Asymptotic Analysis of Finite-Source M/GI/1 Retrial Queueing Systems with Collisions and Server Subject to Breakdowns and Repairs

Methodology and Computing in Applied Probability - This paper deals with a retrial queuing system with a finite number of sources and collision of the customers, where the server is subject to...     

Automatic thermal frequency control of microwave oscillator with dielectric disk resonator

Microwave oscillators that are stabilized by sapphire disk resonators have good short-term relative frequency stability (()=10^–10 over averaging time 1 sec) but inadequate long-term stability. This is mainly due to the high temperature coefficient of frequency of the disk resonator. An automatic frequency-control system based on thermal control of the frequency of the disk resonator was developed to improve the long-term frequency stability of the oscillators. The parameters of the automatic frequency-control system were optimized by computer, which involved solution of the nonstationary problem of the temperature distribution in the disk resonator and examination of the stability of the automatic control system for diffuse propagation of the control signal. Recommendations are given for selection of the heater geometry and frequency-control method. An oscillator with the thermal frequencecy-control system had a long-term relative frequency instability of (0.3–1)·10^–8 per day, which was determined by the stability of the crystal-controlled reference oscillator. The automatic frequency-control system did not appreciably change the noise characteristics of the oscillator.Institute of Problems of Safe Development of Atomic Energy, Russian Academy of Sciences. Translated from Izvestiva Vysshikh Uchenbykh Zavedenii, Radiofizika, Vol. 36, No. 11, pp. 1043–1052, November, 1993.     

Absence of De Giorgi-type theorems for strongly elliptic equations with complex coefficients

One constructs examples of strongly elliptic second-order differential equations in the divergence form with measurable bounded complex coefficients in Rⁿ, n3, whose generalized solutions are not bounded in any neighborhood of the origin.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta, im. V. A. Steklova AN SSSR, Vol. 115, pp. 156–168, 1982.     

Coagulation Peculiarities and Fractionation of Nanodispersed Titanium Dioxide Hydrosol

A coagulation of nanodispersed TiO₂ hydrosol mainly consisting of individual anatase nanocrystallites stabilized with HCl was studied. It was shown that only a part of a dispersed phase coagulates when a certain amount of HCl was added to the sol, and larger nanocrystallites are settled first. The procedure for the separation of the sol into the fractions of various dispersity was developed.     

Differential mobility spectrometry of chlorocarbons with a micro-fabricated drift tube

Chlorocarbons were ionized through gas phase chemistry at ambient pressure in air and resultant ions were characterized using a micro-fabricated drift tube with differential mobility spectrometry (DMS). Positive and negative product ions were characterized simultaneously in a single drift tube equipped with a 3 mCi (63)Ni ion source at 50 degrees C and drift gas of air with 1 ppm moisture. Scans of compensation voltage for most chlorocarbons produced differential mobility spectra with Cl(-) as the sole product ion and a few chlorocarbons produced adduct ions, M (.-) Cl(-). Detection limits were approximately 20-80 pg for gas chromatography-DMS measurements. Chlorocarbons also yielded positive ions through chemical ionization in air and differential mobility spectra showed peaks with characteristic compensation voltages for each substance. Field dependence of mobility was determined for positive and negative ions of each substance and confirmed characteristic behavior for each ion. A DMS analyzer with a membrane inlet was used to continuously monitor effluent from columns of bentonite or synthetic silica beads to determine breakthrough volumes of individual chlorocarbons. These findings suggest a potential of DMS for monitoring subsurface environments either on site or perhaps in situ.     

Flash Photolysis of Diphenyldiazomethane in the Presence of Organic Sulfides

The flash photolysis of diphenyldiazomethane in acetonitrile, benzene, and n-decane solutions saturated with air resulted in the formation of diphenyl carbonyl oxide Ph₂COO which decayed in combination reactions. In the presence of organic sulfides, the transfer of the terminal oxygen atom of Ph₂COO to the sulfur atom was observed. The kinetics of this reaction was studied. The absolute rate constants (k ₆, dm³ mol^–1 s^–1) of the reactions of Ph₂COO with sulfides at 295 K (acetonitrile as a solvent) varied from 4.1 × 10² (Me₂S) to 8.1 × 10⁴ (Ph₂S). The solvent effect on the reaction kinetics and product composition was studied. The mechanism of the process was discussed.     

Kinetics of changes in the modulation period and in dispersion hardening in Cu-Ti-Me alloys

An investigation was made of the kinetics of changes in the flow stress _0.1, modulation period , and electrical resistivity in the course of ageing of Cu-Ti, Cu-Ti-Al, Cu-Ti-Zn, and Cu-Ti-Ga alloys. There were no dispersion hardening effects during the early stages of the precipitation, corresponding to the = const condition. An increase in _0.1. was observed during the stage of coagulation of the secondary phases. The increase in the flow stress was described using a theory of hardening by coherent particles of the new phase but it did not agree with the theory of hardening of alloys exhibiting spinodal precipitation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 81–87, May, 1980.