Mechanical and microstructural properties of redispersible polymer-gypsum composites

Studies on gypsum modified by polymers have been conducted to assess the potential of improvement in the mechanical performance, water resistance and increasing the setting time, facilitating its handling. Gypsum-based compounds made with different additions of redispersible polymers were studied, such as: ethylene-vinyl acetate (EVA), vinyl acetate terpolymer, vinyl laurate and vinyl chloride (VA/VL/VC), and vinyl acetate and vinyl versatate (VA/VeoVA). The influence on setting time, microstructural formation and on the bending performance was assessed, as well as and compression of the hardened gypsum. The composites were prepared using a polymer concentration of 5% and 10%, and water/gypsum ratio of 0.6. The addition of the polymer decreased the structural robustness and change in the microstructure. We concluded that the reduction in the amount of water through additives may allow a more complete and robust training of gypsum crystals and compounds with better mechanical performance223COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESnão te

Aumento da produção de etanol a partir de melaço de cana-de-açúcar pela adição de benzoato

The effect of the addition of sodium benzoate on alcoholic fermentation of molasses medium with 15% total reducing sugars was studied by using industrial yeast Saccharomyces cerevisiae M-300-A. Sodium benzoate was added at the rate of 7.5 miligram to 0,8 grams of dry yeast during 0, 2, 4 e 6 fermentative cycles. The addition of sodium benzoate resulted in an increase in ethanol production and a reduction of yeast growth and glycerol and n-propylic, isobutylic and isoamylic alcoholic contents. The inhibitor did not reduce cell viability; soon after its removal the yeast returned to grow. This fact suggests the possibility of using the benzoate in distilleries.O efeito da adição de benzoato de sódio sobre a fermentação alcoólica de meio de melaço de cana-de-açúcar com 15% de açúcares redutores totais foi estudado utilizando a levedura industrial Saccharomyces cerevisiae M-300-A. Foram adicionados 7,5 miligramas de benzoato de sódio para 0,8 gramas de levedura seca durante 0, 2, 4 e 6 ciclos fermentativos. Com a adição de benzoato ocorreu aumento na produção de etanol, redução do crescimento da levedura e dos teores de glicerol e dos álcoois n-propílico, isobutílico e isoamílico. O inibidor não provocou redução da viabilidade celular e após a retirada do inibidor a levedura voltou a apresentar crescimento. Este fato sugere a possibilidade do uso do benzoato em destilarias de álcool combustível

Topological Charged Black Holes in High Dimensional Spacetimes and Their Formation from Gravitational Collapse of a Type II Fluid

Topological charged black holes coupled with a cosmological constant in $R^{2}\times X^{D-2}$ spacetimes are studied, where $X^{D-2}$ is an Einstein space of the form ${}^{(D-2)}R_{AB} = k(D-3) h_{AB}$. The global structure for the four-dimensional spacetimes with $k = 0$ is investigated systematically. The most general solutions that represent a Type $II$ fluid in such a high dimensional spacetime are found, and showed that topological charged black holes can be formed from the gravitational collapse of such a fluid. When the spacetime is (asymptotically) self-similar, the collapse always forms black holes for $k = 0, -1$, in contrast to the case $k = 1$, where it can form either balck holes or naked singularities.Comment: 14 figures, to appear in Phys. Rev.

Gold nanowires and the effect of impurities

Metal nanowires and in particular gold nanowires have received a great deal of attention in the past few years. Experiments on gold nanowires have prompted theory and simulation to help answer questions posed by these studies. Here we present results of computer simulations for the formation, evolution and breaking of very thin Au nanowires. We also discuss the influence of contaminants, such as atoms and small molecules, and their effect on the structural and mechanical properties of these nanowires

The role of structural evolution on the quantum conductance behavior of gold nanowires during stretching

Gold nanowires generated by mechanical stretching have been shown to adopt only three kinds of configurations where their atomic arrangements adjust such that either the [100], [111] or [110] zone axes lie parallel to the elongation direction. We have analyzed the relationship between structural rearrangements and electronic transport behavior during the elongation of Au nanowires for each of the three possibilities. We have used two independent experiments to tackle this problem, high resolution transmission high resolution electron microscopy to observe the atomic structure and a mechanically controlled break junction to measure the transport properties. We have estimated the conductance of nanowires using a theoretical method based on the extended H\"uckel theory that takes into account the atom species and their positions. Aided by these calculations, we have consistently connected both sets of experimental results and modeled the evolution process of gold nanowires whose conductance lies within the first and third conductance quanta. We have also presented evidence that carbon acts as a contaminant, lowering the conductance of one-atom-thick wires.Comment: 10 page

Criopreservação de protozoários dos gêneros trichomonas donne, 1837 e tritrichomonas kafoid, 1920

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