1. Department of Chemical Engineering, Yonsei University, 134, Sinchon-dong, Seodaemun-gu, Seoul, 120-749, Korea, Advanced Materials Division, Korea Research Institute of Chemical Technology, P. O. Box 107, Yusung, Daejeon 305-600, Korea, and Department of Electrical Engineering & Computer Science, Division of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejon 305-701, Korea