Funding for this research was provided by:
National Natural Science Foundation of China (11601469)
Natural Science Foundation of Hebei Province (A2018203088)
Science Research Project of Education Department of Hebei province (ZD2017079)
Article History
First Online: 10 September 2019
Compliance with ethical standards
:
: The authors declare that there are no conflicts of interest regarding the publication of this paper.
: This article does not contain any studies with human participants or animals performed by any of the authors.
: Informed consent was obtained from all individual participants included in the study.