1. a Graduate School of Materials Science, Nara Institute of Science and Technology , Ikoma, Japan
2. b Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University , Chiyoda, Japan
3. c Research Laboratories , NTT DOCOMO, Inc. , Yokosuka, Japan
4. d School of Information and Computer Science, University of California , Irvine, CA, USA