Post-Doctoral Scientific Research Workstation, Shanghai International Group Co., Ltd. (SIG), Shanghai, China;Post-Doctoral Research Station for Applied Economics, Fudan University, Shanghai, China;Department of Applied Mathematics, Shanghai Finance University, Shanghai, China
Copyright © 2013 Yong Fang et al. This is
an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any
medium, provided the original work is properly cited.