Russian Physics Journal最新文献

In atmospheric optical communication channels, vortex beams transmitting information through the orbital angular momentum (OAM), are associated with the turbulent atmosphere. While propagating in a turbulent atmosphere, the transmitting laser beam undergoes a random phase distortion leading to errors in the OAM decoding and a decrease in the data transfer rate. In the last years, neural networks have been actively used for the OAM decoding in the turbulent atmosphere. The most common approach is to recognize the OAM specified in the initial plane from the turbulence-distorted instantaneous intensity distribution in the receiving plane. This approach allows mitigating the turbulence effect. Our recent work demonstrates a recognition of opposite-sign OAMs using this approach. It is previously assumed that the OAM sign cannot be retrieved from the instantaneous intensity distribution. This paper analyzes features of intensity distributions of vortex beams in a regular refractive medium that characterizes the OAM sign. It is suggested that the revealed features allow neural networks to determine opposite-sign OAMs through the instantaneous intensity distribution in the turbulent atmosphere.

The effect of energy transfer upconversion (ETU) on the properties of a passively Q‑switched (PQS) laser pulse is simulated using the optical system consisting of Nd⁺³:YAG and Cr⁺⁴:YAG as an active medium and saturable absorber, respectively. The rate equation model is proposed and calculated numerically by the Runge-Kutta-Fehelberg method. The results of the proposed model show good agreement for the time behavior of the population inversion density and the photon number density of the PQS laser pulse with the previous theoretical results of the same system. The benchmark enhances the reliability using the model. The simulation shows that upconversion operations lead to a decrease in the pulse energy and increase in the pulse duration. Calculation results show that the ETU effect results in a 3.735% increase in the pulse duration due to a decrease in the pulse energy by 1.226%, and its power reduction by 5.084%. In the case without the ETU effect, the pulse generates at an earlier time than in the case with the ETU effect.

This study investigates the effects of temperature, surface tension, and viscosity on air bubble production in an aqueous methanol solution. Experiments are conducted at three temperatures (293.15, 303.15 and 313.15 K) and varying flow rates. It is shown that lower temperatures and higher surface tension and viscosity lead to smaller bubbles, while increased temperatures promote larger and more frequent bubble formation. Flow rate variations significantly influence the bubble dynamics, with higher flow rates generating more bubbles. Research findings have implications for optimizing gas-liquid interactions in industrial processes.

Using the Quantum Theory of Atoms in Molecules (QTAIM), we explored the bonding characteristics of di-chalcogenide-bridged tri-iron carbonyl clusters [M′₂Fe₃(CO)₁₀]⁻². The properties of the bond critical points, identified in our investigation, align with the previously reported results for transition metal clusters of comparable structure. They include the electron density (ρ_b), the electron density Laplacian (∇²ρ_b), the local energy density H_b, the local kinetic energy density G_b(r), the local potential energy density V_b, the ellipticity ε_b, and the bond delocalization indices δ(A, B). A study of the tri-iron metal core centers reveals no direct paths of the bond or bond critical sites between these metals. Despite the fact that no direct bond paths are observed between the iron atoms bridged by di-chalcogenide ligands, there are indications of enhanced organometallic bonding between the iron atoms. The values of the nonbonding delocalization indices indicate a five center, seven electron (5c–7e) bonding interaction associated with a five-membered Fe₃(μ-M′)₂ ring. The bonding interactions with covalent and electrostatic character are identified in the Fe–M′ bonds (where M′ = S, Se, or Te). The pi-back donation from CO ligands to Fe is also found in strong levels for all compounds, as revealed through the Fe–CO bond delocalization indices δ(Fe···O).

Materials with controlled electromagnetic characteristics are studied in the present work. The complex permittivity spectra of ferrofluids with the following composition: synthetic oil + iron oxide + multiwalled carbon nanotubes (MWCNTs) have been measured using impedance spectroscopy. The multiwalled carbon nanotubes (0.5 and 0.75 wt.%) were added to the composition. The effect of different orientations of the magnetic field relative to the electric field component of an electromagnetic wave on the complex permittivity values is considered. New research results indicate that thin layers of ferrofluid show promise for enhancing safety when using high-frequency radio-electronic devices.

The paper deals with calcium nitride obtained by combustion synthesis of calcium metal pellets in nitrogen at a pressure of 3 to 7 MPa. The nitriding degree for calcium is about 99%. The obtained product composition is investigated by chemical and X-ray diffraction analyses. It is found that α‑ and β‑Ca₃N₂ phases are the primary in the product. Impurity phases include the Ca₂N phase, calcium nitrate and nitrite, and others.

The work explores the physical concept of structure-phase states of water and water solutions low-stable to external impacts. The concept provides a way to understand the physical principles behind various effects in water and water solutions. In particular, this approach allows the role of external impacts (temperature, mechanical shaking, etc.) in the Epstein effect to be explained. The thermodynamic and phase stability analysis of physical systems is used to propose an adequate mechanism of system transition to a new structure-phase state under a weak external impact. Moreover, in spite of the fact that the external impact is weak, it can lead to considerable structure-phase changes in the system state, since the structural units in the initial and final states, although close thermodynamically, can differ significantly in symmetry. The physical reasons for the poor reproducibility of the results of studying the characteristics of the structure of water and aqueous solutions at ultra-high dilution are discussed together with the value of the low external impact required for the transition to the new structure-phase state.

High thermal resistance of ZrB₂–SiC composite ceramics makes it a promising candidate for creating heat-protective structures operating at temperatures exceeding 2000 °C. A significant advantage of ZrB₂–SiC composite ceramics is self-healing of defects under cyclic temperature effects. The paper investigates self-healing of artificial defects on the surface of ZrB₂–SiC composite ceramics at 1200, 1400 and 1600 °C annealing. It is shown that the most efficient self-healing process occurs after 1600 °C annealing. It is found that defect self-healing increases due to the higher temperature and increased SiC content in composite ceramics.

The results of an experimental study of the temperature of the target of a sputter-deposition magnetron system and a computer simulation of its behavior are presented. The magnetron system has a planar geometry and functions under vacuum (without gas fill) at a residual pressure of down to 3 ∙ 10⁻⁵ Тоrr. The study is performed for different magnetron target thicknesses, shapes, operating parameters, and materials. It is shown that under all of the operating modes the target temperature in the racetrack zone (high-intensity sputtering) remains to be lower than 230 °C, which allows ruling out the effect of thermal evaporation and sublimation on the processes of magnetron discharge functioning under vacuum. Using computer simulation, possible methods and approaches to decrease the target temperature are determined.

A composite of Si₃N₄-Si₂N₂O‑TiN is synthesized by nitriding a mixture of ferrosilicon-ilmenite-ammonium fluoride under a combustion mode followed by the acid leaching of iron-containing phases. The influence of the principal parameters of self-propagating high-temperature synthesis on the combustion rate, the amount of absorbed nitrogen, and the phase composition of the combustion products is studied. It is found out that an addition of 1% NH₄F causes a more complete nitrification of ferrosilicon, compared to that of 0.5%, due to an intensification of the processes of iron silicide nitrification by ammonium released during decomposition of ammonium fluoride. In the course of oxidation of the composite in air at 800 °C, TiN is completely oxidized to TiO₂, and an oxidation of Si3N4 starts at a temperature higher than 1000 °C to form SiO₂.