1. School of Electrical Engineering, Korea University, 145 Anam-dong, Seongbuk-gu, Seoul 136-701, Republic of Korea
2. Membrane and Separation Technology Division, CSIR-Central Glass and Ceramic Research Institute, 196, Raja S. C. Mullick Road, Kolkata 700 032, India
3. Department of Information Display, Kyung Hee University, Dongdaemoon-gu, Seoul 130-701, Republic of Korea