0 10 20 30 40 50 60 0 2e-06 4e-06 6e-06 Eq.8 MC data 0 0.1 0.2 0.3 0.4 0.5 k$_{c}$R$_{2}$$^{2}$/D$_{1}$ 0 2e-07 4e-07 6e-07 v[R 1 /MC cycle] a) b) Figure 7: Sedimentation velocity for a passive colloid in a concentration gradient of solute, generated by a planar source and absorbed at a planar sink. The dimensionless combination k$_{c}$R 2 $_{2}$/D$_{1}$ measures the solute concentration gradient (note the colloid does not chuck in these simulations; solute is introduced into the simulation box at the source plane with rate k$_{c}$ ). The black circles indicate analytical results from Eq.(8), whereas the red squares are simulation data. (a): the case R$_{1}$/R$_{2}$ = 10 (b): the case R$_{1}$/R$_{2}$ = 100 . 27