  A diffusion-deposition model for glassy dynamics in compacting granular
systems is treated by time scaling and by a method that provides the exact
asymptotic (long time) behavior. The results include Vogel-Fulcher dependence
of rates on density, inverse logarithmic time decay of densities, exponential
distribution of decay times and broadening of noise spectrum. These are all in
broad agreement with experiments. The main characteristics result from a
marginal rescaling in time of the control parameter (density); this is argued
to be generic for glassy systems.
