In this paper we are interested in generalizing Keller-type eigenvalue estimates for the non-
selfadjoint Schrödinger operator to the Dirac operator, imposing some suitable rigidity …

The one-dimensional Dirac operator with a singular interaction term which is formally given
by A⊗| δ 0>< δ 0|, where A is an arbitrary 2× 2 matrix and δ 0 stands for the Dirac …

In this paper, we establish an analytic enclosure for the spectrum of unbounded linear
operators~ A admitting an n*n matrix representation in a Hilbert space H=H_1⊕⋯⊕H_n. For …

A two-dimensional contact problem for an elastic layer of a finite thickness is considered with
the effects of friction and wear taken into account. It is assumed that the contact zone is …

We introduce concepts of essential numerical range for the linear operator pencil. In contrast
to the operator essential numerical range, the pencil essential numerical ranges are, in …

We establish new analytic results for a general class of rational spectral problems. They
arise eg in modelling photonic crystals whose capability to control the flow of light depends …

We prove that the eigenvalues of the n-dimensional massive Dirac operator D _0+ VD 0+ V,
n ≥ 2 n≥ 2, perturbed by a potential V, possibly non-Hermitian, are contained in the union …

In this paper we show that for the domain intersection dom T∩ dom T⁎ of a closed linear
operator and its Hilbert space adjoint everything is possible for very common classes of …

We introduce the new concepts of pseudo numerical range for operator functions and
families of sesquilinear forms as well as the pseudo block numerical range for n× n operator …

We study location of eigenvalues of one-dimensional discrete Schrödinger operators with
complex ℓ^ p ℓ p-potentials for 1 ≤ p ≤ ∞ 1≤ p≤∞. In the case of ℓ^ 1 ℓ 1-potentials, the …