1. Jackson Laboratory, E. I. du Pont de Nemours and Company, Deepwater, New Jersey 08023, Marshall Laboratory, E. I. du Pont de Nemours and Company, Philadelphia, Pennsylvania 19146, Central Research and Development, Experimental Station, E. I. du Pont de Nemours and Company, Wilmington, Delaware 19880-0356, and Corporate Center for Analytical Sciences, Experimental Station, E. I. du Pont de Nemours and Company, Wilmington, Delaware 19880-0323