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

The binding energy of the ground and first excited states of a hydrogen-like impurity electron in monolayer graphene is studied by a variational approach. It is shown that the binding energies of the impurity electron can be tuned by changing the value of the gap and the effective fine structure constant. An analytical expression for the dipole matrix element of the electron transition from the ground to the first excited state of a hydrogen-like impurity in graphene is found.

The structural and reflective properties (total reflectance and scattering) of black silicon layers formed by reactive ion etching have been studied. Reflectance spectra were determined in the visible, near-infrared, and near-ultraviolet wavelength ranges. The influence of etching duration on the optical behavior of black silicon layers is studied and the possibilities of their use in solar cells and photodetectors are discussed.

The stability of heterogeneous biopolymers is extremely important for maintaining their conformation and carrying out biological functions. The conformational stability of these molecules determines their ability to preserve the necessary structure for biological processes such as catalytic activity, molecular recognition, and cellular interactions. Within the framework of the Generalized Model of the Polypeptide Chain (GMPC), the correlation function of a two-component heteropolymer has been computed as a function of distance, specifically the number of repeating units between two monomers in a helical state, using the method of super-matrices. Through this research, dependencies of the correlation function on the number of repeating units between monomers in the helical state have been obtained for several realizations and different temperatures, particularly around the melting temperature. An interpolation dependency has been proposed for the curve at the melting temperature, expressed as a sum of exponential and power functions. This model allows for a more accurate description of the correlation function behavior under critical conditions close to the melting temperature. The exponential part of the model reflects intense decay of correlation at short distances, while the power function describes mild changes at longer distances.

An analysis of the properties of lead metasilicate powders synthesized by the microwave method and low-melting (900°C) glass obtained based on it has been conducted. Physical and chemical studies have shown that the synthesized lead metasilicate and the glass obtained from it are promising materials for use in various fields, namely as a wide-bandgap semiconductor, photocatalyst, and glass used for protection against ionizing radiation.

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.