Studies of columns of beads under external vibrations

As a toy model for dissipative granular materials, we investigate a one-dimensional column of beads undergoing external vibrations. The analysis is both experimental and numerical. We display the crossover from a condensed to a fluidized state of the column; the parameters are the agitation, the number of beads, and the momentum restitution coefficient. We find clustered states for high dissipation and/or a large number of beads. Our experimental findings support the appearance of a fluidized regime at low dissipation and of a Feigenbaum-type bifurcation scenario at high dissipation.