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2007 | Buch

The Extended Field of Operator Theory

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As this volume demonstrates, at roughly 100 years of age operator theory remains a vibrant and exciting subject area with wide ranging applications. Many of the th papers found here expandon lectures givenat the 15 International Workshop on Operator Theory and Its Applications, held at the University of Newcastle upon th th Tyne from the 12 to the 16 of July 2004. The workshop was attended by close to 150 mathematicians from throughout the world, and is the ?rst IWOTA to be held in the UK. Talks ranged over such subjects as operator spaces and their - plications, invariant subspaces, Kre? ?n space operator theory and its applications, multivariate operator theory and operator model theory, applications of operator theory to function theory, systems theory including inverse scattering, structured matrices, and spectral theory of non-selfadjoint operators, including pseudodi?- ential and singular integral operators. These interests are re?ected in this volume. As with all of the IWOTA proceedings published by Birkh¨ auser Verlag, the - pers presented here have been refereed to the same high standards as those of the journal Integral Equations and Operator Theory. BANACH C* ALGEBRAS H CONTROL HILBERT KREIN OPERATOR THEORY INTERPOLATION VON NEUMANN A few words about the above image which graced the workshop programme and bag. In commuting between home in Hexham and work in Newcastle, I often x Editorial Preface travel by train.

Inhaltsverzeichnis

Frontmatter
Inverse Scattering to Determine the Shape of a Vocal Tract
Abstract
The inverse scattering problem is reviewed for determining the cross sectional area of a human vocal tract. Various data sets are examined resulting from a unit-amplitude, monochromatic, sinusoidal volume velocity sent from the glottis towards the lips. In case of nonuniqueness from a given data set, additional information is indicated for the unique recovery.
Tuncay Aktosun
Positivity and the Existence of Unitary Dilations of Commuting Contractions
Abstract
The central result of this paper is a method of characterizing those commuting tuples of operators that have a unitary dilation, in terms of the existence of a positive map with certain properties. Although this positivity condition is not necessarily easy to check given a concrete example, it can be used to find practical tests in some circumstances. As an application, we extend a dilation theorem of Sz.-Nagy and Foiaş concerning regular dilations to a more general setting
J. Robert Archer
The Infinite-dimensional Continuous Time Kalman-Yakubovich-Popov Inequality
Abstract
We study the set M Σ of all generalized positive self-adjoint solutions (that may be unbounded and have an unbounded inverse) of the KYP (Kalman-Yakubovich-Popov) inequality for a infinite-dimensional linear time-invariant system Σ in continuous time with scattering supply rate. It is shown that if M Σ is nonempty, then the transfer function of Σ coincides with a Schur class function in some right half-plane. For a minimal system Σ the converse is also true. In this case the set of all HM Σ with the property that the system is still minimal when the original norm in the state space is replaced by the norm induced by H is shown to have a minimal and a maximal solution, which correspond to the available storage and the required supply, respectively. The notions of strong H-stability, H-*-stability and H-bistability are introduced and discussed. We show by an example that the various versions of H-stability depend crucially on the particular choice of HM Σ. In this example, depending on the choice of the original realization, some or all HM Σ will be unbounded and/or have an unbounded inverse.
Damir Z. Arov, Olof J. Staffans
From Toeplitz Eigenvalues through Green’s Kernels to Higher-order Wirtinger-Sobolev Inequalities
Abstract
The paper is concerned with a sequence of constants which appear in several problems. These problems include the minimal eigenvalue of certain positive definite Toeplitz matrices, the minimal eigenvalue of some higher-order ordinary differential operators, the norm of the Green kernels of these operators, the best constant in a Wirtinger-Sobolev inequality, and the conditioning of a special least squares problem. The main result of the paper gives the asymptotics of this sequence.
Albrecht Böttcher, Harold Widom
The Method of Minimal Vectors Applied to Weighted Composition Operators
Abstract
We study the behavior of the sequence of minimal vectors corresponding to certain classes of operators on L 2 spaces, including weighted composition operators such as those induced by Möbius transformations. In conjunction with criteria for quasinilpotence, the convergence of sequences associated with the minimal vectors leads to the construction of hyperinvariant subspaces.
Isabelle Chalendar, Antoine Flattot, Jonathan R. Partington
The Continuous Analogue of the Resultant and Related Convolution Operators
Abstract
For a class of pairs of entire matrix functions the null space of the natural analogue of the classical resultant matrix is described in terms of the common Jordan chains of the defining entire matrix functions. The main theorem is applied to two inverse problems. The first concerns convolution integral operators on a finite interval with matrix valued kernel functions and complements earlier results of [6]. The second is the inverse problem for matrix-valued continuous analogues of Szegő orthogonal polynomials.
Israel Gohberg, Marinus A. Kaashoek, Leonid Lerer
Split Algorithms for Centrosymmetric Toeplitz-plus-Hankel Matrices with Arbitrary Rank Profile
Abstract
Split Levinson and Schur algorithms for the inversion of centrosymmetric Toeplitz-plus-Hankel matrices are designed that work, in contrast to previous algorithms, for matrices with any rank profile. Furthermore, it is shown that the algorithms are related to generalized ZW-factorizations of the matrix and its inverse.
Georg Heinig, Karla Rost
Schmidt-Representation of Difference Quotient Operators
Abstract
We consider difference quotient operators in de Branges Hilbert spaces of entire functions. We give a description of the spectrum and a formula for the spectral subspaces. The question of completeness of the system of eigenvectors and generalized eigenvectors is discussed. For certain cases the s-numbers and the Schmidt-representation of the operator under discussion is explicitly determined.
Michael Kaltenbäck, Harald Woracek
Algebras of Singular Integral Operators with Piecewise Continuous Coefficients on Weighted Nakano Spaces
Abstract
We find Fredholm criteria and a formula for the index of an arbitrary operator in the Banach algebra of singular integral operators with piecewise continuous coefficients on Nakano spaces (generalized Lebesgue spaces with variable exponent) with Khvedelidze weights over either Lyapunov curves or Radon curves without cusps. These results “localize” the Gohberg-Krupnik Fredholm theory with respect to the variable exponent.
Alexei Yu. Karlovich
Pseudodifferential Operators with Compound Slowly Oscillating Symbols
Abstract
Let V (ℝ) denote the Banach algebra of absolutely continuous functions of bounded total variation on ℝ. We study an algebra \( \mathfrak{B} \) of pseudodifferential operators of zero order with compound slowly oscillating V (ℝ)-valued symbols (x, y) ↦ a(x, y, ·) of limited smoothness with respect to x, y ∈ ℝ. Sufficient conditions for the boundedness and compactness of pseudodifferential operators with compound symbols on Lebesgue spaces L p(ℝ) are obtained. A symbol calculus for the algebra \( \mathfrak{B} \) is constructed on the basis of an appropriate approximation of symbols by infinitely differentiable ones and by use of the techniques of oscillatory integrals. A Fredholm criterion and an index formula for pseudodifferential operators A\( \mathfrak{B} \) are obtained. These results are carried over to Mellin pseudodifferential operators with compound slowly oscillating V (ℝ)-valued symbols. Finally, we construct a Fredholm theory of generalized singular integral operators on weighted Lebesgue spaces L p with slowly oscillating Muckenhoupt weights over slowly oscillating Carleson curves.
Yuri I. Karlovich
Extension of Operator Lipschitz and Commutator Bounded Functions
Abstract
Let (B(H) ‖·‖) be the algebra of all bounded operators on an infinite-dimensional Hilbert space H. Let B(H)sa be the set of all selfadjoint operators in B(H). Throughout the paper we denote by α a compact subset of ℝ and by B(H)sa(α) the set of all operators in B(H)sa with spectrum in α:
$$ B(H)_{sa} (\alpha ) = \{ A = A^* \in B(H): Sp(A) \subseteq \alpha \} . $$
We will use similar notations A sa, A sa(α) for a Banach *-algebra A. Each bounded Borel function g on α defines, via the spectral theorem, a map Ag(A) from B(H)sa(α) into B(H). Various smoothness conditions when imposed on this map define the corresponding classes of operator-smooth functions.
Edward Kissin, Victor S. Shulman, Lyudmila B. Turowska
On the Kernel of Some One-dimensional Singular Integral Operators with Shift
Abstract
An estimate for the dimension of the kernel of the singular integral operator with shift \( \left( {I + \sum\limits_{j = 1}^n {a_j (t)U^j } } \right)P_ + + P_ - :L_2 (\mathbb{R}) \to L_2 (\mathbb{R}) \) is obtained, where P ± are the Cauchy projectors, (U ψ)(t) = ψ(t+h), h ∈ ℝ+, is the shift operator and a j(t) are continuous functions on the one point compactification of ℝ. The roots of the polynomial \( 1 + \sum\limits_{j = 1}^n {a_j (\infty )\eta ^j } \) are assumed to belong all simultaneously either to the interior of the unit circle or to its exterior.
Viktor G. Kravchenko, Rui C. Marreiros
The Fredholm Property of Pseudodifferential Operators with Non-smooth Symbols on Modulation Spaces
Abstract
The aim of the paper is to study the Fredholm property of pseudodifferential operators in the Sjöstrand class OPS w where we consider these operators as acting on the modulation spaces M 2, p (ℝN). These spaces are introduced by means of a time-frequency partition of unity. The symbol class S w does not involve any assumptions on the smoothness of its elements.
In terms of their limit operators, we will derive necessary and sufficient conditions for operators in OPS w to be Fredholm. In particular, it will be shown that the Fredholm property and, thus, the essential spectra of operators in this class are independent of the modulation space parameter p ∈ (1, ∞).
Vladimir S. Rabinovich, Steffen Roch
On Indefinite Cases of Operator Identities Which Arise in Interpolation Theory
Abstract
Operator identities involving nonnegative selfadjoint operators play a fundamental role in interpolation theory and its applications. The theory is generalized here to selfadjoint operators whose negative spectra consist of a finite number of eigenvalues of finite total multiplicity. It is shown that such identities are closely associated with generalized Nevanlinna functions by means of the Kreĭn-Langer integral representation. The Potapov fundamental matrix inequality is generalized to this situation, and it is used to formulate and solve an operator interpolation problem analogous to the definite case.
James Rovnyak, Lev A. Sakhnovich
Singular Integral Operators in Weighted Spaces of Continuous Functions with Oscillating Continuity Moduli and Oscillating Weights
Abstract
We present a survey of some results on the theory of singular integral operators with piece-wise continuous coefficients in the weighted spaces of continuous functions with a prescribed continuity modulus (generalized Hölder spaces H ω(Γ, ρ)) together with some new results related to oscillating (non-equilibrated) characteristics and oscillating weights.
Natasha Samko
Poly-Bergman Spaces and Two-dimensional Singular Integral Operators
Abstract
We describe a direct and transparent connection between the poly-Bergman type spaces on the upper half-plane and certain two-dimensional singular integral operators.
Nikolai Vasilevski
Weak Mixing Properties of Vector Sequences
Abstract
Notions of weak and uniformly weak mixing (to zero) are defined for bounded sequences in arbitrary Banach spaces. Uniformly weak mixing for vector sequences is characterized by mean ergodic convergence properties. This characterization turns out to be useful in the study of multiple recurrence, where mixing properties of vector sequences, which are not orbits of linear operators, are investigated. For bounded sequences, which satisfy a certain domination condition, it is shown that weak mixing to zero is equivalent with uniformly weak mixing to zero.
László Zsidó
Metadaten
Titel
The Extended Field of Operator Theory
herausgegeben von
Michael A. Dritschel
Copyright-Jahr
2007
Verlag
Birkhäuser Basel
Electronic ISBN
978-3-7643-7980-3
Print ISBN
978-3-7643-7979-7
DOI
https://doi.org/10.1007/978-3-7643-7980-3