Funding for this research was provided by:
Natural Science Foundation of Hunan Province (2017JJ4004)
Natural Science Foundation of Hunan Province (2017JJ5011)
National Natural Science Foundation of China (11372107)
Article History
Received: 30 September 2018
Accepted: 3 January 2019
First Online: 14 January 2019
Competing interests
: The authors declare that they have no competing interests.