Research at the University of California at Irvine was supported by (a) the National Aeronautics and Space Administration;
Langley Research Center (Grant NGT-1-52135);
and (b) the Army Research Office (Grants ARO AASERT DAAG 55-98-1-0141 and ARO DAAG55-98-1-0088). Sincere thanks go to the unknown reviewer whose comments;
corrections;
and suggestions helped strengthen the manuscript;