Том 45, № 2 (2019)
- Жылы: 2019
- Мақалалар: 35
- URL: https://journals.rcsi.science/1063-7850/issue/view/12908
Article
An Investigation of the Effect of the Thermal Coupling Time Delay on the Synchronization of VO2-Oscillators
Аннотация
The effect of the time delay of thermal coupling on the synchronization of two VO2-oscillators has been studied for the first time. A modification of the methods for determining high order synchronization parameters has been proposed. The dependence of these parameters on the magnitude of the time delay and distance between the oscillators in the presence of internal noise has been studied. The results will contribute to the development of technology for creating three-dimensional neural networks.
Formation of Weak Singularities on the Surface of a Dielectric Fluid in a Tangential Electric Field
Аннотация
The process of interaction between nonlinear waves on a free surface of a nonconducting fluid in a strong tangential electric field is simulated numerically (effects of the force of gravity and capillarity are neglected). It is shown that singular points are formed at the fluid boundary in a finite time; at these points, the boundary curvature significantly increases and undergoes a discontinuity. The amplitude and slope angles of the boundary remain small. The singular behavior of the system is demonstrated by spectral functions of the fluid surface—they acquire a power dependence. Near the singularity, the boundary curvature demonstrates a self-similar behavior typical for weak root singularities.
The Optical Effect of Light Polarization Plane Rotation in DNA-Containing Materials
Аннотация
Using the example of DNA water solutions, a manifestation of the light polarization plane rotation effect has been shown (in comparison with a number of dyes). Numerical values of the rotation angle have been established that significantly exceed those for water solutions of dyes and sugar traditionally used in saccharimeters and polarimeters. Therefore, another optical effect in biostructuring optical materials has been identified and confirmed.
Experimental Determination of the Radial Displacement Field in the Neck of Samples after a Tensile Test
Аннотация
This Letter presents the results of a study of the radial displacement fields arising upon stretching of cylindrical samples before their disintegration. The object of study was sv-07Kh16N6 stainless steel wire containing filiform defects oriented along the sample axis. Using X-ray tomography of the sample necks, the coordinates of the defect points in the sample are determined and the displacement field is recovered from them. The resulting dependence is represented by an approximate formula.
Analysis of the Structure of Multilayer Nanocrystalline Coatings Based on Plasma Mass Transfer Parameters Calculated by the Monte Carlo Method
Аннотация
The results of the simulation of plasma fluxes onto the surface of rotating substrates during the combustion of a vacuum arc of the Cr–Ti–Mo cathode system are presented. The structure and composition of the arc-PVD Ti0.15Cr0.74Mo0.11N0.84 coatings are experimentally studied. The numerical simulation results of the coating structures based on experimental data were analyzed. The possibility of the simulation of the structure of multilayer, multicomponent coatings and the concentration distribution of chemical elements and its components is shown by calculating the plasma fluxes using the Monte Carlo method.
Determination of Some Photoluminescence Parameters of Ca(AlxGa1 –x)2S4:Eu2+
Аннотация
We synthesized a solid solution of Ca(AlxGa1 – x)2S4 activated with europium ions Eu2+. The photoluminescence spectra and photoluminescence excitation spectra of the crystals at 300 K for x = 0.2 are measured. The dependence of the luminescence intensity on the temperature in the range of 10–300 K is investigated. Based on the experimental results, the redshift, the Stokes shift, the activation energy, and the lifetime of the Eu2+ ions are determined.
Internal Friction at the Grain Boundaries with Elongated Pores
Аннотация
A model of internal friction at a grain boundary containing equidistant parallel cylindrical pores is presented. Variable shear stress induces a mutual displacement of the interfacial regions matched at the segments between pores depending on their position. The values of scattered energy at each segment and total internal friction are determined. The temperature dependence of the internal friction has a form of a wide peak.
Stable Multilayer Reflective Coatings for λ(HeI) = 58.4 nm for the KORTES Solar Telescope
Аннотация
Multilayer aluminum-based structures reflecting at λ(HeI) = 58.4 nm were studied. Spectral and angular dependences of the reflection coefficient of these coatings were determined using a laboratory reflectometer and at the ELETTRA and BESSY II synchrotrons. The optical characteristics of multilayer Ru/Al and Mo/Al mirrors with a protective MoSi2 layer were found to be stable: the absolute change in the reflection coefficient within 18 months of storage in air was no larger than 1.5%. The peak near-normal reflection coefficient for Mo/Al mirrors at 58.4 nm was R = 26.1% with FWHM Δλ0.5 = 10 nm of the reflection curve.
Contraction of Microwave Discharge in the Reactor for Chemical Vapor Deposition of Diamond
Аннотация
It was found that in a hydrogen-methane mixture in microwave plasma reactor for diamond deposition, there is a threshold pressure after which the contraction of microwave discharge occurs. The results of measurements of gas temperature and spatial distributions of optical emission intensity of discharge are presented. The mechanism of discharge contraction is discussed.
A High-Voltage Switching Power Supply for Cold Plasma Jets
Аннотация
Solid-Phase Epitaxy of BiFeO3 Films with Magnetoelectric Properties on Sapphire
Аннотация
The ferroelectric domain structure has been investigated in bismuth-ferrite rhombohedral phase films prepared on the rhombohedral plane of sapphire by solid-phase epitaxy. The piezoelectric modulus has been estimated to be d33 ~ 2 pm/V. In films of the Bi25FeO39–BiFeO3 and Bi2Fe4O9–BiFeO3 systems on sapphire, the magnetoelectric-switching effect has been observed in bismuth ferrite crystallites without deposition of exchange-coupled layers. The values of the magnetic moment in bismuth ferrite microcrystallites have been estimated.
Specific Features of the Nonlinear Diffusion of a Strong Pulsed Magnetic Field near the Conductor Edge
Аннотация
The nonlinear diffusion of a strong magnetic field to a conductor with the boundaries forming a right dihedral angle has been considered. In a transverse field with induction oriented perpendicular to the angle edge, the current density is maximum in the conductor bulk rather than near the edge (as for linear diffusion). In a longitudinal field with induction oriented parallel to the edge, the current density at the vertex of the angle at the strong-field diffusion is zero (as in a weak field); however, the maxima of the current density, temperature, and Lorentz force shift to the conductor bulk with an increase in the field strength.
Synthesis of Oxygen-Doped Graphitic Carbon Nitride from Thiourea
Аннотация
We have synthesized oxygen-doped graphite-like carbon nitride (g-C3N4) by the thermal treatment of the thiourea at 450–550°C. With an increase in the annealing temperature, the oxygen concentration in g-C3N4 increases, and the band-gap of the material decreases from 2.64 to 2.47 eV. The semiconductor properties of g-C3N4 doped with oxygen are confirmed by its high photocatalytic activity, determined by decoloration of a Rhodamine B aqueous solution in the presence of g-C3N4 upon irradiation with visible light.
The Application of Empirical Potentials for Calculation of Elastic Properties of Graphene
Аннотация
The elastic properties of a flat graphene layer calculated using the classical empirical Tersoff, Brenner, AIREBO, PPBE-G, and LCBOP potentials have been compared. It is shown that, although the popular Brenner and AIREBO potentials have been developed formally taking into account the elastic properties of graphene, they give significant discrepancies in the values of Young’s modulus and Poisson’s ratio. Among the potentials under consideration, the LCBOP potential yields the values of these parameters that are closest to experimental data and results of ab initio calculations in the limit of zero elongation. For the quantitative simulation of mechanical phenomena in graphene-based systems, the potential parameters should be fitted to reproduce elastic properties of graphene completely taking into account system deformations and dependences of these constants on the elongation.
The Effect of Low-Temperature Heat Treatment on the Superelasticity in Ti–50.6 at % Ni Single Crystals
Аннотация
As a result of low-temperature aging at 573 K for 1.5 h of Ti–50.6 at% Ni [001]-oriented single crystals quenched from 1253 K, a high-strength state is obtained due to the precipitation of Ti3Ni4 nanoscale particles (d < 10 nm). The aging leads to the development of the B2–B19' martensitic transformation through an intermediate R phase, a reduction in the B19' martensite formation temperatures by 40–60 K, an increase in the strength properties of the B2 phase from 730 to 2100 MPa, and an extension of the superelasticity interval ΔTSE in compression from ΔTSE = 60 to 170 K (compared to quenched crystals).
Model of Laser Plasma Acceleration in the Fields of a Spiral Electrodynamic Line
Аннотация
The acceleration of a plasmoid, for the formation of which a conical spiral expanding in the direction of the expected plasma acceleration is used, in a rapidly increasing magnetic field of complex geometry has been considered. An algorithm for calculating the longitudinal magnetic field in the approximation of replacing a spiral line with a system of rings of variable radius has been presented. A mathematical model that is based on the interaction of the plasmoid magnetic moment with gradient of the longitudinal magnetic field decay has been proposed to analyze the efficiency of the acceleration. The possibility of deuterons reaching an average speed exceeding 106 m/s has been shown.
Ion–Electron Recombination and Heat Fluxes in High-Frequency Ion Thrusters
Аннотация
Heat fluxes emitted from plasma to the surface of structural elements of high-frequency (HF) ion thrusters with perforated electrodes of the ion-optical system have been studied. Radiation fluxes formed during ion–electron recombination on surfaces in contact with plasma are considered taking into account their spatial distribution and partial reflection from surfaces. New expressions for the heat fluxes are obtained that should be used as boundary conditions in numerical models for the calculation of temperature fields in HF ion thrusters.
A Method of Helical Wave Front Demultiplexing
Аннотация
Machine learning methods were used to construct a demultiplexer for helical wave front separation into orthogonal modes. The accuracy of wave front demultiplexing into eight modes at a signal-to-noise ratio of –3 dB is about 95% in a broad range of signal carrier frequencies. For nonstationary parameters of signals, the proposed demultiplexer accuracy exceeds that of the classical correlation method.
Recognizing Arm Motions by Fluctuation Analysis of EEG Signals
Аннотация
We consider the task of recognition of fragments of multichannel electroencephalogram (EEG) records corresponding to motions of the human arm and to mental representation of these motions. It is shown that the problem of recognition can be solved by processing short EEG segments by the method of fluctuation analysis. The obtained results suggest that fluctuation analysis can be used as an algorithm of the digital signal processing in development of the neurointerface software.
The Optoelectronic Two-Wave Method for Remote Monitoring of the Content of Methane in Atmosphere
Аннотация
The optoelectronic two-wave method has been developed and a block scheme of the corresponding optoelectronic device has been proposed for remote monitoring of the content of methane in atmosphere. The optoelectronic device employs light-emitting diodes (LEDs) based on GaAlAsSb/GaInAsSb/GaAlAsSb (3.12 μm) and GaAlAsSb/GaInAsSb/GaAlAsSb (3.39 μm) structures as the sources of reference and probing radiation, respectively.
Frequency Conversion of High-Power Gyrotron Radiation under Conditions of Raman Backscattering on an Auxiliary Electron Beam
Аннотация
The regime of Raman backscattering of a pumping wave that is cocurrent with an electron beam into the counterpropagating wave can be used for the radiation frequency conversion in high-power gyrotrons. The absolute instability developing in this system ensures generation of a scattered signal in the absence of external resonators, which allows the frequency of scattered radiation to be smoothly controlled within 20–40% by varying the electron energy in the case of high-power (megawatt) gyrotrons used as sources of pumping radiation.
Scanning Near-Field Optical Nanospectrophotometry: a New Method for Nanoscale Measurements of the Absorption Spectra of Single Nanoobjects
Аннотация
A new experimental method for nanoscale measurements of the absorption spectra of single nanoobjects has been developed based on scanning near-field optical microspectroscopy (SNOM) and nanospectrophotometry (NSP). The main distinctive feature of the proposed SNOM-NSP technique consists in depositing a sample onto a coverglass followed by its probing in the total internal reflection spectroscopy mode. This approach allows the number of analyzed samples to be significantly increased and provides the possibility of combining measurements with other optical techniques. The proposed SNOM-NSP method has been successfully used for studying single plasmonic nanoparticles and their complexes with Rhodamine 6G dye.
The Electroforming Effect in Polycrystalline Fullerene C60 Films
Аннотация
Long-term exposure of a polycrystalline fullerene C60 film in a constant electric field of 1–4 MV/cm produces an electroforming effect manifested by increase in conductivity of the film within several orders of magnitude. After this electroforming, the current–voltage (I–U) characteristic shows a high degree of current stability and reproducibility of results. In fields of 105–106 V/cm, the I–U characteristics of electroformed films are determined by the space-charge limited current. The concentration (Nt ≈ 4 × 1021 m–3) of carrier traps and their energy (Et ≈ 0.176 eV) have been estimated.
Deep-Level Defects in a Photovoltaic Converter with an Antireflection Porous Silicon Film Formed by Chemical Stain Etching
Аннотация
Defects in the semiconductor structure of a photovoltaic converter (PVC) with a p–n junction and antireflection film of porous silicon manufactured using chemical stain etching were studied by the current deep-level transient spectroscopy technique. The influence of the regime of porous silicon film formation on the transformation of deep-level defects and the main PVC characteristics is explained.
The Influence of Space Charge on the Transport of Charged Particles Generated during Electrospray in Crossed Gasdynamic and Electric Fields
Аннотация
The transport of charged particles generated during electrospray in a longitudinal gasdynamic field has been studied in a model system comprising two coaxial electrodes and a collector grid. The process has been numerically simulated with omission of the role of a space charge. A comparison of the results shows that the space charge is a key factor determining the transport of charged particles: the model transport efficiency in the absence of space charge reaches 80–100%. In experiment, the efficiency strongly depends on the space charge and amounts to 70–80% for its minimum values, while decreasing to 20–30% with increasing electrospray current.
BaTiO3/LaSrMnO3 Heterostructure Grown on Sapphire for Ferroelectric Tunneling Junctions
Аннотация
BaTiO3/LaSrMnO3 (BTO/LSMO) structures with a ferroelectric layer thickness of 10 nm have been formed on r-cut sapphire substrate by means of high-frequency magnetron sputtering. Investigations of the sample structure showed the presence of a crystalline phase, while measurements of electrical properties revealed piezoelectric response of the BTO films. The study of local current–voltage characteristics showed dependence of the sample resistance on the prehistory of voltage application as determined by ferroelectric hysteresis of the BTO layer.
Electron Microscopy and Elemental Composition of the Near-Surface Layer of Electron-Irradiated LiF Crystals
Аннотация
Electron microscopy and optical vibrational spectroscopy techniques have been used to study Li nanoparticles formed on the cleaved surface of lithium fluoride (LiF) crystals irradiated by 4-MeV electron beam to a total fluence of 5 × 1016 cm–2. It is suggested that ionization accompanying this intense irradiation leads to radiolysis of the target and removal of fluorine from interblock boundaries, where lithium cations are collected and mutually oriented to form microwires. This functional surface may be of practical interest.
Growth of GaN Nanotubes and Nanowires on Au–Ni Catalysts
Аннотация
Arrays of GaN nanowires (NWs) and nanotubes (NTs) have been grown by metalorganic vapor phase epitaxy using a gold–nickel film as the catalyst. The simultaneous formation of both NTs and NWs in one process in the presence of various Au–Ni catalyst compositions is explained. It is established that NTs grow on solid catalyst particles, while NWs grow according to the classical vapor–liquid–solid mechanism. The optoelectronic properties of obtained NTs and NWs have been studied using photo- and cathodoluminescence techniques.
Lasers Based on Quantum Well-Dots Emitting in the 980- and 1080-nm Optical Ranges
Аннотация
The main characteristics of edge-emitting lasers with active regions based on nanoheterostructures of a new type—quantum well-dots (QWDs) operating at various wavelengths—are compared. The QWD structures operating at 980- and 1080-nm wavelengths demonstrated minimum values of threshold current density (160 and 125 A/cm2), high internal quantum efficiency (74 and 85%), and low internal losses (1.1 and 0.9 cm–1), respectively.
Hydroxyapatite Nanoclusters in Subendothelial Structures of Aortic Demilunes of Patients with Calcified Aortic Stenosis
Аннотация
We have studied X-ray diffraction (XRD) patterns of calcinates isolated from aortic demilunes of patients with calcific aortic stenosis. It is shown that the observed XRD pattern is formed by spherical formations of hexagonal hydroxyapatite with diameters distributed according to the lognormal law. A model of the structure of these formations is constructed and the possible mechanisms of their nucleation and encapsulation of hydroxyapatite particles in the restricted porous space of the basal membrane of aortic valve demilunes are discussed.
Controlled Synthesis of Graphene on Copper Using the Method of Implantation of Carbon Recoil Atoms
Аннотация
A method of graphene synthesis on the surface of copper foil by cold implantation of carbon recoil atoms is considered. It is established that monolayer graphene films are formed on the surface of carbon-implanted copper foil under certain conditions (annealing temperature and duration, cooling rate) of postimplantation processing.
Studying the Characteristics of Transistors Based on Gallium Nitride Heterostructures Grown by Ammonia Molecular Beam Epitaxy on Sapphire and Silicon Substrates
Аннотация
Ammonia molecular-beam epitaxy has been used to grow gallium nitride (GaN) transistor heterostructures on sapphire and silicon substrates. GaN transistors with a 1.2-mm periphery fabricated on substrates of both types exhibited similar high static characteristics: saturation current density above 0.75 A/mm, transconductance above 300 mS/mm, and breakdown voltage above 120 V. Measurements of the small-signal parameters showed that transistors based on silicon substrates possessed high gain in a frequency range up to 5 GHz; the specific output power at 1 GHz amounted to 5 W/mm for transistors on sapphire substrate and 2 W/mm for transistors on silicon substrate.
Laser Excitation of Torsional Vibrations in Optical Microfibers
Аннотация
Comparative analysis of mechanisms of the laser excitation of torsional vibration modes in optical microfibers shows that special attention should be devoted to the Sadovsky effect manifested in polarization-anisotropic optical microfibers. Estimations of the efficiency of this mechanism for the excitation of torsional vibrations and polarization modulation in the proposed types of anisotropic quartz microfibers shows the possibility of creating new types of polarization elements—optically controlled fiber polarization devices and sensitive elements for resonance fiber-optic sensors.
The Influence of the InAlAs Layer Surface Morphology on the Temperature Dependence of Parameters of Au/Ti/n-InAlAs(001) Schottky Diodes
Аннотация
Growth-related structural defects present on the surface of InAlAs layers grown by molecular beam epitaxy on InP(001) substrates influence the temperature dependences of the current–voltage characteristics of Au/Ti/InAlAs Schottky barriers. It is established that these defects in the form of pits cause the appearance of regions with reduced barrier height. At a surface density of ≥107 cm–2, these defects significantly influence the parameters of the Schottky barriers at temperatures below 200 K.