1. Faculty of Engineering; Hokkaido University; Kita-13, Nishi-8, Kita-ku Sapporo 060-8628 Japan
2. Graduate School of Engineering; Hokkaido University; Kita-13, Nishi-8, Kita-ku Sapporo 060-8628 Japan
3. Furukawa Electric Co. Ltd.; 601-2, Otorizawa Nikko 321-2336 Japan
4. Institute for Materials Research; Tohoku University; Katahira-2-1-1, Aoba-ku Sendai 980-8577 Japan