Uncertainty calculations in the certification of reference materials. 2. Homogeneity study

 Many reference materials undergo a batch certification, which implies that a small number of samples is taken from a batch, characterised, and these results are then assumed to be representative of all remaining samples. An important aspect in this design is the translation of the characterisation data to a single sample, as usually the laboratory will be using only one sample of the batch. This form of homogeneity is very important and can be influenced to a certain extent by well-designed sample preparation procedures. Another subsampling problem associated with many reference materials is that only a small test portion is drawn from the sample to carry out the measurement. Obviously, this test portion must be representative of the sample, otherwise the certified value is still not applicable. Both kinds of homogeneity tests are examined in the paper and evaluated using practical examples. Received: 31 May 2000 · Accepted: 29 July 2000     

中国硒研究历史回顾（上）

过去50年中,中国微量元素科学和营养科学中最重要的发现,就是认识了硒对人体健康的重要性。在诸多微量元素中,没有哪一个元素能像硒那样对人类产生如此深刻而又广泛的影响。从硒的生物必需性、硒的生物效应两面性、硒的抗癌性、硒的延寿作用及富硒产品开发五个方面回顾了中国的硒研究历程。     

Human health risk assessment of heavy metals via consumption of contaminated vegetables collected from different irrigation sources in Lahore,Pakistan

Soil pollution with heavy metals due to discharge of untreated urban and industrial wastewater is a major threat to ecological integrity and human well-being. The presenting study aimed to determine human health risks associated via food chain contamination of heavy metals routing from irrigation of urban and industrial wastewater. Irrigated water, soil and vegetables were analyzed for Cr²⁺, Co²⁺, Ni²⁺, Cu²⁺, Pb²⁺, Cd²⁺, Mn²⁺ and Zn²⁺; transfer factor (TF), daily intake of metals (DIM) and health risk index (HRI) were also calculated. Cr²⁺, Pb²⁺ and Cd²⁺ in vegetables cultivated by wastewater exceeded the permissible limits (European Union, 2002) while TF was lower for all metals except Co²⁺ and HRI was found to be maximum for Spinacia oleracea (2.42 mg/kg) and Brassica campestris (2.22 mg/kg) cultivated by wastewater. S. oleracea, B. campestris, Coriandrum sativum posed a severe health risk with respect to Cd and Mn.     

Occurrence of Phthalates in Bottled Drinks in the Chinese Market and Its Implications for Dietary Exposure

Ubiquitous occurrences of phthalic acid esters (PAEs) or phthalates in a variety of consumer products have been demonstrated. Nevertheless, studies on their occurrence in various types of bottled drinks are limited. In this study, fifteen PAEs were analyzed in six categories of bottled drinks (n = 105) collected from the Chinese market, including mineral water, tea drinks, energy drinks, juice drinks, soft drinks, and beer. Among the 15 PAEs measured, DEHP was the most abundant phthalate with concentrations ranging from below the limit of quantification (LOQ) to 41,000 ng/L at a detection rate (DR) of 96%, followed by DIBP (DR: 88%) and DBP (DR: 84%) with respective concentration ranges of below LOQ to 16,000 and to 4900 ng/L. At least one PAE was detected in each drink sample, and the sum concentrations of 15 PAEs ranged from 770 to 48,004 ng/L (median: 6286 ng/L). Significant differences with respect to both PAE concentrations and composition profiles were observed between different types of bottled drinks. The median sum concentration of 15 PAEs in soft drinks was over five times higher than that detected in mineral water; different from other drink types. Besides DEHP, DBIP, and DBP, a high concentration of BMEP was also detected in a tea drink. The estimated daily dietary intake of phthalates (EDI_drink) through the consumption of bottled drinks was calculated based on the concentrations measured and the daily ingestion rates of bottled drink items. The EDI_drink values for DMP, DEP, DIBP, DBP, BMEP, DAP, BEEP, BBP, DCP, DHP, BMPP, BBEP, DEHP, DOP, and DNP through the consumption of bottled mineral water (based on mean concentrations) were 0.45, 0.33, 12.5, 3.67, 2.10, 0.06, 0.32, 0.16, 0.10, 0.09, 0.05, 0.81, 112, 0.13, and 0.20 ng/kg-bw/d, respectively, for Chinese adults. Overall, the EDI_drink values calculated for phthalates through the consumption of bottled drinks were below the oral reference doses suggested by the United States Environmental Protection Agency (U.S. EPA).     

Influence of relative response factor in the determination of organic microcontaminants with isotopically labeled standards

The use of isotopically labeled internal standards in the analysis of organic microcontaminants entails the determination of relative response factors (RRFs) of the unlabeled with respect to the labeled compounds. RRFs were measured daily during 28 replicate polychlorobiphenyl (PCB) analyses on two different sets of samples. Daily RRFs allowed more precise results to be attained than those provided by mean RRFs, the latter being the mean of all the daily RRFs obtained during the same series of analyses. Analytical applications to food matrices are presented, including the PCB contamination profile of an olive oil and that found in a matrix of Italian national mean diet. Based on the latter sample, also the polycyclic aromatic hydrocarbon (PAH) daily intake of Italians is assessed. Seven PAHs are determined.     

How Different Snacks Produce a Distinct Effect in Salivary Protein Composition

Saliva secretion changes in response to different stimulation. Studies performed in animals and humans suggest that dietary constituents may influence saliva composition, although the dynamics of these changes, and how they are specific for each type of food, are little known. The objective of the present study was to access the short-term effects of different foods in salivation and salivary protein composition. Twelve participants were tested for four snacks (yoghurt, bread, apple and walnuts). Non-stimulated saliva was collected before and at 0′, 5′ and 30′ after each snack intake. Flow rate, total protein, alpha-amylase enzymatic activity and salivary protein profile were analyzed. Yoghurt and apple were the snacks resulting in higher salivary changes, with higher increases in flow rate and alpha-amylase activity immediately after intake. The expression levels of immunoglobulin chains decreased after the intake of all snacks, whereas cystatins and one pink band (proline-rich proteins—PRPs) increased only after yoghurt intake. Walnut’s snack was the one resulting in lower changes, probably due to lower amounts eaten. Even so, it resulted in the increase in one PRPs band. In conclusion, changes in saliva composition varies with foods, with variable changes in proteins related to oral food processing and perception.     

轻卡进气管的结构优化及其声学性能

为有效降低轻卡进气管的噪声,首先通过原始进气管的噪声实验,测试得出噪声的主要贡献频率,结合管道的布置情况,进行了消声器(谐振腔)的设计,进而完成对进气管的优化设计;通过专业声学分析软件LMS Virtual.Lab对优化前后的进气管进行声学性能的模拟研究,得出了谐振腔对声场的具体影响;通过噪声实验,分析出加装谐振腔的进气管相比于原始进气管的降噪效果。研究结果表明:在所研究的进气管噪声的主要贡献频率下(即125 Hz、180 Hz、465 Hz、640 Hz),加装谐振腔后,传递损失均能得到有效增加;在怠速工况和加速工况下,优化后的进气管噪声值均能满足限定值。因此,通过添加谐振腔来优化进气管可以达到较好的降噪效果。该研究可为汽车进气管降噪元件的优化设计提供一定的指导。     

Euler flow in a supersonic mixed‐compression inlet

Numerical simulation of a two‐dimensional mixed compression supersonic inlet is carried out by solving unsteady compressible Euler equations via a stabilized finite element method. The geometry of the inlet is similar to the one used by Anderson and Wong for experimental investigation for Mach 3 flow. The computations are capable of simulating the start‐up problems associated with the inlet. The critical back pressure for the successful operation of the inlet is computed. The effect of inlet back pressure on the total pressure recovery and the flow distortion level is analysed. Contrary to the popular belief, it is found that in addition to the throat to inlet capture area ratio, the ramp geometry close to the throat plays an important role in the start‐up dynamics. It is demonstrated via simulations that, everything else being same, the geometries of ramp upstream of the throat that are associated with a curvature higher than a certain threshold, result in unstarting the intake. Copyright © 2005 John Wiley & Sons, Ltd.     

燃气轮机进气道内部复杂三维流动研究

本文采用高分辨率多块多网格方法,数值研究工业燃气轮机非轴对称进气道内部的复杂三维流动。文中描述了所采用的数值方法,给出了进气道内部流场的细节,分析了进气道出口流场的非轴对称情况。     

我国食品卫生安全风险评估模型

食品卫生安全关系到国计民生,建立适合于我国的食品卫生安全保障体系尤为重要.人群食物摄入量模型用"对数正态分布"估计食物摄入量分布,在对国家依据气候、地理、经济等因素进行地域划分的基础上提出了能够保证小样本空间条件下采样均匀的"层次化样本分配模型"用于采样点的选取和各采样点样本数量的分配;污染物分布模型用"贝塔分布"估计食物中的污染物分布,并采用样本在时间轴上平移的方法解决了数据在时间上的不完整性问题;风险评估模型基于人群食物摄入量和食物污染物分布模型,提出"矩元法"对污染物摄入量进行评估,并给出了模型数值化求解和右分位点确定的相关算法.实验表明,风险评估模型所确定的右分位点能有效地反映当前食品卫生安全状况.