1. Dept. of Chemical EngineeringUniversity of MichiganAnn Arbor MI 48109‐2136
2. Dept. of Chemical and Biological EngineeringUniversity of Colorado BoulderBoulder CO 80309
3. Fritz‐Haber‐Institut der Max‐Planck‐Gesellschaft, Theory Dept., Faradayweg 4‐6Berlin D‐14195 Germany