1. Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa 240-0196, Japan
2. National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
3. Fuji Electric Co., Ltd., 4-18-1 Tsukama, Matsumoto, Nagano 390-0821, Japan