Differential Characteristics of the Overexpanded Gas Jet Flow Field in the Vicinity of the Nozzle Edge

Technical Physics - A parametric study of the features of the flow field of a plane and axisymmetric overexpanded ideal gas jet in the vicinity of the nozzle edge has been conducted over the entire...     

High resolution neutron diffraction study on Fe81B19 metallic glass

The structure factor of Fe₈₁B₁₉ metallic glass was measured by the conventional and time-of-flight neutron diffraction methods in the 0.4<Q<24 Å^-1 momentum transfer range, yielding high resolution (～0.26 Å) in r-space. The pair distribution function obtained by Fourier transformation is resolved into subpeaks. The distances and distribution widths of the Fe-B and Fe-Fe first neighbours, the partial coordination numbers and the short range order parameter are given. The results clearly indicate preferential chemical bonding between iron and boron atoms.     

Extreme shockwave systems in problems of external supersonic aerodynamics

The stationary shockwave systems (the sequences of shocks, isentropic expansion and compression waves), which arise at a planar supersonic flow of perfect inviscid gas around the bodies are investigated theoretically. The domains of the existence of shockwave systems under consideration are found analytically and numerically for the model problems of supersonic aerodynamics (the flow around a single plate, the plate with the frontal shield, polygonal profiles), the parameters of systems are determined, which provide the extrema of the force and thermal loadings as well as of the aerodynamic coefficients of streamlined bodies.     

XPS study of the oxidation of nanosize Ni/Si(100) films

The XPS (X-ray photoelectron spectroscopy) study of nickel oxide nanolayers obtained by magnetron sputtering of the metal and its subsequent oxidation in air at different temperatures (400°C and 1000°C) was performed. Silicon(100) was used as a substrate. Surface of the initial Ni/Si structure was shown to contain not only Ni metal, but also the NiO oxide. Annealing at 400°C results in a complete oxidation of the metal film. At a high-temperature annealing (1000°C), nickel interacts both with oxygen and silicon substrate to form NiSi silicide and a composite Ni-Si-O phase in transition layer. Electronconductivity of NiO films is determined by intercrystallite barriers. Activation energies of film electroconductivity in model gases (O₂, Ar, H₂) were found.     

Catalysts Based on Fiberglass Support: IV. Platinum Catalysts Based on Fiberglass Support in Oxidation of Hydrocarbons (Propane and n-Butane) and Sulfur Dioxide

Platinum catalysts (0.003–0.52% Pt) based on leached sodium silicate and boron silicate fiberglass supports are studied in the complete oxidation of hydrocarbons (n-butane and propane) and high-temperature SO₂ oxidation. It was shown that platinum localized in the bulk of the glass matrix show a higher activity and thermal stability than metal particles supported on the outer surface of fiberglass. The experimental results for hydrocarbon oxidation on platinum-containing fiberglass gauzes at short contact times are discussed.     

Study of temperature fields in a rectangular plate with a temperature-dependent internal source with the aid of fast expansions

The approximate analytic solution of the problem of temperature field in a rectangular plate with an internal temperature- dependent source is obtained by the method of fast expansions. The critical value of a parameter characterizing heat release, which fundamentally affects the analytic solution form, is found. The maximum solution error is shown to amount to 0.02 at the consideration of the first three terms of the Fourier series in fast expansion. Temperature fields are presented, and an analysis of the influence of the plate sizes and the heat release magnitude on their formation is given. Recommendations on the plate shape choice are given.     

Analytic description of the domain of existence of triple configurations with a negative slope of reflected shock

We consider triple configurations of compression shocks in supersonic flows of an inviscid perfect gas. The boundaries of the domain of existence of shock-wave structures of a new type (triple configurations with a negative slope of the reflected shock or negative triple configurations) on a set of flow parameters have been theoretically investigated.     

Characterization and Spatial Matching of Laser Diode Beams

It is shown that the type of lateral waveguide of a laser diode cannot be determined uniquely based on just the measured magnitude of astigmatism. For a unique determination, the K-factor of Petermann, which characterizes the wavefront curvature at the laser output facet, must be measured as well. In order to determine the type of lateral waveguide, a setup for measuring astigmatic distances in the range 0–200 m with an error of ±2 m and a K-factor with an error of 20% was developed. Operational features of the setup were analyzed, and a technique that allows one to minimize the effect of beam ellipticity on the measurement results was found. Using the technique, the optimization of spatial matching of a laser diode with a ring interferometer of the butterfly type was accomplished. For transformation of the astigmatic elliptical beam into the axially symmetric mode of the interferometer, we have used an optical system that consists of two cylindrical and one spherical lenses. The algorithm for designing the matching system was developed, and the 85% injection of radiation of a AlGaAs laser diode into the principal mode of a ring interferometer was experimentally demonstrated.     

An analysis of boundary conditions in heterostructures

General relations satisfied by scattering matrices, matching matrices for coefficients, transfer matrices, and matching matrices for envelope functions are derived for systems with heteroboundaries. It is shown that the relations found for these matrices are fulfilled to good accuracy within the models proposed for the GaAs/AlAs(001) heterostructure. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 39–44, January, 2008.