Technical Physics Letters最新文献

The efficiency of four modifications of flow conditioners in terms of smoothing velocity profiles and ensuring their reproducibility with varying flow history and turbulence intensity at low Reynolds numbers was experimentally studied. The relevance of the work is due to the problem of increasing the accuracy of gas flow measurement in complex gas-dynamic conditions, especially in the region of laminar–turbulent transition. An approach has been identified that allows for the leveling of velocity profile deformations in a wide range of flow histories with a flow turbulence level not exceeding 14% and down to a lower Reynolds number value of 943.

Spanwise heterogeneous surface roughness can induce secondary flows of Prandtl’s second kind, which significantly affect momentum and heat transfer. Despite a large number of numerical studies of such flows, experimental data remain rather limited. In this paper, an experimental study of turbulent flow in a rectangular channel with walls formed by alternating smooth sections and strips of discrete roughness is performed. The fields of mean velocities and turbulence characteristics are obtained using the SIV method, and the structure of secondary flows is reconstructed. Measurements of hydraulic resistance are carried out for various surface configurations and Reynolds numbers. It is shown that heterogeneous roughness leads to the formation of large-scale secondary flows in the form of counter-rotating vortices with a transverse velocity of up to 5% of the main flow velocity. A correlation between the intensity of secondary flows and the hydraulic resistance coefficient is revealed, indicating a significant role of secondary circulation in momentum transfer mechanisms in the channel.

In this study, we used the Monte Carlo method to simulate the interaction of alpha particles with Ga₂O₃ and assess radiation damage. The findings show that alpha particles are primarily stopped by electrons, with ionization dominating energy dissipation, while phonon and vacancy‑related losses contribute negligibly. Over the investigated energy range, ionization loss increased with radiation energy, while both phonon and vacancy losses decreased. At a radiation energy of 2.05 MeV, ionization accounts for 99.41% of the total energy loss, while phonon excitation and vacancy formation contribute only 0.03 and 0.52%, respectively. As the radiation energy increased from 2.05 to 5.48 MeV, the peak energy absorbed by Ga and O atoms decreased from 0.81 and 0.84 eV to 0.62 eV, respectively. Alpha particles in Ga₂O₃ have a spatial distribution similar to a tadpole. The calculated maximum values were 0.0347 for displacement per atom (DPA), 1.63 × 10²¹ cm^–3 for V_Ga concentration, and 1.65 × 10²¹ cm^–3 for V_O concentration. These results demonstrate that alpha particle irradiation causes substantial damage in Ga₂O₃, posing a critical threat to both material integrity and device functionality.

The heat transfer coefficient in a plane channel was estimated theoretically. In the framework of assumptions made in the present research, a correlation in the form of Lyon’s integral was obtained for energy equation. It was employed for analytical estimation of heat transfer coefficient in laminar flows and liquid metal flows, in which molecular heat transfers prevail over turbulent one. The computational results comply with the literature.

In this paper, we investigate the occurrence of Majorana zero modes in carbon nanotubes in contact with a conventional superconductor and placed in a longitudinal magnetic field. The influence of nanotube geometry, determined by chirality indices ((n,m)), on the conditions for the formation of the topological superconducting phase is considered. It is shown that chirality changes the electronic structure of the nanotube, the spin–orbit interaction and the effective chemical potential, which determine the conditions of the topological phase transition. To describe the system, an effective model based on the Bogolyubov–de Gennes Hamiltonian is constructed, which allows one to obtain a criterion for the occurrence of Majorana null modes. Based on the developed model, a method for selecting the most favorable geometries of carbon nanotubes is proposed. Numerical results show that certain chiralities minimize the effective chemical potential and facilitate the transition of the system to the topological phase. The obtained results show that the geometry of the carbon nanotube is an effective parameter for controlling the topological properties of the system and can serve as a criterion for choosing the chiralities that are most promising for the experimental implementation of Majorana zero modes.

An actuator rod (control device) is examined for the stability coefficient under a given load. It was found that commonly known calculation methods do not allow for the geometric features of the rod to be fully taken into account. To take into account the geometric features of the rod, a numerical experiment was carried out in the Compass APM FEM software environment. The numerical experiments conducted allow us to draw the following conclusions. When the ratio of the diameters of the inner hole to the diameter of the rod is 85%, as well as 71%, and when the ratio of the lengths of the inner hole to the length of the rod is from 100 to 31%, the presence of the inner hole greatly affects the safety factor, which varies in the range from 0.54 to 1.6. When the diameter ratio decreases, the length of the inner hole has virtually no effect on the safety factor, but in the range of length ratios from 100 to 50%, the safety factor is less than the recommended 1.8.

The paper presents a methodology for experimental research and a test bench for determining the flow coefficient during the flow of a two-phase working fluid through cracks. The dependences of the influence of the degree of dryness of the wet refrigerant vapor and the gap resistance on the flow coefficient during the outflow of the working fluid through the gap were established. A method for determining the coefficient of flow of wet vapor through cracks is proposed, implemented on the basis of the method of S.E. Zakharenko for dry saturated vapor and a correction function for the degree of dryness of the vapor. Artificial refrigerants used in air conditioning systems, such as R32 and R410a, which belong to the HFC class, and R22, which belongs to the HCFC class, are considered as the working fluid.

The paper considers the important issue of change in the pressure drop when the seal wears out. An engineering calculation method was developed that allows one to determine how the pressure drop across seals will change during their stepwise wear, depending on the cylinder diameter and pressure ratio. The equivalent clearance of a worn seal was determined experimentally to be 6, 9, and 14 µm for cylinder diameters of 20, 50, and 80 mm, respectively. Based on the results of the numerical experiment, the dependences of the pressure drop on the seals were obtained depending on the number of worn seals and the pressure ratio in the cylinder.

Previously developed combined methods of stray light compensation for time cameras of time-of-flight systems have demonstrated high efficiency in laboratory conditions, but their operation in real livestock buildings faces additional destabilizing factors: rapid changes in illumination (movement of the Sun, switching on/off LED lamps), dustiness of protective optics, and dynamic shadows from animals and personnel, as well as the movement of objects (animals). This paper presents the results of long-term field trials on a dairy farm (120 heads). A unique dataset (ToF + RGB + reference laser scanner) was collected in 12 different lighting scenarios. Based on this data, a physics-informed neural network (PINN) is a deep-learning neural network that takes raw intensity and phase data (224 × 171 pixels) as input and directly reconstructs depth without iteratively solving the inverse problem. The network uses regularization based on the diffusion approximation and the wet film model. After optimization on a Raspberry Pi 5 single-board computer, the processing time of one frame was 8.2 ms (120 fps), which is ten times faster than the previous algorithmic solution. Moreover, the root-mean-square depth error on moving animals is reduced by 72% compared to pure spectral filtering (from 28.4 to 7.9 mm) and by 41% compared to the best method (9.1 mm → 7.9 mm). The neural network approach also automatically compensates for dust on the camera’s protective glass and slow temperature drifts. The developed system has been put into trial operation as part of a robotized milking installation.

The important topic of autonomous operation of a compressor machine is considered. It has been shown that at present, there is not a single branch of the national economy in which compressor machines are not used to one degree or another. It has been shown that cylinder–piston seals are the node that fails most frequently. The goal is to achieve a service life of 60 000 h, which is achieved by installing additional seals on the piston. It shows how many seals need to be installed on a piston to achieve a service life of 60 000 h, depending on the material used, the cylinder diameter, and the pressure ratio in the cylinder.