Luís A. Nunes Amaral

We investigate sandpile models where the updating of unstable columns is done according to a stochastic rule. We examine the effect of introducing nonlocal relaxation mechanisms. We find that the models self-organize into critical states that belong to three different universality classes. The models with local relaxation rules belong to a known universality class that is characterized by an avalanche exponent tau approximate to 1.55, whereas the models with nonlocal relaxation rules belong to new universality classes characterized by exponents tau approximate to 1.35 and tau approximate to 1.63. We discuss the values of the exponents in terms of scaling relations and a mapping of the sandpile models to interface models.