1. Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka Nagaoka, Niigata 940-2188, Japan
2. College of Science and Technology, Nihon University, 7-24-1 Narashinodai, Funabashi, Chiba 274-8501, Japan
3. Japan Broadcasting Corporation (NHK) Science and Technology Research Laboratories, 1-10-11 Kinuta, Setagaya-ku, Tokyo 157-8510, Japan