Nonuniversal critical spreading in two dimensions

Continuous phase transitions are studied in a two dimensional nonequilibrium model with an infinite number of absorbing configurations. Spreading from a localized source is characterized by nonuniversal critical exponents, which vary continuously with the density {φ} in the surrounding region. The exponent {δ} changes by more than an order of magnitude and {η} changes sign. The location of the critical point also depends on {φ}, which has important implications for scaling. As expected on the basis of universality, the static critical behavior belongs to the directed percolation class. {} 1996 The American Physical Society.