Experimental study of the reverse flow in the forward separation region in a pulsating flow around a spiked body

The flow with a free-stream Mach number M _∞ = 6 around a cylindrical body with a sharp spike is studied. The existence of a supersonic reverse flow for one of the phases of the pulsating flow regime is experimentally validated. A range of spike lengths is determined, which ensures a region of a supersonic reverse flow near the side surface of the spike. The time of existence of the supersonic reverse flow region is shown to be 0.15 of the period of pulsations if the spike length equals the model diameter. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 30–39, July–August, 2007.     

Searching for preferential arrival directions of ultrahigh-energy cosmic rays on the Moscow State University EAS array

There is evidence for possible clustering in the arrival directions of extensive air showers (EASs). A program for analyzing EAS arrival directions has been developed to investigate this problem and the database of the Moscow State University EAS array for 1982–1989 has been analyzed. The distributions in equatorial coordinates have been derived for cosmic rays with energies E ≥ 2 × 10¹⁵ eV and zenith angles <40°. The uniformity of the derived distributions is verified using various statistical tests.     

High-pressure clathrate hydrate of acetone

X-ray diffraction study of quenched sample of acetone clathrate hydrate synthesized at 0.8 GPa was carried out. It was shown that the host frameworks of the hydrate comprise uniform cavities which are similar to that of recently characterized structure of high-pressure tetrahydrofurane hydrate. The unique peculiarity of investigated hydrate is decrease in the crystallographic symmetry of the hydrate arising from ordering in guest subsystem.     

Updating the Chemiluminescence Oxygen‐Aftereffect Method for Determining the Rate Constant of the Peroxy‐Radical Self‐Reaction: Oxidation of Cyclohexene

Updating the facile chemiluminescence oxygen‐aftereffect method, most suitable for determining the rate constant (k_t) of the peroxy‐radical self‐reaction (main chemiluminescence channel), pertained to considering the sensitivity of such a method toward a disturbing influence of the peroxy radicals of the initiator of the chain oxidation process. Such a disturbance may derive from the side chemiluminescent reaction, which involves peroxy radicals of both hydrocarbon and initiator. To examine the applicability and limitations of the chemiluminescence method under present scrutiny, cyclohexene was used as the model oxidizable hydrocarbon substrate. Computer simulations of the reaction and chemiluminescence kinetics have demonstrated the validity of the considered methodology at the value of the rate constant of the propagation of the overall chain process by peroxy radicals of the initiator higher than 1 m ^?1 s^?1. Despite that the chemiluminescence time profile and the stationary level of the total chemiluminescence intensity depend on the kinetics of the side chemiluminescence channel and on the ratio of the excited‐state generation yields in the mentioned reaction channel and in the main chemiluminescence process, the value of k_t assessed by the oxygen‐aftereffect method has been found independent of variation of these characteristics.     

Strain softening in stretched DNA

The microscopic mechanics of DNA stretching was characterized using extensive molecular dynamics simulations. By employing an anisotropic pressure-control method, realistic force-extension dependences of effectively infinite DNA molecules were obtained. A coexistence of B and S DNA domains was observed during the overstretching transition. The simulations revealed that strain softening may occur in the process of stretching torsionally constrained DNA. The latter observation was qualitatively reconciled with available experimental data using a random-field Ising model.     

Efficient methodology for selective alkylation of hydrazine derivatives

Formation and use of a nitrogen dianion for selective hydrazine alkylation is reported. The scope and limitations of a new method were demonstrated. The novel method provides fast and easy access to substituted hydrazines, which are widely used as drugs, pesticides, and precursors for a variety of compounds in organic synthesis. [reaction: see text]     

The first synthesis of furazano[3,4‐b][1,6]naphthyridines

Reaction of 6‐acetyl‐7‐aminofurazano[3,4‐b]pyridines with DMFDMA afforded N,N‐dimethylformamidines that were cyclized to the novel furazan‐fused [1,6]naphthyridine system by treatment with sodium methylate in good yield. The tricyclic system is characterized by X‐ray crystallography.