Физика низких температур, 2015, № 06http://dspace.nbuv.gov.ua:80/xmlui/handle/123456789/1221872024-03-02T02:54:55Z2024-03-02T02:54:55ZInvestigations of thermal conductivity of simple van der Waals crystal-based nanocompositesNikonkov, R.V.Stachowiak, P.Romanova, T.V.Jeżowski, A.Sumarokov, V.V.http://dspace.nbuv.gov.ua:80/xmlui/handle/123456789/1279402018-01-01T01:03:03Z2015-01-01T00:00:00ZInvestigations of thermal conductivity of simple van der Waals crystal-based nanocomposites
Nikonkov, R.V.; Stachowiak, P.; Romanova, T.V.; Jeżowski, A.; Sumarokov, V.V.
The experimental setup for obtaining and determination of the thermal conductivity of simple van der Waals
crystal-based nanocomposites is described. Preliminary thermal conductivity results of measurements carried out
in the temperature range 1–40 K on two samples of methane crystals containing nanoparticles of hydroxyapatite
are presented. These results confirm usability of the setup and its suitability as a proper experimental method for
investigations of the thermal conductivity of the nanocomposites.
2015-01-01T00:00:00ZLow-temperature thermodynamics of Xe-doped fullerite C₆₀Klochko, M.S.Strzhemechny, M.A.http://dspace.nbuv.gov.ua:80/xmlui/handle/123456789/1279392018-01-01T01:02:56Z2015-01-01T00:00:00ZLow-temperature thermodynamics of Xe-doped fullerite C₆₀
Klochko, M.S.; Strzhemechny, M.A.
Using a model of the fullerene C₆₀ molecule with carbon atoms uniformly distributed over its surface, the potential
energy U(n) of a Xe atom in an octahedral void of C₆₀ is calculated. Within the framework of threedimensional
harmonic oscillator, the lowest energy levels are estimated and the contribution of xenon impurity
atoms to the heat capacity of the Xe–C₆₀ system is determined. The contribution of Xe dopants to the total heat
capacity is shown to be essential compared to that of pure fullerite. Using the calculated energy spectrum we estimated
the contribution of Xe atoms to the thermal expansivity of C₆₀ with 37% of Xe. This contribution is in a
qualitative agreement with experimental findings. We estimated the Grüneisen parameter Г due to the anisotropic
part of U(n) to show that the negative part of Г is negligible due to the very small width of the five lower
oscillatory wave functions.
2015-01-01T00:00:00ZWave turbulence on the surface of liquid hydrogen in restricted geometry: the influence of the boundary conditionsBrazhnikov, M.Yu.Levchenko, A.A.Mezhov-Deglin, L.P.Remizov, I.A.http://dspace.nbuv.gov.ua:80/xmlui/handle/123456789/1279382018-01-01T01:02:54Z2015-01-01T00:00:00ZWave turbulence on the surface of liquid hydrogen in restricted geometry: the influence of the boundary conditions
Brazhnikov, M.Yu.; Levchenko, A.A.; Mezhov-Deglin, L.P.; Remizov, I.A.
Formation of low frequency harmonics on turbulent distribution in the system of waves on the surface of liquid
hydrogen has been studied in the frequency range 1–100 Hz (capillary-gravity waves). It is shown that the
geometry of the experimental cell has a significant influence on the direct cascade of capillary waves generated
by monochromatic force as well as on the direction of the wave energy transfer from the range of pumping towards
that of dissipation. Besides a direct turbulent cascade, single half-frequency harmonic generation was observed
in a cylindrical cell under high pump power. In a square cell we observed not only a half-frequency harmonic
but a number of low frequency harmonics below the driving frequency generated by the nonlinear threewave
interaction. In the case of a rectangular cell we observed formation of incommensurate low frequency harmonics
caused by the three-wave interaction of capillary waves and generation of a wave mode of ~1 Hz in the
frequency range of gravity waves which could be attributed to the four-wave interaction.
2015-01-01T00:00:00ZEnergy spectrum of the quantum vortices configurationsNemirovskii, S.K.http://dspace.nbuv.gov.ua:80/xmlui/handle/123456789/1279372018-01-01T01:02:50Z2015-01-01T00:00:00ZEnergy spectrum of the quantum vortices configurations
Nemirovskii, S.K.
The energy spectra of the 3D velocity field, induced by various vortex filaments configurations are reviewed.
The especial attention is paid to configurations generating the Kolmogorov type energy spectrum E(k) ∝ k⁻⁵/³. The
motivation of this work is related to the problem of modeling classical turbulence with a set of chaotic vortex filaments.
The quantity <v(k)v(–k)> can be exactly calculated, provided that we know the probability distribution functional P({s(ξ,t)}) of vortex loops configurations. The knowledge of P({s(ξ,t)}) is identical to the full solution of
the problem of quantum turbulence and, in general, P is unknown. One of the simplifications is to investigate various
truthful vortex configurations which can be elements of real vortex tangles. These configurations are: the uniform
and nonuniform vortex arrays, the straight lines with excited Kelvin waves on it and the reconnecting vortex
filaments. We demonstrate that the spectra E(k), generated by the these configurations, are close to the Kolmogorov
dependence ∝ k⁻⁵/³, and discuss the reason for this as well as the reason for deviation.
2015-01-01T00:00:00Z