Fund: The research was supported by the Fundamental Research Funds for the Central Universities (Grant Nos. 2019CDXYST0016; 2018CDXYST0024), the China Scholarship Council (Grant No. 201606055028), the National Natural Science Foundation of China (Grant No. 11671060), the MOE Project of Humanities and Social Sciences on the West and the Border Area (Grant Nos. 20XJC910001; 14XJC910001) and Chongqing Key Laboratory of Analytic Mathematics and Applications. |