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We prove that any complete, uniformly elliptic Weingarten surface in Euclidean $3$-space whose Gauss map image omits an open hemisphere is a cylinder or a plane. This generalizes a classical theorem by Hoffman, Osserman and Schoen for…

Differential Geometry · Mathematics 2020-07-23 Isabel Fernandez , Jose A. Galvez , Pablo Mira

We solve the problem of best approximation by partial isometries of given rank to an arbitrary rectangular matrix, when the distance is measured in any unitarily invariant norm. In the case where the norm is strictly convex, we parametrize…

Functional Analysis · Mathematics 2016-11-08 Jorge Antezana , Eduardo Chiumiento

This article studies a particular process that approximates solutions of the Beltrami equation (straightening of ellipse fields, a.k.a. measurable Riemann mapping theorem) on $\mathbb{C}$. It passes through the introduction of a sequence of…

Complex Variables · Mathematics 2025-08-05 Arnaud Chéritat , Guillaume Tahar

The functorial mathematical definition of conformal field theory was first formulated approximately 30 years ago. The underlying geometric category is based on the moduli space of Riemann surfaces with parametrized boundary components and…

Complex Variables · Mathematics 2017-06-09 David Radnell , Eric Schippers , Wolfgang Staubach

Applying the Bonk-Kleiner characterization of Ahlfors 2-regular quasispheres, we show that a metric two-sphere $X$ is a quasisphere if and only if $X$ is linearly locally connected and carries a weak metric doubling measure, i.e., a measure…

Complex Variables · Mathematics 2017-10-04 Atte Lohvansuu , Kai Rajala , Martti Rasimus

Harmonic maps from Riemann surfaces arise from a conformally invariant variational problem. Therefore, on one hand, they are intimately connected with moduli spaces of Riemann surfaces, and on the other hand, because the conformal group is…

Differential Geometry · Mathematics 2017-10-05 Jürgen Jost , Enno Keßler , Jürgen Tolksdorf , Ruijun Wu , Miaomiao Zhu

In the theory of Teichm\"uller space of Riemann surfaces, we consider the set of Riemann surfaces which are quasiconformally equivalent. For topologically finite Riemann surfaces, it is quite easy to examine if they are quasiconformally…

Complex Variables · Mathematics 2019-08-30 Hiroshige Shiga

A quasisymmetric graph is a curve whose projection onto a line is a quasisymmetric map. We show that this class of curves is related to solutions of the reduced Beltrami equation and to a generalization of the Zygmund class $\Lambda_*$.…

Complex Variables · Mathematics 2012-11-13 Leonid V. Kovalev , Jani Onninen

We investigate a quasisymmetrically invariant counterpart of the topological Hausdorff dimension of a metric space. This invariant, called the topological conformal dimension, gives a lower bound on the topological Hausdorff dimension of…

Metric Geometry · Mathematics 2023-06-23 Claudio A. DiMarco

All spherically symmetric Riemannian metrics of constant scalar curvature in any dimension can be written down in a simple form using areal coordinates. All spherical metrics are conformally flat, so we search for the conformally flat…

General Relativity and Quantum Cosmology · Physics 2015-06-19 Patryk Mach , Niall Ó Murchadha

The aim of this paper is to investigate the equivalence conditions for uniform perfectness of quasi-metric spaces. We also obtain the invariant property of uniform perfectness under quasim\"obius maps in quasi-metric spaces. In the end, two…

Complex Variables · Mathematics 2019-03-05 Qingshan Zhou , Yaxiang Li , Ailing Xiao

We consider a generalization of Riemannian geometry that naturally arises in the framework of control theory. Let $X$ and $Y$ be two smooth vector fields on a two-dimensional manifold $M$. If $X$ and $Y$ are everywhere linearly independent,…

Optimization and Control · Mathematics 2007-05-23 Andrei A. Agrachev , Ugo Boscain , Mario Sigalotti

We show that if $f:X\to Y$ is a quasisymmetric mapping between Ahlfors regular spaces, then $\dim_H f(E)\leq\dim_H E$ for "almost every" bounded Ahlfors regular set $E\subseteq X$. If additionally, $X$ and $Y$ are Loewner spaces then…

Complex Variables · Mathematics 2016-03-07 Christopher J. Bishop , Hrant Hakobyan , Marshall Williams

We prove that Ahlfors 2-regular quasisymmetric images of the Euclidean plane are bi-Lipschitz images of the plane if and only if they are uniformly bi-Lipschitz homogeneous with respect to a group. We also prove that certain geodesic spaces…

Metric Geometry · Mathematics 2022-07-11 David M. Freeman

Conformal mapping, a classical topic in complex analysis and differential geometry, has become a subject of great interest in the area of surface parameterization in recent decades with various applications in science and engineering.…

Graphics · Computer Science 2021-04-23 Gary P. T. Choi

We demonstrate that the complex plane and a class of generalized Grushin planes $G_r$, where $r$ is a function satisfying specific requirements, are quasisymmetrically equivalent. Then using conjugation we are able to develop an analytic…

Complex Variables · Mathematics 2014-10-22 Colleen Ackermann

The paper presents an analog of the old result by the author and V. Voevodsky, according to which a Riemann surface admits a conformal structure, defined by an equilateral triangulation, if and only if the corresponding algebraic curve can…

Algebraic Geometry · Mathematics 2022-12-16 George B. Shabat

We initiate a study of the quasisymmetric uniformization of naturally arising random fractals and show that many of them fall outside the realm of quasisymmetric uniformization to simple canonical spaces. We begin with the trace, the graph…

Metric Geometry · Mathematics 2024-12-10 Gefei Cai , Wen-Bo Li , Tim Mesikepp

A conformal map from a Riemann surface to a Euclidean space of dimension greater than or equal to three is explained by using the Clifford algebra, in a similar fashion to quaternionic holomorphic geometry of surfaces in the Euclidean…

Differential Geometry · Mathematics 2019-08-16 Katsuhiro Moriya

We prove the existence of "half-plane differentials" with prescribed local data on any Riemann surface. These are meromorphic quadratic differentials with higher-order poles which have an associated singular flat metric isometric to a…

Geometric Topology · Mathematics 2013-02-26 Subhojoy Gupta