Evolution of the grain-size distribution in the core center for different values of the parameters v_g and c_d, as labeled in the panels. The different color curves correspond to different amounts of time the simulation was run for in terms of the cloud lifetime τ_cl (see Eq. (15)). Here τ_cl = 2.6 × 10⁵ years. In each case the initial distribution is an MRN distribution from 5 to 250 nm, which is shown as the black dashed line.