1. Department of Materials Science and Technology, Nagaoka University of Technology, Kamitomioka 1603-1, Nagaoka, Niigata 940-2188, Japan
2. Research Fellow of the Japan Society for the Promotion of Science (DC), 5-3-1 Koji-machi, Chiyoda-ku, Tokyo 102-0083, Japan
3. Department of Materials Engineering, National Institute of Technology, Nagaoka College, Nishikatakai 888, Nagaoka, Niigata 940-8532, Japan