• Title/Summary/Keyword: essentially p-hyponormal operators

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SPECTRAL CONTINUITY OF ESSENTIALLY p-HYPONORMAL OPERATORS

  • Kim, An-Hyun;Kwon, Eun-Young
    • Bulletin of the Korean Mathematical Society
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    • v.43 no.2
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    • pp.389-393
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    • 2006
  • In this paper it is shown that the spectrum ${\sigma}$ is continuous at every p-hyponormal operator when restricted to the set of essentially p-hyponormal operators and moreover ${\sigma}$ is continuous when restricted to the set of compact perturbations of p-hyponormal operators whose spectral pictures have no holes associated with the index zero.

POSINORMAL TERRACED MATRICES

  • Rhaly, H. Crawford, Jr.
    • Bulletin of the Korean Mathematical Society
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    • v.46 no.1
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    • pp.117-123
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    • 2009
  • This paper is a study of some properties of a collection of bounded linear operators resulting from terraced matrices M acting through multiplication on ${\ell}^2$; the term terraced matrix refers to a lower triangular infinite matrix with constant row segments. Sufficient conditions are found for M to be posinormal, meaning that $MM^*=M^*PM$ for some positive operator P on ${\ell}^2$; these conditions lead to new sufficient conditions for the hyponormality of M. Sufficient conditions are also found for the adjoint $M^*$ to be posinormal, and it is observed that, unless M is essentially trivial, $M^*$ cannot be hyponormal. A few examples are considered that exhibit special behavior.