Article History
First Online: 6 March 2019
Compliance with Ethical Standards
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: This study was supported by a grant from National Key R&D Program of China (grant number: 2016YFC1301500) and National Science and Technology Major Project of China (grant number: 2015BAI12B02 and 2017YFC1310901).
: Ming Yang, Xiaochuan Huo, Zhongrong Miao and Yongjun Wang have no conflicts of interest that are directly relevant to the contents of this article.