Symmetry of positive solutions of elliptic equations with mixed boundary conditions in a sub-spherical sector

Abstract

The paper is devoted to the qualitative properties of positive solutions to a semilinear elliptic equation in a planar sub-spherical sector. Under certain range of amplitudes, we prove some monotonicity properties via the method of moving planes. The symmetry properties follow from the uniqueness of the corresponding over-determined problem by Farina and Valdinoci (2013 Am. J. Math.).