一种确定BOD5分析中水样稀释比的简便方法

本文提出用快速法测定出COD_(Cr)值后,按稀释倍数通式c_n=COD_(Cr)/6.5×2~(n-1))(n=1,2,3)计算出三个适当的稀释倍数.与其他方法相比,本方法简便、可靠,普遍适用,可保证样品BOD_5分析一次成功.在BOD_5分析监测中具有实际意义和推广价值.     

Using design effects from previous cluster surveys to guide sample size calculation in emergency settings

A good estimate of the design effect is critical for calculating the most efficient sample size for cluster surveys. We reviewed the design effects for seven nutrition and health outcomes from nine population-based cluster surveys conducted in emergency settings. Most of the design effects for outcomes in children, and one-half of the design effects for crude mortality, were below two. A reassessment of mortality data from Kosovo and Badghis, Afghanistan revealed that, given the same number of clusters, changing sample size had a relatively small impact on the precision of the estimate of mortality. We concluded that, in most surveys, assuming a design effect of 1.5 for acute malnutrition in children and two or less for crude mortality would produce a more efficient sample size. In addition, enhancing the sample size in cluster surveys without increasing the number of clusters may not result in substantial improvements in precision.     

Geographic sampling of urban soils for contaminant mapping: how many samples and from where

Properly sampling soils and mapping soil contamination in urban environments requires that impacts of spatial autocorrelation be taken into account. As spatial autocorrelation increases in an urban landscape, the amount of duplicate information contained in georeferenced data also increases, whether an entire population or some type of random sample drawn from that population is being analyzed, resulting in conventional power and sample size calculation formulae yielding incorrect sample size numbers vis-à-vis model-based inference. Griffith (in Annals, Association of American Geographers, 95, 740–760, 2005) exploits spatial statistical model specifications to formulate equations for estimating the necessary sample size needed to obtain some predetermined level of precision for an analysis of georeferenced data when implementing a tessellation stratified random sampling design, labeling this approach model-informed, since a model of latent spatial autocorrelation is required. This paper addresses issues of efficiency associated with these model-based results. It summarizes findings from a data collection exercise (soil samples collected from across Syracuse, NY), as well as from a set of resampling and from a set of simulation experiments following experimental design principles spelled out by Overton and Stehman (in Communications in Statistics: Theory and Methods, 22, 2641–2660). Guidelines are suggested concerning appropriate sample size (i.e., how many) and sampling network (i.e., where).

北京地表水中三氟乙酸的测定

三氟乙酸是HFC-134a等氯氟烃替代品的降解产物,对植物和土壤微生物群落的生长有一定抑制作用。笔者建立了测定TFA质量浓度的实验方法:将样品中的三氟乙酸与硫酸二甲酯在浓硫酸介质中衍生为三氟乙酸甲酯(MTFA),利用MTFA的易挥发性,以顶空进样和气相色谱-质谱联用的方法检测样品中MTFA的质量浓度,进而得到环境水样中TFA的质量浓度。并应用该方法测定了北京部分地表水体中三氟乙酸的质量浓度。测定结果:北京青年湖水样和北海水样中的ρ(三氟乙酸)分别为78和93ng L,而北京大学自来水水样中ρ(三氟乙酸)低于方法检测限10ng L。      

基于BP网络理论的岩爆预测方法

选取影响岩爆的一些主要因素,如地应力大小、岩石抗压和抗拉强度、岩石弹性能量指数,采用人工神经网络理论,根据国内外一些岩石地下工程实例构造样本集,建立了一种新的岩爆预测模型.此模型可以直接应用于岩石地下工程,对岩爆的发生与否及烈度大小进行预测.实例表明,预测结果与实际情况符合得很好,说明了此模型的有效性.     

水中烷基汞检测技术的研究进展

简述了水中烷基汞的分析测定技术,包括富集材料的种类和性能,水样富集处理方法,色谱和毛细管电泳分离技术,光谱、质谱及其他多种检测技术的联合应用等,并对水中烷基汞的分析检测技术发展进行了展望。     

A More Cost-Effective Emap Benthic Macrofaunal Sampling Protocol

Benthic macrofaunal sampling protocols in the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) are to collect 30 to 50 random benthic macrofauna [defined as animals retained on a 0.5 mm (East and Gulf Coasts, USA) or a 1.0 mm mesh sieve (West Coast, USA)] samples per reporting unit using a 0.044 m² (East and Gulf Coasts) or 0.1 m² (West Coast) grab. Benthic macrofaunal community conditions in the reporting unit are characterized by cumulative distribution functions (CDFs) on end points of interest, such as number of species (S), abundance (A), and Shannon--Wiener diversity (H′). An EMAP and a companion field study were conducted concurrently in Tillamook Bay (Oregon, USA) to compare the cost effectiveness of benthic macrofauna samples collected using the EMAP West Coast (0.1 m² × ≥7 cm deep, 1.0 mm mesh), a 0.01 m² × 5 cm deep, 1.0 mm mesh, and a 0.01 m² × 5 cm deep, 0.5 mm mesh sampling protocol. Cost was estimated in relative laboratory sample-processing time. Sampling protocols were judged equally effective for EMAP purposes if, after linear transformation to adjust for scale changes in end point distributions, their S, A, and H′ CDFs were not significantly different. The 0.01 m² × 5 cm deep, 1.0 mm mesh sampling protocol was the most cost effective.     

液-液微萃取气相色谱法测定小量水样中痕量硝基苯

使用 FID检测器和 DB-1大口径毛细柱不需要对有机相进行干燥处理。借助 1 0 ml容量瓶和自制的玻璃吸管 ,不必进行两相分离操作 ,萃取和取样操作均可在容量瓶中一次完成。利用有溶剂效应的柱温程序提高了柱效和检测灵敏度。 1 0 ml水样可获得 0 .5 μg/ L的检测下限。方法的精密度优于 4 % ,回收率大于 95 %。     

江南水网地区中小城市空气质量预报研究

利用湖州2002年7月至2004年12月的空气污染浓度资料及常规气象资料,探讨了江南水网地区气象因素对环境空气质量的影响,并结合区域气候特征及污染现状对影响环境空气质量的因素进行了研究分析.将天气类型科学分类,分别建立了区域空气质量预报的总体回归模型和分类回归模型.两种模型均可通过统计检验,分类统计模型较总体统计模型实际业务预报精度有所提高,最后采用DELPHI语言将预报流程制作了软件.     

石墨炉原子吸收法测定环境水样中四乙基铅的方法探讨

通过对双硫腙目视比色法测定四乙基铅的方法进行改进,利用四乙基铅标制作工作曲线,用浓硝酸取代溴-硝酸进行消解,使有机铅变成无机铅后,用石墨炉原子吸收方法定量测定。此方法操作简单、节省试剂,对测定环境水样中四乙基铅的灵敏度、准确度都有很大提高。该方法的最低检出浓度为0.02μg/L,测量范围为0.1~80μg/L,回收率88%~101%。