Modeling the impact of the introduction of crack-cocaine in the prevalence of HIV/AIDS in a community of illicit drug users - Burattini, Marcelo Nascimento; Massad, Eduardo; Coutinho, Francisco Antonio Bezerra; Menezes, R. X.; Azevedo Neto, Raymundo Soares de (International Conference on Mathematical and Computer Modelling and Scientific Computing, 1997)