1. U.S. Army Natick Soldier Center, Soldier and Biological Chemical Command, Natick MA 01760-5018.
2. Corresponding author. E-mail: ann.barrett@natick.army.mil Phone: (508) 233-4516. Fax: (508) 233-5181.
3. Present address, Campbell Soup Company, Campbell Place, Camden NJ 08103.
4. U.S. Army Research Laboratory, Aberdeen Proving Grounds MD.