On the stiffness of the sand pile profile

The existence of a critical gradient is an important feature of many transport models. [M. Kotschenreuther er nl., Phys, Plasmas 2, 2381 (1995)], However, fundamental differences exist in the dynamics near marginal stability, depending on whether the transport phenomena are controlled by strict (linear) marginal stability or by a self-organized criticality. One of the most striking differences is in the stiffness of the profiles, In this paper, a sand pile model is used to gain some basic understanding of the stiffness of the profile under different dynamics. (C) 1998 American Institute of Physics.