Spectrochemical Determination of Metallic Pollutants At Sub Ppm Levels In Fresh Water Samples

Abstract

A quantitative method to analyse fresh water samples for ultratrace pollutants such as Cd, Cr, Fe, Mn, Ni, Pb, V and Zn has been developed. the impurities in the water sample were preconcentrated by the method of slow evaporation and collected on specpure graphite which was subsequently analysed by d.c. are excitation using NaF as the carrier. the mean relative standard deviation of the method employed is + 15%. the accuracy of the method reported has been found to be quite satisfactory as borne out by the results of the Intercomparison Run conducted by the International Atomic Energy Agency, Vienna for the determination of trace elements in water. the detection limits for the various elements are as follows: Ni, Pb, V : 1 ng/ml; Cd, Cr, Mn: 2 ng/ml; Fe: 15 ng/ml and Zn : 20 ng/ml. Some of these detection limits have been compared with those obtained in some of the recent techniques such as AAS, Laser Induced Fluorescence (LIF) and Laser Enhanced Ionization (LEI) or Opto-Galvanic Spectrometry(òGS). It has been found that there is a tenfold increase in sensitivity for Pb in the present method as compared to the above techniques except LEI while the detection limits obtained for other elements are comparable with those in other techniques.     

不确定环境下基于交叉评价的模糊综合评价方法

由于环境的不确定性,多属性决策中客观数据和主观因素并存,决策者很难做出精准的评判.借鉴DEA交叉评价的思想,将量化数据用交叉评价方法进行处理,得出平均交叉效率值作为模糊综合评价的指标进行二次评价.建立了不确定环境下基于交叉评价的模糊综合评价模型,并通过评价实例验证了模型的客观、全面性.     

Arguing About the Effectiveness of Assessments for the Classroom

Approaches to test score use and test purpose lack the well-developed methodological guidelines and established sources of evidence available for intended score interpretation. We argue in this paper that this lack fails to reflect the ultimate purpose of a test score—to help solve an important problem faced by intended test users. We explore the treatment of intended test purpose and test score use under the chain of assumption/inferences perspective identified within an argument-based approach to validity. Next, we revisit the notion of test score use and argue that, at least for classroom assessments based on complex constructs, such as learning progressions in math and science, test score use can be more effectively conceptualized as part of a potential solution to solving a problem, or “job-to-be-done.”. We argue for shifting from the definition of validity to the concept of effectiveness. Finally, we illustrate an argument- based approach to test score effectiveness by contrasting effectiveness arguments for interim assessments based on a conventional test blueprint or a test blueprint augmented with learning progressions.     

On the addition of two incoherent unsteady noise records of similar statistical structures. Part 2: effects of long time span and diurnal variations

The present study is a follow-up of a previous investigation of the author in an attempt to understand how the statistical structures of noise records will affect that of the resultant noise record formed from their addition. This issue becomes particularly important when statistical indices such as L₁₀ and L₉₀ of the resultant noise record are required for planning or assessment purposes. Long time span sound pressure level records were obtained from 18 well-separated independent sites in the high-rise residential areas of Hong Kong. The results obtained from their addition are compared with those of the 25-min record addition done by the author previously. The diurnal variations of the addition results are also discussed. In general, the present results suggest that there is weak correlation between the long time span records. The currently adopted logarithmic addition procedure still over-estimates the noise climate and only limited improvement is found when compared to the results of the 25-min cases. The present results further confirm the importance of the noise statistical structures in the environmental noise impact assessment.     

基于锥形量热仪试验的聚合物材料火灾危险评价研究

简述了锥形量热仪的试验原理,以聚合物材料锥形量热仪试验数据为基础,导出了火势增长指数（FGI）、放热指数（THRI6min）、发烟指数（TSPI6min）和毒性气体生成速率指数（ToxGI）4个评价聚合物材料火灾危险的参数,并利用这四个参数对ABS、PS、PVC、PA 4类16种商用塑料样品的火灾危险性逐项进行了分析评价.在此基础上,采用层次分析法的原理对样品的火灾危险进行了综合评价,结果表明,ABS、PS、PVC、PA四类样品的火灾综合危险依次减小.     

基于可信性理论的工程投标模糊风险评估

工程项目投资决策需要考虑承包商自身、业主、项目、竞争对手等方面的情况,需要对各种风险因素进行分析.结合我国当前建筑市场信息化程度不高,难以获取充分历史数据的特点以及国内外相关文献,提出了一种基于可信性理论的工程投标模糊风险评估方法,并给出了详细计算步骤.最后结合算例验证了方法的可行性和实用性.     

Uncertainty evaluation in proficiency testing: state-of-the-art, challenges, and perspectives

The evaluation of measurement uncertainty, and that of uncertainty statements of participating laboratories will be a challenge to be met in the coming years. The publication of ISO 17025 has led to the situation that testing laboratories should, to a certain extent, meet the same requirements regarding measurement uncertainty and traceability. As a consequence, proficiency test organizers should deal with the issues measurement uncertainty and traceability as well. Two common statistical models used in proficiency testing are revisited to explore the options to include the evaluation of the measurement uncertainty of the PTRV (proficiency test reference value). Furthermore, the use of this PTRV and its uncertainty estimate for assessing the uncertainty statements of the participants for the two models will be discussed. It is concluded that in analogy to Key Comparisons it is feasible to implement proficiency tests in such a way, that the new requirements can be met. Received: 29 September 2000 Accepted: 3 December 2000     

从PISA视角分析新加坡初中Discover Chemistry教材中的科学探究思想

基于2015年经济合作与发展组织公布的PISA测试的最新结果，以及新加坡学生的科学成绩，结合新加坡初中科学教学大纲对新加坡初中化学教材中体现的科学探究思想进行分析。以Discover Chemistry教材为素材，从中选取实验类、调查类、反思和交流类探究活动，挖掘其蕴含的科学素养，分析教材中的探究思想，旨在为我国教科书中的科学探究内容的编写与修改提供启示，也为教师和学生开展有效的探究活动提供借鉴。     

Should non-significant bias be included in the uncertainty budget?

The bias of an analytical procedure is calculated in the assessment of trueness. If this experimental bias is not significant, we assume that the procedure is unbiased and, consequently, the results obtained with this procedure are not corrected for this bias. However, when assessing trueness there is always a probability of incorrectly concluding that the experimental bias is not significant. Therefore, non-significant experimental bias should be included as a component of uncertainty. In this paper, we have studied if it is always necessary to include this term and which is the best approach to include this bias in the uncertainty budget. To answer these questions, we have used the Monte-Carlo method to simulate the assessment of trueness of biased procedures and the future results these procedures provide. The results show that non-significant experimental bias should be included as a component of uncertainty when the uncertainty of this bias represents at least a 30% of the overall uncertainty. Received: 29 May 2001 Accepted: 10 December 2001