Funding for this research was provided by:
National Natural Science Foundation of China (61376099)
Foundation for Fundamental Research of China (JSZL2016110B003)
Major Fundamental Research Program of Shaanxi (2017ZDJC-26)
111 Project (B12026)
Text and Data Mining valid from 2018-03-05
Received: 14 December 2017
Accepted: 23 February 2018
First Online: 5 March 2018
: WL, SpC, and QqW are Ph.D students in the Xidian University. SlW is a doctor in the Xidian University. HxL is a professor in the Xidian University.
: The authors declare that they have no competing interests.
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