Abstract. In this note we investigate the spatial behavior of a linear equation of fourth order which models several mechanical situations when dispersive and dissipative effects are taken into account. In particular, this equation models the extensional vibration of a bar when we assume that external friction, with a rough substrate for example, is present. We show that for such an equation a Phragmén-Lindelöf alternative of exponential type can be obtained. A bound for the amplitude term in terms of boundary data is obtained. Moreover, when friction is absent, we obtain exponential decay results in the case of harmonic vibrations and we prove a polynomial decay estimate for general solutions.
Introduction.In recent years much attention has been directed to the study of the damping of end effects in several thermomechanical situations and to the general study of the spatial behavior of solutions of partial differential equations and systems. The history and development of these questions was extensively surveyed by Horgan and Knowles [11] in a work periodically updated by Horgan [9,10]. Moreover, the books by Ames and Straughan [1], Flavin and Rionero [6] and Antontsev et al. [2] are devoted to such matters. The energy method is widely used to study the spatial behavior of solutions of partial differential systems.In this note we investigate the spatial behavior of a linear equation of fourth order which is encountered in several frameworks when we take into account dispersive effects.