On Schurity of Finite Abelian Groups

A finite group G is called a Schur group, if any Schur ring over G is associated in a natural way with a subgroup of Sym(G) that contains all right translations. Recently, the authors have completely identified the cyclic Schur groups. In this article, it is shown that any abelian Schur group belongs to one of several explicitly given families only. In particular, any noncyclic abelian Schur group of odd order is isomorphic to ?₃ × ?_{3 ^k} or ?₃ × ?₃ × ? _p where k ≥ 1 and p is a prime. In addition, we prove that ?₂ × ?₂ × ? _p is a Schur group for every prime p.     

2-mm resonance oscillator operating on the second spatial harmonic of a two-row periodic orotron structure

Orotron generation in the resonance BWO mode on the second spatial harmonic of a two-row periodic structure with the parameters l= 0.6 mm and d/l ～ 0.8 (l is the period and d is the groove width) has been observed for the first time. With a change in the voltage from 4.7 to 11 kV and the corresponding adjustment of the open resonator, frequency tuning in the range 94–140 GHz was obtained.     

Morphological transformations of native petroleum emulsions. I. Viscosity studies

Emulsions of water in as-recovered native crude oils of diverse geographical origin evidently possess some common morphological features. At low volume fractions varphi of water, the viscosity behavior of emulsions is governed by the presence of flocculated clusters of water droplets, whereas characteristic tight gels, composed of visually monodisperse small droplets, are responsible for the viscosity anomaly at varphi approximately 0.4-0.5. Once formed, small-droplet gel domains apparently retain their structural integrity at higher varphi, incorporating/stabilizing new portions of water as larger-sized droplets. The maximum hold-up of disperse water evidently is the close-packing limit of varphi approximately 0.74. At higher water contents (up to varphi approximately 0.83), no inversion to O/W morphology takes place, but additional water emerges as a separate phase. The onset of stratified flow (W/O emulsion gel + free water) is the cause of the observed viscosity decrease, contrary to the conventional interpretation of the viscosity maximum as a reliable indicator of the emulsion inversion point.     

One-step synthesis of heterocyclic privileged medicinal scaffolds by a multicomponent reaction of malononitrile with aldehydes and thiols

Heterocyclic privileged medicinal scaffolds involving pyridine, 1,4-dihydropyridine, chromeno[2,3-b]pyridine, and dihydro-1,4-dithiepine frameworks are prepared via a single-step multicomponent reaction of structurally diverse aldehydes with various thiols and malononitrile. Mechanistic studies of the synthetic pathway leading to pyridines reveal that 1,4-dihydropyridines undergo oxidation by the intermediate Knoevenagel adducts rather than by air oxygen. The use of o,o'-disubstituted aromatic aldehydes leads to the corresponding 1,4-dihydropyridines, whereas salicylic aldehydes result in chromeno[2,3-b]pyridines. Reactions of ethanedithiol as a thiol component produce dimeric pyridines with sterically unencumbered aldehydes, while o,o'-disubstituted aromatic aldehydes give dihydro-1,4-dithiepines. Thus, depending on the aldehyde and thiol types, diverse libraries of medicinally relevant compounds can be prepared by a simple one-step process involving no chromatography.     

Helical ordering of hydrogen bonds between pairs of DNA bases

The interaction between hydrogen bonds and conformational elastic degrees of freedom has been investigated using the simplest model of a double-strand DNA molecule. The hydrogen bonds are described in terms of two-level quantum systems. After excluding conformational degrees of freedom, one has effective interaction among two-level systems. In the ground state of an ideal double helix, hydrogen bonds in a DNA molecule also have a helical order induced by conformational degrees of freedom. The pitch of the hydrogen-bond helix (and even its sign under certain conditions) is different from that of the basic helix pitch and, generally speaking, is incommensurate with the latter. This effect can, possibly, lead to an inversion of the sign of the circular dichroism in spectral bands, which was detected in some experiments. Zh. éksp. Teor. Fiz. 115, 940–950 (March 1999)     

Isomorphism of Coloured Graphs with Slowly Increasing Multiplicity of Jordan Blocks

n -vertex edge coloured graphs with multiplicity of Jordan blocks bounded by k can be done in time . Received: November 29, 1994     

Asymmetry of the propagation of conformational excitations in a double-strand DNA molecule

A very simple model describing the conformational degrees of freedom of a double-strand DNA molecule is proposed. It is shown that the characteristic modes of the model consist of an acoustic (longitudinal with respect to the axis of the double helix) and two transverse optical modes. The latter modes are directly related with the deformations of the ideal structure of the double helix, which necessarily leads to softening of one of the optical modes on a finite wave vector. It is found that the conformational excitations propagating in DNA are asymmetric. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 11, 766–770 (10 December 1999)     

2-Adic wavelet bases

Within the theory of multiresolution analysis, a method of constructing 2-adic wavelet systems that form Riesz bases in L ²(ℚ₂) is developed. A realization of this method for some infinite family of multiresolution analyses leading to nonorthogonal Riesz bases is presented.     

Purification of Xenogeneic Bone Matrix by Extraction with Supercritical Carbon Dioxide and Evaluation of the Obtained Material

An environmentally friendly method of osteoplastic material production is proposed for reconstructive surgery needs based on treatment of xenogeneic bone matrix with supercritical carbon dioxide. The method provides the best extraction of lipids and fatlike substances at minimum cost of extracting agent and processing time; it allows the significant reduction of costs and facilitates the manufacture of surgical implants. The advantages of the obtained material in comparison with the known commercial analogue are demonstrated by in vitro experiments on the cellular model.     

Probing structural integrity of single walled carbon nanotubes by dynamic and static compression

We report on a first study of single walled carbon nanotubes (SWCNTs) after application of dynamic (shock) compression. The experiments were conducted at 19 GPa and 36 GPa in a recovery assembly. For comparison, an experiment at a static pressure of 36 GPa was performed on the material from the same batch in a diamond anvil cell (DAC). After the high pressure treatment the samples were characterized by Raman spectroscopy and transmission electron microscopy (TEM). After exposure to 19 GPa of shock compression the CNT material exhibited substantial structural damage such as CNT wall disruption, opening of the tube along its axis (“unzipping”) and tube shortening (“cutting”). Dynamic compression to 36 GPa resulted in essentially complete CNT destruction whereas at least a fraction of the nanotubes was recovered after 36 GPa of static compression though severely damaged. The results of these shock wave experiments underline the prospect of using SWCNTs as reinforcing units in material WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)