1. Kanto Gakuin University,Dept. of Electrical and Electronic Engineering,Yokohama, Kanagawa,Japan,236-8501
2. Osaka Research Institute of Industrial Science and Technology,Research Division of Product Reliability,Izumi, Osaka,Japan,594-1157
3. Sekii PE Laboratory,Chiba, Chiba,Japan,275-0005
4. Tokyo City University,Dept. of Mechanical System Engineering,Setagaya, Tokyo,Japan,158-8557