104 citations · 288 across the 40 of their papers we have counts for
26 papers · 1 filter
A sharp bound for the functional calculus of -contractions
Felix L. Schwenninger, Jens de Vries
Let be a -contraction and a rational function mapping the closed unit disk into itself. With a new characterization of -contractions we prove that \begin{align*} \big…
The algebraic numerical range as a spectral set in Banach algebras
Hanna Blazhko, Daniil Homza, Felix L. Schwenninger +2
We investigate when the algebraic numerical range is a -spectral set in a Banach algebra. While providing several counterexamples based on classical ideas as well as combinatori…
The double-layer potential for spectral constants revisited
F. L. Schwenninger, J. de Vries
We thoroughly analyse the double-layer potential's role in approaches to spectral sets in the spirit of Delyon--Delyon, Crouzeix and Crouzeix--Palencia. While the potential is well…
Continuous maximal regularity in locally convex spaces
Karsten Kruse, Felix L. Schwenninger
We study maximal regularity with respect to continuous functions for strongly continuous semigroups on locally convex spaces as well as its relation to the notion of admissible ope…
Admissible operators for sun-dual semigroups
Sahiba Arora, Felix L. Schwenninger
We extend classical duality results by Weiss on admissible operators to settings where the dual semigroup lacks strong continuity. This is possible using the sun-dual framework, wh…
The lattice structure of negative Sobolev and extrapolation spaces
Sahiba Arora, Jochen Glück, Felix L. Schwenninger
It is well-known that the Sobolev spaces are vector lattices with respect to the pointwise almost everywhere order if , but not if .…
Limit-case admissibility for positive infinite-dimensional systems
Sahiba Arora, Jochen Glück, Lassi Paunonen +1
In the context of positive infinite-dimensional linear systems, we systematically study -admissible control and observation operators with respect to the limit-cases $p=\infty…
On Abstract Spectral Constants
Felix L. Schwenninger, Jens de Vries
We prove bounds for a class of unital homomorphisms arising in the study of spectral sets, by involving extremal functions and vectors. These are used to recover three celebrated r…
Sun dual theory for bi-continuous semigroups
Karsten Kruse, Felix L. Schwenninger
The sun dual space corresponding to a strongly continuous semigroup is a known concept when dealing with dual semigroups, which are in general only weak-continuous. In this pap…
Characterization of Orlicz admissibility
René Hosfeld, Birgit Jacob, Felix L. Schwenninger
In this note we extend two characterizations of admissible operators with respect to to more general Orlicz spaces. The equivalent conditions are given by the proper…
On equicontinuity and tightness of bi-continuous semigroups
Karsten Kruse, Felix L. Schwenninger
In contrast to classical strongly continuous semigroups, the study of bi-continuous semigroups comes with some freedom in the properties of the associated locally convex topology.…
Laplace-Carleson embeddings and infinity-norm admissibility
Birgit Jacob, Jonathan R. Partington, Sandra Pott +2
A full characterization of the boundedness of Laplace--Carleson embeddings on is provided, in terms of the Carleson intensity of the respective measure and of a suitable…
A refinement of Baillon's theorem on maximal regularity
Birgit Jacob, Felix Schwenninger, Jens Wintermayr
By Baillon's result, it is known that maximal regularity with respect to the space of continuous functions is rare; it implies that either the involved semigroup generator is a bou…
Crouzeix's Conjecture and related problems
Kelly Bickel, Pamela Gorkin, Anne Greenbaum +3
In this paper, we establish several results related to Crouzeix's conjecture. We show that the conjecture holds for contractions with eigenvalues that are sufficiently well-separat…
Integral input-to-state stability of unbounded bilinear control systems
René Hosfeld, Birgit Jacob, Felix Schwenninger
We study input-to-state stability of bilinear control systems with possibly unbounded control operators. Natural sufficient conditions for integral input-to-state stability are giv…
Strong input-to-state stability for infinite dimensional linear systems
Robert Nabiullin, Felix Schwenninger
This paper deals with strong versions of input-to-state stability and integral input-to-state stability of infinite-dimensional linear systems with an unbounded input operator. We…
On continuity of solutions for parabolic control systems and input-to-state stability
Birgit Jacob, Felix Schwenninger, Hans Zwart
We study minimal conditions under which mild solutions of linear evolutionary control systems are continuous for arbitrary bounded input functions. This question naturally appears…
Remarks on the Crouzeix-Palencia proof that the numerical range is a -spectral set
Thomas Ransford, Felix Schwenninger
Crouzeix and Palencia recently showed that the numerical range of a Hilbert-space operator is a -spectral set for the operator. One of the principal ingredients of thei…
Functional calculus estimates for Tadmor-Ritt operators
Felix Schwenninger
We show -functional calculus estimates for Tadmor-Ritt operators (also known as Ritt operators), which generalize and improve results by Vitse. These estimates are in c…
A law for cosine families with to
Felix L. Schwenninger, Hans Zwart
For being a cosine family on a unital normed algebra, we show that the estimate implies that …
Functional calculus for -semigroups using infinite-dimensional systems theory
Felix Schwenninger, Hans Zwart
In this short note we use ideas from systems theory to define a functional calculus for infinitesimal generators of strongly continuous semigroups on a Hilbert space. Among others,…
On measuring unboundedness of the -calculus for generators of analytic semigroups
Felix Schwenninger
We investigate the boundedness of the -calculus by estimating the bound of the mapping : $f\mapsto f(A)T(\varepsilo…
Zero-two law for cosine families
Felix Schwenninger, Hans Zwart
For being a strongly continuous cosine family on a Banach space, we show that the estimate implies that …
Less than one implies zero
Felix Schwenninger, Hans Zwart
In this paper we show that from the estimate we can conclude that equals . Here is a stro…