Funding for this research was provided by:
National Natural Science Foundation of China (11126245)
Discipline Construction Fund of Central University of Finance and Economics
China Scholarship Council (CSC–[2014]3072)
Article History
Received: 3 November 2017
Accepted: 11 June 2018
First Online: 22 June 2018
Competing interests
: The author declares that they have no competing interests.