Vol 74, No 3 (2019)

A review of physical regularities in formation of the the spatial structure of proteins during their folding, that is, the folding of a homochiral polypeptide chain into a unique native configuration, is presented, including the mathematical models of this process. The materials of this review are summarized in a new phenomenological model for the formation of hierarchies of sign-alternating chiral structures and also in a new mathematical model for the formation of α-helices as autowave structures. Some folding thermodynamic aspects associated with symmetry factors are discussed.

A method for constructing eigenmodes of an infinite waveguide of a constant rectangular cross section with low losses in the walls, which are described by the Shchukin—Leontovich boundary conditions, is discussed. The dispersion characteristics of these waveguides are constructed.

The data on photo- and electroexcitation amplitudes of most nucleon resonances in the mass range up to 2.0 GeV determined from the CLAS experiments on exclusive π⁺π⁻p photo-electroproduction off protons in collaboration between the Jefferson Lab and Moscow State University are presented. The first (and, currently, the only available) data on electroexcitation amplitudes from CLAS in a wide range of photon virtualities Q² <5.0 GeV² reveal the nucleon resonance structure as a complex interplay between the inner core of three dressed quarks and an external meson-baryon cloud. These results shed light on the strong QCD dynamics, which underlies the generation of excited nucleon states with different structural features from confined quarks and gluons. The future prospects of these studies in the new era of experiments with the CLAS 12 detector, which began in the spring of 2018, are outlined.

Turbulent fluctuations of density and pressure in air and argon in a shock tube have been investigated, as well as their interaction with a shock wave reflected from a perforated plate at the end of the shock tube. The Mach number of the incident shock was 1.9–3.9, while that of the reflected shock was 1.4–2.4. The turbulent length scale behind the incident shock was measured. That behind the reflected shock was a few times less than that behind the incident shock. It was established that overpressure occurs in the turbulent flow behind the reflected shock compared with the laminar flow, all other things being equal. The value of the overpressure is 12% in argon and 9% in air.

The problem of the influence of the nonlocality effect on the optical characteristics of plasmon nanolaser resonators is considered. This was performed within the framework of the generalized nonlocal optical response model; we took the nonlocality into account. Based on an extension of the discrete sources method, we performed a comparative analysis of the frequency characteristics of the field intensity in both the far and near zones, depending on the geometry of the resonator. The shapes of layered nonspherical resonators were considered. We established that, taking the nonlocality effect into account, one obtains a decrease of the intensity of plasmon resonance by up to 2.5 times.

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 (the Mach numbers of flows are 1.16–1.47 and the density is 0.02–0.20 kg/m³). It is shown that in an airflow with a vortex zone, the surface discharge develops as a 1–3-mm-wide channel 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.

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.

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

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.

We hereby clarify the following correct mathematical formof formula (5) and formulas in the text above it for the Bessel coefficients of a dual-frequency undulator: