Anomalous transport in disordered systems under the influence of external fields

We discuss two models for the description of anomalous diffusion, these bei ng the continuous time random walk scheme, and fractional diffusion equatio ns. We show their interrelations, and combine both approaches for the descr iption of anomalous transport in constant external velocity and force field s. For an arbitrary external force F(x), we introduce a fractional Fokker-P lanck equation, which generalises the two Einstein relations. (C) 1999 Else vier Science B.V. All rights reserved.