Том 64, № 8 (2019)

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.