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501.
Otto Vogl Gary D. Jaycox William J. Simonsick 《Journal of polymer science. Part A, Polymer chemistry》2002,40(8):923-935
Computer‐based calculations were used to simulate the mass spectra for a number of uniform macromolecules having fixed, well‐defined chain lengths. The presence of naturally occurring carbon, hydrogen, oxygen, and halogen isotopes introduced significant levels of mass heterogeneity into these systems. For a given polymer, mass variability was demonstrated to be a function of both the elemental composition and degree of polymerization of the polymer chain. In many cases, these natural variations in mass exceeded the molecular weight of one or more monomeric repeat units along the polymer backbone, effectively blurring the mass distinction between uniform polymer constructs formed from N and N+1 repeat units. The significance of isotopic diversity and its potential impact on the synthesis and physiochemical properties of highly uniform macromolecules is also discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 923–935, 2002 相似文献
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基于SMMC模型的数据多流形结构分析研究 总被引:1,自引:0,他引:1
采用混合多流形谱聚类模型(SMMC)对独立子空间、非独立子空间,非线性良分离及非线性交叉等流形聚类中的四种典型数据进行聚类,并与其他流形聚类方法进行比较,发现SMMC模型聚类效果良好且具有强鲁棒性和泛化能力.将SMMC模型运用于具有混合多流形结构的工件外部边缘轮廓进行聚类,结果显示SMMC模型能够很好的将其分为三类.针对SMMC模型复杂度高、选取参数困难及运行时间长的问题,提出了基于模拟退火遗传算法SMMC模型,结果发现改进后的模型能够大大缩短运行时间. 相似文献
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Three different sol–gel routes were used in order to study the stability and the crystallinity of the ternary system Y2O3, Ti(OBu)4, Rb2CO3. Different techniques such as FTIR, 13C NMR TGA, DTA and XRD were used to characterize xerogels and final products. Results demonstrated that using hexanoic acid during the sol step preparation influences structural changes in the precursor gel. The effect of heat treatment to eliminate the organic material from xerogels was investigated by thermal gravimetry and differential thermalanalysis. According to the ratio of acetic acid to hexanoic acid, the phase structure of TiO2, viz. anatase to rutile phase, could tailored. The photocatalytic activity of the prepared catalysts, under sunlight irradiation, was evaluated using 2‐naphthol as a pollutant model. Results showed a great enhancement in the photocatalytic efficiency for doped TiO2 sample prepared in the presence of 30acet–70hex. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
507.
David Jesch Francesca di Mare Johannes Janicka Amsini Sadiki 《International Journal of Computational Fluid Dynamics》2013,27(5):181-201
ABSTRACTA novel, efficient method to account for multivariate probability density functions (PDFs) in the context of the flamelet generated manifolds (FGM) approach in a large eddy simulation (LES) framework is presented and discussed. It consists of applying the ‘Correlation Set by Simulated Annealing (CSSA)’ algorithm on univariate samples of each control variable to recombine them into multivariate samples in joint space, while accounting for the needed covariances. This is done on the fly and on a cell-by-cell basis. Thereby, the assumption of statistical independence of the control variables has been relaxed. The PDF is represented in a discrete manner and the integration is replaced through ensemble averaging. Consequently, the shape of the PDF no longer appears in the look-up table. The algorithm has been validated in the context of LES calculations of two configurations. Compared to a conventional pre-integrated FGM approach, the required CPU time has increased only modestly. 相似文献
508.
Daniela Acetti Christian Langel Elisabetta Brenna Claudio Fuganti Marco Mazzotti 《Journal of chromatography. A》2010,1217(17):2840-2846
The pharmaceutically relevant compound (RS,RS)-2-(2,4-difluorophenyl)butane-1,2,3-triol, an important intermediate in the production of different antifungal drugs, is synthesized in racemic form. For further use in the laboratory the compound has to be separated into its pure enantiomers. This work describes the different steps required to set up a chiral separation using intermittent simulated moving bed chromatography (I-SMB). Furthermore, the effect of feed concentration on the choice of the operating conditions is presented in the frame of the triangle theory. The experiments are carried out at increasing total feed concentration ranging from 3 to 15 g/L. The results demonstrate that a successful I-SMB separation could be carried out thus separating 4.5 g of the racemic mixture and fulfilling the specified purity specification of 98% for both enantiomers. 相似文献
509.
The Peng–Robinson cubic equation of state (CEOS) is widely used to predict thermodynamic properties of pure fluids and mixtures. The usual implementation of this CEOS requires critical properties of each pure component and combining rules for mixtures. Determining critical properties for components of heavy asymmetric mixtures such as bitumen is a challenge due to thermolysis at elevated temperatures. Group contribution (GC) methods were applied for the determination of critical properties of molecular representations developed by Sheremata for Athabasca vacuum tower bottoms (VTB). In contrast to other GC methods evaluated, the Marrero–Gani GC method yielded estimated critical properties with realistic, non-negative values, followed more consistent trends with molar mass and yielded normal boiling points consistent with high temperature simulated distillation data. Application of classical mixing rules to a heavy asymmetric mixture such as bitumen yields saturated liquid density and bubble pressure estimates in qualitative agreement with experimental data. However the errors are too large for engineering calculations. In this work, new composite mixing rules for computing co-volumes of asymmetric mixtures are developed and evaluated. For example, composite mixing rules give improved bubble point predictions for the binary mixture ethane + n-tetratetracontane. For VTB and VTB + decane mixtures the new composite mixing rules showed encouraging results in predicting bubble point pressures and liquid phase densities. 相似文献
510.
病态方程组的条件数较大,当输入数据有微小扰动或计算过程中的舍入误差都可能引起输出数据的很大扰动,使得解严重失真,因此求解此类方程组是相当困难的.本文尝试使用模拟退火算法来求解病态线性方程组,得到了较好的结果,并与传统的求解方法作了简单的比较. 相似文献