  In particle systems subject to a nonuniform drive, particle migration is
observed from the driven to the non--driven region and vice--versa, depending
on details of the hopping dynamics, leading to apparent violations of Fick's
law and of steady--state thermodynamics. We propose and discuss a very basic
model in the framework of independent random walkers on a pair of rings, one of
which features biased hopping rates, in which this phenomenon is observed and
fully explained.
