Bayesian testing procedure on the lifetime performance index of products following Chen lifetime distribution based on the progressive type-II censored sample

[[abstract]]With the high demands on the quality of high-tech products for consumers, assuring the lifetime performance is a very important task for competitive manufacturing industries. The lifetime performance index CL is frequently used to monitor the larger-the-better lifetime performance of products. This research is related to the topic of asymmetrical probability distributions and applications across disciplines. Chen lifetime distribution with a bathtub shape or increasing failure rate function has many applications in the lifetime data analysis. We derived the uniformly minimum variance unbiased estimator (UMVUE) for CL, and we used this estimator to develop a hypothesis testing procedure of CL under a lower specification limit based on the progressive type-II censored sample. The Bayesian estimator for CL is also derived, and it is used to develop another hypothesis testing procedure. A simulation study is conducted to compare the average confidence levels for two procedures. Finally, one practical example is given to illustrate the implementation of our proposed non-Bayesian and Bayesian testing procedure.[[notice]]補正完

The evaluation on the process capability index CL for exponentiated Frech’et lifetime product under progressive type I interval censoring

[[abstract]]We present the likelihood inferences on the lifetime performance index CL to evaluate the performance of lifetimes of products following the skewed Exponentiated Frech’et distribution in many manufacturing industries. This research is related to the topic of skewed Probability Distributions and Applications across Disciplines. Exponentiated Frech’et distribution is a generalization of some lifetime distributions. The maximum likelihood estimator for CL for lifetimes with exponentiated Frech’et distribution is derived to develop a computational testing procedure so that experimenters can implement it to test whether the lifetime performance reached the pre-assigned level of significance with a given lower specification limit under progressive type I interval censoring. At the end, two examples are provided to demonstrate the implementation on the algorithm for our proposed computational testing procedure.[[notice]]補正完

Azacitidine for treating acute myeloid leukaemia with more than 30% bone marrow blasts: A Single Technology Appraisal

Report commissioned by the NIHR HTA ProgrammeThis report was commissioned by the NIHR HTA Programme as project number 15/64/10

Probabilistic Models for Life Cycle Management of Energy Infrastructure Systems

The degradation of aging energy infrastructure systems has the potential to increase the risk of failure, resulting in power outage and costly unplanned maintenance work. Therefore, the development of scientific and cost-effective life cycle management (LCM) strategies has become increasingly important to maintain energy infrastructure. Since degradation of aging equipment is an uncertain process which depends on many factors, a risk-based approach is required to consider the effect of various uncertainties in LCM. The thesis presents probabilistic models to support risk-based life cycle management of energy infrastructure systems. In addition to uncertainty in degradation process, the inspection data collected by the energy industry is often censored and truncated which make it difficult to estimate the lifetime probability distribution of the equipment. The thesis presents modern statistical techniques in quantifying uncertainties associated with inspection data and to estimate the lifetime distributions in a consistent manner. Age-based and sequential inspection-based replacement models are proposed for maintenance of component in a large-distribution network. A probabilistic lifetime model to consider the effect of imperfect preventive maintenance of a component is developed and its impact to maintenance optimization is illustrated. The thesis presents a stochastic model for the pitting corrosion process in steam generators (SG), which is a serious form of degradation in SG tubing of some nuclear generating stations. The model is applied to estimate the number of tubes requiring plugging and the probability of tube leakage in an operating period. The application and benefits of the model are illustrated in the context of managing the life cycle of a steam generator

Random Number Generators

The quasi-negative-binomial distribution was applied to queuing theory for determining the distribution of total number of customers served before the queue vanishes under certain assumptions. Some structural properties (probability generating function, convolution, mode and recurrence relation) for the moments of quasi-negative-binomial distribution are discussed. The distribution’s characterization and its relation with other distributions were investigated. A computer program was developed using R to obtain ML estimates and the distribution was fitted to some observed sets of data to test its goodness of fit

Understanding Travel Behaviour: Some Appealing Research Directions

This paper presents one researchers perception of selective emphases in the body of travel behaviour research which have had and/or may in the future have a non-marginal impact on the way that research activity is undertaken. Some of the contributions are well established and have moved from state of the art to state of practice; other efforts are relatively new and maturing in their role as paradigms of thought. The contributions can broadly be grouped into four classes of research: decision paradigms, in particular the interpretation of the choice process within a broad activity framework, and the recognition that agents making decisions do not always operate in a perfectly competitive market; releasing the analytical formalism of the choice/decision process from the restrictive IIA paradigm of the great majority of applied travel choice modelling - moving to nested structures, free variance and correlation among alternatives, random taste weights, accommodating unobserved heterogeneity and mixed 'logits'; combining sources of preference and choice data, including joint analysis of market and experimental choice data, interfaces between attitudinal and behavioural data, and generalising valuation to valuation functions; and advances in the study of the dynamics of traveller behaviour, especially the timing of change and its importance in establishing hurdle dates for forecasting traffic and revenue for infrastructure projects

An economic analysis of the quality of primary care for the management of comorbidities in patients living with dementia

The thesis examines the quality of primary care services across a range of comorbid conditions in patients with dementia. The key aims were to assess whether their dementia diagnoses may hinder access to high quality care compared to patients without a cognitive impairment older adults, the health implications of this, and whether quality could be modified. An economic framework is proposed, suggesting that the quality of care received is a function of the supply and demand for quality. Patients with dementia may have a diminishing demand for quality due to a decreased comprehension of their health status as cognitive function declines. On the supply side, quality care provided by physicians may be a function of the availability of resources and the motivation to provide high quality care, which could be financial or not. A systematic literature review and meta-analysis was conducted and highlighted that a diagnosis of dementia is associated with not meeting quality indicators for a range of non-dementia conditions. Subsequent analysis on the English Longitudinal Survey of Ageing, including care quality indicators specifically selected for UK older adults, supports these findings in suggesting that quality is unequal between patients with dementia and patients without cognitive impairments. Further analysis showed that meeting some of these indicators was associated with improved survival and could reduce social care use in patients with dementia, implying that care quality should be improved. In order to assess how care quality and the consequential health outcomes could be improved for patients with dementia, later analyses in this thesis aimed to identify interventions or policies that could improve care quality. Pay-for-performance measures (the Quality and Outcomes Framework) as well as higher levels of cognitive function in patients with dementia appear to be associated with higher quality care. I developed an early model to evaluate the potential cost-effectiveness of introducing a cognition and independence promoting intervention or expanding the QOF to provide additional incentives for patients with dementia. Expanding the QOF does not appear to be cost-effective compared to current practices, though there may be some benefit in promoting cognition and independence in patients with dementia. However, further research on the valuation of health in patients with dementia is required to validate these findings within current willingness-to-pay frameworks for healthcare. The findings of this thesis show that there are some inequalities in the delivery of high-quality primary care, to the detriment of health of patients with dementia. It is implicated that there may be economically efficient strategies to improve health outcomes for patients with dementia by promoting independence

Temperature effects on the static, dynamic and fatigue behaviour of composite materials used in wind turbine blades

Many Canadian regions have strong winds that are interesting for wind energy production. However, these same regions are often quite remote and the Canadian climate is atypical for the wind energy industry. The high level of uncertainty about the turbines durability and the profitability of wind plants under such environments thus hinders the development of wind energy projects in Canada. Among the many uncertainties related to Canadian operating conditions, one specific concern is about the durability of wind turbine blades in Northern climates. The goal of this thesis is thus to clarify the effects of temperature and strain rate on the strength, stiffness and fatigue performance of composite materials as used in the wind energy sector. It thus focuses on glass fibre reinforced composites, which is the mainstream material for wind turbine blades. Wind turbine blades are basically beam exposed to a combination of axial, bending (in and out of the rotor plane) and torsional loads. In order to resist these loads, laminates used in the different parts of the blade are mostly made of a combination of longitudinal and ±45◦ plies. In order to improve the basic understanding of the mechanics of failure, two simple laminate configurations are studied, namely: • The unidirectional laminate loaded in the fibre direction, which is the main load bearing component of the blade structure. • The [±45]s bias-ply laminate, which provides shear stiffness to the blades structure. The temperatures considered are limited to those that could realistically be encountered in Canada’s climate, namely an extreme wintertime low of -40℃ to a summertime high of 60℃, which is deemed representative of a part exposed to direct sunlight in the summer. Similarly, fatigue frequencies are limited to a maximum of 24 Hz. It was found that the static strength and stiffness of both laminate configurations were strongly affected by both low and high temperatures. A significant increase of both properties was measured at low temperature, while high temperature strongly degraded them. However, while the high temperature fatigue durability followed the same trend as the static strength, the low temperature fatigue performance was only slightly affected, and even less so for unidirectional laminates. Both a vertical shift and a change in slope of the S–N curve with temperature was observed. At low temperature, this change of slope favours the fatigue strength under a high fatigue load, but reduces expected lives at lower load levels. This finding may be particularly significant in the context of wind turbine blade durability since they generally need to operate at low fatigue stresses, but over very long periods. Frequency effects were mostly not significant within the range explored. Nevertheless, experiments suggest that higher frequencies may have a slightly deleterious effect. An approach to predict the effect of temperature on the probabilistic S–N curve of fibre dominated composites with minimal experimental requirements is also proposed. This method is based on a cyclic strength degradation model, for which the parameters change with temperature is correlated with temperature effect on static strength. Since the latter is also an input for the cyclic strength degradation model, a function describing its temperature dependence is also suggested. The predictions obtained by the model are very good for both strength and fatigue life. Finally, models are developed for describing the static strength as well as the storage and loss modulus as a function of temperature across multiple transitions. The latter model also has provision for evaluating frequency effects on the storage modulus and glass transition temperature. These models provide a very good description of the dynamic response of polymers and composites on which they were validated (epoxies and epoxy based composites). Moreover, they provide a unambiguous definition of the glass transition temperature and allows for the evaluation of temperature and frequency effects on both the storage modulus without using the time-temperature superposition principle. Results show that if the time-temperature shift factors are calculated from the model, they are continuous across the glass transition. This suggests that the commonly expected discontinuity in this region may actually only be a side effect of neglecting the glass transition frequency dependence in conventional time-temperature superposition approaches

Modeling Reliability Growth in Accelerated Stress Testing

Qualitative accelerated test methods improve system reliability by identifying and removing initial design flaws. However, schedule and cost constraints often preclude sufficient testing to generate a meaningful reliability estimate from the data obtained in these tests. In this dissertation a modified accelerated life test is proposed to assess the likelihood of attaining a reliability requirement based on tests of early system prototypes. Assuming each prototype contains an unknown number of independent competing failure modes whose respective times to occurrence are governed by a distinct Weibull law, the observed failure data from this qualitative test are shown to follow a poly-Weibull distribution. However, using an agent-based Monte Carlo simulation, it is shown that for typical products subjected to qualitative testing, the failure observations result from a homogenous subset of the total number of latent failure modes and the failure data can be adequately modeled with a Weibull distribution. Thus, the projected system reliability after implementing corrective action to remove one or more failure modes can be estimated using established quantitative accelerated test data analysis methods. Our results suggest that a significant cost and time savings may be realized using the proposed method to signal the need to reassess a product’s design or reallocate test resources to avoid unnecessary maintenance or redesigns. Further, the proposed approach allows a significant reduction in the test time and sample size required to estimate the risk of meeting a reliability requirement over current quantitative accelerated life test techniques. Additional contributions include a numerical and analytical procedure for obtaining the maximum likelihood parameter estimates and observed Fisher information matrix components for the generalized poly-Weibull distribution. Using this procedure, we show that the poly-Weibull distribution outperforms the best-fit modified Weibull alternatives in the literature with respect to their fit of reference data sets for which the hazard rate functions are non-monotone