| Citation | Distinguished for his work on magnetohydrodynamics (MHD) and especially dynamo theory, but also for his significant contributions to linear and nonlinear stability theory. By powerful use of asymptotic analysis, he has solved a number of very difficult problems in Applied Mathematics. By a new pseudo-Lagrangian technique for studying lightly damped fluid systems, he elucidated previously inexplicable features of Braginskii's geodynamo. The same technique, in the hands of Andrews and McIntyre, subsequently provided now well known insights into nonlinear wave propagation. In recent work, the candidate provided explicit examples of steady fast dynamo action, so disproving a conjecture made by distinguished Soviet theorists, that such dynamos did not exist. The candidate identified new rotating modes of nonlinear convection in rotating systems, and in collaboration with Childress, established a now celebrated MHD dynamo model in a rapidly rotating Benard layer; he also gave the first demonstration that situations exist where oscillatory MHD dynamos generate magnetic fields more readily than steady flows can. Assisted by E.R. Priest, he provided the first mathematically satisfactory account of the Petschek mechanism of magnetic field line reconnection. The candidate also gave the first complete solution of the Stefan (freezing) problem in cylindrical geometry; with C.A. Jones, he provided the first completely correct solution of the spherical Taylor problem. |