Fund: The project was partially supported by the National Natural Science Foundation of China (Grant No. 11671102), the Natural Science Foundation of Guangxi (Grant Nos.~2017GXNSFAA198349; 2016GXNSFAA3800163), the Program on the High Level Innovation Team and Outstanding Scholars in Universities of Guangxi Province and the Program on the Basic Ability Promotion for Young and Middle-aged Teachers of Guangxi. |