1. Mathematical Soft Matter Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna, Okinawa 904-0495, Japan
2. Accademia Nazionale dei Lincei, Palazzo Corsini, Via della Lungara 10, 00165 Roma, Italy
3. Department of Mathematics, Università di Roma TorVergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy