Funding for this research was provided by:
National Natural Science Foundation of China (71690233)
National Natural Science Foundation of China (61473301)
National Natural Science Foundation of China (71701203)
Article History
Received: 5 March 2018
Accepted: 13 April 2018
First Online: 29 April 2018
Competing interests
: The authors declare that they have no competing interests.
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