R. Besseling, Eric R. Weeks, A. B. Schofield, and W. C. K. Poon,

Using fast confocal microscopy we image the three-dimensional
dynamics of particles in a yielded hard-sphere colloidal
glass under steady shear. The structural relaxation,
observed in regions with uniform shear, is nearly isotropic
but is distinctly different from that of quiescent
metastable colloidal fluids. The inverse relaxation time
(tau_alpha)^(-1) and diffusion constant *D*, as functions
of the *local* shear rate gamma-dot, show marked shear
thinning with (tau_alpha)^(-1) ~ D ~ gamma-dot^0.8 over more
than two decades in gamma-dot. In contrast, the *global*
rheology of the system displays Herschel-Bulkley behavior.
We discuss the possible role of large scale shear localization
and other mechanisms in generating this difference.