Journal of Experimental and Theoretical Physics最新文献

A spectral quasilinear approach to the problem of TEM-Weibel instability in an anisotropic collisionless plasma is developed, which takes into account only the integral nonlinear interaction of modes through the joint variation of the spatially averaged particle velocity distribution induced by these modes. Within this approximation, a closed system of equations is obtained for the one- and two-dimensional evolution of spatial modes (harmonics) of the distribution function of particles and the electromagnetic field under conditions when the plasma anisotropy axis, the wave vector, and the magnetic field of the modes are orthogonal to each other. The numerical solution of this system of equations is compared with the available results of one-dimensional analytical quasilinear theory in the region of its applicability, as well as with the results of two-dimensional simulation by the particle-in-cell method, which also takes into account the direct four-wave interaction of modes. It is established that in the simplest cases of one-dimensional and axially symmetric two-dimensional problems for a bi-Maxwellian plasma, quasilinear phenomena play the leading role at a quite long stage of nonlinear development of turbulence. It is noted that at a later stage of decay of turbulence and in a more general formulation of the problem, in particular, in the presence of an external magnetic field, the direct nonlinear interaction of modes can manifest itself along with quasilinear phenomena. Based on the analysis carried out, the contribution of certain nonlinear effects to the evolution of the spatial spectrum of Weibel turbulence is revealed, and the properties of this turbulence are studied, including the self-similar character and qualitatively different stages of the dynamics of unstable modes.

Cylindrically bent diamond single-crystal plates have a great potential for creating energy dispersive spectrometers and focusing crystal monochromators. When they are designed, it is necessary to take into account the significant stresses that appear on bending the plates. The strain tensor and the elastic stress fields in a cylindrically bent single-crystal (110) diamond plate are calculated. The calculations are based on experimental data obtained by local Laue diffraction. The calculation results can be used to design new X-ray optical devices with the ability to control their parameters.

We describe a new method for the formation of optical ghost images, in which radiation in the object arm is detected by several detectors. The advantage of the proposed method is demonstrated, which is the smaller number of illumination patterns required for reconstructing the object image as compared to traditional schemes of ghost imaging. We propose variants of algorithms for measurement reduction to the form relevant to the imaging of the object of investigation, which are aimed at improvement of the performance of the computing component of the endoscope. The fiber-optic version of ghost imaging considered here is suitable for investigating hard-to-reach abdomens and organs of human organism, which permit the introduction of a thin fiber-optic bundle, thus extending its applicability as compared to traditional optic endoscopic methods.

The thermodynamic properties of the Boltzmann hard sphere system is discussed. It was found that zero point energy decreases with temperature so slowly that it turned out to be an almost a constant addition to the classical value. In result the heat capacity of the system differs little from the classical value of 3/2 k everywhere except for the narrow region of low temperatures, where heat capacity drops to zero. The predicted linear temperature contribution to the heat capacity like in ideal Fermi gas was clearly detected in the quantum hard sphere system at the lowest temperatures.

The artificial neuron proposed earlier for use in superconducting neural networks is experimentally studied. The fabricated sample is a single-junction interferometer, part of the circuit of which is shunted by an additional inductance, which is also used to generate an output signal. A technological process has been developed and tested to fabricate a neuron in the form of a multilayer thin-film structure over a thick superconducting screen. The transfer function of the fabricated sample, which contains sigmoid and linear components, is experimentally measured. A theoretical model is developed to describe the relation between input and output signals in a practical superconducting neuron. The derived equations are shown to approximate experimental curves at a high level of accuracy. The linear component of the transfer function is shown to be related to the direct transmission of an input signal to a measuring circuit. Possible ways for improving the design of the sigma neuron are considered.

The fragmentation of a drop of liquid (water, alcohol, glycerin) under the action of an air shock wave with a pressure of 0.2 and 3.2 atmg is studied experimentally and theoretically. The experiments are carried out using an air shock tube, and the liquid drop diameter is approximately 0.6 and 2 mm. The process is studied using high-speed video recording. Dispersed liquid particles from ≈5 μm in size are detected, liquid particle size distributions are plotted, and the particle velocities are determined. The experimental results are compared with the results of computational–theoretical estimation.

Reply to the comment on the article “On the time integral of electromagnetic field,” J. Exp. Theor. Phys. 136, 406 (2023)).

The spectra of the optically detected magnetic resonance for single NV^– centers have been experimentally studied in two solid-state samples in the range of hyperfine interactions between the electron spin and the nitrogen nucleus spin in the same NV^– center. This study has been aimed at reaching a maximal microwave frequency resolution in the experimental setup used. For measurements, two low-nitrogen (no higher than 50 ppb) diamond single-crystal samples have been grown. Measured time (T_{2}^{*}) of the spin decoherence in NV^– centers was about 2 μs in one sample and 20 μs in the other. For both samples, the spectrum of the optically detected magnetic resonance for the hyperfine splitting of a single NV^– center and ¹⁴N atom has been taken and investigated. The resolution in these samples has been estimated at a level of 3.5 and 0.18 MHz, respectively. It has been noted that the resolution of the spectrum improves with increasing time (T_{2}^{*}) of the spin decoherence of the single NV^– center.

Two devices intended for copper cylindrical liner gasdynamic acceleration to velocities of 5–7 km/s using the chemicals explosion energy have been investigated. It has been demonstrated that the acceleration of quasi-isentropically and isentropically loaded liners under the conditions of high-level dynamics, symmetry of deposition, and suppression of shock-induced dusting is feasible.

We have performed the Monte Carlo simulation of the processes of secondary ionization of water induced by cascade decays of inner-shell vacancies in an iron atom placed in water. We have obtained the spectra of electrons and photons emitted during the decay of vacancies in the K and L shells of the iron atom. The dependences of the number of secondary ionization events and the energy absorbed as a result of these processes on the radius of the sphere in which such processes occur have been calculated. The decay of a single 1s vacancy in an iron atom generates on the average 232 events of secondary ionization induced by an electron impact, in which the energy of 3274 eV is absorbed, as well as 18 secondary photoionization events, in which the energy of 256 eV is absorbed. The dependences of the dose absorbed in water on the distance from the iron atom have been calculated.