Ruelle, P. 1990-93 Scholar Born 1963 Ottignies, Belgium. Ph.D. 1990 Louvain. Appointments: Research Assoc., Louvain 1993-. Address: Institut de Physique Theorique et Mathematique, Chemin du Cyclotron No.2, B-1348 Louvain-la-Neuve, Belgium. E-mail: ruelle_at_fyma.ucl.ac.be