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

The dielectric properties of nanocrystalline glass-ceramics based on perlite were investigated in the frequency range of 100 – 1 × 10⁶ Hz and the temperature range of 25–350°C. Relaxation peaks were observed in the temperature dependences of the dielectric permittivity and dielectric losses, shifting toward higher temperatures with increasing frequency, which made it possible to determine the activation energy of the relaxation process. The frequency dependence of the temperature coefficient of dielectric permittivity additionally confirms the relaxation nature of the observed phenomenon. The obtained results are consistent with the Maxwell–Wagner interfacial polarization model, indicating a heterogeneous structure of the material.

A hydrothermal–microwave method has been developed for the synthesis of bismuth metasilicate from water-soluble bismuth compounds and sodium silicate. The bismuth silicate obtained in the form of a nanodispersed powder exhibits high photocatalytic activity and radiation resistance. The characteristics of the synthesized bismuth silicate were determined using differential thermal analysis, X-ray phase analysis, UV–VIS, and IR spectroscopy. In the temperature range of 600–800°C, crystalline phases of bismuth silicates with compositions Bi₂SiO₅, Bi₄Si₂O₁₂, and Bi₂SiO₂₀ are formed. The photocatalytic activity of the samples was studied in the degradation reaction of methylene blue under UV irradiation. Physicochemical studies have shown that the synthesized bismuth silicate is a promising material for various applications as a wide-bandgap semiconductor, photocatalyst, and radiation shielding material. The conducted research demonstrates the efficiency of microwave synthesis of bismuth silicates: the synthesis and heat-treatment times are reduced (by 3–5 times), and energy consumption is lowered (by 70–80%) compared to conventional synthesis methods.

This work presents an experimental investigation into a novel microwave band-pass filter architecture based on interacting conducting ring resonators. Leveraging the inherent resonant behavior of copper rings, the design achieves multiple narrow passbands within the 1–12 GHz frequency range. By systematically varying both the inter-resonator spacing and the number of rings, the study identifies an optimal configuration—particularly at an inter-ring distance of 6.75 mm—that maximizes the quality factor and transmission amplitude. Experimental results reveal distinct resonances at 2.2, 4.2, 6.6, 8.6, and 11.2 ± 0.2 GHz, corresponding to the fundamental and higher-order harmonic modes. The demonstrated filtering mechanism, characterized by compact size, tunable frequency response, and low insertion loss, offers a scalable solution for modern wireless communication systems. These findings indicate significant potential for integration into next-generation 5G and emerging 6G networks, providing a cost-effective alternative to conventional filter designs.

The influence of a black silicon (b-Si) interlayer on the photovoltaic characteristics of tandem perovskite/silicon cells was investigated by numerical modeling in the SCAPS-1D software environment. It is shown that a 640 nm thick nanotextured b-Si interlayer increases the efficiency of the modeled device from 27.17 to 28.97%. The primary contribution to the efficiency gain is attributed to an increase in short-circuit current density, resulting from exceptionally low reflection and enhanced light trapping in the bottom silicon subcell. The qualitative agreement between the simulation results and the experiment, as well as the dominant contribution of optical effects to the observed performance improvement, is demonstrated. Using parametric analysis, the optimal thickness of the b-Si interlayer (∼530 nm) was determined, ensuring current matching between the subcells and a maximum efficiency of 29%.

This paper investigates the nonrelativistic approximation in the first-order 39-component theory for a spin-3/2 particle in curved spacetime under external electromagnetic fields. Starting from the generally covariant matrix equations, generalized via the Weyl-Fock-Ivanenko tetrad method, we employ explicit forms of the four main ({{{Gamma }}^a}) matrices of dimension (16 times 16) within the corresponding first-order system. The analysis is carried out for spacetime metrics that permit the existence of nonrelativistic equations. To separate the large and small components of the complete wave function, three projective operators are constructed from the fourth-order minimal polynomial of the (Gamma _{16 times 16}^0) matrix. The explicit forms of these components are obtained, and the set of independent variables is identified; in particular, only four large components are independent. Following the standard procedure, we derive the nonrelativistic system of equations for a 4-component wave function. The resulting Hamiltonian includes contributions from the electromagnetic field and additional geometric terms expressed through the Ricci rotation coefficients, Ricci scalar R and Ricci tensor ({R_{ab}}). We also isolate the term describing the interaction between the magnetic moment of the spin-3/2 particle and the external magnetic field. This interaction term is expressed via the spin matrices ({S_i}) and the components of the magnetic field vector B.

We describe the non-barotropic variational principle in both Lagrangian and Eulerian forms. Thus, we must consider a non-barotropic equation of state in which the internal energy is a function of both density and specific entropy. This implies an extension of our previous work on barotropic flows to the more general non barotropic flows case and may serve in the future for the study of the implications of variational analysis on the redefinition of conserved quantities of topological significance such as circulation and helicity.

The modal properties of a terahertz (THz) pulse propagating in a parallel-plate waveguide partially filled with a nonlinear crystal – either lithium niobate (LiNbO₃) or 4N, N dimethylamino 4N methylstilbazolium tosylate (DAST), are investigated. THz pulses are generated remotely in the nonlinear crystal via optical rectification of a femtosecond Ti:sapphire laser pulse. A numerical analysis of the mode composition of the THz pulse in the structure of a “metallic parallel-plate waveguide partially filled with a nonlinear crystal” was performed using MATCAD and COMSOL software. The study demonstrates the possibility of achieving single-mode coupling between the input linearly polarized optical pulse and the THz pulse with an ultra-broad spectral bandwidth of 0.1–2.6 THz. By numerically determining the width and height of the nonlinear crystal for given waveguide dimensions and known dielectric permittivity (ε) of the crystal, conditions for single-mode propagation of the THz pulse were achieved. It is also shown that as the THz frequency increases, a greater portion of the pulse energy is confined within the nonlinear crystal. At the same time, the remainder propagates in the surrounding air-filled region.

A method of optical transmission imaging of strongly scattering objects is proposed, based on point-by-point spatial scanning of a beam of pulsed-periodic laser radiation over the surface of the object under study and recording the number of transmitted light pulses at each scanning point using a patented photoreceiver that selectively registers short light pulses regardless of the level of background illumination. The conditions for obtaining “proportional” and “contour” images of model and biological objects are determined. The features of the method are a low level of required average radiation power, high image recording speed, and a wide operational spectral range, which makes it promising for use in biomedical diagnostics, materials quality control, security, and other areas.

An acoustoplasma discharge is experimentally investigated when low-intensity acoustic oscillations are far from the intensity region where shock waves exist. The frequency range of 20–50 kHz is considered, when non-axial modes, rather than a plane longitudinal wave, propagate in the discharge tube. The discharge trajectory in the tube is shown to take the form of a planar sinusoid. The calculated and experimentally measured spectra of acoustic oscillations arising during discharge current modulation and sound dispersion for non-axial modes are presented. The dispersion is found to be significant. The spectrum of non-axial modes has a band structure. In acoustoplasma, the transition from one frequency band to the next is characterized by a phase transition. Within each band, dispersion can be either normal or anomalous, depending on the frequency. When moving from one band to the next, dispersion becomes anomalous.

Computational methods of quantum chemistry were used to study the energy pathways of possible reactions of ammonia with hydrogen and oxygen atoms, as well as with the hydroxyl radical. The B3LYP, M062X, MP2 and CBS-QB3 methods were used to localize stationary points on the potential energy surface of the system containing the above reagents. A number of intermediate compounds formed during the interaction of ammonia with atoms and radicals were identified, and information on the structure and thermochemical parameters of the intermediates formed was obtained. Based on the calculation results, diagrams of the energy levels of the systems under consideration were constructed. The results obtained demonstrate the important role of the NH₃ + H, NH₃ + O and NH₃ + OH reactions in the processes of ammonia combustion.