Cyclically coupled spreading and pair annihilation
  Recently it has been shown that the transition of the 1+1-dimensional annihilation-fission process 2X->3X, 2X->0 exhibits an unusual type of nonequilibrium critical behavior. The phenomenological properties of critical clusters are characterized by two different dynamic modes for spreading and diffusion. In order to describe the interplay of these modes, we introduce an effective model which involves two species of particles A and B. The A-particles perform an ordinary directed percolation process while the B particles diffuse and annihilate. Both subsystems are cyclically coupled by particle transmutation A <-> B. The resulting critical behavior is in many respects similar to the one observed in the annihilation-fission process. 
Haye Hinrichsen