On a class of extremal quasi-conformal mappings
On a fundamental variational lemma for extremal quasiconformal mappings.
On a Hölder type estimate for quasisymmetric functions
We give a Hölder type estimate for normalized ρ-quasisymmetric functions, improving some results of J. Zając.
On a modification of the Poisson integral operator
Given a quasisymmetric automorphism γ of the unit circle T we define and study a modification Pγ of the classical Poisson integral operator in the case of the unit disk D. The modification is done by means of the generalized Fourier coefficients of γ. For a Lebesgue's integrable complex-valued function f on T, Pγ[f] is a complex-valued harmonic function in D and it coincides with the classical Poisson integral of f provided γ is the identity mapping on T. Our considerations are motivated by the...
On a paper of Carleson.
On a result by Clunie and Sheil-Small
In 1984 J. Clunie and T. Sheil-Small proved ([2, Corollary 5.8]) that for any complex-valued and sense-preserving injective harmonic mapping F in the unit disk D, if F(D) is a convex domain, then the inequality |G(z2)− G(z1)| < |H(z2) − H(z1)| holds for all distinct points z1, z2∈ D. Here H and G are holomorphic mappings in D determined by F = H + Ḡ, up to a constant function. We extend this inequality by replacing the unit disk by an arbitrary nonempty domain Ω in ℂ and improve it provided F...
On a theorem of Lindelöf
We give a quasiconformal version of the proof for the classical Lindelöf theorem: Let f map the unit disk D conformally onto the inner domain of a Jordan curve C. Then C is smooth if and only if arh f'(z) has a continuous extension to D. Our proof does not use the Poisson integral representation of harmonic functions in the unit disk.
On a theorem of Nehari and quasidiscs.
On an asymptotically sharp variant of Heinz's inequality.
On an extremum problem in the class of mappings, quasiconformal in the mean.
On boundary correspondence under quasiconformal mappings.
On boundary homeomorphisms of trans-quasiconformal maps of the disk.
On complexification and iteration of quasiregular polynomials which have algebraic degree two
We prove that each degree two quasiregular polynomial is conjugate to Q(z) = z² - (p+q)|z|² + pqz̅² + c, |p| < 1, |q| < 1. We also show that the complexification of Q can be extended to a polynomial endomorphism of ℂℙ² which acts as a Blaschke product (z-p)/(1-p̅z) · (z-q)/(1-q̅z) on ℂℙ²∖ℂ². Using this fact we study the dynamics of Q under iteration.
On Convergence and Quasiregularity of Interpolating Complex Planar Splines.
On Dittmar's approach to the Beltrami equation
We recall an old result of B. Dittmar. This result permits us to obtain an existence theorem for the Beltrami equation and some other results as a direct consequence of Moser's classical estimates for elliptic operators.
On Dyakonov type theorems for harmonic quasiregular mappings
We prove two Dyakonov type theorems which relate the modulus of continuity of a function on the unit disc with the modulus of continuity of its absolute value. The methods we use are quite elementary, they cover the case of functions which are quasiregular and harmonic, briefly hqr, in the unit disc.
On folding solutions of the Beltrami equation.
On geometric convergence of discrete groups
One of the basic questions in the Kleinian group theory is to understand both algebraic and geometric limiting behavior of sequences of discrete subgroups. In this paper we consider the geometric convergence in the setting of the isometric group of the real or complex hyperbolic space. It is known that if is a non-elementary finitely generated group and a sequence of discrete and faithful representations, then the geometric limit of is a discrete subgroup of . We generalize this result by...
On Hölder regularity for elliptic equations of non-divergence type in the plane
This paper is concerned with strong solutions of uniformly elliptic equations of non-divergence type in the plane. First, we use the notion of quasiregular gradient mappings to improve Morrey’s theorem on the Hölder continuity of gradients of solutions. Then we show that the Gilbarg-Serrin equation does not produce the optimal Hölder exponent in the considered class of equations. Finally, we propose a conjecture for the best possible exponent and prove it under an additional restriction.
On isomorphisms of geometrically finite Möbius groups