Funding for this research was provided by:
13th Five-Year Plan National Science and Technology Support Program (2016YFD0500907)
Innovative Research Project of Graduate Students in Southwest University for Nationalities (CX2017SZ056)
Article History
Received: 4 July 2017
Accepted: 28 August 2017
First Online: 23 October 2017
Compliance with ethical standards
: This article does not contain any studies with human participants or animals performed by any of the authors and is in compliance with ethical standards for research.
: The authors declare no conflict of interest.
Free to read: This content has been made available to all.