1. Scuola di IngegneriaUniversità degli Studi della Basilicata 85100 Potenza Italy
2. Department of Mechanics Mathematics and ManagementPolitecnico di Bari v.le Japigia 182 70126 Bari Italy
3. Physics Department M. MerlinCNR Institute for Photonics and Nanotechnologies U.O.S. Bari via Amendola 173 70126 Bari Italy
4. Department of Mechanical EngineeringImperial College London South Kensington Campus, Exhibition Road London SW7 2AZ UK
5. Center for Nonlinear ScienceUniversity of North Texas P.O. Box 311427 Denton TX 76203‐1427 USA