Abstract
In this paper we study the free boundary problem arising as a limit as ɛ → 0 of the singular perturbation problem \({\textrm{div}(A(x)\nabla u) = \Gamma(x) \beta_\varepsilon(u)}\) , where A = A(x) is Holder continuous, β ɛ converges to the Dirac delta δ0. By studying some suitable level sets of u ɛ, uniform geometric properties are obtained and show to hold for the free boundary of the limit function. A detailed analysis of the free boundary condition is also done. At last, using very recent results of Salsa and Ferrari, we prove that if A and Γ are Lipschitz continuous, the free boundary is a C 1,γ surface around \({\mathcal{H}^{N-1}}\) a.e. point on the free boundary.
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Moreira, D.R., Teixeira, E.V. A singular perturbation free boundary problem for elliptic equations in divergence form. Calc. Var. 29, 161–190 (2007). https://doi.org/10.1007/s00526-006-0060-y
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DOI: https://doi.org/10.1007/s00526-006-0060-y