Funding for this research was provided by:
the National Natural Science Foundation of China (61471262)
the International (Regional) Cooperation and Exchange (61520106002)
the Doctoral Fund of Ministry of Education of China (20130032110010)
Article History
Received: 27 October 2016
Revised: 3 July 2017
Accepted: 6 July 2017
First Online: 14 July 2017