1. Faculty of Computer Science, Dalhousie University, Goldberg Computer Science Building, 6050 University Avenue, B3H 4R2, Halifax, NS, Canada
2. Institute of Mathematical Sciences and Computing, University of São Paulo, CP 668, 13560-970 São Carlos, SP, Brazil
3. São Carlos Institute of Physics, University of São Paulo, CP 369, 13560-970 São Carlos, SP, Brazil