Yucheng Tu
We prove an sharp anisotropic isoperimetric inequality for a domain outside an Euclidean ball in $\mathbb{R}^n$ for $n\geq 2$. The proof applies the ABP method to a Neumann boundary value problem.
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We settle the case of equality for the relative isoperimetric inequality outside any arbitrary convex set with not empty interior.
Quantitative estimates for the relative isoperimetric problem and its gradient flow outside convex bodies in the plane
本文研究了平面中凸体外的相对等周问题，提出了三个定量结果，包括临界点的刚性估计、梯度流收敛速率以及最小化问题的稳定性，首次采用流方法证明稳定性。
We show the counter-intuitive fact that some weighted isoperimetric problems on the half-space $ \mathbb{R}^N _+ $, for which half-balls centered at the origin are stable, have no solutions. A particular case is the measure $dμ= x_N ^{α} \, dx$, with $α\in (-1,0)$. Some results on stability and nonexistence for weighted isoperimetric problems on $\mathbb{R}^N $ are also obtained.
In this note we present the solution of some isoperimetric problems in open convex cones of $\R^n$ in which perimeter and volume are measured with respect to certain nonradial weights. Surprisingly, Euclidean balls centered at the origin (intersected with the convex cone) minimize the isoperimetric quotient. Our result applies to all nonnegative homogeneous weights satisfying a concavity condition in the cone. When the weight is constant, the result was established by Lions and Pacella in 1990.
The weighted isoperimetric inequality and Sobolev inequality outside convex sets
利用λ_w-ABP方法建立凸集外的加权毛细等周不等式，并基于此发展毛细Schwarz对称化技术，证明加权Pólya-Szegö原理和尖锐加权毛细Sobolev不等式，推广了半空间上的加权Sobolev不等式。
The isoperimetric inequality for the capillary energy outside convex sets
该研究解决了任意接触角下凸集外毛细曲面的等周问题，证明了支撑在凸集上的曲面毛细能量大于同条件平面球冠的能量，推广了Choe-Ghomi-Ritoré不等式。
The minimizers of the anisotropic fractional isoperimetric inequality with respect to the convex body $K$ in $\mathbb{R}^n$ are shown to be equivalent to star bodies whenever $K$ is strictly convex and unconditional. From this a Pólya-Szegö principle for anisotropic fractional seminorms is derived by using symmetrization with respect to star bodies.
Isoperimetric inequalities and spectral consequences in warped product manifolds
研究扭曲积流形上的中心等周不等式，推导几何条件并改进Cheeger不等式，得出极小正特征值的下界。
Bifurcations in Isoperimetric Problems with Nonlocal Interactions
研究基于液滴模型的等周问题，探讨非局部相互作用下的分岔现象，发现非球形解在球体家族中分岔，体积可无限大，而其他区域无分岔。
The isoperimetric inequality for the capillary energy outside convex cylinders
本文研究了凸无限圆柱外具有一般接触角的毛细管表面的等周问题，证明了凸圆柱上任意表面的毛细管能量严格大于同体积同接触角的球冠能量，首次将 Choe-Ghomi-Ritoré 相对等周不等式从直角情形推广到一般角度。
Stability of the ball in isoperimetric inequalities between two fractional perimeters
研究在s-周长和t-周长之间等周不等式中，球作为近球集的局部极小值问题，通过将F函数表示为参数函数u的泛函，并证明其关于Sobolev范数的稳定性结果。
We characterize the volume-constrained minimizers of a nonlocal free energy given by the difference of the $t$-perimeter and the $s$-perimeter, with $s$ smaller than $t$. Exploiting the quantitative fractional isoperimetric inequality, we show that balls are the unique minimizers if the volume is sufficiently small, depending on $t-s$, while the existence vs. nonexistence of minimizers for large volumes remains open. We also consider the corresponding isoperimetric problem and prove existence and regularity of minimizers for all $s,\,t$. When $s=0$ this problem reduces to the fractional isoper…
} In this article, we put forward a Neumann eigenvalue problem for the bi-harmonic operator $Δ^2$ on a bounded smooth domain $\Om$ in the Euclidean $n$-space ${\bf R}^n$ ($n\ge2$) and then prove that the corresponding first non-zero eigenvalue $Υ_1(\Om)$ admits the isoperimetric inequality of Szegö-Weinberger type: $Υ_1(\Om)\le Υ_1(B_{\Om})$, where $B_{\Om}$ is a ball in ${\bf R}^n$ with the same volume of $\Om$. The isoperimetric inequality of Szegö-Weinberger type for the first nonzero Neumann eigenvalue of the even-multi-Laplacian operators $Δ^{2m}$ ($m\ge1$) on $\Om$ is also exploited.
We consider a variational problem involving competition between surface tension and charge repulsion. We show that, as opposed to the case of weak (short-range) interactions where we proved ill-posedness of the problem in a previous paper, when the repulsion is stronger the perimeter dominates the capacitary term at small scales. In particular we prove existence of minimizers for small charges as well as their regularity. Combining this with the stability of the ball under small $C^{1,γ}$ perturbations, this ultimately leads to the minimality of the ball for small charges. We cover in particul…
Weighted isoperimetric ratios and extension problems for fractional conformal Laplacians
本研究建立了加权等周问题与分数阶共形拉普拉斯算子延拓问题的关联，推导了半空间与单位球上加权泊松积分的精确不等式并分类极值，构造CCE流形上的加权等周变分问题并证明其与Chang-González延拓的联系，给出极值存在准则并提出猜想。
The Euclidean mixed isoperimetric-isodiametric inequality states that the round ball maximizes the volume under constraint on the product between boundary area and radius. The goal of the paper is to investigate such mixed isoperimetric-isodiametric inequalities in Riemannian manifolds. We first prove that the same inequality, with the sharp Euclidean constants, holds on Cartan-Hadamard spaces as well as on minimal submanifolds of $\mathbb{R}^n$. The equality cases are also studied and completely characterized; in particular, the latter gives a new link with free boundary minimal submanifolds …
Isoperimetric and Michael-Simon inequalities on manifolds with asymptotically nonnegative curvature
该研究在渐近非负曲率流形上证明等周不等式成立，在紧集外非负曲率流形上推导Michael-Simon不等式，采用ABP方法并结合几何与谱性质完成证明，拓展了相关不等式的适用条件。
We prove the stability of the ball as global minimizer of an attractive shape functional under volume constraint, by means of mass transportation arguments. The stability exponent is $1/2$ and it is sharp. Moreover, we use such stability result together with the quantitative (possibly fractional) isoperimetric inequality to prove that the ball is a global minimizer of a shape functional involving both an attractive and a repulsive term with a sufficiently large fixed volume and with a suitable (possibly fractional) perimeter penalization.
We consider isoperimetric problem with a nonlocal repulsive term given by the Newtonian potential. We prove that regular critical sets of the functional are analytic. This optimal regularity holds also for critical sets of the Ohta-Kawasaki functional. We also prove that when the strength of the nonlocal part is small the ball is the only possible stable critical set.
We prove some old and new isoperimetric inequalities with the best constant using the ABP method applied to an appropriate linear Neumann problem. More precisely, we obtain a new family of sharp isoperimetric inequalities with weights (also called densities) in open convex cones of $\mathbb{R}^n$. Our result applies to all nonnegative homogeneous weights satisfying a concavity condition in the cone. Remarkably, Euclidean balls centered at the origin (intersected with the cone) minimize the weighted isoperimetric quotient, even if all our weights are nonradial ---except for the constant ones. W…
Let $Ω$ be a bounded $C^{2}$ domain in $\R^n$, and let $Ω^{\ast}$ be the Euclidean ball centered at 0 and having the same Lebesgue measure as $Ω$. Consider the operator $L=-÷(A\nabla)+v\cdot \nabla +V$ on $Ω$ with Dirichlet boundary condition. We prove that minimizing the principal eigenvalue of $L$ when the Lebesgue measure of $Ω$ is fixed and when $A$, $v$ and $V$ vary under some constraints is the same as minimizing the principal eigenvalue of some operators $L^*$ in the ball $Ω^*$ with smooth and radially symmetric coefficients. The constraints which are satisfied by the original coefficie…
We prove an isoperimetric inequality of the Rayleigh-Faber-Krahn type for a nonlinear generalization of the first twisted Dirichlet eigenvalue. More precisely, we show that the minimizer among sets of given volume is the union of two equal balls.
We give a complete characterization of all isoperimetric sets contained in a domain of the Euclidean plane, that is bounded by a Jordan curve and satisfies a no-neck property. Further, we prove that the isoperimetric profile of such domain is convex above the volume of the largest ball contained in it, and that its square is globally convex.
A weighted relative isoperimetric inequality in convex cones is obtained via the Monge-Ampere equation. The method improves several inequalities in the literature, e.g. constants in a theorem of Cabre--Ros--Oton--Serra. Applications are given in the context of a generalization of the log-convex density conjecture due to Brakke and resolved by Chambers: in the case of $α-$homogeneous ($α>0$), concave densities, (mod translations) balls centered at the origin and intersected with the cone are proved to uniquely minimize the weighted perimeter with a weighted mass constraint. In particular, if th…
A spectral isoperimetric inequality on the n-sphere for the Robin-Laplacian with negative boundary parameter
本文研究带负边界参数的Robin-Laplacian在n维球面上的谱等周问题，证明固定周长小于半球周长时测地球最大化第一Robin特征值，并给出基于体积差的定量稳定性结果。
The aim of this paper is to prove the existence of minimizers for a variational problem involving the minimization under volume constraint of the sum of the perimeter and a non-local energy of Wasserstein type. This extends previous partial results to the full range of parameters. We also show that in the regime where the perimeter is dominant, the energy is uniquely minimized by balls.
In this paper we prove the existence of a maximum for the first Steklov-Dirichlet eigenvalue in the class of convex sets with a fixed spherical hole under volume constraint. More precisely, if $Ω=Ω_0 \setminus \bar{B}_{R_1}$, where $B_{R_1}$ is the ball centered at the origin with radius $R_1>0$ and $Ω_0\subset\mathbb{R}^n$, $n\geq 2$, is an open bounded and convex set such that $B_{R_1}\Subset Ω_0$, then the first Steklov-Dirichlet eigenvalue $σ_1(Ω)$ has a maximum when $R_1$ and the measure of $Ω$ are fixed. Moreover, if $Ω_0$ is contained in a suitable ball, we prove that the spherical shel…
In this paper we first introduce quermassintegrals for free boundary hypersurfaces in the $(n+1)$-dimensional Euclidean unit ball. Then we solve some related isoperimetric type problems for convex free boundary hypersurfaces, which lead to new Alexandrov-Fenchel inequalities. In particular, for $n=2$ we obtain a Minkowski-type inequality and for $n=3$ we obtain an optimal Willmore-type inequality. To prove these estimates, we employ a specifically designed locally constrained inverse harmonic mean curvature flow with free boundary.
Let $c, k_1,..., k_N $ be non-negative numbers, and define a measure $μ$ in the wedge $W:= \{x\in \mathbb{R} ^N :\, x_i >0, i=1,...,N\} $ by $dμ= e^{c|x|^2} x_1 ^{k_1}...x_N ^{k_N} \, dx $. It is shown that among all measurable subsets of $W$ with fixed $μ$ -measure, the intersection of $W$ with a ball centered at the origin renders the weighted perimeter relative to $W$ a minimum.
On Poincaré constants related to isoperimetric problems in convex bodies
本文研究凸体中庞加莱常数的下界估计，通过引入刻画区域平坦程度的额外项细化 Acosta-Duran 不等式，并在二维情形给出以直径和内切圆半径表示的精确 Bonnesen 型不等式，同时证明球在定宽凸体中最大化庞加莱常数。
We study the optimal constant in a Sobolev inequality for BV functions with zero mean value and vanishing outside a bounded open set. We are interested in finding the best possible embedding constant in terms of the measure of the domain alone. We set up an optimal shape problem and we completely characterize the behavior of optimal domains.
Among all $C^{\infty}$ bounded domains with equal volume, we show that the second eigenvalue of the Robin plate is uniquely maximized by an open ball, so long as the Robin parameter lies within a particular range of negative values. Our methodology combines recent techniques introduced by Freitas and Laugesen to study the second eigenvalue of the Robin membrane problem and techniques employed by Chasman to study the free plate problem. In particular, we choose eigenfunctions of the ball as trial functions in the Rayleigh quotient for a general domain; such eigenfunctions are comprised of ultra…
First Eigenvalue and Torsional Rigidity: Isoperimetric Inequalities for the Fractional Laplacian
本文研究了分数阶拉普拉斯算子在等周不等式中的性质，证明了在具有相同扭刚度的集合中，球体是第一特征值最小的集合，并建立了相关反Holder不等式。
An isoperimetric inequality for the second Robin eigenvalue of the Weighted Laplacian
本文证明在特定条件下，球体是最大化加权拉普拉斯算子第二罗宾特征值的最优形状。
Let D be a bounded domain in n-dimensional Euclidean space, where n>2, and let 1<p< (2n)/(n-2). We prove a reverse-Holder inequality for functions realizing equality in the Sobolev inequality, which finds a lower bound for their (p-1)-norm in terms of their p-norm. This inequality is sharp, and it is an equality if and only if the domain is a round ball. Our result generalizes a theorem of Payne and Rayner and our proof relies on integral rearrangements and an analysis of the ODE corresponding to the radial case.
The purpose of this note is to prove dispersive estimates for the wave equation outside a ball in R^d. If d = 3, we show that the linear flow satisfies the dispersive estimates as in R^3. In higher dimensions d $\ge$ 4 we show that losses in dispersion do appear and this happens at the Poisson spot.
We obtain a sharp quantitative isoperimetric inequality for nonlocal $s$-perimeters, uniform with respect to $s$ bounded away from $0$. This allows us to address local and global minimality properties of balls with respect to the volume-constrained minimization of a free energy consisting of a nonlocal $s$-perimeter plus a non-local repulsive interaction term. In the particular case $s =1$ the $s$-perimeter coincides with the classical perimeter, and our results improve the ones of Knüpfer and Muratov concerning minimality of balls of small volume in isoperimetric problems with a competition b…
Some isoperimetric inequalities involving the boundary momentum
本文研究涉及边界动量的等周不等式，在凸集类中证明了加权曲率积分泛函的上下界，强化了经典 Aleksandrov-Fenchel 不等式，并探讨了高维情形下边界动量泛函的形状优化问题，证明圆球在近球集类中是稳定的最大化子。
Global existence of spherically symmetry solutions for isothermal Euler-Poisson system outside a ball
本文针对用于建模奇异夸克星等致密星体的带自引力等温Euler-Poisson系统，借助分数阶Lax-Friedrichs格式与补偿紧性理论，证明了球外球对称全局熵解的存在性。
We develop further the theory of symmetrization of fractional Laplacian operators contained in recent works of two of the authors. The theory leads to optimal estimates in the form of concentration comparison inequalities for both elliptic and parabolic equations. In this paper we extend the theory for the so-called \emph{restricted} fractional Laplacian defined on a bounded domain $Ω$ of $\mathbb R^N$ with zero Dirichlet conditions outside of $Ω$. As an application, we derive an original proof of the corresponding fractional Faber-Krahn inequality. We also provide a more classical variational…
We consider spherically symmetric supercritical focusing wave equations outside a ball. Using mixed analytical and numerical methods, we show that the threshold for blowup is given by a codimension-one stable manifold of the unique static solution with exactly one unstable direction. We analyze in detail the convergence to this critical solution for initial data fine-tuned to the threshold.
This paper is concerned with volume-constrained minimization problems derived from Gamow's liquid drop model for the atomic nucleus, involving the competition of a perimeter term and repulsive nonlocal potentials. We consider a large class of potentials, given by general radial nonnegative kernels which are integrable on $\mathbb{R}^n$, such as Bessel potentials, and study the behavior of the problem for large masses (i.e., volumes). Contrarily to the small mass case, where the nonlocal term becomes negligible compared to the perimeter, here the nonlocal term explodes compared to it. However, …
In this note we prove that the ball is a maximiser of some Schatten $p$-norms of the Riesz potential operators among all domains of a given measure in $\mathbb R^{d}$. In particular, the result is valid for the polyharmonic Newton potential operator, which is related to a nonlocal boundary value problem for the poly-Laplacian extending the one considered by M. Kac in the case of the Laplacian, so we obtain and isoperimetric inequalities for its eigenvalues as well, namely, analogues of Rayleigh-Faber-Krahn and Hong-Krahn-Szegö inequalities.
In this article, we present two different approaches for obtaining quantitative inequalities in the context of parabolic optimal control problems. Our model consists of a linearly controlled heat equation with Dirichlet boundary condition $(u_f)_t-Δu_f=f$, $f$ being the control. We seek to maximise the functional $\mathcal J_T(f):=\frac12\int_{(0;T)\times Ω} u_f^2$ or, for some $ε>0$, $\mathcal J_T^ε(f):=\frac12\int_{(0;T)\times Ω} u_f^2+ε\int_Ωu_f^2(T,\cdot)$ and to obtain quantitative estimates for these maximisation problems. We offer two approaches in the case where the domain $Ω$ is a bal…
An isoperimetric inequality for twisted eigenvalues with one orthogonality constraint
研究带正交约束的扭曲特征值的等周不等式，证明其下界由两个特定半径的不相交球并集及bang-bang型正交函数唯一达到，并揭示与Dirichlet特征值最优形状的连续插值关系。
Sharp dynamical isoperimetric principle for mean curvature flow
本文为弱平均曲率流建立了尖锐动力等周原理，证明在初始面积固定的流中标准收缩球面唯一最大化消亡时间，并给出最优消亡时间估计及抛物测度等周不等式。
A stability result in terms of the perimeter is obtained for the first Dirichlet eigenvalue of the Laplacian operator. In particular, we prove that, once we fix the dimension $n\geq2$, there exists a constant $c>0$, depending only on $n$, such that, for every $Ω\subset\mathbb{R}^n$ open, bounded and convex set with volume equal to the volume of a ball $B$ with radius $1$, it holds \begin{equation*} λ_1(Ω)-λ_1(B)\geq c\left(P(Ω)-P(B) \right)^{2}, \end{equation*} where by $λ_1(\cdot)$ we denote the first Dirichlet eigenvalue of a set and by $P(\cdot)$ its perimeter. The hearth of the present pap…
In 1989 Almgren and Lieb proved a rearrangement inequality for the Sobolev spaces of fractional order $W^{s,p}$. The case $p = 2$ of their result implies the nonlocal isoperimetric inequality \[ \frac{P_s(E)}{|E|^{\frac{N-2s}N}} \ge \frac{P_s(B_1)}{|B_1|^{\frac{N-2s}N}},\ \ \ \ \ \ \ 0<s<1/2, \] where $P_s$ indicates the fractional $s$-perimeter, and $B_1$ is the unit ball in $\RN$. In this note we explicitly compute the best constant, and show that for any $0<s<1/2$, one has \[ \frac{P_s(B_1)}{|B_1|^{\frac{N-2s}N}} = \frac{N π^{\frac N2 + s} \G(1-2s)}{s \G(\frac N2+1)^{\frac{2s}N} \G(1-s)\G(\…
Isoperimetric bounds for the weighted Neumann and Steklov eigenvalues in dimensions three through six
该论文确定了三维至六维有界欧几里得域上质量归一化第一加权 Neumann 特征值和 Steklov 特征值的尖锐等周界，并解决了 Vinokurov 提出的问题 1.12。
Center stable manifolds for the radial semi-linear wave equation outside a ball
本文研究三维球外大指数幂型非线性波动方程，构造每个稳态解对应的中心稳定流形，完整刻画全局解动力学，并分析其附近解的行为。
We show that the solutions of the three-dimensional critical defocusing nonlinear wave equation with Neumann boundary conditions outside a ball and radial initial data scatter. This is to our knowledge the first result of scattering for a nonlinear wave equation with Neumann boundary conditions. Our proof uses the scheme of concentration-compactness/rigidity introduced by Kenig and Merle, extending it to our setup, together with the so-called channels of energy method to rule out compact-flow solutions. We also obtain, for the focusing equation, the same exact scattering/blow-up dichotomy belo…
We consider the problem of minimising the $k$th eigenvalue, $k \geq 2$, of the ($p$-)Laplacian with Robin boundary conditions with respect to all domains in $\mathbb{R}^N$ of given volume $M$. When $k=2$, we prove that the second eigenvalue of the $p$-Laplacian is minimised by the domain consisting of the disjoint union of two balls of equal volume, and that this is the unique domain with this property. For $p=2$ and $k \geq 3$, we prove that in many cases a minimiser cannot be independent of the value of the constant $α$ in the boundary condition, or equivalently of the volume $M$. We obtain …
Quantitative isoperimetric inequalities for classical capillarity problems
本文研究欧几里得半空间中带常数边界权重的毛细管等周问题，利用ABP型技巧给出尖锐等周不等式的新证明，并通过定量ABP方法与选择型论证相结合，建立了关于最优截断球的Fraenkel不对称性和边界接触部分不对称性的两个定量估计。
In this paper, we consider the initial-boundary value problems with several fundamental boundary conditions (the Dirichlet/Neumann/Robin boundary condition) for the multi-component system of semi-linear classical damped wave equations outside a ball. By applying a test function approach with a judicious choice of test functions, which approximates the harmonic functions being subject to these boundary conditions on $\partial Ω$, simultaneously we have succeeded in proving the blow-up result in a finite time as well as in catching the sharp upper bound of lifespan estimates for small solutions …
An isoperimetric inequality for Neumann eigenvalues with radial log-concave measures
该研究针对带径向对数凹测度的空间中原点对称Lipschitz区域，证明了Witten-Laplacian前n个非零Neumann特征值调和平均的尖锐等周不等式，扩展了此前的相关结果。
In constant curvatures spaces, there are a lot of characterizations of geodesic balls as optimal domain for shape optimization problems. Although it is natural to expect similar characterizations in rank one symmetric spaces, very few is known in this setting. In this paper we prove that, in a non-compact rank one symmetric space, the geodesic balls uniquely maximize the first Steklov eigenvalue among the domains of fixed volume, extending to this context a result of Brock in the Euclidean space. Then we show that a stability version of the ensuing Brock-Weinstock inequality holds. The idea be…
For any compact surface $Σ$ with smooth, non-empty boundary, we construct a free boundary minimal immersion into a Euclidean Ball $\mathbb{B}^N$ where $N$ is controlled in terms of the topology of $Σ$. We obtain these as maximizing metrics for the isoperimetric problem for the first non-trivial Steklov eigenvalue. Our main technical result concerns asymptotic control on eigenvalues in a delicate glueing construction which allows us to prove the remaining spectral gap conditions to complete the program by Fraser--Schoen and the second named author to obtain such mazimizing metrics. Our construc…
We study the dependence of the eigenvalues of time-harmonic Maxwell's equations in a cavity upon variation of its shape. The analysis concerns all eigenvalues both simple and multiple. We provide analyticity results for the dependence of the elementary symmetric functions of the eigenvalues splitting a multiple eigenvalue, as well as a Rellich-Nagy-type result describing the corresponding bifurcation phenomenon. We also address an isoperimetric problem and characterize the critical cavities for the symmetric functions of the eigenvalues subject to isovolumetric or isoperimetric domain perturba…
We study a defocusing semilinear wave equation, with a power nonlinearity $|u|^{p-1}u$, defined outside the unit ball of $\mathbb{R}^{n}$, $n\ge3$, with Dirichlet boundary conditions. We prove that if $p>n+4$ and the initial data are nonradial perturbations of large radial data, there exists a global smooth solution. The solution is unique among energy class solutions satisfying an energy inequality. The main tools used are the Penrose transform and a pointwise decay estimate for the exterior linear wave equation perturbed with a large, time dependent potential.
We prove a sharp upper bound and a lower bound for the first nonzero eigenvalue of the Wentzell-Laplace operator on compact manifolds with boundary and an isoperimetric inequality for the same eigenvalue in the case where the manifold is a bounded domain in a Euclidean space. We study some fourth order Stekolv problems and obtain isoperimetric upper bound for the first eigenvalue of them. We also find all the eigenvalues and eigenfunctions for two kind of fourth order Stekolv problems on a Euclidean ball.
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