1. Graduate School of Engineering and Resource Science, Department of Mathematical Science and Electrical - Electronic - Computer Engineering, Akita University, 1-1, Tegata Gakuen-machi, Akita-shi, Akita 010-8502, Japan
2. SWCC Showa Cable Systems Co., Ltd., 4-1-1, Minami Hashimoto, Sagamihara-shi, Kanagawa 229-1133, Japan