1. Department of Applied Mathematics and Statistics, Johns Hopkins University, Baltimore, MD 21218, USA
2. Department of Mathematics and Statistics, University of Massachusetts Amherst, Amherst, MA 01003, USA
3. Department of Mathematics and Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61820, USA
4. European Commission, Joint Research Centre, I-21027 Ispra (VA), Italy
5. Grupo de Física No Lineal, Departamento de Física Aplicada I, Universidad de Sevilla. Escuela Politécnica Superior, C/ Virgen de África, 7, 41012 Sevilla, Spain
6. Instituto de Matemáticas de la Universidad de Sevilla (IMUS). Edificio Celestino Mutis. Avda. Reina Mercedes s/n, 41012 Sevilla, Spain