All Russia Research Institute of Automatics

Josephson junctions based on topological insulators are expected to host Majorana-type bound states that promote a 4π-periodic current-phase relationship. One experimental consequence of this periodicity is the absence of odd Shapiro steps in the current-voltage characteristics under microwave radiation. Here, we experimentally study the frequency-dependent amplitude of Shapiro steps in a ballistic Josephson junction involving a 23 nm-thick single nanocrystal of topological insulator Bi2Te2.3Se0.7 connected to two planar Nb-electrodes. We observe a progressive suppression of the first step while decreasing the frequency below 2 GHz. Using the two-channel thermal resistively shunted junction (tRSJ) model, we show that despite a ballistic regime, the overheating phenomena are enough to account for the observed effect. Our results highlight the complex physics of Josephson junctions and underscore that the missing first Shapiro step alone is not a definitive signature of topological superconductivity. Josephson junctions based on topological insulators are expected to host Majorana bound states which are accompanied by the experimental absence of odd Shapiro steps in current-voltage characteristics. Here, the authors investigate Shapiro steps in a ballistic junction with Bi2Te2.3Se0.7, finding that overheating effects, rather than topological superconductivity, are sufficient to explain the suppression of the first step, challenging conventional interpretations.

The diode effect in superconducting materials has been actively investigated in recent years. Plenty of different devices have been proposed as a platform to observe the superconducting diode effect. In this work, we discuss the possibility of a highly efficient superconducting diode design with controllable polarity. We propose a mesoscopic device that consists of two separated superconducting islands with proximity-induced ferromagnetism deposited on top of a three-dimensional topological insulator. Using the quasiclassical formalism of the Usadel equations, we demonstrate that the sign of the diode efficiency can be controlled by magnetization tuning of a single superconducting island. Moreover, we show that the diode efficiency can be substantially increased in such a device. We argue that the dramatic increase of the diode efficiency is due to competing contributions of the two superconducting islands to the supercurrent with single helical bands linked through the topological insulator surface.

An experimental design is proposed for studying a thermal wave that occurs in plasma under large electron temperature gradients, when the proportionality between the heat flux and the temperature gradient is violated. The heat flux becomes nonlocal under these conditions, i.e., it depends on the distribution of plasma parameters in a certain volume. Existing models for describing heat flux give conflicting predictions for some problems, so a more accessible experimental setup is needed for studying heat transfer in the laboratory and verifying numerical codes. The experimental setup proposed in this work minimizes the influence of hot electrons of another nature and distinguishes between radiative preheating. The effect under study is important in the development of certain laser thermonuclear fusion schemes, as well as in experiments with a significant energy input into the plasma.

BACKGROUND: Typically, mobile robots shall have high maneuverability, requiring additional drives that allow for changing the propulsion unit geometry and complex motion control systems. Existing software used to simulate the movement of rigid body systems do not always allow for the accurate description of the propulsion unit (wheels) interaction with the complex ground, challenging the development of advanced control algorithms. AIM: To develop a movement simulation for mobile robots, combining the advanced software for mathematical modeling of rigid body system movement and an algorithm to detect the contact of wheels with the ground relief based on a modified GJK algorithm. METHODS: The approach proposed to solve the problem of propulsion unit contact with track irregularities is based on the GJK algorithm used to search for wheel intersections with the ground relief. The output of the algorithm allowed to determine contact forces and moments that describe the tire–ground interaction based on its elastic damping and traction properties. RESULTS: The authors propose a mathematical model of the wheel interaction with uneven ground for multiple contact points. The model is based on a modified GJK algorithm and allows to determine contact points and interaction forces when simulating the mobile robot movement at a speed close to real time. The paper presents an assessment of the model’s effectiveness and its suitability for developing automatic movement control algorithms for mobile robots. CONCLUSION: The developed model allows to study efficiently the mobile robot movement when negotiating large obstacles and uneven grounds with multiple contact points of the propulsion unit with the ground. The study confirms that the model is suitable for and may be used in mathematical simulation models to design motion control laws for a mobile robot.

ABSTRACT Using the method of metal‐vapor synthesis (MVS), new hybrid materials based on collagen (Coll) and conjugates of dihydroquercetin (DHQ) with silver nanoparticles (AgNPs) were obtained. The MVS is an efficient route for the purposeful synthesis of metallic nanoparticles and their derived composites. AgNPs nanoparticles synthesized in 2‐propanol were used to prepare dihydroquercetin‐silver conjugate (AgNPs@DHQ) and collagen‐dihydroquercetin‐silver conjugate (Coll‐AgNPs@DHQ). The nanocomposites were characterized using X‐ray photoelectron spectroscopy, powder X‐ray diffraction, and scanning electron microscopy. Minimum inhibitory concentrations against E. coli and B. cereus were determined to evaluate the antibacterial activities of the nanocomposites. MTT, Neutral red uptake, and colony‐forming efficiency assays were applied to characterize the cytotoxicity and antitumor potential of the new hybrid nanomaterials. ABTS radical scavenging activity assay was performed to evaluate the antioxidant activity of the synthesized samples. In AgNPs, only the Ag 0 state was found, while in AgNPs@DHQ, two different Ag 0 and one Ag + states were found. The AgNPs@DHQ sample showed general cytotoxicity inhibiting the metabolic activity and vitality of both normal and tumor human cell types, while Coll‐AgNPs@DHQ demonstrated good biocompatibility, selective antitumor properties, and improved antioxidative potential. These findings highlight the potential of the synthesized Coll‐AgNPs@DHQ nanocomposite for biomedical and healthcare applications.

Gradient approximation from grid data is a critical component of high-order numerical schemes. However, certain problems are highly sensitive to the quality of gradient reconstruction, particularly those involving the development of hydrodynamic instabilities. In such cases, even minor perturbations, including numerical ones, can significantly alter the dynamics of the process. This study identifies scenarios where asymmetry in gradient reconstruction on adaptive meshes leads to the formation of Richtmyer–Meshkov instability in one-dimensional problem without actual perturbations. To address this issue, a modified least squares method is proposed. The new approach ensures symmetry and eliminates numerical instability, thereby improving the robustness of numerical solutions.

The results of numerical modeling of the dynamics of a charged particle beam in the electrode system of a miniature linear accelerator are presented, considering secondary processes. The possibility of minimizing the negative effects associated with secondary processes, such as electrode sputtering and secondary electron emission, was estimated. The calculations were performed at various combinations of the operating pressure and accelerating voltage in the pressure range of 2–8 mTorr and accelerating voltages of 60–100 kV.

The basis of the neutron generator is a miniature linear accelerator, which allows us to obtain a specific size of the generating region of neutron radiation with specified parameters of the neutron flux. Numerical modeling can help solve the problem of creating an accelerator with a strictly specified ion beam size on a target. Based on the simulation result, it will be possible to select the appropriate optimal physical and geometric characteristics of the Penning ion source and the ion-optical system. The initial data for the simulation are the spatial and energy distributions of ions emitted from the ion source. The purpose of the study was to experimentally determine these characteristics. The energy spectra and spatial distributions of ions are given for various discharge combustion modes as functions of the working gas pressure and the voltage at the anode. The relationship between the discharge VAC and the sagging potential inside the discharge, as well as their effect on the plasma emission boundary, is shown. Data on the width of ion beams and energy spectra at half-height are presented. The maximum value of the energy spectra is two and more times less than the corresponding value of the voltage applied to the anode. The gas pressure had little effect on the shape of the energy spectra. The profiles of the ion beams differed during probe diagnostics of the ion source in two perpendicular planes.

The DANSS detector is located near the power reactor at the Kalinin Nuclear Power Plant (at distances of 10.9–12.9 m) and is able to detect up to 5000 antineutrino events per day. The results of the search for Large Extra Dimensions in the simplest case of a single dominant large extra dimension are discussed. The particle oscillations to a finite-size extra dimension are assumed in this theory, and its predictions depend on the difference between the squared masses, as well as on the absolute scale of the neutrino masses. The sensitivity of the experiment to Large Extra Dimensions for various values of the model parameters such as the size of the large extra dimension a and the lightest-neutrino mass $${{m}_{0}}$$ can be determined by its Monte Carlo simulation. No statistically significant indications of the existence of Large Extra Dimensions have been obtained from the analysis of almost 5.8 million antineutrino events (the statistical confidence of the best point is only 2.0σ (1.8σ) for the normal (inverted) ordering of neutrino masses). The bounds have been determined for the size of the extra dimension and the lightest neutrino mass. These bounds for a number of regions are the best in the world. These bounds exclude a large fraction of the parameters preferable for explaining the gallium anomaly and the reactor antineutrino anomaly in this model, including the corresponding best points.