STUDIES OF COLUMNS OF BEADS UNDER EXTERNAL VIBRATIONS

As a toy model for dissipative granular materials, we investigate a on e-dimensional column of beads undergoing external vibrations. The anal ysis is both experimental and numerical. We display the cross-over fro m a condensed to a fluidized state of the column; the parameters are t he agitation, the number of beads, and the momentum restitution coeffi cient. We find clustered states for high dissipation and/or a large nu mber of beads. Our experimental findings support the appearance of a f luidized regime at low dissipation and of a Feigenbaum-type bifurcatio n scenario at high dissipation.