基于迭代小波变换的光谱信号本底扣除方法研究

本底会对光谱分析结果产生很大的干扰作用,为获取特征峰的有效信息,必须首先去除本底。该文提出了一种基于小波变换的本底扣除算法,通过对光谱及后续光谱迭代进行小波变换,利用逼近系数估计本底,直到本底收敛。提出了判断多次估计的本底最大误差是否足够小的收敛准则。利用该算法去除本底后,即可进行特征峰信息的提取。分别利用仿真光谱和实验能量色散X射线荧光光谱对算法进行了验证,并与传统小波变换和多项式拟合法进行了对比。结果表明,该算法能够更准确扣除光谱本底,对其他光谱的本底扣除也具有借鉴意义。     

Robust curve fitting method for optical spectra by least median squares (LMedS) estimator with particle swarm optimization (PSO).

A curve fitting technique for optical spectra based on a robust estimator, least median squares (LMedS), is introduced in this study. For the effective calculation of LMedS, particle swarm optimization (PSO) is also introduced. Unlike a standard curve fitting method using least squares (LS) estimator, the method based on LMedS estimator is less influenced by outliers in experimental data. Two kinds of data sets, simulated data with outliers and temperature-dependent near-infrared (NIR) spectra of oleic acid (OA) are applied for the demonstration of the proposed method. The results clearly reveal that, compared with the LS estimator, the proposed method can effectively reduce undesirable effects of low SN ratio and can yield more accurate fitting results.     

活性炭中甲烷水合物的分解动力学

在封闭体系内,在初始分解压力0.1 MPa,温度范围276～265 K之间,测定了 五组甲烷水合物在活性炭中的解动力学数据。分析了甲烷水合物在活性炭中分解的 物理过程,提出了以微分方程表达的宏观分解动力学模型。使用单步积分的吉尔（ Gear)方法解得微分方程的数值解,结合单纯形最优化方法拟合模型参数,模型计 算值与实验值符合良好。     

Multilayer characterization by energy dispersive X-ray reflectivity technique

An experimental setup was developed to verify the feasibility of silicon drift detector to be used for the multilayer characterization by means of multilayer energy dispersive X-ray reflectivity. Such a detector allows high count rates up to 3 × 10⁵ cps and can be used in principle for the direct beam intensity measurement, which is to be done for the X-ray multilayer reflectivity patterns obtaining. A series of measurements were performed for Mo/B₄C multilayer sample. A quality of the experimentally obtained data turns out to be enough to perform a sample structure exploration using a numerical procedure of experimental data fitting. Due to low cost and short time, required for the measurements, an experimental technique proposed has a good perspective to be used for some practical applications in industry.     

Target transform fitting in a voltammetric study of metal complexation

In this work target transform fitting (TTF) is proposed as a hard-model based data analysis method to analyze differential pulse polarograms recorded in a successive metal complexation system. In such cases, equations for both complexation equilibria and shape of the differential pulse polarogram for individual species are available. Utilizing TTF to fit these models in separate stages, stability constants and E_1/2 values of species were estimated. In the first stage, E_1/2 values of all species were acquired using the shape-equation of voltamograms and projection of a test vector into the row space of data matrix. In the second stage, using equations derived from relationships among species’ concentrations in complexation equilibria and a non-linear parameter fitting algorithm, the optimum values of overall formation constants were estimated. Finally, rank annihilation (RA) method was employed for calculation of diffusion coefficients. In spite of the fact that proposed method is a hard-model based approach, obtained results show that analysis can be performed correctly even in presence of unknown species. The reliability of the method was tested analyzing simulated data and also polarograms obtained from Cd(II) and 1, 10-phenanthroline complexation system. This experimental system yields three successive complexes which are relatively inert from electrochemical point of view. The results were in a good agreement with reported results in the literature.     

Enthalpy Relaxation in Glasses: Regression analysis of integral DSC data

A new method of calculation of parameters of enthalpy relaxation models is proposed. Regression analysis treatment compares the experimental and calculated values of relaxation enthalpy. The experimental values of relaxation enthalpy are obtained by numerical integration of the difference between the two DSC curves. Contrary to the overall shape of the DSC curve the integral values are not affected by particular heat flow conditions during the DSC experiment. The Narayanaswamy's numerical model based on the Kohlrausch—William—Watts relaxation function was used to calculate the theoretical values of relaxation enthalpy. The application of the proposed method on the DSC experimental data of enthalpy relaxation of As₂Se₃ is shown.This revised version was published online in November 2005 with corrections to the Cover Date.     

Convolution and finite difference approach: Application to cyclic voltammetry and spectroelectrochemistry

A method combining finite difference analysis of concentration profiles and convolution of faradaic current is proposed for the study of electrochemical systems involving fast electron transfers and secondary homogeneous chemical reactions by large amplitude techniques such as cyclic voltammetry. It amounts to carrying out the fitting of experimental data with the formal kinetics of the assumed mechanism automatically inside the computer. The conditions of applicability are those where the system is under mixed diffusion-chemical reaction kinetic control. Accuracy is first evaluated in simulated experiments testing separately and then simultaneously the two main steps of the treatment: finite difference resolution and numerical convolution. It is shown that the method not only provides a determination of the rate constant of the rate determining step but may also serve to mechanism diagnosis. The practical applicability of the method is illustrated on the example of the electrodimerization of acetophenone in acetonitrile. Extension of the method to the treatment of data obtained by combined electrical and spectrochemical experiments is discussed.     

基于非接触式电导信号的土壤速效钾含量检测方法

该文针对土壤中速效钾含量采用传统测定法操作复杂、检测时效滞后的问题,建立了基于非接触式电导检测信号快速检测土壤速效钾含量的分析方法。采用高效毛细管电泳/非接触式电导检测仪获取河南潮土的非接触式电导检测信号,并使用导数法与高斯曲线拟合法相结合进行初步峰谱识别,按条件进行峰值过滤后,引入基于Levenberg-Marquardt(L-M)的高斯分峰拟合算法,实现了单峰和重叠峰的拟合计算,得到高斯峰和相应的特征参数,包括峰位、峰高、半峰宽和峰面积;最后将拟合得到的高斯峰及相应的特征参数表征原始非接触式电导检测信号离子峰谱信息结合偏最小二乘法(PLS),确定特征参数与土壤速效钾含量的关系,建立模型,实现了对土壤中速效钾含量的预测。结果表明,将基于L-M的高斯分峰拟合算法结合偏最小二乘法应用于非接触式电导检测信号测定土壤速效钾含量时具有较高精度,回归模型决定系数(R~2)为0.856 4,相对分析误差(RPD)为2.639,适用于土壤速效钾的快速检测分析。     

Ab initio calculation of vibrational force fields: Determination of non-redundant symmetry coordinates by least-square component analysis

A general procedure is described for vibrational analysis, using an ab initio force constant matrix which is transformed into the generalized valence force field. A method using numerical least-square fitting and redundancy elimination is proposed to determine the valence-symmetry coordinates in terms of the internal coordinate displacements. The computer program was customized to simplify the data deck construction and to input most of the data directly from the GAUSSIAN 8X output file.     

Artificial neural network modification of simulation-based fitting: application to a protein-lipid system

Simulation-based fitting has been applied to data analysis and parameter determination of complex experimental systems in many areas of chemistry and biophysics. However, this method is limited because of the time costs of the calculations. In this paper it is proposed to approximate and substitute a simulation model by an artificial neural network during the fitting procedure. Such a substitution significantly speeds up the parameter determination. This approach is tested on a model of fluorescence resonance energy transfer (FRET) within a system of site-directed fluorescence labeled M13 major coat protein mutants incorporated into a lipid bilayer. It is demonstrated that in our case the application of a trained artificial neural network for the substitution of the simulation model results in a significant gain in computing time by a factor of 5 x 10(4). Moreover, an artificial neural network produces a smooth approximation of the noisy results of a stochastic simulation.     

Comprehensive kinetic studies on isothermal and non-isothermal reactions of some aluminium compounds

Residual differences after model fitting were investigated in both isothermal and non-isothermal kinetics in order to make numerical comparisons between several models and various parameter-estimating methods. Data from two independent experimental series were evaluated. A large data set, collected earlier under isothermal conditions from decompositions and hydrothermal reactions of aluminium hydroxides and oxides, was processed first. It showed that mechanical activation of the starting gibbsite affected reactivity of samples in several subsequent reactions for all model equations tried. The relative residual deviation concept is introduced, and statistics were applied to find a model that fits a certain reaction in most of the cases. In the second study, the sulphate decomposition step of aluminium sulphate octadecahydrate was investigated. TG curves were measured using a constant heating rate. Dynamic models were fitted by three mathematical methods, including a new general purpose one. Fitting ability of the methods with various complexity were compared on the basis of residual deviations obtained after integration of the model equations. As well as evaluating the best fit, this new parameter-estimating method provides a statistical analysis of the reliability of the whole model fitting process.     

Accessing the applicability of polarized protein‐specific charge in linear interaction energy analysis

The reliability of the linear interaction energy (LIE) depends on the atomic charge model used to delineate the Coulomb interaction between the ligand and its environment. In this work, the polarized protein‐specific charge (PPC) implementing a recently proposed fitting scheme has been examined in the LIE calculations of the binding affinities for avidin and β‐secretase binding complexes. This charge fitting scheme, termed delta restrained electrostatic potential, bypasses the prevalent numerical difficulty of rank deficiency in electrostatic‐potential‐based charge fitting methods via a dual‐step fitting strategy. A remarkable consistency between the predicted binding affinities and the experimental measurement has been observed. This work serves as a direct evidence of PPC's applicability in rational drug design. © 2014 Wiley Periodicals, Inc.     

EMULSION POLYMERIZATION IN A SEED-FED CONTINUOUS STIRRED-TANK REACTOR

A numerical method has been developed to predict the particle size distribution (PSD) of the product latex from a steady-state polydisperse-seeded continuous reactor. Simulations have been carried out for the emulsion polymerization of vinyl chloride based on the experimental conditions reported by Berens(l). The simulation results can be reasonably well fitted to the PSD data published by Berens. The radical desorption constant, k_d, for Berens’ vinyl chloride emulsion polymerization can be estimated by fitting the simulated PSD to experimental measurements. The simulation work presented in this article demonstrates that the combination of mathematical modeling and PSD measurements can be a useful tool in studying radical transport rates and aqueous phase termination phenomena. The simulation results also indicate that the continuum diffusion theory for free radical absorption by the particles leads to a better PSD fit than a model based on equal diffusion rates per unit area.     

Simple expressions for diffusion coefficient determination of adsorption within spherical and cylindrical absorbents using direct simulation method

Various analytical expressions for solute adsorption kinetics within porous absorbents of defined geometry (planar sheet, cylinder, and sphere) are available in the literature. However, these expressions are limited for practical numerical evaluation because they are based on infinite series. An investigation of these expressions has been carried out and then accurate but simple expressions derived that enable rapid determination of effective diffusion coefficients for adsorption within geometrically categorical absorbents. These involve directly fitting calculated kinetic adsorption curves to experimental ones. A simple one point method is also proposed to estimate the effective diffusion coefficient for an adsorption process within these simple geometrical absorbents as an initial value for a best fit.     

Effective GA approach for a direct evaluation of reaction kinetic within EPDM accelerated sulphur crosslinking

A direct genetic algorithm (GA) approach with kinetic base, to provide effective numerical estimates of vulcanization level for EPDM cross-linked with accelerated sulphur is presented. The model requires a preliminary characterization of rubber through standard rheometer tests. A recently presented kinetic exponential model is used as starting point to develop the algorithm proposed. In such a model, three kinetic constants have to be determined by means of a non-linear least-squares curve fitting. The approach proposed circumvents a sometimes inefficient and not convergent non-linear data fitting, disregarding at a first attempt reversion and finding the local minimum of a suitable two-variable error function, to have an estimate of the first two kinetic constants. A comparison between present GA approach and traditional gradient based algorithms is discussed. The last constant, representing reversion is again evaluated through a minimization performed on a single variable error function. The applicability of the approach is immediate and makes the model extremely appealing when fast and reliable estimates of crosslinking density of cured EPDM are required. To show the capabilities of the approach proposed, a comprehensive comparison with both available experimental data and results obtained numerically with a least square exponential model for a real compound at different temperatures is provided.     

Measurement of the solubility of metal complexes in supercritical carbon dioxide using a UV–vis spectrometer

A new apparatus based on the circulation method was developed to measure the solubility of metal complexes in supercritical carbon dioxide (scCO₂) at a wide range of temperatures and pressures. A UV–vis spectrometer, which was connected to a small saturation cell through optical fibers, was used to determine solubility. The solubilities of cobalt(III) acetylacetonate (Co(acac)₃) and chromium(III) acetylacetonate (Cr(acac)₃) in scCO₂ were measured to check the validity of both the apparatus and the method and to accumulate new solubility data. The solubility data for Cr(acac)₃ obtained in this study were in good agreement with the data reported in the literature.The measured solubilities of Co(acac)₃ and Cr(acac)₃ were also correlated with the empirical equation including the three adjustable parameters, based on the equation proposed by Chrastil. The parameters were determined by fitting the equation to the experimental data for each metal complex and the calculated results closely replicated the experimental data.     

Comparison of global models of sub-bituminous coal devolatilization by means of thermogravimetric analysis

Coal gasification and combustion are strongly dependent on devolatilization step. Aim of this work is to obtain the parameters of global kinetics of devolatilization of a sub-bituminous coal with high sulfur content. The kinetic parameters are obtained by means of TG experimental data, and applying different approaches to extrapolate the data to industrial relevant conditions. The simpler method is a model-free one which supposes a single step process whose Arrhenius kinetic parameters (A and E _a) have to be determined. Another common approach is the distributed activation energy model (DAEM) which assumes a series of first order parallel reactions occurring and sharing the same pre-exponential factor, A, with a continuous distribution of the activation energy. For the fitting of the experimental data, a numerical solution to DAEM and two approximate methods have been evaluated. Moreover, the results of these kinetic methods based on empirical approaches were compared with simulated data obtained using a more complex model based on percolation theory with cross-linking mechanism and vapor–liquid equilibrium (chemical percolation devolatilization, CPD model), which allows to simulate the coal pyrolysis from volatile yield data.     

New method for deriving accurate thermodynamic properties from speed-of-sound

We have solved numerically the nonlinear partial differential equation that links speed of sound and compression factor subjected to boundary conditions in the gaseous phase. This method has as similar accuracy as other numerical method based on an initial-values numerical integration in the low-density regime, but for higher densities, this new approach is more accurate and less sensitive to errors in both boundary conditions and speed-of-sound. The method was tested by comparing our numerical calculations against a reference equation of state in the fluid region of densities up to the critical density and temperatures between slightly above the critical temperature and four times the critical temperature. We also analysed and estimated uncertainties of derived thermodynamic properties from this method. Finally, the method was applied to argon and ethane experimental data.     

Adsorption of inulinases in ion-exchange columns

Theuse of adsorption columns packed with ion-exchange resins for recovering, concentrating and purifying proteins is now widespread. The present work consists of a study on the dyamic behavior ofadsorption columns that uses two kinds of adsorbents: a cationic and an anionic resin. A frontal analysis of the columns was performed with experimental data obtained from Fructozyme, a mixture of inulinase en zymes. The parameters of a Langmuir type of isotherm and adsorption kinetics were obtained from experimental tests in a batch system. A numerical technique based on orthogonal colocation and a fourth-order Runge-Kutta method was coupled with a nonlinear optimization method to predict the coefficients of the rate equations, which are fundamental for scale-up purposes.     

基于小波的恒电量瞬态响应信号的滤波处理

利用小波变换的阈值法对恒电量响应信号进行滤波处理, 同时与传统的时域和频域的滤波方法进行分析比较, 并且讨论了小波变换的分解层数对恒电量响应信号滤波效果的影响. 结果表明, 利用小波变换可以在时域和频域同时对恒电量响应信号取得良好的去噪效果. 这不仅能提高时域曲线拟合的精度, 还大大地提高了恒电量频谱解析的可靠性. 在实际应用中, 小波变换的分解层数取5～7层可以收到满意的效果.