1. a Advanced Research Laboratory , Hitachi, Ltd. , Kokubunji, tokyo 185, Japan
2. b Hitachi Research Laboratory , Hitachi, Ltd. , 4026 Kuji-cho, Hitachi , Iberaki , 319-12 , Japan
3. c Imaging Materials Laboratory, Research Center , Mitsubishi Chemical Industries Ltd. , 1000 Kamoshida, Midoriku, Yokohama , Kanagawa , 227 , Japan