Funding for this research was provided by:
Natural Science Foundation of China (61672535, 61502540)
Natural Science Foundation of Hunan Province (2019JJ20025, 2019JJ40406)
Article History
Received: 7 June 2019
Accepted: 19 August 2019
First Online: 28 August 2019
Competing interests
: The authors declare that they have no competing interests.