1. University of Perpignan Via Domitia, PROMES CNRS UPR 8521, Tecnosud-Rambla de la Thermodynamique, Perpignan 66100, France e-mail:
2. Associate Professor University of Perpignan Via Domitia, PROMES CNRS UPR 8521, Tecnosud-Rambla de la Thermodynamique, Perpignan 66100, France e-mail:
3. PROMES CNRS UPR 8521, Department of Mathematics, Florida State University, Thallahassee, FL 32306 e-mail: