Chisinau, Moldova

Slavonic University
Chisinau, Moldova
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Gurzadyan A.V.,Slavonic University | Kocharyan A.A.,Monash University
International Journal of Modern Physics D | Year: 2017

A framework is developed enabling the global analysis of the stability of cosmological models using the local geometric characteristics of the infinite-dimensional superspace, i.e. using the generalized Jacobi equation reformulated for pseudo-Riemannian manifolds. We give a direct formalism for dynamical analysis in the superspace, the requisite equation pertinent for stability analysis of the universe by means of generalized covariant and Fermi derivative is derived. Then, the relevant definitions and formulae are retrieved for cosmological models with a scalar field. © 2017 World Scientific Publishing Company

Nagornyi V.D.,Axispoint Inc. | Zanimonskiy Y.M.,Ukrainian Academy of Sciences | Zanimonskiy Y.Y.,Slavonic University
Metrologia | Year: 2011

The correction due to the finite speed of light is among the most inconsistent in absolute gravimetry. Formulae reported by different authors yield corrections scattered up to 8 νGal for no obvious reasons. The problem, though noted before, has never been studied, and nowadays the correction is rather postulated than rigorously proven. In this paper we make an attempt to revise the subject. Like other authors, we use physical models based on signal delays and the Doppler effect; however, in implementing the models we additionally introduce two scales of time associated with moving and stationary reflectors, derive a set of rules to switch between the scales and establish the equivalence of trajectory distortions as obtained from either time delay or distance progression. The obtained results enabled us to produce accurate correction formulae for different types of instruments, and to explain the differences in the results obtained by other authors. We found that the correction derived from the Doppler effect is accountable only for two-thirds of the total correction due to the finite speed of light, if no signal delays are considered. Another major source of inconsistency was found in the tacit use of simplified trajectory models. © 2011 BIPM & IOP Publishing Ltd.

Kazaryan E.M.,Slavonic University | Shahnazaryan V.A.,Slavonic University | Sarkisyan H.A.,Slavonic University | Sarkisyan H.A.,Yerevan State University
Optics Communications | Year: 2014

An analytical solution of the quantum problem of an electron on a spherical segment with angular confinement potential in the form of rectangular impenetrable walls is presented. It is shown that the problem is reduced to finding solution of hypergeometric equation. On the basis of the obtained results the optical interband transitions in this system are discussed, and the threshold frequency and absorption coefficient both for single structure and non-interacting ensemble are calculated. The influence of electric field on system is discussed and it is shown that in such type of structure linear Stark shift takes place. Quantum transitions in the presence of electric field are considered and it is shown that the selection rule for an orbital quantum number analogue is removed. © 2013 Elsevier B.V.

Harutyunyan V.A.,Slavonic University
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2014

With the use of WKB (Wentzel-Kramers-Brillouin) method the quantum-mechanical problem of single-particle states in semiconductor quantized cylindrical and spherical layers is solved. Explicit analytical dependences of the energy spectrum and wave functions of charge carriers on geometrical sizes of the system and quantum numbers of radial and orbital movements of the particles are obtained. The results of analytical solution are compared with the results of numerical calculations. The results obtained are used to calculate coefficients of interband optical absorption in cylindrical and spherical heterolayers. © 2013 Elsevier B.V.

Harutyunyan V.A.,Slavonic University
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2014

The single-particle states in a cylindrical nanotube placed in the field of charged ring are considered theoretically in the effective-mass approximation. The electrostatic field of charged ring creates an additional quantum well the symmetry axes of system. It is shown, that this quantum well can be described as one-dimensional modified Coulomb-like potential By using a variation-method the wave functions and energy levels of the first two states of charge carriers in the well were obtained. The interband and intraband electro-optical transitions in the tube are also considered. © 2013 Elsevier B.V.

Paployan V.A.,Slavonic University
Journal of Contemporary Physics | Year: 2015

The results of calculations of frequency of collective oscillations of electrons in metallic nanoshells are presented. The influence of interaction retardation is taken into account by the Rayleigh method. It is shown that the retardation results in a considerable decrease of the oscillation frequency, which, in its turn, reduces the radiation width of the spectrum. As a result, the spectral sensitivity of nanoshells is increasing. © 2015, Allerton Press, Inc.

Tevosyan H.K.,Slavonic University
Journal of Contemporary Physics | Year: 2012

Quantum states and energy levels of an electron in a spherical quantum dot with a modified Pöschel-Teller potential are studied. Analytical expressions for the wave function and energy of particle in the absence of impurity are obtained. Within the framework of variational method the impurity states are studied and by using numerical methods the dependences of the particle energy on the parameters of the spherical quantum dot are derived. Dependences of the electron binding energy on the half-width and depth of the potential well are revealed. © 2012 Allerton Press, Inc.

Nagornyi V.D.,Metromatix Inc. | Zanimonskiy Y.M.,Ukrainian Academy of Sciences | Zanimonskiy Y.Y.,Slavonic University
Metrologia | Year: 2011

In the paper by Rothleitner and Francis (2011 Metrologia 48 187-95) the correction due to the finite speed of light in absolute gravimeters is analysed from the viewpoint of special relativity. The relativistic concepts eventually lead to the two classical approaches to the problem: analysis of the beat frequency, and introduction of the retarded times. In the first approach, an additional time delay has to be assumed, because the frequency of the beam bounced from the accelerated reflector differs at the point of reflection from that at the point of interference. The retarded times formalism is equivalent to a single Doppler shift, but results in the same correction as the beat frequency approach, even though the latter explicitly combines two Doppler shifts. In our comments we discuss these and other problems we found with the suggested treatment of the correction. © 2011 BIPM & IOP Publishing Ltd.

Gevorgyan A.H.,Slavonic University
Journal of Contemporary Physics | Year: 2016

Intra-subband transitions caused by light absorption in a parabolic quantum well is considered taking into account the scattering by ionized impurity centers. To calculate the scattering matrix element, the Born approximation is used and the interaction with the impurity is described by the Coulomb potential. An analytical expression for the absorption coefficient of processes with the initial absorption of photon and further scattering by an ionized impurity center is obtained. For absorption coefficient the frequency characteristics and dependence on the width of quantum well are examined. © 2016, Allerton Press, Inc.

Dvoyan K.G.,Slavonic University
Physica B: Condensed Matter | Year: 2012

Confined states of a positronium (Ps) in the spherical quantum dot (QD) are theoretically investigated in three size-quantization (SQ) regimes: strong, weak and intermediate. In the strong SQ regime, analytical expressions for the wave functions (WFs) and energy of the electronpositron pair are obtained. In the weak SQ regime, the Ps energy and binding energy are analytically calculated. To calculate the Ps energy in the intermediate SQ regime, variational and numerical methods are used. It is shown that, in the corresponding limits, the results obtained by variational method agree with those obtained in the strong and weak SQ regimes. © 2011 Elsevier B.V. All rights reserved.

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