Distribution functions for the same cases as in Fig. 3. The only difference is the diffusion coefficient. It is the same as in Fig. 3 up to the momentum 0.1p_max and independent of p for higher momenta. Above 0.1p_max, the slopes s for the solid blue and red lines are 2.33 and 2.16, respectively. We note that all the lines will be straight horizontal up to p_max in the case of a uniform flow speed u₂(x) = const.