Journal of Contemporary Physics (Armenian Academy of Sciences)最新文献

The binding of ligands with receptors was theoretically studied in the case when the number of ligands in solution fluctuates under the influence of fluctuations of the external environment. A multiplicative stochastic differential equation has been obtained that describes the time change in the number of ligand-receptor complexes. The average number of ligand-receptor complexes and its variance were calculated. An isotherm of the binding of ligands to receptors was obtained. It has been shown that the presence of multiplicative noise leads to the fact that the process of binding of ligands to receptors becomes threshold—in the region of low concentrations of ligands at a certain ratio between the binding parameters and the intensity of the multiplicative noise, the formation of a ligand-receptor complex does not occur. It has been shown that with increasing ligand concentration, the relaxation time of the average number of ligand-receptor complexes decreases, and with increasing noise intensity it increases. It is also shown that at low values of the external noise intensity, the dispersion is proportional to the external noise intensity and increases linearly with increasing noise intensity.

A theoretical study of X-ray diffraction on a superlattice with overlapping stacking faults is carried out. Expressions for the X-ray reflection coefficient in the directions of satellites, depending on the wave’s phase jump on the stacking faults and the depth of their occurrence are obtained. For comparison with an ideal superlattice, the relative change in the reflection coefficient is obtained.

The results of numerical modeling of thermal processes in locally inclined targets made of pressed molybdenum powder with holders of titanium and copper are presented. The simulation was conducted to determine the suitability of such targets for irradiation with high-intensity proton beams in the “Nirta Solid Compact Model TS06” target module for producing the medical radioisotope Tc-99m. Calculations were carried out using the Fluid Flow (Fluent) engineering package of the ANSYS Workbench software platform on models of targets with axially symmetric corrugations in the irradiation zone. It is shown that the target temperature decreases on locally inclined targets with titanium and copper holders due to corrugation. On targets with copper holders, it is also possible to increase the maximum irradiation current by 1.5 times compared to standard flat targets, comparable with previously obtained results for targets with niobium holders. It has been established that on locally inclined targets with titanium holders, corrugation does not provide a practically significant increase in the maximum irradiation current due to the low thermal conductivity of titanium.

The possibility of applying a dielectric lens as a highly directional antenna in the terahertz range is investigated. Theoretical expressions have been obtained and analyzed that make it possible to compute the shape of the lens profile and the radiation pattern of the created lens antenna. The effectiveness of the proposed lens antenna in the specified range is shown, and the results of experimental studies of the created lens antenna are also presented.

An assessment of the uncertainty in the calculation of fast neutron fluence on the reactor pressure vessel of the second unit of the Armenian Nuclear Power Plant (ANPP) was conducted, considering uncertainties in neutron–nuclear interaction cross-sections. Using the Monte Carlo method, the most sensitive region of the reactor to changes in neutron interaction cross-sections was identified. The results indicate that the primary source of fluence uncertainty is in the neutron absorption cross-section in the fast neutron energy region, especially in hydrogen. Data received have significant importance for the long-term safety assessment and life extension of these types of reactors.

The influence of a two-component TiO₂:ZrO₂ addition on the mechanical properties of a glass-crystalline material synthesized on the base of perlite has been studied. A relationship has been established between Young’s modulus, microhardness, and the content of the TiO₂:ZrO₂ addition to the original batch. The kinetics of crystallization of the resulting material were studied using the method of non-isothermal differential thermal analysis (DTA). Based on the results of SEM studies, it was established that the addition of TiO₂:ZrO₂ results in an increase in the concentration of nucleation sites and a decrease in the size of the resulting crystallites, which ultimately is the physical reason for the increase in the microhardness of the synthesized glass ceramics.

A new type of multilayer energy-absorbing substrate has been proposed, the layers of which are stuck together by an elastic glue. When the impactor collides with an obstacle, part of the kinetic energy of this impactor is spent on the displacement of separate layers of the substrate relative to each other, which increases the maximum velocity of penetration of the barrier. The dependence of the maximum velocity of penetration of the barrier on the displacement of the substrate layers, as well as the dependence of the energy spent on sliding layers on the area of the deformed part of the substrate, have been studied. It is shown that, at the same impact energy, the depth of deformation of the proposed substrate is 1.5 times less than that of substrates in which the sliding of layers is absent. The use of the proposed substrate in ceramic protective structures allows one to significantly reduce the surface density of the structure.

A comparative study of the complex formation of ethidium bromide (EtBr) and methylene blue (MB) with synthetic single-stranded (ss-) polynucleotides poly(rA) and poly(rU) was conducted. The absorption spectra of these ligands decreased upon interaction with ss-polynucleotides and poly(rA)-poly(rU) formed at their hybridization. In the case of the MB-polynucleotide complexes, the fluorescence intensity decreases, while in the case of EtBr, the fluorescence intensity increases along with the enhancement of concentrations of polynucleotides. Based on the fluorescence spectra analysis of the complexes EtBr with ss- and hybrid ds-polynucleotides, the binding curves in Scatchard coordinates were constructed (r/C_f and r), and the values of the binding parameters of polynucleotides determined, including the binding constant value K and the number of bases n (base pairs at hybridization) per binding site..

In a two-layer meta surface consisting of periodically arranged rods, there is a strong dispersion of the transmission coefficient in the microwave region of the spectrum. The observed phenomenon is the result of the resonant interaction of the microwave with the rod, where a standing wave with axial symmetry is formed, as well as the effective electrical interaction between the rods of adjacent layers. The transmission coefficient curve found in the experiment has an acute peak, which allows the structure to be used as a bandpass filter. It was found that the resonant frequency shifts to the low-frequency region as the length of the rods, their diameter, and the distance between the layers increases, which opens up the possibilities of controlling the microwave.

The possibility of increasing the resolution of X-ray phase-contrast imaging with a device based on a triple Laue-case interferometer is considered. To address one of the drawbacks of this scheme—the distortion of the interference pattern during diffraction of the object wave on the interferometer analyzer—it is proposed to replace the analyzer with two crystalline blocks of equal thickness. These blocks act as a diffraction lens, suppressing the mentioned distortions. Numerical simulations demonstrate that the low coherence of the initial radiation increases the quality of phase-contrast imaging using this method.