Jamming transition in a two-dimensional open granular pile with rolling resistance

We present a molecular dynamics study of the jamming/unjamming transition in two-dimensional granular piles with open boundaries. The grains are modeled by viscoelastic forces, Coulomb friction and resistance to rolling. Two models for the rolling resistance interaction were assessed: one considers a constant rolling friction coefficient, and the other one a strain dependent coefficient. The piles are grown on a finite size substrate and subsequently discharged through an orifice opened at the center of the substrate. Varying the orifice width and taking the final height of the pile after the discharge as the order parameter, one can devise a transition from a jammed regime (when the grain flux is always clogged by an arch) to a catastrophic regime, in which the pile is completely destroyed by an avalanche as large as the system size. A finite size analysis shows that there is a finite orifice width associated with the threshold for the unjamming transition, no matter the model used for the microscopic interactions. As expected, the value of this threshold width increases when rolling resistance is considered, and it depends on the model used for the rolling friction.Comment: 9 pages, 6 figure

Analysis of the velocity field of granular hopper flow

We report the analysis of radial characteristics of the flow of granular material through a conical hopper. The discharge is simulated for various orifice sizes and hopper opening angles. Velocity profiles are measured along two radial lines from the hopper cone vertex: along the main axis of the cone and along its wall. An approximate power law dependence on the distance from the orifice is observed for both profiles, although differences between them can be noted. In order to quantify these differences, we propose a Local Mass Flow index that is a promising tool in the direction of a more reliable classification of the flow regimes in hoppers

O impacto da emigração recente no número de nados-vivos em Portugal

A recente crise económica observada em Portugal não foi exclusiva do país e registou repercussões massivas a nível internacional. Desde 2008, em Portugal, registaram-se os mais variados cortes no investimento e despesa pública, resultando num grande aumento da taxa de desemprego. Realizaram-se algumas tentativas de minoração dos efeitos da crise económica com a institucionalização de medidas de austeridade como o Programa de Estabilidade e Crescimento (PEC), mas estas não evitaram a intervenção do Fundo Monetário Internacional (FMI), trazendo a Troika a Portugal (Alves, 2015; Ribeiro et al., 2015). Durante o seu período em Portugal (2011 – 2014), o país não conseguiu manter a capacidade para atrair novos residentes ou até de fazer regressar aqueles que tinham há muito saído em busca de melhores condições de vida, voltando a ser um país com forte emigração à semelhança do já observado no passado. Apesar desta emigração se dividir entre temporária e permanente, a verdade é que, muito provavelmente, alguns daqueles que pensaram sair do país apenas temporariamente, poderão passar a emigrantes permanentes

New liquid supports in the development of integrated platforms for the reuse of oxidative enzymes and polydopamine production

Polydopamine (PDA), a bioinspired polymer from mussel adhesive proteins, has attracted impressive attention as a novel coating for (nano) materials with an adequate conformal layer and adjustable thickness. Currently, PDA is obtained from dopamine chemical oxidation under alkaline conditions, limiting its use in materials sensible to alkaline environments. Envisaging a widespread use of PDA, the polymerization of dopamine by enzymatic catalysis allows the dopamine polymerization in a large range of pHs, overcoming thus the limitations of conventional chemical oxidation. Moreover, the conventional method of polymerization is a time-consuming process and produces PDA films with poor stability, which restricts its applications. On the other hand, the main bottleneck of enzyme-based biocatalytic processes is the high cost of the single use of the enzyme. In this work, laccase was used to catalyse dopamine polymerization. To improve its performance, a liquid support for integrating the laccase and its reuse together with the PDA production and recovery was developed using aqueous biphasic systems (ABS). Firstly, dopamine polymerization by laccase was optimized in terms of pH, temperature and initial dopamine concentration. It was demonstrated that the highest enzymatic polymerization of dopamine was achieved at pH 5.5, 30°C and 2 mg ml−1 of dopamine. Then, ABS composed of polymers, salts and ionic liquids were evaluated to optimize the laccase confinement in one phase while PDA is recovered in the opposite phase. The most promising ABS allowing the separation of laccase from the reaction product is composed of polypropylene glycol (400 g mol−1) and K2HPO4. The polymerization of dopamine in ABS leads to a remarkable improvement of polymerization of 3.9-fold in comparison to the conventional chemical PDA polymerization. The phase containing the confined laccase was reused for four consecutive reaction cycles, with a relative polymerization of 68.9% in the last cycle. The results of this work proved that ABS are a promising approach to create a liquid support for enzyme reuse allowing the process intensification efforts. The use of biocatalysts in ABS emerges as sustainable and alternative platforms from environmental and techno-economic points of view.publishe

Ocorrência do míldio da videira em diferentes épocas de podas em Petrolina - PE.

Suplemento. Edição dos Resumos do 44 Congresso Brasileiro de Fitopatologia, Bento Gonçalves, ago. 2011

Diversidade genética em populações de Sclerotinia sclerotiorum na cultura de feijoeiro (Phaseolus vulgaris L.).

Este trabalho teve como objetivo determinar a estrutura genética de três populações de campo de S. sclerotiorum obtidas nos Estados de Goiás, Minas Gerais e Mato Grosso

Three-vortex configurations in trapped Bose-Einstein condensates

We report on the creation of three-vortex clusters in a $^{87}Rb$ Bose-Einstein condensate by oscillatory excitation of the condensate. This procedure can create vortices of both circulation, so that we are able to create several types of vortex clusters using the same mechanism. The three-vortex configurations are dominated by two types, namely, an equilateral-triangle arrangement and a linear arrangement. We interpret these most stable configurations respectively as three vortices with the same circulation, and as a vortex-antivortex-vortex cluster. The linear configurations are very likely the first experimental signatures of predicted stationary vortex clusters.Comment: 4 pages, 4 figure

Contribuição da pesquisa de melhoramento genético para elevação da produtividade da lavoura arrozeira do Rio Grande do Sul.

Este trabalho visa quantificar a contribuição dos programas de melhoramento genético de arroz irrigado do IRGA e da Embrapa para o caráter rendimento de grãos no período de 1983 (safra 1982/83) a 2011 (safra 2010/11)