An approach to uncertainty estimation in determining polycyclic aromatic hydrocarbons in fuel-contaminated soils

An estimation of uncertainty contribution in the entire set of the analytical data of polycyclic aromatic hydrocarbons (PAHs) in soil during a full year is presented. The analyses were performed as part of a project devoted to the assessment of the natural attenuation of selected PAHs in agricultural soil contaminated by a fuel spill. In particular, we investigated the effect of natural attenuation on the PAH dissipation rate in plots of two types of scenarios in agricultural soils. One of them was previously affected by an accidental fuel spill 10 years ago, and the other one was non-affected. The major components for estimating uncertainty contributions have been evaluated based on intermediate precision from different levels of PAH mass fraction, sample locations, and long term data set. An analysis of variance (ANOVA) test was applied to the mass fractions of clean or blank soil sub-samples versus contaminated soil sub-samples for grouping comparable data. Variables of influence in this study were site, month, and lysimeter of sampling (referring to a stainless steel box, with side lengths of 50 cm). Study sites or the spatial arrangement of lysimeter showed a clear effect in sub-sample results with the lowest mass fraction levels for heavier PAH, while monthly sampling was the variable of most significant influence for the more strongly contaminated sub-sample results.

Finally, the results of the PAH mass fractions in contaminated soil sub-samples indicated a monthly variation for which lighter, volatile PAHs rapidly decreased while the less volatile did not change.     

非稳定流巷道火灾试验系统的研制

介绍了巷道火灾试验系统的构成,测定燃烧区膨胀热阻时测点位置的确定方法,火灾时期烟气温度、壁温及岩体温度、烟流中CO2及O2体积分数、沿程压力和风速等的测试方法及测试仪表精度,系统抗干扰方法,数据采集和处理软件的功能以及测试系统的调试方法.系统采用无补偿导线经济地解决了巷道燃烧区测温热电偶冷端温度补偿的方法,使测温系统误差由过去的10%左右下降到3%.     

DISTRIBUTED RUNOFF FORMULATION DESIGNED FOR A PRECISION AGRICULTURAL LANDSCAPE MODELING SYSTEM1

A precision scale landscape model designed for agricultural applications is described in this paper. The Precision Agricultural Landscape Modeling System (PALMS) is a combination of two process‐based models: a diffusive wave runoff model with ponding (described in detail) and a biosphere model with a crops module (briefly reviewed). Several innovations, including numerical formulations for the hydrologic properties of the soil surface with crusting, slope/tillage angle interactions, and change of roughness and detention storage with cumulative precipitation have been included. The model is compared to observations on one 1.8 ha field planted with maize and soybeans during four growing seasons, and one 24 ha field planted with maize during one growing season. Daily average soil moisture is simulated well (within 5 percent volumetric), except in extended runoff/ponding episodes. Physical processes not simulated in the model suggest possible explanations for model errors. Planned improvements for PALMS are also presented.     

用通用有限元程序分析精密设备基础沉降的方法

采用弹性有限元方法计算了设备对地基的附加应力 ,根据土力试验数据验算了地基的沉降 ,完成了要用专门的土力学程序分析计算的工作 ,得到满意的结果。本文的工作对于精确分析基础沉降有借鉴作用。     

ESTIMATES OF MEAN CHLOROPHYLL-a CONCENTRATION: PRECISION,ACCURACY, AND SAMPLING DESIGN1

ABSTRACT: Data from 56 north-temperate lakes and reservoirs are used to develop models predicting temporal variance as a function of the mean chlorophyll-a concentration. Trophy, as estimated by mean chlorophyll-a concentration, is shown to have little effect on the sampling effort required to achieve a pre-determined level of precision for lakes sampled year-round. Collecting ten observations results in a coefficient of variation that averaged 20 percent; collecting more than ten observations yields increasingly marginal improvements in precision. The same guidelines apply to mesotrophic or eutrophic lakes sampled in the summer, whereas oligotrophic lakes sampled in the summer require fewer observations to achieve the same level of precision. The bias resulting from collecting too few observations is minimized if five or more observations are collected.     

影响水体中营养盐分析测定准确性因素探讨

对影响水体中营养盐分析测定准确性的各因素进行了详细深入地探讨和分析,并通过实验室验证实验对盐效应影响营养盐分析测定准确性方面进行了首次界定,明确地给出了盐度变化是否会对硝酸盐分析测定产生影响以及其影响程度,并首次最终界定盐度范围。将实验结果应用到实际监测工作中,取得了良好的预期效果,为国家海洋局节能减排专项的顺利实施作出了直接贡献。     

Effect Of Reagent (Dye) Addition In Wet Chemical Method Of Sulfur Dioxide Determination In Ambient Air

For measurement of sulfur dioxide (SO₂) in ambient air, the United States Environment Protection Agency (US EPA) had recommended the PRA dye-based colorimetric method as a reference technique. The method has been developed and applied in many countries for a longtime; however information regarding the sensitivity of the method with respect to sampling and analysis conditions is not available. Collaborative studies conducted in some of the South East Asian countries indicated substantial variations (of the order of 50%) in the measured concentrations against the true values. It was observed that dye used for color development plays an important role and even a slight variation in the way the dye solution is prepared can cause substantial variation in the measured SO₂ concentration. Because a major objective of air quality measurements is to relate air pollution concentration to the effects of air pollution, it is important that the method used should yield accurate levels of the pollutant, so that appropriate management plans can be devised and implemented effectively. In the present investigation, therefore, the role of dye used in SO₂ monitoring method has been highlighted. Different makes of dyes prepared in different modes were used to study the variation in the measured SO₂ concentration levels. Specifications of all the dyes were also tested. Need for use of certified reference material (CRM) for SO₂ has also been emphasized.     

自然环境条件下精密器材的失效机理及其对策研究

研究了精密器材在各种自然环境条件下的失效机理,改善其“内包装”微环境条件,避免精密器材由于受到各种自然环境因素的影响而造成损坏或失效,确保精密器材的性能和各项技术指标始终处于完好状态,对于提高精密器材储存的经济效益和军事效益,具有十分重要的意义。     

小型高精度恒温箱设计与应用

介绍了一种用于给倾角传感器提供恒温环境的小型高精度恒温箱的设计与实现。此恒温箱要求体积小、温度控制精度在±0．05℃以内。文中介绍了恒温箱的结构设计和温控算法并给出了详细的实验结构,证明了研制的这种高精度恒温箱不仅其控温精度高,且与同类产品比其体积小,安装调试方便。     

Deposition in boreal forests in relation to type, size, number and placement of collectors

Open precipitation and throughfall was collected at a Norway spruce stand in Finland using funnel-type collectors and at a black spruce stand in Canada using trough-type collectors. The presence or absence of a rim on the funnel, funnel diameter (9, 14 and 20 cm) and length of sampling period (1, 2 and 4 weeks) on monthly values were evaluated at the Norway spruce stand, and the number of collectors required for defined levels of accuracy and precision of throughfall loads to be reached and the influence of the spatial arrangement of collectors on solute concentrations was studied at both stands. The presence of a rim had no significant effect on open precipitation and throughfall amounts, but did on throughfall DOC, Ca²⁺, Mg²⁺, K⁺, Na⁺ and Cl⁻ ion loads. Deposition loads increased with decreasing funnel diameter; for open precipitation, this was due to increased catch efficiency while for throughfall the increase was attributed to canopy interaction and leaching of litter trapped in the collectors. Calculated monthly H⁺ loads decreased and those for all other constituents increased with collection period length. Using 15 collectors at the Norway spruce stand would allow throughfall loads to be determined to within 20% of the true mean weekly value with a confidence level of 95% for most solute, but not for NH₄ ⁺–N, NO₃ ⁻–N, Mg²⁺ and SO₄ ²⁻-S. Using 15 trough collectors, the same confidence level at the more heterogeneous black spruce stand would only be achieved for H⁺, Cl⁻, DOC and SO₄ ²⁻-S loads. In both stands, using either random or systematic placements of throughfall collectors gave similar results.