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111.
The paper presents a new formulation of the integral boundary element method (BEM) using subdomain technique. A continuous approximation of the function and the function derivative in the direction normal to the boundary element (further ‘normal flux’) is introduced for solving the general form of a parabolic diffusion‐convective equation. Double nodes for normal flux approximation are used. The gradient continuity is required at the interior subdomain corners where compatibility and equilibrium interface conditions are prescribed. The obtained system matrix with more equations than unknowns is solved using the fast iterative linear least squares based solver. The robustness and stability of the developed formulation is shown on the cases of a backward‐facing step flow and a square‐driven cavity flow up to the Reynolds number value 50 000. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
112.
Fukuji Higashi Kanako Sugishita 《Journal of polymer science. Part A, Polymer chemistry》2004,42(1):44-51
A two‐stage co‐oligomerization of the oligomers initially formed from an equimolar mixture of isophthalic acid (IPA) and terephthalic acid (TPA) and 2,2‐bis(4‐hydroxyphenyl)propane (BPA, 50 mol %) with bisphenols (BPs, 20 mol %) was carried out using a tosyl chloride/dimethylformamide/pyridine condensing agent. The distributions of the resulting oligomers (nx‐mers), which were quenched with methanol, were determined by a combination of gel permeation chromatography (GPC) and NMR. These distributions (presented by molar percentage) were conveniently calculated with the equation nx (mol %) = nx (% mol by GPC) × n0 (mol % by NMR)/n0 (% mol by GPC), where nx (% mol) = nx (wt % by GPC)/its molecular weight. The results showed the distributions of the preformed IPA/TPA‐BPA oligomers to be in fairly good accord with those obtained directly from GPC and to be supported by the NMR results. The calculation was applied to the co‐oligomers prepared up to a reaction of 0.7, at which there was an increase in the number of higher oligomers indivisible by GPC and the distributions could no longer be determined by molar percentage. The calculated distributions are discussed in relation to the results of copolycondensation. The sequence distributions in the resulting co‐oligomers, which were also examined by NMR, are compared with those in the copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 44–51, 2004 相似文献
113.
Thomas Pautzsch Elisabeth Klemm 《Journal of polymer science. Part A, Polymer chemistry》2004,42(12):2911-2919
Poly{bis(4,4′‐tert‐butyl‐2,2′‐bipyridine)–(2,2′‐bipyridine‐5,5′‐diyl‐[1,4‐phenylene])–ruthenium(II)bishexafluorophosphate} ( 3a ), poly{bis(4,4′‐tert‐butyl‐2,2′‐bipyridine)–(2,2′‐bipyridine‐4,4′‐diyl‐[1,4‐phenylene])–ruthenium(II)bishexafluorophosphate} ( 3b ), and poly{bis(2,2′‐bipyridine)–(2,2′‐bipyridine‐5,5′‐diyl‐[1,4‐phenylene])–ruthenium(II)bishexafluorophosphate} ( 3c ) were synthesized by the Suzuki coupling reaction. The alternating structure of the copolymers was confirmed by 1H and 13C NMR and elemental analysis. The polymers showed, by ultraviolet–visible, the π–π* absorption of the polymer backbone (320–380 nm) and at a lower energy attributed to the d–π* metal‐to‐ligand charge‐transfer absorption (450 nm for linear 3a and 480 nm for angular 3b ). The polymers were characterized by a monomodal molecular weight distribution. The degree of polymerization was approximately 8 for polymer 3b and 28 for polymer 3d . © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2911–2919, 2004 相似文献
114.
Jeremy R. Lizotte Sara G. Anderson Timothy E. Long 《Journal of polymer science. Part A, Polymer chemistry》2004,42(7):1547-1556
A novel dinitroxide mediating agent that was suitable for stable free‐radical polymerization was synthesized and used in the block copolymerization of styrene and t‐butyl styrene. Quantitative yields of a novel dinitroxide based on 1,6‐hexamethylene diisocyanate and 4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy were obtained. Various experimental parameters, including the nitroxide‐to‐initiator molar ratio, were examined, and it was determined that the polymerization was most controlled under conditions similar to those of conventional 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐mediated stable free‐radical polymerization. Moreover, the dinitroxide mediator proved to be a viable route for the facile two‐step synthesis of triblock copolymers of styrene and t‐butyl styrene. However, the dinitroxide mediation process resulted in a higher than expected level of nitroxide decomposition, which resulted in polymers possessing a terminal alkoxyamine and an adjacent hydroxylamine rather than a preferred internal bisalkoxyamine. This decomposition resulted in the formation of diblock copolymer species during the triblock copolymer synthesis. Gel permeation chromatography was used to monitor the chain‐end decomposition kinetics, and the determined observed rate constant (5.89 × 10?5 s?1) for decomposition agreed well with previous studies for other dinitroxide mediating agents. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1547–1556, 2004 相似文献
115.
Dong Il Han Hoe Jin Hah Hong-Woo Park Sang Man Koo 《Journal of Sol-Gel Science and Technology》2004,32(1-3):47-51
Composite silica particles were synthesized by a two-step (acid-base) process in an aqueous solution with a mixture of organoalkoxysilane monomers. The two-step process separates the hydrolysis and condensation procedures to easily control condensation rate. In this study, the silane monomers used were phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), methyltrimethoxysilane (MTMS), and tetraethyl-orthosilicate (TEOS). The physical properties of the resultant composite particles were investigated with the change in the molar ratio of monomers. The size of the particles increased with increasing the molar ratio of RaSi(OR)3/RbSi(OR)3 or RaSi(OR)3/TEOS (Ra: phenyl; Rb: vinyl, methyl). 相似文献
116.
Fukuji Higashi Kaori Kira 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2725-2733
The solution polyesterification of dicarboxylic acids in pyridine, the activated intermediates of which were difficult to dissolve in tosyl chloride/dimethylformamide/pyridine, was investigated in the presence of lithium chloride. The solubility of the activated dicarboxylic acids was largely improved by the presence of the salt, and the polycondensation with bisphenols was greatly facilitated. The salt was more effectively added to a pyridine solution of dicarboxylic acids than to the activated dicarboxylic acids in pyridine. The favorable additive effect on the improved solubility was attributed to a lowered degree of association of the activated dicarboxylic acids, which led to distributions of the resulting oligomers from bisphenols at an earlier stage closer to the theoretical ones and yielded better polycondensation results. The reaction, which proceeded through favorable distributions of the co‐oligomers, produced copolymers of higher inherent viscosities and slightly block sequence distributions determined by NMR. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2725–2733, 2004 相似文献
117.
Hidetaka Tobita 《Journal of Polymer Science.Polymer Physics》2004,42(14):2801-2812
The matrix formula developed in the context of heterochain theory, M?w = M?wp + WF ( I ? M )?1 S , was applied to describe the molecular weight development during free‐radical multicomponent polymerization. All of the required probabilistic parameters are expressed in terms of the kinetic‐rate constants and the various concentrations associated with them. In free‐radical polymerization, the number of heterochain types, N, needs to be extrapolated to infinity, and such extrapolation is conducted with only three different N values. This matrix formula can be used as a benchmark test if other approximate approaches can give reasonable estimates of the weight‐average molecular weights. The moment equations with the average pseudo‐kinetic‐rate constants for branching and crosslinking reactions may provide poor estimates when the copolymer composition drift during polymerization is very significant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2801–2812, 2004 相似文献
118.
Cr3+:MgAl2O4晶体EPR参量及其电子精细光谱的研究 总被引:4,自引:0,他引:4
考虑了SS(Spin-Spin)作用和SOO(Spin-Other-Orbit)作用,采用完全对角化方法,结合自旋Hamiltonian理论,研究了Cr3+∶MgAl2O4晶体EPR参量及其吸收光谱,理论与实验符合甚好. 在此基础上,进一步研究了4A2(3d3)离子EPR参量的微观起源. 研究表明,EPR参量起源于四种微观机制:(1) SO(Spin-Orbit) 耦合机制;(2) SS耦合机制;(3)SOO耦合机制;(4) SO~SS~SOO总联合作用机制. 在这些机制中,SO机制是最主要的. 相似文献
119.
根据有限元法单元划分的思想,提出了一种新颖的模拟光腔模式及光束传输的特征向量法. 该方法的关键之处在于基于衍射积分理论构造了一种新的光束传输矩阵,通过求解特征矩阵方程可一次性得到谐振腔的一系列特征向量,每一列特征向量即代表了腔镜上光场的一个确定模式的振幅及相位分布. 并可采用该方法模拟光场传输到腔内或腔外任意地方的场分布. 该方法将传统方法中大量的迭代过程转化成为本征积分方程特征向量的求解过程,并与初值取值无关,且可一次性求得多个模式分布,从而可方便地分析谐振腔的模式鉴别能力. 特征向量法对圆形镜共焦
关键词:
谐振腔
特征向量法
模式分布 相似文献
120.