Физика низких температур, 2011, № 05
http://dspace.nbuv.gov.ua:80/handle/123456789/115072
2024-03-28T10:42:54ZNumerical study of the diffusive-like decay of the vortex tangle without mutual friction
http://dspace.nbuv.gov.ua:80/handle/123456789/118576
Numerical study of the diffusive-like decay of the vortex tangle without mutual friction
Kondaurova, L.P.; Nemirovskii, S.K.
The numerical simulation of the diffusive-like decay of the vortex tangle without mutual friction was performed. The simulation was made with the use of the localized induction approximation. The early developed by authors algorithm, which is based on consideration of crossing lines, was used for vortex reconnection processes. We have determined the influence of different factors on decay of an inhomogeneous vortex tangle: a diffusion (large vortex loops break up to smaller ones which go away from initial volume), change of length owing to reconnection processes, the eliminations of small vortices below the space resolution, the insertion and removing of points to supply numerical algorithm stability. The obtained numerical results demonstrate that the vortex tangle, initially localized in the small region, is smearing into ambient space. The time evolution of vortex line density inside the initial domain satisfactory agrees with the ones, obtained from the solution of diffusion equation.
2011-01-01T00:00:00ZTorsional oscillation of the vortex tangle. Possible applications to oscillations of solid ⁴He
http://dspace.nbuv.gov.ua:80/handle/123456789/118575
Torsional oscillation of the vortex tangle. Possible applications to oscillations of solid ⁴He
Nemirovskii, S.K.
Torsional oscillation of the vessels with quantum fluids is one of oldest and most popular methods for the study of quantized vortices. The recent and very bright example is the discovery of the supersolidity of the solid helium. In the torsion oscillation experiments the drop in the period of oscillations with achievement of some small temperature has been observed. This effect was attributed to the appearance of the superfluid component. This phenomenon depends on many various factors and has various explanations. But, if to adopt (at least hypothetically, at this stage) that the phenomenon of “supersolidity” (dissipativeless flow) is realized, we must consider the relaxation of the vortex system (we can call it as vortex tangle, vortex fluid, chaotic set of vortices, etc.). We have to do it for the very simple reason, that the only way to involve the superfluid component into rotation is the presence of the polarized vortices (with nonzero mean polarization along the axis of rotation). In the present work we submit the approach describing the vortex tangle relaxation model for the torsional oscillation responses of quantum systems, having in mind to apply it for the study of solid ⁴He. It is shown that the rotation of the superfluid component occurs in the relaxation-like manner with the relaxation time dependent on the amplitude of oscillation (as well as on the temperature and pressure). The study of this problem shows that there is a quasi-linear solution explaining the (amplitude dependent) shift of period. There is also an imaginary shift of the frequency (also the amplitude-dependent), which describes an additional dissipation. The results of the theory are compared with the recent measurements.
2011-01-01T00:00:00ZClassical capillary turbulence on the surface of quantum liquid He-II
http://dspace.nbuv.gov.ua:80/handle/123456789/118574
Classical capillary turbulence on the surface of quantum liquid He-II
Abdurakhimov, L.V.; Brazhnikov, M.Yu.; Remizov, I.A.; Levchenko, A.A.
Superfluid helium-4 is a unique liquid for experimental study of capillary wave turbulence due to its very low viscosity. We have studied the influence of amplitude and spectral characteristics of the excitation force on the behavior of the turbulent cascade of capillary waves in the cylindrical cell of diameter 30 mm. We have found that the experimental results can be explained within the framework of the wave turbulence theory (WTT) when the amplitude of pumping is relatively high. However, a very interesting phenomenon was observed at moderate amplitudes of harmonic surface excitation. It was detected the deviation of the turbulent spectrum from the power law function predicted by WTT at high frequencies — local maximum — that can be interpreted as wave energy accumulation. Our estimations show that the special case of wave turbulence is realized in our measurements, namely, discrete turbulence which is characterized by the strong influence of discreteness of cell resonant frequencies on the mechanism of the nonlinear interaction.
2011-01-01T00:00:00ZInfrared light interaction with impurity gels in superfluid helium
http://dspace.nbuv.gov.ua:80/handle/123456789/118573
Infrared light interaction with impurity gels in superfluid helium
Izotov, A.N.; Efimov, V.B.
The quick cooling of impurity–helium mixture into superfluid helium formats a distinctive soft matter — impurity–helium gel, clusters of which conglutinate into nanoparticles. The sizes of the particles and its mutual interaction depend on the nature of impurity atoms and impurity–helium coupling. In the paper we describe an experimental setup and preliminary results of experimental investigation of infrared absorption by water–helium gel. The comparison of the infrared spectra of gel absorption with water and ice indicates on some peculiarity of interaction in water molecules in water–helium gel.
2011-01-01T00:00:00Z