Evolution of particle radial positions with respect to time in the case of run SI30-3-2-d. The smallest species drift outwards, while species with sizes τ_s > 10⁻² drift inwards. Compared to the run with continuous size distribution shown in Fig. 27 the spreading of the positions is smaller because of the lack of differential radial drift in these discrete species. Differential radial drift is therefor completely dominant in spreading the size distribution of particles.