EPR and DFT study of the ethylene reaction with O− radicals on the surface of nanocrystalline MgO

Research on Chemical Intermediates - Different radical forms of oxygen (O?, O 2 ? and O 3 ? ) on the surface of nanocrystalline MgO are well known. It was earlier demonstrated...     

Synthesis and mechanism of formation of 5-benzylidene-2-thioxo-2,3-dihydro-(1H,5H)-pyrimidine-4,6-diones difluoromethoxy derivatives

Reactions of 5-benzylidene-2-thioxo-2,3-dihydro-(1H,5H)-pyrimidine-4,6-diones with a singlet difluorocarbene afford difluoromethoxy derivatives in 20–34% yield. The quantum-chemical analysis of the reaction mechanism showed that N,N-dimethylformamide is involved into the formation of difluoromethoxy derivatives.     

Harmonic analysis on spherical homogeneous spaces with solvable stabilizer

For all spherical homogeneous spaces G/H, where G is a simply connected semisimple algebraic group and H a connected solvable subgroup of G, we compute the spectra of representations of G on spaces of regular sections of homogeneous line bundles over G/H.     

Hydrojet engine with pulse detonation combustion of liquid-fuel

An experimental prototype of an engine of a new type for water transport—pulse detonation hydroramjet—was designed, built, and tested for the first time. Firing test of the prototype with a 2-L combustor was performed on a specially designed test stand with a thrust-measuring frame capable of producing an approach water stream in the form of a submerged jet with a velocity up to 10 m/s. The specific impulse was experimentally measured, ranging from 370 s at high operation frequency (20 Hz) to 1200 s at low operation frequency (1 Hz); i.e., the measured specific impulse of the pulse detonation hydroramjet exceeded that of the best modern liquid rocket engines.     

Molecular dynamics simulation analysis of small-angle neutron scattering by a solution of stearic acid in benzene

Data of small-angle neutron scattering by a diluted solution of stearic acid in deuterated benzene have been analyzed using the results of molecular dynamics simulation. The molecular dynamics simulation approach has been used to calculate the time-averaged distribution of the neutron scattering length density at the interface between the acid molecule and the solvent. It has been shown that the organization of the solvent at the interface with the acid molecule leads to a modulation of the neutron scattering length density and makes a significant contribution to the scattering. This contribution should be taken into account when interpreting the experimental small-angle neutron scattering curves for both the considered system and its analogues.     

High temperature magnetic ordering in the 4d perovskite SrTcO3

We present evidence for possibly the highest magnetic ordering temperature in any compound without 3d transition elements. Neutron powder diffraction measurements, at both time-of-flight and constant wavelength sources, were performed on two independently prepared SrTcO3 powders. SrTcO3 adopts a distorted perovskite structure with G-type antiferromagnetic ordering and has a moment of 1.87(4)μB per Tc cation at room temperature with an extraordinarily high Néel point close to 750 °C. Electronic structure calculations reveal extensive mixing between the technetium 4d states and oxygen states proximal to the Fermi level. This hybridization leads to a close relationship between magnetic ordering temperature and moment formation in SrTcO3.     

Pressure‐Induced Intersite BiM (M=Ru, Ir) Valence Transitions in Hexagonal Perovskites

Pressure‐induced charge transfer from Bi to Ir/Ru is observed in the hexagonal perovskites Ba_3+nBiM_2+nO_9+3n (n=0,1; M=Ir,Ru). These compounds show first‐order, circa 1 % volume contractions at room temperature above 5 GPa, which are due to the large reduction in the effective ionic radius of Bi when the 6s shell is emptied on oxidation, compared to the relatively negligible effect of reduction on the radii of Ir or Ru. They are the first such transitions involving 4d and 5d compounds, and they double the total number of cases known. Ab initio calculations suggest that magnetic interactions through very short (ca. 2.6 Å) M? M bonds contribute to the finely balanced nature of their electronic states.     

Nonmonotonic behavior of the concentration in the kinetics of dissolution of fullerenes

A cluster model for the dissolution of C₆₀ fullerenes in a nonpolar solvent has been proposed. This model provides the explanation of a maximum experimentally observed in the time dependence of the solution concentration during dissolution. The model is based on the kinetic equations of nucleation theory and involves a balance between the flux of fullerene molecules from the solid phase and the sedimentation of large clusters from the solution. The formation of clusters is described using the drop model. Analysis of the numerical solutions of the equations reveals four qualitatively different dissolution regimes depending on the relation between the model parameters.     

Review of results of HF scattering by artificial ionospheric turbulence obtained with UTR-2 radio telescope

The results of bistatic-radar and transillumination studies of the F-layer under the influence of powerful radio waves (Sura heating facility, Nizhny Novgorod) are presented. A highly directional receiving antenna (UTR-2, Kharkov) made it possible to detect and interpret a number of fine-structure characteristics of the Doppler spectrum of a signal scattered by a heated region. It is shown that, in addition to regular drift, there exists relative ordered motion of inhomogeneities in a perturbed region. The relative velocity is estimated. Deformation of the spectrum of a scattered signal in the states of development and relaxation is established and studied, and possible mechanisms of this phenomenon are discussed. Quasi-periodic variations of the amplitude and frequency of a scattered signal with periods of 30 sec to 5 min are detected. A comparison is made with the results of simultaneous radio transillumination of a heated region by signals from the point source Cassiopeia.Scientific-Research Radio-Physics Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 4, pp. 479–492, April, 1994.     

Gamma-ray bursts from evaporating primordial black holes

It is believed that the detection of gamma-ray bursts from evaporating primordial black holes is highly improbable in the near future since the expected photon flux, consisting mainly of photons with energies ? GeV, is too low. Contrary to this point of view, we show that a large fraction of the black hole power at the final stage of evaporation (the last 10³ s) can be liberated as a burst of soft γ-ray emission of duration 10^?1–10³ s and luminosity 10²⁸–10³¹ erg/s in the energy range 0.1–1 MeV. According to our calculations of the black hole evaporation rate (within the Standard Model of elementary particles), when the black hole temperature exceeds approximately 10 GeV, the charged particle outflow from a black hole forms a well-defined plasma and can be described in the hydrodynamic approximation. In this case more than half of the rest energy of a black hole can be converted into soft gamma-rays due to the presence of the magnetic field with energy density comparable to that of charged particles. We consider various mechanisms leading to such transformation and estimate their efficiency. It is shown that, at least, some of the gamma-ray bursts detected by BATSE can be associated with evaporating black holes.