1. Department of Mechanical Engineering The University of Iowa Iowa City IA 52242 USA
2. Department of Electrical and Computer Engineering The University of Iowa Iowa City IA 52242 USA
3. Department of Chemistry The University of Iowa Iowa City IA 52242 USA
4. College of Biological and Agricultural Engineering Jilin University Changchun 130022 P. R. China
5. School of Materials Science and Engineering Jiangsu University Zhenjiang 212013 P. R. China