Linear response theory of sedimentation and diffusion in a suspension of spherical particles

We discuss the problem of sedimentation and diffusion in a suspension of interacting spherical particles. We consider external forces acting on the particles and study the linear response of density and current on the basis of the generalized Smoluchowski equation. The theory leads to a natural distinction between a hydrodynamic and a diffusion current. Each of these is defined as an observable in terms of the generalized mobility matrix. We derive general relations for the response functions.