Funding for this research was provided by:
Guangdong Province higher vocational colleges & schools Pearl River scholar funded scheme (2016)
project of Shenzhen Science and Technology Innovation Committee (JCYJ20170817114522834, JCYJ20160608151239996)
Received: 26 February 2019
Accepted: 3 May 2019
First Online: 28 May 2019
: The authors declare that they have no competing interests.
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