Freie Universität Berlin, Institut für Mathematik I, Arnimallee 2-6, D 14195 Berlin, Germany pflueger@math.fu-berlin.de
Abstract: We study a semilinear elliptic boundary value problem in an unbounded domain of $R^{n}$ $(n \geq 3)$ which arises for example in electromagnetic wave propagation in fibres. We consider nonlinear boundary conditions of the form $\partial u / \partial n = Q(x) |u|^{q-1} u$ $(q>1)$. A Mountain Pass Lemma approach and a comparison argument are used to construct a nontrivial solution of this problem.
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