1. School of Natural and Applied ScienceNorthwestern Polytechnical University Xi'an 710072 P. R. China
2. Department of Mechanical EngineeringNational University of Singapore 9 Engineering Drive 1 117575 Singapore
3. School of Mechanical and Materials EngineeringWashington State University Pullman WA 99164 USA
4. College of Bioresources Chemical and Materials EngineeringShaanxi University of Science and Technology Xi'an 710021 P. R. China
5. College of Chemistry and Chemical EngineeringXi'an Shiyou University Xi'an 710065 P. R. China