Funding for this research was provided by:
China National Social Sciences Research Funds (No. 14 BRK012)
Minzu University of China (No. 2017YQ10)
Article History
Received: 14 July 2017
Accepted: 4 January 2018
First Online: 5 February 2018
Ethics approval and consent to participate
: Not applicable.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.