1. School of Engineering, Brown University, Providence, Rhode Island 02912, USA
2. Department of Physics and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680-749, South Korea
3. Deptartment of Physiology and Biophysics, Inha University College of Medicine, Incheon 402-752, South Korea
4. Research and Development Center, I-MTS Co. LTd., Namdong, Incheon 405-846, South Korea