A continued fraction operator technique for viscoelasticity problems involving anisotropic aging materials

The convergence of representations of proper continued fractions with arguments in the form of a Volterra operator with a nondifference core is examined. The problem of determining safe loads for an aging fibrous composite is solved by expanding irrational functions of an integral operator as a continued fraction and it is shown that the resulting solution converges. Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 29, pp. 71–77, 1999.     

Nitriding of Stainless Steel in Electron-Beam Plasma in the Pulsed and DC Generation Modes

The influence of electron-beam parameters on the thickness and phase composition of a hardened layer formed upon the nitriding of austenitic stainless steel 12Cr18Ni10Ti in plasma produced by a beam in a low-pressure (3 Pa) nitrogen-argon mixture is studied. The results obtained in the DC and pulse-periodic modes of beam generation with the same mean current and electron energy are compared. In this case the negative bias voltage applied to the samples is 100 V. The nitriding temperature of 400°C is maintained at a mean beam current of 2.6 A and various combinations of frequency (100–500 Hz) and current pulse durations (0.1–0.3 ms) with an amplitude of 80 A. The mean ion-plasma current densities in the DC and pulsed modes are close in magnitude (2–3 mA/cm² at 400°C). The high pulsed ion-current density (35–70 mA/cm²) creates conditions under which the surface sputtering rate during the pulse exceeds the growth rate of the nitrided layer. The nitriding of steel in the pulsed and DC modes over four hours gives the same result. Hardened layers with a thickness of 7–8 μm and a microhardness of the surface component of 15 ± 1 GPa in which the main phase is a supersaturated nitrogen solid solution (expanded austenite) are formed. A possible explanation is that nitriding in an electron-beam plasma proceeds mainly under the action of long-lived active neutral nitrogen particles rather than as a result of ion bombardment.     

Lifetime Extension of the Gas Discharge Detectors with Plasma Etching of Silicon Deposits in 80%CF<Subscript>4</Subscript> + 20%CO<Subscript>2</Subscript>

A method of elimination of silicon compounds from the anode wire of an aged proportional counter is presented. The aging of a counter with a 70%Ar + 30%CO₂ and a 60%Ar + 30%CO₂ + 10%СF₄ working mixture was stimulated by a ⁹⁰Sr β source. To accelerate the process of aging, the gas mixture flow to the counter was supplied through a pipe with RTV coated wall. As a result, the amplitude of the signal decreased 70% already at accumulated charge of Q = 0.03 C/cm. The etching of the silicon compounds on the wire surface with an 80%CF₄ + 20%CO₂ gas mixture discharge led to full recovery of the operating characteristics of detector and an increase in the lifetime. A scanning electron microscopy and X-ray spectroscopy analysis of the recovered wire surface were performed. In accordance with the results, a good quality of wire cleaning from SiO₂ compounds was obtained.     

On a new mechanism of polariton–polariton scattering

Condensate states of a two-dimensional exciton–polariton system have been considered under the conditions of direct resonant photoexcitation. It has been theoretically predicted that splitting of eigenmodes with orthogonal polarizations leads to the emergence of a new channel of parametric scattering. A polariton condensate spontaneously decays into a set of states in a finite region of the momentum space, thus leading to a strong inhomogeneity in the distributions of the intensity and polarization even in the case of a strictly constant amplitude and zero in-plane momentum of the external field. The new scattering mechanism makes possible self-oscillating and chaotic states of polariton systems.     

Use of Lorentz Transformations for Noninertial Frames of Reference

By analogy with the calculation of the path of a mass point in terms of the integral of the point velocity with respect to time, such that the point has a constant velocity V(t _i) within a time interval dt _i, then changes this velocity stepwise by V(t _i+1), moves with this velocity within a time interval dt _i+1, etc., an accelerated motion of an observer with a clock is represented by alternating states of rest in a sequence of inertial frames of reference and instantaneous jumps from one frame of reference into another. Lorentz transformations are used to calculate the readings of a resting clock observed from a noninertial frame of reference represented in this manner, during the rest of a noninertial observer in a next-in-turn inertial frame of reference belonging to the mentioned sequence, and upon a jump. For the observation from a noninertial frame of reference, the relation of the time interval counted by the resting clock to the time interval counted by the accelerated clock and to the acceleration has been obtained.     

Oscillations of cylinders in a linearly stratified fluid

The paper studies theoretically and experimentally hydrodynamic loads that act on horizontally placed cylinders of rhombic and square cross sections, oscillating harmonically in a linearly stratified fluid. An analytical solution is found with the use of affine similitude. Hydrodynamic force coefficients were evaluated experimentally from Fourier transforms of records of damped oscillations in a time—frequency region. It is shown that for polygonal contours, hydrodynamic loads change abruptly if the slope of the polygon sides coincides with the slope of the internalwave group velocity vector.     

Operational characteristics of a plasma cathode with a grid stabilization in a two-stage ion source

The discharge characteristics and the parameters of the cathode plasma in a two-stage ion source with a grid plasma cathode and a magnetic trap in the anode region are investigated. It is shown that an increase in the gas pressure and the accompanying increase in the reverse ion current in the bipolar diode between the cathode and anode plasmas lead to an increase in the cathode plasma potential and a transition of the cathode into the regime of electron emission from the open plasma boundary. The dependence of the ion current extracted from the anode plasma on the area of the exit aperture of the hollow cathode and the mesh size of the grid plasma cathode is explained. The conditions at which the ion emission current from the anode plasma is maximum are determined. The potential difference at the bipolar diode is measured by using the probe method. It is shown that, when the gas pressures reaches a critical value determined by the mesh size of the grid plasma cathode, the discharge passes into a contracted operating mode, in which the ion current extracted from the anode plasma decreases severalfold.     

Shearing interferometry of predischarge phenomena in deionized water

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 41–45, May–June, 1988.     

Reaction of 4-methyl-4-tribromomethylcyclohexa-2,5-dien-1-one with zinc metal

4-Methyl-4-tribromomethylcyclohexa-2,5-dien-1-one reacts with zinc dust in absolute DMF to give a mixture of 4-bromo-5-methylcyclohepta-2,4,6-trien-1-one, 4-methyl-cyclohepta-2,4,6-trien-1-one, and 4-dibromomethyl-4-methylcyclohexa-2,5-dien-1-one. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 177–178, January, 1998.     

Synthesis and study of some imidazole derivatives

The preparation of esters of 4(5)-hydioxymethylimidazole with mono-, di-, and trichloroacetic acids is described. It has been established that in the reaction of imidazolylmethyl chloroacetate with diethanolamine, the latter is alkylated with the imidagolylmethyl part of the ester, giving rise to bis(2-hydroxyethyl)aminomethylimidazole.For communication II, see [1].