1. Department of Materials Science and Engineering, Seoul National University, Seoul, 151-744, Korea
2. Department of Nuclear Medicine, Seoul National University, Bundang Hospital, Seoul, 463-707, Korea
3. Pohang Accelerator Laboratory, POSTECH, Pohang, 790-784, Korea
4. Center for Craniofacial Molecular Biology, Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, California 90033, United States
5. School of Engineering and Department of Physics, Brown University, Providence, Rhode Island 02912, United States