Russian Physics Journal最新文献

In the last ten years, perovskite solar cells (PSCs) have significantly improved their power conversion efficiency. The improvement is a good sign for this solar technology. The paper investigates the current state of PSCs, focusing on their development, material properties, and device performance. The impact of the absorber layer thickness and temperature on the PSC performance is considered through the simulation, achieving 1.271 V open circuit voltage, 34.57 mA/cm² short-circuit current density, 89.14% fill factor, and 39.20% conversion efficiency. Finally, this study ends by talking about what future research should focus on and how PSCs can change the photovoltaic industry for the better.

This paper presents the results of calculations and experimental investigations of steady-state current-voltage characteristics and electric field distribution made for single-element (pad) and multi-element X‑ray sensors based on high-resistive chromium-compensated gallium arsenide (HR-GaAs:Cr). Experimental IV-curves of pad sensors have been used to verify and optimize the calculation model. The model was optimized by varying the concentration of thermal acceptors and potential barrier height. The main criterion of optimization was the best agreement between the calculated and measured IV characteristics of the pad sensors. Furthermore, we applied the optimized model to calculate the IV-curves and electric field strength profiles within pixel sensors. Reults of our calculations reveal that in the voltage range from 0.05 to 1 V, the dark current is governed by both the electron and hole components; however, at voltages above 10 V, the contribution of holes to the dark current prevails. It is demonstrated that the distribution of the electric field strength within the sensor volume remains unchanged when the temperature varies from +25 to +50 °C.

This article presents the design and development of a low-temperature Stirling engine with external heat supply intended for use in autonomous cogeneration power systems. The engine utilizes thermal energy from a solar collector, which heats the working fluid to temperatures ranging from 90 to 100 °C. A key innovation of the proposed system lies in the significantly increased swept volume of the displacer, which exceeds the volume of the power piston by a factor of 20 to 40. This configuration enables stable engine operation under relatively low temperature differentials between the heater and the cooler. Experimental investigations, supported by results of numerical modeling, confirmed the feasibility and efficiency of the proposed design. Under operating conditions with a temperature differential of approximately 65–75 °C and a working fluid pressure of up to 0.3 MPa, the engine demonstrated a mechanical output ranging from 5 to 15 W, with a corresponding thermal efficiency of 2 to 4%. Notable performance improvements were observed when air was replaced by helium as the working medium and a regenerator was incorporated into the system. The cogeneration capability of the system is realized through the recovery and utilization of residual heat from the cooling circuit for space heating and domestic hot water supply. The engine is designed for fully autonomous operation in remote or off-grid areas, including rural settlements, greenhouse complexes, and other energy-demanding infrastructures. When integrated with a solar collector and thermal energy storage unit, the system offers the potential for continuous, around-the-clock electricity and heat generation.

It is determined that an important peculiarity of a homogenous deformation in the BCC→HCP→BCC transformations of a V-Cr-W-ZrC alloy is the operation of this deformation mode at different structural levels. The formation of multilevel (micro + meso + nano) structural states under these conditions is observed with high density of nanovolumes measuring a few nanometers, high local internal stresses and stored deformation energy. A possibility is demonstrated of a multiple increase of the impact strength of this alloy by a transformation of these nanovolumes into the crystals with discrete low-angle boundaries.

The effect of holding time of the Ti4Al3V alloy, fabricated by wire electron-beam additive manufacturing (WEBAM), at 900 °C on its microstructure and mechanical properties has been investigated. An α/β microstructure is formed after quenching and aging at 575 °C. Increasing the holding time from 6 to 10 h leads to an increase in the microhardness (by 6.5%) and yield strength, reaching up to 585 MPa in the horizontal direction and 681 MPa in the vertical direction along with improved ductility. The thickness of the α‑laths remains unchanged, indicating that the temperature of 900 °C has limited influence on their coarsening.

The laser weld quality significantly correlates with characteristics of the molten pool forming during the process. This paper aims at understanding and predicting the molten pool characteristics in the EN24 steel, a high-strength alloy widely used in demanding applications. The applied dual approach includes (1) the numerical simulation in COMSOL Multiphysics for the heat transfer and the molten pool behavior and (2) a series of welding experiments with the EN24 steel. A Taguchi L9 orthogonal array design is used in the experiments, systematically varying two key factors, namely the laser power (1500, 1650, 1800 W) and scanning speed (10, 14, 18 mm/s), each at three distinct levels. The numerical simulation focused on the heat transfer in solids, offers information about how these parameters affect the molten pool width, depth, and overall shape. Experimental validation based on the metallographic analysis of weld cross-sections, verifies modeling patterns. This integrated approach not only validates the predictive power, but also provides a better understanding of the complex relationship between welding parameters and the molten pool morphology in the EN24 steel, giving a way for more efficient process optimization and the higher weld quality.

Mechanical impacts on the DNA molecule induce a partial strain energy transfer to the breakage work of hydrogen bonds and stacking interaction between nitrogenous bases. The torsion effect on the DNA molecule provides a nonuniform hydrogen bond breakage in its certain regions. This paper presents mathematical simulation of the potential energy distribution of hydrogen bonds at the external torsion effect on the ATXN2 gene. It is shown that at the normal expansion of the CAG tract, the number of additional breaks does not exceed the critical threshold, which is essential for maintaining the stability of the genetic material. The proposed DNA mathematical model determines the energy parameters of hydrogen bonds, predicts structural changes in the molecule, and identifies potential locations of unstable regions.

The effect of the duration of high-energy mechanical activation (HEMA) of the 3Nb‑0.88Al powder mixture precursors and a subsequent annealing at 300 and 500 °C on their microhardness is studied. It is found out that the precursor microhardness after one-minute HEMA decreases under the thermal impact. The HEMA intervals are identified, which are characterized by increased microhardness of precursors after their annealing at 300 °C. The values of microhardness are observed to be much larger after the thermal treatment at 500 °C, except for those mechanically activated for 1 and 1.5 min. It is hypothesized that it is the higher mixing efficiency improving with the HEMA duration, which favors an increase in the volume fraction of ordered compounds in the course of subsequent anneals.

The structural-phase state and microhardness of 12% chromium reduced-activation ferritic-martensitic steel have been investigated after thermomechanical treatments involving deformation in the austenitic region at various temperatures, followed by aging at 700 °C for 100 h. For the three studied deformation temperatures (1100, 1000, and 900 °C), the steel microstructure after aging is qualitatively similar: martensitic laths are located within the former austenite grains, with M₂₃C₆ carbide particles along their boundaries and MX carbonitrides inside the structural elements. The former austenite grains do not change in size during aging, while the average width of the martensitic laths increases by a factor of 2.5. The size and volume fraction of the MX particles remain unchanged after aging. However, aging leads to the intense precipitation and growth of M₂₃C₆ carbide particles. The steel microstructure after plastic deformation at 1000 °C is the most stable under aging conditions at 700 °C for 100 h. In this structural state, the smallest average sizes of carbide phase particles and a higher dislocation density are observed compared to deformation at other temperatures. These microstructural changes result in a 2–2.5-fold decrease in the steel microhardness values after aging compared to the state after deformation and quenching.

In this work, the formation of structure, porosity, and mechanical properties of tin bronze BrOC4‑3 produced by wire arc additive manufacturing (WAAM) has been investigated for the first time under different heat inputs (210, 299, and 524 kJ/m). It is shown that heat input systematically affects the residence time of the bronze in the liquid phase, which in turn determines the nature of pore formation due to evaporation of low-melting alloying elements. At low heat input (210 kJ/m), pores are uniformly distributed throughout the layer volume, with a volumetric fraction reaching 18.5 ± 1.5%. In contrast, at high heat input (524 kJ/m), the prolonged lifetime of the molten pool promotes buoyant rise and escape of gas bubbles, reducing the overall porosity to 4.0 ± 1.5% and localizing remaining pores in the upper part of the layer. A correlation between the yield strength and the size of elongated FCC-Cu grains has been established: the maximum yield strength is achieved at a heat input of 299 kJ/m, which corresponds to the minimum length-to-diameter (l/d) ratio of the elongated grains. The obtained results demonstrate the possibility of targeted control over the microstructure and properties of additively manufactured tin bronze through adjustment of processing parameters.