LEVER TO THE EDITOR Non-equilibrium critical behaviour on fractal lattices

Abstract. A simple one-component surface reaction model exhibiting a critical point has been studied on deterministic fractal lattices with fractal dimension 1 i D, < 2. Results from time-dependent simulations show a change in the value of the critical exponents with D,. Two of the exponents interpolate very nicely between the values in one and two dimensions. Non-equilibrium phase transitions have been studied intensively in recent years. Special attention has been devoted to the question of universality classes. A large variety of non-equilibrium models such as the contact process [ I, 21, Schlogl's first model 13-51, directed percolation [6-81, Reggeon field theory [9,4] and the ZGB model [lo, 111, all of which exhibit a continuous transition from an active state tn an absorbing state, have the same critical behaviour. Studies of related models via computer simulations [12-151, field theoretic arguments 116,171 and series expansions [le] demonstrate the robustness of this universality class against a wide range of changes in the local kinetic rules such as multi-particle processes, diffusion and changes in the number of chemical components. So currently there is substantial evidence in favour of the conjectur