1. Sandia National Laboratories, Albuquerque, New Mexico 87185, and Department of Chemical Engineering, University of California, Santa Barbara, California 93106
2. Sandia National Laboratories, Albuquerque, New Mexico 87185
3. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218
4. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
5. E.I. Dupont, Experimental Station Laboratory, ESL 323-109B, Wilmington, Delaware 19880