Lower bound for the convergence rate of nonstationary Jacobi-like iteration

Stationary and nonstationary Jacobi-like iterative processes for solving systems of linear algebraic equations are examined. For a system whose coefficient matrix A is an H-matrix, it is shown that the convergence rate of any Jacobi-like process is at least as high as that of the point Jacobi method as applied to a system with 〈A〉 as the coefficient matrix, where 〈A〉 is a comparison matrix of A.     

Structure and hydration of polycytidylic acid from the data of infrared spectroscopy, EHF dielectrometry and computer modeling

The aim of this paper is to summarize the original results concerned with the elucidation of the role of water environment in the formation of different structures of polyribocytidylic acid (poly(rC)), depending on the pH, temperature and ion content. To solve this problem, we studied the hydration of poly(rC)-K⁺ in films differing in water content, by methods of infrared spectroscopy and piezogravimetry, and in solution, using the dielectric measurements at a wavelength of 7.6 mm (extremely high frequencies — EHF). The experimental results were confirmed by a Monte Carlo simulation of the interaction between water molecules and single-strand and double-strand poly(rC) fragments in clusters of 800 water molecules. A model of hydration of double-strand complex of poly(rC)⁺-poly(rC) has been proposed based on our results and the known X-ray parameters of the complex. The obtained results and proposed structure of poly(rC)⁺-poly(rC) suggest that, the stabilization of this complex occurs due to intra- and inter-chain water bridges, together with the hydrogen bonds between neutral and protonated cytosines in pairs.     

A novel application of the chiral reagent (s)-2-N-(N′benzylprolyl)-aminobenzaldehyde: Synthesis of optically pure α-methylvaline and α-methylglutamic acid

The synthesis of -methyl substituted amino acids using Ni(II) complexes of the Schiff base obtained from alanine and (S)-2-N-(N'-benzylpropyl)amino-benzaldehyde is described. This complex was alkylated with isopropyl bromide, gramine iodomethylate, and methyl acrylate (in a Michael reaction). From the resulting mixtures of products, diastereomerically pure complexes were obtained by crystallization or silica gel chromatography. Both (S)- and (R)-enantiomers of the optically active amino acids -Me-Val and -Me-Glu were obtained after decomposing the diastereomerically pure complexes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1536–1542, July, 1991.     

Asymmetric synthesis of (R)-S-(1,2,4-triazol-3-yl)cysteines by nucleophilic addition of triazolethiols to a NiII complex with a chiral dehydroalanine Schiff base

An efficient method was developed for the asymmetric synthesis of (R)-S-(1,2,4-triazol-3-yl)cysteines by the addition of 3,4-disubstituted 1,2,4-triazole-5-thiols at the electrophilic C=C bond in a Ni^II complex of a Schiff base of dehydroalanine with (S)-N-(N-benzylprolyl)aminobenzophenone. The stereoselectivity of the formation of diastereomeric complexes with the (S,R) configuration under conditions of thermodynamic control of the nucleophilic addition exceeds 94%. Acid treatment of the reaction mixtures afforded enantiomerically pure (R)-S-hetarylcysteines (ee >98%).     

Algorithm and computer-program search for variants of polyomino packings in plane

An algorithm and a computer program that can be used in the search for all possible periodic packings of a specified set of polyominoes with a specified packing factor have been developed. The algorithm is based on the method of discrete modeling of molecular packings.     

Asymmetric opening of styrene oxide with p-toluidine catalyzed by BINOL polyols and their lithium complexes

Opening of racemic styrene oxide with p-toluidine catalyzed by chiral BINOL-derived polyols proceeded regioselectively mainly with the formation of 2-phenyl-2-(p-tolylamino)-ethanol with low ee values.     

Inverse problem in the layer-by-layer growth model

The problem of finding structural features of growing structures for which a specified growth shape is allowable is considered within the model of layer-by-layer growth of tilings or packings and the generalization of this model to connectivity graphs. In particular, the problem of revealing growth shapes that are impossible for periodic structures is solved.     

First observation of the doubly charmed baryon Xi(+)(cc)

We observe a signal for the doubly charmed baryon Xi(+)(cc) in the charged decay mode Xi(+)(cc)-->Lambda(+)(c)K-pi(+) in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1+/-0.5 events, a statistical significance of 6.3sigma. The observed mass of this state is 3519+/-1 MeV/c(2). The Gaussian mass width of this state is 3 MeV/c(2), consistent with resolution; its lifetime is less than 33 fs at 90% confidence.     

Assembly models for nanosized growth nuclei of crystal structures

Different growth models of crystal structures are briefly considered. A metric model of layer-by-layer sectoral growth proposed in [1] is described along with its application for computer modeling of the assembly of nanosized crystal growth nuclei by clusterizing the unit cell content.     

Modern Russian mass spectrometers for the atomic industry

Product quality control within the nuclear fuel cycle is a subject of special concern in Russia nowadays. Earlier, mass spectrometers of foreign production were commonly used for elemental and isotope analysis of samples. Currently, a series of domestic mass spectrometers MTI-350 has been developed and their production has been organized in Russia. The series comprises an automated MTI-350G mass spectrometer for the isotope analysis of uranium hexafluoride; thermal ionization MTI-350T mass spectrometer for the isotope analysis of uranium, plutonium, and mixed oxide (MOX) fuels; an MTI-350GS mass spectrometer for controlling the production of uranium hexafluoride; and an MTI-350GP mass spectrometer for the determination of the impurity concentration in uranium hexafluoride. The article considers operation principles, analytical characteristics, and the advantages of the above mass spectrometers.