  We investigate the role of gravity on convection in a dense granular shear
flow. Using a microgravity modified Taylor-Couette shear cell under the
conditions of parabolic flight microgravity, we demonstrate experimentally that
secondary, convective-like flows in a sheared granular material are close to
zero in microgravity and enhanced under high-gravity conditions, though the
primary flow fields are unaffected by gravity. We suggest that gravity tunes
the frictional particle-particle and particle-wall interactions, which have
been proposed to drive the secondary flow. In addition, the degree of plastic
deformation increases with increasing gravitational forces, supporting the
notion that friction is the ultimate cause.
