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Published online by Cambridge University Press: 28 January 2013
Let L be a linear, closed, densely defined in a Hilbert space operator,not necessarily selfadjoint. Consider the corresponding wave equations
(1) ¨w+Lw=0, w(0)=0, ẇ(0)=f, ẇ=dwdt, f∈H.(2) ¨u+Lu=fe−ikt, u(0)=0, u̇(0)=0,
where k > 0 is a constant. Necessary and sufficient conditions aregiven for the operator L not to have eigenvalues in the half-planeRez < 0 and not to have a positive eigenvalue at a given point kd2 > 0. These conditions are given in terms of the large-timebehavior of the solutions to problem (1) for generic f.
Sufficient conditions are given for the validity of a version of the limiting amplitudeprinciple for the operator L.
A relation between the limiting amplitude principle and the limiting absorption principleis established.