Tile patterns in excitable media subject to non-solenoidal flow fields

The propagation of spiral waves in excitable media subject to a non-solenoi dal advective field which satisfies the no-penetration condition on the bou ndaries of the domain is studied numerically, and it is shown that, dependi ng on the amplitude and spatial frequencies of the velocity field, the spir al wave may be distorted highly, break up into a number of smaller spiral w aves. or exhibit polygonal shapes or the patterns. These patterns reflect t he symmetry/asymmetry of the velocity field and are characterized by thick regions of high concentration at stagnation points where the velocity gradi ent is largest, and thin ones which are parallel to the velocity vector. It is also shown that the advective field distorts the spiral wave by decreas ing its thickness where the velocity is largest due to the stretching of th e wave, and by increasing it at the stagnation points where the curvature o f the wave is largest. (C) 2001 Elsevier Science Ltd. All rights reserved.