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

Ocorrência do besouro tigre Neotropical, Cylindera suturalis helvaea (W. Horn, 1903) (Coleoptera, Cicindelidae), em bancos de areia do Reservatório da Barragem da Pedra, Rio de Contas, Bahia, Brasil

The occurrence of the tiger beetle Cylindera (Plectographa) suturalis helvaea (W. Horn, 1903) in sandbanks of Reservoir Barragem da Pedra, Bahia, Brazil, is registered. Adult beetles were collected using entomological nets on sandbanks between May and September 2003. Cicindelids are one of the most conspicuous groups among invertebrates. That is why thay are well suited for bioindication of biodiversity as well as of disturbance and modification in terrestrial ecosystems.Neste estudo é registrada a ocorrência do besouro tigre Cylindera (Plectographa) suturalis helvaea (W. Horn, 1903) em bancos de areia no Reservatório da Barragem da Pedra, Bahia, Brasil. Indivíduos adultos foram coletados utilizando-se de redes entomológicas, entre os meses de Maio e Setembro de 2003. Cicindelídeos são um dos mais conspícuos grupos de invertebrados, sendo considerados como bons indicadores de biodiversidade assim como de distúrbios e modificações nos ecossistemas terrestres

The double traveling salesman problem with partial last-in-first-out loading constraints

In this paper, we introduce the double traveling salesman problem with partial last-in-first-out loading constraints (DTSPPL). It is a pickup-and-delivery single-vehicle routing problem, where all pickup operations must be performed before any delivery operation because the pickup-and-delivery areas are geographically separated. The vehicle collects items in the pickup area and loads them into its container, a horizontal stack. After performing all pickup operations, the vehicle begins delivering the items in the delivery area. Loading and unloading operations must obey a partial last-in-first-out (LIFO) policy, that is, a version of the LIFO policy that may be violated within a given reloading depth. The objective of the DTSPPL is to minimize the total cost, which involves the total distance traveled by the vehicle and the number of items that are unloaded and then reloaded due to violations of the standard LIFO policy. We formally describe the DTSPPL through two integer linear programming (ILP) formulations and propose a heuristic algorithm based on the biased random-key genetic algorithm (BRKGA) to find high-quality solutions. The performance of the proposed solution approaches is assessed over a broad set of instances. Computational results have shown that both ILP formulations have been able to solve only the smaller instances, whereas the BRKGA obtained good-quality solutions for almost all instances, requiring short computational times

Efeitos da leucena e da adubação NPK sobre a cultura do feijão no cerrado.

An experiment was carried out in a poor cerrado soil at Patrocinio, state of Minas Gerais, in order to determine the effect of Leucaena leucocphala, as a green manure, and chemical fertilization on the yield of beans (Phaseolus vulgaris). Treatments included leucena plus a 2 x 2 x 2 factorial, as levels of 0 and 40kg/ha of N (as ammonium sulfate), 0 and 70kg/ha of P2O5 (as ordinary super-phosphate), and 0 and 60 kg/ha of K2O (as potassium chloride). Additional treatments were 0-0-0 and 40-70-60- kg/ha of N-P2O5-k2O, both without the green manure. The leucena and the NPK fertilization had the same effect, increasing the bean yield from 83 to 350 kg/ha. With leucena, the superphosphate had the greatest effect, followed by the nitrogenous fertilizer. The complete chemical fertilization associated with the green manuring resulted in the hihest yield of 900 kg/ha