Funding for this research was provided by:
Philosophy and Social Science Foundation of Hunan Province (2017JJ3134, 2016NK2115)
Scientific research fund of Hunan province education department (17C0935)
National Natural Science Foundation of China (31672640, 31372530)
Article History
Received: 13 August 2018
Accepted: 10 September 2018
First Online: 19 September 2018