Maximum of the distribution function as the time increases. Again the cases of R_A = 10^-4 (upper panel) and R_A = 10^-3 (lower panel) are shown. The black and red lines denote the cases of single injection and continuous particle injection, respectively. The thick lines simply show cubic fits of the actual simulation data. Additionally, the average particle rigidity is shown in the lower panel (dotted line). (This figure is available in color in electronic form.)