Yerevan, Armenia
Yerevan, Armenia

Yerevan State University is a public university in Yerevan, Armenia. Founded on May 16, 1919, it is the largest university in the country with 110 departments. Of its 3,150 employees, 1,190 comprise the teaching staff which includes 25 academicians, 130 professors, 700 docents , and 360 assistant lecturers. The university has 400 researchers, 1,350 post-graduate students, and 8,500 undergraduates, including 300 students from abroad. Instruction is in Armenian, but instruction in Russian and English for foreign students is arranged according to need. The academic year is from September 1 through June 30. Wikipedia.


Time filter

Source Type

Escherichia coli molecular hydrogen (H 2) production was studied during mixed carbon (glucose and glycerol) fermentation at pH 6.5. Wild type cells in the assays supplemented with glucose produced H 2 at ~2 fold lower level than cells grown on glucose only. When compared to the wild type, H 2 production in the assays added with glucose was decreased by ~2 fold in fhlA, hyfG and double fhlA hyfG mutants and by ~1.5 fold in hyaB, hybC, and double hyaB hybC mutants. However, in the assays with glycerol, no measurable H 2 production was detected. Taken together, these results suggest that during mixed carbon fermentation, H 2 could be produced with low efficiency via Hyd-3 and Hyd-4. This is a novel finding for Hyd-4 activity at pH 6.5. The insignificant decrease of H 2 production in the strains with defects in Hyd-1 and Hyd-2 was probably due to an interaction between the Hyd enzymes and their organization in the bacterial membrane. In the glucose assays, H 2 production in the wild type cells was inhibited ~2 fold by 0.3mM N,N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of the F 0F 1-ATPase. This inhibition was the same for fhlA and hyfG fhlA mutants but not hyaB, hybC, hyfG or hyaB hybC mutants. The results indicate that the FhlA protein coded by the fhlA gene might interact with the F 0F 1-ATPase. We propose that this interaction is mediated by mixed carbon fermentation. © 2012 Elsevier B.V..


Balyan M.K.,Yerevan State University
Journal of Synchrotron Radiation | Year: 2014

A numerical method of reconstruction of an object image using an X-ray dynamical diffraction Fraunhofer hologram is presented. Analytical approximation methods and numerical methods of iteration are discussed. An example of a reconstruction of an image of a cylindrical beryllium wire is considered. The results of analytical approximation and zero-order iteration coincide with exact values of the amplitude complex transmission coefficient of the object as predicted by the resolution limit of the scheme, except near the edges of the object. Calculations of the first- and second-order iterations improve the result at the edges of the object. This method can be applied for determination of the complex amplitude transmission coefficient of amplitude as well as phase objects. It can be used in X-ray microscopy.© 2014 International Union of Crystallography.


Balyan M.K.,Yerevan State University
Journal of Synchrotron Radiation | Year: 2014

Taking into account background correction and using Fourier analysis, a numerical method of an object image correction using an X-ray dynamical diffraction Fraunhofer hologram is presented. An example of the image correction of a cylindrical beryllium wire is considered. A background correction of second-order iteration leads to an almost precise reconstruction of the real part of the amplitude transmission coefficient and improves the imaginary part compared with that without a background correction. Using Fourier analysis of the reconstructed transmission coefficient, non-physical oscillations can be avoided. This method can be applied for the determination of the complex amplitude transmission coefficient of amplitude as well as phase objects, and can be used in X-ray microscopy. © 2014 International Union of Crystallography.


Avetisyan Y.H.,Yerevan State University
Optics Letters | Year: 2010

A scheme of terahertz (THz)-wave surface-emitted difference-frequency generation (SEDFG), which lacks the drawbacks associated with the usage of periodically orientation-inverted structures, is proposed. It is shown that both material birefringence of the bulk LiNbO3 crystal and modal birefringence of GaAs/AlAs waveguide are sufficient to obtain SEDFG up to a frequency of ∼3 THz. The simplicity of the proposed scheme, along with the fact that there is a much smaller THz-wave decay in nonlinear crystal, makes it a good candidate for the practical realization of efficient THz generation. The use of a GaAs waveguide with an oxidized AlAs layer is proposed for enhanced THz-wave SEDFG in the vicinity of the GaAs polariton resonance at 8 THz. © 2010 Optical Society of America.


H2 has a great potential as an ecologically-clean, renewable and capable fuel. It can be mainly produced via hydrogenases (Hyd) by different bacteria, especially Escherichia coli and Rhodobacter sphaeroides. The operation direction and activity of multiple Hyd enzymes in E. coli during mixed-acid fermentation might determine H2 production; some metabolic cross-talk between Hyd enzymes is proposed. Manipulating the activity of different Hyd enzymes is an effective way to enhance H2 production by E. coli in biotechnology. Moreover, a novel approach would be the use of glycerol as feedstock in fermentation processes leading to H2 production. Mixed carbon (sugar and glycerol) utilization studies enlarge the kind of organic wastes used in biotechnology. During photo-fermentation under limited nitrogen conditions, H2 production by Rh. sphaeroides is observed when carbon and nitrogen sources are supplemented. The relationship of H2 production with H+ transport across the membrane and membrane-associated ATPase activity is shown. On the other hand, combination of carbon sources (succinate, malate) with different nitrogen sources (yeast extract, glutamate, glycine) as well as different metal (Fe, Ni, Mg) ions might regulate H2 production. All these can enhance H2 production yield by Rh. sphaeroides in biotechnology Finally, two of these bacteria might be combined to develop and consequently to optimize two stages of H2 production biotechnology with high efficiency transformation of different organic sources. © 2015 Informa Healthcare USA, Inc.


Balyan M.,Yerevan State University
Journal of Synchrotron Radiation | Year: 2013

An X-ray dynamical diffraction Fraunhofer holographic scheme is proposed. Theoretically it is shown that the reconstruction of the object image by visible light is possible. The spatial and temporal coherence requirements of the incident X-ray beam are considered. As an example, the hologram recording as well as the reconstruction by visible light of an absolutely absorbing wire are discussed. © 2013 International Union of Crystallography Printed in Singapore-all rights reserved.


We analyze the periodic motion in the conformal mechanics describing particles moving near the horizon of extreme Reissner-Nordström and axion-dilaton (Clément-Gal'tsov) black holes. For this purpose, we extract the (two-dimensional) compact (angular) parts of these systems and construct their action-angle variables. In the first case, we obtain the well-known spherical Landau problem, which possesses hidden so(3) symmetry, while in the latter case the system does not have a hidden constant of motion. In both the cases, we indicate the existence of 'critical points', separating the regions of periodic motions with qualitatively different properties. © 2012 IOP Publishing Ltd.


Gevorgyan A.H.,Yerevan State University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

In the present paper we investigated the optical properties of a stack of right- and left- hand chiral photonic crystal layers. The problem is solved by Ambartsumian's layer addition modified method. We investigated the reflection spectra peculiarities of this system and showed that in contrast to a single cholesteric liquid crystal (CLC) layer this system has multiple photonic band gaps (PBGs) (at light normal incidence). We showed that this system has unique polarization properties, particularly the eigenpolarizations (EPs) of the system are degenerated (i.e., the two EPs coincide) for an even number of layers and, in contrast to ordinary gyrotropic systems, the polarization plane rotation decreases if the system thickness is increased, the rotation sign depends on the first sublayer chirality sign, the system is very sensitive to the change of the sublayer number in the system, etc. We also investigated the influence of sublayer thicknesses, incidence angle, the sublayer local dielectric anisotropies, the sublayer helix pitches on the reflection peculiarities, and other optical parameters of the system. © 2012 American Physical Society.


Balyan M.K.,Yerevan State University
Acta Crystallographica Section A: Foundations of Crystallography | Year: 2010

The theoretical investigation of double-slit dynamical X-ray diffraction in ideal crystals shows that, on the exit surface of crystals, interference fringes similar to Youngs fringes are formed. An expression for the period of the fringes was obtained. The visibility of the fringes depending on temporal and spatial coherent properties of the incident beam is studied. The polarization state of the incident beam also affects the visibility of the fringes, which in turn depends on the size of the slits. The deviation from Braggs exact angle causes a shift of the fringes and can also affect the amplitude of the intensity. One of the parameters on which the visibility of the fringes depends is the source-crystal distance. The proposed scheme can be used as a Rayleigh X-ray interferometer. Use of the scheme as a Michelson X-ray stellar interferometer is also possible. © 2010 International Union of Crystallography Printed in Singapore - all rights reserved.


Gevorgyan A.H.,Yerevan State University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

In the present paper we consider reflection spectra peculiarities of a cholesteric liquid crystal (CLC) cell with two defect layers. We consider both the isotropic and anisotropic defect cases. The problem is solved by Ambartsumian's modified layer addition and Muller's matrix methods. We investigated the influence of the defect layer thicknesses and location changes in the CLC cell on the defect modes and the photonic band gap. In particular, we considered (in detail) the cases when the defect layers are half-wave or quarter-wave plates. We also investigated the influence of dielectric borders on the reflection spectra. We showed that the subject system possesses the property of structural nonreciprocity, and that the system can work as a tunable filter, a mirror, and a low threshold laser. We also showed that the system can work as a light modulator, or as an optical diode, or as a system for getting linearly polarized light with electrically tunable polarization plane rotation, as well as a device for getting linearly polarized light from nonpolarized light, again with electrically tunable polarization plane rotation. © 2011 American Physical Society.

Loading Yerevan State University collaborators
Loading Yerevan State University collaborators