Department of Management Science and Engineering, School of Government, Beijing Normal University,
Beijing, China
Department of Management Science and Engineering, School of Government, Beijing Normal University,
Beijing, China
Copyright © 2015 Ping Gao, Handong Li 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.