1. Bell Labs, Physical Sciences and Engineering Research Division, Murray Hill, NJ; University of California, Santa Cruz, CA; University of Maryland, College Park, MD; Technical University, Vienna, Austria; ERS Co. LLC, Santa Cruz, CA 95064 e-mail:
2. Flextronics Corporation, Milpitas, CA 95035 e-mail:
3. Bordeaux University, Bordeaux, France e-mail: