1. Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang, Kyungbuk 790-784, Korea
2. Department of Internal Medicine and WHO Collaborating Center of Viral Hepatitis, The Catholic University of Korea, 505 Banpo-dong, Seocho-gu, Seoul 137-701, Korea