Funding for this research was provided by:
National Natural Science Foundation of China (11701489)
Natural Science Foundation of Hunan Province (2018JJ3481, 2018JJ2373)
Education Department of Hunan Province (18B054)
Article History
Received: 8 July 2019
Accepted: 6 December 2019
First Online: 13 December 2019
Competing interests
: The authors declare that they have no competing interests.