Structure factor, S(k), for a cyclically-sheared suspension of particles that are sedimenting under gravity. At high sedimentation speed (left image), nothing remarkable occurs. At low sedimentation speed (right image), density fluctuations vanish at long lengthscales.

Suspensions appear in a wide range of industrial settings, and dispersing particles in a uniform manner throughout a fluid is an important challenge. We studied how shear can be used to control the spatial distribution of particles that are settling under gravity in a viscous liquid. We discovered that at sufficiently low sedimentation speeds, extremely homogeneous mixtures are automatically obtained, without any fine tuning of the driving. See the paper here.