Evolution of the radial concentration of the particle layer for our 2D models that trigger strong concentration of solids. Three cases of different dimensionless stopping time τ_s, solid abundance Z, and model resolution are presented. The colors show the column density of the particles Σ_p as a function of radial position x and time t, where Σ_p, x, and t are normalized by the initial gas column density Σ_g,0, the vertical scale height of the gas H, and the local orbital period P, respectively. In each case, the left and right panels are from models with a computational domain of 0.2H× 0.2H and 0.4H× 0.4H, respectively. The timespan for case (c) is 2.5 times that for cases (a) and (b).