Geodesic
A remark on the essential spectra of quasi-similar dominant contractions
Glasgow mathematical journal, Tome 31 (1989) no. 2, pp. 165-168

Voir la notice de l'article provenant de la source Cambridge University Press

We consider operators, i.e. bounded linear transformations, on an infinite dimensional separable complex Hilbert space H into itself. The operator A is said to be dominant if for each complex number λ there exists a number Mλ(≥l) such that ∥(A – λ)*x∥ ≤ Mλ∥A – λ)x∥ for each x∈H. If there exists a number M≥Mλ for all λ, then the dominant operator A is said to be M-hyponormal. The class of dominant (and JW-hyponormal) operators was introduced by J. G. Stampfli during the seventies, and has since been considered in a number of papers, amongst then [7], [11]. It is clear that a 1-hyponormal is hyponormal. The operator A*A is said to be quasi-normal if Acommutes with A*A, and we say that A is subnormal if A has a normal extension. It is known that the classes consisting of these operators satisfy the following strict inclusion relation: 
Duggal, B. P. A remark on the essential spectra of quasi-similar dominant contractions. Glasgow mathematical journal, Tome 31 (1989) no. 2, pp. 165-168. doi: 10.1017/S0017089500007680
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