Sedimentation, Péclet number, and hydrodynamic screening.

The sedimentation of hard spheres in a Newtonian solvent is studied as a function of Péclet number in the low-concentration limit. Two functional forms for the sedimentation velocity as a function of particle concentration are realized in the limit of high and low Péclet numbers. We argue that a more ordered phase occurs for large Péclet numbers. Measurements of settling in sheared suspensions support these contentions. Recent explanations of sedimentation in suspensions are examined in light of these results.