1. Co-first author. Department of Mathematics, City University of Hong Kong, Kowloon, Hong Kong.
2. Co-first author. Department of Mathematics, The Chinese University of Hong Kong, Shatin, NT, Hong Kong.
3. Department of Mathematics, City University of Hong Kong, Kowloon, Hong Kong, and Hong Kong Centre for Cerebro-Cardiovascular Health Engineering, Hong Kong Science Park, Pak Shek Kok, NT, Hong Kong.
4. Corresponding author. Department of Mathematics, City University of Hong Kong, Kowloon, Hong Kong.
5. Department of Mathematics, University of Hong Kong, Pok Fu Lam, Hong Kong.
6. Department of Mathematics, The Chinese University of Hong Kong, Kowloon, Hong Kong.