Ben Sharp, Peter Topping
We derive a selection of energy estimates for a generalisation of a critical equation on the unit disc in $\mathbb{R}^2$ introduced by Rivière. Applications include sharp regularity results and compactness theorems which generalise a large amount of previous geometric PDE theory, including some of the theory of harmonic and almost-harmonic maps from surfaces.
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This paper is concerned with the quantitative homogenization of the steady Stokes equations with the Dirichlet condition in a periodically perforated domain. Using a compactness method, we establish the large-scale interior $C^{1, α}$ and Lipschitz estimates for the velocity as well as the corresponding estimates for the pressure. These estimates, when combined with the classical regularity estimates for the Stokes equations, yield the uniform Lipschitz estimates. As a consequence, we also obtain the uniform $W^{k, p}$ estimates for $1<p<\infty$.
In a previous paper we developed a regularity and compactness theory in Euclidean ambient spaces for codimension 1 weakly stable CMC integral varifolds satisfying two (necessary) structural conditions. Here we generalize this theory to the setting where the mean curvature (of the regular part of the varifold) is prescribed by a given $C^{1, α}$ ambient function $g$ and the ambient space is a general $(n+1)$-dimensional Riemannian manifold; we give general conditions that imply that the support of the varifold, away from a possible singular set of dimension $\leq n-7,$ is the image of a $C^{2}$…
We give two structural conditions on a codimension $1$ integral $n$-varifold with first variation locally summable to an exponent $p>n$ that imply the following: whenever each orientable portion of the $C^{1}$-embedded part of the varifold (which is non-empty by the Allard regularity theory) is stationarity and the $C^{2}$-immersed part of it is stable with respect to the area functional for volume preserving deformations, its support, except possibly on a closed set of codimension $7$, is an immersed constant-mean-curvature (cmc) hypersurface of class $C^{2}$ that can fail to be embedded only…
Regularity and compactness for critical points of degenerate polyconvex energies
该研究针对二维退化多凸能的Lipschitz临界点，证明其雅可比行列式为常数，且近似临界点序列的雅可比行列式强收敛，解决了2003年的一个公开数学问题。
In this paper the method of compensated compactness is applied to the problem of isometric immersion of a two dimensional Riemannian manifold with negative Gauss curvature into three dimensional Euclidean space. Previous applications of the method to this problem have required decay of order $t^{-4}$ in the Gauss curvature. Here we show that the decay of Hong $t^{-2-δ/2}$ where $δ\in(0,4)$ suffices.
Regularity and compactness theory of stable free-boundary minimal hypersurfaces
本文建立了稳定自由边界极小超曲面的Schoen-Simon正则性与紧性理论，通过倾斜函数的ε-正则性和De Giorgi迭代证明层片定理，并推广了自由边界Almgren-Pitts存在性理论到任意维数。
Degenerate parabolic equations -- compactness and regularity of solutions
本文提出一种新方法，通过动力学公式化约化，解决了退化抛物方程熵解的正则性与紧性问题，并证明了非齐次情形弱解的存在性。
In 1996, Shi generalized the epsilon-regularity theorem of Schoen and Uhlenbeck to energy-minimizing harmonic maps from a domain equipped with a bounded measurable Riemannian metric. In the present work we prove a compactness result for such energy-minimizing maps. As an application, we combine our result with Shi's theorem to give an improved bound on the Hausdorff dimension of the singular set, assuming that the map has bounded energy at all scales. This last assumption can be removed when the target manifold is simply-connected.
Quantitative regularity for minimizing intrinsic fractional harmonic maps
本文研究极小化内蕴分数阶调和映射，结合修正Luckhaus引理与定量分层理论证明紧性、奇异集体积估计及改进的维数界。
Some recent developments on isometric immersions via compensated compactness and gauge transforms
本文通过补偿紧致性和规范变换技术，探讨了低正则性下等距浸入问题的分析发展，包括高斯-科达齐-里希方程的弱连续性和子流形理论基本定理。
Given any strictly convex norm $\|\cdot\|$ on $\mathbb{R}^2$ that is $C^1$ in $\mathbb{R}^2\setminus\{0\}$, we study the generalized Aviles-Giga functional \[I_ε(m):=\int_Ω \left(ε\left|\nabla m\right|^2 + \frac{1}ε\left(1-\|m\|^2\right)^2\right) \, dx,\] for $Ω\subset\mathbb R^2$ and $m\colonΩ\to\mathbb R^2$ satisfying $\nabla\cdot m=0$. Using, as in the euclidean case $\|\cdot\|=|\cdot|$, the concept of entropies for the limit equation $\|m\|=1$, $\nabla\cdot m=0$, we obtain the following. First, we prove compactness in $L^p$ of sequences of bounded energy. Second, we prove rigidity of zero-…
In this paper we develop some new techniques to study the multiscale elliptic equations in the form of $-\text{div} \big(A_\varepsilon \nabla u_{\varepsilon} \big) = 0$, where $A_\varepsilon(x) = A(x, x/\varepsilon_1,\cdots, x/\varepsilon_n)$ is an $n$-scale oscillating periodic coefficient matrix, and $(\varepsilon_i)_{1\le i\le n}$ are scale parameters. We show that the $C^α$-Hölder continuity with any $α\in (0,1)$ for the weak solutions is stable, namely, the constant in the estimate is uniform for arbitrary $(\varepsilon_1, \varepsilon_2, \cdots, \varepsilon_n) \in (0,1]^n$ and particularl…
In this paper we establish a number of implications between various qualitative and quantitative versions of the global regularity problem for the Navier-Stokes equations, in the periodic, smooth finite energy, smooth $H^1$, Schwartz, or mild $H^1$ categories, and with or without a forcing term. In particular, we show that if one has global well-posedness in $H^1$ for the periodic Navier-Stokes problem with a forcing term, then one can obtain global regularity both for periodic and for Schwartz initial data (thus yielding a positive answer to both official formulations of the problem for the C…
An extrapolation result in the variational setting: improved regularity, compactness, and applications to quasilinear systems
本文在 Gelfand 三元组上的 SPDE 变分框架中，利用线性强制对的对称性将时间 $L^2$ 估计外推至 $L^p$（$p>2$）估计，并基于紧嵌入得到普适紧性结果，进而证明二阶拟线性方程组弱解的全局存在性。
A wedge product theorem of compensated compactness theory with critical exponents on Riemannian manifolds
本文研究了黎曼流形上弱收敛微分形式楔积的极限行为，提出并证明了补偿紧致性定理，扩展了Briane等人的div-curl引理，探讨了Gauss-Codazzi-Ricci方程和等距浸入的L^p外几何弱连续性。
Weak Continuity of the Cartan Structural System and Compensated Compactness on Semi-Riemannian Manifolds with Lower Regularity
研究半黎曼流形上低正则性Cartan结构系统的弱连续性，推导其L^p弱连续性并构造等距浸入。
Rough Axisymmetric Euler Dynamics: Global Energy Compactness and Kinetic Passage Across Regularity Breakdown
该研究建立了粗糙轴对称欧拉流的全局能量紧性，并利用它构造了碰撞动力学方程的流体动力学极限，实现了跨越欧拉正则性破缺的能量守恒延拓。
In this paper, we extend the uniform regularity estimates obtained by M. Avellanda and F. Lin in the paper of Compactness methods in the theory of homogenization (Comm. Pure Appl. Math. 40(1987), no.6, 803-847) to the more general second order elliptic systems in divergences form, with rapidly oscillating periodic coefficients. We establish not only sharp $W^{1,p}$ estimates, Holder estimates, Lipschitz estimates and non-tangential maximal function estimates for the Dirichelt problem on a $C^{1,η}$ domain, but also a sharp $O(\varepsilon)$ convergence rate in $H_0^1(Ω)$ by virtue of the Dirich…
We prove global regularity, scattering and a priori bounds for the energy critical Maxwell-Klein-Gordon equation relative to the Coulomb gauge on (1+4)-dimensional Minkowski space. The proof is based upon a modified Bahouri-Gerard profile decomposition [1] and a concentration compactness/rigidity argument by Kenig-Merle [10], following the method developed by the first author and Schlag [20] in the context of critical wave maps.
We prove boundary regularity and a compactness result for parabolic nonlocal equations of the form $u_t-Iu=f$, where the operator $I$ is not necessarily translation invariant. As a consequence of this and the regularity results for translation invariant case, we obtain $C^{1,α}$ interior estimates in space for non translation invariant operators under some hypothesis on the time regularity of the boundary data.
Partial Regularity of Navier-Stokes Equations
本文用几何方法结合新的紧性引理与调和函数单调性，证明了Navier-Stokes方程的解在Hausdorff维数1的集合外正则。
The Fractional-Logarithmic Laplacian: Potentials, Regularity, and Critical Compact Embeddings
本文研究分数-对数拉普拉斯算子的势理论和正则性，探讨其临界紧嵌入性质，提出新的对数Bessel空间，并讨论其与经典Bessel空间的关系。
By means of the concentrated compactness method of Bahouri-Gerard and Kenig-Merle, we prove global existence and regularity for wave maps with smooth data and large energy from 2+1 dimensions into the hyperbolic plane. The argument yields an apriori bound of the Coulomb gauged derivative components of our wave map relative to a suitable norm (which holds the solution) in terms of the energy alone. As a by-product of our argument, we obtain a phase-space decomposition of the gauged derivative components analogous to the one of Bahouri-Gerard.
Regularity criteria for the surface growth model with a forcing term
本文通过紧致性方法，建立了一类合适弱解的正则性准则，表明解的Hölder正则性可通过若干尺度不变量的小性条件得出，并得到奇异集的一维双抛物面测度为零的局部正则性结果。
We consider the fully nonlinear equation with variable-exponent double phase type degeneracies $$ \big[|Du|^{p(x)}+a(x)|Du|^{q(x)}\big]F(D^2u)=f(x). $$ Under some appropriate assumptions, by making use of geometric tangential methods and combing a refined improvement-of-flatness approach with compactness and scaling techniques we obtain the sharp local $C^{1,α}$ regularity of viscosity solutions to such equations.
We consider a family of second-order parabolic systems in divergence form with rapidly oscillating and time-dependent coefficients, arising in the theory of homogenization. We obtain uniform interior $W^{1,p}$, Hölder, and Lipschitz estimates as well as boundary $W^{1,p}$ and Hölder estimates, using compactness methods. As a consequence, we establish uniform $W^{1,p}$ estimates for the initial-Dirichlet problems in $C^{1}$ cylinders.
Compactness of solutions to the Yamabe problem. III
对于10维或11维非局部共形平坦紧致黎曼流形上Yamabe方程的爆破解序列，我们建立了爆破点附近渐近轮廓的精确估计，以及爆破点处Weyl张量及其共变导数的精确衰减估计.如果正质量定理在10维和11维中成立，这些估计将意味着Yamabe方程在这样的流形上的解集的紧性。
We prove that there exists an interval of time which is uniform in the vanishing viscosity limit and for which the Navier-Stokes equation with Navier boundary condition has a strong solution. This solution is uniformly bounded in a conormal Sobolev space and has only one normal derivative bounded in $L^\infty$. This allows to get the vanishing viscosity limit to the incompressible Euler system from a strong compactness argument.
Interior pointwise regularity for elliptic and parabolic equations in divergence form and applications to nodal sets
本文利用紧性方法与扰动技术证明散度型椭圆和抛物方程弱解的最优内部逐点 $C^{k,\alpha}$ 正则性，并将其用于刻画解的节点集结构。
A Variational Theory for The Area of Legendrian Surfaces
该研究提出Legendrian约束下曲面面积的新临界点概念PHSLVs，建立其紧性与最优正则性，推广Schoen-Wolfson理论，并证明两个变分存在性结果。
This work addresses an extension of the Aubin-Lions-Simon compactness result to generalized Bochner spaces $L^2(0,T;H(t))$, where $H(t)$ is a family of Hilbert spaces, parameterized by $t$. A compactness result of this type is needed in the study of the existence of weak solutions to nonlinear evolution problems governed by partial differential equations defined on moving domains. We identify the conditions on the regularity of the domain motion in time under which our extension of the Aubin-Lions-Simon compactness result holds. Concrete examples of the application of the compactness theorem a…
$C^{1, α}$-regularity for functions in solution classes and its application to parabolic normalized $p$-Laplace equations
本文在椭圆性常数足够接近时证明解类函数的全局$C^{1, α}$正则性，并借助紧性论证与迭代过程，将其应用于$p$接近2时的抛物型规范化$p$-Laplace方程，得到全局正则性结果。
In this paper, we establish $C^{1, α}$ regularity upto the boundary for a class of degenerate fully nonlinear elliptic equations with Neumann boundary conditions. Our main result Theorem 2.1 constitutes the boundary analogue of the interior $C^{1, α}$ regularity result established in [21] for equations with similar structural assumptions. The proof of our main result is achieved via compactness arguments combined with new boundary Hölder estimates for equations which are uniformly elliptic when the gradient is either small or large.
Existence and higher regularity of statistically steady states for the stochastic Coleman-Gurtin equation
本文研究受加性高斯噪声扰动的带记忆半线性Volterra方程，证明其存在不变测度，并通过引入适应记忆核的函数空间恢复紧性，进而利用Lyapunov结构证明统计稳态具有更高正则性。
In this paper, we investigate the Sobolev regularity for mean-field games in the whole space $\Rr^d$. This is achieved by combining integrability for the solutions of the Fokker-Planck equation with estimates for the Hamilton-Jacobi equation in Sobolev spaces. To avoid the mathematical challenges posed due to the lack of compactness, we prove an entropy dissipation estimate for the adjoint variable. This, together with the non-linear adjoint method, yields uniform estimates for solutions of the Hamilton-Jacobi equation in $W^{1,p}_{loc}(\Rr^d)$.
We study the inviscid limit of the free boundary Navier-Stokes equations. We prove the existence of solutions on a uniform time interval by using a suitable functional framework based on Sobolev conormal spaces. This allows us to use a strong compactness argument to justify the inviscid limit. Our approach does not rely on the justification of asymptotic expansions. In particular, we get a new existence result for the Euler equations with free surface from the one for Navier-Stokes.
In this paper, we prove borderline gradient continuity of viscosity solutions to Fully nonlinear elliptic equations at the boundary of a $C^{1,\dini}$-domain. Our main result Theorem 3.1 is a sharpening of the boundary gradient estimate proved by Ma-Wang following the borderline interior gradient regularity estimates established Daskalopoulos-Kuusi-Mingione. We however mention that, differently from the approach in the interior case which depends on $W^{1,q}$ estimates, our proof is slightly more geometric and is based on compactness arguments inspired by the techniques in the fundamental work…
Concentration-compactness via profile decomposition for systems of coupled Schrödinger equations of Hamiltonian type
本文针对非紧群不变的 Hamiltonian 型耦合 Schrödinger 方程组，利用弱轮廓分解的集中紧性、反演约化与极小极大变分方法证明基态存在性，并给出正则性、Pohozaev 恒等式及一类 Lane-Emden 系统的无解结果。
In this note we give a proof of the Sobolev and Morrey embedding theorems based on the representation of functions in terms of the fundamental solution of suitable partial differential operators. We also prove the compactness of the Sobolev embedding. We first describe this method in the classical setting, where the fundamental solution of the Laplace equation is used, to recover the classical Sobolev and Morrey theorems. We next consider degenerate Kolmogorov equations. In this case, the fundamental solution is invariant with respect to a non-Euclidean translation group and the usual convolut…
On the compactness of artificial compressibility approximations of weak solutions for fluid problems in deforming domains
本文针对变形域上牛顿流体的人工可压缩逼近，证明了独立于可压缩参数的弱解时间积分等度连续性，为可压缩性消失时的收敛提供了替代紧致性论证。
Dissipative hyperbolic systems of \textit{regularity-loss} have been recently received increasing attention. Usually, extra higher regularity is assumed to obtain the optimal decay estimates, in comparison with that for the global-in-time existence of solutions. In this paper, we develop a new frequency-localization time-decay property, which enables us to overcome the technical difficulty and improve the minimal decay-regularity for dissipative systems. As an application, it is shown that the optimal decay rate of $L^1(\mathbb{R}^3)$-$L^2(\mathbb{R}^3)$ is available for Euler-Maxwell equation…
Due to the dissipative structure of \textit{regularity-loss}, extra higher regularity than that for the global-in-time existence is usually imposed to obtain the optimal decay rates of classical solutions to dissipative systems. The aim of this paper is to seek the lowest regularity index for the optimal decay rate of $L^{1}(\mathbb{R}^n)$-$L^2(\mathbb{R}^n)$. Consequently, a notion of minimal decay regularity for dissipative systems of regularity-loss is firstly proposed. To do this, we develop a new time-decay estimate of $L^p(\mathbb{R}^n)$-$L^{q}(\mathbb{R}^n)$-$L^{r}(\mathbb{R}^n)$ type b…
We consider a function U satisfying a degenerate elliptic equation on (0,+\infty)\times R^N with mixed Dirichlet-Neumann boundary conditions. The Neumann condition is prescribed on a bounded domain Ω\subset R^N of class C^{1;1}, whereas the Dirichlet data is on the exterior of Ω. We prove Holder regularity estimates of U/d^s, where d is a distance function defined as d(z) := dist(z;R^N\setminusΩ), for z\in (0,+\infty)\times R^N. The degenerate elliptic equation arises from the Caffarelli-Silvestre extension of the Dirichlet problem for the fractional Laplacian. Our proof relies on compactness…
We establish uniform with respect to the Mach number regularity estimates for the isentropic compressible Navier-Stokes system in smooth domains with Navier-slip condition on the boundary in the general case of ill-prepared initial data. To match the boundary layer effects due to the fast oscillations and the ill-prepared initial data assumption, we prove uniform estimates in an anisotropic functional framework with only one normal derivative close to the boundary. This allows to prove the local existence of a strong solution on a time interval independent of the Mach number and to justify the…
We establish $C^{σ+α}$ interior estimates for concave nonlocal fully nonlinear equations of order $σ\in(0,2)$ with rough kernels. Namely, we prove that if $u\in C^α(\mathbb R^n)$ solves in $B_1$ a concave translation invariant equation with kernels in $\mathcal L_0(σ)$, then $u$ belongs to $C^{σ+α}(\overline{ B_{1/2}})$, with an estimate. More generally, our results allow the equation to depend on $x$ in a $C^α$ fashion. Our method of proof combines a Liouville theorem and a blow-up (compactness) procedure. Due to its flexibility, the same method can be useful in different regularity proofs fo…
This paper is concerned with the existence and regularity of global attractor $\mathcal A$ for a Kirchhoff wave equation with strong damping and memory in the weighted time-dependent spaces $\mathcal H$ and $\mathcal H^{1}$, respectively. In order to obtain the existence of $\mathcal A$, we mainly use the energy method in the priori estimations, and then verify the asymptotic compactness of the semigroup by the method of contraction function. Finally, by decomposing the weak solutions into two parts and some elaborate calculations, we prove the regularity of $\mathcal A$.
This paper considers the initial value problem for a class of fifth order dispersive models containing the fifth order KdV equation $$\partial_tu - \partial_x^5u - 30u^2\partial_xu + 20\partial_xu\partial_x^2u + 10u\partial_x^3u = 0.$$ The main results show that regularity or polynomial decay of the data on the positive half-line yields regularity in the solution for positive times.
We establish the existence and sharp global regularity results ($C^{0, γ}$, $C^{0, 1}$ and $C^{1, α}$ estimates) for a class of fully nonlinear elliptic PDEs with unbalanced variable degeneracy. In a precise way, the degeneracy law of the model switches between two different kinds of degenerate elliptic operators of variable order, according to the null set of a modulating function. Such sharp regularity estimates generalize and improve, to some extent, earlier ones via geometric treatments. Our results are consequences of geometric tangential methods and make use of compactness, localized osc…
Boundary pointwise regularity for the $p$-Laplace equation on $C^{1,\mathrm{Dini}}$ domains
本文研究 $p$-Laplace 方程在 $C^{1,\mathrm{Dini}}$ 域上的边界逐点正则性，通过扰动法和紧性论证，建立了 Lipschitz、Hopf 引理及 $C^1$ 正则性。
On the relation between decay and regularity of solutions to the modified Korteweg-de Vries equation
本文研究加权 Sobolev 空间中修正 KdV 方程解的正则性与衰减关系，证明强多项式衰减可推出解具有更高的实际正则性。
Regularity and decay of global solutions for the 4D Navier-STokes equations posed on smooth domains
本文研究四维Navier-Stokes方程在有界光滑域上的初边值问题，证明了在初始数据受限条件下正则解的存在唯一性、指数衰减及额外正则性。
Higher Hölder regularity for degenerate fully nonlinear elliptic equations with Hamiltonian terms
针对带变指数双相退化律和哈密顿项的完全非线性椭圆方程，在哈密顿系数和源项消失的点处获得梯度Hölder正则性改进，并在局部极值处建立关于消失率的Sharp Schauder型估计。
We consider radially symmetric, energy critical wave maps from (1 + 2)-dimensional Minkowski space into the unit sphere $\mathbb{S}^m$, $m \geq 1$, and prove global regularity and scattering for classical smooth data of finite energy. In addition, we establish a priori bounds on a suitable scattering norm of the radial wave maps and exhibit concentration compactness properties of sequences of radial wave maps with uniformly bounded energies. This extends and complements the beautiful classical work of Christodoulou-Tahvildar-Zadeh [3, 4] and Struwe [31, 33] as well as of Nahas [22] on radial w…
Regularity of solutions to degenerate normalized $p$-Laplacian equation with general variable exponents
本文研究带一般变指数的退化正规化$p$-Laplacian方程，利用紧性论证等方法建立粘性解的局部$C^{1,α'}$正则性，还得到相关退化自由传输问题的几乎最优逐点$C^{1,τ}$正则性，论证基于新的改进振荡型估计结合局部分析。
Decay and regularity properties for the dispersion generalized Benjamin-Ono equation
该研究探讨色散广义Benjamin-Ono方程解的空间衰减性质，通过加权能量估计与伪微分方法建立加权Sobolev空间的持久性性质，证明两时刻衰减可提升解的正则性，改进了相关已有结果。
The $C^{p'}$-regularity conjecture near $p=2$
本文证明当 $p>2$ 充分接近 $2$ 时 $C^{p'}$-正则性猜想在所有维度成立，通过改进 $p$-调和函数梯度的 Hölder 估计并确定最优指数首阶渐近，方法结合紧致性、调和刚性与间隙估计。
This paper is concerned with the existence and the regularity of global solutions to the linear wave equation associated with two-point type boundary conditions. We also investigate the decay properties of the global solutions to this problem by the construction of a suitable Lyapunov functional.
We investigate existence and uniqueness for the stochastic liquid crystal flow driven by colored noise on the two-dimensional torus. After giving a natural uniqueness criterion, we prove local solvability in $L^p$-based spaces, for every $p>2.$ Thanks to a bootstrap principle together with a Gyöngy-Krylov-type compactness argument, this will ultimately lead us to prove the existence of a particular class of global solutions which are partially regular, strong in the probabilistic sense, and taking values in the "critical space" $L^2\times H^1.$
We consider the Cauchy problem on nonlinear scalar conservation laws with a diffusion-type source term related to an index $s\in \R$ over the whole space $\R^n$ for any spatial dimension $n\geq 1$. Here, the diffusion-type source term behaves as the usual diffusion term over the low frequency domain while it admits on the high frequency part a feature of regularity-gain and regularity-loss for $s< 1$ and $s>1$, respectively. For all $s\in \R$, we not only obtain the $L^p$-$L^q$ time-decay estimates on the linear solution semigroup but also establish the global existence and optimal time-decay …
Global regularity and sharp decay to the 2D Hypo-Viscous compressible Navier-Stokes equations
本文研究二维非牛顿可压缩纳维-斯托克斯方程的全局正则性及最优时间衰减率，通过改进的傅里叶分裂方法和李特伍德-帕莱伊分解理论，建立了低正则性数据的最优衰减率。
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