R e v i e w s

Biophysics and medical physics

Moscow University Physics Bulletin 2019. N 3.

A review of the physical laws of spatial structure formation in proteins during folding - process by which a homochiral polypeptide chain acquires a unique native configuration - is presented, including mathematical models of the process. The review materials are summarized by a new phenomenological model for the formation of hierarchies of alternating chiral structures, as well as by a new mathematical model for the formation of -helices as autowave structures. The thermodynamic aspects of folding associated with symmetry factors are discussed.

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Engineering physics

Moscow University Physics Bulletin 2019. N 3.

In this experiment, the biasing effect on the control of turbulence in IR-T1 tokamak was investigated. The radial profile of the average density, the relative level of fluctuations and their power spectrum were obtained in the presence of biasing with two positive and negative polarities by using an array of Langmuir probe (Rake probe). Biasing was more effective in reducing the fluctuations at the edge of the plasma than in the more internal regions, but the spectral power of fluctuations in the inner regions decreased faster. Striking issue is that the positive bias has been more effective than negative bias in increasing of confinement.

Show AbstractMoscow University Physics Bulletin 2019. N 3.

Time domain 3D computation of convection heating in vapor environment of preliminary frozen muscular tissue with phase change and time depended temperature of vapor was carried out. The temperature fields on the surface and inside muscular tissue were obtained. Heat transfer characteristic of the muscular tissue in vapor environment with temperature varying from 10 to 20 °C was experimentally measured.

Show AbstractBiophysics and medical physics

Moscow University Physics Bulletin 2019. N 3.

There exist many radioisotopes known as suitable for the diagnosis of cancer diseases and for many other medical field uses. One of the most known and widely used among them is 67Ga due to its preferable specifications such as 3.26 days of half-life and possibility of production from cyclotrons via charged particle induced reactions. In this study investigations of the cross-section calculations for different production routes of 67Ga, by considering the charged particle induced reactions on different isotopes, and the effects of level density models to these calculations have been aimed. Moreover, the total activity calculations for 67Ga have been performed for these investigated reactions. The cross-section calculations have been done via TALYS 1.8 code by employing Constant Temperature Fermi Gas, Back-Shifted Fermi Gas and Generalised Superfluid models. Obtained calculation results have been reviewed by comparing them with not only each other but also literature data taken from Experimental Nuclear Reaction Data (EXFOR) database both visually and statistically.

Show AbstractTheoretical and mathematical physics

Moscow University Physics Bulletin 2019. N 3.

The eigen-modes construction method of an infinite waveguide of a constant rectangular cross-section with losses in the walls, described by Schukin-Leontovich boundary conditions, is proposed. The dispersion characteristics of the waveguide are constructed.

Show AbstractMoscow University Physics Bulletin 2019. N 3.

The latest (November 2018) experimental data on neutrino mixing is analyzed in the framework of standard, cobimaximal and exponential parameterizations. The logarithm of the mixing matrix is found and the matrix elements values for the exponential and cobimaximal mixing matrix forms are determined. The exponential form allows factorization of the matrices responsible for the rotations in the real space and the CP violation in the form of the rotation in imaginary space. Exponential form also allows easy verification of complementarity of quark and neutrino mixing. In the exponential mixing parameterization the angle between the rotation axis for quarks neutrinos is studied and the complementarity of quark and neutrino mixing is investigated. Entries for the cobimaximal matrix are identified to comply with experimental data and provide exact quark-neutrino mixing complementarity. Jarlskog invariant is employed to study the degree of CP violation for various parameters of mixing matrices in the standard, cobimaximal and exponential parameterizations. The mixing matrix is studied as the group SU(3) element with the help of the exponential parameterization. SU(3) group parameters φ и are written for the mixing matrix; their dependence of the degree of the CP violation is explored.

Show AbstractPhysics of nuclei and elementary particles

Moscow University Physics Bulletin 2019. N 3.

The results on photo- and electroexcitation amplitudes of most nucleon resonances in the mass range up to 2.0 GeV determined from the CLAS experimental data on exclusive $\pi^+\pi^-p$ photo-/electroproduction off protons in collaboration between the Jefferson Lab and Moscow State University are presented. The first and only available results on electroexcitation amplitudes from CLAS in a wide range of photon virtualities $Q^2$ $<$ 5.0 GeV$^2$ revealed the nucleon resonance structure as a complex interplay between the inner core of three dressed quarks and external meson-baryon cloud. These results shed light on the strong QCD dynamics which underlines the generation of excited nucleon states of different structural features from confined quarks and gluons. The future prospects of these studies in the new era of experiments with the CLAS12 detector, which started successfully in Spring of 2018, are outlined.

Show AbstractRadiophysics, electronics, acoustics

Moscow University Physics Bulletin 2019. N 3.

Density and pressure fluctuations have been investigated experimentally in turbulent flows of air and argon in a shock tube as well as the interaction of the reflected shock wave with turbulence. The shock wave reflected from the perforated end of the shock tube and interacted with the turbulent flow. The Mach number of the incident shock wave varied from 1.9 to 3.9. The Mach number of the reflected shock were equal to 1.4 – 2.4. We measured the length scale of the turbulent fluctuation behind the incident shock. It was found that the pressure behind the reflected shock in a turbulent flow is greater than the corresponding value in the laminar flow ceteris paribus. The overpressure is equal to 12% in argon and to 9% in air.

Show AbstractOptics and spectroscopy. Laser physics

Moscow University Physics Bulletin 2019. N 3.

The problem of the nonlocality effect influence on the optical characteristics of plasmon nanolaser resonators is considered. Accounting for non-locality is performed within the framework of the Generalized Non-Local Optical Response model. Based on the extension of the Discrete sources method, a comparative analysis of the frequency characteristics of the field intensity is accomplished in both the far and near zones, depending on the geometry of the resonator. The shapes of layered non-spherical resonators were considered. It has been established that taking into account the nonlocality effect leads to a decrease in the intensity of plasmon resonance up to 2.5 times.

Show AbstractChemical physics, physical kinetics, and plasma physics

Moscow University Physics Bulletin 2019. N 3.

The characteristics of a distributed sliding surface discharge with a duration of ~300 ns (plasma sheet) in a non-uniform supersonic airflow with a vortex zone behind a thin wedge have been studied in a shock tube channel. The spatial distribution of the discharge radiation, the spectra of the discharge radiation, and the discharge current are analyzed in the flows behind plane shock waves with Mach numbers 2.4-3.5 (Mach numbers of flows 1.16-1.47, density 0.02-0.20 kg /m3. It is shown that in an airflow with a vortex zone, the surface discharge develops as a channel 1-3 mm wide, located in the region of low density behind the wedge. The calculated electron concentration in the discharge channel is an order of magnitude higher than the electron concentration when a discharge is initiated in a homogeneous medium.

Show AbstractPhysics of Earth, atmosphere, and hydrosphere

Moscow University Physics Bulletin 2019. N 3.

The paper presents the results of numerical simulation of the propagation of HF radio waves in an artificially disturbed ionosphere during a Cyclone-3 vehicle launch from the Plesetsk cosmodrome on December 18, 1991 and a powerful industrial explosion with a magnitude of M = 2.4 on the Kola Peninsula on April 8, 1990. A specially developed set of Python scripts allows three-dimensional modeling of ray trajectories in the geometric optics approximation by solving a bicharacteristic system for eikonal equation. The developed programs use geomagnetic field from the IGRF model, and the ionospheric electron density distribution according to radio tomography data. Ionogram modeling is performed using three-dimensional homing method based on the Nelder-Mead simplex minimization. It is shown that artificial ionospheric irregularities during the periods of the studied events are quasi-wave perturbations that have a significant effect on the ray paths of the HF of radio waves and ionograms of vertical and oblique sounding. This manifests itself in the form of characteristic features of ray paths with multiple reflections from local maxima of the electron density and additional traces on ionograms caused by the passage of traveling ionospheric disturbances.

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