Affiliation: | LATP, Université de Provence, 39 rue Joliot-Curie, 13453 Marseille, France ; MAB, Université de Bordeaux 1, 351 cours de la Libération, 33405 Talence Cedex, France ; University of North Carolina, Department of Mathematics, CB 3250, Phillips Hall, Chapel Hill, NC 27599 ; Indiana University, Department of Mathematics, Rawles Hall, Bloomington, IN 47405 |