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

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.

Cubic boron nitride (c-BN) is an ultrawide band gap, superhard material with significant potential for applications under extreme temperatures and pressures. Nevertheless, two major challenges hinder its practical utilization in technology: (i) the difficulty in producing high-quality c-BN films, and (ii) the challenge of effectively n- and p-doping its matrix. This theoretical study focuses on investigating the solubility limits of silicon (Si) and carbon (C) in the c-BN and wurtzite BN (WZ–BN) on the basis of the strictly regular solution approximation. These elements are key candidates as n-type dopants in BN, addressing a critical concern in the realization of c-BN based electronics. The calculated Gibbs free energies of binary mixtures within the temperature range of 800–3000 K indicate that the presence of unstable regions, and consequently, miscibility gaps, are a prevalent characteristic of this system. The analysis reveals that the immiscibility gap is influenced not only by temperature, but also by the crystallographic structure. The calculated results of Si solubility limit in BN–Si binary system are in a good agreement with the latest experimental results. The findings presented here are applicable to the fabrication of multicomponent bulk crystals, epitaxial thin films, and nanostructures based on BN–Si–C solid solutions.

In this study, we have performed investigations on the structural stability, electronic band structures, magnetic exchange couplings, and half-metallic performance of Cr_xCa_{1– x}Se materials using computational methods of density functional theory via GGA-WC, GGA-PBE and, TB-mBJ exchange-correlation potentials. The Cr_xCa_1–xSe compounds are thermodynamically stable and synthesizable owing to their negative formation energies. The structural parameters of Cr_xCa_1–xSe with GGA-WC and GGA-PBE approximations appear to be in excellent concordance compared to the experimental data and recent theoretical calculations. According to GGA-PBE and TB-mBJ calculations, the Cr_xCa_1–xSe compounds revealed integral magnetic moments and a half-metallic behavior with better half-metallic gaps, and spin-polarization of 100%. The Cr_xCa_1–xSe alloys appear to be better materials for use in spintronic devices.

The Er³⁺/Yb³⁺ co-doped Y₄GeO₈ crystal powders were successfully synthesized using a high-temperature solid-phase method. The crystal structure of the obtained phosphors was confirmed to be pure Y₄GeO₈ through X-ray diffraction (XRD) analysis. A regression equation correlating Er³⁺/Yb³⁺ doping concentrations with luminescent intensity was established based on the optimized theoretical model derived from experimental design. The optimal concentrations of Er³⁺ and Yb³⁺ under 980 nm laser excitation were determined as 7.41 and 21.34%, respectively, while under 1550 nm laser excitation, the concentrations were 2.66 and 17.42%, respectively. The fluorescence emission spectra of the up-conversion samples were measured, revealing intense green and red emissions with peaks at 542, 546, and 654 nm under 980 nm excitation, and peaks at 546, 557, and 663 nm under 1550 nm excitation. These peaks correspond to transitions from ²H_11/2 to ⁴I_15/2, ⁴S_3/2 to ⁴I_15/2, and ⁴F_9/2 to ⁴I_15/2 energy levels. The relationship between up-conversion luminescence and laser operating current for the optimal samples under 980 nm and 1550 nm was investigated, uncovering that up-conversion luminescence occurs through both two-photon and three-photon processes. A detailed analysis and discussion of the up-conversion luminescence mechanisms were conducted. Furthermore, the relationship between up-conversion fluorescence and temperature for the optimal samples was studied, revealing excellent temperature-sensing characteristics under 980 nm and 1550 nm laser excitations. The calculated illumination region coordinates for the optimal samples under 980 nm and 1550 nm wavelength excitations were (0.5558, 0.4362) and (0.5256, 0.4687), respectively. The research highlights the potential of rare-earth ion-doped up-conversion luminescent materials for diverse anti-counterfeiting applications. In particular, the Y₄GeO₈: Yb³⁺/Er³⁺ phosphors, incorporating a dual-excitation mechanism, enhance the security of anti-counterfeiting strategies in multifaceted scenarios. The study underscores the promising developments in this field.