Search results for "funktioteoria"

Two‐dimensional metric spheres from gluing hemispheres

2022

We study metric spheres (Z,dZ) obtained by gluing two hemispheres of S2 along an orientation-preserving homeomorphism g:S1→S1, where dZ is the canonical distance that is locally isometric to S2 off the seam. We show that if (Z,dZ) is quasiconformally equivalent to S2, in the geometric sense, then g is a welding homeomorphism with conformally removable welding curves. We also show that g is bi-Lipschitz if and only if (Z,dZ) has a 1-quasiconformal parametrization whose Jacobian is comparable to the Jacobian of a quasiconformal mapping h:S2→S2. Furthermore, we show that if g−1 is absolutely continuous and g admits a homeomorphic extension with exponentially integrable distortion, then (Z,dZ) …

Sobolev homeomorphic extensions onto John domains

2020

Given the planar unit disk as the source and a Jordan domain as the target, we study the problem of extending a given boundary homeomorphism as a Sobolev homeomorphism. For general targets, this Sobolev variant of the classical Jordan-Schoenflies theorem may admit no solution - it is possible to have a boundary homeomorphism which admits a continuous $W^{1,2}$-extension but not even a homeomorphic $W^{1,1}$-extension. We prove that if the target is assumed to be a John disk, then any boundary homeomorphism from the unit circle admits a Sobolev homeomorphic extension for all exponents $p<2$. John disks, being one sided quasidisks, are of fundamental importance in Geometric Function Theory.

Rungen lause ja sovelluksia inversio-ongelmiin

2018

Quasisymmetric extension on the real line

2015

We give a geometric characterization of the sets $E\subset \mathbb{R}$ that satisfy the following property: every quasisymmetric embedding $f: E \to \mathbb{R}^n$ extends to a quasisymmetric embedding $f:\mathbb{R}\to\mathbb{R}^N$ for some $N\geq n$.

Yhdesti yhtenäisten tasoalueiden konformisten itsekuvausten ryhmät sup-metriikassa

2014

Harmoniset funktiot kompleksialueessa ja konformikuvaukset

2014

Tämän tutkielman tarkoituksena on syventää tietoja kompleksianalyysistä tutustumalla harmonisiin funktioihin ja konformikuvauksiin. Funktioita, jotka toteuttavat Laplacen yhtälön, kutsutaan harmonisiksi funktioiksi. Harmonisten funktioiden määrittämiseen voidaan käyttää Cauchy-Riemannin yhtälöitä. Harmoniset funktioit ovat yhteydessä analyyttisiin funktioihin, sillä harmonisten funktioiden avulla voidaan selittää analyyttisten kuvausten teoriaa ja päinvastoin. Tämän tutkielman kannalta tärkeimpiä analyyttisiä kuvauksia ovat injektiiviset kuvaukset, jotka tunnetaan myös konformikuvauksina. Konformikuvaukset ovat alueiden välisiä kuvauksia, jotka säilyttävät kulmien suuruuden ja suunnan ja jo…

Quasiconformal Jordan Domains

2020

We extend the classical Carath\'eodory extension theorem to quasiconformal Jordan domains $( Y, d_{Y} )$. We say that a metric space $( Y, d_{Y} )$ is a quasiconformal Jordan domain if the completion $\overline{Y}$ of $( Y, d_{Y} )$ has finite Hausdorff $2$-measure, the boundary $\partial Y = \overline{Y} \setminus Y$ is homeomorphic to $\mathbb{S}^{1}$, and there exists a homeomorphism $\phi \colon \mathbb{D} \rightarrow ( Y, d_{Y} )$ that is quasiconformal in the geometric sense. We show that $\phi$ has a continuous, monotone, and surjective extension $\Phi \colon \overline{ \mathbb{D} } \rightarrow \overline{ Y }$. This result is best possible in this generality. In addition, we find a n…

Weighted Hardy Spaces of Quasiconformal Mappings

2019

We establish a weighted version of the $H^p$-theory of quasiconformal mappings.

Radial symmetry of p-harmonic minimizers

2017

"It is still not known if the radial cavitating minimizers obtained by Ball [J.M. Ball, Discontinuous equilibrium solutions and cavitation in nonlinear elasticity, Phil. Trans. R. Soc. Lond. A 306 (1982) 557--611] (and subsequently by many others) are global minimizers of any physically reasonable nonlinearly elastic energy". The quotation is from [J. Sivaloganathan and S. J. Spector, Necessary conditions for a minimum at a radial cavitating singularity in nonlinear elasticity, Ann. Inst. H. Poincare Anal. Non Lineaire 25 (2008), no. 1, 201--213] and seems to be still accurate. The model case of the $p$-harmonic energy is considered here. We prove that the planar radial minimizers are indee…