Funding for this research was provided by:
National Science Foundation of China (41661003)
Natural Science Foundation of Ningxia Province (NX16010)
First Class Disciplines Program in Western China of Ningxia Province (NXYLXK2017B06)
“Light of West China” Program of the Chinese Academy of Sciences (XAB2017AW01)
Article History
Received: 9 March 2017
Accepted: 28 May 2018
First Online: 2 June 2018
Compliance with ethical standards
:
: The authors declare that they have no conflict of interest.