Funding for this research was provided by:
Strategic Priority Research Program of the Chinese Academy of Sciences (XDB02060007)
Beijing Municipal Commission of Science and Technology (Z161100000216124)
Article History
Received: 6 April 2017
Accepted: 15 August 2017
First Online: 31 August 2017
<!--Emphasis Type='Bold' removed-->Compliance with Ethical Standards
: This study was funded by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB02060007), and Beijing Municipal Commission of Science and Technology (Z161100000216124).
: This article does not contain any studies with human participants performed by any of the authors.
: All authors declare that they have no conflict of interest.