1. Department of Applied Materials Science, College of Engineering, Osaka Prefecture University, Gakuen-cho 1-1, Sakai, Osaka 593, Japan, Department of Nuclear Engineering, College of Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka 565, Japan, and Research Institute for Advanced Science and Technology, Osaka Prefecture University, Gakuen-cho 1-2, Sakai, Osaka 593, Japan