GABRIELLA CARISTI is an Associate Professor of Mathematical Analysis at the University of Trieste, Italy. The author or coauthor of numerous scientific publications on ordinary differential equations and elliptic and parabolic systems, she is a member of the Unione Matematica ltaliana. Dr. Caristi received the Research degree (1981) from the University of Trieste, Italy. ENZO MITIDIERI is a Professor of Mathematics at the University of Trieste, Italy. He is the author or coauthor of several journal articles on elliptic systems and evolution equations, the coeditor of Semigroup Theory and Applications and Semigroup Theory and Evolution Equations (both titles, Marcel Dekker, Inc.), and a member of the National Group on Functional Analysis. Dr. Mitidieri received the Research degree ( 1983) from the University of Trieste, Italy.