Formation of a two-dimensional periodic structure of local melting regions on a silicon surface upon pulsed light irradiation

The first results regarding the formation of a two-dimensional periodic structure of local melting regions on a silicon surface upon pulsed light irradiation are presented. The conditions are established, and the mechanism of the formation of such structures is discussed. Zh. Tekh. Fiz. 67, 97–99 (December 1997)     

Effect of iodine sorption on the free volume of polycarbonate

 The effect of iodine sorption on the free volume of polycarbonate is investigated by Positron Annihilation Lifetime method. The observed results are interpreted in terms of the Charge Transfer Complex formation and precipitation of iodine at the initial and final stages of sorption, respectively. At higher levels of sorption, changes in the second lifetime and its intensity seem to suggest a conformational transformation, probably due to the net change in the amorphous-crystalline boundary regions of the polymer matrix. The free volume cavities have been predominantly occupied by I^- ₃ species and the diffusion process obeys Fick’s law. An exponential type correlation has been observed between fractional free volume and the diffusion coefficient. Received: 13 June 1996/Accepted: 20 September 1996     

A poincaré-bendixson theorem for analytic families of vector fields

We provide a characterization of the limit periodic sets for analytic families of vector fields under the hypothesis that the first jet is non-vanishing at any singular point. Also, applying the family desingularization method, we reduce the complexity of some of these sets.     

Influence of the sulfonate countercation on the thermal stability of nafion perfluorosulfonate membranes

We report a strong dependence of the thermal stability of Nafion® perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation-exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i.e., Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate-coun-terion interaction. © 1993 John Wiley & Sons, Inc.     

Increasing the accuracy of eigenvalue computation in the spectral problem

A simple method is proposed for increasing the accuracy of computation of the eigenvalues of elliptic operators, which does not require high-order accurate schemes.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 63, pp. 63–68, 1987.     

Synthesis and ring-chain isomerism of acid chlorides and amides of 2-(2-pyridyl and 2-quinolylcarbonyl) benzoic acids

The reaction of 2-(2 pyridytcarbonyl)benzoic acid with thionyl chloride affords an unexpected product of the intramolecular acylation of the pyridine nitrogen atom, namely, 6,11-dioxo-6,11-dihydrobenzo[blquinotizinium chloride. At the same time, 2-(2-quinotylcarbonyl)benzoic acid forms the expected cyclic acid chloride, namely, 3-(2-gitinotyl)-3-chlorophthalide in this reaction. Both compounds acylate ammonia and primary amines, including those with bulky alkyl groups (tert-butyl, 1-adamantyl, and 1,1,3,3-tetramethylbutyl) with the formation of 2-R-3-hydroxy-3-(2pyridyl- or 2-quinolyl)isoindolines. The protonation of the pyridine nitrogen atom of N-(1,1,3,3-tetramethylbutyl)-2-(2pyridylcarbonyl)benzamide, obtained in the open amide form, is accompanied by the closing of the isoindotinone ring; the deprotonation is accompanied by ring opening.Riga Technical University, Riga LV-1048. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 499–504, April, 1994. Original article submitted March 17, 1994.     

Hydroxyl-containing mesogens. Synthesis and liquid-crystalline properties of 2-o-hydroxyarylpyrimidines

We have synthesized 5-alkyl(alkoxy)-2-(o-lzydroxy-p-alkoxyphenyl)pyrimidines and considered the effect of the OH group on the inesomorphism. We have found that in binuclear o-hydroxyarylpyrimidines, an ortho OH group forming an intramolecular hydrogen bond increases T_mp, inhibits the appearance of nematic properties, and promotes the appearance of a smectic A.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 30, No. 1, pp. 90–92, January, 1994.     

Lipids of cottonseed and palm oils and compositions based on them

The phsicochemical indices and the fatty-acid and triacylglycerol compositions of cottonseed and palm oils, of cottonseed oil hydrogenate, and of compositions based on them have been determined with the aid of IR and UV spectroscopies, GLC analysis, and chemical transformations. The compositions and amounts of the main classes of lipids in the initial oils and the hydrogenate have been studied. It has been found that in the process of hydrogenation the amount of oxygenated components falls. The work was conducted with the financial support of the Uzbek Fund for Fundamental Investigations.     

An investigation of the membranotropic properties of the plant toxin thionin isolated fromPyrularia pubera

It has been shown by the ESR of spin probes that thionin initially interacts with with negatively charged membranes electrostatically and then passes into the membranes to a depth comparable with the length of the hydrophobic sections of the protein loops.Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Brigham Young University, Provo, Utah, USA. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 594–597, July–August, 1993.