J. DAVID LOGAN, PhD, is Willa Cather Professor of Mathematics at the University of Nebraska–Lincoln. Dr. Logan is the author of several books in applied mathematics, including An Introduction to Nonlinear Partial Differential Equations, published by Wiley. He is an Editor of Communications on Applied Nonlinear Analysis and has authored numerous research papers in the areas of mathematical physics, combustion and detonation theory, hydrogeology, and mathematical ecology.