Now showing 1 - 10 of 17
  • Publication
    Universal Taylor series, conformal mappings and boundary behaviour
    (Annales De L'Institit Fourier, 2013-12)
    A holomorphic function f on a simply connected domain Ω is said to possess a universal Taylor series about a point in Ω if the partial sums of that series approximate arbitrary polynomials on arbitrary compacta K outside Ω (provided only that K has connected complement). This paper shows that this property is not conformally invariant, and, in the case where Ω is the unit disc, that such functions have extreme angular boundary behaviour.
      315
  • Publication
    Existence of universal Taylor series for non-simply connected domains
    (Springer-Verlag, 2012-05-27)
    It is known that, for any simply connected proper subdomain Ω of the complex plane and any point ζ in Ω, there are holomorphic functions on Ω that possess “universal” Taylor series expansions about ζ; that is, partial sums of the Taylor series approximate arbitrary polynomials on arbitrary compacta in ℂ\Ω that have connected complement. This paper shows, for nonsimply connected domains Ω, how issues of capacity, thinness and topology affect the existence of holomorphic functions on Ω that have universal Taylor series expansions about a given point.
      412Scopus© Citations 12
  • Publication
    Boundary behaviour of universal Taylor series
    (Elsevier Masson, 2014-02) ;
    A power series that converges on the unit disc D is called universal if its partial sums approx- imate arbitrary polynomials on arbitrary compacta in CnD that have connected complement. This paper shows that such series grow strongly and possess a Picard-type property near each boundary point.
      459Scopus© Citations 9
  • Publication
    Stationary Boundary Points for a Laplacian Growth Problem in Higher Dimensions
    It is known that corners of interior angle less than π/2 in the boundary of a plane domain are initially stationary for Hele–Shaw flow arising from an arbitrary injection point inside the domain. This paper establishes the corresponding result for Laplacian growth of domains in higher dimensions. The problem is treated in terms of evolving families of quadrature domains for subharmonic functions.
      312
  • Publication
    Universal Taylor series for non-simply connected domains
    It is known that, for any simply connected proper subdomain Omega of the complex plane and any point zeta in Omega, there are holomorphic functions on Omega that have "universal" Taylor series expansions about zeta; that is, partial sums of the Taylor series approximate arbitrary polynomials on arbitrary compacta in C\Omega that have connected complement. This note shows that this phenomenon can break down for non-simply connected domains Omega, even when C\Omega is compact. This answers a question of Melas and disproves a conjecture of Müller, Vlachou and Yavrian.
      676Scopus© Citations 13
  • Publication
    Two-phase quadrature domains
    Recent work on two-phase free boundary problems has led to the investigation of a new type of quadrature domain for harmonic functions. This paper develops a method of constructing such quadrature domains based on the technique of partial balayage, which has proved to be a useful tool in the study of one-phase quadrature domains and Hele-Shaw flows.
      540Scopus© Citations 16
  • Publication
    Boundary Behaviour of Universal Taylor Series on Multiply Connected Domains
    A holomorphic function on a planar domain Ω is said to possess a universal Taylor series about a point ζ of Ω if subsequences of the partial sums of the Taylor series approximate arbitrary polynomials on arbitrary compact sets in C∖Ω that have connected complement. In the case where Ω is simply connected, such functions are known to be unbounded and to form a collection that is independent of the choice of ζ. This paper uses tools from potential theory to show that, even for domains Ω of arbitrary connectivity, such functions are unbounded whenever they exist. In the doubly connected case, a further analysis of boundary behaviour reveals that the collection of such functions can depend on the choice of ζ. This phenomenon was previously known only for domains that are at least triply connected. Related results are also established for universal Laurent series.
      418Scopus© Citations 6
  • Publication
    Harmonic functions which vanish on a cylindrical surface
    (Elsevier, 2016-01-15) ;
    Suppose that a harmonic function h on a finite cylinder vanishes on the curved part of the boundary. This paper answers a question of Khavinson by showing that h then has a harmonic continuation to the infinite strip bounded by the hyperplanes containing the flat parts of the boundary. The existence of this extension is established by an analysis of the convergence properties of a double series expansion of the Green function of an infinite cylinder beyond the domain itself.
      309Scopus© Citations 9
  • Publication
    Sets of determination for the Nevanlinna class
    (London Mathematical Society, 2010-11-06)
    This paper characterizes the subsets E of the unit disc D with the property that the supremum of |f| over E equals the supremum over D for all functions f in the Nevanlinna class.
      341Scopus© Citations 1
  • Publication
    Recent progress on fine differentiability and fine harmonicity
    (American Mathematical Society, 2012-12-15)
    This paper describes recent results concerning the notions of differentiability and harmonicity with respect to the ne topology of classical potential theory.
      406