1. G. W. Coulston, R. Harlow, N. Herron, DuPont Company, Wilmington, DE 19880-0262, USA.
2. S. R. Bare, Dow Chemical Company, Midland, MI 48674, USA. H. Kung, K. Birkeland, G. K. Bethke, Ipatieff Laboratory, Northwestern University, Evanston, IL 60208-3000, USA.
3. P. L. Lee, Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA.