Spatiotemporal irregularity in an excitable medium with shear flow

We consider an excitable medium moving with relative shear, subjected to a localized disturbance that in a stationary medium would produce a pair of s piral waves. The spiral waves so created are distorted and then broken by t he motion of the medium. Such breaks generate new spiral waves, and so a "c hain reaction" of spiral wave births and deaths is observed. This leads to a complicated spatiotemporal pattern, the "frazzle gas" [term suggested by Markus et at, Nature (London) 371, 402 (1994)], which eventually fills the whole medium. In this paper, we display and interpret the main features of the pattern. [S1063-651X(99)09407-6].