Zobrazeno 1 - 8
of 8
pro vyhledávání: '"Hubert Klaja"'
Publikováno v:
Bulletin of the London Mathematical Society. 50:986-996
We study different operator radii of homomorphisms from an operator algebra into $B(H)$ and show that these can be computed explicitly in terms of the usual norm. As an application, we show that if $\Omega$ is a $K$-spectral set for a Hilbert space o
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::caede4f54632ecfeb7b261b09b604142
https://doi.org/10.1112/blms.12191
https://doi.org/10.1112/blms.12191
Autor:
Thomas Ransford, Hubert Klaja
Publikováno v:
Journal of Functional Analysis. 272:4158-4164
In a Banach algebra, the spectrum satisfies σ ( a b ) ∖ { 0 } = σ ( b a ) ∖ { 0 } for each pair of elements a , b . We show that this is no longer true for the exponential spectrum, thereby solving a problem open since 1992. Our proof depends o
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::ea8db1fd3a8f5a31355364887848e096
https://doi.org/10.1016/j.jfa.2017.02.017
https://doi.org/10.1016/j.jfa.2017.02.017
Publikováno v:
Operators and Matrices. :749-757
We define and study a numerical-range analogue of the notion of spectral set. Among the results obtained are a positivity criterion and a dilation theorem, analogous to those already known for spectral sets. An important difference from the classical
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_dedup___::7c090426c4471d56e5181e8d0b26e9b3
https://doi.org/10.7153/oam-11-51
https://doi.org/10.7153/oam-11-51
Publikováno v:
Proceedings of the American Mathematical Society. 144:3009-3018
Let T T be an operator on a Hilbert space H H with numerical radius w ( T ) ≤ 1 w(T)\le 1 . According to a theorem of Berger and Stampfli, if f f is a function in the disk algebra such that f ( 0 ) = 0 f(0)=0 , then w ( f ( T ) ) ≤ ‖ f ‖ ∞
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_dedup___::b28a5aaab60551333a2998da79cdfe03
https://doi.org/10.1090/proc/12955
https://doi.org/10.1090/proc/12955
Autor:
Hubert Klaja
Publikováno v:
Studia Mathematica. :1-11
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::dad63daeefe85efe7d77a51e60bb19dd
https://doi.org/10.4064/sm8241-3-2016
https://doi.org/10.4064/sm8241-3-2016
Autor:
Hubert Klaja
Publikováno v:
Integral Equations and Operator Theory. 83:429-445
In this paper, we prove that every diagonal operator on a Hilbert space of which is of multiplicity one and has perfect spectrum admits a rank one perturbation without eigenvalues. This answers a question of Ionascu.
18 Pages
18 Pages
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_dedup___::fe669ed7acf45d44100a7acb9a030b2b
https://doi.org/10.1007/s00020-015-2250-5
https://doi.org/10.1007/s00020-015-2250-5
Publikováno v:
Complex Analysis and Operator Theory. 10:97-107
We consider Dirichlet spaces with superharmonic weights. This class contains both the harmonic weights and the power weights. Our main result is a characterization of the Dirichlet spaces with superharmonic weights that can be identified as de Brange
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::c2775a178fbd94edbe20683950114f35
https://doi.org/10.1007/s11785-015-0474-7
https://doi.org/10.1007/s11785-015-0474-7
Autor:
Hubert Klaja
Publikováno v:
Journal of Mathematical Analysis and Applications. 411:177-195
The aim of this paper is to describe the closure of the numerical range of the product of two orthogonal projections in Hilbert space as a closed convex hull of some explicit ellipses parametrized by points in the spectrum. Several improvements (remo
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_dedup___::e5cb99583554dfe2362e42fe4ef3da5b
https://doi.org/10.1016/j.jmaa.2013.09.024
https://doi.org/10.1016/j.jmaa.2013.09.024