Kharkiv Polytechnic Institute

www.kpi.kharkov.ua/
Kharkov, Ukraine

The National Technical University "Kharkiv Polytechnic Institute" ), in the city of Kharkiv, is the largest and oldest technical university in eastern Ukraine. Founded in 1885, it is the second-oldest technical university in the Russian Empire and in the territory of modern Ukraine . Wikipedia.

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Sobol' O.V.,Kharkiv Polytechnic Institute
Technical Physics Letters | Year: 2016

The dependence of elastic moduli for different directions on the nonstoichiometry with respect to carbon atoms in octahedral interstices of face-centered cubic crystalline lattice is established for the first time for metastable tungsten carbide (β-WC1–x phase). It is shown that with decreasing content of carbon atoms in the tungsten carbide lattice it is compressed, which is accompanied by the growth of the contribution of metallic component, thus determining higher density of the coating material and change of elastic characteristics for different crystallographic directions. This makes it possible to obtain carbide coatings with the required ratio of elastic constants via corresponding technological regimes, which is especially important in formation of coatings with predominant crystallite growth orientation. © 2016, Pleiades Publishing, Ltd.


Belozyorov V.Y.,Kharkiv Polytechnic Institute
Applied Mathematics and Computation | Year: 2011

The new existence conditions of homoclinic orbits for the system of ordinary quadratic differential equations are founded. Further, the realization of these conditions together with the Shilnikov Homoclinic Theorem guarantees the existence of a chaotic attractor at 3D autonomous quadratic system. Examples of the chaotic attractors are given. © 2010 Elsevier Inc. All rights reserved.


Milykh V.I.,Kharkiv Polytechnic Institute
Technical Electrodynamics | Year: 2017

The estimation of the turbo-generator rotor work was conducted under turbo-generator unbalanced loading within the framework of its standard limitations on the basis of the multiposition numerical calculations of the rotating magnetic field. The results of calculations at the asymmetrical loading which were carried out by the example of 35MW turbo-generator are compared with similar results with symmetrical loading. The form of temporal functions and harmonic composition of the EMF in the rotor winding and in its slot wedges are analyzed, the estimation of currents caused by these EMF is done. Level of the variable EMF in the field winding is very significant, however the variable component of current in it isn't a serious problem. EMF in the rotor wedges reach tens of volts, currents - of the order of 2.5 kA, and in different wedges they differ markedly. The temporal functions of the magnetic induction variable component on the surface of the spinning rotor, whose values increase significantly because of the unbalanced load, are also examined.


Gomonay H.V.,Kharkiv Polytechnic Institute | Loktev V.M.,NASU Bogolyubov Institute for Theoretical Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Recent experiments show that spin-polarized current may influence the state of generally accessory element of spin valves, an antiferromagnetic (AFM) layer, which is used for "pinning." Here we study the dynamics of AFM component of the "pinned" ferromagnetic (FM) layer induced by simultaneous application of the spin-polarized current and external magnetic field. We find stability range of such a configuration of FM/AFM system in which orientation of FM magnetization is parallel to AFM vector. We calculate the field dependence of the critical current for different orientations of the external magnetic field with respect to the crystal axes of FM/AFM bilayer. We show the possibility of stable current-induced precession of AFM vector around FM magnetization with the frequency that linearly depends on the bias current. Furthermore, we estimate an optimal duration of the current pulse required for switching between different states of FM/AFM system and calculate the current and field dependencies of switching time. The results obtained reveal the difference between dynamics of ferromagnets and antiferromagnets subjected to spin transfer torques. © 2010 The American Physical Society.


Moskalets M.,Kharkiv Polytechnic Institute
Physical Review Letters | Year: 2014

I present the Floquet scattering matrix theory of low-frequency heat fluctuations in driven quantum-coherent conductors in the linear response regime and beyond. The Floquet theory elucidates the use of the Callen-Welton fluctuation-dissipation theorem for a description of heat fluctuations in a multiterminal case. The intrinsic fluctuations of energy of dynamically excited electrons are identified as the fundamental source of heat noise not revealed by the electrical noise. The role of backscattering in the increase of heat noise above the level defined by the Callen-Welton theorem is highlighted. The exception is the case when a conductor is driven by a Lorentzian voltage pulse with quantized flux. The heat noise in this case falls down to the level pertaining to a linear response regime. © 2014 American Physical Society.


Gomonay O.,Kharkiv Polytechnic Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

Antiferromagnets (AFMs), in contrast to ferromagnets, show a nontrivial magnetic structure with zero net magnetization. However, they share a number of spintronic effects with ferromagnets, including spin pumping and spin-transfer torques. Both phenomena stem from the coupled dynamics of free carriers and localized magnetic moments. In the present paper I study the adiabatic dynamics of spin-polarized electrons in a metallic AFM exhibiting a noncollinear 120° magnetic structure. I show that the slowly varying AFM spin texture produces a non-Abelian gauge potential related to the time and space gradients of the Néel vectors. Corresponding emergent electric and magnetic fields induce rotation of spin and influence the orbital dynamics of free electrons. I discuss both the possibility of a topological spin Hall effect in the vicinity of topological AFM solitons with nonzero curvature and rotation of the electron spin traveling through the AFM domain wall. © 2015 American Physical Society.


Moskalets M.,Kharkiv Polytechnic Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

A new principle of manipulation of an electron phase is proposed. The phase is added not directly to an electron but to a finite-length portion of the Fermi sea associated with it, which I name a phase carrier. This phase can be read out with the help of an imbalanced interferometer, where the phase carrier interferes with the reference Fermi sea. As a result of such interference, the same value but opposite sign charge appears at the interferometer's outputs. A phase carrier can be created, for instance, with the help of an on-demand single-electron source able to produce excitations with multiple-peak density profiles. © 2014 American Physical Society.


Moskalets M.,Kharkiv Polytechnic Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

Two single-particle sources coupled in series to a chiral electronic waveguide can serve as a probabilistic source of two-particle excitations with tunable properties. The second-order correlation function, characterizing the state of emitted electrons in space-time, is expressed in terms of the Floquet scattering matrix of a source. It is shown that the Fourier transform of the correlation function, characterizing the emitted state in energy space, can be accessed with the help of an energy resolved shot-noise measurement. The two-electron state emitted adiabatically is discussed in detail. In particular, the two-electron wave function is represented via two different sets of single-particle wave functions accessible experimentally. © 2014 American Physical Society.


Zubarev E.N.,Kharkiv Polytechnic Institute
Physics-Uspekhi | Year: 2011

Reactive diffusion in nanomaterials differs widely from that in bulk materials. Reviewed in this paper are the basic models and experimental data on how diffusion and phase transformations occur in multilayer nanosystems as these are being prepared and subsequently thermally annealed. The growth kinetics of amorphous silicide phases in Sc/Si and Mo/Si multilayer periodic systems are studied using the combination of high-resolution transmission electron microscopy and small-angle X-ray diffraction. A model is proposed for silicon diffusion through amorphous silicide that undergoes structural relaxation and crystallization as it grows. Anisotropic diffusion and growth of the silicide phase at adjacent interfaces are studied, and the diffusion parameters are measured for the earliest stages of diffusion annealing. © 2011 Uspekhi Fizicheskikh Nauk, Russian Academy of Sciences.


Moskalets M.,Kharkiv Polytechnic Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

I analyze the correlation function of currents generated by a periodically driven quantum capacitor emitting single electrons and holes into a chiral waveguide. I compare adiabatic and nonadiabatic transient working regimes of a single-electron emitter and find a striking difference between the correlation functions in the two regimes. Quite generally, for a system driven with frequency Ω the correlation function depends on two frequencies ω and ℓΩ-ω, where ℓ is an integer. For an emitter driven nonadiabatically the correlation functions for different ℓ are similar and almost symmetric in ω, while in the case of adiabatic driving the correlation functions for ℓ≠0 are highly asymmetric in ω and exceed significantly the one corresponding to ℓ=0. Under optimal operating conditions the correlation function for odd ℓ is zero. © 2013 American Physical Society.

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