1. Graduate School of Science and Technology, Niigata University, Niigata 950-2181
2. Atsugi Laboratories, Fujitsu Ltd., Morinosato-Wakamiya, Atsugi, Kanagawa 243-0197
3. Research Institute for Applied Mechanics, Kyushu University, Fukuoka 816-8580
4. Center for Low Temperature Science, Tohoku University, Sendai 980-8577