1. Applied Mathematics Laboratory, Courant Institute of Mathematical Sciences, New York University, New York, New York 10012, USA
2. Physique et Mécanique des Milieux Hétérogènes, ESPCI ParisTech, Paris, France
3. Department of Physics, New York University, New York, New York 10003, USA and NYU-ECNU Institute of Mathematical Sciences at NYU-Shanghai, Shanghai 200122, China