1. Hitachi, Ltd., Energy Research Laboratory 1168 Moriyama-cho, Hitachi-shi, Ibaraki-ken, 316 Japan
2. Hitachi, Ltd., Advanced Research Laboratory, P. 0. Box 2 Kokubunji, Tokyo, 185 Japan
3. Tokyo Electric Power Company, Inc., 1-3, 1-chome, Uchisaiwai-cho, Chiyoda-ku, Tokyo, 100 Japan