1. Graduate School of Science and Technology; Shizuoka University; 3-5-1 Johoku Naka-ku Hamamatsu 432-8561 Japan
2. Institute of Plasma Physics; Chinese Academy of Sciences; P.O. Box 1126 Hefei 230031 PR China
3. Research and Technology Center; Yazaki Corp.; 1500 Misyuuku Susono 410-1194 Japan