This research is sponsored in part by the Defense Advanced Research Projects Agency (DARPA), and Rome Laboratory, Air Force Materiel Command, USAF, under agreement number F30602-95-1-0018 and in part by the Department of the Navy, Office of Naval Research under contract number N00014-95-1-0591. Views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing official policies or endorsements, either expressed or implied, of the Air Force, of the Department of the Navy, Office of Naval Research or the United States Government.