A theoretical study of a special detonation regime of operation of a pulse detonation device with a variable cross section detonation combustion chamber and a valveless supply system

The results of a theoretical study of the special detonation regime that arises in a pulse detonation device with a variable cross section combustion chamber are presented. The problem is solved analytically within the framework of the one-dimensional approximation. In contrast to the standard version of arbitrary discontinuity disintegration, the problem is solved for a variable cross section at the location of the diaphragm. Since the pulse detonation device operated with a valveless system of fuel and oxidizer supply, a fuel flowed through it over the entire period before spark ignition. This peculiarity of the operation of the combustion chamber was also taken into account. The proposed approach was used to perform calculations for methane-oxygen mixtures, for which extensive experimental data exist. The calculation results are compared to the available experimental data.     

An experimental study of the diffusion-controlled self-ignition of hydrogen in a channel

The pulsed outflow of hydrogen into channels of circular and rectangular cross sections with a surface area of 20 mm² was experimentally studied. It was revealed that the shock wave formed during the outflow of a pulsed jet is the reason why it ignites at the contact surface. The range of initial pressures of hydrogen at which it ignites was determined and the dependence of the distance from the diaphragm at which a flame arises at the contact surface on the pressure in the shock wave front for circular and rectangular cross section channels was obtained.     

Ellipsometric study of the change in the porosity of silica xerogels after chemical modification of the surface with hexamethyldisilazane

Variable angle spectroscopic ellipsometry (VASE) and ellipsometric porosimetry (EP) have been used to study the effect of treatment with hexamethyldisilazane (HMDS) on the porosity of silica xerogel films. Chemical modification of the surface with HMDS was found to reduce the porosity by approximately 15%. This reduction was connected with changes which occur in the silica network, with further condensation or the reaction between neighbouring trimethylsilyl (TMS) surface groups being possible causes.     

Optical absorption resonances of trapped particles

We have previously shown the possibility of the existence of a one-photon resonance with homogeneous width in the center of an absorption line of trapped particles. The results of a detailed investigation of this resonance are given in the first part of the present paper. The second part is devoted to a two-photon resonance in a standing-wave field: the time of coherent interaction with the field is increased for trapped particles, which permits the elimination of transit resonance broadening.     

Adsorption and consumption of atomic fluorine on SiO2 surface

In accordance with ellipsometric data, the adsorption of fluorine atoms on SiO₂ obtained through the hightemperature oxidation of silicon, proves to be reversible. Chemical interaction of F with SiO₂ is shown to be the basic route of F consumption, whereas heterogeneous recombination contributes only slightly under the experimental conditions studied (P=0.1 Torr, T=20–250°C).

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SiO₂, . , SiO₂ . SiO₂, (P=0, 1 , T=20–250°C) .

     

Possibility of Creating a 62.6 nm Frequency Standard in Helium Using Stimulated Raman Scattering

Optics and Spectroscopy - The possibility of creating a frequency standard at the forbidden transition $${{2}^{3}}S{\kern 1pt} - {\kern 1pt} {{1}^{1}}S$$ (62.6 nm) of a helium atom using stimulated...