Funding for this research was provided by:
National Natural Science Foundation of China (61702058)
China Postdoctoral Science Foundation (2017M612948)
the Scientific Research Foundation of CUIT (KYTZ201717)
the Scientific Research Foundation of CUIT (J201706)
Received: 7 March 2018
Accepted: 12 June 2018
First Online: 27 June 2018
: The authors declare that they have no competing interests.
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