Superfluid β phase of He 3 Dmitriev, V. V.; Kutuzov, M. S.; Soldatov, A. A. ...
Physical review letters,
12/2021, Letnik:
127, Številka:
26
Journal Article
We propose methods for estimation of the number of the sources and their localization in complex mechanical systems. These methods are based on the matching vibrational field obtained using finite ...element modeling with the measured field from vibration sensors. A modification of the MUSIC (Multiple Signal Classification) algorithm, which is often employed in direction-of-arrival estimation of wavefield sources, is effectively used to localize several simultaneously operating sources of vibration. Numerical simulation and experimental testing in mechanical systems showed the superior efficiency of the proposed method in comparison with the methods previously used to solve similar problems.
Magnetic materials generate demagnetizing field that depends on geometry of the sample and results in a shift of magnetic resonance frequency. This phenomenon should occur in porous nanostructures as ...well, e.g., in globally anisotropic aerogels. Here, we report results of nuclear magnetic resonance experiments with liquid
3
He confined in anisotropic aerogels with different types of anisotropy (nematic and planar aerogels). Strands of aerogels in pure
3
He are covered by a few atomic layers of paramagnetic solid
3
He which magnetization follows the Curie–Weiss law. We have found that in our samples the nuclear magnetic resonance shift in solid
3
He is clearly seen at ultralow temperatures and depends on value and orientation of the magnetic field. The obtained results are well described by a model of a system of non-interacting paramagnetic cylinders. The shift is proportional to the magnetization of solid
3
He and may complicate nuclear magnetic resonance experiments with superfluid
3
He in aerogel.
Possible experiments on the observation of the P,T - odd Faraday effect (rotation of polarization plane for the light, propagating through a medium in the presence of an external electric field, P - ...is the space inversion, T - is the time reflection) caused by the electron electric dipole moment in atoms and molecules, are discussed theoretically. An observation is assumed to be performed on the basis of modern intra-cavity absorption spectroscopy (ICAS) combined with atomic (molecular) beam techniques. The P,T - odd optical rotation is due to the linear Stark splitting of atomic or molecular levels. This leads to the difference between the refractive indexes for the right and left circularly polarized photons.
•The P,T - odd optical rotation is due to the linear Stark splitting of atomic or molecular levels.•Theoretical predictions of the de,deeqv values in frames of the Standard Model (SM) are still far from the experimental bounds.•A new idea of how to observe the P,T - odd Faraday effect was based on the considerable progress in the ICAS made during the last decades.
We present results of nuclear magnetic resonance (NMR) experiments in superfluid
3
He in two samples of nematic aerogel consisting of nearly parallel mullite strands. The samples were cut from the ...same piece of the aerogel, but one of them was squeezed by 30% in the direction transverse to the strands. In both samples, the superfluid transition of
3
He occurred into the polar phase, where no qualitative difference between NMR properties of
3
He in these samples was found. The difference, however, has appeared on further cooling, after the transition to the polar-distorted A phase (PdA phase) with the orbital part of the order parameter in the 2D Larkin–Imry–Ma (LIM) state. In the squeezed sample, the 2D LIM state is anisotropic, which results in changes in the NMR, which can be used as an additional marker of the PdA phase and have allowed us to measure the value of the anisotropy.
Algorithms are realized for localizing vibration activity sources in complex mechanoacoustic systems using finite element modeling. For the case of one source, the localization method was used in the ...least squares form applied to the first eigenvector of the sample correlation matrix. It is shown that frequency summation can significantly increase the localization accuracy in this case. Considerable attention is paid to assessing the number of simultaneously operating vibration sources and the possibility of correctly localizing them. The efficiency of two source localization methods was compared: the maximum likelihood method calculated for a single source and the MUSIC (Multiple Signal Classification) method specially modified for this problem. It is shown that the modified MUSIC method is more efficient in solving the localization problem with two sources compared to the maximum likelihood method calculated for a single source. It is noted that the maximum likelihood method calculated for two or more sources cannot be applied because of the too high computational complexity.
We present experiments on nematic aerogel oscillating in superfluid
3
He. This aerogel consists of nearly parallel mullite strands and is attached to a vibrating wire moving along the direction of ...the strands. Previous nuclear magnetic resonance experiments in
3
He confined in similar aerogel sample have shown that the superfluid transition of
3
He in aerogel occurs into the polar phase and the transition temperature (
T
ca
) is only slightly suppressed with respect to the superfluid transition temperature of bulk
3
He. In present experiments, we observed a change in the resonant properties of the vibrating wire at
T
=
T
ca
and found that an additional resonance mode coupled to the main resonance is excited below
T
ca
.
Computed tomography (CT) is a nondestructive high-resolution way to investigate the three-dimensional structure of samples (ice, rock, etc.). The results of CT analysis of glacial cores consisting of ...firn and ice extracted on the Western plateau of the Elbrus Mountain (5100–5150 m a.s.l.) in the summer of 2017 are presented in the article. The core taken from the depth of 20.31–21.87 m and consisting of three sections (average length is 52 cm each) was analyzed. In order to maintain the natural negative temperature of the glacial core, a special cryothermos has been created. It conserved the temperature at the level of −25 °C. Data on the structural features of the samples and the three-dimensional pattern of the ice-firn density were obtained. Correlations between the density and some chemical elements had been established. The CT data made it possible also to determine sizes of ice crystals. Comparison of cross sections of cores with firn and ice thin sections (30 in total) has shown that the crystal structure is best displayed in the ice inter-layers since it is impossible to determine reliably sizes of the firn grains at the given survey resolution. Also, the use of the CT method made it possible to determine inclination of the firn layers within the ice core, which is caused by the inheritance of the slope of the surface microrelief and internal inhomogeneities of the firn thickness. Calculations showed that the angle of inclination of the layers varies from 6 to 9°.
We report the results of theoretical and experimental investigation of spin diffusion in the normal phase of liquid
3
He confined in planar aerogel, which is a material consisting of nanostrands ...almost parallel to a specific plane and randomly oriented in this plane. Using spin echo technique, we measure the spin diffusion coefficients in the directions perpendicular and parallel to the plane. We see good agreement between the experiment and the theory.
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