ACKNOWLEDGMENTS

The author would like to thank the editors at Wiley and HEP, particularly Hongying Chen, Shelley Chow, James Murphy, Clarissa Lim, and Shalini Sharma, for their encouragement, assistance, and proof-reading. Special thanks must also be given to the three anonymous referees for their very helpful and constructive comments and suggestions.

The work was supported in part by the Royal Society London, the Royal Academy of Engineering London, the Recruitment Program of Global Experts of Hubei Province, the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of the Beijing Municipality (PHR/IHLB), the Massachusetts Institute of Technology and Harvard University.