Funding for this research was provided by:
NSFC (11601409, 11201362)
Natural Science Foundations of Shaanxi Province of China (2016JM1009)
Natural Science Foundations of Department of Shaanxi Province of China (2017JK0344)
Received: 1 September 2019
Accepted: 28 October 2019
First Online: 8 November 2019
: The authors declare that they have no competing interests.