For hard spheres in shear flow, the function u(r) arises from the solution to the steady-state two-body Smoluchowski convection-diffusion equation or two-body Smoluchowski equation with shear flow.
The function u(r) arises for hard spheres undergoing shear flow; it is derived from the solution to the steady-state two-body Smoluchowski convection-diffusion equation or two-body Smoluchowski equation in the presence of shear flow.