The features of X-ray resonant absorption and scattering, which are the basis of unique methods for studying the electronic, magnetic, phonon, and structural properties of condensed media, are considered. The theoretical description is carried out within the quasi-relativistic approximation of Dirac equation. This makes it possible not only to describe the experimentally observed phe-nomena, but also to predict new spin-position effects in resonance scattering.
Show AbstractA modification of the effective Yukawa-type nucleon-nucleon interaction is developed in detail to accelerate the calculation of the real part of the optical potential of the interaction of light spherical projectile nuclei with heavy deformed target nuclei. This nucleus-nucleus potential is calculated using the double folding model. The modification consists of replacing the standard exchange part of NN-forces with a finite interaction radius by an exchange part with zero interaction radius and significantly increased amplitude. It is shown that the Coulomb barriers calculated in both approaches for 11 reactions have no significant differences, and the modified amplitude value does not depend on the reaction. The proposed modification allows speeding up the calculations by a factor of 100, while the error in the height of the barrier does not exceed 0.15%.
Show AbstractAn experimental system for detection of back-scattered electrons (BSE) in the scanning electron microscope (SEM) for three-dimensional (3D) visualization of the microstructure topography is described. The 3D surface topography reconstruction is carried out according to the algorithm of profile reconstruction from the preliminarily determined angular dependencies of BSE with the use of a calibration specimen. It is shown that the instrument function of the detector system, i.e., the detector response function, as well as the geometric factor, that takes the transformation of the angle distribution for single and multiple scattering of BSEs into consideration, cause a significant impact on the detected signal.
Show AbstractThe effect of interface inhomogeneity on the exchange bias field value in the ferromagnet/antiferromagnet bilayer system is investigated by computer simulation. The case of a thin ferromagnetic film on a thick antiferromagnetic substrate is studied. The Ising model and Metropolis algorithm are used for research. The inhomogeneity of the substrate surface is modeled as random point nonmagnetic impurities. The exchange bias field is determined by the hysteresis loop offset. The dependence of the exchange bias field on the concentration of impurities on the substrate surface at different temperatures is calculated.
Show AbstractIn this work, we calculated efficient pairwise potentials using the prototype potential method and taking the chemical fraction and the fraction caused by the size effect into account. Unknown efficiency values of individual pair displacements were found using the fitting of values of short-range order parameters calculated by the Krivoglaz–Clapp–Moss method to their known experimental values. The values of the effective pairwise potentials determined by this method were used to calculate the short-range order parameters.
Show AbstractThe process of formation of a protein structure consisting of an irregular part and a regular spiralized secondary structure (a right-handed α helix) is considered as a sequential rearrangement of a linear chain of amino-acid residues that form a primary structure on ribosomes during the subsequent folding of the polypeptide chain into a right-handed α helix. Monomers of the protein structure (aminoacid residues) are represented in the form of spheres; the positions of their centers are determined by the coordinates of the α carbon atoms. The equations of motion for the residues are based on the two-particle model of motion in the Lennard-Jones potential and the data on the spatial arrangement of carbon atoms in the α helix.
Show AbstractStudying the possibility of using cone beam computed tomography (CBCT) for radiation therapy treatment planning is an important and topical task. Increasing numbers of patients, all things being equal, choose radiation therapy as the main treatment for oncological diseases. Consequently, the workload of the radiation therapy department is also increasing. At the same time, not every clinic has a CT scanner used only for simulation. Usually, there is a CT that works for both the diagnostic department and radiation therapy. To carry out a simulation it is necessary to register for the study, which delays treatment and can adversely affect the treatment result. In this work, the influence of voltage, current, and pulse duration on the change in the Hounsfield units and on the calculation of the dose are investigated. Calibration curves are obtained for various CBCT scan parameters. It is shown that using the Hounsfield units obtained for this regime reduces errors in the calculation of dose distributions. CT-based treatment plans are still certainly superior to CBCT-based plans. However, if it is not possible to scan on a CT, then one can use CBCT-images. It is recommended to use the high voltage mode and the calibration curve obtained for this scan mode. However, the use of CBCT images for areas with high electron density is not recommended
Show AbstractA mathematical model of laser ranging of artificial Earth satellites (AES) in elliptical orbits has been developed. The numerical analysis of the model showed that the centers of the spots formed on the Earth’s surface by light pulses reflected from the AES retroreflector are located at significant (300–1400 m) distances from the laser station. Therefore, when ranging AES’s in elliptical orbits, it is necessary to separate the receiving telescope from the laser station, make it mobile by installing it on a moving platform, and move it behind the centers of the spots of the reflected pulses. This will significantly increase the AES ranging distance, because the light energy flux received by the moving telescope is hundreds of times greater than the energy flux received by the stationary telescope of the laser station.
Show AbstractThe variation in the magnetoresistance of a spin-valve sensor during its linear movement in an inhomogeneous field of a magnetic label at different orientations of the magnetic moment of the spin-valve structure is considered. It is shown that the shape of the sensor signal and its value critically depend on the initial orientation of the magnetic moment and the trajectory of the sensor in the field of the magnetic label.
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