Calculation of characteristics of heat and mass transfer during destruction of thermoprotective material

The process of nonstationary heat and mass transfer in a carbon-epoxy composite under the action of a high-enthalpy flow is analyzed numerically within the framework of the mathematical model of a reacting medium. Analytical solutions have been obtained for the value of mass entrainment from the material surface, depending on the entrainment velocity at the expense of pyrolysis of the carbon-epoxy composite. The solutions obtained are in agreement with the results of numerical integration for constant and variable parameters of retardation. The possibility of simplifying the boundary conditions is analyzed, and recommendations for performing serial calculations are offered.Research Institute of Applied Mathematics and Mechanics, Tomsk 634050. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 4, pp. 76–84, July–August, 1994.     

Luminescence of CVD ZnO nanocrystals of different shapes

The effect of the shape and dimensions of zinc oxide nanocrystals on the threshold and directionality of UV lasing in the nanocrystals has been investigated. The results indicate that hexagonal columnar nanocrystals have the lowest optical threshold pump power at nanoresonator diameters of 100–200 nm, comparable to the absorption path length of the excitation light. The laser radiation is shown to have a mode structure, being directed predominantly along the prism axis. The lasing mechanism in prismatic nanocrystals differs from that in hexagonal-pyramidal nanocrystals. Electron microscopy results show that the ZnO nanocrystals are highly uniform in shape and size and that these parameters depend on the chemical vapor deposition conditions.     

Perfect tunneling of a structure containing a left-handed material layer

Tunneling of monochromatic radiation obliquely incident on a plane-layered structure is investigated. In the structure, a left-handed material layer (with a negative refractive index) is surrounded by layers with positive refractive indexes. Conditions for resonance amplification of evanescent waves that occurs simultaneously with perfect tunneling, i.e., reflection-free transmission of radiation through the plane-layered structure, are revealed.     

Effect of Compressive and Stretching Strains on the Dislocation Luminescence Spectrum in Silicon

Semiconductors - The photoluminescence of silicon strained by four-point bending at the temperature 600°C is studied. The so-called dislocation luminescence lines D1, D2, D3, and D4 are...     

Numerical Study of the Effect of Rotation on the Behavior of the Conjugate Heat and Mass Transfer on the Surface of a Spherically Blunted Cone Exposed to a Hypersonic Flow at an Angle of Attack with Ablation from the Surface

The processes of heating a body in a high-enthalpy spatial flow with allowance for body rotation around its longitudinal axis and ablation of the thermal protection material are studied by means of mathematical simulation. The obtained solution of the problem in conjugate formulation allowed us to take into account the effect of nonisothermic characteristics of the shell on the heat and mass transfer in the boundary layer.     

Direct spectral power density estimation from a discrete-time representation of stochastic analog quantization for an analog random process

Raising the performance is considered for the direct estimation of spectral power density for analog random processes. The solution is based on using sign analog-stochastic quantization of the random processes. Experimental results are presented. Translated from Izmeritel’naya Tekhnika, No. 3, pp. 13–17, March, 2009.     

Some results of mathematical simulation of the process of peat ignition

A formulation and numerical solution of the problem about peat layer ignition as a result of the action of a creeping fire bed are proposed based on a mathematical model of a porous reactive medium. Ignition of the initial reagent is shown to be determined by processes of drying, peat pyrolysis, oxidation of carbon oxide, and moisture content. The results of the numerical solution are compared with experimental data, and an estimate of the mass content of combustion products contaminating the atmosphere is presented.