Geodesic
On the Spectra of Some Non-Normal Operators
Bulletin of the Malaysian Mathematical Society, Tome 31 (2008) no. 2 Cet article a éte moissonné depuis la source Bulletin of the Malaysian Mathematical Society website

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In this paper, we prove the following: (1) If T is invertible ω-hyponormal completely non-normal, then the point spectrum is empty. (2) If T1 and T2 are injective ω-hyponormal and if T and S are quasisimilar, then they have the same spectra and essential spectra. (3) If T is ( p,k )-quasihyponormal operator, then σ jp ( T )- {0} = σ ap ( T )- {0} . (4) If T ∗ , S ∈ Β(Η) are injective (p, k)-quasihyponormal operator, and if XT = SX , where X ∈ Β(Η) is an invertible, then there exists a unitary operator U such that UT = SU and hence T and S are normal operators.
Classification : 47A10, 47B20. 
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     author = {M. H. M. Rashid and M. S. M. Noorani and A. S. Saari},
     title = {On the {Spectra} of {Some} {Non-Normal} {Operators}},
     journal = {Bulletin of the Malaysian Mathematical Society},
     year = {2008},
     volume = {31},
     number = {2},
     url = {http://geodesic.mathdoc.fr/item/BMMS_2008_31_2_a2/}
}
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M. H. M. Rashid; M. S. M. Noorani; A. S. Saari. On the Spectra of Some Non-Normal Operators. Bulletin of the Malaysian Mathematical Society, Tome 31 (2008) no. 2. http://geodesic.mathdoc.fr/item/BMMS_2008_31_2_a2/