contribuindo para a propagação da piscicultura no Estado. Neste cenário destaca-se o tambaqui, representando o melhor candidato nativo para a piscicultura intensiva na Amazônia e em outras áreas do Brasil. Devido a crescente relevância desta espécie na aqüicultura da região Norte e nacional, o presente trabalho propõe-se a detalhar o processo espermatogênico de tambaquis criados em cativeiro, através de estudos histológicos e de estimativas dos níveis plasmáticos de esteróides sexuais

Análise sensorial de cafés de lavouras em conversão para o sistema de produção orgânico.

Com o objetivo de se verificar o efeito do manejo orgânico sobre a qualidade do café, bem como compará-lo com lavouras submetidas ao manejo convencional foi montado esse experimento no município de Lavras, MG. O experimento foi implantado em lavoura cafeeira anteriormente cultivada sob o sistema convencional, cultivar Catuaí Amarelo, espaçamento de 4,0 x 0,6 m, com 6 anos de idade. Para os tratamentos orgânicos, empregou-se o delineamento látice balanceado 4 x 4 com 5 repetições em esquema fatorial 3 x 2 x 2 além de 4 tratamentos adicionais. O fatorial constou da utilização de 3 fontes de matéria orgânica (Farelo de mamona, cama de frango e esterco bovino), com ou sem aplicação de casca de café e de adubação verde. Para efeito de comparação também havia no mesmo talhão uma lavoura submetida ao manejo convencional. De acordo com os resultados obtidos verificou-se que no 1º ano de conversão, de modo geral, não foram observadas diferenças entre os tratamentos orgânicos e nem entre os tratamentos orgânicos comparados com a testemunha em relação a qualidade do café; já no 2º ano, observou-se superioridade em termos qualitativos de alguns tratamentos orgânicos em relação à lavoura submetida ao manejo convencional; verificou-se efeito positivo do esterco bovino e da adubação verde na qualidade do café