Real analytic families of harmonic functions in a planar domain with a small hole

We consider a Dirichlet problem in a planar domain with a hole of diameter proportional to a real parameter ?   and we denote by _u?$u_{?}$ the corresponding solution. The behavior of _u?$u_{?}$ for ?   small and positive can be described in terms of real analytic functions of two variables evaluated at (?,1/log??)$(?,1/\log ??)$. We show that under suitable assumptions on the geometry and on the boundary data one can get rid of the logarithmic behavior displayed by _u?$u_{?}$ for ?   small and describe _u?$u_{?}$ by real analytic functions of ?. Then it is natural to ask what happens when ? is negative. The case of boundary data depending on ? is also considered. The aim is to study real analytic families of harmonic functions which are not necessarily solutions of a particular boundary value problem.     

Bohr radius for subordinating families of analytic functions and bounded harmonic mappings

The class consisting of analytic functions f   in the unit disk satisfying f+αzf^′+γz²f^″$f+\alpha z{f}^{\prime }+\gamma z^2{f}^{″}$ subordinated to some function h is considered. The Bohr radius for this class is obtained when h is respectively convex or starlike. The Bohr radius for analytic functions mapping the unit disk into a concave-wedge domain as well as for bounded harmonic mappings are also established.     

Real analytic generalized functions

Real analytic generalized functions are introduced and investigated. The analytic singular support and analytic wave front of a generalized function in are introduced and described. Authors’ addresses: S. Pilipović, Department of Mathematics and Informatics, University of Novi Sad, Trg D. Obradovića 4, 21000 Novi Sad, Serbia; D. Scarpalezos, U.F.R. de Mathématiques, Université Paris 7, 2 Place Jussieu, Paris 5^e, 75005, France; V. Valmorin, Université des Antilles et de la Guyane, Département Math-Info, Campus de Fouillole, 97159 Pointe á Pitre Cedex, France     

Real analytic generalized functions

Real analytic generalized functions are introduced and investigated. The analytic singular support and analytic wave front of a generalized function in G(W){\cal G}(\Omega) are introduced and described.     

Simple eigenvalues for the Steklov problem in a domain with a small hole. A functional analytic approach

Let be a bounded open domain of . Let denote the outward unit normal of . We assume that the Steklov problem Δu = 0 in and on has a simple eigenvalue of . Then we consider an annular domain obtained by removing from a small‐cavity size of ε > 0, and we show that under proper assumptions there exists a real valued and real analytic function defined in an open neighborhood of (0,0) in and such that is a simple eigenvalue for the Steklov problem Δu = 0 in and on for all ε > 0 small enough, and such that . Here denotes the outward unit normal of , and δ_2,2 ≡ 1 and δ_2,n ≡ 0 if n ≥ 3. Then related statements have been proved for corresponding eigenfunctions. Copyright © 2013 John Wiley & Sons, Ltd.     

Free interpolation of harmonic functions by analytic functions

In the paper one describes the subsets E of the unit circle, for which L¦_E=H¦_E (the functions from the Lebesgue space on the circumference are assumed to be harmonically continued into the circle). The condition consists of two parts: the Carleson-Newman conditions and some geometric condition. One obtains partial results for the sets E such that L _E ¹ =H¹¦_E. It is shown that if the set E does not satisfy the Blaschke condition, then for 1 < p < we have L^P¦_E=H^P¦_E if and only if E lies on the Lobachevskii line.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Maternaticheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 107, pp. 209–212, 1982.The author expresses his deep gratitude to his scientific adviser V. P. Khavin for useful discussions.     

Normal families of harmonic functions

A condition on the majorant (depending on a single coordinate) of a family of functions harmonic in a sphere is determined whose satisfaction guarantees normality of the family.Translated from Matematicheskie Zametki, Vol. 3, No. 5, pp. 547–552, May, 1968.]     

On one representation of analytic functions by harmonic functions

Let u(x) be a function analytic in some neighborhood D about the origin, $ \mathcal{D} Let u(x) be a function analytic in some neighborhood D about the origin, ⊂ ℝ ⁿ . We study the representation of this function in the form of a series u(x) = u ₀(x) + |x|² u ₁(x) + |x|⁴ u ₂(x) + …, where u _k (x) are functions harmonic in . This representation is a generalization of the well-known Almansi formula. Original Russian Text ? V. V. Karachik, 2007, published in Matematicheskie Trudy, 2007, Vol. 10, No. 2, pp. 142–162.     

Integral representations of analytic and harmonic functions

Doklady Mathematics -     

Estimates of analytic functions in Jordan domain

The classical estimates for analytic functions in a disc are carried over to functions which are analytic in Jordan domains whose boundaries are Lipschitz and Radon curves. Singular integrals, maximal estimates, and Lusin's inequality are considered. Analytic functions, the moduli of whose boundary values satisfy the conditions of B. Muckenhoupt are studied in detail. Properties of conformal maps and their level lines connected with the Muckenhoupt conditions on the moduli of the boundary derivatives are considered. This consideration lets one give real proofs of various distortion theorems for conformal maps of Lipschitz domains.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 73, pp. 70–90, 1977.     

An extension of Lewis's Lemma,renormalization of harmonic and analytic functions,and normal families

An extension of a lemma due to J. Lewis is established and is used to give rapid proofs of some classical theorems in complex function theory such as Montel's theorem and Miranda's theorem. Another application of Lewis's Lemma yields a general normality criterion for families of harmonic and holomorphic functions. This criterion permits a quick proof of Bloch's classical covering theorem for holomorphic functions (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Indefinite metric and scattering by a domain with a small hole

For the problem of plane waves scattered by a domain with a small hole, we suggest a model based on the theory of self-adjoint extensions of symmetric operators in a space with indefinite metric. For two-dimensional problems of scattering on a line with a hole and on a semi-ellipse connected by a hole with a half-plane, we justify the choice of extension that guarantees the coincidence of the model solution with the solution of the actual problem in the far zone with a high degree of accuracy.Translated fromMatematicheskie Zametki, Vol. 58, No. 6, pp. 837–850, December, 1995.The authors are grateful to B. S. Pavlov and L. M. Grigoryan for useful discussion.The work was partially supported by the State Commission on Higher Education of the Russian Federation under grant No. 94-2.7-1067.     

Distributional boundary values of harmonic and analytic functions

A theory for distributional boundary values of harmonic and analytic functions is presented. In this analysis there arise several indicators that measure the growth of these functions near the boundaries. An extension of the Phragmén-Lindelöf maximum principle is derived. Furthermore, the algebraic properties of the space of real periodic distributions are studied. By introducing a new product, the harmonic product, the boundary conditions involving harmonic functions are transformed into ordinary differential equations.     

Representation of functions analytic in a closed domain by series of rational functions

A method is given for representing functions analytic in a closed Jordan domain by series of the form (where the poles _n lie outside the domain) and a bound is obtained for the coefficients A_n.Translated from Matematicheskie Zametki, Vol. 4, No. 2, pp. 191–200, August, 1968.     

Cyclicity of zeros of families of analytic functions

Let be a family of holomorphic functions in the unit disk , which are also holomorphic in a parameter . We express cyclicity (=generalized multiplicity) of a zero of at via some algebraic characteristics of the ideal generated by the Taylor coefficients of . As an example we estimate the cyclicity of the family of generalized exponential polynomials.