Some results on comparison of maintenance policies

1. IntroductionMaintenance policies are followed to reduce the incidence of system failure or to returna failed system to the operating state. FOr example, if a component fails, one strategy isto replace it. Another strategy is not to wait for it to fail, but to replace it at some earIiertime, which belongs to maintenance poIicies problems. The most usefuI replacemeflt policiesare the age replacemeni policy and the block replacement policy. See [l,2] for a discussionof these policies. Compa…     

实验室能力验证的发展

实验室能力验证对于判定实验室的检测能力非常重要。回顾了国际实验室能力验证的起源和发展,重点分析了我国能力验证的发展历程和成就,探讨了我国实验室能力验证中存在的问题和有争议的技术要点。     

确定观测站点预报雨量的两种方法

对2005年高教社杯全国大学生数学建模竞赛C题"雨量预报方法的评价"的解决方法进行了讨论.给出了确定观测站点预报雨量的距离权重法与插值法,并进行了比较.同时,对预报质量的进一步提高进行了探讨.     

Establishment of SI-traceable reference values for the content of various elements in the IMEP-14 sediment sample

For the first time in the International Measurement Evaluation Programme (IMEP)-14, a sediment sample was offered to analytical laboratories to perform measurements of As, Cd, Cr, Cu, Fe, Pb, Hg, Ni, U and Zn. In line with IMEP policy, the results were presented according to the certified / assigned reference values established by several reference laboratories around the world. The certification campaign is described in detail. Isotope dilution mass spectrometry was applied as a primary method of measurement, whenever possible, to achieve SI-traceable results. For reference measurements of As, Fe, Hg and Zn, k₀-neutron activation analysis and Zeeman atomic absorption spectrometry were applied. The reference values (ranges) were characterised as ”certified” (for Cd, Cr, Pb, Ni and U) or ”assigned” (for As, Cu, Fe, Hg and Zn) according to IMEP policy. The measurement uncertainty of the certified / assured reference values was calculated according to the ISO/BIPM Guide. Received: 7 June 2001-10-27 Accepted: 19 August 2001     

The development of gas standards and calibration techniques for measurements of vehicle, aircraft and industrial emissions, natural gas, occupational exposure and air quality

 The National Physical Laboratory (NPL) is involved in the dissemination of nationally traceable standards to which measurements of air quality, occupational exposure and air pollution source emissions, and natural gas analyses, can be referenced. This has required the development of national primary gas standards using absolute gravimetric and other techniques, and the development of dynamic calibration techniques for gaseous species which would be unstable in high-pressure cylinders. The methodology used for preparing gas standards gravimetrically is described, together with the rigorous quality assurance measurements and consistency checks which are used to demonstrate their accuracy and stability. The uncertainty budget assigned to these standards will also be summarised. NPL primary standards are used to certify traceable 'secondary' gas standards which are disseminated so as to ensure the accuracy of gas analysis measurements. Examples of the applications of these secondary standards are presented. The gas standards are employed in proficiency testing of industrial stack-testing organisations, and results of the initial rounds are presented. NPL gas standards are also now being used as the basis of the United Kingdom Environment Agency's new type-approval and certification scheme for continuous industrial stack-emission analysers. A recent important international initiative, in the field of gas analyses, is the agreement by national standards laboratories across the world to demonstrate the equivalence of their calibrations, by means of key comparisons between them. These worldwide key comparisons are complemented in Europe through the EUROMET initiative which seeks to establish the equivalence and comparability of calibration standards held at national standards laboratories across Europe. Examples of these intercomparisons are presented. Received: 23 March 2000 / Accepted: 18 August 2000     

传统重量法在铂钌样品测定中的合理运用

作为铂样品国际实验室间比对分析的参加单位,实验室接受了一种铂一钌合金试样并要求按指定的方法进行分析,选择了重量法测定其中铂含量(ISO 11210-1995).已知该试样中钌的含量在5%(质量分数)左右.为消除钌对铂测定的干扰,对原方法作了以下改进:①将在 950 ℃灼烧(NH,4),2PtCl,6 沉淀所得的海绵状铂称重后重新用王水溶解.溶液有黑色不溶物,经证明为钌,将溶液用紧质滤纸过滤,滤纸及不溶物经 950 ℃灼烧并称重,记其量为钌.②在滤液中按第一次沉淀相同的方法将铂以氯铂酸铵形式沉淀,过滤并在 950 ℃灼烧后称得其重量.按文中给出的公式计算铂含量,此计算公式中包括扣除钌含量的计算项.按此改进的方法测得合金中铂的含量与实验室用其他方法所测得的结果一致.     

Trace analysis of per- and polyfluorinated alkyl substances in various matrices-How do current methods perform?

Per- and polyfluorinated alkyl substances (PFAS) are a group of industrial chemicals, some of which have been produced for over 50 years. Scarcely one decade ago, their ubiquity in wildlife, humans and the global environment was discovered. This urged the need for robust and reliable, yet very sensitive analytical methods allowing for their determination in various matrices. This article reviews the state-of-the-art in trace analysis of ionic and neutral PFAS in humans as well as environmental samples such as wildlife, water, solid matrices and air. Analytical protocols for PFAS determination in food and consumer products are also included. The methods are critically discussed in terms of their advantages, shortcomings, possibilities, limitations, and potential for further development.     

A simple method to compute economic order quantities: Some observations

Teng [2] presents an arithmetic–geometric mean method to be applied to determine the optimal lot size for the EOQ/EPQ models, taking into account backorders. Although the arithmetic–geometric mean method is correct, arguments as to when (not) to use the arithmetic–geometric mean inequality as optimization method are not complete. Moreover, this optimization method does not focus on the method for deriving the optimal backorders level. The main purpose of this work is to overcome these shortcomings, presents a discussion of when (not) to use the cost minimization method and derives the optimal backorders level.     

基于第一HJ距离的线性因子模型两两比较研究

从统计意义上比较不同模型的改进效力有助于挑选出最接近金融数据生成过程的定价模型,是资产定价研究的重要课题。我们借鉴Kan和Robotti~([1])的研究成果,基于第一HJ距离构造了广义似然比检验,以台湾市场丰富的数据资料为基础,对8种常见的线性因子模型(包括基于金融资产价格的线性因子模型)进行了模型两两差异性检验。研究发现:VM和CAPM、FF3和LM这两组模型无明显差异,表明波动率冲击因子和流动性因子未带来显著的模型改进效力。由于部分定价因子可能具有共同的解释能力,VM和IVM、IVM和HSM、HSM和VanM、VanM和SkewM这多组模型间也未表现出显著的差异。同时,引入条件信息是否能改善模型效力视不同模型而定,在10%的显著性水平下,FF3、LM、VanM、SkewM的条件信息模型较无条件信息模型有所改进。