1. Institute for Study of the Earth’s Interior, Okayama University, Misasa, Tottori 682-0193, Japan, Advanced Technology Research Laboratories, Nippon Steel Corp., 20-1 Shintomi, Futtsu, Chiba 293-8511, Japan, and JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan