  Experiments on spherical particles in a 3D Couette cell vibrated from below
and sheared from above show a hysteretic freezing/melting transition. Under
sufficient vibration a crystallized state is observed, which can be melted by
sufficient shear. The critical line for this transition coincides with equal
kinetic energies for vibration and shear. The force distribution is
double-peaked in the crystalline state and single-peaked with an approximately
exponential tail in the disordered state. A linear relation between pressure
and volume ($dP/dV > 0$) exists for a continuum of partially and/or
intermittently melted states over a range of parameters.
