1. NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
2. Faculty of Science and Engineering, Yamato University, Suita, Osaka 564-0082, Japan
3. College of Engineering, Nihon University, Koriyama, Fukushima 963-8642, Japan