Bogdan Georgiev, Guillaume Roy-Fortin
We study solutions of uniformly elliptic PDE with Lipschitz leading coefficients and bounded lower order coefficients. We extend previous results of A. Logunov concerning nodal sets of harmonic functions and, in particular, prove polynomial upper bounds on interior nodal sets of Steklov eigenfunctions in terms of the corresponding eigenvalue $ λ$.
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We investigate the geometric properties of Steklov eigenfunctions in smooth manifolds. We derive the refined doubling estimates and Bernstein's inequalities. For the real analytic manifolds, we are able to obtain the sharp upper bound for the measure of interior nodal sets.
We prove sharp upper and lower bounds for the nodal length of Steklov eigenfunctions on real-analytic Riemannian surfaces with boundary. The argument involves frequency function methods for harmonic functions in the interior of the surface as well as the construction of exponentially accurate approximations for the Steklov eigenfunctions near the boundary.
We investigate the interior nodal sets $\mathcal{N}_λ$ of Steklov eigenfunctions on connected and compact surfaces with boundary. The optimal vanishing order of Steklov eigenfunctions is shown be $Cλ$. The singular sets $\mathcal{S}_λ$ are finite points on the nodal sets. We are able to prove that the Hausdorff measure $H^0(\mathcal{S}_λ)\leq Cλ^2$. Furthermore, we obtain an upper bound for the measure of interior nodal sets $H^1(\mathcal{N}_λ)\leq Cλ^{\frac{3}{2}}$. Here those positive constants $C$ depend only on the surfaces.
Hausdorff measure bounds for nodal sets of Steklov eigenfunctions
本文研究有界$\mathcal{C}^2$区域内Steklov特征函数的节点集，建立了与特征值无关的Hausdorff测度下界，并给出含$\lambda\log(\lambda+e)$因子的近乎精确上界。
This article concerns the asymptotic geometric character of the nodal set of the eigenfunctions of the Steklov eigenvalue problem $$ -Δϕ_{σ_j}=0,\quad\text{ on }Ω,\qquad\qquad \partial_νϕ_{σ_j}=σ_j ϕ_{σ_j}\quad \text{ on }\partialΩ$$ in two-dimensional domains $Ω$. In particular, this paper presents a dense family $\mathcal{A}$ of simply-connected two-dimensional domains with analytic boundaries such that, for each $Ω\in \mathcal{A}$, the nodal set of the eigenfunction $ϕ_{σ_j}$ "is $not$ dense at scale $σ_j^{-1}$". This result addresses a question put forth under "Open Problem 10" in Girouard…
We prove sharp $L^p$ estimates for the Steklov eigenfunctions on compact manifolds with boundary in terms of their $L^2$ norms on the boundary. We prove it by establishing $L^p$ bounds for the harmonic extension operators as well as the spectral projection operators on the boundary. Moreover, we derive lower bounds on the size of nodal sets for a variation of the Steklov spectral problem. We consider a generalized version of the Steklov problem by adding a non-smooth potential on the boundary but some of our results are new even without potential.
Let $(Ω, g)$ be a real analytic Riemannian manifold with real analytic boundary $\partial Ω$. Let $ψ_λ$ be an eigenfunction of the Dirichlet-to-Neumann operator $Λ$ of $(Ω, g, \partial Ω)$ of eigenvalue $λ$. Let $\mathcal N_{λ_j}$ be its nodal set. Then $\mathcal H^{n-2} (\mathcal N_λ) \leq C_{g, Ω} λ.$ This proves a conjecture of F. H. Lin and K. Bellova.
We discuss a Steklov-type problem for Maxwell's equations which is related to an interior Calderón operator and an appropriate Dirichlet-to-Neumann type map. The corresponding Neumann-to-Dirichlet map turns out to be compact and this provides a Fourier basis of Steklov eigenfunctions for the associated energy spaces. With an approach similar to that developed by Auchmuty for the Laplace operator, we provide natural spectral representations for the appropriate trace spaces, for the Calderón operator itself and for the solutions of the corresponding boundary value problems subject to electric or…
Let $(Ω,g)$ be a compact, analytic Riemannian manifold with analytic boundary $\partial Ω= M.$ We give $L^2$-lower bounds for Steklov eigenfunctions and their restrictions to interior hypersurfaces $H \subset Ω^{\circ}$ in a geometrically defined neighborhood of $M$. Our results are optimal in the entire geometric neighborhood and complement the results on eigenfunction upper bounds in the author's previous work.
Let $(Ω,g)$ be a compact, real-analytic Riemannian manifold with real-analytic boundary $\partial Ω.$ The harmonic extensions of the boundary Dirchlet-to-Neumann eigenfunctions are called Steklov eigenfunctions. We show that the Steklov eigenfuntions decay exponentially into the interior in terms of the Dirichlet-to-Neumann eigenvalues and give a sharp rate of decay to first order at the boundary. The proof uses the Poisson representation for the Steklov eigenfunctions combined with sharp $h$-microlocal concentration estimates for the boundary Dirichlet-to-Neumann eigenfunctions near the cosph…
The exterior Steklov problem for Euclidean domains
研究欧几里得外部区域上的Steklov特征值问题，给出多种等价表述，并证明凸域上第一外部Steklov特征值的Escobar型下界，该下界由边界主曲率表示且对球达到最优。
Closed nodal lines and interior hot spots of the second eigenfunction of the Laplacian on surfaces
我们在总面积固定的单位圆盘上建立了一个单参数S^{1}-不变度量族，其中Laplace算子的第二本征值在Neumann和Dirichlet边界条件下都是简单的，并且有一个具有封闭节线的本征函数.在Neumann边界条件下，我们还证明了该特征函数在一个内点处达到极大值，从而为单连通曲面上的热点猜想提供了一个反例.这是一个更强的结果，在这个家庭的度量任何给定的（有限）数量的S^{1}不变的特征值可以是任意小，而非不变的频谱变得任意大。
We obtain upper and lower bounds for Steklov eigenvalues of submanifolds with prescribed boundary in Euclidean space. A very general upper bound is proved, which depends only on the geometry of the fixed boundary and on the measure of the interior. Sharp lower bounds are given for hypersurfaces of revolution with connected boundary: we prove that each eigenvalue is uniquely minimized by the ball. We also observe that each surface of revolution with connected boundary is isospectral to the disk.
We study oscillations in the eigenfunctions for a fractional Schrödinger operator on the real line. An argument in the spirit of Courant's nodal domain theorem applies to an associated local problem in the upper half plane and provides a bound on the number of nodal domains for the extensions of the eigenfunctions. Using the combinatorial properties of noncrossing partitions, we turn the nodal domain bound into an estimate for the number of sign changes in the eigenfunctions. We discuss applications in the periodic setting and the Steklov problem on planar domains.
Let $ Ω\subset R^2$ be a bounded piecewise smooth domain and $ϕ_λ$ be a Neumann (or Dirichlet) eigenfunction with eigenvalue $λ^2$ and nodal set ${ N}_{ϕ_λ} = {x \in Ω; ϕ_λ(x) = 0}.$ Let $H \subset Ω$ be an interior $C^ω$ curve. Consider the intersection number $$ n(λ,H):= \# (H \cap N_{ϕ_λ} ).$$ We first prove that for general piecewise-analytic domains, and under an appropriate "goodness" condition on $H$, $$ n(λ,H) = {\mathcal O}_H(λ) (*)$$ as $λ\rightarrow \infty.$ We then prove that the bound in $(*)$ is satisfied in the case of quantum ergodic (QE) sequences of interior eigenfunctions, p…
Lower bounds for the low Steklov eigenvalues
针对具有 b 个边界分支的紧致连通可定向黎曼流形，通过迹不等式和边界环的电阻解释，获得了低 Steklov 特征值（σ_k, 1≤k≤b-1）的几何下界，揭示了内部几何对低特征值的影响。
We consider a Laplace eigenfunction $φ_λ$ on a smooth closed Riemannian manifold, that is, satisfying $-Δφ_λ= λφ_λ$. We introduce several observations about the geometry of its vanishing (nodal) set and corresponding nodal domains. First, we give asymptotic upper and lower bounds on the volume of a tubular neighbourhood around the nodal set of $φ_λ$. This extends previous work of Jakobson and Mangoubi in case $ (M, g) $ is real-analytic. A significant ingredient in our discussion are some recent techniques due to Logunov (cf. \cite{L1}). Second, we exhibit some remarks related to the asymptoti…
Functional Inequalities for doubly weighted Brownian Motion with Sticky-Reflecting Boundary Diffusion
本文研究了具有粘性反射边界的流形上双重加权布朗运动的Poincaré和Logarithmic Sobolev常数上界，采用能量交互和加权Reilly公式进行插值分析，同时得到Steklov特征值和边界迹算子的上界。
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