Paper in which we describe how an artificial chemistry on a planar graph easily generates islands of activity with barriers with much lower activity between them
A. Lindgren, and K. Eriksson. Proceedings of the Ninth International Conference on the Simulation and Synthesis of Living Systems, ALIFE'9, page 456. Boston, (12-15 September 2004)
J. Busch, and W. Banzhaf. Proceedings, Fourth International Conference on MultiAgent Systems, page 371--372. Boston, MA, USA, IEEE Computer Society, (July 2000)