Browsing by Subject "Failure time data analysis"
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Item A flexible bathtub hazard model for nonrepairable systems(Texas Tech University, 1985-12) Jaisingh, Lloyd RNot availableItem Checking the censored two-sample accelerated life model using integrated cumulative hazard difference(Texas Tech University, 2004-08) Lee, Seung-HwanIn this dissertation, soma lack-of-fit tests will be discussed for the censored two-sample accelerated life model. Conventional scale estimators with two-sample censored data such as rank-based estimators and minimum distance estimators have difficulties to apply easily due to the fact that their asymptotic variances involve the unknown density, or they require soma strict conditions. The object of this work is to provide an asymptotically equivalent martingale-based stochastic process of some estimating functions, which is easier to apply than existing methods from the literature. An extreme value of the observed process compared with simulated realizations of the approximation process would indicate the model misspecifications. The approximation process involving the martingale structure can be achieved through some approximation procedures of the observed process under the two-sample scale model. The p-value applied to the approximation of the observed process leads to the construction of the lack-of-fit tests. Comparison of the processes enables one to get some information visually from the graph about how the model is misspecified.Item Estimating equations for two-sample scale estimation with censored data(Texas Tech University, 1998-12) Williams, Michael JNot availableItem One-stage and two-stage machining economics problems with stochastic tool life and penalty cost for tool failure during production(Texas Tech University, 1985-12) Koulamas, Christos P.Item Reliability analysis for nonrepairable systems subject to dormancy(Texas Tech University, 1985-05) Landers, Thomas Lee.Item Reliability of electro-mechanical components subject to on/off cycling and continuous operation under multiple stresses(Texas Tech University, 1988-12) Teng, Niann-hwaPower on/off and continuous operation are two important factors impacting the reliability of electronic and electromechanical components. In the reliability field, only limited work has been done to model component reliability involving transient phases and on/off cycling. This is due to difficulties in collecting data as well as establishing meaningful models which fit the data. The purpose of this research was to study and model simple electro-mechanical components over a two-phase (on/off) life cycle under multiple stresses. In addition, this research was directed at determining a criterion for selecting between continuous and on/off operating policies. A reliability experiment was designed to study the on/off switching effect and continuous operation effect, under multiple load and voltage stresses, for simple electro-mechanical dc motors. A real-time C program was used for control and to monitor the lifetimes of the dc motors. A failure mode analysis was used to study the physical causes by which the motors failed. Based on the results obtained, it was concluded that only one mode (a brush/commutator) failure mode was present. Continuous operation provided a longer life than on/off operation under the same environmental conditions, when off-time was removed. A general reliability model, based on the twoparameter Weibull proportional hazards life distribution, was developed. Due to the proportional hazards (common Weibull shape) nature of the model, a set of acceleration factors were developed to relate the stress levels. The calculated stress factor included multiple stresses. Using this reliability model, different operating policies under different multiple stresses can be studied. The stress factor reliability model was extended to develop a simple policy decision rule. The rule compares the inverse of the stress factor with the demand duty cycle to determine the most effective operating policy. Hence, a quantitative analysis model, based on predicted reliability, has been developed to determine whether a continuous running policy or an on/off operation policy should be specified.Item Some nonparametric methods in estimating the hazard rate function(Texas Tech University, 1989-12) Chen, DafengThe hazard rate function h{x) = f{x)/[1-F{x)], corresponding to a distribution function F with density function / , is one of the most important parameters in reliability and other fields, since h{x)dx can be interpreted as the probability that an object fails in the time interval [x,x + dx] given that the object has survived to time x. A problem of considerable interest, especially to reusability engineers, is the estimation of h from a sample of n independent and identically distributed nonnegative lifetimes X1 , X2,…,Xn , with or without censoring. By censoring we mean that the occurrence of the random event of interest (called a failure) is prevented by the previous occurrence of another event (called a censoring event). If the censoring event is also a random variable, we have the randomly censored model. If there are several randomly censoring events, we have the multiple competing risks model. This paper discusses three nonparametric estimators of the hazard rate function h: the Fourier integral estimator, the nearest neighbor estimator in the multiple competing risks model, and the discrete maximum penalized-likelihood estimator in the randomly censored model. The asymptotic behavior of these estimators will be studied and conditions for strong consistency will be given.