1. National Chemical Laboratory for Industry, 1‐1 Higashi, Tsukuba, Ibaraki, 305, Japan
2. Central Research Institute of Electric Power Industry, 2‐6‐1 Nagasaka, Yokosuka, Kanagawa, 240‐01, Japan
3. Fuji Electric Corporate Research and Development, Limited, 2‐2‐1, Nagasaka, Yokosuka, Kanagawa, 240‐01, Japan