Fast deflagration-to-detonation transition

Studies of fast deflagration-to-detonation transition in gas and drop air-fuel explosive mixtures are reviewed. Fast deflagration-to-detonation transition is understood as the appearance of detonation at which a turbulent flame is sped up to a much lower velocity than that required for the classic deflagration-to-detonation transition in a straight tube with smooth or rough walls. The main goal of studies was to determine conditions under which fast deflagration-to-detonation transition was possible in weakly sensitive explosive mixtures at very low ignition energies. Examples of fast deflagration-to-detonation transitions checked experimentally and by multidimensional numerical calculations are given, including deflagration-to-detonation transitions (1) in a tube segment with regular obstacles of a special shape, (2) in tube coils, and (3) in tubes with U-shaped bends. In all cases, fast deflagration-to-detonation transition occurs because of the formation of distributed ignition zones in reflections of a running shock wave formed by an accelerated flame. The use of various combinations of reflecting elements can induce fast deflagration-to-detonation transition in an air mixture of aviation kerosene at ignition energies at a level of 5 J.     

A modified model of the ignition of a magnesium particle

A model of the ignition of an isolated magnesium particle in an oxidative atmosphere is suggested. The model takes into account the nonstationary character of the heat flux onto the surface of the particle and the nonuniformity of temperature distribution inside the particle. Calculations were performed to demonstrate the influence of these factors on the macrokinetic parameters of the empirical law of the oxidation of magnesium particles and the time characteristics of their ignition in hot air at atmospheric pressure.     

Some distinctive features in the behavior of small-scale artificial ionospheric irregularities at mid-and high latitudes

We present the results of experimental studies of some features in the behavior of small-scale artificial irregularities (SSAIs) at mid-and high latitudes based on the “Sura” and EISCAT/HEATING HF facilities. Observations were performed by the method of aspect scattering using a network of diagnostic paths having a common reception point located near St. Petersburg. We found that an extremely long duration of the second (slow) stage of SSAI relaxation of up to 5 min occurs in the evening hours when the ionosphere above the “Sura” facility is illuminated by the Sun, but the solar terminator travels through the magnetically conjugated ionosphere. The conjecture is made that the processes initiated by the terminator are mostly responsible for secondary ionospheric turbulence maintaining the irregularities above “Sura.” A drastic increase in the Doppler spectra width of the scattered signals is revealed when the magnetically conjugate point of the ionosphere is located on the shade side of the terminator, but the ionosphere above the “Sura” facility is still lighted. It is assumed that the “ run away” of photoelectrons from the day to the night side could reduce the threshold of excitation of artificial irregularities, leading to an increase in their intensity. The presence of fairly intense scattered signals was detected from the “Sura” and EISCAT/HEATING experimental results both under conditions of pulsed HF heating after continuous heater-on periods and cycled HF heating by short pulses. In the case of pulsed heating by short pulses with duration τ_p < 100 ms and average radiated power P_a below the threshold power P_thr of the SSAI generation cutoff the irregularities can be maintained due only to striction parametric instabilities. The excitation of irregularites under the cycled HF pumping with the pulse duration τ_p = 384 ms for P_a comparable with P_thr was detected. The aspect-angle dependence, or the so-called magnetic zenith effect, was found in the SSAI intensity. The residual turbulence aftereffects played a significant role in the SSAI development. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 8, pp. 678–694, August 2007.     

Two-prong πHe interactions at 106 MeV

π^-4He interactions at 106MeV, with two secondary charged particles in the final state, have been studied using a self-shunted streamer chamber in a 0.65T magnetic field and equipped with two CCD videocameras for obtaining digitized stereo-images of nuclear events occurring within the fiducial volume of the streamer chamber. Branching ratios for the various interaction channels are deduced. Evidence is presented for a reaction channel involving a γ produced in the final state, as well as for the first observation of direct Δ^- -resonance production. Cross-section distributions for the elastic and quasi-elastic interaction channels are also reported.     

A note on Δ 2 0 -Spectra of linear orderings and degree spectra of the successor relation

In this paper we construct linear orderings whoseΔ ₂ ⁰ -spectra coincide with classes of all high₀ and high₁ degrees, respectively. We also prove that there exists a computable linear ordering such that its degree spectrum of the successor relation coincides with a fixed nonempty class of degrees which represents a Σ ₁ ⁰ -spectrum of some Ø′-computable linear ordering.     

Light sensitivity of photoconducting polymer systems with polymethine dyes based on derivatives of 2(4)-methylquinoline and indole

The photosensitivity of conducting polymer films with newly synthesized polymethine dyes is investigated. It is demonstrated that the photosensitivity of polymer films based on poly(o-hydroxyamide) with transport indole molecules forming intermolecular complexes with dyes is two or three times higher than the photosensitivity of the polymer films containing indole as a structural component of the dye. The introduction of the indole-containing dye into the photoconducting poly(vinylcarbazole) leads to an increase in the photo-conductivity by one and a half orders of magnitude. In this case, the quantum yield increases to η = 0.085. A correlation is revealed between the electronic structure of the dyes, the characteristics of the photoconduction in the materials under investigation, and the mechanisms of charge relaxation in the samples. An increase in the photoconductivity of the films results in the crossover from the drift mechanism of charge relaxation to the relaxation mechanism associated with intrinsic electrical conduction.     

Synthesis and Analgesic Activity of New Heterocyclic Cyanothioacetamide Derivatives

Russian Journal of General Chemistry - The reaction of cyanothioacetamide with aromatic aldehydes and 1,3-dicarbonyl compounds followed by aminomethylation or S-alkylation gave a series of...     

N-alkylation of <Emphasis Type="Italic">N</Emphasis>-trimethylsilylimidazole

The reaction of N-trimethylsilylimidazole with alkyl chloroacetates is studied. This process yields a mixture of N-alkylation and quarternization products in the ratio dependent on the reaction conditions. The reaction mechanism is discussed. ¹H NMR data show that high melting point and low solubility of 1-imidazolylacetic acid in organic solvents are evidently caused by the formation of strong intermolecular hydrogen bonds, whereas in water zwitterionic structures with the protonation of both nitrogen atoms are formed.     

Field shifts and lowest order QED corrections for the ground 1 1S and 2 3S states of the helium atoms

The bound state properties of the ground 1 1S(L=0) state and the lowest triplet 2 3S(L=0) state of the 3He, 4He, and infinityHe helium atoms are determined to very high accuracy from the results of direct numerical computations. To compute the bound state properties of these atoms the author applied his exponential variational expansion in relative/perimetric three-body coordinates. For the ground 1 1S(L=0) state and the lowest triplet 2 3S(L=0) state of the 3He, 4He, and infinityHe atoms the author also determined the lowest order QED corrections and the field component of isotopic shift (=field shift). For the 2 3S(L=0) state of the 3He atom the hyperfine structure splitting is evaluated. The considered properties of the ground 1 1S state and the lowest 2 3S state in the 3He and 4He atoms are of great interest in a number of applications.     

Aminomethylation of N-methylmorpholinium 6-amino-4-aryl-3,5-dicyano-1,4-dihydropyridine-2-selenolates as an approach to the preparation of 3,5,7,11-tetraazatricyclo[7.3.1.02,7]tridec-2-ene-8-selenone derivatives

A reaction of N-methylmorpholinium 6-amino-4-aryl-3,5-dicyano-1,4-dihydropyridine-2-selenolates with primary amines and excess of formaldehyde leads to 3,5,7,11-tetraazatricyclo[7.3.1.0^2,7]tridec-2-ene-8-selenone derivatives. The same compounds were obtained by a multicomponent cascade cyclocondensation of benzaldehyde, cyanoselenoacetamide, primary amine, and excess of formaldehyde.