1. School of Mathematical Sciences, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China;
2. Department of Civil Engineering, The University of Hong Kong, Hong Kong, China;
3. Guangdong-Hong Kong-Macau Joint Laboratory for Smart Cities, The University of Hong Kong, Hong Kong, China;
4. Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China;
5. Division of Applied Mathematics, Brown University, Providence, Rhode Island 02912