Funding for this research was provided by:
National Natural Science Foundation of China (11604286, 51661032)
Shaanxi Provincial Natural Science Foundation (15JK1833)
Yan’an University National Natural Science Foundation (YD2015-07, YDBK2014-01)
the Shanxi Provincial College students’ innovative projects (D2017143, D2017163)
Article History
Received: 9 April 2018
Accepted: 5 September 2018
First Online: 9 March 2019