Transition to hexagonal pattern under the variation of intrinsic length   scales of a reaction diffusion system
  The intrinsic length scales of a reaction diffusion system (Gierer-Meinhardt model)is varied by quasi-statically changing the diffusion constant of the activator and a transition from rolls to hexagon is detected. The transition is hysteretic or first order like. From stability analysis, we also analytically show the possibility of such transitions. 
Julian Sienkiewicz and A. Bhattacharyay