1. Assistant Professor, Graduate School and Faculty of Information Science and Electrical Engineering, Kyushu Univ., 744 Moto-oka, Nishi-ku, Fukuoka-shi, Fukuoka 819-0395, Japan (corresponding author).
2. Adviser, Tokyo Electric Power Services Co. Ltd., 1-7-12 Shinonome, Koto-ku, Tokyo 135-0062, Japan; Professor Emeritus, Engineering, Hiroshima Univ., 1-4-1 Kagamiyama, Higashi-Hiroshima-shi, Hiroshima 739-8527, Japan.