Modeling Strategies for the Propagation of Terminal Double Bonds During the Polymerization of N‐Vinylpyrrolidone and Experimental Validation

Based on a recently suggested reaction mechanism, which involves the production and propagation of terminal double bonds (TDBs), kinetic models for the polymerization of N‐vinylpyrrolidone in aqueous solution are developed. Two modeling strategies, the classes and the pseudodistribution approach, are applied to handle the multidimensional property distributions that result from this reaction mechanism and to get detailed structural property information, e.g., on the chain length distribution and the distribution of TDBs. The structural property information is then used to develop reduced models with significantly lower computational effort, which can be used for process design, on‐line applications or coupled to computational fluid dynamic simulations. To validate the derivations, the models are first compared against each other and finally to experimental results from a continuous stirred tank reactor. The evolution of monomer conversion and molecular weight average data as well as molecular weight distributions can be represented very well by the models that are derived in this article. These results support the correctness of the reaction mechanism predicted by quantum mechanical simulations.     

Connecting structural relaxation with the low frequency modes in a hard-sphere colloidal glass

Structural relaxation in hard-sphere colloidal glasses has been studied using confocal microscopy. The motion of individual particles is followed over long time scales to detect the rearranging regions in the system. We have used normal mode analysis to understand the origin of the rearranging regions. The low-frequency modes, obtained over short time scales, show strong spatial correlation with the rearrangements that happen on long time scales.     

The distribution of impurities in lysozyme crystals

The effective distribution coefficient, K_Ieff, of turkey egg white lysozyme into host hen egg white lysozyme crystals was measured for varying levels of relative supersaturation, impurity concentrations and temperatures. Turkey egg white lysozyme served as a test impurity of high homology to hen egg white lysozyme. K_Ieff increased with increasing host protein concentration and temperature, consistent with a kinetically controlled incorporation process. The principles of slow crystal growth rate to limit impurity incorporation were applied to a commercial source of lysozyme with concomitant improvement in purity of re-crystallized protein.     

The effect of topical anesthesia on vocal fold motion

The objective of this study was to determine if topical anesthesia to the larynx and pharynx affects vocal fold motion during dynamic voice evaluation with transnasal flexible endoscopy. Transnasal dynamic laryngeal examinations of 10 patients with no voice complaints were evaluated by five blinded fellowship-trained laryngologists. Each patient was examined before and after application of topical anesthetic. Reviewers rated briskness of right and left vocal fold movement and longitudinal tension on a visual analogue scale. Statistical comparisons were made between individual subject scores before and after anesthetic application. Inter-rater reliability was also assessed. No statistical difference was observed between subject scores before and after anesthetic application. Average intraclass correlation coefficients were 0.643 and 0.591 for pre- and postanesthesia scores, respectively. Application of topical anesthesia to the larynx and pharynx does not affect vocal fold motion.     

Mesh adaptation as a tool for certified computational aerodynamics

Mesh convergence order is a key for certification of the accuracy of numerical solutions. A few available results and tools in mesh adaption are synthetized in order to specify a mesh converging method for adaptive calculation of compressible flows including shocks or viscous layers. The main design property for this method is early second‐order convergence, where early means that the second‐order convergence is obtained with coarse meshes. Copyright © 2004 John Wiley & Sons, Ltd.     

等离子体边界层扩散时间演化的稳定性与突变 *

解析分析了外界控制下等离子体边界层扩散过程时间演化的稳定性与突变条件,并将这些条件应用于JFT-2M Tokamak,结果表明,一阶共振下粒子注入或(和)外加电场的无量纲幅值(ε₁或(和)ε₂)满足一定条件时系统处于稳定状态;二阶共振下当ε₁或(和)ε₂等于某值时系统会发生突变,从低约束态跃迁至高约束态.     

Determining a 'safe' high-mass limit in matrix-assisted laser desorption/ionisation time-of-flight mass spectra of coal derived materials with reference to instrument noise

Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd.     

Synthesis of New N-Pivot Lariat Crown Ethers Containing a Propylene Linkage in the Side Arm

A series of new 15- and 18-membered N-pivot lariat aza-crown ethers having a propylene linkage in the side arm was prepared starting from functionalized diethanolamines and functionalized lariat aza-crown ethers containing the easily modified benzotriazole moiety. Addition reactions of such derivatives to electron-rich vinyl ethers or vinylamides followed by displacement of the benzotriazolyl group in the addition products by hydrogen (by reduction with LiAlH(4)) gives a variety of N-(3-oxo-3-substituted)- and N-(3-aza-3-substituted)propylene side-armed derivatives of aza-crown ethers. Stability constants for the complexes of several synthesized lariats with metal cations are discussed.