Utilização de cerca elétrica para contenção de aves no sistema semi-confinado de produção.

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First-principles investigation of Ag-Cu alloy surfaces in an oxidizing environment

In this paper we investigate by means of first-principles density functional theory calculations the (111) surface of the Ag-Cu alloy under varying conditions of pressure of the surrounding oxygen atmosphere and temperature. This alloy has been recently proposed as a catalyst with improved selectivity for ethylene epoxidation with respect to pure silver, the catalyst commonly used in industrial applications. Here we show that the presence of oxygen leads to copper segregation to the surface. Considering the surface free energy as a function of the surface composition, we construct the convex hull to investigate the stability of various surface structures. By including the dependence of the free surface energy on the oxygen chemical potential, we are able compute the phase diagram of the alloy as a function of temperature, pressure and surface composition. We find that, at temperature and pressure typically used in ethylene epoxidation, a number of structures can be present on the surface of the alloy, including clean Ag(111), thin layers of copper oxide and thick oxide-like structures. These results are consistent with, and help explain, recent experimental results.Comment: 10 pages, 6 figure

Galinheiro móvel com estrutura metálica para criação de frangos em semiconfinamento.

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Influence of the rainfall in the content of nutrients in litter in agroforestry systems managed with burning and without burning in Amazon.

This study evaluated the nutrient content of the litter, testing different treatments with burning and no burning, of the vegetation, to identify which one provides better efficiency in operation and production of nutrients in different seasonal conditions. The study area is located on the property of the family farmer, initially selected by a diagnosis socioeconomic, community Benjamin Constant, in northeastern Para. Litter was collected during two periods: dry season (November) and rainy (March) in 2009. For the collection of litter samples, we used collectors measuring (0.25 × 0.25 m2), which were placed directly on the soil surface. The collected material was stored in paper bags and taken to the laboratory for Chemical Analysis of the Brazilian Agricultural Research Corporation (EMBRAPA), which was determined by analyses of macronutrients (N, P, K, Ca, Mg, Na) and micronutrients (Fe, Cu, Mn, Zn). The highest concentrations of macronutrients were found in N for agroforestry systems with and without burning in two seasons (wet and dry). All macronutrients showed influence of seasonality, which was verified by the wide variation in nutritional behavior. The decreasing concentration of nutrients was presented N > Ca > Mg > Na > K > P in agroforestry system with burning, with maximum values of all nutrients in the rainy season, and N, P, K, Ca, Na in higher concentrations in agroforestry system without burning, and showed only the Mg peak in agroforestry system with burning. The behavior of the concentration of nutrients was opposite to that observed one, for all elements analyzed showed a reduction in the concentrations of nutrients in the dry season. The decreasing concentration of nutrients was presented Fe > Mn > Zn > Cu

Density functional calculations of nanoscale conductance

Density functional calculations for the electronic conductance of single molecules are now common. We examine the methodology from a rigorous point of view, discussing where it can be expected to work, and where it should fail. When molecules are weakly coupled to leads, local and gradient-corrected approximations fail, as the Kohn-Sham levels are misaligned. In the weak bias regime, XC corrections to the current are missed by the standard methodology. For finite bias, a new methodology for performing calculations can be rigorously derived using an extension of time-dependent current density functional theory from the Schroedinger equation to a Master equation.Comment: topical review, 28 pages, updated version with some revision