1. Department of Physics, Faculty of Science, Nagoya University, Chikusa-ku, Nagoya 464-01, Japan
2. Department of Earth and Space Science, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan
3. Department of Biophysics, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606, Japan
4. School of Computer and Cognitive Science, Chukyo University, Toyota, Aichi 470-03, Japan