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排序方式: 共有117条查询结果,搜索用时 15 毫秒
31.
32.
Jayant V. Deshpande Jesse Frey Omer Ozturk 《Environmental and Ecological Statistics》2006,13(1):25-40
Ranked-set sampling from a finite population is considered in this paper. Three sampling protocols are described, and procedures
for constructing nonparametric confidence intervals for a population quantile are developed. Algorithms for computing coverage
probabilities for these confidence intervals are presented, and the use of interpolated confidence intervals is recommended
as a means to approximately achieve coverage probabilities that cannot be achieved exactly. A simulation study based on finite
populations of sizes 20, 30, 40, and 50 shows that the three sampling protocols follow a strict ordering in terms of the average
lengths of the confidence intervals they produce. This study also shows that all three ranked-set sampling protocols tend
to produce confidence intervals shorter than those produced by simple random sampling, with the difference being substantial
for two of the protocols. The interpolated confidence intervals are shown to achieve coverage probabilities quite close to
their nominal levels. Rankings done according to a highly correlated concomitant variable are shown to reduce the level of
the confidence intervals only minimally. An example to illustrate the construction of confidence intervals according to this
methodology is provided. 相似文献
33.
空气中挥发性有机物监测技术的研究进展 总被引:13,自引:0,他引:13
讨论了空气中挥发性有机化合物(VOCs)的监测分析方法研究进展。重点介绍了空气中VOCs的采集、分析和测定;简要叙述了样品前处理的新方法--固相微萃取法(SPME)与其它前处理方法的研究概况。 相似文献
34.
Krupa SV 《Environmental pollution (Barking, Essex : 1987)》2002,120(3):565-594
Wet deposition is one of two processes governing the transfer of beneficial and toxic chemicals from the atmosphere on to surfaces. Since the early 1970s, numerous investigators have sampled and analyzed precipitation for their chemical constituents, in the context of "acidic rain" and related atmospheric processes. Since then, significant advances have been made in our understanding of how to sample rain, cloud and fog water to preserve their physico-chemical integrity prior to analyses. Since the 1970s large-scale precipitation sampling networks have been in operation to broadly address regional and multi-regional issues. However, in examining the results from such efforts at a site-specific level, concerns have been raised about the accuracy and precision of the information gathered. There is mounting evidence to demonstrate the instability of precipitation samples (e.g. with N species) that have been subjected to prolonged ambient or field conditions. At the present time precipitation sampling procedures allow unrefrigerated or refrigerated collection of wet deposition from individual events, sequential fractions within events, in situ continuous chemical analyses in the field and even sampling of single or individual rain, cloud and fog droplets. Similarly analytical procedures of precipitation composition have advanced from time-consuming methods to rapid and simultaneous analyses of major anions and cations, from bulk samples to single droplets. For example, analytical techniques have evolved from colorimetry to ion chromatography to capillary electrophoresis. Overall, these advances allow a better understanding of heterogeneous reactions and atmospheric pollutant scavenging processes by precipitation. In addition, from an environmental perspective, these advances allow better quantification of semi-labile (e.g. NH4+, frequently its deposition values are underestimated) or labile species [e.g. S (IV)] in precipitation and measurements of toxic chemicals such as Hg and PCBs (polychlorinated biphenyls). Similarly, methods now exist for source-receptor studies, using for example, the characterization of reduced elemental states and/or the use of stable isotopes in precipitation as tracers. Future studies on the relationship between atmospheric deposition and environmental impacts must exploit these advances. This review provides a comprehensive and comparative treatment of the state of the art sampling methods of precipitation and its physico-chemical analysis. 相似文献
35.
采用流动式采样与气相色谱-质谱联用法研究了意大利撒丁岛Noak’s Ark自然生态区四种主要灌木树种Juniperus phoenicea(腓尼基桧),Pistacia lentiscus(黄连木),Phillyrea angustifilia,Chamaerops humilis(欧洲矮棕)的排放速率和排放特征。结果表明,JuniPerus phoenicea(腓尼基桧),Pistacia lentiscus(黄连本),Phillyrea angustifilia主要排放萜烯类化合物,其中包括α-蒎烯、β-蒎烯、苎烯、戊花烃、莰烯、β-水芹烯、桧烯、β-香叶烯和3-蒈烯等;Chamaerops humilis(欧洲矮棕)主要排放异戊二烯。在标准条件下(温度30℃,PAR为1000μmo1.m^-2.s^-1),四种树种的排放速率分别为0.15、2.10、0.20和1.87μg/g(DW).h。 相似文献
36.
GABRIELLA SUSZTER ÁRPÁD AMBRUS MARIANNA SCHWEIKERT TURCU PHILIPP MARTIN KLAUS 《Journal of environmental science and health. Part. B》2013,48(5):531-552
The efficiency of four sample processing methods was tested with eight different types of soils representing the major proportion of cultivated soils. The principle of sampling constant was applied for characterizing the efficiency of the procedures and testing the well-mixed status of the prepared soil. The test material was 14C-labeled atrazine that enabled keeping the random error of analyses ≤ about 1%. Adding water to the soil proved to be the most efficient and generally applicable procedure resulting in about 6% relative sample processing uncertainty for 20 g test portions. The expected error is inversely proportional to the mass of test portion. Smashing and manual mixing of soil resulted in about four times higher uncertainty than mixing with water. Grinding of soil is applicable for dry soils only, but the test procedure applied was not suitable for estimating a typical uncertainty of processing dry soil samples. Adding dry ice did not improve the efficiency of sample processing. 相似文献
37.
介绍了限流孔烟气采样器的设计原理、主要技术指标、设计指标说明及采样器主要性能。通过测定SO2标准气体和比对试验,表明限流孔烟气采样器控制流量稳定,计量采气体积准确,应用结果满意。 相似文献
38.
通过对TSP、SO2浓度在不同高度实测研究.得出平顶山市SO2在1.5m至20m不同高度监测,高度影响无显著性差异;TSP在5m至15m不同高度监测,高度影响无显著性差异。 相似文献
39.
随着我国环境保护力度的不断加大,环境调查工作正在有序的开展,其中场地土壤、地下水污染是环境调查的重点,而科学的调查采样方法则是确保调查结果准确性、客观性的必然要求。有鉴于此,首先从污染场地特征分析、调查目标两个角度介绍了场地环境调查的准备工作,然后探讨了布点中的前期准备以及具体方法,最后围绕土壤样品以及地下水样品的采集与保存做了分析。 相似文献
40.
地下水有机污染调查采样精密度评估方法探讨 总被引:1,自引:0,他引:1
对国际标准化组织(ISO)在《水样采集与处理的质量控制指南》中提出的采样精密度控制方法不完全适用于地下水有机污染调查评价工作的部分进行了分析。在华北平原地下水有机污染调查评价工作的基础上,探讨了一种改进的采样精密度控制与评估方法,提高相关工作的质量控制水平。 相似文献