Variability associated with testing corn for aflatoxin

The sampling, subsampling (both coarse and fine ground meal), and analytical variances associated with testing shelled corn for aflatoxin were estimated by the use of 500 g samples, 50 g subsamples, and the CB method of analysis. The magnitudes of the variance components increased with an increase in the aflatoxin concentration. Functional relationships were developed to predict the variance for a given aflatoxin concentration and any size sample, subsample, and number of analyses. At 20 ppb total aflatoxin, the coefficient of variantion associated with a 4.54 kg sample, 1 kg subsample of coarsely ground meal (passes a #14 screen), a 50 g subsample of finely ground meal (passes a #20 screen) and one analysis were 21, 8, 11, and 26%, respectively.     

Sample variance measurement of mixing

Relationships between the statistical properties of a mixture, the variance in concentration among a number of samples taken from the mixture, and the size and geometry of the samples are considered, using a continuum model. Sample variance is shown to depend on an integral of the product of the mixture correlation function and a function depending only on the sample shape. Analytical and numerical methods for evaluating the sample shape function are presented, as well as a simple, general approximation valid for small distances. Some familiar results relating sample variance to sample size are shown to be special cases of the more general result. Theoretical aspects of mixture correlograms are also considered. An argument is made for assigning correolgram shapes on a physical basis, and some examples are given. All mixtures in which molecular diffusion is negligible are shown to have a correlogram whose initial slope is determined by the interfacial area per unit volume. The complete correlogram for a mixture with randomly arranged clumps is derived, and a model correlogram for layered mixtures with no long-range order is proposed. The theory is compared to experimental results to show that it correctly describes real mixtures.     

Sample Preparation for Analysis of Wood Sugars by Anion Chromatography

We investigated the degradation of sugars during acid hydrolysis and the effects of other aspects of sample preparation on measurement of wood sugars by anion exchange HPLC using pulsed amperometric detection. Loss of sugars in standards ranged from 6.4% for arabinose to 15.7% for mannose. Measurements of wood samples to which standard was added before hydrolysis were very close to the sum of wood samples and standards hydrolyzed and analyzed separately except in the case of galactose, which was in significantly lower amounts (4.7% lower) in the combined samples. There was greater variance among injections of individual replicates than among replicates. Other, minor procedural details were investigated.     

移动窗递推PLS软测量建模及其工业应用

讨论了基于递推部分最小二乘(RPLS)算法的软测量建模方法及其应用.针对过程的时变特性,采用移动窗RPLS算法,在线修正样本的均值和方差,实时更新模型参数,兼顾了建模样本的饱和性、样本信息的完整性.然后将软测量模型应用于工业异构化装置,在线估计对二甲苯(PX)的含量.针对大量工业数据,进行仿真计算,得到模型的最大相对误差、相对均方误差和跟踪性能指标分别为2.68%、0.17%和0.9569,说明该软测量模型具有良好的预测能力和跟踪性能.接着讨论了建模样本长度对模型性能的影响,指出其最佳的样本长度为20～50.     

Estimation of mixing index and contact number by spot sampling

Most of the available definitions of the mixing index, which specifies homogeneity or distribution of the composition in a solids mixture, are based on the variance of the concentration of a certain component among spot samples. However, for a solid—solid chemical reaction or any process involving contact between different solid phases, its rate is proportional to the contact points or area among particles of the different phases. Thus a definition of a microscopic and geometric mixing index based on the number of contact points appears to be of practical significance.The contact number is the number of contact points between two different types of particles for one key particles, a particle species which is selected as a reference. In this paper, the estimation of the mean contact number from spot samples is considered. An expression for estimating the contact number from spot samples is derived. Expressions for the expected value (population mean contact number) and the variance of this mean contact number are also derived. To verify these expression, random numbers with a uniform distribution are generated to simulate a binary component mixture in the completely mixed state. Results of the simulation are in reasonably good agreement with the derived expressions. The mixing index based on the mean contact number is able to indicate the homogeneity of a mixture with regular packing arrangement. In such a mixture, particles are packed either cubically or hexagonally in each layer, and therefore it is difficult to estimate the homogeneity of the mixture from the sample variance.     

Frequency distributions and spatially dependent variability of ammonium and nitrate concentrations in soil under grazed and ungrazed grassland

The frequency distributions of soil NO ₃ ^- and NH ₄ ⁺ concentrations under grazed and ungrazed grassland were found to be lognormal, irrespective of time of year or soil depth. The variance and skewness of the sample values increased with stocking density and use of N fertilizer. An analysis of the spatial dependence of the variability using the semivariogram showed a high nugget variance, even when three sample values from each sampling point were averaged. Most of the variance was therefore short-range (occurring within a distance of 0.4 m), suggesting that the sample volume for soil mineral N measurement should be as large as is practicably possible. As an estimate of the average mineral N content, the geometric mean of the sample values consistently underestimated the true arithmetic mean of the population from which the same was drawn. The conventional estimate of the arithmetic mean for lognormally distributed samples values was satisfactory when the sample number was > 50 and the (log) variance < 0.75 (µg N cm^–3). However, for data with larger variances, high coefficients of skewness and fewer observations, Sichel's estimator was a more efficient measure of the true population mean.     

Automatic calibration for on-line process monitoring in continuous-flow systems

An automatic procedure for calibration in continuous-flow systems is proposed. A flow gradient unit in the sample channel, controlled via a switching valve, delivers a concentration gradient of the standard so that the standard concentration varies with time after the flow-rate gradient is started. Thus, the signal (absorbance)- concentration relationship can be determined and checked for (recalibration) as frequently as required. The procedure was applied to a simulated continuous monitoring of hydrazine in waters, as well as to specific water samples that were spiked with hydrazine at different concentrations.     

Variability associated with testing cottonseed for aflatoxin

The sampling, subsampling, and analytical variance associated with testing cottonseed for aflatoxin were estimated by use of 4.54 kg samples, 100 g subsamples, and the Velasco method of analysis. Regression analysis indicated that each of the above variance components is a function of the concentration of aflatoxin in the populations tested. Functional relationships are presented to determine the sampling, subsampling, and analytical variance for any size sample, subsample, and number of analyses. Paper 4821 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, NC 27607.     

Soy lecithin phospholipid determination by fourier transform infrared spectroscopy and the acid digest/arseno-molybdate method: A comparative study

A study was conducted to determine the accuracy and precision of phospholipid analysis by a simple Fourier transform infrared spectroscopy (FTIR) method relative to the conventional phospholipid phosphorus analysis by the acid digest/arseno-molybdate method by Bartlett. Commercial soy lecithins of known concentrations of phospholipid were prepared and the phospholipid content measured by the FTIR and Bartlett methods. The coefficients of determination and of variances using the two methods were determined. The coefficient of determination for the FTIR method was >0.976 while that for the Bartlett method was ∼0.821. The coefficients of variances (CV) for 1–20% phospholipid concentration range using 10 replicate samples were found to lie between 3.59 and 9.45% for the FTIR method, while the Bartlett method had much higher CV for the same range and replicates (8.95 to 48.73%), signifying the higher accuracy and precision of the FTIR compared to the Bartlett method in the determination of the actual percentage of phospholipid. The Bartlett method gave no significant difference in the phospholipid levels at smaller concentrations, indicating its limitation in accurately determining percentage phospholipid of samples at low concentrations. The one-way analysis of variance at the 1–20% phospholipid concentration range showed that there were significant differences in the mean percentage phospholipid levels for the FTIR data, which was therefore able to distinguish samples with small differences in phospholipid levels. The FTIR method gave consistently reliable results within the range chosen (1–20% phospholipid content). FTIR is a fast, simple, and reliable analytical tool for quantitative phospholipid analysis.     

Optimization of wear resistance of PU/TiO2 coatings on aluminum surfaces

In this paper the effects of structural and process variables on wear resistance of polyurethane/titanium dioxide coatings on aluminium surface is studied. The parameters were polyol molecular weight, diisocyanate type, surface pretreatment method, NCO/OH ratio and pigment volume concentration. The experiments were carried out based on the design of experiments using Taguchi method. The analysis of variance showed that among the parameters studied, polyol molecular weight and pigment volume concentration have the most significant effects on wear resistance. Coatings with higher molecular weight polyol represent more resistance due to higher elongation at break of polymer which consequently increase the wear resistance of coating. The pigment particles provide equivalent physical crosslinks, so it increases the wear resistance. The optimum sample was prepared according to the best levels of each factor, and its morphology was examined by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy.     

Determination of wax concentration in sunflower seed oil

Isothermal crystallization of waxes was studied by using an optical setup. The induction time of crystallization was assessed as a function of wax concentration. The relationship was found to be a decreasing exponential curve. The wax content of some of the solutions prepared in the laboratory was determined by calculating the crystallization induction time. The values obtained were compared to those from different methods (cold test, microscopic, and turbidimetric methods). The results obtained with the optical setup method are similar to those obtained with other methods for concentrations greater than 100 ppm. An analysis of variance test was used to verify the authenticity of the values obtained with the optical method. Results showed that the method used to determine wax concentration, the concentration of the sample, and the relationship between both parameters do not affect significantly the values of percentage relative errors (P<0.05) obtained for concentrations greater than 100 ppm. Values obtained for wax content within the range 0–100 ppm could not be compared since the microscopic and turbidimetric methods are not sensitive enough, unlike the optical setup, to detect wax amounts in such low concentration.     

Aluminium‐filled low‐density polyethylene—structural,morphological, and mechanical properties

Low‐density polyethylene (LDPE) was filled with aluminium (Al) powder having concentrations of 1, 4, and 6% w/w. The samples in the form of disc containing the above concentration of Al powder were obtained using hot press molder. The structural properties have been investigated using density measurement and WAXD techniques. The morphology of pure LDPE and Al‐filled LDPE samples has been studied from scanning electron micrographs. The modulus of elasticity of the samples has been determined using Instron tensile tester. Results indicate that the crystallinity of LDPE component increases with the concentration of aluminium filler. Morphological changes also have been observed. The Young's modulus (Y) generally increases and becomes maximum for 4% Al‐filled LDPE sample. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Method for distinguishing Brønsted-acid sites in mixtures of H-ZSM-5, H-Y and silica-alumina

We have examined the adsorption and reaction of ethylamine, isopropylamine, 2-ethylhexylamine, cyclooctylamine, and diphenylethylamine on H-ZSM-5, H-Y, and silica-alumina samples using temperature-programmed desorption (TPD) and thermogravimetric analysis (TGA). Each of the amines decomposes at Brønsted-acid sites to alkene and ammonia products above 550 K by a reaction similar to the Hofmann elimination reaction, so that the number of molecules which decompose can be used to measure the number of acid sites in the sample. For H-ZSM-5, the concentration of sites determined using ethylamine and isopropylamine was approximately equal to the framework aluminum concentration; however, adsorption of cyclooctylamine and 2-ethylhexylamine in H-ZSM-5 was limited so that only a fraction of the sites were counted using these probe molecules. For the silica-alumina and H-Y samples, the concentrations of Brønsted-acid sites could be determined using ethylamine, isopropylamine, 2-ethylhexylamine, or cyclooctylamine; and the site concentrations determined in this way were essentially dependent of which amine was used. 2,2-Diphenylethylamine adsorption was limited on both silica-alumina and H-Y samples, but a much higher fraction of the Brønsted-acid sites on the silicaalumina sample could be counted. These results indicate that TPD-TGA measurements with various amines can be used to determine the concentration of Brønsted-acid sites in each of the components of a fluid-catalytic-cracking catalyst.     

Measurements of High Oleic Purity in Peanut Lots Using Rapid,Single Kernel Near-Infrared Reflectance Spectroscopy

High oleic peanuts have improved shelf life vs. conventional peanuts. Purity (percentage of high oleic peanuts within a lot) is critical to ingredient performance and final lot value. Contamination can result from unintentional mix-ups at the breeder/seed level, improper production handling, or due to physiologically immature high oleic kernels. Therefore, industry groups have established unofficial sampling plans to monitor purity. Assuming equivalent measurement performance and simple random sampling, increasing the sample size decreases variance among replicated sample test results and increases the precision of estimated lot purity. A novel instrument (QSorter Explorer by QualySense AG) using near-infrared reflectance spectroscopy was evaluated for high speed (20 kernels per second) high oleic purity measurements. The study objectives were to assess instrument performance in: (1) measuring oleic acid (%) in runner peanuts and (2) estimating the true high oleic purity of artificially mixed peanut lots. Three grades (Jumbo, Medium, and No 1) of US Runner mini-lots each at seven different contamination levels (0, 5, 10, 20, 30, 50, and 100%) were prepared. Oleic acid (%) of individual kernels was measured by scanning replicated samples of 10, 50, 100, and 500 kernels using the QSorter Explorer. The variance associated with each sample size and lot contamination level on returned purity values is discussed in the context of binomial sampling. Overall, the demonstrated measurement performance and capacity of the QSorter Explorer to process much larger sample sizes suggest this instrument can better identify true high oleic peanut lot purity vs. other currently available technologies.     

P-ZSM-5-水吸附制冷工质对制冷性能预测

采用不同浓度磷酸溶液浸渍法改性ZSM-5沸石分子筛,测定温度为303 K时不同浓度改性试样的饱和吸附量,筛选出最佳改性试样并测定其吸附等温线;在此基础上对最佳改性试样进行制冷性能预测,采用D-A方程简略式进行吸附制冷模拟仿真,探讨冷凝温度、脱附温度对系统制冷系数(COP)及制冷量(Qref)的影响.吸水性能结果表明:试样改性后吸附量均大于未改性试样,存在最佳改性质量分数(6.32%,磷酸质量分数),最佳改性质量分数试样的饱和吸附量为1.299 g/g.制冷性能结果表明:在最佳工况(Ta2=Tc=303 K、Te=278 K、Tg2=378 K)时,计算得到COP为1.097,Qref为1 691.126 kJ/kg,性能优于常规吸附制冷工质对.     

结核分枝杆菌特异性IFNγ体外释放试验全血检测试剂盒的质量评价

目的评价结核分枝杆菌特异性IFNγ体外释放试验(interferon γ release assay,IGRA)全血检测试剂盒的质量。方法采用10个结核分枝杆菌特异性IGRA全血检测试剂盒检测参考样品,以参考样品检测值和样品浓度进行线性回归,获得线性回归方程及相关系数(R^2)。按各试剂盒说明书判定参考样品,以阳性的最低参考样品浓度作为相应试剂盒的最低检测浓度。结果 10个结核分枝杆菌特异性IGRA全血检测试剂盒的R2均高于0. 9,最低检测浓度分布在0. 4~2 IU/mL之间。结论结核分枝杆菌特异性IGRA全血检测试剂盒的质量稳定,线性分析和最低检测浓度检测可用于该试剂盒IFNγ测定部分的质量控制。     

The influence of Cu,Fe, Ni,Pb and Zn on gum formation in the Brazilian automotive gasoline

In this research work, the effect of different concentrations of copper, iron, lead, zinc and nickel ions on the tendency for gum formation in gasohol fuel is investigated. For that purpose, a gasohol sample has been doped with these five metals ions at concentration levels of 0.25, 1.0, 2.0 and 3.0 μg ml^− 1. Washed gum content tests have been carried out using ASTM D 381 on samples stored for 7, 14, and 28 days. The results show that gum formation is strongly affected by Cu and Fe, with a much weaker effect from Ni and Zn, and an almost negligible effect from Pb. A variance analysis (ANOVA) of the experimental results shows that an increase in metal concentration strongly increases the rate of gum formation for all metal ions investigated, particularly Cu and Fe, while an increase in storage time has only a much weaker effect, being negligible for Zn.     

Effects of the annealing atmosphere on the microstructure and properties of BiFe0.99Zn0.01O3 films

BiFe_0.99Zn_0.01O₃ (BFZO) films were annealed in different atmospheres (Air, N₂ and O₂) on ITO/glass substrates. The influences of the different annealing atmospheres on the oxygen vacancy concentration, microstructure, ferroelectric behavior, leakage current, leakage mechanism, aging and dielectric performance of the BFZO films were studied. The crystallization and grain development for the sample annealed in an O₂ atmosphere improved, and the concentrations of the Fe²⁺ and oxygen vacancies were the lowest among the samples studied herein. The BFZO film had the lowest leakage current density and the best ferroelectric performance in an O₂ annealing atmosphere among the samples studied herein, and the leakage was due to the F-N tunneling effect mechanism. From the perspective of the volume effect, the aging model was established, and the aging mechanism of the BFZO films was discussed in depth. Compared with Air and N₂, the annealed film in O₂ exhibited no obvious aging.     

Real-time monitoring of drug concentration in a continuous powder mixing process using NIR spectroscopy

A non-destructive NIR spectroscopic method was used to acquire on-line spectra of a continuous mixing process, and evaluate the performance of this novel system. Partial least squares (PLS) calibration models were developed and used for real-time determination of active ingredient concentration on the blends produced with a continuous mixer. The NIR method was developed for concentrations ranging from 0 to 15% (w/w) of acetaminophen (APAP), the active pharmaceutical ingredient used in the experiments. The calibration model's overall accuracy was 0.41% (w/w), and estimated through the root mean square error of cross validation (RMSECV) for samples predicted using leave-class-out cross validation. In this cross validation, each concentration was defined as a class, and when a sample of a specific concentration was predicted all samples of that concentration were left out of the calibration model. The precision of the calibration model was also estimated at various concentration levels, to facilitate the differentiation between the variation in drug concentration due to the analytical method's measurement uncertainty and the variation in the drug distribution throughout the powder blend. The results obtained are very promising since in three of the five powder mixes, the variation in the drug concentration in the powder blends was similar to that of the analytical method indicating a high degree of blend homogeneity     

An in situ heating study of hydrogen-containing adsorbates on polycrystalline diamond surfaces using elastic recoil detection

Elastic recoil detection (ERD) was used to measure the concentration of hydrogen on as-deposited, heated, and air-exposed polycrystalline diamond films in order to relate the surface peak often observed in ERD spectra to the thermodynamic behavior of hydrogen on the surface of polycrystalline diamond. A surface peak corresponding to an enhanced hydrogen surface concentration was observed on all as-deposited samples. When each sample was heated in vacuum, the enhanced surface concentration decreased with increasing temperature and completely disappeared at 400°C, at which the surface concentration was equal to the bulk concentration. The surface and bulk concentrations remained the same for the duration of the heating process (129 h), however, the enhanced surface concentration reappeared when the heated samples were exposed to air, suggesting that the enhanced ERD peak is comprised primarily of weakly-bonded hydrogen-containing adsorbates such as water. By accounting for surface roughness of the samples and examining the temperature-dependent behavior of the surface peak, the thickness of the enhanced surface layer was determined to be in accordance with results reported by others using nuclear reaction analysis and much less than the thickness predicted by ERD simulation software.