Also issued as Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1991.Includes bibliographical references (p. 234-239).Supported by the Defense Advanced Research Projects Agency. N00014-89-J-1489 Supported by the Air Force Office of Scientific Research. AFOSR 91-0034 Supported by the National Science Foundation. MIP 87-14969 Supported by Lockheed Sanders, Inc.