1. Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Aoba 6-3, Aramaki, Aoba-ku, Sendai 980-8578, Japan
2. Computer Centre, Gakushuin University, Mejiro 1-5-1, Toshima-ku, Tokyo 171-8588, Japan
3. Division of Electrical, Electronic and Information Engineering, Graduate School of Enginnering, Osaka Univerisity, Suita 565-0871, Japan