YanYan Li
We prove $C^1$ regularity of solutions to divergence form elliptic systems with Dini-continuous coefficients
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This paper is concerned with interior regularity of viscosity solutions of non-translation invariant nonlocal fully nonlinear equations with Dini continuous terms. We obtain $C^σ$ regularity estimates for the nonlocal equations by perturbative methods and a version of a recursive Evans-Krylov theorem.
Partial regularity result of elliptic systems with Dini continuous coefficients and $q$-growth
建立了二阶椭圆型方程组散度型向量值解的部分正则性结果。这些系数满足关于增长阶大于2的$(x,u)$的Dini条件。证明了奇异集外解的$C^1$ -正则性。
We consider the boundary value problem associated to the divergence operator with vanishing Dirichlet boundary conditions and we prove the existence of classical solutions under slight assumptions on the regularity of the datum.
In this note we prove an end-point regularity result on the Lp integrability of the second derivatives of solutions to non-divergence form uniformly elliptic equations whose second derivatives are a priori only known to be integrable. The main assumption on the elliptic operator is the Dini continuity of the coefficients. We provide a counterexample showing that the Dini condition is somehow optimal. We also give a counterexample related to the BMO regularity of second derivatives of solutions to elliptic equations.
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。
Boundary Regularity for Fully Nonlinear Parabolic equations on $C^{1,\mathrm{Dini}}$ Domains
本文通过统一的扰动方法，证明了完全非线性抛物型方程在 $C^{1,\mathrm{Dini}}$ 域上的边界逐点 Lipschitz 正则性与 Hopf 引理，并进一步得到了全局 ${W}^{2,δ}$ 正则性。
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…
Lipschitz regularity for Poisson equations involving measures supported on $C^{1,\operatorname{Dini}}$ interfaces
本文研究了测度数据支撑在$C^{1,\operatorname{Dini}}$接口上的Poisson方程，通过扰动论证和Green函数估计推导接口上的逐点梯度估计，证明了解的最优Lipschitz正则性及分段可微性，并给出反例验证了假设的极小性。
Non-divergence evolution operators modeled on Hörmander vector fields with Dini continuous coefficients
本文研究了基于霍尔曼德向量场和迪尼连续系数的非发散演化算子，构建了基本解并证明了相关柯西问题的存在性。
In this paper, we consider the pointwise boundary Lipschitz regularity of solutions for the semilinear elliptic equations in divergence form mainly under some weaker assumptions on nonhomogeneous term and the boundary. If the domain satisfies C^{1,\text{Dini}} condition at a boundary point, and the nonhomogeneous term satisfies Dini continuous condition and Lipschitz Newtonian potential condition, then the solution is Lipschitz continuous at this point. Furthermore, we generalize this result to Reifenberg C^{1,\text{Dini}} domains.
We establish local interior Lipschitz continuity of the solutions of a class of free boundary elliptic problems assuming the coefficients of the equation of Dini mean oscillation in at least one direction. The novelty in this regularity result lies in the fact that it allows discontinuous coefficients in all but one variable.
We discuss conditions for Lipschitz and C^1 regularity for a uniformly elliptic equation in divergence form with coefficients that were introduced by Gilbarg & Serrin. In particular, we find cases where Lipschitz or C^1 regularity holds but the coefficients are not Dini continuous, or do not even have Dini mean oscillation. The form of the coefficients also enables us to obtain specific conditions and examples for which there exists a weak solution that is not Lipschitz continuous.
The pointwise gradient estimate for weak solution pairs to the stationary Stokes system with Dini-BMO coefficients is established via the Havin-Maz'ya-Wolff type nonlinear potential of the nonhomogeneous term. In addition, we present a pointwise bound for the weak solutions under no extra regularity assumption on the coefficients.
Pointwise regularity of the free boundary for the parabolic obstacle problem
研究抛物型障碍问题$$\lap u-u_t=fχ_{\{u>0\}}, \quad u\geq 0,\quad f\in L^p \quad \mbox{with}\quad f(0)=1$$，得到了两个单调性公式，一个适用于一般自由边界点，一个适用于奇异自由边界点.这些被用来证明二阶泰勒展开在奇点（逐点Dini条件下），估计的错误（逐点双Dini条件下）。在$f$是Dini连续的假设下，证明了正则点集局部是（抛物）$C^1$ -曲面，奇点集局部包含在（抛物）$C^1$流形的并中.
Boundary Lipschitz Regularity and the Hopf Lemma for Fully Nonlinear Elliptic Equations
针对完全非线性椭圆方程粘性解的边界正则性问题，提出将曲边界视为超平面扰动的统一简洁方法，证明内外C^{1,\text{Dini}}条件分别对应边界Lipschitz连续性与Hopf引理成立，并验证该条件的最优性。
We study the regularity properties of the second order linear operator in $\mathbb{R}^{N+1}$: \begin{equation*} \mathscr{L} u := \sum_{j,k= 1}^{m} a_{jk}\partial_{x_j x_k}^2 u + \sum_{j,k= 1}^{N} b_{jk}x_k \partial_{x_j} u - \partial_t u, \end{equation*} where $A = \left( a_{jk} \right)_{j,k= 1, \dots, m}, B= \left( b_{jk} \right)_{j,k= 1, \dots, N}$ are real valued matrices with constant coefficients, with $A$ symmetric and strictly positive. We prove that, if the operator $\mathscr{L}$ satisfies Hörmander's hypoellipticity condition, and $f$ is a Dini continuous function, then the second ord…
We consider second-order elliptic equations in non-divergence form with oblique derivative boundary conditions. We show that any strong solutions to such problems are twice continuously differentiable up to the boundary provided that the mean oscillations of coefficients satisfy the Dini condition and the boundary is locally represented by a $C^1$ function whose first derivatives are Dini continuous. This improves a recent result in [6]. An extension to fully nonlinear elliptic equations is also presented.
We consider divergence form, second-order strongly parabolic systems in a cylindrical domain with a finite number of subdomains under the assumption that the interfacial boundaries are $C^{1,\text{Dini}}$ and $C^{γ_{0}}$ in the spatial variables and the time variable, respectively. Gradient estimates and piecewise $C^{1/2,1}$-regularity are established when the leading coefficients and data are assumed to be of piecewise Dini mean oscillation or piecewise Hölder continuous. Our results improve the previous results in \cite{ll,fknn} to a large extent. We also prove a global weak type-$(1,1)$ es…
Boundary Lipschitz Regularity and the Hopf Lemma on Reifenberg Domains for Fully Nonlinear Elliptic Equations
该研究针对完全非线性椭圆方程，提出统一方法证明Reifenberg区域上的边界Lipschitz正则性与Hopf引理，明确内外Reifenberg $C^{1,\mathrm{Dini}}$条件对应的成立情形，拓展了常规条件下的已有结论。
Estimates for fundamental solutions of parabolic equations in non-divergence form
本文构造非散度形式二阶抛物方程的基本解，证明其满足次高斯估计，并在系数Dini连续时建立高斯界，方法可推广至方程组。
Pointwise estimates for the heat equation. Application to the free boundary of the obstacle problem with Dini coefficients
研究了抛物型方程解的点态正则性。作为第一个结果，我们证明了，如果平均振荡的模$Δu -u_t$在原点是Dini（在$L^p$平均），那么原点是一个勒贝格连续点（仍然在$L^p$平均）的$D^2 u$和$\dd_t u$。我们将这一点态正则性结果推广到Dini右手边的抛物障碍问题。特别是，我们证明了障碍物问题的解决方案，在正则点的自由边界，泰勒扩展到两个空间和一个时间（在$L^p$平均）。此外，我们还得到了泰勒展开式误差的定量估计。我们的方法是基于衰变估计矛盾，使用爆破参数和刘维尔型定理。作为我们的方法的一个副产品，我们推导出的规则点的自由边界局部包含在$C^1$超曲面的抛物线距离$\sqrt{x^2 +|t|}$。
In this paper, we prove that any $W^{2,1}$ strong solution to second-order non-divergence form elliptic equations is locally $W^{2,\infty}$ and piecewise $C^{2}$ when the leading coefficients and data are of piecewise Dini mean oscillation and the lower-order terms are bounded. Somewhat surprisingly here the interfacial boundaries are only required to be $C^{1,\text{Dini}}$. We also derive global weak-type $(1,1)$ estimates with respect to $A_{1}$ Muckenhoupt weights. The corresponding results for the adjoint operator are established. Our estimates are independent of the distance between these…
In this paper, we show that $W^{1,p}$ $(1\leq p<\infty)$ weak solutions to divergence form elliptic systems are Lipschitz and piecewise $C^{1}$ provided that the leading coefficients and data are of piecewise Dini mean oscillation, the lower order coefficients are bounded, and interfacial boundaries are $C^{1,\text{Dini}}$. This extends a result of Li and Nirenberg (\textit{Comm. Pure Appl. Math.} \textbf{56} (2003), 892-925). Moreover, under a stronger assumption on the piecewise $L^{1}$-mean oscillation of the leading coefficients, we derive a global weak type-(1,1) estimate with respect to …
Internal Schauder estimates for Hörmander type equations with Dini continuous source
该研究针对满足Hörmander条件的光滑自伴向量场构成的二阶Hörmander算子，在源项Dini连续的条件下，通过建立各向异性情形下的Taylor公式，证明了方程解的二阶导数同样具有Dini连续性。
We show that weak solutions to conormal derivative problem for elliptic equations in divergence form are continuously differentiable up to the boundary provided that the mean oscillations of the leading coefficients satisfy the Dini condition, the lower order coefficients satisfy certain suitable conditions, and the boundary is locally represented by a $C^1$ function whose derivatives are Dini continuous. We also prove that strong solutions to oblique derivative problem for elliptic equations in nondivergence form are twice continuously differentiable up to the boundary if the mean oscillation…
Spatial $C^1$, $C^2$, and Schauder estimates for nonstationary Stokes equations with Dini mean oscillation coefficients
本文研究了非稳 Stokes 方程在不同形式下，利用 Dini 平均振荡系数的弱解和强解的空间可导性及 Schauder 估计。
We study the stationary Stokes system in divergence form. The coefficients are assumed to be merely measurable in one direction and have Dini mean oscillations in the other directions. We prove that if $(u,p)$ is a weak solution of the system, then $(Du,p)$ is bounded and its certain linear combinations are continuous. We also prove a weak type-$(1,1)$ estimate for $(Du,p)$ under a stronger assumption on the $L^1$-mean oscillation of the coefficients. The corresponding results up to the boundary on a half ball are also established. These results are new even for elliptic equations and systems.
The classical obstacle problem with Hölder continuous coefficients
该研究针对不同连续性条件的二次能量建立两类拟单调性公式，推导了Hölder连续系数下经典障碍问题的自由边界正则性，丰富了障碍问题的正则性理论。
Higher order boundary Harnack principles in Dini type domains
本文研究Dini型区域中散度型椭圆方程的高阶边界Harnack原理，通过分析退化辅助方程，在双重及三重Dini条件下建立解及其比值的C^k估计。
We extend and improve the results in \cite{DK16}: showing that weak solutions to full elliptic equations in divergence form with zero Dirichlet boundary conditions are continuously differentiable up to the boundary when the leading coefficients have Dini mean oscillation and the lower order coefficients verify certain conditions. Similar results are obtained for non-divergence form equations. We extend the weak type-(1, 1) estimates in \cite{DK16} and \cite{Es94} up to the boundary and derive a Harnack inequality for non-negative adjoint solutions to non-divergence form elliptic equations, whe…
We construct the Green function for second order elliptic equations in non-divergence form when the mean oscillations of the coefficients satisfy the Dini condition and the domain has $C^{1,1}$ boundary. We also obtain pointwise bounds for the Green functions and its derivatives.
We present a new method for the existence and pointwise estimates of a Green's function of non-divergence form elliptic operator with Dini mean oscillation coefficients. We also present a sharp comparison with the corresponding Green's function for constant coefficients equations.
We study Green functions for the pressure of stationary Stokes systems in a (possibly unbounded) domain $Ω\subset \mathbb{R}^d$, where $d\ge 2$. We construct the Green function when coefficients are merely measurable in one direction and have Dini mean oscillation in the other directions, and $Ω$ is such that the divergence equation is solvable there. We also establish global pointwise bounds for the Green function and its derivatives when coefficients have Dini mean oscillation and $Ω$ has a $C^{1,\rm{Dini}}$ boundary. Green functions for the flow velocity of Stokes systems are also considere…
This paper is concerned with the nodal set of weak solutions to a broken quasilinear partial differential equation, \begin{equation*} \mbox{div} (a_+ \nabla u^+ - a_- \nabla u^-) = \mbox{div} f, \end{equation*} where $a_+$ and $a_-$ are uniformly elliptic, Dini continuous coefficient matrices, subject to a strong correlation that $a_+$ and $a_-$ are a multiple of some scalar function to each other. Under such a structural condition, we develop an iteration argument to achieve higher-order approximation of solutions at a singular point, which is also new for standard elliptic PDEs below Hölder …
Geometric sets of elliptic equations with Dini coefficients
本文研究具有 Dini 系数的散度型椭圆方程，建立加倍指标的几乎单调性，获得临界集和节点集的体积估计，并证明切线映射的定量唯一性及 Minkowski 型估计。
On the threshold nature of the Dini continuity for a Glassey derivative-type nonlinearity in a critical semilinear wave equation
本文研究含临界 Glassey 指数导数型非线性项的半线性波动方程，利用 Zhou 特征线方法与加权 $L^{\infty}$ 估计，证明 Dini 连续性是决定有限时间爆破与小数据全局存在的正则性阈值。
Regularity for the normalized p-Laplacian equation with an arbitrary degeneracy law
本文研究退化规范化p-Laplace方程的内部正则性，在退化律满足一般假设且其逆满足Dini连续条件时，通过超平面逼近方法证明解具有C^1正则性。
Regularity of elliptic equations in double divergence form and applications to Green's function estimates
本文研究了双散度形式椭圆方程的正则性，证明了解在零水平集上可微，并建立了导数的点估计，改进了Leitão等人2020年的结果。同时，建立了非发散形式二阶均匀椭圆算子在有界$C^{1,α}$域中的格林函数的全局点估计。
In this paper, we study the nonhomogeneous Dirichlet problem concerning general semilinear elliptic equations in divergence form. We establish that the boundary Lipschitz regularity of solutions under some more weaker conditions on the coefficients, the boundary, the boundary function and the nonhomogeneous term. In particular, we assume that the nonhomogeneous term satisfies Dini continuity condition and Lipschitz Newtonian potential condition, which will be the optimal conditions to obtain the boundary Lipschitz regularity of solutions.
Partial regularity of the gradient for subsolutions
本文研究了亚解的梯度部分正则性，证明了在特定几何条件下，亚调和函数的梯度上半连续，并扩展到一般算子和Dirichlet问题的边界行为。
Boundary regularity and Hopf lemma for nondegenerate stable operators
本文针对满足外部C^{1,dini}性质的有界开集，证明了非退化稳定积分微分算子方程解的尖锐边界Hölder正则性与Hopf型边界引理，并展示了估计在s→1-时的稳健性，从而恢复二阶方程经典结果。
Boundary estimates for non-divergence equations in $C^1$ domains
本文在$C^1$领域中研究非散度方程的边界估计，通过显式连续模扩展了经典霍普-奥列尼克引理，并统一了利普希茨正则性理论。
We study qualitative properties of solutions to double divergence form elliptic equations (or stationary Kolmogorov equations) on~$\mathbb{R}^d$. It is shown that the Harnack inequality holds for nonnegative solutions if the diffusion matrix $A$ is nondegenerate and satisfies the Dini mean oscillation condition and the drift coefficient $b$ is locally integrable to a power $p>d$. We establish new estimates for the $L^p$-norms of solutions and obtain a generalization of the known theorem of Hasminskii on the existence of a probability solution to the stationary Kolmogorov equation to the case w…
We study stationary Stokes systems in divergence form with piecewise Dini mean oscillation coefficients and data in a bounded domain containing a finite number of subdomains with $C^{1,\rm{Dini}}$ boundaries. We prove that if $(u, p)$ is a weak solution of the system, then $(Du, p)$ is bounded and piecewise continuous. The corresponding results for stationary Navier-Stokes systems are also established, from which the Lipschitz regularity of the stationary $H^1$-weak solution in dimensions $d=2,3,4$ is obtained.
Lipschitz regularity of homogenization with continuous coefficients: Dirichlet problem
本研究针对连续系数散度型椭圆系统，通过将数据正则性条件弱化为积分条件，推广了Avellaneda-Lin的均匀化Lipschitz正则性结果，并指出系数具有Dini平均振荡。
Differentiability of Solutions to Second-Order Elliptic Equations via Dynamical Systems
对一类散度型二阶椭圆型方程，研究了其所有解在给定点处Lipschitz连续或可微的系数条件.我们假设系数的连续模满足平方-迪尼条件，并得到额外的条件，例子表明是尖锐的。我们的结果扩展了以前的作者谁假设的连续模满足Dini条件。我们的方法涉及到一个动力系统的解的渐近性质的研究，该动力系统是由椭圆型方程的系数。
Boundary estimates for parabolic non-divergence equations in $C^1$ domains
本文研究了抛物非散度方程在$C^1$领域边界的正则性，通过显式连续模扩展了Hopf-Oleinik引理和Dini边界结果，并统一了Lipschitz领域与$C^{1-\varepsilon}$正则性的证明。
We consider vector-valued solutions to a linear transmission problem, and we prove that Lipschitz-regularity on one phase is transmitted to the next phase. More exactly, given a solution $u:B_1\subset \mathbb{R}^n \to \mathbb{R}^m$ to the elliptic system \begin{equation*} \mbox{div} ((A + (B-A)χ_D )\nabla u) = 0 \quad \text{in }B_1, \end{equation*} where $A$ and $B$ are Dini continuous, uniformly elliptic matrices, we prove that if $\nabla u \in L^{\infty} (D)$ then $u$ is Lipschitz in $B_{1/2}$. A similar result is also derived for the parabolic counterpart of this problem.
We obtain conditions for the differentiability of weak solutions for a second-order uniformly elliptic equation in divergence form with a homogeneous co-normal boundary condition. The modulus of continuity for the coefficients is assumed to satisfy the square-Dini condition and the boundary is assumed to be differentiable with derivatives also having this modulus of continuity. Additional conditions for the solution to be Lipschitz continuous or differentiable at a point on the boundary depend upon the stability of a dynamical system that is derived from the coefficients of the elliptic equati…
Interior $BMO$ regularity for elliptic equations in divergence form
本文研究了椭圆方程在散度形式下弱解的内部BMO正则性，并证明了系数假设的最优性。
Note on Green's functions of non-divergence elliptic operators with continuous coefficients
本文改进了Kim和Lee的结果，证明当非散度型椭圆算子系数具有Dini平均振荡时，其格林函数在极点附近与冻结常系数方程的格林函数具有相同的渐近行为。
Interior pointwise $C^{1}$ and $C^{1,1}$ regularity of solutions for general semilinear elliptic equation in nondivergence form
该研究在更弱假设下推导非散度型一般半线性椭圆方程$L^n$-粘性解的内点逐点$C^1$与$C^{1,1}$正则性，推广了非齐次项相关结果，给出无界系数下的正则性判定条件。
Hölder regularity for non divergence form elliptic equations with discontinuous coefficients
本文研究非变分椭圆型方程强解的二阶导数在Morrey空间中的整体正则性。
Optimal regularity for the no-sign obstacle problem
本文证明了一般障碍型问题$$ \lap u = fχ_{\{u\neq 0\}}\textup{in $B_1$}, $$的最优$C^{1,1}(B_\frac12)$ -正则性，其中假定$f*N$是$C^{1,1}(B_1)$，$N$是牛顿位势.这是人们希望得到$C^{1,1}$ -正则性的最弱假设。作为副产品的$C^{1,1}$ -正则性，我们能够证明，在一个标准的厚度假设的零集接近一个自由边界点$x^0$，自由边界是局部的$C^1$ -图接近$x^0$，提供$f$是迪尼。这完全解决了这个问题的最佳规律性的问题，在过去的二十年中一直受到广泛关注。
Maximal parabolic regularity for divergence operators including mixed boundary conditions
证明了散度型椭圆二阶算子$A$在分布空间上满足极大抛物正则性，即使其下的区域是高度非光滑的，$A$的系数也是不连续的，并且$A$是用混合边界条件补的.应用于非光滑数据的拟线性抛物型方程。
We consider viscosity solutions to non-homogeneous degenerate and singular parabolic equations of the $p$-Laplacian type and in non-divergence form. We provide local Hölder and Lipschitz estimates for the solutions. In the degenerate case, we prove the Hölder regularity of the gradient. Our study is based on a combination of the method of alternatives and the improvement of flatness estimates.
We prove quasi-monotonicity formulae for classical obstacle-type problems with quadratic energies with coefficients in fractional Sobolev spaces, and a linear term with a Dini-type continuity property. These formulae are used to obtain the regularity of free-boundary points following the approaches by Caffarelli, Monneau and Weiss.
We investigate weighted Sobolev regularity of weak solutions of non-homogeneous parabolic equations with singular divergence-free drifts. Assuming that the drifts satisfy some mild regularity conditions, we establish local weighted $L^p$-estimates for the gradients of weak solutions. Our results improve the classical one to the borderline case by replacing the $L^\infty$-assumption on solutions by solutions in the John-Nirenberg \textup{BMO} space. The results are also generalized to parabolic equations in divergence form with small oscillation elliptic symmetric coefficients and therefore imp…
Two-sided Gaussian estimates for fundamental solutions of second-order parabolic equations in non-divergence form
本文在最小正则性假设下，通过局部有界性和对偶算子的弱Harnack不等式，建立了二阶抛物方程基本解的双侧高斯界，并避免了前人工作中所需的归一化对偶解。
We consider the regular Lagrangian flow X associated to a bounded divergence-free vector field b with bounded variation. We prove a Lusin-Lipschitz regularity result for X and we show that the Lipschitz constant grows at most linearly in time. As a consequence we deduce that both geometric and analytical mixing have a lower bound of order $t^{-1}$ as $t \to \infty$.
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