1. School of Engineering Medicine, Beihang University, Beijing 100083, China
2. School of Mathematics, Shandong University, Jinan 250100, China
3. Department of Mathematics, University of South Carolina, Columbia, SC 29208, USA
4. School of Mathematical Sciences, Fudan University, Shanghai 200433, China
5. Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, China