Temperature measurementin gaseous and liquid reacting media in the case of their shock compression

This paper describes the results of measuring the temperatures of gaseous and liquid reacting media, which was carried out by the thermocouple method with the use of a battery (copper–Constantan–copper) of planar thermocouples, placed in the medium under study. It is shown that convective heat transfer lasting for 0.5–1.5 μs equalizes the temperatures of the “hot” thermocouple junctions and the environment. The relationship between the voltage occurring on the thermobattery during this heating and time was determined using a pulse oscilloscope. The measured maximum voltage was used to determine the temperature of the medium. A series of experiments was carried out on measuring the temperatures of water and emulsion explosive matrix, which were compressed by a shock wave, as well as the detonation products of ammonite with sodium hydrogen carbonate at various mass ratios. The estimates of heat fluxes from the detonation products to the metallic surfaces of the thermobattery contacting with them are obtained.     

Highly efficient SHG of a sequence of laser pulses with a random peak intensity and duration

One of the methods of obtaining a highly efficient second-harmonic generation (SHG) for laser pulses with random amplitudes and durations is mathematically modeled. The essence of the method proposed consists of the use of quadratic nonlinearity of the medium under conditions of a large mismatch between the wave numbers of the fundamental wave and the second harmonic. In the literature, the SHG under these conditions is referred to as the cascade SHG. Under certain conditions, this process is equivalent to the action similar to that of the cubic nonlinearity. This allows one to implement the both compression and decompression of laser pulses due to the cascade generation at a fairly low intensity of the pulses such that the Kerr nonlinearity does not manifest itself. The cascade generation is shown to enable one to implement tenfold or higher suppression of fluctuations of the input peak intensity of the laser radiation in the regime of free generation, which potentially makes it possible to implement the SHG under optimum conditions for all pulses in the sequence.     

Study of oxide nanostructure catalysts on polypropylene carrying agents for the removal of organic contaminants from water

Catalytic activity of oxide nanostructure catalysts fixed on the surface of polymeric carrying agents was studied in relation to the removal of organic substances difficultly decomposed by the chemical oxidation in the processes of ozonation of aqueous solutions.     

The bistable mode of second harmonic generation by femtosecond pulses

The possibility of controlling the efficiency of second harmonic generation by femtosecond pulses is demonstrated. By the phase shift in a certain cross section of the medium, switching from the low-efficient to the high-efficient generation state (and vice versa) is realized. The switching contrast in terms of the conversion efficiency is up to 4 (or more) and in terms of the peak intensity at the center of the pulse it is as high as 9. A new class of optical switches based on this effect is suggested.     

Achieving high-efficiency second harmonic generation in a sequence of laser pulses with random peak intensity. Part II. Suppression of intensity fluctuations in a quadratic-nonlinearity medium

The study examines suppression of peak intensity fluctuations in a sequence of fixed-energy femtosecond pulses by so-called cascade second harmonic generation (SHG). In Part II we analyze the propagation of a sequence of subpulses in an optical fiber without self-interaction characterized by cubic nonlinearity and large wavenumber detuning between the principal mode and the second harmonic. The propagation regimes discovered for a sequence of femtosecond pulses ensure suppression of peak intensity fluctuations. The mean peak intensity can be simultaneously increased by chirping the pulses in a particular section and also by adjusting the wavenumber detuning and increasing the quadratic nonlinearity while at the same time reducing to zero the phase of the distribution when the pulses pass to a new part of the nonlinear system. For Part I, See Prikladnaya Matematika i Informatika, No. 27, pp. 5–24, 2007; English Translation: Computational Mathematics and Modeling, Vol. 19, No. 4, pp. 333–342, 2008. Translated from Prikladnaya Matematika i Informatika, No. 28, pp. 5–36, 2008.     

Achieving high-efficiency second harmonic generation in a sequence of laser pulses with random peak intensity. Part III. Propagation of pulses in a bulk medium

Interpretation of geoelectric fields gives rise to multidimensional inverse problems, which include many problems for quasi-layered media. Such problems are solved by an iterative-asymptotic method. In the present article we consider a particular implementation of the method designed for a certain model of the medium, a certain method of solving the one-dimensional inverse problem, and a certain representation of magnetotelluric sounding data. For Parts I and II, see Prikladnaya Matematika i Informatika, No. 26, pp. 5–24, 2007 and No. 28, pp. 50–65, 2008; English translation: Computational Mathematics and Modeling, Vol. 19, No. 4, pp. 333–342, 2008 and Vol. 20, No. 1, pp. 1–25, 2009. Translated from Prikladnaya Matematika i Informatika, No. 29, pp. 5–18, 2008.     

Chemistry ofα-hydroxyamino oximes

The reaction of anti-α-hydroxyamino oximes with ketones gives substituted 1-hydroxy-3-imidazoline 3-oxides. The action of hydrogen chloride on the latter and on their acetyl derivatives leads to the isomeric 2-isoimidazole N-oxides differing by the position of the N-oxide oxygen in the isoimidazole ring. The structure of the latter compounds has been established by means of IR, UV, and PMR spectra and has been confirmed by independent synthesis.     

Conversion of N-(1-oximino-1-phenylpropyl-2)-α-phenylnitrone into imidazole N-oxide derivatives

Treatment of N-(1-anti-oximino-1-phenylpropyl-2)--phenylnitrone with benzoic anhydride in benzene leads to simultaneous formation of benzoyl derivatives both of the corresponding nitrone and of 1-hydroxymethyl-2, 4-diphenyl-3-imidazoline-3-oxide. Treatment of the latter with hydrogen chloride led to the isolation of 5-methyl-2, 4-diphenylimidazol-3-oxide. Its isomer 4-methyl-2, 5-diphenylimidazol-3-oxide is formed by the action of HCl on syn and anti isomers of N-(1-oximino-1-phenylpropyl-2)--phenylnitrone. IR and UV spectra are used to determine the structures of the compounds, which are confirmed by synthesis.     

Air-gap embedding GaN template for enhanced emission from light-emitting diodes

Selective growth by metal-organic chemical vapor deposition (MOCVD), and electrochemical etching of a heavily Si-doped GaN (n⁺-GaN) interlayer were employed to obtain air-gaps embedded in a u-GaN layer. As confirmed by Raman spectroscopy, the introduction of an n⁺-GaN, which was later etched to obtain air-gaps, also enhanced the strain-compliance of GaN epilayer on sapphire substrate. An enhanced electroluminescence emission was observed from the light-emitting diodes (LEDs) fabricated on the air-gap embedding template. Using theoretical LED simulation, it was discerned that the increase in optical emission from the LED was caused predominantly by the redirection of photons at GaN/air-gap interface. Finite-difference time domain (FDTD) simulation method was employed to understand the mechanism of optical emission enhancement and its spatial variation over the LED surface.     

Efficient second-harmonic generation for a high-intensity femtosecond pulse in the absence of group synchronism of interacting waves

A method is proposed to compensate for the influence of the group velocity mismatch on the frequency conversion efficiency for any ratio between the coefficients of square and cubic nonlinearities. The method allows the limiting efficiency of the frequency doubling to be achieved. This efficiency corresponds to the cases of phase and group synchronisms. For this purpose, it is necessary to apply a low-frequency phase modulation of the input radiation at the frequency of the first harmonic in combination with the optimal selection of the wavenumber mismatch. In practice, under certain conditions, this modulation can be obtained only with the aid of the wavenumber mismatch, whose optimal value is determined by the group velocity mismatch. The generation efficiency can be increased several times by introducing a phase shift in certain cross sections of the medium.