1. Hitachi Research Laboratory, Hitachi, Ltd., 7-1-1 Omika-cho, Hitachi 319-1292, Japan
2. Hitachi Industrial Equipment Systems Co., Ltd., AKS Bldg., 3 Kanda, Neribei-cho,
Chiyoda-ku, Tokyo 101-0022, Japan
3. Fracture and Reliability Research
Institute, Graduate School of Engineering, Tohoku University, 6-6-11 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan