It was pointed out that the black hole quasinormal modes resulting from a piecewise approximate potential are drastically distinct those pertaining to original metric. In particular, instead of lining up parallel imaginary axis, spectrum is found stretch along real axis. this work, we prove if there single discontinuity in effective potential, no matter how insignificant it is, asymptotical beh...

We present approximation algorithms for point-to-surface registration problems which have applications in medical navigation systems. One of the central tasks of such a system is to determine a “good” mapping (the registration transformation or registration for short) of the coordinate system of the operation theatre onto the coordinate system of a 3D model M of a patient, generated from CRor M...

It is well-known that the topological boundary of the spectrum of an operator is contained in the approximate point spectrum. We show that the one-sided version of this result is not true. This gives also a negative answer to a problem of Schmoeger. Denote by L(X) the algebra of all bounded linear operators acting in a Banach space X. For T ∈ L(X) denote by σ(T ), σl(T ) and σπ(T ) the spectrum...

pulse echo b - scan imaging systems have been used for years in medical diagnosis. the theroy of such systems have been investigated by several researchers. in this paper, we introduce a new model for b - scan imaging system based on gaussian type transducer. an imaging system is normally identified by its point response function. this function describes the image of a single physical point obj...

Exploiting a spectral criterion for a system not to be AT we give some new examples of zero entropy systems without the AT property. Our examples include those with finite spectral multiplicity – in particular we show that the system arising from the Rudin-Shapiro substitution is not AT. We also show that some nil-rotations on a quotient of the Heisenberg group as well as some (generalized) Gau...

In cellular networks, a recent trend is to make spectrum access dynamic in the spatial and temporal dimensions, for the sake of efficient utilization of spectrum. In such a model, the spectrum is divided into channels and periodically allocated to competing base stations using an auction-based market mechanism. An efficient auction mechanism is essential to the success of such a dynamic spectru...

let $varphi(z)=z^m, z in mathbb{u}$, for some positive integer $m$, and $c_varphi$ be the composition operator on the bergman space $mathcal{a}^2$ induced by $varphi$. in this article, we completely determine the point spectrum, spectrum, essential spectrum, and essential norm of the operators $c^*_varphi c_varphi, c_varphi c^*_varphi$ as well as self-commutator and anti-self-commutators of $c_...