Molecular reorientation and phase transition in pyridinium hexafluoroantimonate

The temperature dependence of ¹H and ¹⁹F NMR second moment and spin lattice relaxation times in high (v _L = 60 MHz and low (B ₁ = 2 mT) magnetic fields allow one to determine both ion dynamics in polycrystalline pyridinium hexafluoroantimonate. The solid-solid phase transition discovered at 268 K appears to be connected with symmetrization of energy barriers for pseudohexagonal cation reorientation. The energy difference Δ characterizing the inequivalence of the potential wells can be treated as an order parameter. The effect of coupling of the rotational modes of cations and anions is found at the phase transition.     

DSC and EPR analysis of some radiation sterilized alkaloids

The effect of ionising radiation on the physico-chemical properties of salts of three alkaloids has been studied: codeine phosphate (COD), papaverine hydrochloride (PAP) and pilocarpine hydrochloride (PIL). These compounds in the solid state were irradiated with an e-beam of the energy of 9.96 MeV to achieve doses ranging from 25 to 400 kGy, and then they were subjected to organoleptic analysis, thermal analysis (differential scanning calorimetry, DSC), electron resonance (EPR) spectroscopy, scanning electron microscopy observations and X-ray diffraction study. The most informative were the results provided by the EPR and DSC methods. The EPR spectra revealed the presence of long-lived radicals whose concentration was directly proportional to the dose of irradiation for all the compounds studied. (PIL 2.14 × 10¹⁶ spin/g, COD 6.85 × 10¹⁵ spin/g, PAP 2.50 × 10¹⁴ spin/g—for the dose of 100 kGy). The DSC results revealed a decrease in the melting point by 5.9 °C for COD and by 0.8 °C for PIL after irradiation with 200 kGy, which is indicative of products of radiolysis, of which at least one is non-white, and changes the colour of the compounds. PAP, for which no decrease in the melting point and no colour change was observed and for which the concentration of free radicals was the lowest, was found to be most stable from among the compounds studied. It will probably be suitable for radiation sterilisation. The other two compounds COD and PIL show much lower radiochemical stability and should be subjected to more detailed examination to establish the mechanism of radiolysis and the possibility of radiation sterilisation. Our results have confirmed the earlier reports on high radiochemical stability of PAP, but do not confirm the resistance to ionising radiation of COD and PIL.     

Gold(I)-catalyzed intramolecular tandem addition/Friedel-Crafts reactions between acyclic enamides and 1-arylalkynes

Electron-deficient acyclic enamine derivatives react with electron-rich 1-arylalkynes using cationic gold(I) species as catalysts in an intramolecular process to form annulated 1-amido-substituted indene derivatives as the major products. Yields for this process range between 21% and 98%. In some cases, a two-step process that includes a subsequent alkene isomerization is needed.     

Asymmetric Diels-Alder Reaction of 1-Methoxybuta-1,3-diene with (2R)-N-Glyoxyloylbornane-10,2-sultam

Starting from sultam 1 , the chiral dienophile (2R)-N-glyoxyloylbornane-10,2-sultam ( 4 ) was readily prepared. Non-catalyzed atmospheric- and high-pressure as well as [Eu(fod)₃]-promoted [4 + 2] cycloadditions of 1-methoxy-buta-1,3-diene ( 5 ) to chiral dienophile 4 , leading with high asymmetric induction to 6-methoxy-3,6-dihydro-2H-pyran-2-yl derivatives 6 – 9 , are described. The extent and direction of asymmetric induction in these reactions were established by ¹H-NMR analysis and chemical correlation, respectively. Stereochemical models for both non-catalyzed and [Eu(fod)₃]-promoted reactions are proposed.     

Stratified two-stage sampling in domains: Sample allocation between domains, strata, and sampling stages

In the paper, formulae for optimum sample allocation between domains, strata in the domains, and sampling stages are presented for stratified two-stage sampling in domains under fixed sample size of SSUs from PSUs.     

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     

Refractive index dispersion in Y2O3 thin films obtained by different methods

We have studied refractive index dispersion in Y₂O₃ thin films obtained by stepwise vaporization and high-frequency ion plasma spraying in different atmospheres. We have established that regardless of the method used to obtain the films, the spectral dependence of the refractive index in the visible region of the spectrum is mainly determined by transitions from the band of 2p states of the oxygen, forming the highest unoccupied level of the valance band, to the bottom of the conduction band, formed by the 4d5s states of the ytrrium. For the studied films, we have determined the parameters of the single-oscillator approximation, the dispersion energy, the ionicity of the chemical bond, and the coordination number. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 129–132, January–February, 2006.     

Systematic investigation of the avalanche effect in highly thulium-doped fiber amplifiers

The avalanche energy transfer in highly thulium doped fiber amplifiers (TDFA) pumped at 1056 nm with laser diodes was investigated. Amplified spontaneous emission (ASE) at 800 nm and 1470 nm as well as the remaining pump power were measured as function of the pump power to explain the efficiency of the energy transfer between thulium ions. As proof of our theory, fiber amplifiers based on self-made fluoride fibers doped with 2000 and 5000 ppm thulium were realized and their gain and noise figure was measured. A gain of more than 25 dB and a noise figure of less than 4 dB was achieved at a pump power of 210 mW in a TDFA using the 5000 ppm thulium fiber, whereas a gain maximum of only 5.6 dB was observed with the 2000 ppm TDF. These investigations are of special importance since until now almost all TDFAs have used 2000 ppm fibers. PACS 83.80.Ab; 32.80.Bx; 42.65.Yj