三峡水库岸边排污的特性及数值模拟研究

数值模拟是研究和解决三峡水库污水岸边排污的重要手段之一．针对三峡水库岸边污水排放的特点,分析并阐述了排污口附近的水流和污染物分布特性及其所带来的数值困难．基于这些分析,讨论了深度平均二维模型和不同分层三维模型在模拟三峡库区岸边排污问题中的优势和不足,为库区岸边侧向排污数值模型的进一步发展奠定了基础．     

On Conservative Confidence Intervals

The subject of the paper – (conservative) confidence intervals – originates in applications to auditing. Auditors are interested in upper confidence bounds for an unknown mean for all sample sizes n. The samples are drawn from populations such that often only a few observations are nonzero. The conditional distribution of an observation given that it is nonzero usually has a very irregular shape. However, it can be assumed that observations are bounded. We propose a way to reduce the problem to inequalities for tail probabilities of certain relevant statistics. Note that a traditional approach involving limit theorems forces to impose additional conditions on regularity of samples and leads to approximate or asymptotic bounds. In the case of , as a statistic we can use sample mean, say , and we have to use Hoeffding [7] inequalities, since currently they are the best available. This leads to upper confidence bounds for which are of (asymptotic) size at most in the case of risk =0.05, where is the unknown standard deviation. We have , where is the bound in a model with normally distributed observations. It seems that the bound is very robust and can be improved replacing Hoeffding's inequalities by more refined ones. The commonly used Stringer bound (it is still not known whether it is an upper confidence bound) is of asymptotic size c with equality only for Bernoulli distributions, and the ratio c / can be arbitrary large already for rather simple distributions. Our bounds can involve a priori information (professional judgment of an auditor) of type ₀ or/and ₀, which leads to improvements. Most of the results also hold for sampling without replacement from finite populations. The i.i.d. condition can be replaced by a martingale-type dependence assumption. Finally, the results can be extended to the noni.i.d. case and for settings with several samples.     

食品中邻苯二甲酸酯类化合物的分析方法研究进展

邻苯二甲酸酯是应用最广泛的增塑剂,具有生殖、发育毒性及致癌性,是近年来食品污染的一个重要来源。该类化合物种类多、同系物和同分异构体性质接近、在基体中含量范围宽,高效样品前处理、高选择性分离和高灵敏检测、降低本底干扰等技术是食品中邻苯二甲酸酯类化合物准确测定面临的挑战。本文综述了液液萃取、液液微萃取、固相萃取、固相微萃取、基质固相萃取等传统及新型的提取与净化技术在食品样品分析中的应用,比较分析了气相色谱、液相色谱、串联质谱、高分辨质谱以及酶联免疫、离子迁移谱等快速检测技术的特点,并展望了发展趋势。     

电感耦合等离子体质谱测定地质样品中Pb同位素比值

铅有 4个天然的同位素 ,由于放射衰变、宇宙的辐射及人类的活动 ,使 2 0 6Pb/2 0 4 Pb,2 0 7Pb/2 0 4 Pb及2 0 8Pb/2 0 4 Pb值在自然界中呈现相应的变化 ,而这种变化使得铅同位素成为一种有效的示踪手段和地质年代学研究的工具 ,同时在环境质量监控、放射性污染追踪及人类社会的变迁等方面有着广泛应用 .热电离质谱 (TIMS)分析技术对于大多数的同位素比值测定具有极高的精密度和准确度 ,但对于铅的测定由于难以获得一个高度浓缩且稳定不变的同位素作为内标进行质量偏移校正 [1] ,使其测定的准确度受到影响 .Rehkamper等 [2 ,3 ] 研究了…     

重金属污染土壤修复技术研究进展

概述了土壤重金属污染的特点、现状及污染的来源,主要从工程措施、农业措施、改良措施和生物修复措施四方面对国内外各种修复技术进行分析与评论,指出各类措施的原理、优缺点、实用性。同时,提出了当前土壤重金属污染与修复技术研究的重点。     

乳化剂OP对锌,镉,铅电位溶出的增敏作用

在０．０１７ｍｏｌ／Ｌ Ｈ２ＳＯ４－ＨＮＯ３混合酸介质中,乳化剂ＯＰ对锌、镉、铅的电位溶出有显著的增敏作用。在电位－１．５０Ｖ下电解富集６０ｓ时,锌、镉、铅的检出限分别为０．１３μｇ／２０ｍＬ,０．０１６μｇ／２０ｍＬ及０．０２０μｇ／２０ｍＬ;线性范围分别为０．０５～０．５０μｇ／２０ｍＬ,０．０５～０．０８μｇ／２０ｍＬ及０．１０～０．８０μｇ／２０ｍＬ,与峰高呈良好的线性关系。此法用于环境水     

Sample Duplication Method for Monte Carlo Simulation of Large Reaction-Diffusion System

The sample duplication method for the Monte Carlo simulation of large reaction-diffusion system is proposed in this paper. It is proved that the sample duplication method will effectively raise the efficiency and statistical precision of the simulation without changing the kinetic behaviour of the reaction-diffusion system and the critical condition for the bifurcation of the steady-states. The method has been applied to the simulation of spatial and time dissipative structure of Brusselator under the Dirichlet boundary condition. The results presented in this paper definitely show that the sample duplication method provides a very efficient way to sol-'e the master equation of large reaction-diffusion system. For the case of two-dimensional system, it is found that the computation time is reduced at least by a factor of two orders of magnitude compared to the algorithm reported in literature.     

Headspace‐single drop microextraction with a commercial capillary electrophoresis instrument

Automated coupling of headspace‐single drop microextraction (HS‐SDME) and CE has been demonstrated using a commercial CE instrument. When a drop hanging at the inlet tip of a capillary for CE is used as the acceptor phase, HS‐SDME becomes a simple but powerful sample pretreatment technique for CE before injection to facilitate sample cleanup and enrichment. By combining HS‐SDME with an on‐line sample preconcentration technique, large volume sample stacking using an electroosmotic flow pump, the sensitivity can be improved further. The overall enrichment factors for phenolic compounds were from 1900 to 3400. HS‐SDME large volume sample stacking using an electroosmotic flow pump was successfully applied to a red wine sample to obtain an LOD of 4 nM (0.8 ppb) for 2,4,6‐trichlorophenol which is a precursor for 2,4,6‐trichloroanisole causing the foul odor in wine called cork taint.     

Adjustable microwave absorption properties of flake shaped (Ni0.5Zn0.5)Fe2O4/Co nanocomposites with stress induced orientation

Flake shaped (Ni_0.5Zn_0.5)Fe₂O₄/Co nanocomposites were successfully fabricated by co-precipitating of Ni-Zn ferrite on the surface of cobalt nanoflakes. The electromagnetic characteristics of the samples were studied at the frequency of 0.1–14 GHz. The results showed that the cobalt nanoflakes in compacted nanocomposites were well orientated, and the nanocomposites were characterized with low optimal reflection loss (RL) of −33.8 dB at 11.5 GHz and broad RL bandwidth for <−20 dB in the frequency range of 7.6–12.1 GHz. At the same time, the position of the absorptive band can be adjusted by changing the mass ratio of ferrite to cobalt in the nanocomposites. It is proposed that the excellent microwave absorption properties are related to the combination of strong shape anisotropy of cobalt nanoflakes and adjustable dielectric loss.     

直接进样超高效液相色谱-三重四极杆质谱法快速测定环境水样中草甘膦、氨甲基膦酸、草铵膦及乙烯利残留

建立了一种简便、直接进样的超高效液相色谱-三重四极杆质谱法（UPLC-MS/MS）快速测定环境水样中草甘膦、氨甲基膦酸、草铵膦及乙烯利的残留。环境水样经0.22 μm滤膜过滤或冷冻离心去除杂质后,滤液无需衍生化直接进行定量分析。4种农药通过Metrosep A Supp 5柱（150 mm×4.0 mm,5 μm）分离,以碳酸氢铵-氨水溶液为流动相进行梯度洗脱,在负离子模式下以MRM方式进行检测。结果表明,4种农药在0.50~50.0 μg/L范围内相关系数（r）均大于0.999,线性关系良好,方法检出限为0.05~0.09 μg/L。实际水样在低、中、高3种加标浓度水平下,回收率分别为76.3%~108%、83.0%~107%和87.0%~105%,相对标准偏差分别为2.0%~12.3%、2.4%~5.6%和2.7%~6.8%。使用该方法对海南省34个水样进行测定,其中30个饮用水源地水样中均未检出4种农药,槟榔园附近3个水样均检出草甘膦和氨甲基膦酸,香蕉园附近的1个水样检出草铵膦和氨甲基膦酸。与传统的衍生化方法比较,该方法操作简便,重现性好,准确性高,不受基体干扰,适用于环境水样中草甘膦、氨甲基膦酸、草铵膦及乙烯利的残留检测。