1. Departamento de Métodos Cuantitativos, CUNEF Universidad, Madrid, Spain
2. Department of Mathematics and Volen Center for Complex Systems, Brandeis University, Waltham, MA, USA
3. Dipartimento di Matematica, Università di Pavia, Pavia, Italy
4. Department of Mathematical Sciences, Kent State University, Kent, OH, USA
5. Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH, USA