1. Campus Duque de Caxias, Universidade Federal do Rio de Janeiro, Rio de Janeiro 25240-005, Brazil
2. Consiglio Nazionale delle Ricerche, IMEM Institute, 43124 Parma, Italy
3. Department of Mathematical, Physical and Computer Sciences, University of Parma, Parco Area delle Scienze 7/a (Campus), 43124 Parma, Italy