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Power law velocity fluctuations due to inelastic collisions in numerically simulated vibrated bed of powder}
Distribution functions of relative velocities among particles in a vibrated
bed of powder are studied both numerically and theoretically. In the solid
phase where granular particles remain near their local stable states, the
probability distribution is Gaussian. On the other hand, in the fluidized
phase, where the particles can exchange their positions, the distribution
clearly deviates from Gaussian. This is interpreted with two analogies;
aggregation processes and soft-to-hard turbulence transition in thermal
convection. The non-Gaussian distribution is well-approximated by the
t-distribution which is derived theoretically by considering the effect of
clustering by inelastic collisions in the former analogy.Comment: 7 pages, using REVTEX (Figures are inculded in text body)
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Hydrodynamic Description of Granular Convection
We present a hydrodynamic model that captures the essence of granular
dynamics in a vibrating bed. We carry out the linear stability analysis and
uncover the instability mechanism that leads to the appearance of the
convective rolls via a supercritical bifurcation of a bouncing solution. We
also explicitly determine the onset of convection as a function of control
parameters and confirm our picture by numerical simulations of the continuum
equations.Comment: 14 pages, RevTex 11pages + 3 pages figures (Type csh
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