European University at Kiev

Kiev, Ukraine

European University at Kiev

Kiev, Ukraine

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Trokhimchuck P.P.,European University at Kiev
Proceedings of the International Conference on Advanced Optoelectronics and Lasers, CAOL | Year: 2016

The problem of modeling of mixed processes of Relaxed Optics (RO) is discussed. Correlations between photoinized, plasmic and thermal processes and radiated and unradiated relaxation are analyzed for various regimes of irradiation. The problem of creation stable structures is discussed too. © 2016 IEEE.

Brik M.G.,University of Tartu | Kityk I.V.,Czestochowa University of Technology | Parasyuk O.V.,European University at Kiev | Myronchuk G.L.,European University at Kiev
Journal of Physics Condensed Matter | Year: 2013

The quaternary chalcogenide crystal Cu2CdGeS4 was studied both experimentally and theoretically in the present paper. Investigations of polarized fundamental absorption spectra demonstrated a high sensitivity to external light illumination. The photoinduced changes were studied using a cw 532 nm green laser with energy density about 0.4 J cm-2. The spectral maximum of the photoinduced anisotropy was observed at spectral energies equal to about 1.4 eV (energy gap equal to about 1.85 eV) corresponding to maximal density of the intrinsic defect levels. Spectroscopic measurements were performed for polarized and unpolarized photoinducing laser light to separate the contribution of the intrinsic defect states from that of the pure states of the valence and conduction bands. To understand the origin of the observed photoinduced absorption near the fundamental edge, the benchmark first-principles calculations of the structural, electronic, optical and elastic properties of Cu2CdGeS4 were performed by the general gradient approximation (GGA) and local density approximation (LDA) methods. The calculated dielectric function and optical absorption spectra exhibit some anisotropic behavior (shift of the absorption maxima in different polarizations) within the 0.15-0.20 eV energy range not only near the absorption edge; optical anisotropy was also found for the deeper inter-band transition spectral range. Peculiar features of chemical bonds in Cu2CdGeS4 were revealed by studying the electron density distribution. Possible intrinsic defects are shown to affect the optical absorption spectra considerably. Pressure effects on the structural and electronic properties were modeled by optimizing the crystal structure and calculating all relevant properties at elevated hydrostatic pressure. The first estimations of the bulk modulus (69 GPa (GGA) or 91 GPa (LDA)) and its pressure derivative for Cu2CdGeS4 are also reported. © 2013 IOP Publishing Ltd.

Brenych Y.,European University at Kiev
2013 12th International Conference: The Experience of Designing and Application of CAD Systems in Microelectronics, CADSM 2013 | Year: 2013

The K-Winner-Take-All (KWTA) classifier is presented in this article. Its architecture is demonstrated. The basic steps of KWTA classifier are described. Its algorithm is presented. The KWTA structure is demonstrated. Its advantages and limitations are analyzed. © 2013 Lviv Polytechnic Natl Univ.

Reshak A.H.,University of South Bohemia | Reshak A.H.,University Malaysia Perlis | Kityk I.V.,Czestochowa University of Technology | Kityk I.V.,European University at Kiev | And 3 more authors.
Journal of Physical Chemistry B | Year: 2013

The linear and nonlinear optical properties of Ag2In 2SiS6 and Ag2In2GeS6 are calculated so as to obtain further insight into the electronic properties. The influence of using different exchange correlation potentials and the effect of replacing Si by Ge on the geometry, chemical bonding, and on the optical properties are presented. There is notable increasing in the energy band gap when moving from LDA to GGA, EVGGA then to mBJ. The effect of replacing Si by Ge atom causes a geometric change, which leads to large changes in the linear as well as the nonlinear optical susceptibilities. For the linear optical properties, it causes to increase the amplitude of the left-hand hump of ε2 average(ω) as well as a small shift of the main peak to lower energies. We have evaluated ε1 average(0) and find that a smaller energy gap yields a larger ε1(0) value. From the calculated refractive indices we obtained the birefringence, which is important for second harmonic generation (SHG) and optical parametric oscillation (OPO) as it is defined by the phase-matching condition. The second-order nonlinear optical susceptibilities, namely, the SHG are investigated for χ111 (2)(ω), χ122 (2)(ω), χ133 (2)(ω), χ221 (2)(ω), and χ331 (2)(ω). We find that χ 111 (2)(ω) is the dominant component. The microscopic second order hyperpolarizability, β111, for the dominant component χ111 (2)(ω) was obtained. We should emphasize that replacing Si by Ge enhances the linear and nonlinear optical susceptibilities so that Ag2In2GeS6 shows higher values of the linear and nonlinear optical susceptibilities and β111 in comparison to Ag2In2SiS 6. © 2013 American Chemical Society.

Khyzhun O.Y.,Ukrainian Academy of Sciences | Ocheretova V.A.,Kharkiv Polytechnic Institute | Fedorchuk A.O.,Lviv National University of Veterinary Medicine and Biotechnologies | Parasyuk O.V.,European University at Kiev
Optical Materials | Year: 2014

We report on studies of the electronic structure of Ag 2CdSnS4 single crystal grown by the horizontal gradient freeze technique. For the crystal under consideration, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that Ag2CdSnS4 single crystal surface is very rigid with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface does not induce any significant changes of values of the binding energies of core-level electrons as well as the energy distribution of electronic states within the valence-band region. The Ar+ bombardment does not change the elemental stoichiometry of the Ag2CdSnS4 surface. For the Ag2CdSnS4 compound, the X-ray emission bands representing the energy distribution of the valence Ag d, Cd d and S p states were recorded and compared on a common energy scale with the XPS valence-band spectrum. Results of such a comparison indicate that the S 3p states contribute predominantly in the upper and central portions of the valence band of the Ag2CdSnS4 single crystal. In addition, our data reveal that the Ag 4d and Cd 4d states contribute mainly in the central portion and at the bottom of the valence band, respectively. © 2014 Elsevier B.V. All rights reserved.

Fedorchuk A.O.,Lviv National University of Veterinary Medicine and Biotechnologies | Parasyuk O.V.,European University at Kiev | Kityk I.V.,European University at Kiev | Kityk I.V.,Czestochowa University of Technology
Materials Chemistry and Physics | Year: 2013

A new approach to describe anion sub-lattice for chalcogenide compounds is proposed. The approach is developed on the base of wurtzite and sphalerite structures and includes consideration of the second coordination sphere of anion atoms. A variety of discussed examples show that the second coordination surrounding may be formed both by single anion atoms and by atom pairs or more complex configurations. Considering some chalcogenide compounds, the efficiency of such approach is demonstrated for the search of some similarities between the compounds and for optimization of corresponding quantum chemical calculations. © 2013 Elsevier B.V. All rights reserved.

Kormosh Z.,European University at Kiev | Matviychuk O.,European University at Kiev
Chinese Chemical Letters | Year: 2013

The characteristics, performance and application of membrane sensors based on ion-pair Brilliant Green mefenamate are described. The sensor's response to the mefenamate ion has the sensitivity of (86.0 ± 2.0) mV/pC over the range of 9 × 10-5-1 × 10-2 mol/L and the detection limit of 4.5 × 10-5 mol/L at pH 8.5-12. The sensor is easily assembled at a relatively low cost and has fast response time (5-10 s). The proposed sensor displayed good selectivity for mefenamate ion in the presence of different substances. It was used to determine mefenamic acid in pharmaceuticals. © 2013 Zholt Kormosh.

Khyzhun O.Y.,Ukrainian Academy of Sciences | Bekenev V.L.,Ukrainian Academy of Sciences | Denysyuk N.M.,Ukrainian Academy of Sciences | Parasyuk O.V.,European University at Kiev | Fedorchuk A.O.,Lviv National University of Veterinary Medicine and Biotechnologies
Journal of Alloys and Compounds | Year: 2014

We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb2Cl5 using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb2Cl5 is dominated by contributions of the Cl 3p-like states, which contribute mainly at the top of the valence band with also significant contributions throughout the whole valence-band region. In addition, the bottom of the conduction band of TlPb 2Cl5 is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb2Cl 5 compound is an indirect-gap material with band gap of 3.42 eV. The X-ray photoelectron core-level and valence-band spectra for pristine and Ar + ion-irradiated surfaces of a TlPb2Cl5 polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb 2Cl5 surface. © 2013 Elsevier B.V. All rights reserved.

Mamchych T.,European University at Kiev | Wallin F.,Mälardalen University
Energy Procedia | Year: 2014

Residential electricity consumption is an important part of general energy use. Its detailed investigation, however, requires rich empirical data, here the data of Swedish households. The individual consumption is a time series of readings at certain time intervals (hourly, every ten minutes, or every minute, say). Series exhibit patterns, in terms of which they may be compared, and it is desirable to model similarity. Classical statistical methods (correlation, factor, and cluster analyses) are presently used for this purpose; they have the advantage of being more explicit than the techniques of adaptive data analysis that may recently have become excessively popular. The present work is methodological, preceding any massive statistical analyses. Factor analysis allowed describing individual styles in terms of time intervals (during a day) of maximal variability. Cluster analysis was used for finding groups of days with similar patterns; the obtained clusters can help interpreting the results of other methods. Comparing two households requires comparing two sets of time series; correlation analysis quantified the similarity between them. © 2014 Published by Elsevier Ltd.

Rachkovsky V.P.,European University at Kiev
Naukovyi Visnyk Natsionalnoho Hirnychoho Universytetu | Year: 2013

Purpose: To calculate the resistance of the massif around the mine working during development of diamond deposits. Methodology: By the method of mathematical modeling we have determined the stability of the equilibrium state of the bottom of stope in vertical opening located in kimberlite rock taking into account the equilibrium of the infinite space of the cavity under the load at a depth of 1000 meters. Findings: We have created the model of the cylindrical vertical opening stability and determined appearance of local critical pressure in the surrounding massif during its deformation. The system of diamond deposits mining with ore shrinkage in mined-out spaces. Originality: We have created a combination of axisymmetric computational model blocks of stress state of the cylindrical stope with axial compression and external pressure determining the stability of the kimberlite rock. Practical value: We have developed the methodology of substantiation of geotechnology parameters of mining of Ukrainian kimberlite deposits and guidelines for assessment of technologic parameters of stopes in kimberlite pipes.

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