David Kalaj
It is proved the following theorem, if $w$ is a quasiconformal harmonic mappings between two Riemann surfaces with smooth boundary and aproximate analytic metric, then $w$ is a quasi-isometry with respect to Euclidean metric.
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Let E be a compact set in the plane, g be a K-quasiconformal map, and let 0<t<2. Then H^t (E) = 0 implies H^{t'} (g E) = 0, for t'=[2Kt]/[2+(K-1)t]. This is a refinement of a set of inequalities on the distortion of Hausdorff dimensions by quasiconformal maps proved by K. Astala in his celebrated paper on area distortion for quasiconformal maps and answers in the positive a Conjecture of K. Astala in op. cit.
We prove existence of solutions to a nonlinear transport equation in the plane, for which the velocity field is obtained as the convolution of the classical Cauchy Kernel with the unknown. Even though the initial datum is bounded and compactly supported, the velocity field may have unbounded divergence. The proof is based on the compactness property of quasiconformal mappings.
Quasiconformal Extensions of Harmonic Univalent Mappings of the Unit Disk
本文研究单位圆盘内调和单叶映射的拟共形延拓条件，证明调和强星形映射可延拓至全平面并给出显式延拓函数，同时探讨圆盘外调和映射的可延拓性。
In this paper, we extend Ahlfors's univalent criteria and Ahlfors's quasiconformal extension for analytic functions to harmonic mappings defined in the unit disk. Moreover, we give a general quasiconformal extension of harmonic Teichmüller mappings, whose maximal dilatation estimate is asymptotically sharp.
We study one-parameter curves on the universal Teichmüller space $T$ and on the homogeneous space $M=\Diff S^1/\Rot S^1$ embedded into $T$. As a result, we deduce evolution equations for conformal maps that admit quasiconformal extensions and, in particular, such that the associated quasidisks are bounded by smooth Jordan curves. Some applications to Hele-Shaw flows of viscous fluids are given.
The main aim of this article is to establish certain relationships between $K$-quasiconformal harmonic mappings and John disks. The results of this article are the generalizations of the corresponding results of Ch.~Pommerenke \cite{Po}.
We prove that a harmonic quasiconformal mapping defined on a finitely connected domain in the plane, all of whose boundary components are either points or quasicircles, admits a quasiconformal extension to the whole plane if its Schwarzian derivative is small. We also make the observation that a univalence criterion for harmonic mappings holds on uniform domains.
In this paper, we investigate the relationships between linear measure and harmonic mappings.
In this article, we first discuss the Lipschitz characteristic and the linear measure distortion of $K$-quasiconformal harmonic mappings. Then we give some characterizations of the radial John disks with the help of Pre-Schwarzian of harmonic mappings.
In this article, we continue our investigations of the boundary behavior of harmonic mappings. We first discuss the classical problem on the growth of radial length and obtain a sharp growth theorem of the radial length of $K$-quasiconformal harmonic mappings. Then we present an alternate characterization of radial John disks. In addition, we investigate the linear measure distortion and the Lipschitz continuity on $K$-quasiconformal harmonic mappings of the unit disk onto a radial John disk. Finally, using Pommerenke interior domains, we characterize certain differential properties of $K$-qua…
In this paper we extend Rado-Choquet-Kneser theorem for the mappings with Lipschitz boundary data and essentially positive Jacobian at the boundary, without restriction on the convexity of image domain. It is an extension of a recent result of Alessandrini and Nesi \cite{ale}. Some applications for the family of quasiconformal harmonic mappings between Jordan domains are given.
Harmonic K-quasiconformal Koebe functions: construction and application to Pavlovic's problem
本文构造了调和K-准共形柯西函数，填补了几何函数论中的基础空白，提出了统一的极值函数框架，并探讨了调和K-准共形映射的极值理论。
We prove that if the Schwarzian norm of a given complex-valued locally univalent harmonic mapping $f$ in the unit disk is small enough, then $f$ is, indeed, globally univalent and can be extended to a quasiconformal mapping in the extended complex plane.
Sharp bounds for the growth and distortion of the analytic part of convex K-quasiconformal harmonic mappings
本文给出了保向凸K-拟共形调和映射解析部分增长与畸变的精确上下界。
The purpose of this paper is to explore conditions which guarantee Lipschitz-continuity of harmonic maps w.r.t. quasihyperbolic metrics. For instance, we prove that harmonic quasiconformal maps are Lipschitz w.r.t. quasihyperbolic metrics.
Topological Characteristics of Harmonic Quasiconformal Unit Disk Automorphisms in the Uniform Topology
本文研究赋予一致收敛拓扑的单位圆盘调和拟共形自同胚空间 $HQ(\mathbb{D})$，探讨并揭示了其可分性、紧性、道路连通性与完备性等重要拓扑性质。
In the present paper, we discuss several basic properties of a class of quasiconformal close-to-convex harmonic mappings with starlike analytic part, such results as coefficient inequalities, an integral representation, a growth theorem, an area theorem, and radii of close-to-convexity of partial sums of the class, are derived.
On Koebe-type functions for harmonic quasiconformal mappings
本文研究了谐波准共形映射中Koebe型函数的性质，建立了相关的一致性条件、范数、系数不等式及生长和面积定理，改进了已有结果。
Let $D$ and $Ω$ be Jordan domains with Dini's smooth boundaries and and let $f:D\mapsto Ω$ be a harmonic homeomorphism. The object of the paper is to prove the following result: If $f$ is quasiconformal, then $f$ is Lipschitz. This extends some recent results, where stronger assumptions on the boundary are imposed, and somehow is optimal, since it coincides with the best condition for Lipschitz behavior of conformal mappings in the plane and conformal parametrization of minimal surfaces.
In this article, we establish the Bohr inequalities for the sense-preserving $K$-quasiconformal harmonic mappings defined in the unit disk $\mathbb{D}$ involving classes of Ma-Minda starlike and convex univalent functions, usually denoted by $\mathcal{S}^*(ψ)$ and $\mathcal{C}(ψ)$ respectively, and for $\log (f(z)/z)$ where $f$ belongs to the Ma-Minda classes or satisfies certain differential subordination. We also estimate Logarithmic coefficient's bounds for the functions in $\mathcal{C}(ψ)$ for the case $ψ(\mathbb{D})$ be convex.
Bohr inequality and Bohr-Rogosinski inequality for $K$-Quasiconformal harmonic mappings
本文研究单位圆盘上解析部分从属于凹单叶函数类、Ma-Minda凸与星形函数类的$K$-拟共形保向调和映射，证明了若干精确的Bohr型及Bohr-Rogosinski型不等式，推广了已有结果。
We prove that for harmonic quasiconformal mappings $α$-Hölder continuity on the boundary implies $α$-Hölder continuity of the map itself. Our result holds for the class of uniformly perfect bounded domains, in fact we can allow that a portion of the boundary is thin in the sense of capacity. The problem for general bounded domains remains open.
We study quasiconformal maps on non-rigid Carnot groups equipped with Carnot metric. We show that for most non-rigid Carnot groups N, all quasiconformal maps on N must be biLipschitz.
Quasiconformal homeomorphisms of the unit ball $B^n$ of ${\mathbb R}^n, n \ge 3,$ onto itself with identity boundary values are studied. A spatial analogue of Teichmüller's theorem is proved.
The Bohr's phenomenon for certain K-quasiconformal harmonic mappings
本文研究单位圆盘中K-拟共形保向调和映射的玻尔现象，建立了改进玻尔不等式、精细玻尔不等式及玻尔-罗戈辛斯基不等式的多个精确版本。
It is known for some time that there exists an energy-minimal diffeomorphism between two doubly-connected domains $Ω$ and $D$ provided that $\mathrm{Mod}(Ω)\le \mathrm{Mod}{D}$ and that diffeomorphism is harmonic \cite{tedi}. In this note we give a short proof of the fact that for given annuli $Ω$ and $D$ satisfying the condition $\mathrm{Mod}(Ω)\le \mathrm{Mod}(D)$ there exist a $K-$quasiconformal harmonic diffeomorphism $f:Ω\onto D$, where $K=K(τ)$, $τ=\mathrm{Mod}(Ω)/ \mathrm{Mod}(D)$ and $\lim_{τ\to 1}K(τ)=1$.
Bohr Phenomenon for $K$-quasiconformal Harmonic Mappings Involving One Parameter
本文研究$K$-拟共形调和映射的Bohr型不等式，涉及参数或凸组合，并推广至凹单叶函数类，推广了已有结果。
If $Ω$ is a simply connected domain in $\overline{\mathbb C}$ then, according to the Ahlfors-Gehring theorem, $Ω$ is a quasidisk if and only if there exists a sufficient condition for the univalence of holomorphic functions in $Ω$ in relation to the growth of their Schwarzian derivative. We extend this theorem to harmonic mappings by proving a univalence criterion on quasidisks. We also show that the mappings satisfying this criterion admit a homeomorphic extension to $\overline{\mathbb C}$ and, under the additional assumption of quasiconformality in $Ω$, they admit a quasiconformal extension …
We prove that every quasiconformal mapping from the harmonic $β$-Bloch space between the unit ball and a spatial domain with $C^1$ boundary is globally $α$-Hölder continuous for $α<1-β$, with the Hölder coefficient that does not depend neither on the mapping nor on $β$. An analogous result also holds for Lipschitz continuous, quasiconformal harmonic mappings for $α<1$. This extends some results from the complex plane obtained by Warschawski in \cite{Warschawski} for conformal mappings and Kalaj in \cite{Kalaj6} for quasiconformal harmonic mappings.
Using normal family arguments, we show that the degree of the first nonzero homogenous polynomial in the expansion of $n$ dimensional Euclidean harmonic $K$-quasiconformal mapping around an internal point is odd, and that such a map from the unit ball onto a bounded convex domain, with $K< 3^{n-1}$, is co-Lipschitz. Also some generalizations of this result are given, as well as a generalization of Heinz's lemma for harmonic quasiconformal maps in $\mathbb R^n$ and related results.
Hardy spaces of harmonic quasiconformal mappings and Baernstein's theorem
本文研究单位圆盘内规范化 $K$-拟共形调和映射，证明其几何子类解析与余解析部分的 Baernstein 型极值定理，并据此给出积分均值估计及属于 Hardy 空间 $h^p$ 的 $p$ 范围。
Improved Hölder Continuity of Quasiconformal Maps
本文结合等周不等式与拟圆长度分析，改进复平面拟共形映射的 Hölder 连续性下界，刻画极值子并应用于椭圆偏微分方程。
Our goal is to provide a survey of some topics in quasiconformal analysis of current interest. We try to emphasize ideas and leave proofs and technicalities aside. Several easily stated open problems are given. Most of the results are joint work with several coauthors.
Here we give an alternate proof of a sufficient condition due to J. Mateu, J. Orobitg, and J. Verdera for a quasiconformal map of the plane with dilatation supported in a smooth domain to be bi-Lipschitz. We also extend this theorem to cover boundaries with certain types of corners.
We show that quasiconformal maps on many Carnot groups must be biLipschitz. In particular, this is the case for 2-step Carnot groups with reducible first layer. These results have implications for the rigidity of quasiisometries between negatively curved solvable Lie groups.
Harmonic quasiconformal mappings between $\mathscr{C}^1$ smooth Jordan domains
本文证明具有 $\mathscr{C}^1$ 边界的 Jordan 域间的调和拟共形映射对任意 $\alpha<1$ 全局 Hölder 连续但非 Lipschitz，推广了 Warschawski 的经典定理。
Bohr-type inequalities for classes of analytic maps and K-quasiconformal harmonic mappings
本文通过结合经典Bohr不等式的改进版本与面积测度方法，推广并精化了解析自映射类及K-拟共形调和映射类的Bohr型不等式，并证明结果最优。
Area Theorems and Quasiconformal Extensions of Harmonic Mappings with a Pole
本文针对单位圆盘中具有单极点且允许对数奇异性的单叶调和映射，建立了广义面积定理，并给出了显式k-拟共形延拓的充分条件。
We describe all quasiconformal maps on the higher (real and complex) model Filiform groups equipped with the Carnot metric, including non-smooth ones. These maps have very special forms. In particular, they are all biLipschitz and preserve multiple foliations. The results in this paper have implications to the large scale geometry of nilpotent Lie groups and negatively curved solvable Lie groups.
We establish that every $K$-quasiconformal mapping of $w$ of the unit disk $\ID$ onto a $C^2$-Jordan domain $Ω$ is Lipschitz provided that $Δw\in L^p(\ID)$ for some $p>2$. We also prove that if in this situation $K\to 1$ with $\|Δw\|_{L^p(\ID)}\to 0$, and $Ω\to \ID$ in $C^{1,α}$-sense with $α>1/2,$ then the bound for the Lipschitz constant tends to $1$. In addition, we provide a quasiconformal analogue of the Smirnov absolute continuity result over the boundary.
For the result on 1-quasiconformal maps, see the paper by Cowling and Ottazzi. The result on quasiconformal maps on Carnot groups with reducible first layer will appear in a forthcoming paper by Enrico Le Donne and Xiangdong Xie.
Coefficients and Integral Mean Estimates for $K$-Quasiconformal Harmonic Mappings
本文证明了K-拟共形调和映射相关的系数猜想成立，确定了其所属Hardy空间与加权Bergman空间的$p$范围，改进了相关估计并讨论了奇性映射的平行结果。
The Bohr's Phenomenon for the class of K-quasiconformal harmonic mappings
本文研究K-准共形保形调和映射类中的改进玻尔不等式及其精炼版本，通过引入非负量S_ρ(h)和替代主项系数的方法，获得单位圆盘内调和映射的精确玻尔-罗戈辛斯基半径。
We derive a quasiconformal extension to 3-space of the Weierstrass-Enneper lifts of a class of harmonic mappings defined in the unit disk. The extension is based on fibrations of space by circles in domain and image that correspond to each other in a natural way. Convexity plays an essential role in the analysis. As a corollary we derive a sufficient condition for the underlying harmonic mapping to be univalent in the disk, with an explicit quasiconformal extension to the extended plane that generalizes the well known formula by Ahlfors-Weill.
Barrlund's distance function and quasiconformal maps
本文研究Barrlund度量，给出其相对于其他度量的精确界，并证明拟共形映射下该度量的精确形变结果。
Suppose that $f$ is a $K$-quasiconformal self-mapping of the unit disk $\mathbb{D}$, which satisfies the following: $(1)$ the biharmonic equation $Δ(Δf)=g$ $(g\in \mathcal{C}(\overline{\mathbb{D}}))$, (2) the boundary condition $Δf=φ$ ($φ\in\mathcal{C}(\mathbb{T})$ and $\mathbb{T}$ denotes the unit circle), and $(3)$ $f(0)=0$. The purpose of this paper is to prove that $f$ is Lipschitz continuos, and, further, it is bi-Lipschitz continuous when $\|g\|_{\infty}$ and $\|φ\|_{\infty}$ are small enough. Moreover, the estimates are asymptotically sharp as $K\to 1$, $\|g\|_{\infty}\to 0$ and $\|φ\|_…
Quasiconformal curves and quasiconformal maps in metric spaces
本文研究度量空间中拟共形曲线与拟共形映射的关系，证明拟共形曲线满足解析定义及模不等式下界，给出满足度量定义的充分条件，并表明拟共形映射在适当假设下是拟共形曲线，且内蕴度量下结论依然成立。
A quantitative version of an inequality obtained in \cite[Theorem~2.1]{mathz} is given. More precisely, for normalized $K$ quasiconformal harmonic mappings of the unit disk onto a Jordan domain $Ω\in C^{1,μ} $ ($0<μ\le 1$) we give an explicit Lipschitz constant depending on the structure of $Ω$ and on $K$. In addition we give a characterization of q.c. harmonic mappings of the unit disk onto an arbitrary Jordan domain with $C^{2,α}$ boundary in terms of boundary function using the Hilbert transformations. Moreover it is given a sharp explicit quasiconformal constant in terms of the boundary fu…
On the coefficients estimate of K-quasiconformal harmonic mappings
本文针对Wang等人提出的K-拟共形调和映射系数猜想，证明其对星形、近凸及典型实K-拟共形调和映射成立，还建立了凸K-拟共形调和映射的精确系数估计，为该猜想提供了肯定性支撑。
Affine balancing of complex dilatations: affine invariants and optimal distortion of harmonic quasiconformal mappings
本文针对调和拟共形映射，引入仿射外接半径与仿射直径作为仿射不变量，刻画最优仿射平衡下的最小畸变，并建立锐利双边界及二阶估计，统一极值畸变问题。
The present article concerns the Bohr radius for $K$-quasiconformal sense-preserving harmonic mappings $f=h+\overline{g}$ in the unit disk $\mathbb{D}$ for which the analytic part $h$ is subordinated to some analytic function $φ$, and the purpose is to look into two cases: when $φ$ is convex, or a general univalent function in $\ID$. The results state that if $h(z) =\sum_{n=0}^{\infty}a_n z^n$ and $g(z)=\sum_{n=1}^{\infty}b_n z^n$, then $$\sum_{n=1}^{\infty}(|a_n|+|b_n|)r^n\leq \dist (φ(0),\partialφ(\ID)) ~\mbox{ for $r\leq r^*$} $$ and give estimates for the largest possible $r^*$ depending o…
We consider extensions of differential fields of mappings and obtain a lower energy bound for quasiconformal extension fields in terms of the topological degree. We also consider the related minimization problem for the $q$-harmonic energy, and show that the energy minimizers admit higher integrability.
Indecomposable Quasiconformal Maps of Manifolds
本文研究了闭合manifold上不可分解的准共形映射的存在性，核心方法是构造具有任意小共形扭曲的映射组合，主要贡献是证明了此类映射的不可分解性。
R. Fehlmann and M. Vuorinen proved in 1988 that Mori's constant $M(n,K)$ for $K$-quasiconformal maps of the unit ball in $\mathbf{R}^n$ onto itself keeping the origin fixed satisfies $M(n,K) \to 1$ when $K\to 1 .$ We give here an alternative proof of this fact, with a quantitative upper bound for the constant in terms of elementary functions. Our proof is based on a refinement of a method due to G.D. Anderson and M. K. Vamanamurthy. We also give an explicit version of the Schwarz lemma for quasiconformal self-maps of the unit disk. Some experimental results are provided to compare the various …
Piecewise quasiconformal dynamical systems of the unit circle
本文研究单位圆上分段拟共形覆盖映射，给出共轭可拟共形或David扩张到单位圆盘的充分条件，推广了分段解析情形，并应用于映射分类、Blaschke乘积共形配对及抛物 basins 几何。
In this paper, we establish a three circles type theorem, involving the harmonic area function, for harmonic mappings. Also, we give bounds for length and area distortion for harmonic quasiconformal mappings. Finally, we will study certain Lipschitz-type spaces on harmonic mappings.
We study the mean radius growth function for quasiconformal mappings. We give a new sub-class of quasiconformal mappings in $\mathbb{R}^n$, for $n\geq 2$, called bounded integrable parameterization mappings, or BIP maps for short. These have the property that the restriction of the Zorich transform to each slice has uniformly bounded derivative in $L^{n/(n-1)}$. For BIP maps, the logarithmic transform of the mean radius function is bi-Lipschitz. We then apply our result to BIP maps with simple infinitesimal spaces to show that the asymptotic representation is indeed quasiconformal by showing t…
Length control for foliations by Jordan curves via smooth quasiconformal maps
针对单连通域上Jordan曲线叶状结构的长度控制问题，构造光滑5-拟共形映射，以ε=2/157肯定回答了Bouchala与Koskela提出的p=2及附近的可积性问题。
We study quasiconformal mappings of the unit disk that have planar extension with controlled distortion. For these mappings we prove a bound for the modulus of continuity of the inverse map, which somewhat surprisingly is almost as good as for global quasiconformal maps. Furthermore, we give examples which improve the known bounds for the three point property of generalized quasidisks. Finally, we establish optimal regularity of such maps when the image of the unit disk has cusp type singularities.
Existence of quasiconformal maps with maximal stretching on any given countable set
本文针对 $\mathbb{R}^d$ 中任意有界可数集构造在每一点均达到最大拉伸的 $K$-拟共形映射，从而将平面极值构造推广至一般维数。
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