FIG. 6.
(Color online) Illustration of the hard- and soft-core interactions in a two-species system containing black and red (or light gray in the print version) cells. The left panel shows the exclusion regions (circular disks with two distinct sizes) associated with the two types of cells, which are proportional to the actual sizes of the cells. The black cells have a larger exclusion region than the red cells. The middle panel illustrates the soft-core repulsive interaction (large concentric overlapping circles of the solid black disks) between the black cells. Such a repulsive interaction will drive the black cells to arrange themselves in a perfect triangular lattice in the absence of other species. The right panel illustrates the soft-core repulsive interaction (large concentric overlapping circles of the solid red disks) between the red cells.