Funding for this research was provided by:
National Natural Science Foundation of China (11501342)
Natural Science Foundation of Shanxi Province (201701D221007)
the Scientific and Technological Innovation Programs of Higher Education Institutions of Shanxi Province (201802068, 201802069)
Article History
Received: 5 April 2019
Accepted: 13 August 2019
First Online: 2 September 2019
Competing interests
: The authors declare that they have no competing interests.