Russian Physics Journal最新文献

The plasma emission generated by a low-pressure, pulsed-periodic discharge in different gases containing a small amount of water vapor is studied. Broadband radiation is detected in argon, nitrogen, and air, as well as in their mixtures with water vapor. It is shown that this radiation has a maximum intensity at low water vapor concentrations, increases with the increasing specific energy input, and is attributed to the H₂(a³Σ_g⁺) → H₂(b³Σ_u⁺) transition of the hydrogen molecule. The emission spectra of water and hydrogen vapor, as well as mixtures of argon, nitrogen, and air with water vapor are presented.

Dry sliding of C235 steel against quench-hardened C45 steel is performed at a high-density alternating electric current. The contact layer is subjected to plastic deformation. The formation of a tribolayer consisting mainly of FeO and α‑Fe phases is demonstrated. The contact surface is found to contain two sectors with different morphological features. One of the sectors shows the signs of melt formation. Using an EDX analysis, higher oxygen content is demonstrated in the melt zone, compared with that in the other sector. Oxygen serves as an indicator of FeO formation. A decrease in the oxygen concentration is found with the increasing distance from the sliding surface. It is noted that this is not indicative of a gradient structure. These data are used to calculate the melt layer thickness, which decreases with the decreasing electrical power at the contact spot. The maximum power at the contact spots causes the formation of a melt layer thinner than 7 μm under mild wear conditions. The calculation serves as the evidence for melt formation due to Joule heat, but not due to electric arc formation. A tribolayer scheme consisting of three sublayers is proposed.

This study investigates how changes in vibrational frequencies upon electronic transition (the squeezing effect) affect internal conversion rate constant (k_IC) calculations in an indocyanine molecule. Results obtained demonstrate that the squeezing effect alters k_IC by only 0.38%, making it negligible. This occurs because the modes with significant frequency shifts (12–55%) are low-frequency (< 100 cm^–1) and contribute minimally to k_IC, while the modes that dominate k_IC exhibit negligible frequency shifts (1–2%). Notably, the Lagrange multiplier technique incorrectly estimates k_IC for molecules with low-frequency modes that have large Huang–Rhys factors, since such modes undergo substantial frequency shifts.

The effect of multi-cycle combined processing (ЕCAP combined with ultrasonic exposure) on the structure, mechanical, and corrosion properties of the bioresorbable Mg‑8.6Zn‑1.2Zr alloy is examined. It is shown that this deformation processing scheme allows achieving a tensile strength of 305 MPa. There is a tendency for the corrosion rate to decrease with an increase in the number of deformation cycles, and a value of 3.0±0.2 mm/y is achieved. This is attributed to an increase in the proportion of recrystallized grains in the Mg‑8.6Zn‑1.2Zr alloy structure.

A possibility of designing an adaptive plasma antenna for satellite communications is discussed. The feasibility of dynamically tuning the plasma antenna parameters is evaluated. The laser radiation intensity required to create a long plasma channel in an aerosol with an electron density of 10¹⁰–10¹⁷ cm^–3 is estimated. It is shown that the high-frequency electric current through the ionized channel or dielectric rod is localized in the peripheral region. Therefore, it is proposed to use the plasma formation rather than the dielectric in the rod antenna to excite the HE₁₁ surface wave. The simulations in CST Studio Suite 2022 show that as the plasma channel length increases from 0.1 to 8 m, the antenna beamwidth narrows from 70 to 20°, remaining unchanged with a further increase in the plasma channel length.

The paper presents a hybrid physico-mathematical model for the quantitative analysis and prediction of optical losses in standard fiber-optic cables subjected to mechanical loading. The stress-strain state is calculated by the finite element modeling in ANSYS Mechanical, which is combined with numerical solutions of the Helmholtz equation in COMSOL Multiphysics to describe the light propagation. It is shown that tension and microbending cause the stress redistribution in the fiber core and a change in the refractive index according to ∆n = −0.5n³pε, leading to an increase in the attenuation coefficient following the exponential law α = α₀exp(kσ). Numerical results are in good agreement with the experimental data (R = 0.95, deviation < 7%). The developed model is aimed at practical production and diagnostic tasks in fiber-optic network operation implemented in AO ‘Kazakhtelecom’ and the QarTech Innovation and Industrial Hub. The results make it possible to predict the optical degradation without the structural modification of the cable and provide a basis for design of quasi-distributed fiber-optic sensors applicable to telecommunication and energy systems.

The paper focuses on the dependence σ = f(ρ^½) between the flow stress and the square root of average scalar dislocation density for the Cu-Al system alloys in a low-stability state with regard to the types of the dislocation structure. This linear dependence σ = f(ρ^½) is obtained in a wide range of strain (at each stage), temperature, and grain size at different content of the second element. It is found that at a given strain stage, a transition from the main dislocation structure to another indicates to a transition to the next stage. In this case, this dependence demonstrates changes in the slope of the curve. It is shown that these changes can be caused by two reasons: the formation of the new type of the dislocation structure and changes in the deformation mechanism associated with the number of microtwin systems and a transition from one slip system to several of them.

Experiments show that in a wide range of strain, content of the solid solution, temperature, and grain size, the relation σ = σ_f + mαGbρ^½ is satisfied. The deviation from the linear dependence σ = f(ρ^½) and changes in the dimensionless factor mα are attributed to the formation of new dislocation structures and another deformation mechanisms. In alloys consisting of the higher content of the alloying element, the substructural hardening is supplemented by the twinning mechanism.

Using the method of numerical simulation, the formation of localized adiabatic shear bands in the sheets made of AZ31 magnesium alloy is studied by dynamic punching at the following velocities: 10, 25, 50 and 100 m/s. The computations involve the alloy material fracture, using the critical level of specific energy of shear deformations as a fracture criterion.

The present study investigates the prediction of wear behavior of AA7075/SiC composites using supervised machine learning (ML) algorithms, emphasizing the role of hyperparameter tuning in enhancing model accuracy. Experimental wear data were generated through pin-on-disc tests under varying SiC reinforcement contents (0–9 wt.%), applied loads, sliding velocities, and sliding distances. Two ensemble-based ML algorithms—Random Forest (RF) and Extreme Gradient Boosting (XGBoost)—have been developed to model the nonlinear relationship between input process parameters and wear rate. Hyperparameter optimization using Grid Search significantly improved predictive performance, yielding R² ≈ 0.89 and RMSE ≈ 0.0009 for both models. Statistical and residual analyses confirmed that the tuned models provided unbiased and normally distributed errors, ensuring strong generalization capability. The results indicated that SiC reinforcement was the most influential parameter in reducing wear rate, followed by load and sliding distance. The study demonstrates that integrating experimental tribological data with optimized ML algorithms offers a robust and efficient framework for data-driven prediction and process optimization in aluminum matrix composites.

Austenitic stainless steels, particularly SS304, are highly regarded for their outstanding mechanical performance and resilience under load, making them a popular choice in a wide range of industrial applications. SS304 stainless steel is frequently used in environments where both mechanical strength and corrosion resistance are critical, e.g., in chemical processing, food and beverage industries, and marine environments. This study investigates the effect of multiple weld repairs and post-weld heat treatment (PWHT) on the microstructure and mechanical properties of SS304 weld joints. Repeated welding causes a significant carbide segregation and the formation of non-metallic inclusions, leading to embrittlement, reduced ductility and mechanical properties. Grain boundary sensitization results from multiple weld repairs; due to non-uniform thermal cycles carbide segregation ultimately causes sensitization. Moreover, very disturbed grain microstructure is ameliorated to the coarse-grained austenite matrix, which promotes ductility. Specifically, ultimate tensile strength (UTS) and yield strength (YS) decline by 37.8% and 24%, respectively, after the first weld repair, with further reductions observed after the second repair. Heat treatment, particularly a stress relieving process, effectively mitigates these adverse effects by promoting the uniform diffusion of carbides and other precipitates in the austenite matrix, reducing embrittlement, relieving residual stresses and coarsening grain boundaries. PWHT further mitigates the UTS by 4.7% and 6.3% for the first and second weld repairs, respectively, while the YS decreases by 8.5% and 9.1%. Percent elongation, a key indicator of ductility, increases by 46% for initial weld samples and approximately by 71% and 68% for repaired samples following PWHT.