Funding for this research was provided by:
National Natural Science Foundation of China (61673099)
Research Program for Liaoning Excellent Talents in University (LJQ2014027)
Hebei Province Natural Science Foundation (F2015501047)
Fundamental Research Funds for the Central Universities (N162304006)
Article History
Received: 15 December 2017
Accepted: 1 August 2018
First Online: 10 August 2018
Competing interests
: The authors declare that they have no competing interests. All authors of this article declare that there is no conflict of interests regarding the publication of this article. We have no proprietary, financial, professional, or other personal interest of any nature or kind in any product, service, and/or company that could be construed as influencing the position presented in, or review of this article.