径向基-偏最小二乘-贝叶斯方法及其在化学模式分类中的应用

提出一种用于模式分类的RBF-PLS—Bayes方法。它集成地应用径向基(RBF)变换与偏最小二乘(PLS)方法，从原有模式中提取出分类能力甚强的成分，然后进行贝叶斯(Bayes)判别。这种集成方法尤其适用于复杂化学信息的模式分类，本文将其应用于两种类型的化学模式分类问题，均取得了令人满意的效果。与经典的判别分析方法和单纯的神经网络方法相比，具有明显的优越性。     

Least-squares numerical Rayleigh-Ritz and minimum-variance methods for molecular calculations

A general method is presented to find in a least-squares sense a set of orthogonal eigenfunctions and their eigenvalues from local energy and numerical integration methods or by any other dissymmetric approach to solve the eigenvalue problem of a Hermitian operator. By this method a generalization of the minimum variance method to more than one eigenfunction is obtained, which is a variant of Scott's method. Also a new method is derived—called the minimum-overlap method—that is a least-squares numerical version of the standard Rayleigh-Ritz method. Test calculations on the atoms Be and Tm and the molecules H₂ and CO have been performed with both numerical Hartree-Fock and Hartree-Fock-Slater methods. The least-squares solutions are an improvement over other methods in the case of accurate basis sets. Numerical Hartree-Fock calculations of moderate accuracy are found to be considerably faster than the analytic method.     

Looking Beyond the Column: An Investigation into Method Irreproducibility for an Active Pharmaceutical Ingredient

Irreproducibility during initial development of a high performance liquid chromatography method is seldom investigated in a thorough and careful manner when working in an industrial setting. For a drug project in the early developmental stages, the LC method is often changed, sometimes drastically, if one encounters irreproducibility in the method. Too often a method is deemed irreproducible due to column lot variability, diluent effects, or pH effects with little or no experiments taking place for justification and little thought given to why the irreproducibility may have occurred in the first case. In this paper, a case study is presented in which a systematic approach was carried out in order to determine the exact reason why method irreproducibility was occurring. The findings of the investigation were then drawn onto change a method with poor reproducibility into one that is rugged without the need to start from the beginning and develop a new method.     

An improved sealed quartz‐tube method for the determination of hydrogen isotopes in water

Hydrogen stable isotope analysis has been a valuable tool in the fields of geochemistry and ecological research as well as many other research fields. The methods are mainly divided into the dual‐inlet method (off‐line method) and continuous flow method. The dual‐inlet method is complicated and inefficient, but it is still important because of its high precision and wide application range. Although the continuous flow method improves the experimental efficiency, the memory effect is noticeable and the accuracy is reduced. An improved sealed quartz‐tube method is proposed in this paper. The sample is sealed in a capillary tube and placed in a quartz tube containing chromium powder. It is then packaged, evacuated, reacted at a high temperature, and analyzed for hydrogen isotope ratio. Excellent data accuracy, good reproducibility (<1‰), and no memory effect occurred in the method. The process is relatively simple, and the experimental efficiency is greatly improved, which provides an effective method for the analysis of hydrogen isotopes in complex liquid samples.     

Efficient binomial leap method for simulating chemical kinetics

The binomial tau-leaping method of simulating the stochastic time evolution in a reaction system uses a binomial random number to approximate the number of reaction events. Theory implies that this method can avoid negative molecular numbers in stochastic simulations when a larger time step tau is used. Presented here is a modified binomial leap method for improving the accuracy and application range of the binomial leap method. The maximum existing population is first defined in this approach in order to determine a better bound of the number reactions. To derive a general leap procedure in chemically reacting systems, in this method a new sampling procedure based on the species is also designed for the maximum bound of consumed molecules of a reactant species in reaction channel. Numerical results indicate that the modified binomial leap method can be applied to a wider application range of chemically reacting systems with much better accuracy than the existing binomial leap method.     

A combination of the tree-code and IPS method to simulate large scale systems by molecular dynamics

An IPS/Tree method which is a combination of the isotropic periodic sum (IPS) method and tree-based method was developed for large-scale molecular dynamics simulations, such as biological and polymer systems, that need hundreds of thousands of molecules. The tree-based method uses a hierarchical tree structure to reduce the calculation cost of long-range interactions. IPS/Tree is an efficient method like IPS/DFFT, which is a combination of the IPS method and FFT in calculating large-scale systems that require massively parallel computers. The IPS method has two different versions: IPSn and IPSp. The basic idea is the same expect for the fact that the IPSn method is applied to calculations for point charges, while the IPSp method is used to calculate polar molecules. The concept of the IPS/Tree method is available for both IPSn and IPSp as IPSn/Tree and IPSp/Tree. Even though the accuracy of the Coulomb forces with tree-based method is well known, the accuracy for the combination of the IPS and tree-based methods is unclear. Therefore, in order to evaluate the accuracy of the IPS/Tree method, we performed molecular dynamics simulations for 32,000 bulk water molecules, which contains around 10(5) point charges. IPSn/Tree and IPSp/Tree were both applied to study the interaction calculations of Coulombic forces. The accuracy of the Coulombic forces and other physical properties of bulk water systems were evaluated. The IPSp/Tree method not only has reasonably small error in estimating Coulombic forces but the error was almost the same as the theoretical error of the ordinary tree-based method. These facts show that the algorithm of the tree-based method can be successfully applied to the IPSp method. On the other hand, the IPSn/Tree has a relatively large error, which seems to have been derived from the interaction treatment of the original IPSn method. The self-diffusion and radial distribution functions of water were calculated each by both the IPSn/Tree and IPSp/Tree methods, where both methods showed reasonable agreement with the Ewald method. In conclusion, the IPSp/Tree method is a potentially fast and sufficiently accurate technique for predicting transport coefficients and liquid structures of water in a homogeneous system.     

Development of effective Stokesian dynamics method for ferromagnetic colloidal dispersions (cluster-based Stokesian dynamics method)

We have developed a new Stokesian dynamics (SD) method for nondilute colloidal dispersions, which enables us to reduce drastically the computation time. To verify the validity of the present method, which is called the "cluster-based SD method," three-dimensional simulations of a ferromagnetic colloidal dispersion have been carried out for a simple shear flow. The correlation function and viscosity have been evaluated to compare the results obtained by the present method with those obtained by the ordinary SD method and by the method of ignoring hydrodynamic interactions between particles. The results obtained here are summarized as follows. The transient properties from an initial state obtained by the present method agree well with those obtained by the ordinary method, even if a radius r(clstr), which defines the cluster formation, is taken as a small value such as r(clstr)=1.2d (d is the particle diameter). Also, the equilibrium properties such as the pair correlation function and viscosity obtained by the present cluster-based method are in satisfactory agreement with those obtained by the ordinary SD method. Furthermore, the cluster-based method drastically reduces the computation time to about one-fourteenth to one-seventieth that of the ordinary method. It is clear from these results that the cluster-based SD method is significantly superior to the ordinary SD method for ferromagnetic colloidal dispersions for which a large model system such as N=1000 or 10,000 is indispensable in simulations.     

A dissipative exponentially-fitted method for the numerical solution of the Schrödinger equation

A dissipative exponentially fitted method is constructed in this paper for the numerical integration of the Schr?dinger equation. We note that the present method is a nonsymmetric multistep method (dissipative method) An application to the bound-states problem and the resonance problem of the radial Schr?dinger equation indicates that the new method is more efficient (i.e. more accurate and more rapid) than the classical dissipative method and other well-known methods. Based on the new method and the method of Raptis and Allison(19) a new variable-step method is obtained. The application of the new variable-step method to the coupled differential equations arising from the Schr?dinger equation indicates the efficiency of the new approach.     

Looking Beyond the Column: An Investigation into Method Irreproducibility for an Active Pharmaceutical Ingredient

Irreproducibility during initial development of a high performance liquid chromatography method is seldom investigated in a thorough and careful manner when working in an industrial setting. For a drug project in the early developmental stages, the LC method is often changed, sometimes drastically, if one encounters irreproducibility in the method. Too often a method is deemed irreproducible due to column lot variability, diluent effects, or pH effects with little or no experiments taking place for justification and little thought given to why the irreproducibility may have occurred in the first case. In this paper, a case study is presented in which a systematic approach was carried out in order to determine the exact reason why method irreproducibility was occurring. The findings of the investigation were then drawn onto change a method with poor reproducibility into one that is rugged without the need to start from the beginning and develop a new method.

     

一种提高化妆品中甲醛含量检测的稳定性和灵敏度的双波长光谱方法

提出了一种基于双波长光谱法(以500 nm吸光度为基准并结合414 nm处的吸光度)快速测定化妆品中甲醛含量的方法。结果表明:采用单波长的计算方法(不考虑基线漂移)产生的误差时,平行试验结果之间的相对标准偏差(RSD)可达11.5%,而该方法的RSD最大仅为0.46%。同时该方法能够有效地校正扣除萃取液颜色和基线漂移的影响,且定量下限为7.4 mg/kg。该方法具有分析时间短、操作便捷、灵敏度高、结果准确的优点,适用于化妆品中甲醛的检测。     

Numerical solution of the nonlinear Poisson–Boltzmann equation: Developing more robust and efficient methods

We present a robust and efficient numerical method for solution of the nonlinear Poisson-Boltzmann equation arising in molecular biophysics. The equation is discretized with the box method, and solution of the discrete equations is accomplished with a global inexact-Newton method, combined with linear multilevel techniques we have described in an article appearing previously in this journal. A detailed analysis of the resulting method is presented, with comparisons to other methods that have been proposed in the literature, including the classical nonlinear multigrid method, the nonlinear conjugate gradient method, and nonlinear relaxation methods such as successive overrelaxation. Both theoretical and numerical evidence suggests that this method will converge in the case of molecules for which many of the existing methods will not. In addition, for problems which the other methods are able to solve, numerical experiments show that the new method is substantially more efficient, and the superiority of this method grows with the problem size. The method is easy to implement once a linear multilevel solver is available and can also easily be used in conjunction with linear methods other than multigrid. © 1995 by John Wiley & Sons, Inc.     

Determination of vanadium in biological tissue by anion exchange chromatography and neutron activation analysis

A method is described for determination of vanadium in biological tissues. This method consists of a wet digestion of the tissue with nitric acid followed by anion exchange chromatography, neutron irradiation, and radioassay. The chromatographic separation will allow the decontamination of vanadium from radioactivatable sodium and chlorine which are present in large quantities in biological tissues. The validity of the method is evaluated by employing NBS-SRM 157 and 157a Bovine Liver employing the method of standard additions. The method is successfully applied to human, cow and rat liver specimens. The detection limit of the method is one ppb.     

On-Line Standard Addition Technique for the Determination of Elements in the Samples with High Dissolved Solids by ICP-OES: Application to Determination of Rare Earth Elements in Geological Samples

A simple and rapid on-line standard addition method for analysis of samples with high dissolved solids by ICP-OES is reported. The method involves on-line addition of standard solutions to the sample using a T-piece, prior to the sample introduction system. The standard addition method is commonly used in the analysis of samples with complex matrices. However, the conventional standard addition method is a tedious and time-consuming process. Therefore, in this study, on-line standard addition technique was offered to significantly decrease the analysis time and increase the simplicity of the standard addition method. The performance of the proposed method was tested by determination of rare earth elements in geological samples. This method showed a high level of accuracy in comparison with external calibration and internal standard addition methods.     

Development and validation of an assay method for the determination of trifluoroacetic acid in a cyclosporin-like drug

An improved method for the assay of trifluoroacetic acid (TFA) in a cyclosporin-like drug substance is presented, based on ion chromatography with suppressed conductivity detection. Column fouling by the drug molecule is avoided by use of a sample preparation method in which the drug substance is precipitated at alkaline pH whilst the TFA remains in solution. The new method requires a smaller sample mass than a previous method based on headspace-GC-FID whilst achieving an improvement in sensitivity. During validation, the method's performance was found to be consistent with usual acceptance criteria, and the method was found to be robust in routine use.     

有机酸分析的柱后缓冲电导法与紫外法、直接电导法的比较

柱后缓冲电导法采用柱后调节pH值,电导检测器检测的方法检测有机酸,它避免了经常使用的紫外法选择性差,直接电导法灵敏度低的缺点,是可以实现有机酸准确定量的一种新型分析方法.本文比较了这三种方法的分析结果.     

Using the adhesive interaction between atomic force microscopy tips and polymer surfaces to measure the elastic modulus of compliant samples

An atomic force microscope (AFM) method for measuring surface elasticity based on the adhesive interactions between an AFM tip and sample surfaces is introduced. The method is particularly useful when there is a large adhesion between the tip and soft samples, when the indentation method would be less accurate. For thin and soft samples, this method will have much less interference from the substrate than is found using the indentation method because there is only passive indentation induced by tip-sample adhesion; in contrast, a large indentation with a sharp tip in the sample may break its stress-strain linearity, or even make it fracture. For the case where it is difficult to accurately locate the tip-sample contact point, which is problematic for the indentation method, the method based on adhesive interactions is helpful because it does not require locating the tip-sample contact point when fitting the whole retraction force curve. The model is tested on PDMS polymers with different degrees of cross-linking.     

A multilayered approach to approximating solute polarization

A hybrid multilayered "ONIOM"-type approach to solvation is presented in which the basic free energy of hydration is taken from the Poisson Boltzmann method and the contribution to the solute polarization is taken from a quantum mechanical implementation of the Born method. The method has been tested on the 52 neutral molecules used in the AM1-SM2 parameterization, and the polarized continuum method is taken as the standard by which the results are assessed. Regression analysis shows that the method gives a small improvement over the standard Poisson Boltzmann method or a dramatic improvement over the Born method. The system presented here represents one of the more straightforward applications of the multilayered approach to solvation, but other more sophisticated approaches are discussed.     

New background correction method for liquid chromatography with diode array detection, infrared spectroscopic detection and Raman spectroscopic detection

A new method to eliminate the background spectrum (EBS) during analyte elution in column liquid chromatography (LC) coupled to spectroscopic techniques is proposed. This method takes into account the shape and also intensity differences of the background eluent spectrum. This allows the EBS method to make a better estimation of the background eluent spectrum during analyte elution. This is an advantage for quantification as well as for identification of analytes. The EBS method uses a two-step procedure. First, the baseline spectra are modeled using a limited number of principal components (PCs). Subsequently, an asymmetric least squares (asLS) regression method is applied using these principal components to correct the measured spectra during elution for the background contribution. The asymmetric least squares regression needs one parameter, the asymmetry factor p. This asymmetry factor determines relative weight of positive and negative residuals. Simulations are performed to test the EBS method in well-defined situations. The effect of spectral noise on the performance and the sensitivity of the EBS method for the value of the asymmetry factorp is tested. Two applications of the EBS method are discussed. In the first application, the goal is to extract the analyte spectrum from an LC-Raman analysis. In this case, the EBS method facilitates easy identification of unknown analytes using spectral libraries. In a second application, the EBS method is used for baseline correction in LC-diode array detection (DAD) analysis of polymeric standards during a gradient elution separation. It is shown that the EBS method yields a good baseline correction, without the need to perform a blank chromatographic run.     

原子吸收光谱法测定镉镍电池浸渍液中硅

提出用一氧化二氮乙炔火焰原子吸收光谱法测定镉镍电池浸渍液中硅含量.方法具有良好的灵敏度,干扰少,重现性好.硅量在5～50μg/mL范围内与吸光度呈良好的线性关系.其相对标准偏差均为1.0%;标准加入回收率在97.0%～103.0%范围内,适用于镉镍电池浸渍液中硅的分析.完全达到了实验室分析质量控制的要求.     

叠加内标法色谱定量分析

 叠加内标法是指在色谱定量分析中将内标法与叠加法结合的一种新的定量方法。叙述了叠加内标法定量的理论依据 ,规定了其操作步骤 ,并详细说明了这种方法的适用条件和优缺点。