  Experimental measurements of the response of a two dimensional system of
plastic beads subjected to steady shear are reported. The beads float at the
surface of a fluid substrate and are subjected to a slow, steady-shear in a
Couette geometry. The flow consists of irregular intervals of solid-like,
jammed behavior, followed by stress relaxations. We report on statistics that
characterize the stress fluctuations as a function of several parameters
including shear-rate and packing density. Over a range of densities between the
onset of flow to the onset of buckling (overpacking) of the system, the
probability distribution for stress fluctuations is essentially independent of
the packing density, particle dispersity, and interaction potential (varied by
changing the substrate). Finally, we compare the observed stress fluctuations
with those observed in other complex fluids.
