Effect of high pressure on the fluctuation paraconductivity in Y0.95Pr0.05Ba2Cu3O7-d single crystals

R.V. Vovk,N.R. Vovk,G.Ya Khadzhai,O.V. Dobrovolskiy,Z.F. Nazyrov 한국물리학회 2014 Current Applied Physics Vol.14 No.12

The effect of high hydrostatic pressure up to 17 kbar on the fluctuation conductivity of lightly Pr-doped Y1xPrxBa2Cu3O7d (x z 0.05) single crystals is investigated. We show that in contrast to non-doped YBa2Cu3O7d samples, application of a high pressure leads to a substantial increase of the pressure derivative of the coherence length dxc/dP and a temperature shift of the 2D-3D crossover point. Possible mechanisms of the influence of high pressure on the critical temperature and the coherence length are discussed within the framework of a model assuming the presence of singularities in the charge carriers electron spectrum typical for lattices with strong coupling.

Synthesis and Characterization of Three-dimensional Polymer Produced by Mutual Condensation of Ethylenediamine and $C_{60}$

Vovk, O.,Lee, Joong-Kee Korean Carbon Society 2004 Carbon Letters Vol.5 No.2

The polymer with contents of $C_{60}$ up to 57 wt.% was produced by mutual condensation of fullerene $C_{60}$ and ethylenediamine. The investigations of this polymer as well as pristine fullerene to comparison were carried out by FT-IR and UV-Vis spectroscopy, ToF-SIMS, TGA, and elemental analysis. At least three kinds of components was revealed as building blocks of polymer. The fullerene cage underwent only distortion but didn't destroy during formation of polymer. The pure fullerene was found as an intermediate of the thermal decomposition of polymer. The conclusion that this polymer could serve as precursor to produce carbon nanomaterial with high concentration curved graphene sheets and can be used for gas adsorption and electrochemical application was made.

Synthesis and Characterization of Three-dimensional Polymer Produced by Mutual Condensation of Ethylenediamine and C60

O. Vovk,Joong-Kee Lee 한국탄소학회 2004 Carbon Letters Vol.5 No.2

The polymer with contents of C60 up to 57 wt.% was produced by mutual condensation of fullerene C60 and ethylenediamine. The investigations of this polymer as well as pristine fullerene to comparison were carried out by FT-IR and UV-Vis spectroscopy, ToF-SIMS, TGA, and elemental analysis. At least three kinds of components was revealed as building blocks of polymer. The fullerene cage underwent only distortion but didn't destroy during formation of polymer. The pure fullerene was found as an intermediate of the thermal decomposition of polymer. The conclusion that this polymer could serve as precursor to produce carbon nanomaterial with high concentration curved graphene sheets and can be used for gas adsorption and electrochemical application was made.

Electrochemical characteristics of amophous carbon coated silicon electrodes

Oleg Mikhalovich Vovk,나병기,Byung Won Cho,Joong Kee Lee 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.4

The properties of carbon films deposited by the radio frequency plasma sputtering of a fullerene C60 target were investigated to elucidate the dependence on the plasma power. A radio frequency argon plasma power ranging from 50 to 300W at a pressure of 1.3 Pa was applied for sputtering. This corresponds to a self-bias potential on the target ranging from −95 to −250 V and a maximum argon ion energy ranging from 240 to 575 eV. The analysis of the G and D peaks in the Raman spectra shows that the films are similar to tetragonal hydrogenated amorphous carbon annealed at 600-1,000℃. The electron band structure of the carbon films deposited by the sputtering of C60 depends on the plasma power. The coating effect of these carbon films on the capacity performance of the silicon film electrode of lithium secondary batteries was significant in our experimental range. An electrochemical test revealed that such carbon thin film on the silicon electrode plays an important role in mitigating the capacity fading during the charge and discharge processes. The test revealed that the film formed at a plasma power of 300 W is the most effective.

Transverse resistance of YBa2Cu3O7-δ single crystals

R.V. Vovk,G.Ya Khadzhai,O.V. Dobrovolskiy,Z.F. Nazyrov,A. Chroneos 한국물리학회 2015 Current Applied Physics Vol.15 No.5

Measured is the transverse electrical resistance of YBa2Cu3O7-δ single crystals with different oxygen deficiency values (δ) in the temperature range Tc - 300 K. The experimental data are approximated by an empiric expression accounting for the fluctuation conductivity near Tc and the semiconductor-like resistance regime. Our analysis of the concentration dependences of the fitting parameters, in particular, reveals that the resistance temperature dependence is largely affected by the sample's nonhomogeneity. The latter, in turn, causes a Tc anisotropy and variable-range hopping conductivity between different phases. The deduced maximal values of the basal-plane coherence length, ξxy(0), are comparable with those for low-temperature superconductors.

Innovation and investment strategies to intensify the potential modernization and to increase the competitiveness of microeconomic systems

Tulchynska, Svitlana,Vovk, Olha,Popelo, Olha,Saloid, Stanislav,Kostiunik, Olena International Journal of Computer ScienceNetwork S 2021 International journal of computer science and netw Vol.21 No.6

Within the article, strategic guidelines for the modernization of microeconomic systems are identified. Modernization levels of the potential implementation are formalized for enterprises: contractile, extensive technical, technological, progressive, adaptive, steady, intensive, creative, absolute and leader modernization. This allowed to specify the directions and tasks of the enterprise modernization at different management levels. Accordingly, the conditions and criteria for selecting resource tools are set. It is proved that the strategies of the potential modernization of enterprises must be carried out at four main management levels: first, at the enterprise level; secondly, for a particular type of product / service; third, by functional directions of modernization of separate spheres of the enterprise activity or responsibility, fourth, at the level of structural units of the enterprise. It is substantiated that in the processes due to the activation of the potential modernization, the resources are transformed into the results of the innovation implementation and the investment strategies modernization. A system of tasks for the corporate strategies implementation in order to modernize microeconomic systems has been formed. Key vectors of the activation determine the nature and properties of investment resources and necessary innovations to enhance the modernization potential. Therefore, the system of innovation and investment strategies' modernization, based on the vector and resource provision of the modernization process, is specified:

Surface-Coated Silicon Anodes with Amorphous Carbon Film Prepared by Fullerene C[sub 60] Sputtering

Arie, Arenst Andreas,Vovk, Oleg Mikhalovich,Lee, Joong Kee The Electrochemical Society 2010 Journal of the Electrochemical Society Vol.157 No.6

Modernization determinants by ensuring economic security of enterprises in the competitive conditions

Tkachenko, Tetiana,Tulchynska, Svitlana,Kostiunik, Olena,Vovk, Olha,Kovalenko, Nataliia International Journal of Computer ScienceNetwork S 2021 International journal of computer science and netw Vol.21 No.8

The study develops methodological aspects for modeling the determining impact of modernization on the enterprise's economic security in development competitive conditions using the model of speed, stability and spaciousness of modernization. Modeling the determining impact of modernization on the enterprise's economic security in a competitive conditions involves: firstly, the formation of estimated modeling indicators in accordance with the speed, stability and spaciousness of the enterprise's modernization; secondly, establishing the weight of indicators in the assessment system using the tools of cognitive judgment; thirdly, the establishment of reference values of sound evaluation indicators; fourthly, the calculations of the integrated impact assessment of the modernization's determining impact modeling on the enterprise's ensuring economic security in a competitive conditions; fifthly, conducting calculations and analytical summarization of the results. To determine a comprehensive integrated indicator of the modernization changes impact on the competitiveness and economic security of enterprises, we use the correlation method of the calculated value with the reference value, as well as use weights for groups of calculations. Approbation of modeling of determining influence of modernization on maintenance of economic safety of the enterprise in competitive conditions of development by authors was carried out concerning such enterprises, as: JSC "Ukrzaliznytsia", SE "Ukraerorukh", SE IA "Boryspil", SE "Ukrposhta", KP "Kyivpastrans".

Peculiarities in the pseudogap behavior in optimally doped YBa2Cu3O7d single crystals under pressure up to 1 GPa

A.L. Solovjov,L.V. Omelchenko,R.V. Vovk,O.V. Dobrovolskiy,S.N. Kamchatnaya,D.M. Sergeev 한국물리학회 2016 Current Applied Physics Vol.16 No.9

The influence of the hydrostatic pressure P up to 0.95 GPa on the excess conductivity s0(T) and the pseudogap D*(T) in optimally doped YBa2Cu3O7d single crystals (Tc x 91.1 K at ambient pressure) is investigated by electrical resistivity measurements. A pronounced enhancement of the pseudogap under pressure of dlnD*/dP z 0.32, which is only a factor of 1.12 smaller than in slightly doped single crystals, is revealed for the first time. This implies a somewhat more moderate increase of the coupling strength in optimally doped cuprates with increasing pressure. Simultaneously, the ratio 2D*(Tc)/kBTc z 5 at P ¼ 0 GPa, which is typical for high-temperature superconductors with strong coupling, increases by 16% with increasing pressure. At the same time, the pressure effect on Tc is minor: dTc/dP z þ0.73 K GPa1, whereas dlnr/dP z (17 ± 0.2)% GPa1 is comparable with that in lightly doped YBCO single crystals. This suggests that the mechanisms of the pressure effect on r(T) and Tc are noticeably different. Independently of pressure, near Tc, s0(T) is well described by the Aslamazov-Larkin (3D-AL) and 2D Hikami- Larkin fluctuation theories, exhibiting a 3De2D crossover with increasing temperature. However, the temperature interval Tc < T < T01, in which s0(T) obeys the classical fluctuation theories, is exceptionally narrow (z1.16 K). Nevertheless, a peculiarity at the temperature T01, up to which the wave function phase stiffness in the superconductor is maintained, is clearly observed in the dependence D*(T). Below T01 a fast growth of D*(T) is revealed for the first time. It can be associated with a sudden increase of the superfluid density, ns, that is the density of fluctuating Cooper pairs (short-range phase correlations) forming in the sample when T approaches Tc.

IT - Education In The Context Of Educational Activities

Marchenko, Olga,Noskova, Margaryta,Fedorenko, Igor,Semenog, Olena,Vovk, Myroslava,Romanyshyn, Ruslana International Journal of Computer ScienceNetwork S 2021 International journal of computer science and netw Vol.21 No.6

The article is based on a model, in the context of which there are two fundamental building blocks of basic library skills and skills in the use of information technology. The former are formed within the framework of educational programs for users of academic libraries, the latter are formed within the framework of initiatives such as the European Computer Driving License. Between the basic and the highest levels of the concept of "information literacy" there are seven heading skills and attributes, the repeated practice of which leads from the position of a competent user to an expert level of reflection and critical awareness of information as an intellectual resource. Freshmen will likely be at the beginning of the arrow, probably practicing only the first four skills, while graduate students and young scientists will be closer to the end and will use seven skills.