1. Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0213
2. Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531
3. Faculty of Integrated Arts and Sciences, The University of Tokushima, Tokushima 770-8502
4. Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397