Numerical Analysis of the Characteristics of an Arc in Laminar and Turbulent Gas Flows

The equations of magnetic gas dynamics are used to calculate the characteristics of an electric arc in a plasmotron channel versus the gas flow rate. The results obtained with the aid of the laminar and the two-parameter k– model of turbulence with allowance for deviations from equilibrium in the plasma and for the swirling of the gas are compared with experimental data. The stability of a laminar flow to the effect of weak hydrodynamic perturbations is investigated.     

Effect of Bound Water on the Fractal Geometry of Nanosized Cracks in Glasses Prepared by Vacuum Pressure-Assisted Sintering

The vibrational properties of fractal nanocracks in vitreous SiO₂samples prepared by vacuum pressure-assisted sintering are investigated by low-frequency Raman scattering spectroscopy. In the Raman spectrum, nanosized discontinuities with a fractal geometry manifest themselves in a specific frequency dependence of the scattering intensity: a monotonic decrease in the intensity according to the law of light scattering by acoustic vibrations localized on fractals is observed instead of the boson peak. The frequency dependence of the low-frequency Raman scattering intensity is analyzed for samples of different origins. A smoothing of the nanocrack profile with a decrease in the amount of bound water in the material is revealed.     

Phase compositions of titanium and chromium coatings produced by reactive deposition in an active gas atmosphere

The structures of titanium-and chromium-based coatings produced by electron-plasma deposition in an active gas atmosphere consisting of N₂, CO₂, C₂H₂, and their binary (50: 50) mixtures have been studied. Phase-composition data are used to analyze the conditions of interaction between a deposited metal and the gas atmosphere. These conditions are shown to be much more severe than in gas-saturation processes under furnace conditions. As a consequence, the reactions of active gases on the coating surface go to completion, and the conditions of phase equilibria during coating formation are shifted toward high active-gas pressures at a given deposition temperature.     

Coherent population trapping on <Superscript>87</Superscript>Rb atoms in small-size absorption cells with buffer gas

Coherent population trapping (CPT) on ⁸⁷Rb atoms in neon atmosphere has been studied in small-size glass absorption cells under conditions of pumping with narrow-band laser radiation at the D₂ line of the main doublet. Parameters of the absorption signal have been measured in 3-mm-diameter cells at buffer gas (Ne) pressures varied within 200–400 Torr, cell temperatures within 65–120°C, and pumping radiation power densities within 30–400 μW/cm². Optimum values of the buffer gas pressures, cell temperature, and pumping power are determined at which the short-term instability of the resonance line is at minimum. Orientational shifts of the CPT resonance signal in gas-filled cells and small-size cells with antirelaxation coating have been compared.