Funding for this research was provided by:
National Natural Science Foundation of China (71471020, 11771059)
Hunan Provincial Natural Science Foundation of China (2016JJ1001)
Scientific Research Fund of Hunan Provincial Education Department (15A003)
Hunan Provincial and CSUST Innovation Foundation for Postgraduate (CX2017B490)
Article History
Received: 11 December 2017
Accepted: 3 April 2018
First Online: 16 May 2018
Competing interests
: The authors declare that they have no competing interests.