The use of models in reliability

The paper reviews the scientific and philosophical basis of the use of models in engineering, particularly in reliability engineering, and their credibility in predicting future outcomes.     

Reliability and risk models based on independent trials

An analysis has been made of the mathematical relationship between two alternative models for reliability and risk estimation under the assumption of mutual independence. In cases where the reliability formulation is expressible as a compound union event, the resultant reliability expressions are analogous to the Bernoulli and Poisson trials processes. Nonparametric inequality relationships aredeveloped that demonstrate that a Bayesian-Bernoulli model always predicts event probabilities that are less than Bernoulli probabilities, which are always less than or equal to probabilities predicted by the finer grained Poisson trials model. An analysis of the maximum relative prediction error indicates when the individual probabilities are less than 0.1, the relative error between the Bernoulli and Poisson models is always less than 5 percent. The results are demonstrated to have utility in system reliability, engineered design lifetime risk analysis, and simulation applications in which the model is based on independent trials.     

基于个人风险的土地利用规划在LNG储备库的应用

对基于个人风险的土地利用规划进行研究,确定方法的框架和程序,并应用于某拟建液化天然气储备库周边的土地利用与布局调整。对拟建天然气储备库可能发生的事故,选取蒸气云爆炸及沸腾液体扩展蒸气爆炸进行讨论。在确定事故发生概率及事故后果的基础上,对拟建液化天然气储备库的个人风险进行计算。借鉴英国土地利用规划中个人风险的可接受标准,在液化天然气储备库周围划分三个风险区域,根据各区域的功能规定及储备库周围土地利用现状,对储备库周围的土地利用进行规划与调整。结果表明,液化天然气储备库附近有两处居民区、一个工厂需要搬迁。基于个人风险的土地利用规划方法在合理确定重大工程选址及周边建筑与设施的布局上是行之有效的方法。     

对几种常见学习类型的探讨

分析比较四种常见学习类型,提出教师应该在对各种常用教学模式和学习类型都能正确理解和灵活运用的前提下,根据教学需要进行合理选择及恰当组合,以达成在传授知识的同时对学生的学习能力进行专门训练的目的.     

The third spatial dimension risk approach for individual risk and group risk in multiple use of space

Buildings above roads and railways are examples of multiple use of space. Safety is one of the critical issues for such projects. Risk analyses can be undertaken to investigate what safety measures that are required to realise these projects. The results of these analyses can also be compared to risk acceptance criteria, if they are applicable. In The Netherlands, there are explicit criteria for acceptability of individual risk and societal risk. Traditionally calculations of individual risk result in contours of equal risk on a map and thus are considered in two-dimensional space only. However, when different functions are layered the third spatial dimension, height, becomes an important parameter. The various activities and structures above and below each other impose mutual risks. There are no explicit norms or policies about how to deal with the individual or group risk approach in the third dimension. This paper proposes an approach for these problems and gives some examples. Finally, the third dimension risk approach is applied in a case study of Bos en Lommer, Amsterdam.     

The use of time domain diakoptics in time discrete models of fields

The principles of diakoptics are extended to time domain solutions and the technique is applied to the solution of fields by introducing space approximating polynomials. Since transmission-line networks provide time-discrete models suitable for exact numerical analysis, the topic is approached by tearing these transmission-line models and then showing how reconnection is made in the time domain.     

Traffic analysis zone level crash estimation models based on land use characteristics

The objective of this paper is to develop crash estimation models at traffic analysis zone (TAZ) level as a function of land use characteristics. Crash data and land use data for the City of Charlotte, Mecklenburg County, North Carolina were used to illustrate the development of TAZ level crash estimation models. Negative binomial count models (with log-link) were developed as data was observed to be over-dispersed. Demographic/socio-economic characteristics such as population, the number of household units and employment, traffic indicators such as trip productions and attractions, and, on-network characteristics such as center-lane miles by speed limit were observed to be correlated to land use characteristics, and, hence were not considered in the development of TAZ level crash estimation models. Urban residential commercial, rural district and mixed use district land use variables were observed to be correlated to other land use variables and were also not considered in the development of the models. Results obtained indicate that land use characteristics such as mixed use development, urban residential, single-family residential, multi-family residential, business and, office district are strongly associated and play a statistically significant role in estimating TAZ level crashes. The coefficient for single-family residential area was observed to be negative, indicating a decrease in the number of crashes with an increase in single-family residential area. Models were also developed to estimate these crashes by severity (injury and property damage only crashes). The outcomes can be used in safety conscious planning, land use decisions, long range transportation plans, and, to proactively apply safety treatments in high risk TAZs.     

The use of ultrasound and micelles in cancer treatment

The high toxicity of potent chemotherapeutic drugs like Doxorubicin (Dox) limits the therapeutic window in which they can be applied. This window can be expanded by controlling the drug delivery in both space and time such that non-targeted tissues are not adversely affected. Recent research has shown that ultrasound (US) can be used to control the release of Dox and other hydrophobic drugs from polymeric micelles in both time and space. It has also been shown using an in vivo rat tumor model that Dox activity can be enhanced by ultrasound in one region, while in an adjacent region there is little or no effect of the drug. In this article, we review the in vivo and in vitro research being conducted in the area of using ultrasound to enhance and target micellar drug delivery to cancerous tissues. Additionally, we summarize our previously published mathematical models that attempt to represent the release and re-encapsulation phenomena of Dox from Pluronic P105 micelles upon the application of ultrasound. The potential benefits of such controlled chemotherapy compels a thorough investigation of the role of ultrasound (US) and the mechanisms by which US accomplishes drug release and/or enhances drug potency. Therefore we will summarize our findings related to the mechanism involved in acoustically activated micellar drug delivery to tumors.     

The use of multiplicative models for analysis of road safety data

Accident ratios are analysed with regard to the variables road-surface skidding resistance and hourly traffic volume. In a first analysis the Additive Conjoint Measurement model (ACM) is used to investigate to what extent the accident ratios can be described as a result of independent contributions of skidding resistance and traffic volume. Furthermore it is considered whether these contributions have to be combined in an additive or multiplicative way. Based on the results of this investigation a second analysis takes place in which a stochastic interpretation of the data is combined with the multiplicative model. This Weighted Poisson model (WPM) is in fact a generalisation of the log-linear model, recently proposed for the analysis of contingency tables. It is concluded that the multiplicative model describes the data better than the additive model. Moreover, there is no interaction between skidding resistance and traffic volume in their effect on accident ratios. The relation between accident ratios and both variables are shown, and the statistics regarding the contributions of the variables are given.     

A review of some epidemiological studies on cancer risk from low-dose radiation or other carcinogenic agents

It is extremely difficult to assess cancer risks accurately due to health effects of low-dose radiation exposure or other carcinogens based on epidemiological studies. For the detection of minute increases of the risk at low-level exposure, most of epidemiological studies lack statistical power, and they involve various complicated confounding factors. This paper reports on a literature survey of epidemiological studies published since 2000 on cancer risks associated with low-dose radiation and other carcinogens to gather major epidemiological data. Integrated risk indices were derived from those data by using, where possible, statistical models. Regarding risk assessment of low-dose radiation exposure, it is important to lower the degree of uncertainty arising from risk estimation. Risk assessment of low-dose radiation exposure could be scientific evidence when uncertainty is considered in comparing carcinogenic risks of radiation with those of other carcinogens.     

Investigation based on the use of several models as a general method of physical modeling

A refined formulation of a theorem on modeling based on the use of several models is presented. It is shown that investigation based on a single model can be treated as a particular case of the method proposed. Advantages of the method developed over existing modeling based on the use of a single object or phenomenon are considered.     

The use of energy windowing to discriminate SNM from NORM in radiation portal monitors

Energy windowing is an algorithmic alarm method that can be applied to plastic scintillator-based radiation portal monitor (RPM) systems to improve operational sensitivity to certain threat sources while reducing the alarm rates from naturally occurring radioactive material. Various implementations of energy windowing have been tested and documented by industry and at Pacific Northwest National Laboratory, and are available in commercial RPMs built by several manufacturers. Moreover, energy windowing is being used in many deployed RPMs to reduce nuisance alarms and improve operational sensitivity during the screening of cargo. This paper describes energy windowing algorithms and demonstrates how these algorithms succeed when applied to “controlled” experimental measurements and “real world” vehicle traffic data.