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Kiev, Ukraine

The National Technical University of Ukraine “Kyiv Polytechnic Institute” is a major university in Kyiv, Ukraine. In January 2012 Webometrics Ranking KPI made it into top 1,000 – taking 957th place out of 20,300 universities, 510th . Wikipedia.

Listopadova V.,National Technical University of Ukraine | Magda O.,Kyiv National Economic University | Pobyzh V.,Institute of Mathematics of NAS of Ukraine
Nonlinear Analysis: Real World Applications

It is shown that the forced Korteweg-de Vries (KdV) equation studied in the recent papers [A.H. Salas, Computing solutions to a forced KdV equation, Nonlinear Anal. RWA 12 (2011) 1314-1320] and [M.L. Gandarias, M.S. Bruzón, Some conservation laws for a forced KdV equation, Nonlinear Anal. RWA 13 (2012) 2692-2700] is reduced to the classical (constant-coefficient) KdV equation by point transformations for all values of variable coefficients. The equivalence-based approach proposed in [R.O. Popovych, O.O. Vaneeva, More common errors in finding exact solutions of nonlinear differential equations: part I, Commun. Nonlinear Sci. Numer. Simul. 15 (2010) 3887-3899] allows one to obtain more results in a much simpler way. © 2012 Published by Elsevier Ltd. Source

Pis'Mennyi E.N.,National Technical University of Ukraine
Applied Thermal Engineering

A new type of extended heat transfer surfaces in the form of incompletely finned flat-oval tubes is proposed. They are easily manufactured, have a high surface extension degree, high convective heat transfer intensity and a low aerodynamic drag. The experimental results of research of thermal and aerodynamic characteristics of such surfaces, their analysis and comparison with the data for the existing round finned tubes are presented. Given are the examples of application of incompletely finned flat-oval tubes in the waste-gas heat utilizers of power plants. © 2016 Elsevier Ltd. All rights reserved. Source

Fokin A.A.,National Technical University of Ukraine | Gerbig D.,Justus Liebig University | Schreiner P.R.,Justus Liebig University
Journal of the American Chemical Society

The properties of single-sheet [n]graphanes, their double-layered forms (diamondoids), and their van der Waals (vdW) complexes (multilayered [n]graphanes) were studied for n = 10-97 at the dispersion-corrected density functional theory (DFT) level utilizing B97D with a 6-31G(d,p) basis set; for comparison, we also computed a series of structures at M06-2X/6-31G(d,p) as well as B3LYP-D3/6-31G(d,p) and evaluated SCS-MP2/cc-pVDZ single-point energies. The association energies for the vdW complexes reach 120 kcal mol -1 already at 2 nm particle size ([97]graphane dimer), and graphanes adopt layered structures similar to that of graphenes. The association energies of multilayered graphanes per carbon atom are rather similar and independent of the number of layers (ca. 1.2 kcal mol -1). Graphanes show quantum confinement effects as the HOMO-LUMO gaps decrease from 8.2 eV for [10]graphane to 5.7 eV for [97]graphane, asymptotically approaching 5.4 eV previously obtained for bulk graphane. Similar trends were found for layered graphanes, where the differences in the electronic properties of double-sheet CH/σ vdW and double-layered CC/σ diamondoids vanish at particles sizes of 1 nm. For comparison, we studied the parent CC/π systems, i.e., the single- and double-sheet [n]graphenes (n = 10-130) for which the association energies demonstrate the same trends as in the case of [n]graphanes; in both cases the band gaps decrease with an increase in system size. The [112]graphene dimer (HOMO-LUMO gap = 0.5 eV) already approaches the 2D metallic properties of graphite. © 2011 American Chemical Society. Source

Bodson M.,University of Utah | Kiselychnyk O.,National Technical University of Ukraine
IEEE Transactions on Automatic Control

Spontaneous self-excitation in induction generators is a fascinating phenomenon triggered by the instability of a zero equilibrium state. Prediction of this condition for various values of free parameters requires many computations of the eigenvalues of a 6$\,\times\,$ 6 matrix over a large space. The technical note uses a novel approach to stability using a transformation of the state-space system and an extension of the Hurwitz test to polynomials with complex coefficients. The analytic formulas that are obtained give the values of the minimum load resistance, the range of capacitor values, and the range of speeds for which spontaneous self-excitation appears. The technical note concludes with an illustration of the results on an example. © 2012 IEEE. Source

Pis'mennyi E.N.,National Technical University of Ukraine
International Journal of Heat and Mass Transfer

A great number of experimental investigations allowing one to reveal the physical mechanism of processes responsible for their thermal and hydraulic performance are carried out in attempt to solve problems of updating constructions and methods of thermal design of heating surfaces of transversely finned tubes widespread in power engineering. Results of flow visualization and investigation of pressure fields and local heat transfer at the fin surface over the Reynolds number range Re = (1.0 ⋯ 6.6)·10 4 are presented for the case of a wide variation of geometric characteristics of finned tubes and parameters of their arrangement in a bundle. Regularities substantially changing the existing concept of transfer processes in the interfin space and in the wake behind a finned tube are revealed. It is found that the flow behavior and the distribution of local heat transfer coefficients over the fin surface change significantly at the fin height-to-finned tube diameter h/d approximately equal to 0.4. The results obtained are generalized in the form of the patterns of flow and heat transfer at the finned tube surface, including seven characteristic regions and four types of flow separation. © 2012 Elsevier Ltd. All rights reserved. Source

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