Longitudinal DC electric discharge in a supersonic air flow

A longitudinal dc electric discharge in a submerged high-pressure supersonic air jet is described. Photographs of the discharge are provided. The experimental voltage across the discharge gap and the discharge current are given for two resistances of the resistor that limits the discharge current over a certain range of the discharge channel length along the air flow. The current-voltage discharge characteristic is provided at a constant discharge length. The main discharge characteristics are obtained from a comparison of the experimental and theoretical results calculated on the basis of the simplest model.     

Global Analysis of the Flows of Fluids with Pressure-Dependent Viscosities

 To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments. While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small, special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place. Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are global in time, for a large class of physically meaningful viscosity-pressure relationships. (Accepted May 1, 2002) Published online November 15, 2002 Communicated by S. S. ANTMAN     

Chalcogenide glass chemical sensors: Research and analytical applications

The paper is devoted to research and development in the field of chalcogenide glass chemical sensors for determination of heavy metal ions in solution. The overview of the solid-state scientific approach and research design of the sensing materials is followed by the original results of the analytical application of the chalcogenide glass sensors for laboratory analysis, industrial control and environmental monitoring.     

Tautomerism of azine derivatives

The tautomeric properties of 4-pyrimidinylmethanes were studied in the case of 2-CH₃- and 2-CF₃-4-pyrimidinylcyanoacetic esters, 2-CH₃-4-pyrimidinylnitromethane, and 4-pyrimidinylnitromethane. It was shown by ¹H and ¹³C NMR spectroscopy that an equilibrium with the participation of three tautomeric forms — pyrimidine form A and pyrimidinylidene forms B and C with o- and p-quinoid orientations of the double bonds in the heteroring — may be realized in aprotic dipolar solvents (dimethyl sulfoxide).See [1, 2] for communications I and II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1544–1548, November, 1978.     

Tautomerism of azine derivatives. 6. Tautomerism of 2-pyrimidinylmethane derivatives

The existence of a pyrimidinyl-pyrimidinylidene tautomeric equilibrium in solutions of 2-pyrimidinylcyanoacetic acid esters in CDCl₃ was observed. Unsymmetrically substituted compounds form two types of ylidene tautomers that differ with respect to the position of the NH proton, the ratio between which is controlled by the substituents in the 4 (6) position. The introduction of both donor and acceptor substituents into the 5 position of the pyrimidine ring increases the amount of the pyrimidine form. The same thing occurs when the polarity of the solvent is decreased. The addition of DMSO or DMF to CDCl₃ leads to conversion of the intrachelate ylidene tautomers to unchelated tautomers. Protonation (CF₃COOH) shifts the equilibrium to favor the ylidene tautomer that has higher basicity.See [1] for communication 5.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 827–831, June, 1984.     

Study of the oxygen exchange kinetics in the nonstoichiometric oxide SrFeO<Subscript>3–δ</Subscript> under isostoichiometric conditions using the oxygen partial pressure relaxation technique

The kinetics of oxygen exchange in the nonstoichiometric strontium ferrite SrFeO_3–δ with the structure of cubic perovskite was studied by the oxygen partial pressure relaxation technique in the isostoichiometric regime at temperatures of 500–900°C in a range of δ from 0.24 to 0.44. An increase in the oxygen nonstoichiometry δ was accompanied by a decrease in the rate of sample relaxation and by an increase in the apparent activation energy of oxygen exchange.     

A high spectral resolution spectrograph with fiber input for the Big Azimuthal Telescope of SAO RAS. Improvement of the spectral module

The paper presents a critical analysis and modernization of separate elements of the optical layout of a high-resolution spectrograph with fiber input for the Big Azimuthal Telescope of the Special Astrophysical Observatory. The modernization is directed mainly at enhancing the light efficiency and making it possible to produce the spectrograph using domestic manufacturers. Renovated versions of the cross-dispersion grism, the projection camera, and the overall characteristics of the system are presented. The resulting efficiency of the whole instrument is given.

     

Asymptotics of the solution to an initial boundary value problem for a singularly perturbed parabolic equation in the case of a triple root of the degenerate equation

For a singularly perturbed parabolic equation, asymptotics of the solution to an initial boundary value problem in the case of a triple root of the degenerate equation is constructed and justified. Essential distinctions from the case of a simple root are the scale of the boundary layer variables and the three-zone structure of the boundary layer.     

Determination of Residual Stresses in Products in Additive Production by the Layer-by-Layer Photopolymerization Method

A computational-experimental model for identifying the residual (shrinkage) stresses arising in parts after their additive manufacturing by the layer-by-layer photopolymerizationmethod is given. The model is based on an analysis of flexible shrinkage strains of a series of specimens shaped as plate-strips with the same parameters but with different polymerization time which is prescribed in their manufacturing on the 3d-printer.