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

Within the frameworks of the defect isotopic model, new expressions for the rapid estimation of the absorption coefficients of longitudinal and transverse hypersonic waves in the alloyed lithium niobate single crystals in the Akhiezer regime have been obtained. It is shown that the introduction of impurities in the crystal results in a change in both the magnitude of the sound attenuation coefficient and its temperature dependence.

Vector non-stationary diffraction electromagnetic fields and fields of charges in an arbitrarily chosen volume in both homogeneous and inhomogeneous media are considered. These formulas are presented in two forms, each of which has its advantages in applications. The generalization of the Kirchhoff–Kottler vector formulas for discontinuous fields in the non-stationary case is also directly obtained.

The electrically small phased antenna array is investigated. High permittivity dielectric and magnetodielectric materials (MDM) are used for antenna array substrates to miniaturize antenna size. To analyze material parameter influence on antenna performance, the same refractive index is considered for dielectric and MDM. The basic parameters of high permittivity-based, and MDM-based microstrip patch antenna arrays are compared. The simulation results show that the usage of MDM results in the improvement in bandwidth and isolation between elements, perfect impedance matching (voltage standing wave ratio (VSWR) < (~1.1) for center frequency) between material and free space over a much wider bandwidth.

The results of the ten years of diamond synthesis from graphite in industrial volumes (2 × 10⁸ carats) based on the PA “Almaz”, Yerevan, Armenia are analyzed. Theoretical studies are used in the physics of first-order phase transitions. The process of diamond growth is described within the frames of the transition state model using the Fokker-Planck and Zeldovich–Frenkel equations. The formation of a diamond carbon phase nucleus is the result of a direct graphite-diamond phase transition under high pressures and temperatures.

The magnetic size effects of single-domain nickel nanoparticles encapsulated in a graphite-like carbon shell (Ni@C nanocomposites) have been studied. Along with ferro- and superparamagnetic characteristics, the samples exhibit paramagnetism due to surface nickel ions formed through charge transfer from the carbon matrix. A detailed analysis of the total curves of magnetization M(H) and coercivity at 10 K was carried out and the corresponding magnetic parameters were determined.

Single crystals of YAlO₃-Er (YAP:Er) are grown by the Bridgman method from melts with different Y/Al ratio. The structural defects and color centers are compared for Y/Al = 1 and Y/Al > 1, as well as formed in the processes of gamma-irradiation and thermal treatment. Based on the obtained data, the growth conditions of YAP:Er crystals free of color centers and twins are determined. Spectral-luminescent properties of crystals are investigated: the absorption and luminescent spectra are registered in the polarized light, the luminescence kinetics is investigated and the lifetime of the ⁴I_13/2 level of Er³⁺ ion is determined.

The results of modeling the electrophysical characteristics of reusable capacitive immunosensors based on the electrolyte-insulator-semiconductor (EIS) structure are presented. Electrophysical and geometrical data on the most common viruses are collected and classified from a unified point of view. The results of theoretical computations of the capacitance and capacitive sensitivity of multiple-use EIS immunosensors for COVID-19 viruses are presented and analyzed.

We study an analytically solvable pseudoscalar interaction potential for the one-dimensional stationary Dirac equation, which consists of power terms proportional to ({{x}^{{ - 1}}}), ({{x}^{{ - 1/3}}}), and ({{x}^{{1/3}}}). This potential is classified as conditionally exactly solvable due to the fixed strength of the first term at a specific constant. We present the general solution to the Dirac equation in terms of non-integer index Hermite functions, which are distinct from the conventional integer index Hermite polynomials. We analyze the energy spectrum of the bound states and the eigenfunctions and compare the results with the case without the ({{x}^{{ - 1/3}}}) term.

Within the framework of a three-dimensional model, the burnup process of the core of the WWER-440 reactor was studied using measurements of the operating cycles of the Armenian NPP (ANPP). Simulation results showed that a model study that takes into account only the temperature dependence of the thermal conductivity of the PATHS (PARCS Advanced Thermal Hydraulic Solver) fuel leads to discrepancies with the measured values of the boron concentration as the cycle time increases. However, taking into account the dependence of thermal conductivity on burnup significantly improved the agreement between the results of PARCS–PATHS (Purdue Advanced Reactor Core Simulator) and measurements. Taking into account the heat transfer of the fuel rod gap further improved the agreement between the simulation and measurement results. For the non-peripheral fuel assemblies, the relative difference between the predicted PARCS–PATHS and measured thermocouple results meet the acceptance criteria (≤10%). For peripheral assemblies that are in contact with the reflector by three faces, the relative error exceeds the acceptance criteria (15%) by 1–2%.