1. Department of Mathematics, National University of Singapore
2. Department of Mathematics, National University of Singapore, Singapore; Sorbonne Université, CNRS, Université de Paris, Laboratoire J.-L. Lions, Paris, France
3. Department of Mathematics, Purdue University, West Lafayette, Indiana, U.S.A.
4. Fujian Provincial Key Laboratory on Mathematical Modeling & High Performance Scientific Computing, and School of Mathematical Sciences, Xiamen University, Xiamen, Fujian, China