1. C. W. Frank, V. Rao, and M. M. Despotopoulou are in the Department of Chemical Engineering, Stanford University, Stanford, CA 94305-5025, USA.
2. R. F. W. Pease is in the Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
3. W. D. Hinsberg, R. D. Miller, and J. F. Rabolt are at the IBM Almaden Research Center, IBM Research Division, 650 Harry Road, San Jose, CA 95120-6099, USA.