Funding for this research was provided by:
Department of Science and Technology of Sichuan Province (2016JY0106)
Education Department of Sichuan Province (16ZA0209)
Article History
Received: 23 September 2018
Accepted: 11 December 2018
First Online: 20 December 2018
Competing interests
: The authors declare that they have no competing interests.
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