On the Li and Tang's isoconversional method for kinetic analysis of solid-state reactions from thermoanalytical data

A criterion for the reaction mechanism as expressed by differential conversion function based on the Li and Tang's isoconversional method is suggested. The suitability of the use of Li and Tang's method for the estimation of a conversion dependent activation energy is discussed.     

Revisiting the method of cumulants for the analysis of dynamic light-scattering data

The method of cumulants is a standard technique used to analyze dynamic light-scattering data measured for polydisperse samples. These data, from an intensity-intensity autocorrelation function of the scattered light, can be described in terms of a distribution of decay rates. The method of cumulants provides information about the cumulants and the moments of this distribution. However, the method does not permit independent determination of the long-time baseline of the intensity correlation function and can lead to inconsistent results when different numbers of data points are included in the fit. The method is reformulated in terms of the moments about the mean to permit more robust and satisfactory fits. The different versions of the method are compared by analysis of the data for polydisperse-vesicle samples.     

Optimization method for simultaneous kinetic analysis

Kinetic analysis is often carried out for simultaneous determinations; thus, a theory to establish its optimal conditions is necessary. A very simple and fast model to find conditions for optimum analytical performance and to predict the quality of simultaneous kinetic analysis has been developed. It is general and applicable to any reaction order or rate constant. The model has been based on the angle between the kinetic vectors and on their norm ratio, which are readily calculated for any kinetic scheme. Evaluation of the proposed model has been carried out by detailed simulations of numerous experimental conditions and analysis by full PCR calculations (when applicable) or nonlinear least-squares fitting. An important conclusion is that analytical performance is determined to a large extent by the stability of the space spanned by the relevant component vectors (in addition to experimental noise and other factors). The quality of the analysis is governed by the angle between the kinetic vectors, while the norm ratio determines the error distribution between components. Optimum conditions for simultaneous kinetic analysis have been studied in several representative examples, regarding the timing of the kinetic monitoring and the effects of concentrations and of rate constant ratios, as well as several other factors of experimental relevance.     

Two-dimensional correlation analysis for a kinetic model of consecutive reactions

We have systematically studied a kinetic scheme of consecutive reactions by using generalized two-dimensional (2D) correlation analysis as reported by Noda. The correlations between reactant-intermediate, intermediate-product, and reactant-product pairs are analyzed with the related rate constants and absorption coefficients. When the reference spectrum is set at zero, the synchronous and asynchronous correlation spectra for the kinetic model are almost free from the influence of poor quality signals. If an appropriate reference spectrum is selected, the intermediate can be feasibly distinguished from other species involved in the reaction. A ratio of asynchronous to synchronous correlation intensity yields a coherence spectrum, which is characterized by different plateau-type peak intensities. When a steady-state condition fits the kinetic model, the peak summation of reactant-intermediate and intermediate-product correlation will approach the intensity of the reactant-product correlation. The coherence spectrum is useful for pattern recognition of the reaction scheme and also provides an effective way to identify the location and the extent of spectral overlap between two peaks.     

一种机械系统动力学响应分析方法

 为了动力学响应分析的通用性及简便性,提出一种新的动力学响应分析方法.将机械系统分解成有序单开链单元,按其正序首先在约束度小于0的单元进行虚拟赋值,然后在其他单元依次进行运动分析,最后可得到维数最低的运动学方程.基于虚功原理导出动力学响应方程通式,对广义速度与广义加速度特殊赋值后通过序单开链法可求出响应方程的各系数,从而确定动力学响应方程.该动力学响应方程的维数等于机械系统自由度,形式简洁,便于求解,平面三自由度并联机构的实例表明了该方法的有效性.     

动态载荷识别位置优化的传递函数相干法

利用多自由度动力学原理对频域载荷识别方法进行分析,对传递函数病态性进行了研究,分析了动态载荷识别方法中响应点位置对传递函数病态性及载荷识别结果的影响.为降低载荷识别误差特别是结构共振频率下的识别误差,基于传递函数的相干分析定义了传递函数相干因子,并提出以最小传递函数相干因子为目标的动态载荷识别位置优化的传递函数相干法....     

Entropy-based method for COP data analysis

Entropy-based data analysis methods have been applied to many science or engineering fields. The centre of pressure (COP) data are often dynamic, non-linear and non-stationary in nature. It is thought that it may be used to analyse COP data, which is often used for evaluating postural stability in ergonomics research. Multi-scale entropy (MSE) and empirical mode decomposition are introduced first; then, three examples are presented to demonstrate the initial applications of the proposed methods, young and elderly subjects: (1) standing with attention; (2) standing with eyes open/closed; and (3) wearing vibratory shoes. The MSE analysis results are compared with traditional COP stabilogram metrics. Based on these applications, MSE can be an effective metric for COP data analysis and other ergonomics research. The cautions of using MSE, including the non-specificity nature and individual baseline variation, are also discussed. There is a good potential for using MSE in ergonomics-related research, especially for ageing ergonomics.     

挂架载荷的动态标定及其数据处理方法研究

研究武器系统挂架载荷的动态标定及其数据处理方法,为挂架载荷力值的测量提供标定模型。采用对挂架上一特征点施加标准的脉冲和阶跃激励,测量应变片对激励的响应输出,通过非参数拟合,获得标定样本数据库,根据最近邻域法确定未知受力值。结果表明,基于非参数拟合的标定方法,可较好地解决复杂环境下应变片输出的噪声干扰,从而提高测量数据的稳健性。     

Superelement method for transient dynamic analysis of structural systems

A superelement algorithm for the transient dynamic analysis of structural systems is presented. The method represents a generalization of existing static and dynamic superelement (substructure) algorithms. Natural frequencies and modal shapes of a fixed boundary substructure are used to obtain equations of motion of a superelement. An implicit time-stepping algorithm is presented for the numerical solution of a resulting superelement system of equations of motion. Numerical examples are given to illustrate the presented approach. The method is believed to be effective for large-scale problems of structural analysis.     

A simple method for dynamic scientometrics using lexical analysis

Techniques for studying problematic networks in science and technology are principally derived either from citation analyses or from lexical methods. The former have been the object of many developments and improvements. A considerable range of applications exists within the practical constraint of their being limited to fields covered by the ISI databases. For the latter, the co-word method has a register of applications that up until now have been more specialized in the sociology of science as it is done, but it has in principle no field limitations. An important question is whether we can extend the application range of this analytical method to take in longer periods, and in particular to deal with historiography either on a large scale (at the level of a research field) or on a small scale (at the level of a process of discovery or invention). Here we propose a way of rendering lexical methods dynamic, more particularly through developing a rudimentary but precise technique to aid historiographical analysis. This method ofcritical variations is illustrated in a working example.     

Direct numerical inversion method for kinetic ellipsometric data. I. Presentation of the method and numerical evaluation

A direct numerical inversion method for the determination of the refractive index and the thickness of the outermost layer of a thin transparent film on top of a multilayer has been developed. This method is based on a second-order Taylor decomposition of the coefficients of the Abelès matrices of the newly grown layer. The variations of the real-time spectroscopic ellipsometry data are expressed as polynomial fuctions depending on the dielectric constant and the thickness of the newly grown layer. The method is fast, capable of single-wavelength and multiwavelength inversion of continuous as well as discontinuous-index profiles, and can be adapted to many different polarimetric instruments.     

Two-dimensional correlation analysis in application to a kinetic model of parallel reactions

By applying generalized two-dimensional (2D) correlation analysis as reported by Noda, we have systematically studied a kinetic model of parallel reactions. Given the related rate constants and absorption coefficients, the correlation between reactant and products are analyzed. The reactant-reactant, reactant-product, and product-product pairs are found to be synchronously correlated, and their intensities increase with increase of the rate constant and the absorption coefficient. On the other hand, only the reactant-product pairs show in the asynchronous spectra. Their intensities also depend proportionally on the rate constant and the absorption coefficient. The influence of signal-to-noise ratio (S/N) and overlapped spectra are further discussed. The resulting synchronous and asynchronous correlation spectra for the kinetic model appear to be weakly influenced by poor quality of the signal when the reference spectrum is set at zero. The ratio of asynchronous to synchronous correlation intensity yields a coherence spectrum. This spectrum remains a constant intensity for all the correlated peaks, being free from the influence of rate constant and absorption coefficient as well as being weakly disturbed by a small S/N ratio. It also provides a way to evaluate the extent of spectral overlap between two peaks. The coherence spectrum is useful to characterize the type of parallel reactions.     

Multivariate curve resolution-alternating least squares and kinetic modeling applied to near-infrared data from curing reactions of epoxy resins: mechanistic approach and estimation of kinetic rate constants

This study describes the combination of multivariate curve resolution-alternating least squares with a kinetic modeling strategy for obtaining the kinetic rate constants of a curing reaction of epoxy resins. The reaction between phenyl glycidyl ether and aniline is monitored by near-infrared spectroscopy under isothermal conditions for several initial molar ratios of the reagents. The data for all experiments, arranged in a column-wise augmented data matrix, are analyzed using multivariate curve resolution-alternating least squares. The concentration profiles recovered are fitted to a chemical model proposed for the reaction. The selection of the kinetic model is assisted by the information contained in the recovered concentration profiles. The nonlinear fitting provides the kinetic rate constants. The optimized rate constants are in agreement with values reported in the literature.     

Robust design for multiple dynamic quality characteristics using data envelopment analysis

The Taguchi method is extensively adopted in various industries to continuously improve product design in response to customer requirements. The dynamic system of the Taguchi method is frequently implemented to design products with flexible applications. However, Taguchi's dynamic system can be employed only for individual quality characteristic, and the relationship between the quality characteristic and the signal factor is assumed to be linear. Because of these restrictions, Taguchi's dynamic system is ineffective for multiple quality characteristics or when the quality characteristic has a nonlinear relationship with the signal factor. This study describes a novel procedure for optimizing a dynamic system based on data envelopment analysis. The proposed procedure overcomes the limitations of Taguchi's dynamic system. Two cases are analyzed to demonstrate the effectiveness of the proposed procedure. The results show that the proposed procedure can enhance multiple dynamic quality characteristics. Copyright © 2008 John Wiley & Sons, Ltd.     

Direct numerical inversion method for kinetic ellipsometric data. II. Implementation and experimental verification

A direct numerical inversion method is applied to the monitoring of thin-film growth. Several improvements of the method, including a correction for weakly absorbing materials, are presented. The method has been successfully applied to the inversion of the growth of constant-refractive-index layers andused for the process calibration of plasma-enhanced chemical vapor deposition of silicon oxynitrides. The validity of this calibration has been successfully tested on a linear index gradient and quintic matching layer between a polycarbonate substrate and a scratch-resistant coating.     

区间随机桁架结构动力特性分析方法研究

摘 要：针对区间随机桁架结构的动力特性分析,提出了一种区间随机有限元方法。当结构的物理参数和几何尺寸同时具有区间随机性时,利用区间因子法和随机因子法建立了结构的刚度矩阵和质量矩阵;从结构振动的瑞利商表达式出发,利用区间运算推导了结构动力特性区间随机变量的计算式;进而利用随机变量的矩法和代数综合法,推导出了结构特征值的数字特征的计算式。最后通过算例分析了区间随机桁架结构参数的区间随机性对其动力特性的影响,计算结果表明该方法是可行和有效的。
     

A new array decomposition method for multiway data analysis

In chemometrics, two-way singular value decomposition (SVD), CANDECOMP-PARAFAC decomposition (PARAFAC), and Tucker decomposition (TUKER) are three main array decomposition methods. There are disadvantages with the three methods. If multiway data are indeed multilinear, PARAFAC and TUCKER can provide more robust and interpretable models compared to two-way SVD. However, PARAFAC is sometimes numerically unstable, and TUCKER cannot guarantee the uniqueness of an approximate solution. This paper proposes a new array decomposition model with multiple bilinear structure. Then, utilizing this model, a new method, called multiple bilinear decomposition (MBD), is proposed as a generalization of two-way SVD. An algorithm is established to successively decompose an array without a full decomposition, which is not based on alternating least squares. Theoretically, the proposed method has an advantage over PARAFAC and TUCKER in its three important properties, including orthonormality of loading vectors, closed-form decomposition, and successive decomposition of variation. The simulation results based on orthogonal PARAFAC models show that the proposed method outperforms PARAFAC with respect to accuracy and robustness of loading estimate and data-fitting of model, even though the former does not use the priori information of multilinear structure. And, especially in the simulation under no noise, the equivalence of loading estimates indicates that as a successive decomposition, MBD is a superior alternative to PARAFAC.     

The analysis of the Generalized-α method for non-linear dynamic problems

 This paper presents the consistency and stability analyses of the Generalized-α methods applied to non-linear dynamical systems. The second-order accuracy of this class of algorithms is proved also in the non-linear regime, independently of the quadrature rule for non-linear internal forces. Conversely, the G-stability notion which is suitable for linear multistep schemes devoted to non-linear dynamic problems cannot be applied, as the non-linear structural dynamics equations are not contractive. Nonetheless, it is proved that the Generalized-α methods are endowed with stability in an energy sense and guarantee energy decay in the high-frequency range as well as asymptotic annihilation. However, overshoot and heavy energy oscillations in the intermediate-frequency range are exhibited. The results of representative numerical simulations performed on relatively simple single- and multiple-degrees-of-freedom non-linear systems are presented in order to confirm the analytical estimates. Received 1 April 2001     

A molecular-level analysis of gas-phase reactions in chemical vapor deposition of carbon from methane using a detailed kinetic model

This work describes a modeling study of methane pyrolysis in chemical vapor deposition (CVD). The model consists of a detailed chemical kinetic model, which includes 241 species and 909 gas-phase reactions for methane pyrolysis mechanism, and a plug-flow model, which describes the transport conditions in CVD. Reasonably good agreements were obtained between the simulation results and the experimental results of methane pyrolysis in CVD of pyrocarbon in a vertical hot-wall deposition reactor without any artificial adjustments. The mole fractions of hydrogen, acetylene, ethylene, and benzene increased with a decreasing growth rate as the residence time and the initial methane pressure increased. Sensitivity analysis and reaction paths were conducted to identify the crucial reaction steps and explain how they impact in this pyrolysis process. Results showed that methane pyrolysis had an incubation stage to form a necessary gas atmosphere for the pyrolysis to move forward and C₃ species were the main direct source for benzene formation. These results should be useful to understand methane pyrolysis at a molecular level in CVD, as well as the relationship between the gas species and the pyrocarbon.     

动力模型拟静力修正方法及误差分析

摘 要：为了降低动力模型修正过程中的计算复杂程度,提出了拟静力模型修正方法。借助特征载荷的概念,将基于动力测量信息的动力模型转化为静力模型进行修正,避免了模型修正过程中特征值和特征向量的计算。利用样条插值方法,解决了测量信息与计算信息间的匹配问题。采用复域灵敏度分析方法对修正过程中的参数灵敏度进行计算,提高了修正过程中的计算效率。研究了测量误差对修正结果的影响,给出了修正参数的统计特性,为评估修正结果的可靠性提供了基础。通过数值算例对提出的方法进行了验证,结果表明本文的方法是有效可靠的。利用建立的方法对润扬大桥北汊斜拉桥桥塔模型进行了修正,修正结果较为精确可靠。