## On Ventcel’s type boundary condition for Laplace operator in a sector.(English)Zbl 1291.35048

Summary: This paper deals with classical solutions of the Dirichlet-Ventcel boundary value problem (BVP) for the Laplace operator in a bounded sector in the plane having opening of the corresponding angle $$\varphi_0>0$$. Ventcel BVP is given by a second order differential operator on the boundary satisfying the Lopatinksii condition there. As the boundary is non smooth, two different cases appear: $$\frac{\pi}{\varphi_0}$$ is irrational and $$\frac{\pi}{\varphi_0}$$ is an integer. At first we prove a uniqueness result via the maximum principle and then the existence of the classical solution. To do this we apply two different approaches: the machinery of the small denominators and the concept of Green function.

### MSC:

 35J25 Boundary value problems for second-order elliptic equations 35A01 Existence problems for PDEs: global existence, local existence, non-existence 35A02 Uniqueness problems for PDEs: global uniqueness, local uniqueness, non-uniqueness 35J08 Green’s functions for elliptic equations
Full Text: