No-flux boundaries stabilize scroll rings in excitable media with   negative filament tension
  Scroll rings in an unbounded excitable medium with negative line tension undergo an instability ending eventually in a "turbulent" state, known as scroll wave (Winfree) turbulence. In this paper we demonstrate by numerical simulations based upon the Oregonator model for the photosensitive Belousov-Zhabotinskii reaction (PBZR) that the Winfree turbulence is suppressed by the interaction of the scroll ring with a confining Neumann boundary. Instead of the Winfree turbulence a stable scroll ring forms due to the boundary interaction. Furthermore, we will discuss the conditions under which boundary-stabilized scroll rings could be observed in the PBZR, taking into account a light-induced excitability gradient in parallel to the scroll ring's symmetry axis. 
Arash Azhand, Rico Buchholz, Florian Buchholz, Jan Totz, and Harald   Engel
nlin.PS