Technical Physics Letters最新文献

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.

A unique design for a reciprocating compressor with a flexible piston is proposed and examined, in which the end surface is made of an elastomeric element and capable of deflecting inward. This design, along with eliminating the linear dead volume, further increases the efficiency by means of the volume created by the deformed elastomeric element. The model for calculating the piston compressor’s working process is refined taking into account an increase in the working chamber volume. With the assumed maximum deflection of the elastomeric element (20% of the piston diameter), the efficiency increases by up to 16% at almost unchanged compressor working temperatures.

A technique for the electrodynamic calculation of the effective permeability tensor of 3D magnetic nanocomposites in a model of a nanostructured gyromagnetic medium as a quasi-continuum one has been developed on the basis of solving a quasi-compatible system of equations. Based on the solution of Maxwell’s equations together with the Landau‒Lifshitz equation of motion of the magnetization vector in a ferromagnet, the electrodynamic calculation of components of the effective permeability tensor of a 3D magnetic nanocomposite based on an opal matrix depending on the relative value of the magnetization field has been carried out taking into account the exchange interaction and in the non-exchange approximation.

In this paper, we propose a cathode groove etching structure in which the surface concentration of the p₂ region can be increased to the surface concentration of the cathode region in order to enhance the cathode shorts effect of SCR with Ni electrode, and analyze the relationship between the dV/dt capability and cathode groove etching structure parameters of the device. Unlike the Al electrode structure, the limitation of surface concentration of the cathode region in the Ni-electrode SCR is that the surface concentration of the shunt contact cannot be as high as that of the cathode region, and the failure of the shunt contact surface to be an ideal ohmic contact is achieved by cathode groove etching. In a thyristor with Ni electrode, cathode groove etching is used to increase the surface concentration of the p₂ region from 10¹⁸ to 10²⁰ cm^–3.

The paper investigates the process of introducing visible and near-infrared optical radiation into a multimode optical fiber through a macrobending region. It has been established that the input coefficient depends significantly on the radiation wavelength, the macrobending radius, and the number of fiber turns. It is shown that decreasing the macrobending radius and increasing the number of turns leads to an increase in the efficiency of radiation input, with the greatest losses observed in the shortwave region of the spectrum. The obtained results allow us to gain a deeper understanding of the mechanism of radiation input through macrobending and can be used in the development of fiber-optic light sensors and other optical devices.