  A gas of noninteracting particles diffuses in a lattice of pulsating
scatterers. In the finite horizon case with bounded distance between collisions
and strongly chaotic dynamics, the velocity growth (Fermi acceleration) is well
described by a master equation, leading to an asymptotic universal
non-Maxwellian velocity distribution scaling as v ~ t. The infinite horizon
case has intermittent dynamics which enhances the acceleration, leading to v ~
t ln t and a non-universal distribution.
