1. Faculty of Health and Welfare Science, Okayama Prefectural University, Kuboki-111, Soja, Okayama 719-11, Japan
2. Faculty of Engineering, Okayama University, Tsushima-naka, Okayama 700, Japan
3. Mitsubisi Heavy Industries, Ltd., Kan-on-shin-machi, Nishi-ku, Hiroshima 733, Japan