ABSTRACT
AUTHORʼS NOTE: Preparation of this essay was partially supported by the U. S. Army Research Institute (Contract #MDA903-90-K-0113) and the Air Force Offi ce of Scientifi c Research under the U. S. Department of Defense University Research Initiative (Grant F49620-01-1-0394). The views, opinions, and fi ndings in this report are those of the author and should not be construed as an offi cial Department of Defense position, policy, or decision.
