Advection of a portion of fluid delimited by an initial square during eight periods of lid oscillation for $Re=50$ and $Str=0.25$⁠. (a) Initial (black) and final (red) shape of the advected portion, (b) distribution of the coarse-grained density D_n corresponding to the final state, indicated by gray scale from 0 (white) to 1 (black). (c) Evolution of the intensity of segregation I (dots) and its least squares exponential fit (line).