Second- and higher-order data generation and calibration: A tutorial

An introduction to multi-way calibration based on second- and higher-order data generation and processing is provided, with emphasis on practical experimental aspects. After a discussion concerning a proper nomenclature scheme, a suitable classification of the obtainable data, and the general features of the available algorithms and their underlying models, a series of examples is discussed in detail, with the purpose of illustrating the great potentiality of the field for the analytical community. Emphasis is directed toward the most popular multi-way data, i.e., second-order or matrix data, which can be conveniently measured in a variety of instruments. Third-order data are being increasingly studied and are also discussed, along with the less explored field of fourth-order data. The estimation of figures of merit, which analysts need to report during method development, is now sufficiently mature to be provided for the general audience.     

A new multivariate variability control chart based on a covariance matrix combination

In the field of multivariate quality control, there are many control charts related to the process mean but few options addressing process variability. Variability control charts have two main drawbacks: the first relates to the number of parameters to tune and the second relates to how changes in the mean affect the performance of these charts. Thus, in this paper, we propose a new multivariate variability control chart, called the multivariate exponentially weighted covariance matrix combination, which solves these two problems. The results show that this new chart performs well in the detection of changes in variance when the mean does not change and outperforms other charts when the mean does change.     

Automatic Debye–Scherrer elliptical ring extraction via a computer vision approach

The accurate calibration of powder diffraction data acquired from area detectors using calibration standards is a crucial step in the data reduction process to attain high‐quality one‐dimensional patterns. A novel algorithm has been developed for extracting Debye–Scherrer rings automatically using an approach based on computer vision and pattern recognition techniques. The presented technique requires no human intervention and, unlike previous approaches, makes no restrictive assumptions on the diffraction setup and/or rings. It can detect complete rings as well as portions of them, and works on several types of diffraction images with various degrees of ring graininess, textured diffraction patterns and detector tilt with respect to the incoming beam.     

设计数字温度计实验的改进

分析AD590设计数字温度计的工作原理,通过简单改进提高实验的精度,并扩展了设计数字温度计的应用空间。     

Second-order advantage with excitation–emission photoinduced fluorimetry for the determination of the antiepileptic carbamazepine in environmental waters

A photochemically induced fluorescence system combined with second-order chemometric analysis for the determination of the anticonvulsant carbamazepine (CBZ) is presented. CBZ is a widely used drug for the treatment of epilepsy and is included in the group of emerging contaminant present in the aquatic environment. CBZ is not fluorescent in solution but can be converted into a fluorescent compound through a photochemical reaction in a strong acid medium. The determination is carried out by measuring excitation–emission photoinduced fluorescence matrices of the products formed upon ultraviolet light irradiation in a laboratory-constructed reactor constituted by two simple 4 W germicidal tubes. Working conditions related to both the reaction medium and the photoreactor geometry are optimized by an experimental design. The developed approach enabled the determination of CBZ at trace levels without the necessity of applying separation steps, and in the presence of uncalibrated interferences which also display photoinduced fluorescence and may be potentially present in the investigated samples. Different second-order algorithms were tested and successful resolution was achieved using multivariate curve resolution-alternating least-squares (MCR-ALS). The study is employed for the discussion of the scopes and yields of each of the applied second-order chemometric tools. The quality of the proposed method is probed through the determination of the studied emerging pollutant in both environmental and drinking water samples. After a pre-concentration step on a C18 membrane using 50.0 mL of real water samples, a prediction relative error of 2% and limits of detection and quantification of 0.2 and 0.6 ng mL⁻¹ were respectively obtained.     

α-NH2 Determination from Biological Infrared Spectra

The use of Mid-infrared spectroscopy for the analysis of food products has only recently developped with the advent of Fourier Transformed spectroscopy and other techniques like Attenuated Total Reflectance, diffused reflection combined to the use of powerful micro-computers. We have recently reported to use a combination of multidimensional statistical analysis and Mid-FTIR spectroscopy for the quantitative determination of sugars in a biological sample. In this paper we have evaluated the use of such a method for the quantitative measurement of α-amino groups from ammo-acids, peptides and proteins. The spectral region where the characteristic absorption bands of such groups are located, ranges between 1200 cm-1 and 1900 cm-1. Water features a major absorption band in this region (1500–1700 cm-1). This superimpose with amide I and II bands.

The standard deviation for each and every wavelength, calculated for all the spectra of the calibration set, show the existence of two absorption bands in the 1500–1900 cm-1 region which means that the observed variations in this zone are not only due to water but are also due to two peaks centered at 1650 cm-1 and 1540 cm-1 (with a hollow at 1600 cm-1) that are characteristic of protids.

The contribution of the first four axes of the PCA, axes 5, 1, 4 and 2, to the total inertia percentage are 2. 37%, 53. 36%, 3. 92% and 28. 82% respectively. The correlation coefficient between the major axis, axis 5, and the chemical values of α-NH₂ is 0. 311 and the second axis, axis 1, increases this value to 0. 541. The first 10 axes were used to establish the prediction equation; the correlation coefficient value is very high: 0. 978.

Good predictions were obtained; mean and standard deviation associated to the predicted concentrations of α-NH₂content, valued 0 g/ml and 0. 12 g/ml respectively. Hence, we have established the possibility of determining, from a MIR spectra, the α-NH₂ content.     

低频UWB SAR天线方向图校准算法

低频UWBSAR具有较大的方位向处理角,因此天线方向图沿方位向的变化不能忽略。本文给出SAR系统的时域处理模型,利用该模型分析天线方向图对系统性能的影响,然后给出天线方向图的校准算法,以及该算法的性能分析。最后通过计算机仿真,验证该算法的有效性,得到的仿真结果和理论分析相吻合。     

Speciation of adsorbates on surface of solids by infrared spectroscopy and chemometrics

Speciation, i.e. identification and quantification, of surface species on heterogeneous surfaces by infrared spectroscopy is important in many fields but remains a challenging task when facing strongly overlapped spectra of multiple adspecies. Here, we propose a new methodology, combining state of the art instrumental developments for quantitative infrared spectroscopy of adspecies and chemometrics tools, mainly a novel data processing algorithm, called SORB-MCR (SOft modeling by Recursive Based-Multivariate Curve Resolution) and multivariate calibration. After formal transposition of the general linear mixture model to adsorption spectral data, the main issues, i.e. validity of Beer–Lambert law and rank deficiency problems, are theoretically discussed. Then, the methodology is exposed through application to two case studies, each of them characterized by a specific type of rank deficiency: (i) speciation of physisorbed water species over a hydrated silica surface, and (ii) speciation (chemisorption and physisorption) of a silane probe molecule over a dehydrated silica surface. In both cases, we demonstrate the relevance of this approach which leads to a thorough surface speciation based on comprehensive and fully interpretable multivariate quantitative models. Limitations and drawbacks of the methodology are also underlined.     

自动光学检测仪工作台运动控制系统的研究

对PCB自动光学检测仪工作台运动控制系统进行了研究。通过优化PID参数．加积分校正，建立螺距补偿表的方法，提高了系统的定位精度及动态特性。