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

Computer simulation was used to study the characteristics of heat propagation processes in a four-layer SiO₂ + LaB₆/Mo/ La_0.99Ce_0.01B₆/Mo sensor mounted on an Al₂O₃ substrate. The sensor has a dielectric absorber made of a composite material consisting of SiO₂ and 30 vol % LaB₆ nanoparticles, a Mo reflector/electrical contact, a La_0.99Ce_0.01B₆ thermoelectric layer, and a Mo heat sink/electrical contact. Heat propagation from the thermalization zone of single photons with an energy of 0.8 eV, localized in the absorber at a depth of 15–80 nm, is examined. Computer modeling was performed using a three-dimensional matrix method based on the equation for heat propagation from a confined volume. The temporal dependences of temperature at various distances from the center of the sensor layer surfaces and the average temperature of the layers surface are studied. The obtained results allow us to calculate the signal-to-noise ratio of the sensor, which determines the efficiency of detecting an absorbed photon. It is shown that this efficiency changes only slightly with changing the depth of the thermalization zone.

A novel scheme for Zernike-type hard X-ray phase-contrast imaging is proposed. The scheme relies on X-ray dynamical diffraction in a two-block crystal system with parallel crystal plates of equal thickness. A phase shifter providing a π/2 phase shift is placed in the inter-block gap of the crystal system. The method operates in a scanning geometry. The proposed imaging setup is compact and does not require conventional focusing optics. Numerical simulations of phase-contrast image formation are performed.

The paper analyzes the main characteristics of a new dynamic capacitor, which is a surface MOS-photovaricap, which is used as a modulating element when detecting signals from high-resistance sensors. Surface MOS-photovaricapes were made on high-resistance p-type silicon substrates with a thin insulating layer of SiO₂ and a semitransparent metal electrode. Capacitance modulation during transimpedance conversion was carried out by LED lighting photovaricape in the optocoupler, which led to the appearance of an alternating voltage on the load resistor, which was subsequently amplified and registered. The results show that MOS-photovaricapes can be effectively used when measuring small constant and slowly changing currents and voltages from high-resistance sensors. This approach allows you to use this electrometric amplifier to register values slowly changing concentrations of gas, various types of radiation and types of particles, etc.

A comparative study of the interaction of the bis-benzimidazole compound H33258 with bovine (BSA) and human (HSA) serum albumins was carried out using fluorescence, absorption, and differential spectroscopy. Fluorescence spectra of H33258 complexes with these proteins were obtained. It was found that at low protein concentrations, the fluorescence intensity of the complexes decreases (up to an albumin/H33258 ratio of ≈1) without any hypsochromic or bathochromic shift in the spectra. At higher protein concentrations, an increase in fluorescence intensity is observed, accompanied by a hypsochromic shift. In the case of HSA, the fluorescence intensity is significantly higher than that of the ligand, whereas for BSA, despite the increase, it becomes nearly comparable to that of the ligand. Differential spectra of the H33258-BSA and H33258-HSA complexes were also obtained, revealing differences between the spectra of these complexes.

The current study examines nonlinear beam dynamics of q-Gaussian laser beams propagating through absorptive thermal quantum plasma considering relativistic-ponderomotive nonlinear effects. There is energy dissipation along propagation distance due to linear absorption, thereby causing distance dependent nonlinear response. By making use of quasi-optical approach along with WKB and paraxial approximations, a modified 2nd order propagation equation governing the evolution of beam width is obtained. Numerical simulations are then conducted for exploring influence of key parameters, including absorption coefficient, laser intensity, plasma density, initial beam radius, q-parameter, and Fermi temperature on beam propagation. The outcome clearly shows that relativistic-ponderomotive nonlinear effects greatly enhance nonlinear focusing, whereas absorption counteracts this effect by reducing beam compression and shifting the focal position. A comparative study with both cold quantum and classical relativistic plasma models highlights the essential contribution of quantum effects to laser propagation through dense plasmas.

The influence of monovalent electrolyte ions (saline solution) on the dipole zwitterionic fragments of phospholipids in the bilayer was studied using x-ray diffraction simultaneously at large and small angles and an optical polarizing microscope. It has been established for solutions of alkali metal chlorides that the intensity of interaction with the lipid bilayer in the series Na⁺, K⁺, Cs⁺, and Li⁺ increases successively. Theoretical and experimental approaches have confirmed the existence of water molecule orientation, which leads to structural changes in the bilayer. The data obtained can be used to create low-inertia displays and sensitive sensors.

Modern unmanned aerial vehicles (UAVs) critically depend on the stability of radio channels used for control and data transmission. Within the framework of this work, a simulation model of the transmitter–receiver chain of the UAV control radio link was developed in the LabVIEW environment, considering the influence of SC-DSB (Double Sideband Suppressed Carrier) type signals. During the study, SC-DSB signal generation was implemented with adjustable parameters of amplitude, carrier frequency, and modulation bandwidth. The receiver chain was modeled, including an input filter, an amplification stage, a detector, and a signal parameter estimation block. To analyze receiver sensitivity, the minimum input signal level was determined at a specified threshold of demodulation error probability. Selectivity was evaluated by introducing a closely spaced interfering signal in frequency and measuring out-of-band signal suppression. As a result of the simulation, dependencies of the signal-to-noise ratio (SNR), error probability, and interference suppression coefficient on the parameters of the SC-DSB signal were obtained. It is shown that carrier suppression alters the energy distribution in the spectrum and leads to increased requirements for filter bandwidth and the dynamic range of the receiver input stages. The obtained results make it possible to quantitatively assess the impact of SC-DSB signals on the sensitivity and selectivity of a UAV receiver.

A hydrothermal–microwave method was developed for the synthesis of potassium–sodium niobate K_0.5Na_0.5NbO₃ (KNN) followed by high-temperature microwave treatment to obtain KNN ceramics. The synthesis was carried out in a microwave reactor at 210°C for 60 min. A KNN powder was obtained, consisting predominantly of agglomerates formed by nanocrystalline particles (crystallites) with sizes of 20–25 nm. X-ray diffraction analysis confirmed the formation of a single-phase orthorhombic perovskite structure of potassium–sodium niobate at relatively low temperatures (200–220°C). After heat treatment in the temperature range of 660–1100°C, the crystallite size increased up to 90 nm, accompanied by grain growth to the micrometer scale, indicating sintering with the formation of KNN ceramics. Measurements revealed a strong temperature dependence of the dielectric properties of KNN samples. Based on the obtained dielectric parameters, the piezoelectric coefficients were estimated, and according to this theoretical evaluation, the material is capable of exhibiting a significant piezoelectric effect. The maximum piezoelectric coefficient d₃₃ of approximately 160–180 pC/N was observed for samples sintered at 660°C. It was established that precise control of the heat-treatment temperature is crucial for optimizing the structure–property relationship in lead-free KNN-based piezoceramics.

The possibility of creating a single-photon detector sensor with a molybdenum absorber and heat sink, lanthanum-cerium hexoboride as the thermoelectric layer, and a sapphire dielectric substrate is considered. Using computer modeling, the absorption of single photons with energies of 0.8, 1.65, and 3.1 eV in a sensor with a surface area of 1 and 0.25 μm² at an operating temperature of 0.5 and 0.8 K is studied. The results of both heat propagation in a three-layer sensor and determination of the signal power, equivalent noise power, and signal-to-noise ratio are presented. The temporal dependences of the temperature in different areas of the sensor and the average surface temperature of the layers are studied. The maximum temperature, the time to reach the maximum, the time of temperature decay to the background level, and the characteristics of the temperature gradient at the boundaries of the thermoelectric layer are determined. Systematization of the obtained data made it possible to determine the optimal sensor design for efficient registration of single photons from the near infrared to ultraviolet spectral region.

Within the framework of the Heitler–London model applied to the hydrogen molecule in its ground state, the contributions to the binding energy from three types of interactions are compared: electron–electron interaction including exchange, internuclear interaction, and the interaction of each electron with the neighboring nucleus. It is shown that, in the first order of perturbation theory, the exchange interaction gives a positive contribution, which corresponds to mutual repulsion rather than the expected attraction. This is because the ground-state wave function of the atom does not change sign. Thus, the attraction between atoms in the first order is due only to the interaction of each electron with the neighboring nucleus. In addition, a coordinate transformation is found that makes it possible to obtain analytical expressions for the normalization coefficient of the two-electron wave function, which allows saving computational time.