title: Dynamics of the breakdown of granular clusters.
abstract: Recently van der Meer et al. studied the breakdown of a granular cluster [Phys. Rev. Lett. 88, 174302 (2002)]. We reexamine this problem using an urn model, which takes into account fluctuations and finite-size effects. General arguments are given for the absence of a continuous transition when the number of urns (compartments) is greater than two. Monte Carlo simulations show that the lifetime of a cluster tau diverges at the limits of stability as tau approximately N(1/3), where N is the number of balls. After the breakdown, depending on the dynamical rules of our urn model, either normal or anomalous diffusion of the cluster takes place.
authors.affiliation: Department of Physics, University of Geneva, CH 1211 Geneva 4, Switzerland.
authors.forename: François
authors.initials: F
authors.lastname: Coppex
authors.forename: Michel
authors.initials: M
authors.lastname: Droz
authors.forename: Adam
authors.initials: A
authors.lastname: Lipowski