Δc/c_core distribution function for sample clusters with their Δa/a_core distribution. The color shade of the solid circles indicates the logarithmic ages (years) of the sample clusters. The size of the symbol is proportional to the number of sample cluster members. The magenta pentagram represents the cluster UBC14, and the cluster UPK88 is marked in the cyan pentagram. The dashed lines in the picture are the grid lines for the radial stratification distribution of sample clusters. Histograms of Δc/c_core and Δa/a_core of the sample clusters are displayed at the right side and top of the picture, respectively. The red curve lines over the histograms are Gaussian fitting lines.