Kinetic isotope effect 13C of cationic polymerization of oxygen-containing heterocycles. Structure of active centres. Mechanism of chain propagation

The results of studying the kinetic isotope effect of cationic polymerization of some oxygen-containing heterocycles are summarized. The use of this method made it possible to establish the oxonium mechanism of chain propagation and the existence of the step of preliminary monomer coordination on an active centre, preceding the polymeric chain propagation step.     

Autocatalysis in the formose reaction

It has been found that carbohydrates naturally present in ppm quantities in paraformaldehyde are the cause of the autocatalysis in the formose reaction of paraformaldehyde solutions. Paraformaldehyde sublimed into Ca(OH)₂ suspension was not transformed to sugars by formose reaction, only to methanol and formate by Cannizzaro reaction. A minute trace of glycolaldehyde — 3 ppm — was sufficient to initiate conventional autocatalysis. A formose reaction scheme in which formaldehyde reacts only with sugars by aldol condensation but not with itself is proposed.

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, , .. . , Ca(OH)₂, , , . — 3 .. — . , , .

     

Colorimetric determination of peroxidase activity in the presence of a polyanion

A procedure was developed for the determination of peroxidase activity with respect to substrates whose oxidation products were insoluble or poorly soluble in the reaction medium. It was demonstrated that the introduction of water-soluble sulfonated polystyrene to a reaction medium containing aniline and hydrogen peroxide made it possible to transform insoluble polyaniline to the highly dispersed state, preventing the formation of a deposit at the walls of the cuvette in the course of analysis. The addition of sulfonated polystyrene to the reaction medium improves the sensitivity of the determination of horseradish peroxidase.     

Finite element simulation of the loss of stable resistance in a foundation-soil system

Summary The fundamentals of the methodology for numerical simulation of non-linear behavior of the foundation-subsoil system by the finite element method are described. Constitutive laws governing the evolution of plastic zones in soil and crack development in concrete are used. These processes are known to proceed monotonously as the load increases, but can suddenly become avalanche-like. The latter phenomenon can terminate in the exhaustion of bearing capacity of the foundation subsoil system or in the stabilization of this system's state, and may be followed by an increase in resistance to loads. The developed algorithms and a code allow simulation of both phenomena. Examples of analysis are given.

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Finite-Element-Modellierung des Verlusts stabilen Widerstandes des Systems Fundament-Bodengründung

Übersicht Die Grundlagen für numerische Modellierung des nichtlinearen Verhaltens vom System Fundament-Bodengründung nach der Finite-Element-Methode werden dargelegt. Angewandt werden Stoffgesetze, die die Entwicklung plastischer Bereiche im Baugrunde und Rißbildung im Beton berücksichtigen. Bekanntlich entwickeln sich diese Erscheinungen in der Regel monoton mit der Belastungssteigerung, können sich aber auch lawinenartig entwickeln. Letztere Erscheinung kann mit der Erschöpfung der Tragfähigkeit des Systems Fundament-Bodengründung oder mit der Stabilisierung des Systems endan, worauf ein weiterer Widerstand gegen die steigende Belastung möglich ist. Ausgearbeitete Algorithmen und ein Programm erlauben es, beide Erscheinungen zu modellieren. Rechenbeispiele sind angeführt.

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Presented at the Workshop on Numerical Methods for Localisation and Bifurcation of Granular Bodies, held at the Technical Univeristy of Gdansk (Poland), September 25–30, 1989     

Low-lying 134Cs excited states from the (n, γ) reaction

Low-energy γ-ray and conversion electron spectra from the ¹³³Cs(n,γ)¹³⁴Cs reaction have been investigated with a bent cyrstal spectrometer, β-speetrometer, Ge(Li) and Si(Li) detectors. Gamma-gamma coincidence measurements were made with the Ge(Li)-Ge(Li) arrangement. Gamma-gamma delayed coincidences have been studied with the use of the Ge(Li)-NaI(Tl) coincidence set-up. The decay of 2.9 h ^134mCs has been investigated with the prism β-spectrometer and Ge(Li) detector. The half-lives of the 176.403 and 257.112 keV levels have been measured to be 49.7 ± 0.8ns and 12.3 ± 1.1 ns respectively. The neutron binding energy B_n have been calculated to be 6891.4 ± 1.3 keV. Spin and parity assignments have been made for almost all the levels. The possible structure of the levels deduced is discussed.     

Long-Term Forecasting of Solar Activity Indices Using Neural Networks

Using artificial neural networks (ANN), we study the possibility for long-term forecasting of the annual mean Wolf numbers and the monthly average solar radiation flux at 2800 MHz. A feedback ANN with error backpropagation was designed and implemented for this purpose. The software allows one to vary the number of input parameters and neurons and the values of the training parameters. The forecast error is calculated and the actual data are graphically compared to the predicted ones. The annual Wolf number was forecasted directly one year ahead using an auxiliary training (warming-up) of the ANN by the previous 18 values of the annual Wolf number entering the training sequence. The prediction efficiency was 92%. Adding the coronal index and the annual solar-radiation flux (i.e., the SF index) to the input parameters leads to some improvement of the forecast. The iterative long-term forecast of the annual Wolf number for 1986-2000 yielded an efficiency of 71%. Using the direct and iterative techniques, the annual Wolf number was forecasted for the rest of the 23rd and the beginning of the 24th cycles (2000-2010).