Vol 42, No 8 (2016)
- Year: 2016
- Articles: 30
- URL: https://journals.rcsi.science/1063-7850/issue/view/12486
Article
Mathematical simulation of a membrane capacitive compensation pressure transducer
Abstract
The operation of a membrane capacitive pressure transducer with electrostatic compensation of the membrane deformation has been mathematically simulated. It is shown that the theory describing these instruments is incorrect and the error in measuring pressure by them may be as high as 25–29% of the measured value, which makes them inappropriate for use in pressure metrology.
Theoretical justification of the von Weimarn law under homogeneous condensation in the free-molecular regime
Abstract
The von Weimarn (Weymarn) law establishes the power dependence for the radius of formed droplets on vapor supersaturation initially created in the system. A theoretical derivation of this law is presented based on the classical Volmer–Becker–Döring–Zel’dovich–Frenkel approach. Analytical expressions have been obtained for all coefficients in this law.
Developing an edge-plasma diagnostic tool for the Globus-M tokamak based on measuring ratios of HeI lines
Abstract
A diagnostic technique that is based on measuring the ratios of neutral-helium line strengths has been developed for peripheral distributions of electron temperature and density of tokamak plasma. The main components of the technique are a four-channel filter-lens imaging polychromator (FLIP-4) and a Phantom Miro M110 high-speed camera for recording the images. The polychromator has been assembled, adjusted, and tested on an optical test bench. The optical system was installed on the spherical Globus-M tokamak. Some preliminary experiments were carried out. Images of the plasma-gun jet were obtained at neutralhelium lines.
Electron heat conductivity of epitaxial graphene on silicon carbide
Abstract
The diagonal component of the electron heat conductivity tensor of epitaxial graphene formed in a semiconductor has been investigated within a simple analytical model. It is shown that the heat conductivity sharply changes at a chemical potential close to the substrate band gap edge. Low-temperature expressions for the heat conductivity are derived.
Extremely deep profiling analysis of the atomic composition of thick (>100 μm) GaAs layers within power PIN diodes by secondary ion mass spectrometry
Abstract
A new opportunity to analyze the atomic composition of thick (>100 μm) epitaxial GaAs layers by SIMS with lateral imaging of the cross section of a structure is demonstrated. The standard geometry of ldepth analysis turns out to be less informative owing to material redeposition from the walls of a crater to its floor occurring when the crater depth reaches several micrometers. The profiles of concentration of doping impurities Te and Zn and concentrations of Al and major impurities in PIN diode layers are determined down to a depth of 130 μm. The element sensitivity is at the level of 1016 at/cm3 (typical for depth analysis at a TOF.SIMS-5 setup), and the resolution is twice the diameter of the probing beam of Bi ions. The possibility of enhancing the depth resolution and the element sensitivity of the proposed analysis method is discussed.
Crystallization of amorphous hydrogenated silicon (a-Si:H) films under irradiation with femtosecond laser pulses
Abstract
Crystallization of thin films of amorphous hydrogenated silicon under the irradiation of femtosecond laser pulses has been studied. It was found that the crystallization has a clearly pronounced threshold nature and depends on the laser emission wavelength. As shown the best results are achieved in crystallization at the laser wavelength range of 740–760 nm.
3D simulation of electron beam squeezed-state generation in a two-section drift tube and analysis of its characteristics
Abstract
A 3D numerical electromagnetic simulation of a vircator in the mode of electron-beam squeezedstate generation is performed. Detailed numerical investigations are carried out, and the dynamics of charged particles in the squeezed state is analyzed. It is shown that the electron beam density (and, as a consequence, effective beam plasma frequency) can be significantly increased in the squeezed state. Hence, the vircator generation frequency and power can also be increased.
A study of specific features of the electronic spectrum of quantum dots in CdSe semiconductor
Abstract
Monolayers of CdSe/CdS/ZnS quantum dots (QDs) formed on the aqueous subphase and transferred to solid substrates by the Langmuir–Blodgett method have been studied. The samples obtained were examined by transmission electron microscopy, atomic-force microscopy, and scanning tunnel microscopy. The structure of the QD monolayer obtained on the substrate was analyzed. Specific features of the electronic spectrum of the quantum objects formed in the samples under study were determined.
Unsteady triple-shock configurations and vortex contact structures initiated by the interaction of an energy source with a shock layer in gases
Abstract
The effect of physical and chemical properties of the gaseous medium on the formation of triple Mach configurations and vortex contact structures and on the stagnation pressure and drag force dynamics has been studied for supersonic flows with external energy sources. For the ratio of specific heats that varies in a range of 1.1–1.4, a significant (up to 51.8%) difference has been obtained for the angles of triple-shock configurations in flows at Mach 4 past a cylindrically blunted plate. When studying the dynamics of the decreases in the stagnation pressure and drag force, it has been revealed that these effects are amplified and the vortex mechanism of drag reduction starts to prevail as the adiabatic index decreases.
A solid-phase mechanism of shock-wave formation of dust particles of heavy metals
Abstract
The possibility of formation of dust particles in solid as a result of shock-wave destruction of the initial crystalline material structure and subsequent coalescence of atomic clusters (nanoparticles), which leads to the aggregation of mesocrystalline particles (grains) in the shocked layer, is discussed.
A mass spectrometer with a membrane interface for oil concentration monitoring in seawater
Abstract
An immersion mass spectrometer with a membrane interface was used for oil detection and oil concentration measurements in seawater by measuring in situ the concentrations of three hydrocarbons: benzene, toluene, and xylene in the region of the specialized Primorsk oil loading seaport in the Gulf of Finland. The recorded mass spectra demonstrated the possibility of measuring the oil concentration in seawater and determining the grade of oil products. The use of a mass spectrometer with a membrane separator interface allows measurements of hydrocarbon concentration with high accuracy, which is currently not provided in commercially available monitors.
Formation of ordered nano- and mesostructures in silicon irradiated with a single femtosecond laser pulse in different environments
Abstract
We report on a new class of ordered nano- and mesostructures, including distinct structured areas with subnanoscale roughness, produced by interaction of single tightly focused femtosecond laser pulses with a monocrystalline silicon surface under different environments. The environment was found to have a significant effect on the final morphology of near-surface layers of silicon.
Asymmetric magnetoimpedance in two-phase ferromagnetic film structures
Abstract
The magnetoimpedance of a film trilayer consisting of magnetically soft and magnetically hard films separated by a high-conductivity nonmagnetic spacer is theoretically investigated. A model for describing the dependences of the sample impedance on the external magnetic field and frequency is proposed, which is based on simultaneous solution of the linearized Maxwell and Landau–Lifshitz equations and takes into account the magnetostatic interaction between the magnetic layers. It is demonstrated that the magnetostatic interaction changes the distribution of magnetization of the magnetically soft film and leads to the occurrence of asymmetry in the field dependence of the impedance. The results obtained can be used in the development of weak magnetic field sensors.
The initial stage of autocatalytic growth of GaAs filamentary nanocrystals
Abstract
The initial stage of growth of autocatalytic GaAs filamentary nanocrystals by the vapor–liquid–crystal mechanism from a Ga droplet with diffusion collection of gallium adatoms from the entire crystal length is investigated. The dependence of the crystal radius on its length at various ratios of fluxes of elements of groups III and V is analyzed theoretically. Various growth regimes (specifically, the regime of radius selffocusing and droplet disappearance) are examined. The calculations for crystals of a small radius are performed with the Gibbs–Thomson effect taken into account.
Processes of carbon disulfide degradation under the action of a pulsed corona discharge
Abstract
Experiments on decomposition of carbon disulfide CS2 in air under the action of a pulsed nanosecond corona discharge have been carried out. The energetic efficiency of the degradation amounted to 290–340 g (kW h)–1, which is significantly higher than with the use of a corona discharge at a constant voltage. The main degradation products are sulfur dioxide SO2, carbonyl sulfide COS, sulfuric acid, and carbon dioxide. Processes occurring in pulsed corona discharge plasma and leading to carbon disulfide degradation are considered. Different methods of air purification from carbon disulfide are compared.
A compact laboratory device for accelerating thin strikers
Abstract
We describe a method for accelerating a thin (~1 mm thick) striker with a diameter of 35 mm in a shock tube channel up to velocities above to ~275 m/s under the pressure of detonation products of acetylene–oxygen fuel mixture. Impact of this striker on a ~1-cm-thick water layer generates a nonstationary decaying shock wave (Taylor wave) with amplitude of ~0.2 GPa on escape from the free surface.
Influence of the anisotropy field gradient on the spectra of spin wave resonance in garnet ferrite films
Abstract
It is established that the spectrum of spin wave (SW) resonance in garnet ferrite films with linear depth profile of the effective anisotropy consists (unlike the spectrum of homogeneous films) of a series of high-intensity SW modes and modes of very low intensity. The distribution of resonance fields of high-intensity SW modes depends on the gradient of the effective anisotropy field. For the same film thickness, the number of these modes increases with the value of gradient.
Structure and nanohardness of granulated ceramics synthesized from suspensions with various Y-ZrO2 concentrations
Abstract
The structure and micromechanical properties of granulated zirconia ceramics synthesized from suspensions with various Y-ZrO2 concentrations have been studied. It is established that an increase in the Y-ZrO2 content up to 25% eliminates the cracking of granules during heat treatment and improves their micromechanical characteristics. It is shown that elevated nanohardness of the synthesized granules is related to an increase in the content of tetragonal t-ZrO2 phase.
Gibbs sampler optimization for analysis of a granulated medium
Abstract
A new variant of the method of probability density distribution recovery for solving topical modeling problems is described. Disadvantages of the Gibbs sampling algorithm are considered, and a modified variant, called the “granulated sampling method,” is proposed. Based on the results of statistical modeling, it is shown that the proposed algorithm is characterized by higher stability as compared to other variants of Gibbs sampling.
Selective excitation of eigenmodes in a multilayer thin film resonator on bulk acoustic waves
Abstract
We consider a method of control over the operating frequency of a resonator on bulk acoustic waves, which is based on the selective excitation of eigenmodes. The frequency switching is achieved by using several layers of a ferroelectric in the paraelectric state and applying a control voltage of appropriate magnitude and polarity to each layer. The principle of selectivity is formulated and the criterion function is defined, which ensure the most effective excitation of a selected eigenmode with the possible suppression of parasitic modes. An example of using this function for a resonator switched between four eigenmodes is presented.
The diffraction efficiency of echelle gratings increased by ion-beam polishing of groove surfaces
Abstract
The efficiency of first-order diffraction on F1 glass echelle gratings for soft X-ray and extreme UV radiation can be significantly increased (by up to ten times) by etching the groove surface with a beam of neutralized Ar ions at 1250-eV energy. The processing was performed at normal incidence of ion beam on the surface of gratings, and the material thickness removed was on a level of 80–300 nm. A principle of optimization of the ion-beam etching process is proposed for solving particular tasks related to the planarization of microstructures with various lateral dimensions.
Studying average electron drift velocity in pHEMT structures
Abstract
Small-signal characteristics of pseudomorphic high-electron-mobility transistors based on donor–acceptor doped heterostructures (DA-pHEMTs) are compared to those of analogous transistors (pHEMTs) based on traditional heterostructures without acceptor doping. It is established that DA-pHEMTs, under otherwise equal conditions, exhibit (despite lower values of the low-field mobility of electrons) a much higher gain compared to that of usual pHEMTs. This behavior is related to the fact that the average electron drift velocity under the gate in DA-pHEMTs is significantly (1.4–1.6 times) higher than that in pHEMTs. This increase in the electron drift velocity is explained by two main factors of comparable influence: (i) decreasing role of transverse spatial transfer, which is caused by enhanced localization of hot electrons in the channel, and (ii) reduced scattering of hot electrons, which is caused by their strong confinement (dimensional quantization) in the potential well of DA-pHEMT heterostructures.
The mechanism of liquid metal jet formation in the cathode spot of vacuum arc discharge
Abstract
We have theoretically studied the dynamics of molten metal during crater formation in the cathode spot of vacuum arc discharge. At the initial stage, a liquid-metal ridge is formed around the crater. This process has been numerically simulated in the framework of the two-dimensional axisymmetric heat and mass transfer problem in the approximation of viscous incompressible liquid. At a more developed stage, the motion of liquid metal loses axial symmetry, which corresponds to a tendency toward jet formation. The development of azimuthal instabilities of the ridge is analyzed in terms of dispersion relations for surface waves. It is shown that maximum increments correspond to instability of the Rayleigh–Plateau type. Estimations of the time of formation of liquid metal jets and their probable number are obtained.
Modeling of phase decomposition of supersaturated solid solutions using the free-energy density functional method
Abstract
The nucleation and growth of particles of the second phase in a one-dimensional binary alloy is considered based on the Cahn–Hilliard equation with allowance for fluctuations. Using the results of modeling, it is shown that the second phase is occupied by the mechanism of solid solution decomposition, which involves simultaneous processes of the fluctuational nucleation of the second phase, diffusion-type growth of precipitations, and absorption of small clusters by coarse ones at the coalescence stage. Composition fluctuations are among the main factors influencing the distribution of solid solution phases.
Flux-gate magnetic field sensor based on yttrium iron garnet films for magnetocardiography investigations
Abstract
A new type of f lux-gate vector magnetometer based on epitaxial yttrium iron garnet films has been developed and constructed for magnetocardiography (MCG) investigations. The magnetic field sensor can operate at room temperature and measure MCG signals at a distance of about 1 mm from the thoracic cage. The high sensitivity of the sensor, better than 100 fT/Hz1/2, is demonstrated by the results of MCG measurements on rats. The main MCG pattern details and R-peak on a level of 10 pT are observed without temporal averaging, which allows heart rate anomalies to be studied. The proposed magnetic sensors can be effectively used in MCG investigations.
Speech signal filtration using double-density dual-tree complex wavelet transform
Abstract
We consider the task of increasing the quality of speech signal cleaning from additive noise by means of double-density dual-tree complex wavelet transform (DDCWT) as compared to the standard method of wavelet filtration based on a multiscale analysis using discrete wavelet transform (DWT) with real basis set functions such as Daubechies wavelets. It is shown that the use of DDCWT instead of DWT provides a significant increase in the mean opinion score (MOS) rating at a high additive noise and makes it possible to reduce the number of expansion levels for the subsequent correction of wavelet coefficients.
Antireflection nanocomposite thick film coatings with quasi-zero refractive index for solar cells
Abstract
Application of nanostructured composite coatings with a quasi-zero refractive index synthesized using the proposed patented technology provides a 25–30% increase in the efficiency of solar cells as compared to that of analogous solar cells with traditional (e.g., silicon nitride) single-layer interference antireflection coating.
The electric conductivity of composites based on various carbonaceous fillers and estimation of their percolation model parameters
Abstract
We have studied the electric conductivity of composites with various carbonaceous fillers (multiwalled carbon nanotubes, colloidal graphite, and amorphous carbon) as a function of the filler content. The widths of critical regions of the percolation transition to the conducting state are determined and the percolation critical exponents are estimated. It is established that there is a tendency to increase in the width of transition region and values of critical exponents when the filler is varied in the following order: carbon nanotubes–colloidal graphite–amorphous carbon.
High-efficiency synthesis of nanoparticles in a repetitive multigap spark discharge generator
Abstract
We describe a method of obtaining aerosol nanoparticles in a repetitive spark discharge generator with 12 interelectrode gaps between tin electrodes, which operates at a pulse repetition frequency of 2.5 kHz. During synthesis of tin oxide nanoparticles in air, the mass productivity of the gas discharge generator reaches up to 9 g/h for primary particles with characteristic sizes within 5–10 nm and agglomerate size on the order of 50 nm.
A method to register hidden photons with the aid of a multi-cathode counter
Abstract
We propose to detect hidden photons (HPs) by using single electrons emitted from the surface of a metal cathode under the action of HPs of cold dark matter. A multiwire gas-discharge proportional counter of special design with four cathodes has been developed. Calibration measurements were performed for determining the efficiency of counting single electrons. Single-electron pulse counting rate in various detector configurations was measured. The upper limits of mixing parameter χ, which characterizes the kinetic mixing of HPs and ordinary photons, are estimated.