Funding for this research was provided by:
the National Nature Science Foundation (51672220)
the 111 Program of MOE (B08040)
the National Defense Science Foundation (32102060303)
the Xi’an Science and Technology Foundation (CXY1706-5, 2017086CGRC049-XBGY005)
the Shaanxi Provincial Science Foundation (2017KW-018)
the NPU Gaofeng Project of China (17GH020824)
Article History
Received: 4 May 2017
Accepted: 29 December 2017
First Online: 9 January 2018