Funding for this research was provided by:
the National Natural Science Foundation of China (61761034)
the National Natural Science Foundation of China (61261020)
the Natural Science Foundation of Inner Mongolia, China (2016MS0616)
Article History
Received: 24 October 2017
Accepted: 18 April 2018
First Online: 3 May 2018
Competing interests
: The authors declare that they have no competing interests.
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