ABSTRACT
We have performed a systematic, large-scale simulation study of granular media in two and three dimensions, investigating the rheology of cohesionless granular particles in inclined plane geometries, i.e., chute flows. We find that over a wide range of parameter space of interaction coefficients and inclination angles, a steady-state flow regime exists in which the energy input from gravity balances that dissipated from friction and inelastic collisions. In this regime, the bulk packing fraction (away from the top free surface and the bottom plate boundary) remains constant as a function of depth z, of the pile. The velocity profile in the direction of flow vx(z) scales with height of the pile H, according to vx(z) proportional to H(alpha), with alpha=1.52+/-0.05. However, the behavior of the normal stresses indicates that existing simple theories of granular flow do not capture all of the features evidenced in the simulations.
ABSTRACT
We report detailed nucleation studies on the liquid-to-solid transition of hexadecane using nearly monodisperse hexadecane-in-water emulsions. A careful consideration of the kinetics of isothermal and nonisothermal freezing shows deviations from predictions of classical nucleation theory, if one assumes that the emulsion droplet population is homogeneous. Similar deviations have been observed previously (3). As an explanation, we propose an argument based on the dynamic generation of droplet heterogeneity mediated by mobile impurities. This proposal is in good agreement with existing data.
ABSTRACT
We measure the increase in the maximum stable angle of a sandpile, theta(c), with the volume fraction, phi of a liquid added to cause cohesion between the grains. For two different liquids, tan theta(c) does not apparently scale with the air-liquid surface tension at low phi, whereas it does at higher phi. This suggests that the liquid forms menisci at asperities on the surfaces of the grains before filling cohesive menisci at intergrain contact points. In this cohesive limit, theta(c)(phi) agrees with a surface roughness theory. Electron and fluorescence microscopy of the dry and wet surfaces of the grains support this model.
