卷 64, 编号 8 (2019)
- 年: 2019
- 文章: 24
- URL: https://journals.rcsi.science/1063-7842/issue/view/12686
Theoretical and Mathematical Physics
Mathematical Modeling of Canopy Forest Fire Spread in the Presence of Fire Breaks and Barriers
摘要
In this paper, we studied the spreading of canopy forest fires in the presence of fire breaks and barriers consisting of hardwood trees by mathematical modeling. Mathematically, this problem is reduced to solving Reynolds equations for a turbulent flow with allowance for chemical reactions. The control volume method was used to obtain a discrete analogue. Using numerical calculations, we obtained distributions of the fields of velocity, temperature, oxygen concentrations, volatile products of pyrolysis and combustion, and volume fractions of the condensed phase. The modeling allowed obtaining contours of the spread of canopy forest fires that depend on the stock and types of forest combustible materials, moisture content, wind speed and direction, etc. We were also able to determine the dependence of the size of fire breaks and barriers on the above parameters, at which a canopy fire stops spreading.
Sedimentation of a Low-Concentration Suspension of Stokes Particles in a Stirred Layer with a Movable Free Boundary
摘要
Numerical Simulation of Thermodynamic Parameters of High-Porosity Copper
摘要
We propose that a modified equation of state be used for calculating the thermodynamically equilibrium TEC2 model for improving the reliability of description of thermodynamic parameters of shock loading of pure materials and heterogeneous mixtures of various porosities. For copper, the parameters of a thermally consistent equation of state have been determined. A reliable description of shock-wave loading of copper has been obtained using a small number of fitting parameters determined from the concordance with experimental data. Thermodynamic parameters have been simulated for copper with various porosities; the compression ratio and the temperature along the shock adiabat have been determined, and the value of heat capacity along the normal isobar has been calculated. The results of calculations are compared with available experimental results obtained by different authors.
Atomic and Molecular Physics
Capture and Dissociative Capture of a Single Electron in the Process of Interaction of Doubly Charged Ions with CO Molecules
摘要
The absolute cross sections of single-electron capture and single-electron capture with dissociation in the interaction between incident He2+, C2+, N2+, and O2+ ions with energies from 6.4 to 36.4 keV and СО molecules were measured. It is demonstrated that the cross section of dissociative capture is much larger than the cross section of single-electron capture for O2+ projectile ions. A qualitative explanation for this effect is provided.
Generation of Lithium Clusters in Helium Plasma Flow
摘要
The formation of lithium clusters in a helium flow is considered within the method considering the widths of energy levels. It is shown that lithium atoms in a plasma flow of inert helium form a cluster consisting of lithium only. In addition to lithium clusters with interatomic distances corresponding to interatomic distances of the equilibrium state, long-lived excitations of clusters with interatomic distances of 13 Bohr radii are observed. However, if excitations are removed, such systems transfer into the ground state or decay. In addition, it is observed that Li–He systems are long-lived under conditions of external excitations but quickly lose helium when these excitations are removed.
Gases and Liquids
Instability Increments for Waves with Different Symmetries on a Space-Charged Jet Moving Relative to a Material Medium
摘要
We have studied the instability increments of capillary waves with an arbitrary symmetry (arbitrary azimuthal numbers m) on the surface of a space-charged cylindrical jet of an ideal incompressible dielectric liquid moving relative to an ideal incompressible material dielectric medium. It is shown that for not very high jet velocities, the axisymmetric mode (m = 0) is the first to become unstable upon an increase in the space charge density, and then the kink mode (m = 1) and flexural-strain mode (m = 2) exhibit instability. It is this sequence of realization of instability of azimuthal modes that determines the regularities of charged jet dispersion in experiments. For jet velocities comparable with those critical for aerodynamic instability realization, the mode with m = 1 is the first to lose its stability. The dependences of maximal increments on wavenumbers have been determined for all azimuthal modes.
On the Stability of a Highly Charged Droplet Suspended in the Superposition of Gravitational and Electrostatic Fields
摘要
For a highly charged droplet suspended at rest in the superposition of gravitational and electrostatic fields, the critical conditions of realization of its instability due to intrinsic and induced charges are determined. All computations are performed in the fourth order of smallness in the stationary deformation of the spherical droplet and in the first order of smallness in the dimensionless amplitude of its capillary oscillations. The dependences of Rayleigh Wcr and Taylor wcr critical parameters on the radius of an initially spherical droplet, density, coefficient of surface tension, gravity acceleration, and number of oscillation mode are found that are different from those for a free droplet. As the number of modes increases, the critical value of the Rayleigh parameter increases and approaches asymptotic value Wcr ≈ 0.95 whereas critical parameter wcr decreases and approaches asymptotic value wcr ≈ 1/25 × 10–4. These variations in Wcr and wcr are explained by the condition of immobility for the mass center in the suspension that couples Wcr, wcr, and gravity acceleration.
Ring Waves on the Surface of a Liquid in a Coulomb Field
摘要
The realization laws of instability of ring waves on the surface of an electroconductive liquid in a Coulomb field are studied. The relation is derived, which links the frequency of ring capillary gravitational waves on the surface of a conductive liquid in an inhomogeneous electrostatic field of point charge with physical parameters of the problem and with the wave number analog. Similar to the Tonks–Frenkel field parameter, a field parameter is determined, which characterizes the surface stability of a conductive liquid in an inhomogeneous Coulomb field. It is established that the critical conditions of instability of ring waves on the surface of electroconductive liquid in a Coulomb field are less strict than the conditions of Tonks–Frenkel instability.
Solid State
Study of Evaporation of Laser-Heated Iron–Carbon Nanoparticles Using Analysis of Thermal Radiation
摘要
Evaporation of iron nanoparticles in carbon shells under pulsed laser irradiation is analyzed. Iron–carbon nanoparticles are synthesized in a shock tube reactor with the aid of pyrolysis of the 0.25% Fe(CO)5 + 0.25% C6H6 mixture in argon. Laser radiation is used for additional heating to temperatures that exceed the evaporation threshold of the iron core of nanoparticles. Time profiles of the thermal radiation of laser-heated nanoparticles are measured. The two-color pyrometry is used to determine the evaporation temperature of nanoparticles, and the laser extinction makes it possible to monitor the loss of volume fraction of the condensed phase upon evaporation. Approximation of experimental signals of laser-heated nanoparticles using model curves is employed to determine effective enthalpy of evaporation of iron–carbon nanoparticles. It is shown that the iron core of nanoparticles is evaporated through the carbon shell and the energy spent by such a process is approximately twice greater than the evaporation enthalpy of bulk iron with free surface.
Pulsed Magnetization of a Short-Circuited HTSC Coil
摘要
We have studied trapped magnetic fields and their relaxation during pulsed magnetization of a 20-turn short-circuited coil made of a stabilized HTSC-2G tape at liquid nitrogen temperature. The highest trapped field is close to the value obtained during field cooling (FC process) and varies insignificantly upon a five-fold increase of the magnetizing pulse amplitude. Copper coating of the tape considerably suppresses pulsed heating effects. Current relaxation at the initial segment is determined by the current passing between superconducting and normal layers and by the form of the current–voltage characteristic. Over long time intervals (t > 100 s), relaxation is determined by the contact resistance of the soldered junction.
Experimental and Computational Study of a High-Speed Collision of an Aluminum Striker with a Solid and Mesh Obstacle
摘要
The results of computational and experimental studies of peculiarities of the process of impact between the striker and obstacle, which imitates shield protection of spacecrafts, have been considered and pictures of fragmentation of the striker and obstacle have been obtained. The numerical calculations were carried out using the method of smooth particle hydrodynamics (SPH). In the experiments, the striker was accelerated using a two-stage light-gas gun; the state of the obstacle and striker at the moment of their interaction was controlled using an X-ray and high-speed video camera. The recording equipment was switched on using induction cross sections. The comparative analysis of the results of numerical simulations and experiments have been considered.
Inelasticity and Nanostructured Dislocation Deformation of Aluminum–Silicon Alloy with a Supermodified Eutectic Structure
摘要
Young’s modulus and the logarithmic decrement of oscillations at a frequency of ~100 kHz as well as the subgrain size and residual stresses in the strontium modified alloy of aluminum with 15 wt % silicon have been studied. The alloy was obtained with a solidification rate of 1 mm/s at the shifted eutectic point. The dependence of inelastic dislocation deformation on the applied oscillating stress has been obtained and analyzed. The effect of strontium modification on the microstrain diagram can be accounted for by transformation of the lamellar fiber structure of eutectic silicon into a superfine fiber structure.
Physical Science of Materials
Effect of Functionalization on the Conductivity and Noise Characteristics of Arrays of Multiwall Carbon Nanotubes
摘要
The electrophysical and noise characteristics of arrays of multiwall carbon nanotubes (MWCNTs) functionalized in various ways were studied. It is demonstrated that the as-prepared and annealed MWCNT arrays have semiconductor-type resistivities and temperature dependences of resistivity, while the arrays of annealed MWCNTs functionalized with acids have metallic properties. Low-frequency 1/f noise in the 0.2‒20 kHz range was observed for all MWCNT arrays. Simple thermal annealing raised the noise level severalfold and annealing with acid treatment resulted in noise reduction and a change in the index of power in its current dependence. The normal amplitude distribution of noise spikes transformed to a lognormal one as the density of as-prepared MWCNT arrays increased. The duration distribution of these spikes became narrower at higher densities.
Structural Transformations in Iron Borate under High-Temperature Annealing
摘要
Scanning electron microscopy and X-ray diffractometry are used to study surface morphology and crystal structure of iron borate FeBO3 annealed at different temperatures. Temperature limits of the structural stability are determined. It is shown that recrystallization to iron orthoborate Fe3BO6 and hematite α-Fe2O3 takes places at temperatures of 800–900°C and above 900°C, respectively.
Solid State Electronics
Comparative Characteristic Analysis of Thermophotovoltaic p-InAsSbP/n-InAs Converters Irradiated on p- and n-Sides
摘要
The basic characteristics of thermophotovoltaic heterostructure p-InAsSbP/n-InAs converters have been simulated. The converters have been designed so that a contact to the irradiated p-InAsSbP layer has a limited area or, in the flip-chip design, radiation is introduced through a contact-free part of the n+-InAs substrate. It has been shown that the design features of the converter influence its efficiency and active region temperature.
Physics of Nanostructures
Features of the Formation and Structure of Barium Titanate Langmuir Films
摘要
Ferroelectric films of stabilized barium titanate nanoparticles have been obtained from the colloidal system of a sodium oleate aqueous solution by the Langmuir–Blodgett method at the KSV NIMA 2002 facility, coagulants with the most characteristic hydrodynamic diameter of ∼200 nm have been found, and a physical model of their formation from barium titanate nanoparticles in this colloid system has been proposed. Homogeneous ferroelectric films with barium titanate particles ∼20 nm in size and a band gap of 3.6 eV have been deposited. The topological and structural features and distribution of chemical elements in the obtained films on different substrates have been studied by the methods of scanning probe and electron microscopy, vibrational and X-ray photoelectron spectroscopy, as well as X-ray diffractometry.
Formation of Nanosized Surface Layers of 03Kh17N12M2 Stainless Steel by Implantation of N+ Ions
摘要
Accumulation of nitrogen in nanosized surface layers of 03Kh17N12M2 stainless steel has been detected upon N+ ion implantation up to 14 at % together with metal nitrides, mainly of chromium nitride CrN and interstitial solid solution. It has been demonstrated that N+ ion implantation accompanied by preliminary irradiation by Ar+ and O+ ions decreases maximum nitrogen concentration by at least two times. It is assumed that this is stipulated by segregation to surface layers of iron atoms upon irradiation by Ar+ ions as well as formation of chromium oxide Cr2O3 and chromium hydroxide CrOOH upon irradiation by O+ ions.
Photonics
Stability of Thin-Film Cu–As2S3 and Ag–As2S3 Structures
摘要
Thin-film Cu–As2S3 and Ag–As2S3 structures obtained by successively evaporating Cu(Ag) and As2S3 in vacuum on glass substrates have been studied. Samples of these structures have been kept in air at room temperature in the dark for 6 months, and transmission spectra have been periodically taken of these samples. The logarithm of inverse transmission coefficient in the transparency domain of As2S3 has been used as a measure that is proportional to the thickness of the metal film. It has been found that for Ag–As2S3 the thickness of the metal film varies with storage time linearly, whereas for Cu–As2S3 this dependence can be described by two different linear sections. From the decrease in metal film thickness, it has been concluded that the Ag–As2S3 structure is more stable than Cu–As2S3. It has been supposed that silver, unlike copper, does not react with As2S3 when the structures are stored in the dark, although it permanently diffuses into As2S3 during storage.
Radiophysics
Method for Recirculation of Signals in the Problem of Observation of a Point Object above a Metal Surface
摘要
Application of ultrawideband centimeter-wavelength signals using recirculation of signals in spatial recirculation loops (emitter–target–element of the receiving antenna–emitter) is analyzed in the problem of localization of the position of a point object above a reflecting metal surface. Determination of the coordinates of object above a metal surface is based on the calculation of a generalized correlation integral in the spectral domain for frequency transmission coefficients of the recirculation loops over all receiving elements with allowance for coordinates of a true object, its mirror reflection, and reference point in space. The results of sounding in the presence and absence of the recirculation are compared.
Electrophysics
New Reflective Lens for an Ion Mirror of a Planar Multi-Reflection Time-of-Flight Mass Spectrometer
摘要
A reflecting lens of a planar ionic mirror formed by a channel adjacent normal to the closing mirror lid is considered. The wide flange of the channel and lid of the mirror have different potentials, are plane-parallel, and separated from each other by a small distance. Using the conformal mapping method, we obtained an exact analytical expression for calculating the lens field. It is shown that in an ion mirror with the proposed reflective lens it is possible to adjust the previously calculated field distribution in order to approach to the theoretically ideal space-time focusing in a wide range of ion energy.
Effect of Air Pressure on Parameters of Beam Current and X-Ray Radiation Generated in a Gas Diode
摘要
Parameters of a beam of runaway electrons and X-ray radiation generated in a gas diode at different atmospheric pressures are studied. It is shown that the maximum beam currents and intensities of X-ray radiation are generated at an air pressure of about 102 Pa. Distribution of beam electrons with respect to energy is determined by the method of attenuation of beam current using aluminum filters with different thicknesses. The maximum of such a distribution corresponds to an electron energy of about 100 keV. The maximum exposure dose of X-ray radiation behind a copper-foil anode with a thickness of 30 μm is about 107 mR. It is shown that the beam electrons absorbed by elements of an X-ray detector affect the shape and amplitude of the desired signal at beam currents of greater than 35 A/cm2.
Physical Electronics
Charging of Ion-Implanted Dielectrics by Electron Irradiation
摘要
The charging kinetics of Al2O3 (sapphire) and SiO2 (α-quartz) dielectrics irradiated by inert gas ions (Ar+), metal ions (Ga+), and protons (H+) has been studied. It has been found that charging kinetics depends considerably on the type of irradiating ion. Also, it has been established that preirradiation of a dielectric target by an ionizing corpuscular radiation (protons, ions) substantially changes the charge characteristics of the dielectric surface. These differences depend on irradiating ion energy, which governs the depth of an accumulated negative charge layer versus the depth of ion preimplantation.
Pulsed and Static Field Emission VAC of Carbon Nanocluster Structures: Experiment and Its Interpretation
摘要
The field emission properties of carbon nanocluster structures and films based on them have been considered. Experimental data, including VAC, at static and pulse modes have been presented. The analysis of size effects, effect of field penetration, and hysteresis effect has been performed. The theoretical explanations of them have been given.
Oxygen on a Cylindrical Tungsten Polycrystal
摘要
Using low-energy (0–25 eV) threshold electron spectroscopy and contact potential difference in vacuum not worse than 2 × 10–8 Pa, oxygen films obtained at 295, 325–1425 (in steps of 50), and 1575 K, including in subsequent heating from the adsorption temperature to 1925 ± 50 K, on the cylindrical surface of a gas-phase tungsten coating 30 μm thick on NbC-1 alloy (Nb – 1% Zr), used as a collector material for thermal emission in space-borne nuclear power plants, have been studied.