Self-organized criticality in a rice-pile model

We present a model for relaxations in piles of granular material. The relaxations are determined by a stochastic rule which models the effect of friction between the grains. We find power-law distributions for avalanche sizes and lifetimes characterized by the exponents [Formula Presented] and [Formula Presented], respectively. For the discharge events, we find a characteristic size that scales with the system size as [Formula Presented], with [Formula Presented]. We also find that the frequency of the discharge events decreases with the system size as [Formula Presented] with [Formula Presented].