Estimating Component Failure Rates From Combined Component and Systems Data: Exponentially Distributed Component Lifetimes

The situation in which test results are available on systems consisting of some of k independent but nonidentical components in series is studied. The underlying distribution of the lifetime of the component is assumed to be an exponential. The method of maximum likelihood is used to obtain estimates, a chi squared approximation is used to approximate the mean and variance of the maximum likelihood estimate, and a method for reducing its bias is presented.     

梯度淋洗离子色谱法测定天然水中多种阴离子的方法研究

基于淋洗液自动发生技术,建立了用离子色谱测定天然水中F-、CHs COO-、C2 H5 COO-、HCOO-、Cl-、NO2-、Br-、NOs-、SO42-、pO43-的方法.采用IonPacAS17-C型阴离子分析柱,采用EG40淋洗液自动发生器在线产生KOH淋洗液进行梯度淋洗,淋洗液流速为1.0 mL/min,分析柱柱温为30℃,进样量为25μL,测定各离子的检出限分布在0.5～3.1 μg/L,相对标准偏差(RSD)小于0.92％;实际天然水样加标回收率总范围为95.2％～101.8％.该方法具有灵敏、快速、准确等优点,适用于天然水中多种阴离子的同时分析测定.     

氟离子荧光探针的研究进展

氟离子是电负性最强、离子半径最小的阴离子,是一个强路易斯碱,在化学、生物学、医学和军事等方面都具有重要作用。适量的氟化物摄入人体可以预防龋齿、治疗骨质疏松症,但是过量的摄入会导致氟斑牙、氟骨症、尿石症以及癌症等疾病,因此氟离子的识别与检测具有重要意义。化学荧光探针具有选择性好、灵敏度高、方便快捷、成本低廉等优点,近年来化学研究者设计合成了大量的氟离子荧光探针。根据识别机理不同,氟离子荧光探针主要划分为3种:氢键型、路易斯酸受体型、氢键和路易斯酸混合型。综述了近年来不同类型的氟离子荧光探针的研究进展,总结了氢键型和路易斯酸型氟离子荧光探针的优缺点,对未来氟离子荧光探针的研究方向进行了展望。     

离子色谱法测定降水中阴离子影响因素的研究

监测降水各种离子特别是F-、Cl-、NO3-、SO24-等阴离子的含量,是研究酸雨危害的前提条件[1]。离子色谱分析具有高灵活性、高选择性、高灵敏度的特点,已经广泛应用于环境等众多领域,是测定很多阴离子和阳离子的有效方法[2];但离子色谱仪在调节和分析过程中还存在许多影响因素,从而对实验结果产生影响。为此,本文对ICS-90型离子色谱仪在降水中F-、Cl-、NO3-、SO42-阴离子分析中出现的三个主要影响因素进行了初步研究和探讨。     

毛细管区带电泳-间接紫外检测法测定饮用水中5种阴离子

目的建立毛细管区带电泳-间接紫外检测法测定饮用水中5种阴离子的新方法。方法样品无需滤膜过滤可直接进样。用未涂覆熔融石英毛细管(75μm×80 cm,有效长度为70 cm)作为分离柱。以20 mmol/L邻苯二甲酸、100 mmol/L二乙醇胺和0.5 mmol/L十六烷基三甲基溴化铵为分离缓冲体系。结果 Cl~-、NO_3~-、SO_4~(2-)、F~-和H_2PO_4~-这5种阴离子的校正峰面积与质量浓度分别在0.5～100.0、0.2～20.0、0.5～100.0、0.2～4.0和0.2～5.0 mg/L范围内呈线性相关,相关系数分别为0.998 8、0.999 9、0.999 7、0.999 7、0.999 8。检出限均为0.05 mg/L,定量限均为0.15 mg/L,方法精密度均小于5%(n=6)。低、中和高质量浓度加标回收率在81.6%～108.6%之间,相对标准偏差在0.6%～3.7%之间(n=6)。用本法分析了7份饮用水样品,并与离子色谱法的结果相比较,除矿泉水中Cl~-结果偏低外,其余基本吻合。结论本方法简单,所用试剂环保,为饮用水中5种阴离子的常规检测提供了一种新方法,但不适合测定水样中低浓度的Cl~-。     

Photocatalytic degradation of chlorobenzene using solar and artificial UV radiation

In this work photocatalytic degradation of chlorobenzene has been studied using solar and artificial UV radiations. The effect of pH and the presence of different anions on the degradation of chlorobenzene has been studied for both cases. Chlorobenzene has been found to be a strongly adsorbing and hence rapidly degrading species when subjected to photocatalysis. The effect of pH in the range of 3–10 and the presence of different anions at a concentration of 0.1 mol dm^?3 on the adsorption was studied. Both pH and the presence of anions affect adsorption and the degradation but the overall effect is negligible (<5%). Copyright © 2004 Society of Chemical Industry     

Objective Bayesian analysis of accelerated competing failure models under Type-I censoring

This paper discusses the Bayesian inference of accelerated life tests (ALT) in the presence of competing failure causes. The time to failure due to a specific cause is described by a Weibull distribution. A two-stage approach is utilized to obtain the estimates of parameters in the model. We use the Bayesian method to estimate the parameters of the distribution of component lifetimes in the first stage, in which two noninformative priors (Jeffreys prior and reference prior) are derived in the case of ALT, and based on these two priors we present the Gibbs sampling procedures to obtain the posterior estimates of the parameters. Besides, to overcome the problem of improper posterior densities under some conditions, we modify the likelihood function to make the posterior densities proper. In the second stage, parameters in the accelerating function are obtained by least squares approach. A numerical example is given to show the effectiveness of the method and a real data from Nelson (1990) is analyzed.