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High-order harmonic generation (HHG) in solids opens new frontiers in ultrafast spectroscopy of carrier and field dynamics in condensed matter, picometer resolution structural lattice characterization and designing compact platforms for attosecond pulse sources. Nanoscale structuring of solid surfaces provides a powerful tool for controlling the spatial characteristics and efficiency of the harmonic emission. Here we study HHG in a prototypical phase-change material Ge2Sb2Te5 (GST). In this material the crystal phase can be reversibly changed between a crystalline and amorphous phase by light or electric current mediated methods. We show that optical phase-switching is fully reversible and allows for dynamic control of harmonic emission. This introduces GST as new addition to materials that enable flexible metasurfaces and photonic structures that can be integrated in devices and allow for ultrafast optical control.

A high mobility of charge carriers and a low sheet resistance in graphene are the key indicators of its quality and applicability in electronic devices. In turn, the mobility of charge carriers in graphene is determined by graphene film smoothness. The electron scattering on structure defects of graphene film (wrinkles and grain boundaries) strongly affects the charge carrier mobility. In this work a simple and ultrafast approach for synthesis of graphene monolayer with the controllable smoothness and wrinkle density onto a resistively heated copper foil is presented. The method is a cold-wall chemical vapor deposition from methane. The fast synthesis of graphene with a full process cycle of 3 min is demonstrated. The structural defect density of polycrystalline graphene is optimized by appropriate combinations of methane concentration in the chamber and duration of synthesis process. Under the lower concentration of methane with the longer synthesis time the lower defect density in graphene appeared. The increase of process time from 30 s up to 10 min (under the decrease of methane concentration from 4.5 % to 0.36 %, respectively) leads to increase of average distance between wrinkles in graphene film from 6 µm to 35 µm. А charge carrier mobility as high as 2170 cm2V−1s−1 and a sheet resistance as low as 318 Ohm/□ under the lowest wrinkle density are measured for graphene polycrystalline monolayer deposited onto SiO2 substrate.

Calculations of heat transport in crystalline materials have recently become mainstream, thanks to machine-learned interatomic potentials that allow for significant computational cost reductions while maintaining the accuracy of first-principles calculations. Moment tensor potentials (MTPs) are among the most efficient and accurate models in this regard. In this study, we demonstrate the application of MTP to the calculation of the lattice thermal conductivity of α and β - Ga 2 O 3. Although MTP is commonly employed for lattice thermal conductivity calculations, the advantages of applying the active learning methodology for potential generation are often overlooked. Here, we emphasize its importance and illustrate how it enables the generation of a robust and accurate interatomic potential while maintaining a moderate-sized training dataset. [ABSTRACT FROM AUTHOR]

Calculations of heat transport in crystalline materials have recently become mainstream, thanks to machine-learned interatomic potentials that allow for significant computational cost reductions while maintaining the accuracy of first-principles calculations. Moment tensor potentials (MTPs) are among the most efficient and accurate models in this regard. In this study, we demonstrate the application of MTP to the calculation of the lattice thermal conductivity of α and β - Ga 2 O 3. Although MTP is commonly employed for lattice thermal conductivity calculations, the advantages of applying the active learning methodology for potential generation are often overlooked. Here, we emphasize its importance and illustrate how it enables the generation of a robust and accurate interatomic potential while maintaining a moderate-sized training dataset. [ABSTRACT FROM AUTHOR]

In the paper, polycrystalline copper deformed by tension under different conditions of loading has been studied using electron backscatter diffraction. The microstructure of areas located on the longitudinal section of the specimens deformed until fracture was examined. The fragmentation of initial grains in case of deformation at room temperature was observed whereas at 400°С, considerable dynamic recovery and recrystallization significantly influenced the microstructure formation. A procedure for computer analysis of the orientation maps has been put forward, which allows separating recrystallized regions from the non-recrystallized ones and further analyzing the misorientation statistics of strain-induced boundaries. A scaling behavior of the strain-induced misorientation distributions was shown to take place. The mechanism of strain-induced boundary evolution was proved to remain unchanged for all studied deformation conditions, in spite of recovery and recrystallization occurring at elevated temperatures.

The recently observed helicity-sensitive response, occurring in graphene based field-effect transistors (FETs) is interpreted as a result of the intrinsic phase asymmetry of these devices and interference of plasmons in the FET channel. The graphene-based plasmonic interferometers presented in this work enable the room temperature detection of THz radiation as well as allows us to distinguish between the rotation direction of circular polarized waves. To illustrate the broadband nurture of the observed effects, similar measurements were carried out at both THz and mid-infrared frequencies. The precise control of the carriers type and their concentration throughout the channel length allows us to demonstrate the helicity-sensitive response over a wide range of the gate potentials (from negative to positive values). We experimentally show that the formation of p–n junction inside the graphene channel leads to additional scattering of excited plasma waves, resulting in the suppression of their interference and consequent reduction of the helicity-sensitive contribution.

The work highlights the results of a study into the dual wedge-shaped wear of composite brake pads for freight wagons. It has been found that the over-normative wear makes the area of a composite brake pad larger in the lower part up to a value directly proportional to the wagon mileage and smaller in the upper part. To assess the braking efficiency of a rail vehicle, a graphical analytical method has been developed; it allows determining the factor of dual wedge-shaped wear of pads depending on the wagon mileage. The results of calculation were verified by comparing two samplings obtained by mathematical and computer modelling. The results of calculation have proven that the hypothesis on the adequacy is not rejected. The results of the study conducted will allow more accurate assessment of the braking efficiency of freight rolling stock to be made, as well as contribute to improving the safety of train traffic.

Discrete chaotic maps are a mathematical basis for many useful applications. One of the most common is chaos-based pseudorandom number generators (PRNGs), which should be computationally cheap and controllable and possess necessary statistical properties, such as mixing and diffusion. However, chaotic PRNGs have several known shortcomings, e.g., being prone to chaos degeneration, falling in short periods, and having a relatively narrow parameter range. Therefore, it is reasonable to design novel simple chaotic maps to overcome these drawbacks. In this study, we propose a novel fractal chaotic tent map, which is a generalization of the well-known tent map with a fractal function introduced into the right-hand side. We construct and investigate a PRNG based on the proposed map, showing its high level of randomness by applying the NIST statistical test suite. The application of the proposed PRNG to the task of generating surrogate data and a surrogate testing procedure is shown. The experimental results demonstrate that our approach possesses superior accuracy in surrogate testing across three distinct signal types—linear, chaotic, and biological signals—compared to the MATLAB built-in randn() function and PRNGs based on the logistic map and the conventional tent map. Along with surrogate testing, the proposed fractal tent map can be efficiently used in chaos-based communications and data encryption tasks.

In this article, we consider designs of simple analog artificial neural networks based on adiabatic Josephson cells with a sigmoid activation function. A new approach based on the gradient descent method is developed to adjust the circuit parameters, allowing efficient signal transmission between the network layers. The proposed solution is demonstrated on the example of a system that implements XOR and OR logical operations.

Josephson junctions (JJs) are superconductor-based devices used to build highly sensitive magnetic flux sensors called superconducting quantum interference devices (SQUIDs). These sensors may vary in design, being the radio frequency (RF) SQUID, direct current (DC) SQUID, and hybrid, such as D-SQUID. In addition, recently many of JJ’s applications were found in spiking models of neurons exhibiting nearly biological behavior. In this study, we propose and investigate a new circuit model of a sensory neuron based on DC SQUID as part of the circuit. The dependence of the dynamics of the designed model on the external magnetic flux is demonstrated. The design of the circuit and derivation of the corresponding differential equations that describe the dynamics of the system are given. Numerical simulation is used for experimental evaluation. The experimental results confirm the applicability and good performance of the proposed magnetic-flux-sensitive neuron concept: the considered device can encode the magnetic flux in the form of neuronal dynamics with the linear section. Furthermore, some complex behavior was discovered in the model, namely the intermittent chaotic spiking and plateau bursting. The proposed design can be efficiently applied to developing the interfaces between circuitry and spiking neural networks. However, it should be noted that the proposed neuron design shares the main limitation of all the superconductor-based technologies, i.e., the need for a cryogenic and shielding system.

Computer simulation of continuous chaotic systems is usually performed using numerical methods. The discretization may introduce new properties into finite-difference models compared to their continuous prototypes and can therefore lead to new types of dynamical behavior exhibited by discrete chaotic systems. It is known that one can control the dynamics of a discrete system using a special class of integration methods. One of the applications of such a phenomenon is chaos-based communication systems, which have recently attracted attention due to their high covertness and broadband transmission capability. Proper modulation of chaotic carrier signals is one of the key problems in chaos-based communication system design. It is challenging to modulate and demodulate a chaotic signal in the same way as a conventional signal due to its noise-like shape and broadband characteristics. Therefore, the development of new modulation–demodulation techniques is of great interest in the field. One possible approach here is to use adaptive numerical integration, which allows control of the properties of the finite-difference chaotic model. In this study, we describe a novel modulation technique for chaos-based communication systems based on generalized explicit second-order Runge–Kutta methods. We use a specially designed test bench to evaluate the efficiency of the proposed modulation method and compare it with state-of-the-art solutions. Experimental results show that the proposed modulation technique outperforms the conventional parametric modulation method in both coverage and noise immunity. The obtained results can be efficiently applied to the design of advanced chaos-based communication systems as well as being used to improve existing architectures.

Developing efficient path-planning algorithms is an essential topic in modern robotics and control theory. Autonomous rovers and wheeled and tracked robots require path generators that can efficiently cover the explorable space with minimal redundancy. In this paper, we present a new path-planning algorithm based on the chaotic behavior of the Courbage–Nekorkin neuron model with a coverage control parameter. Our study aims to reduce the number of iterations required to cover the chosen investigated area, which is a typical efficiency criterion for this class of algorithms. To achieve this goal, we implemented a pseudorandom bit generator (PRBG) based on a Courbage–Nekorkin chaotic map, which demonstrates chaotic behavior and successfully passes all statistical tests for randomness. The proposed PRBG generates a bit sequence that can be used to move the tracked robot in four or eight directions in an operation area of arbitrary size. Several statistical metrics were applied to evaluate the algorithm’s performance, including the percentage of coverage of the study area and the uniformity of coverage. The performance of several competing path-planning algorithms was analyzed using the chosen metrics when exploring two test areas of the sizes 50 × 50 cells and 100 × 100 cells, respectively, in four and eight directions. The experimental results indicate that the proposed algorithm is superior compared to known chaotic path-planning methods, providing more rapid and uniform coverage with the possibility of controlling the covered area using tunable parameters. In addition, this study revealed the high dependence of the coverage rate on the starting point. To investigate how the coverage rate depends on the choice of chaotic map, we implemented six different PRBGs using various chaotic maps. The obtained results can be efficiently used for solving path-planning tasks in both real-life and virtual (e.g., video games) applications.

This document describes how to construct a heroic transmission used in the mechanization of agricultural machinery. The article discusses the basic principles, design features and advantages of heroic transmission. Various methods of designing heroic programs are also considered. Based on the information considered, a method for designing a heroic transmission was developed. Based on the calculation, sketches of the impeller of the hero gear were developed. Based on the sketch of the outer wheel and the eccentricity, the obtained data were substituted into the parametric equation of the eccentroid cycloid, the profile of which is the basis for the construction of the inner wheel of the rocking pair. Based on the sketch, a 3D model of heroic transmission was developed, which was based on mathematical modeling.

This document describes the calculation procedure for selecting the optimal parameters of the boom lifting mechanism in agricultural machinery. A boom lifting scheme was developed. Studies have been carried out to find the optimal values of linear dimensions and angle, at which the required value of the force developed by the drive when lifting the boom with a hydraulic cylinder of the specified dimensions will be minimal. Based on the results of the study, an algorithm was developed for solving the optimization of boom lifting parameters. An expression is obtained for the objective function of optimizing the boom lifting mechanism. Algorithm for selection of optimal parameters of lifting mechanism considering weight of boom, hydraulic cylinder and rod has been developed.

This document describes the effect of undissolved gas on the bulk modulus of the fluid. The concept of liquid compressibility and dependence on composition, temperature and pressure is considered. Various methods of measuring the modulus of volumetric elasticity of the liquid were considered. It was also proposed to improve the mathematical model for calculating the module of volumetric elasticity of a liquid. The results of the study were used to plot the effect of the gas phase content modulus of volumetric elasticity of working fluid at different pressures. It was also concluded that the obtained values describe the need to equip hydraulic drives with devices for degassing working liquids.

This article focuses on the method of balancing the pump jack and optimizing its operation. In the course of the work, the main balancing methods were considered and a method based on changing the balancing value by moving the movable carriage was proposed. In the course of the work, a model was developed that made it possible to simulate loads, the results of which determined the effectiveness of the proposed balancing method. Based on the results of the study, a graph of the change in torque when the support is located during the operation of the drive was built. Based on the results of the work, the corresponding conclusion was made.