Mostrando recursos 1 - 20 de 24

  1. Weighted Banach spaces of Lipschitz functions

    Jiménez-Vargas, A.
    Given a pointed metric space $X$ and a weight $v$ on $\widetilde{X}$ (the complement of the diagonal set in $X\times X$ ), let $\mathrm{Lip}_{v}(X)$ and $\mathrm{lip}_{v}(X)$ denote the Banach spaces of all scalar-valued Lipschitz functions $f$ on $X$ vanishing at the basepoint such that $v\Phi(f)$ is bounded and $v\Phi(f)$ vanishes at infinity on $\widetilde{X}$ , respectively, where $\Phi(f)$ is the de Leeuw’s map of $f$ on $\widetilde{X}$ , under the weighted Lipschitz norm. The space $\mathrm{Lip}_{v}(X)$ has an isometric predual $\mathcal{F}_{v}(X)$ and it is proved that $(\mathrm{Lip}_{v}(X),\tau_{\operatorname{bw}^{*}})=(\mathcal{F}_{v}(X)^{*},\tau_{c})$ and $\mathcal{F}_{v}(X)=((\mathrm{Lip}_{v}(X),\tau_{\operatorname{bw}^{*}})',\tau_{c})$ , where $\tau_{\operatorname{bw}^{*}}$ denotes the bounded weak∗ topology and $\tau_{c}$ the...

  2. Stability of average roughness, octahedrality, and strong diameter $2$ properties of Banach spaces with respect to absolute sums

    Haller, Rainis; Langemets, Johann; Nadel, Rihhard
    We prove that, if Banach spaces $X$ and $Y$ are $\delta$ -average rough, then their direct sum with respect to an absolute norm $N$ is $\delta/N(1,1)$ -average rough. In particular, for octahedral $X$ and $Y$ and for $p$ in $(1,\infty)$ , the space $X\oplus_{p}Y$ is $2^{1-1/p}$ -average rough, which is in general optimal. Another consequence is that for any $\delta$ in $(1,2]$ there is a Banach space which is exactly $\delta$ -average rough. We give a complete characterization when an absolute sum of two Banach spaces is octahedral or has the strong diameter 2 property. However, among all of the...

  3. Generalized frames for operators associated with atomic systems

    Li, Dongwei; Leng, Jinsong; Huang, Tingzhu
    In this paper, we investigate the g-frame and Bessel g-sequence related to a linear bounded operator $K$ in Hilbert space, which we call a $K$ -g-frame and a $K$ -dual Bessel g-sequence, respectively. Since the frame operator for a $K$ -g-frame may not be invertible, there is no classical canonical dual for a $K$ -g-frame. So we characterize the concept of a canonical $K$ -dual Bessel g-sequence of a $K$ -g-frame that generalizes the classical dual of a g-frame. Moreover, we use a family of linear operators to characterize atomic systems. We also consider the construction of new atomic systems...

  4. Vector lattices and $f$ -algebras: The classical inequalities

    Buskes, G.; Schwanke, C.
    We present some of the classical inequalities in analysis in the context of Archimedean (real or complex) vector lattices and $f$ -algebras. In particular, we prove an identity for sesquilinear maps from the Cartesian square of a vector space to a geometric mean closed Archimedean vector lattice, from which a Cauchy–Schwarz inequality follows. A reformulation of this result for sesquilinear maps with a geometric mean closed semiprime Archimedean $f$ -algebra as codomain is also given. In addition, a sufficient and necessary condition for equality is presented. We also prove a Hölder inequality for weighted geometric mean closed Archimedean $\Phi$ -algebras,...

  5. Local matrix homotopies and soft tori

    Loring, Terry A.; Vides, Fredy
    We present solutions to local connectivity problems in matrix representations of the form $C([-1,1]^{N})\to C^{*}(u_{\varepsilon},v_{\varepsilon})$ , with $C_{\varepsilon}(\mathbb{T}^{2})\twoheadrightarrow C^{*}(u_{\varepsilon},v_{\varepsilon})$ for any $\varepsilon\in[0,2]$ and any integer $n\geq1$ , where $C^{*}(u_{\varepsilon},v_{\varepsilon})\subseteq M_{n}$ is an arbitrary matrix representation of the universal $C^{*}$ -algebra $C_{\varepsilon}(\mathbb{T}^{2})$ that denotes the soft torus. We solve the connectivity problems by introducing the so-called toroidal matrix links, which can be interpreted as normal contractive matrix analogies of free homotopies in differential algebraic topology. ¶ To deal with the locality constraints, we have combined some techniques introduced in this article with some techniques from matrix geometry, combinatorial optimization, and classification...

  6. A variant of the Hankel multiplier

    Ghobber, Saifallah
    The first aim of this article is to survey and revisit some uncertainty principles for the Hankel transform by means of the Hankel multiplier. Then we define the wavelet Hankel multiplier and study its boundedness and Schatten-class properties. Finally, we prove that the wavelet Hankel multiplier is unitary equivalent to a scalar multiple of the phase space restriction operator, for which we deduce a trace formula.

  7. Approximate uniqueness for maps from $C(X)$ into simple real rank $0$ C∗-algebras

    Ng, P. W.
    Let $X$ be a finite CW-complex, and let $\mathcal{A}$ be a unital separable simple finite $\mathcal{Z}$ -stable C∗-algebra with real rank $0$ . We prove an approximate uniqueness theorem for almost multiplicative contractive completely positive linear maps from $C(X)$ into $\mathcal{A}$ . We also give conditions for when such a map can, within a certain “error,” be approximated by a finite-dimensional ∗-homomorphism.

  8. On the universal function for weighted spaces $L^{p}_{\mu}[0,1]$ , $p\geq 1$

    Grigoryan, Martin; Grigoryan, Tigran; Sargsyan, Artsrun
    In this article, we show that there exist a function $g\in L^{1}[0,1]$ and a weight function $0\lt \mu(x)\leq1$ so that $g$ is universal for each class $L^{p}_{\mu}[0,1]$ , $p\geq 1$ , with respect to signs-subseries of its Fourier–Walsh series.

  9. Hörmander-type theorems on unimodular multipliers and applications to modulation spaces

    Huang, Qiang; Chen, Jiecheng; Fan, Dashan; Zhu, Xiangrong
    In this article, for the unimodular multipliers $e^{i\mu (D)}$ , we establish two Hörmander-type multiplier theorems by assuming conditions on their phase functions $\mu $ . As applications, we obtain two multiplier theorems particularly fitting for the modulation spaces, thus allowing us to extend and improve some known results.

  10. Daugavet property and separability in Banach spaces

    Rueda Zoca, Abraham
    We give a characterization of the separable Banach spaces with the Daugavet property which is applied to study the Daugavet property in the projective tensor product of an $L$ -embedded space with another nonzero Banach space. The former characterization also motivates the introduction and short study of two indices related to the Daugavet property.

  11. Toeplitz operators on the space of real analytic functions: The Fredholm property

    Domański, Pawel; Jasiczak, Michal
    We completely characterize those continuous operators on the space of real analytic functions on the real line for which the associated matrix is Toeplitz (that is, we describe Toeplitz operators on this space). We also prove a necessary and sufficient condition for such operators to be Fredholm operators. While the space of real analytic functions is neither Banach space nor has a basis which makes available methods completely different from classical cases of Hardy spaces or Bergman spaces, nevertheless the results themselves show surprisingly strong similarity to the classical Hardy-space theory.

  12. New function spaces related to Morrey spaces and the Fourier transform

    Nakamura, Shohei; Sawano, Yoshihiro
    We introduce new function spaces to handle the Fourier transform on Morrey spaces and investigate fundamental properties of the spaces. As an application, we generalize the Stein–Tomas Strichartz estimate to our spaces. The geometric property of Morrey spaces and related function spaces will improve some well-known estimates.

  13. Linear dependency of translations and square-integrable representations

    Linnell, Peter A.; Puls, Michael J.; Roman, Ahmed
    Let $G$ be a locally compact group. We examine the problem of determining when nonzero functions in $L^{2}(G)$ have linearly independent left translations. In particular, we establish some results for the case when $G$ has an irreducible, square-integrable, unitary representation. We apply these results to the special cases of the affine group, the shearlet group, and the Weyl–Heisenberg group. We also investigate the case when $G$ has an abelian, closed subgroup of finite index.

  14. Non-self-adjoint Schrödinger operators with nonlocal one-point interactions

    Kuzhel, Sergii; Znojil, Miloslav
    We generalize and study, within the framework of quantum mechanics and working with $1$ -dimensional, manifestly non-Hermitian Hamiltonians $H=-{d^{2}}/{dx^{2}}+V$ , the traditional class of exactly solvable models with local point interactions $V=V(x)$ . We discuss the consequences of the use of nonlocal point interactions such that $(Vf)(x)=\int K(x,s)f(s)\,ds$ by means of the suitably adapted formalism of boundary triplets.

  15. Characterizations of asymmetric truncated Toeplitz operators

    Câmara, Crisina; Jurasik, Joanna; Kliś-Garlicka, Kamila; Ptak, Marek
    The aim of this paper is to investigate asymmetric truncated Toeplitz operators with $L^{2}$ -symbols between two different model spaces given by inner functions such that one divides the other. The class of symbols corresponding to the zero operator is described. Asymmetric truncated Toeplitz operators are characterized in terms of operators of rank at most $2$ , and the relations with the corresponding symbols are studied.

  16. Duality properties for generalized frames

    Enayati, F.; Asgari, M. S.
    We introduce the concept of Riesz-dual sequences for g-frames. In this paper we show that, for any sequence of operators, we can construct a corresponding sequence of operators with a kind of duality relation between them. This construction is used to prove duality principles in g-frame theory, which can be regarded as general versions of several well-known duality principles for frames. We also derive a simple characterization of a g-Riesz basic sequence as a g-R-dual sequence of a g-frame in the tight case.

  17. Point multipliers and the Gleason–Kahane–Żelazko theorem

    Ghodrat, Razieh Sadat; Sady, Fereshteh
    Let $A$ be a Banach algebra, and let $\mathcal{X}$ be a left Banach $A$ -module. In this paper, using the notation of point multipliers on left Banach modules, we introduce a certain type of spectrum for the elements of $\mathcal{X}$ and we also introduce a certain subset of $\mathcal{X}$ which behaves as the set of invertible elements of a commutative unital Banach algebra. Among other things, we use these sets to give some Gleason–Kahane–Żelazko theorems for left Banach $A$ -modules.

  18. Tent spaces at endpoints

    Ding, Yong; Mei, Ting
    In 1985, Coifman, Meyer, and Stein gave the duality of the tent spaces; that is, $(T_{q}^{p}(\mathbb{R}^{n+1}_{+}))^{\ast}=T_{q'}^{p'}(\mathbb{R}^{n+1}_{+})$ for $1\lt p,q\lt \infty$ , and $(T_{\infty}^{1}(\mathbb{R}^{n+1}_{+}))^{\ast}=\mathscr{C}(\mathbb{R}^{n+1}_{+})$ , $(T_{q}^{1}(\mathbb{R}^{n+1}_{+}))^{\ast}=T_{q'}^{\infty}(\mathbb{R}^{n+1}_{+})$ for $1\lt q\lt \infty$ , where $\mathscr{C}(\mathbb{R}^{n+1}_{+})$ denotes the Carleson measure space on $\mathbb{R}^{n+1}_{+}$ . We prove that $(\mathscr{C}_{v}(\mathbb{R}^{n+1}_{+}))^{\ast}=T_{\infty}^{1}(\mathbb{R}^{n+1}_{+})$ , which we introduced recently, where $\mathscr{C}_{v}(\mathbb{R}^{n+1}_{+})$ is the vanishing Carleson measure space on $\mathbb{R}^{n+1}_{+}$ . We also give the characterizations of $T_{q}^{\infty}(\mathbb{R}^{n+1}_{+})$ by the boundedness of the Poisson integral. As application, we give the boundedness and compactness on $L^{q}(\mathbb{R}^{n})$ of the paraproduct $\pi_{F}$ associated with the tent space $T_{q}^{\infty}(\mathbb{R}^{n+1}_{+})$ , and we extend partially an...

  19. On the composition ideals of Lipschitz mappings

    Saadi, Khalil
    We study some properties of Lipschitz mappings which admit factorization through an operator ideal. Lipschitz cross norms have been established from known tensor norms in order to represent certain classes of Lipschitz mappings. Inspired by the definition of $p$ -summing linear operators, we derive a new class of Lipschitz mappings that is called strictly Lipschitz $p$ -summing.

  20. Sine and cosine equations on hypergroups

    Fechner, Żywilla; Székelyhidi, László
    This article deals with trigonometric functional equations on hypergroups. We describe the general continuous solution of sine and cosine addition formulas and a so-called sine-cosine functional equation on a locally compact hypergroup in terms of exponential functions, sine functions, and second-order generalized moment functions.

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