Atomic hydrogen flux density measured using thin metal films

Using one-or two-layer films of transition metals, it is possible to determine the atomic hydrogen flux density under reduced gas pressure conditions (10⁻¹–10⁻³ Pa). The method consists in monitoring a change in the film resistance caused by selective dissolution of atomic hydrogen in the metal during exposure of the film in a mixed atomic-molecular flow, followed by determining a characteristic time τ required for the hydrogen concentration in the film to reach 63% of the maximum possible level. The hydrogen flux density is then calculated within the framework of a simple mathematical model of the film saturation with hydrogen described by a relaxation law. The proposed method is characterized by a high selective sensitivity to atomic hydrogen. The atomic hydrogen flux density in a mixed atomic-molecular flow can be determined in a range from 5×10¹³ to 10¹⁶ cm⁻² s⁻¹.     

On the prospects of developing high-efficiency piezocomposites based on crystals of solid solutions of ferroelectric relaxors

Electromechanical properties of the 0-0-2-2 type composite based on platelike crystals of solid solutions of ferroelectric relaxors of the Pb(A_1/3Nb_2/3)O₃-PbTiO₃ system (A = Zn, Mg) have been studied for the first time. Factors accounting for the record values of some effective parameters of this composite are considered. The relationship between the components of the elastic compliance tensor of the layered structures forming the composite and the positions of maxima of the effective hydrostatic parameters is established.     

A bidirectional ring fiber laser with a 90° Faraday rotator as the nonreciprocal phase element. II. Experiment

The results of experimental investigation of an Er-doped fiber bidirectional ring laser with a 90° Faraday rotator in the cavity are presented. Two theoretically predicted regimes of the bidirectional generation of modes propagating in opposite directions with either complex-conjugate or orthoconjugate polarization states have been realized in practice. In each of these regimes, stable bidirectional generation of only one longitudinal mode propagating in each direction is possible. The former regime ensures significant stabilization of a nonreciprocal frequency shift between the modes propagating in opposite directions, this shift being determined by the Faraday phase rotator.     

Nanostructural crack arrest

The problem of brittle crack development in a nanocrystalline material has been theoretically studied. Expressions describing the conditions of crack stability are obtained.     

Nanocrystalline Ni coatings strengthened with ultrafine particles

In this study, nanocrystalline Ni powders and thermally sprayed coatings, containing ultrafine AlN particles, were synthesized and characterized. The results indicated that the presence of AlN particles in the powders drastically decreased the dimension of agglomerates formed by cryomilling and increased the surface roughness of the agglomerates. The AlN phase was broken down into ultrafine particles of approximately 30 nm in size. These particles were dispersed in the Ni matrix and enhanced the development of a nanocrystalline structure in the Ni matrix during cryomilling. Selected-area diffraction patterns, obtained from transmission electron microscopy (TEM) and X-ray mapping with scanning electron microscopy (SEM), confirmed the presence of AlN particles in the coatings. The presence of AlN particles also led to an increase in the amount of NiO phase that was distributed in the coating, in the form of ultrafine, round particles. AlN particles increased the microhardness of the Ni coating by approximately 60 pct. Indentation-fracture results also indicated that the fine, dispersed AlN particles raised the apparent toughness of the Ni coating. The synthesized Ni coatings containing ultrafine AlN particles were characterized as equiaxed nanocrystalline grains with an average size of 24 nm, in which twins were observed. The increase in microhardness resulted from both grain refinement and the presence of ultrafine particles. The latter played the primary role in strengthening.     

Experimental and analytical studies of innovative prestressed concrete box-girder bridges

This paper presents experimental and analytical results of four scaled prestressed concrete box-girder bridges with corrugated steel webs. The location of prestressing strands at both ends of the specimens and the thickness of end diaphragms are the two major parameters. Based on the experimental results of all four specimens, their seismic behavior is critically examined, including hysteretic loops, ductility factor, dissipated energy, and failure mode, etc. It was found that both the thickness of end diaphragms and the location of prestressing strands at both ends of the specimens are insignificant when the specimens failed at the mid-span due to concrete crushing, and the proposed analytical model can be used to predict the load-displacement relationship of such bridges.     

Effect of the external coupling of cavities on the stability and output power of a relativistic magnetron

Autooscillation regimes in a relativistic magnetron with external mutual coupling of cavities have been studied. It is demonstrated that the interaction of oscillations under mode competition conditions significantly increases the stability of the working oscillation mode and improves the spectral characteristics of radiation.     

The optimum characteristics of a halogen lamp pumped by transverse RF discharge

We report on the optimized characteristics of a small-size bactericidal lamp pumped by transverse RF (f=1.76 MHz) discharge, operating on a system of the molecular emission bands of chlorine in a wavelength range of 195–310 nm. The spectral characteristics of the plasma emission were measured and the intensity of chlorine emission bands were studied as functions of the total pressure and partial composition of a helium-chlorine mixture. Oscillograms of the pumping current and output radiation intensity were measured and the total output radiation power was determined. It is established that the lamp radiates predominantly in a bactericidal wavelength interval on an electron-vibrational transition at 200 nm in Cl₂** molecules. The optimum partial pressures of helium and chlorine are 100–300 and 90–120 Pa, respectively. The maximum output power of UV emission from the side cylindrical surface of the lamp reached 10 W. The lamp can be used in photochemistry, ecology, genetics, and medicine.