R e g u l a r p a p e r s

Physics of nuclei and elementary particles

Moscow University Physics Bulletin 2020. N 4.

The binding energy per nucleon for nuclear matter, i.e. equation of state (EOS), within the Brueckner-Hartree-Fock (BHF) approach with the consideration of various three-body forces (3BFs) like the phenomenological 3BF and by adding a contact term to the BHF calculations are considered at variance densities. The 3BF contribution turns out to be non-negligible contribution and to have a substantial saturation effect. The calculations are done utilizing the CD-Bonn and Argonne V18 nucleon-nucleon (NN) potentials. These NN potentials give great fitting to the deuteron properties and are phase-shift equivalent. The resultant EOS is compatible with the phenomenological analysis on the saturation point. It is demonstrated that the 3BF influences significantly on the nuclear matter EOS at high densities. Moreover, it is necessary for reproducing the empirical saturation properties for symmetric nuclear matter. The pressure has been also calculated and the suggested approaches reproduce fairly well agreement with the empirical data. We also examined the maximum neutron star masses which are close to two solar masses, which is again compatible with recent observational data. Comparison with other microscopic EOS is presented and discussed.

Show AbstractPhysics of Earth, atmosphere, and hydrosphere

Moscow University Physics Bulletin 2020. N 4.

A method is proposed for testing pressure gauges and z-accelerometers, installed in seafloor observatories. The method is based on the linear relationship between variations of the ocean-bottom pressure and the z-acceleration, observed during seismic movements of the bottom within the frequency band of "forced oscillations". Calculation of the boundaries of this frequency band is based on the ocean depth at the observatory site making use of explicit formulae. In the case of correct calibration of the gauges calculation of the ratios of power spectra of bottom pressure variations and the z-accleration within the band of "forced oscillations" yields constant values equal to the square ratio of the total mean pressure and the gravity acceleration. The conditions for application of the proposed method are formulated.

Show AbstractTheoretical and mathematical physics

Moscow University Physics Bulletin 2020. N 4.

Analytical description of the undulator radiation harmonics generation in an undulator with field harmonics in both orthogonal planes is obtained. The exact expressions for the spectrum and radiation intensity are written in terms of the generalized Bessel and Airy functions. They reduce to the known cases of planar, helical and elliptic undulators with field harmonics in proper limiting cases. Analytical account for the effect of the beam size, electron position in the beam, emittance, energy spread and other characteristics is given; the effect of the constant magnetic components and the beam deviation off the undulator axis is described. The obtained analytical expressions distinguish the contributions of each parameter and beam characteristic on the radiated UR harmonics. Analytical model is employed for the analysis of the free electron laser (FEL) harmonics in the LCLS and LEUTL experiments using the obtained analytical expressions for the Bessel coefficients. The modelling yields good agreement with the experiment. The presence of strong 2nd FEL harmonic is explained in X-ray LCLS FEL and in UV-A LEUTL FEL. It is shown that even harmonics were not caused by undulator field harmonics, neither by betatron oscillation and nor by the beams emittances. We have explained the 2nd harmonic in LCLS experiment by the detected beam deviation off the undulator axis in ~15 μm on the gain length ~1.5 m; in LEUTL experiment the 2nd harmonic is explained by the big angle of the photon-electron interaction on one gain length ≈0.9 m due to wide beams ~0.2 mm in the LEUTL FEL.

Show AbstractMoscow University Physics Bulletin 2020. N 4.

Based on mathematical modeling of the process of forming a pair of images, a ghost one and an ordinary one, in a new setup with quantum biphoton generation, new possibilities for improving the accuracy of measurements and creating the most sparing mode of object illumination are investigated. It is shown that taking into account additional factors (diffraction and non-unit quantum efficiency of the sensors) in ghost imaging leads to missing some information about the research object. Formation and measurement of an image in the object arm of the research object allows to weaken the influence of these factors on the result of processing the measured images if mathematical method of measurement reduction to the form that is characteristic to measurements of the object transparency distribution is used.

Show AbstractMoscow University Physics Bulletin 2020. N 4.

Within the theoretical-field approach, the critical behavior of disordered spin systems with frozen point impurities and additional dipole-dipole interaction has been investigated. The system is described by the Heisenberg model. The calculations are made in a two-loop approximation in three-dimensional space. The Pade-Borel method has been used to sum asymptotic series. It is shown that there is a threshold value of intensity of dipole-dipole interaction, above which the influence of point frozen impurities becomes important. Dependence of critical exponents on dipole-dipole interaction intensity at its small values is obtained.

Show AbstractMoscow University Physics Bulletin 2020. N 4.

We study equations related to the sums of products of polynomials in several variables. One set of polynomials is considered given, and the other is the desired.In the general case of defining polynomials, a series of relations is obtained for the degrees of polynomials and determinants of matrices composed of coefficients of polynomials. On this basis, taking into account the continuity equation, a number of variants of covariant vectors of limited current density are presented.The results can definitely be considered correct if the accelerations are not too large.The case of the dependence of the current vector on a variable is also considered, the value of which upon transition to a stationary state depends on the conditions of such a transition (if these conditions are unknown, then certain uncertainty elements are possible in stationary states).

Show AbstractMoscow University Physics Bulletin 2020. N 4.

For the system of equations of macroscopic electrodynamics with fractional Caputo derivatives with respect to time, a general expression is obtained for retarded potentials. An analog of the Lienard-Wiechert potentials is obtained. All expressions contain nonlocal (time-distributed) delay, which takes into account the temporal dispersion in the system.

Show AbstractRadiophysics, electronics, acoustics

Moscow University Physics Bulletin 2020. N 4.

In this work we present the nanoscale solid state structure is presented in current work. The structure is a 3D matrix of tunnel coupled arsenic dopants in silicon with a system of metallic electrodes leading to them. Structures of 8 metal electrodes, 4 of which converge to a region with a diameter of 50 nm and 4 of which converge to 200 nm region were fabricated on the surface of the arsenic-doped silicon. After removal of a thin highly conducting upper silicon layer, single-electron transport in an array (reservoir) of arsenic impurity atoms located between the electrodes is demonstrated. The value of the Coulomb blockade was ~ 100 mV at a temperature of 4.2 K. The operating temperature of the devices can be significantly increased due to the relatively small effective size of the impurity atoms of arsenic in silicon (3-5 nm). Such system can be used as a reservoir neural network, where the single dopant atoms will be acting as a neurons. The electrodes will be acting as input and output terminals and also will be used for the system configuration.

Show AbstractMoscow University Physics Bulletin 2020. N 4.

Parameters of a readout based on a SQUID magnitometer for an inertial navigation system (INS) with a cryogenic gyroscope were estimated. A "voltage output/angle of rotation"transfer function was calculated and measured for a cryogenic gyroscope imitator. The value is 6.5 mV/deg, thus corresponding to a 4.1 V/deg transfer function of cryogenic gyroscope with diameter of 30 mm. Voltage output instability of SQUID magnitometer was measured on intervals up to 8 hours; drift rate of 10\textsuperscript{-6} deg/h was detected.

Show AbstractOptics and spectroscopy. Laser physics

Moscow University Physics Bulletin 2020. N 4.

Ambipolar organic field-effect transistors which can exhibit spatially localized photoelectric effect are studied. This effect means that in transistor channel a narrow photosensitive region exists, in which the transformation of incident radiation into photocurrent occurs, and its spatial position can be controlled by gate voltage VG. Due to this fact the photocurrent dependence on VG can represent spatial distribution of incident radiation intensity. In current work the response times of such phototransistors were studied by numerical modeling, in particular it is shown that response time to stepwise turning on the incident illumination is about several nanoseconds, and response to voltage VG switch is about several microseconds. Also, the influence of different transistor parameters on its performance was studied in present work. It is shown that comprehensive improvement of external quantum efficiency (EQE), photocurrent to dark current ratio (Jph/Jdark), spatial resolution and response times can be achieved by decrease of channel length. Also, it was shown that the using of the materials, in which photogenerated electron-hole pair distances are higher than 1 nm, can provide higher EQE and Jph/Jdark values without any significant deterioration of spatial and temporal resolution.

Show AbstractMoscow University Physics Bulletin 2020. N 4.

The possibility of using the laser optical-acoustic method to investigate the spatial inhomogeneity of the optical properties of colloidal solutions is demonstrated. The proposed method for reconstruction the spatial distribution of the light extinction coefficient in the medium under study is based on the dependence of the time profile of the excited optoacoustic signal on the light absorption and light scattering coefficients in this medium. Water-based and kerosene-based ferromagnetic fluids with different volume concentrations of magnetite particles were taken as the investigated solutions. Diagnostics of the optical properties of a ferromagnetic fluid with a high spatial resolution is carried out. It is shown that in a near-surface layer with a thickness of tens or hundreds of microns, there is an increase of the light extinction coefficient with depth. A nonlinear dependence of the light extinction coefficient on the fluid concentration at depths of more than 200 microns was found. The value of the relative change in the light extinction with depth depends on the concentration of magnetite particles and the properties of the carrier liquid, as well as on the type of acoustic boundary.

Show AbstractChemical physics, physical kinetics, and plasma physics

Moscow University Physics Bulletin 2020. N 4.

The properties of the model, which is based on the analogy between double liquid mixtures and coupled self-oscillating systems is investigated [Blagonravov L.A. Russian Journal of Physical Chemistry.Vol. 76, N 1. 2002, pp. 59-63]. In this work an expression that is a mapping of a curve in the phase diagram of a two-component system is obtained. The mapping of the boundary curve is presented as the dependence of the ratio of the characteristic fre-quencies attributed to the pure components on the concentration of the mixture. The model also determines the dependence of the square of the frequency ratio on temperature. An important aspect of the model is that the temperature-dependent characteristic frequencies ϑ_a and ϑ_b reflect the properties of pure components (not solutions). The task is to understand in more detail the physical aspects of the model proposed in the work men-tioned above. In the present work, it is shown that the use of Padé approximants makes it possible to determine the nature of the temperature dependence for each characteristic frequency separately based on the temperature de-pendence of the ratio obtained from the experimental data. Keywords: binary liquid mixtures, phase diagram, properties of the pure component, coupled self-oscillating systems, rational functions, Padé approximants.

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