1. Department of Electrical, Electronic and Computer Engineering, Faculty of Engineering, Gifu University, Gifu City 501-1193, Japan
2. Department of Earth and Planetary Science, the University of Tokyo, Bunkyo-ku 113-0033, Tokyo, Japan
3. Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, United States
4. Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba City 305-0801, Ibaraki, Japan