Two step-down tests for equality of covariance matrices

The classical problem of testing the equality of the covariance matrices from k ? 2 p-dimensional normal populations is reexamined. The likelihood ratio (LR) statistic, also called Bartlett’s statistic, can be decomposed in two ways, corresponding to two distinct component-wise decompositions of the null hypothesis in terms of the covariance matrices or precision matrices, respectively. The factors of the LR statistic that appear in these two decompositions can be interpreted as conditional and unconditional LR statistics for the component-wise null hypotheses, and their mutual independence under the null hypothesis allows the determination of the overall significance level.     

Method validation for the analysis of pesticide residues in grain by thin-layer chromatography

Method validation is an important requirement in the practice of pesticide residue analysis and is the process of verifying that a method is fit for its purpose. To make a correct decision on the validity of the method, the following method performance parameters have to be taken into consideration: scope, specificity, limit of detection, limit of quantification, linear range, accuracy, precision, repeatability, reproducibility, recovery, ruggedness and robustness. The goal of this study was to validate previously adapted thin-layer chromatographic methods for the pesticide residue analysis in grain. Confirmation of validation parameters for some compounds was also performed by gas chromatographic analysis.     

基于ACR9000控制器的自动光学检测平台设计 

针对自动光学检测（AOI）平台运行过程中的定位精度控制问题,提出了一种基于速度和加速度前馈控制与PID反馈控制的复合控制算法,该算法对输入量进行跟踪补偿控制以消除系统稳态误差,用于提高AOI平台定位精度。基于开放式的数控系统设计方法设计了AOI平台。在Matlab/Simulink环境下,构建了基于该复合控制算法的定位精度控制仿真模型,仿真结果验证了复合控制算法的有效性。将该复合控制算法作为ACR9000控制器的控制算法,并基于ACR9000控制器进行AOI平台实验研究。应用该AOI平台进行了印刷电路板（PCB）检测实验,实验结果表明文中复合控制算法能够提高AOI平台定位精度,AOI平台的定位精度满足印刷电路板检测要求,可以将该AOI平台用于印刷电路板检测。     

Interactions Between Alkyl Triphenyl Phosphonium Bromides and Polyvinylpyrrolidones in Aqueous Media

The interactions of polyvinylpyrrolidones with alkyl triphenyl phosphonium bromide in aqueous media were investigated with conductometric, fluorimetric and tensiometric techniques. Formation of surfactant-polymer aggregates was detected in the case of C₁₆ and C₁₄ surfactant by these techniques. Tensiometric technique proved to be very sensitive to detect the early stage of association at very low concentrations. The Gibbs free energy of micellization and the dielectric constant values of the micellar interface values were obtained and discussed in terms of strength of interaction between the polymers and surfactants.     

The determination of crown–cation complexation behavior in dioxane/water mixtures by conductometric studies

Using conductance measurements, an attempt has been made to gain detailed information about the specific molecular interactions of crown compounds with metal ions in a 1,4-dioxane/water binary system. Analyses of the transport data of dioxane/water mixtures yielded the mobility of the crown compound action complexes and the ion-pair dissociation constant of the crown compound–electrolyte complex. Binary mixed aqueous solvents are frequently employed in broad areas of chemistry. Their applicability ranges from synthetic and mechanistic studies in organic chemistry to biophysical chemistry, with emphasis on molecular interactions in biologically significant structures. Stability constants of crown compound complexes are determined by various methods, such as potentiometry (with ion selective electrodes), polarography, voltammetry, spectrophotometry, nuclear magnetic resonance, calorimetry and solubility. In this study the conductometry measurements have been carried out with high precision at optimal concentrations in dioxane/water systems. Structures of crown–cation complexes in dioxane/water mixtures are estimated from the conductance parameters (κ, Λ and α) as well as the complex formation constant, K_e = (Λ_MAm − Λ) / (Λ − Λ_MaLbAm) [L]. The conductance behavior of Na⁺, K⁺ chlorides and Na⁺ perchlorates with 18-crown-6, 15-crown-5, and 12-crown-4 have been studied in various dioxane/water systems (50%, 80%, and 85%) at 25°C. The all experimental studies have been made by the ratio 1 : 1 of the metal-ion and the crown ether, K_e. For the calculations, Excel. 5.0 was used as an application program. Copyright © 1998 John Wiley & Sons, Ltd.     

Study of the precision in the purge-and-trap–gas chromatography–mass spectrometry analysis of volatile compounds in honey

Data precision in the analysis by purge-and-trap coupled on-line to gas chromatography–mass spectrometry (P&T-GC–MS) of honey volatiles has been studied by statistical analysis. The contribution of non-random factors to dispersion of quantitative results was proven by comparing several statistical parameters (correlation coefficients, principal component analysis (PCA) eigenvalues and loadings) from both experimental and simulated data. PCA was also useful for grouping volatiles with similar dispersion behaviour; these groups being generally related to compounds with common properties or structural features. The use of area ratios improves data precision for compounds within the same group. Results from this study could be used for a better selection of internal standards in quantitative analysis of volatiles by P&T-GC–MS.     

Targeted metabolomics in cultured cells and tissues by mass spectrometry: Method development and validation

Metabolomics is the identification and quantitation of small bio-molecules (metabolites) in biological samples under various environmental and genetic conditions. Mass spectrometry provides the unique opportunity for targeted identification and quantification of known metabolites by selective reaction monitoring (SRM). However, reproducibility of this approach depends on careful consideration of sample preparation, chemical classes, and stability of metabolites to be evaluated. Herein, we introduce and validate a targeted metabolite profiling workflow for cultured cells and tissues by liquid chromatography–triple quadrupole tandem mass spectrometry. The method requires a one-step extraction of water-soluble metabolites and targeted analysis of central metabolites that include glycolysis, amino acids, nucleotides, citric acid cycle, and the hexosamine biosynthetic pathway. The sensitivity, reproducibility and molecular stability of each targeted metabolite were assessed under experimental conditions. Quantitation of metabolites by peak area ratio was linear with a dilution over a 4 fold dynamic range with minimal deviation R² = 0.98. Inter- and intra-day precision with cells and tissues had an average coefficient of variation <15% for cultured cell lines, and somewhat higher for mouse liver tissues. The method applied in triplicate measurements readily distinguished immortalized cells from malignant cells, as well as mouse littermates based on their hepatic metabolic profiles.     

成像光谱技术在植物非生物胁迫表型高通量分析中的研究进展

植物非生物胁迫是指对植物产生不利影响的非生物因素,非生物胁迫威胁植物发芽、生长、发育和繁殖,是阻碍农作物高效栽培和农业可持续发展的主要因素.植物胁迫精准管理和抗逆植物育种是缓解和解决非生物胁迫的有效途径,其中植物表型分析是一个不可或缺的环节,但是传统滞后的如人工、破坏式表型测量方法很难满足高通量表型分析的需求,制约着植...