Funding for this research was provided by:
National Natural Science Foundation of China (81570465, 30700917)
Article History
Received: 22 January 2018
Accepted: 6 March 2018
First Online: 29 March 2018
Compliance with ethical standards
:
: The authors declare that they have no conflict of interest.
: For this type of study, formal consent is not required.
: Informed consent was obtained from all participants of the study.