1. Materials Engineering Department, Mechanical Engineering Laboratory, AIST, 1-2 Namiki, Tsukuba-shi, Ibaraki 305, Japan
2. Department of Mineral Resources Engineering, School of Science and Engineering, Waseda University, 3-4-1 Ohkubo Shinjuku-ku, Tokyo 169, Japan
3. Institute for Medical and Dental Engineering, Tokyo Medical and Dental University, 2-3-10 Surugadai, Kanda, Chiyoda-ku, Tokyo 101, Japan