Funding for this research was provided by:
National Science Foundation (DMS-1815095)
National Natural Science Foundation of China (11601392)
Fundamental Research Funds for the Central Universities (GK201902005)
Shaanxi Hundred-Talent Program
National Natural Science Foundation of China (11971285)
Article History
Received: 9 August 2019
Accepted: 23 January 2020
First Online: 5 February 2020