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Abstract: An effective computer generation method is presented in this paper to more perfectly and rapidly generate the random distribution domains with large numbers of grains (pores). At first, the geometries of heterogeneous grains and the stationary random distribution model with large numbers of grains are defined. Second, the effective computer generation method, including compactness algorithm and selection algorithm, is described in detail. Then the effectiveness of the generation method and the comparison with the take-and-place method are given, and some examples with different geometries of grains in 2- and 3-dimension cases are illustrated. The computer generation method in this paper has been applied to the computation of effective heat transfer behavior for the composites of the random distribution with large numbers of grains, and some numerical results are demonstrated. The generation method in this paper is able to make the generated samples hold better stochastic property, and it is also suitable to generating samples subjected to non-uniform probability model. [Copyright &y& Elsevier]

Grain-boundary (GB) structure and properties are usually analyzed in terms of ground-state (minimum-energy) GB states. However, global equilibrium is rarely achieved in materials. In this paper, we investigate the nature of GB metastability and its impact on material properties. Higher-energy GB states can be the result of nonequilibrium processes or simply thermal excitations. While the existence of limited GB metastability is widely known for a few simple GBs, we demonstrate that the multiplicity of metastable GB states is, in general, very large. This conclusion is based upon extensive atomistic bicrystal simulations for both symmetric tilt GBs and twist GBs in three very different materials. The energies of these GB states are densely distributed so that the dependence of the GB energy on misorientation is better described as an energy band rather than as a single curve as in the traditional picture. Based upon the distribution of metastable GB states, we introduce a GB statistical-mechanics picture and apply it to predict finite-temperature equilibrium and nonequilibrium properties. When GB multiplicity exists, GB structures can be thought of as domains of different GB states separated by various classes of line defects. The existence of a large set of metastable GB states, very close in energy, suggests an analogy between the behaviors of GBs and glasses and implies the potential for GB engineering. [ABSTRACT FROM AUTHOR]

Indigenous leafy vegetables can play an important part in alleviating hunger and malnutrition in sub-Saharan Africa, but they are often neglected in research. They are important sources of micronutrients including vitamins A and C, iron and other nutrients and are sometimes better nutritional sources than the modern vegetables. The leaves of cultivated plants, such as pumpkins, melons and cowpeas are used as a leafy vegetable, as well as leaves from wild and weedy species from farmers' fields and the veld. These wild and weedy species include amaranth species, Corchorus species and Cleome gynandra amongst others, and all have the potential to be cultivated. The harvested leafy vegetables are perishable, but can be processed and preserved by partial cooking, blanching or drying. This paper provides ecogeographical information and some botanical descriptions; we discuss the importance of leafy vegetables in food security, the monetary value of some of these crops and report on some of the research carried out at ARC-Roodeplaat (Pretoria), South Africa. [ABSTRACT FROM AUTHOR]