Bistable systems with propagating fronts leading to pattern formation.

We discuss a new dynamical transition in the propagation of fronts into an unstable state of a bistable system, which may be relevant for convection experiments, liquid crystals, or systems with thermodiffusion. The physical basis of this transition is explained and described quantitatively with the aid of marginal stability theory for front propagation. In one regime, the propagating front leads to a new form of pattern formation, in which a periodic state is created whose wavelength diverges at the transition with an exponent 3/2.