New inequalities for the A-numerical radius of products and sums operators acting on a semi-Hilbert space, i.e. space generated by positive semidefinite operator A, are established. In particular, every T S which admit A-adjoints, it is proved that ?A(TS) ? 1/2?A(ST) + 1/4 (||T||A||S||A ||TS||A), where ?A(T) ||T||A denote A-operator seminorm an respectively.

The abstract Cauchy problem for the non-stationary bulk queue M(t)|M[k, B]|1 Abstract We derived state probability equations describing the queue M (t)| M [k, B]|1 and formulated as an abstract Cauchy problem to investigate by means of the semi-group theory of bounded linear operators in functional analysis. With regard to the abstract Cauchy problem of this queue, we determined the eigenfuncti...

We study semi-iterative methods for an approximate solution of a linear equation x = Tx+c with a bounded linear operator T acting on a Banach space X, considering separately the cases when λ = 1 is an isolated and accumulation spectral point for T . We give necessary and sufficient conditions for the convergence of a semi-iterative method, utilizing the generalized Drazin inverse introduced by ...

An operator in a Banach space is called upper (lower) semi-Browder if it is upper (lower) semi-Fredholm and has a finite ascent (descent). We extend this notion to n-tuples of commuting operators and show that this notion defines a joint spectrum. Further we study relations between semi-Browder and (essentially) semiregular operators. Denote by L(X) the algebra of all bounded linear operators i...

We consider a semi-classical completely integrable system defined by a ~-pseudodifferential operator Ĥ on the torus T. In order to study perturbed operators of the form Ĥ + ~K̂ , where K̂ is an arbitrary pseudodifferential operator and κ > 0, we prove the conjugacy to a suitable normal form. This is then used to construct a large number of quasimodes.

In the discrete setting of one-dimensional finite-differences we prove a Carleman estimate for a semi-discretization of the parabolic operator ∂t − ∂x(c∂x) where the diffusion coefficient c has a jump. As a consequence of this Carleman estimate, we deduce consistent nullcontrollability results for classes of semi-linear parabolic equations.

Let B be a generator of positivity preserving (shortly, positive) semi-group in L 2 on a space with-nite measure. It is supposed that the semigroup e ?tB ; t > 0; acts continuously from L 2 to L 1. For a measurable function V 0 an estimate for the number of negative eigenvalues of the operator B ? V is obtained, generalizing the similar estimate for the the Schrr odinger operator (the CLR-estim...

inf u 6 Ttu(x) 6 u(x) 6 Ťtu(x) 6 supu for each t > 0 and each x ∈ H. A function u : H −→ R is called k-semi-concave, k > 0, if the function x −→ u(x)−‖x‖2/k is concave. The function u is called k-semi-convex if −u is k-semiconcave. A bounded function u is t-semi-concave if and only if it belongs to the image of the operator Tt, this follows from Lemma 1 and Lemma 3 below. A function is called s...