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91.
During recent years, the direct transformation of aldehydes into esters or amides has developed into a vigorous research area and powerful one-pot oxidative esterification and amidation procedures have been reported. Several concepts that are often complementary in substrate scope, functional group tolerance, and reaction outcome have emerged, thus providing a wide range of alternatives to classical ester and amide synthesis via carboxylic acid intermediates. 相似文献
92.
Wolska L 《Analytical and bioanalytical chemistry》2008,391(7):2647-2652
The results of interlaboratory studies on the determination of selected PAHs in samples of pure water and water containing
suspended matter are presented and discussed in this study. Determinations were performed by independent analytical laboratories
which used different sample-preparation procedures, i.e. liquid-liquid extraction and solid-phase extraction with columns
and speedisks. The study indicates that the results of PAHs determination depend on the type of isolation technique and the
final determination procedure used by a given laboratory. Differences among the determined concentrations of specific PAHs
reached 700%. In this work it has been shown that modern analysis does not offer isolation techniques for PAHs which would
secure their speciation in the aquatic environment. 相似文献
93.
基于无穷远点与相机内参量关系,提出了一种相机内参量及像差系数与外参量解耦标定方法.首先,根据平面单应计算绝对二次曲线在像面的投影方程,线性求解相机内参量;然后,将重投影像点视为理想像点线性求解像差系数,并计算像点重投影误差;最后,将序列图像的平面单应作为待优化参量,以最小化像点重投影误差为目标函数,重复上述过程,输出最优的相机内参量和像差系数.在相同配置下,分别对本文方法和张正友平面靶板标定方法的标定准确度进行仿真与对比分析.基于不同姿态和位置的27幅棋盘格图片,分别利用这两种方法对相机内参量进行标定实验.实验结果表明:与张正友平面靶板标定方法相比,本文方法的标定准确度提高了至少1%;在实物实验中,张正友平面靶板标定方法和本文方法的重投影残差分别为0.064像素和0.008像素. 相似文献
94.
K. Medina-Dzul S. Medina-Peralta C. Carrera-Figueiras M. Sánchez 《International journal of environmental analytical chemistry》2017,97(9):831-840
Beeswax is a complex mixture of lipophilic compounds and other components such as aliphatic alcohols and carotenoids. Then, extraction and clean-up for pesticide analysis in beeswax is a challenge. In this work, a multiresidue method for the analysis of dichlorvos (DCV), diazinon, malathion, methyl parathion and coumaphos (CMF) in beeswax was developed. The proposed approach is based on matrix solid-phase dispersion extraction. The adsorbent for sample clean-up was studied and a simplex-centroid cubic statistical design was applied to evaluate pure solvents and their binary and ternary mixtures to elute the analytes. Finally, Florisil and ethyl acetate were chosen as solid support and eluting solvent, respectively. After extraction, pesticides were separated and detected by gas chromatography/mass spectrometry. The method achieved acceptable recoveries (70–85%; except for DCV, 24–38%) with relative standard deviations below 5%. The repeatability of the method was lower than 8% and interday variability was below 12%. The limit of detection (LOD) for the analytes varies between 0.2 and 2.6 µg?kg?1 and limit of quantification from 0.93 to 8.8 µg?kg?1. LOD reached for CMF was below the maximum residue limit allowed by the legislation of the United States and Canada. 相似文献
95.
Influence of processing procedure on the quality of Radix Scrophulariae: A quantitative evaluation of the main compounds obtained by accelerated solvent extraction and high‐performance liquid chromatography
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Gang Cao Xin Wu Qinglin Li Hao Cai Baochang Cai Xuemei Zhu 《Journal of separation science》2015,38(3):390-394
An improved high‐performance liquid chromatography with diode array detection combined with accelerated solvent extraction method was used to simultaneously determine six compounds in crude and processed Radix Scrophulariae samples. Accelerated solvent extraction parameters such as extraction solvent, temperature, number of cycles, and analysis procedure were systematically optimized. The results indicated that compared with crude Radix Scrophulariae samples, the processed samples had lower contents of harpagide and harpagoside but higher contents of catalpol, acteoside, angoroside C, and cinnamic acid. The established method was sufficiently rapid and reliable for the global quality evaluation of crude and processed herbal medicines. 相似文献
96.
We study the discrete Painlevé equations associated to the affine Weyl group which can be obtained by the implementation of a special limits of -associated equations. This study is motivated by the existence of two -associated discrete both having a double ternary dependence in their coefficients and which have not been related before. We show here that two equations correspond to two different limits of a -associated discrete Painlevé equation. Applying the same limiting procedures to other -associated equations we obtained several -related equations most of which have not been previously derived. 相似文献
97.
We revisit the method of Chvátal, Cook, and Hartmann to establish lower bounds on the Chvátal-Gomory rank, and develop a simpler method. We provide new families of polytopes in the 0/1 cube with high rank, and we describe a deterministic family achieving a rank of at least (1+1/e)n−1>n. Finally, we show how integrality gaps lead to lower bounds. 相似文献
98.
To comply with the EU Noise Directive 2002/49/EC, Member States are required to produce strategic noise maps for designated areas, including mapping road traffic noise from major roads. These maps must be presented using the EU indicators Lden and Lnight. However, the most common noise indicator used in Ireland at present is the LA10,18h indicator arising from the use of the Calculation of Road Traffic Noise (CRTN) prediction method. Therefore, a relationship needs to be established between LA10,18h and Lden and Lnight, separately. In addition to noise mapping these indicators are used for noise abatement purposes, so the proposed relationship must be accurate and robust. In 2002, the UK’s Transport Research Laboratory (TRL) published a paper describing mathematical procedures that could be used to convert values of LA10 to Lden and Lnight. These procedures were then adopted for use in Ireland. This paper examines the suitability of the TRL conversion methods 1 and 3 for use under Irish road conditions. Method 2 was not considered in this study, as it was a methodology not applicable in an Irish scenario. Studies concluded that where hourly traffic data are available, the conversion methodology outlined in TRL Method 1 is robust and reproducible. However, in the absence of hourly traffic data where daily traffic counts are used, the relevant conversion procedures produce variable results for both Lden and Lnight when applied to Irish road conditions. To reduce the variability, new conversion procedures were developed, specifically for Irish road conditions. 相似文献
99.
100.
《Mathematical Methods in the Applied Sciences》2018,41(14):5582-5592
We introduce a new idea of algorithmic structure, called assigning algorithm, using a finite collection of a subclass of strictly quasi‐nonexpansive operators. This new algorithm allows the iteration vectors to take steps on a pattern which is based on a connected directed acyclic graph. The sequential, simultaneous, and string‐averaging methods for solving convex feasibility problems are the special cases of the new algorithm which may be used to reduce idle time of processors in parallel implementations. We give a convergence analysis for such algorithmic structure with perturbation. Also, we extend some existence results of the split common fixed point problem based on the new algorithm. The performance of the new algorithm is illustrated with numerical examples from computed tomography. 相似文献