Funding for this research was provided by:
National Key R&D Program of China (2016YFA0602601)
Special Items Fund of Beijing Municipal Commission of Education of China, Program of Beijing Energy Development Research Center of China (NYJD20170101)
National Social Science Fund of China (15ZDA011)
Article History
Received: 31 July 2018
Accepted: 14 November 2018
First Online: 21 November 2018