Abstract
We consider the Friedrichs inequality for functions defined on a disk of unit radius Ω and equal to zero on almost all boundary except for an arc λε of length ɛ, where ɛ is a small parameter. Using the method of matched asymptotic expansions, we construct a two-term asymptotics for the Friedrichs constant \(C(\Omega ,\partial \Omega \backslash \bar \gamma _\varepsilon )\) for such functions and present a strict proof of its validity. We show that \(C(\Omega ,\partial \Omega \backslash \bar \gamma _\varepsilon ) = C(\Omega ,\partial \Omega ) + \varepsilon ^2 C(\Omega ,\partial \Omega )(1 + O(\varepsilon ^{2/7} ))\). The calculation of the asymptotics for the Friedrichs constant is reduced to constructing an asymptotics for the minimum value of the operator −Δ in the disk with Neumann boundary condition on λε and Dirichlet boundary condition on the remaining part of the boundary.
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Dedicated to Arlen Mikhailovich Il’in
Original Russian Text © R.R.Gadyl’shin, E.A. Shishkina, 2012, published in Trudy Instituta Matematiki i Mekhaniki UrO RAN, 2012, Vol. 18, No. 2.
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Gadyl’shin, R.R., Shishkina, E.A. On Friedrichs inequalities for a disk. Proc. Steklov Inst. Math. 281 (Suppl 1), 44–58 (2013). https://doi.org/10.1134/S0081543813050052
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DOI: https://doi.org/10.1134/S0081543813050052