Hazard Rate Research Papers - Academia.edu (original) (raw)

The aim of the research was to monitor and assess landslide hazards by remote sensing data processing and GIS spatial analysis. The automatic classification of remote sensing images provides many useful land use information to combine in... more

The aim of the research was to monitor and assess landslide hazards by remote sensing data processing and GIS spatial analysis. The automatic classification of remote sensing images provides many useful land use information to combine in a GIS environment with other spatial factors influencing the occurrence of landslide. The upper part of Susa Valley, in the Italian Western Alps, was chosen as test area because of a large variety of remote sensing data available by ISPRS WG VIII/2 with the aim to exchange information and experience in the field of geomatic techniques. It is well known that the occurrence of landslides is controlled by a lot of morphological, geological, and human factors. We have chosen, regarding the available data, the following factors: acclivity, aspect, lithology, land use and precipitations. We have built up a mathematical predictive model enabling actual/potential unstable slopes. It is a linear model where the hazard score depends on instability factors and...

We propose in this article a unified approach to functional estimation problems based on possibly censored data. The general framework that we define allows, for instance, to handle density and hazard rate estimation based on randomly... more

We propose in this article a unified approach to functional estimation problems based on possibly censored data. The general framework that we define allows, for instance, to handle density and hazard rate estimation based on randomly right-censored data, or regression. Given a collection of histograms, our estimation procedure consists in selecting the best histogram among that collection from the data,

This paper provides a method for evaluating the residual lives of water pipes using the proportional hazards model (PHM) based on the economically optimal replacement times of pipes. The survival times, which are used in the proportional... more

This paper provides a method for evaluating the residual lives of water pipes using the proportional hazards model (PHM) based on the economically optimal replacement times of pipes. The survival times, which are used in the proportional hazards modeling process, were defined as the economically optimal replacement times of pipes. The break rate of an individual pipe is estimated using the General Pipe Break Model (GPBM). The optimal replacement time of a pipe is obtained using the equivalence relationship between the GPBM and threshold break rate. In order to use the GPBM effectively, the process of estimating the GPBM has been modified in this paper by utilizing additional break data for the time of installation and adjusting the value of the weighting factor (WF) in the GPBM. The residual lives and hazard ratios of the case study pipes, of which the cumulative number of breaks was at least one, were estimated using the estimated survivor function of the constructed PHM. The time-dependency of the pipe material covariate caused the hazard rate of the cast iron pipes to become lower than the hazard rate of the steel pipes after 19 years since installation. The methodology developed in this paper may help utilities identify important factors related to the economics of water pipe maintenance and; therefore more efficiently maintain their water pipes.

We developed the model PHENIPS for spatial and temporal simulation of the seasonal development of Ips typographus at the Kalkalpen National Park in Austria. The model is based on a digital elevation model used for interpolation of... more

We developed the model PHENIPS for spatial and temporal simulation of the seasonal development of Ips typographus at the Kalkalpen National Park in Austria. The model is based on a digital elevation model used for interpolation of temperature and solar radiation to calculate the microclimatic conditions (bark temperature) for the beetles’ development. Additionally, the beetles’ phenology at Kalkalpen National Park was monitored along with air and bark temperature measurements. The onset of host tree infestation in spring was estimated using a lower threshold of 16.5 °C for flight activity and a mean thermal sum of 140 degree-days (dd) from beginning of April 1st onward. Rate of brood development was calculated from accumulated degree-days of hourly temperature data using upper and lower temperature thresholds of 38.9 and 8.3 °C, respectively, and a nonlinear function for calculating effective thermal sums. Re-emergence of parental beetles occurred at a time when 49.7% of the thermal sum for total development (557 dd) was reached. The model includes the discontinuance of the beetle's reproductive activity at a day length <14.5 h. The rate of successful hibernation of established broods is predicted by assessing the developmental stage of initiated generations at the beginning of the cold period. For validation we compared the timing of phenological events in the field with predicted events using both, hourly recorded data at trap trees in the terrain and generated daily topoclimatic data. Using topoclimatic data, the onset of infestation was predicted with a mean absolute error of 1.3 days. The observed onset of emergence of filial beetles in the field was estimated with a mean error of 39 dd. Our PHENIPS explicitly considers the strong effects of regional topography and stand conditions on local air and bark temperature and can be used for precise monitoring of the actual state of bark beetle development at the specific stand/tree level. Using topoclimatic data, PHENIPS simulates the maximum number of generations which is necessary to assess the potential impact of bark beetle outbreaks at regional scale. Further applications of PHENIPS for site-specific hazard rating of bark beetle infestation are discussed.

Most prison systems use quantitative instruments to classify and assign inmates to prison security levels commensurate to their level of risk. Bench and Allen (The Prison Journal 83(4):367-382, 2003) offer evidence that the assignment to... more

Most prison systems use quantitative instruments to classify and assign inmates to prison security levels commensurate to their level of risk. Bench and Allen (The Prison Journal 83(4):367-382, 2003) offer evidence that the assignment to higher security prisons produces elevated levels of misconduct independent of the individual’s propensity to commit misconduct. Chen and Shapiro (American Law and Economics Review, 2007)

Cure models can be used to simultaneously estimate the proportion of cancer patients who are eventually cured of their disease and the survival of those who remain "uncured". One limitation of parametric cure models is that the... more

Cure models can be used to simultaneously estimate the proportion of cancer patients who are eventually cured of their disease and the survival of those who remain "uncured". One limitation of parametric cure models is that the functional form of the survival of the "uncured" has to be specified. It can sometimes be hard to fit survival functions flexible enough

In this study, the effects of vigabatrin on spike-and-wave discharges (SWDs) were measured in WAG/Rij rats, an animal model of absence epilepsy. Vigabatrin was used with the aim of enhancing GABAergic neurotransmission, and in this way to... more

In this study, the effects of vigabatrin on spike-and-wave discharges (SWDs) were measured in WAG/Rij rats, an animal model of absence epilepsy. Vigabatrin was used with the aim of enhancing GABAergic neurotransmission, and in this way to investigate the role of this process in the properties of SWDs. The study was carried out both in the rat, in vivo, and also using a computational model, in order to test different mechanisms that may account for the changes in SWDs after vigabatrin. The model parameters, representing GABA levels, were changed according to the known, and assumed, mechanism of action of the drug. The results show that the computational model can most adequately simulate the data obtained in vivo on the assumption that the enhancement of GABAergic neurotransmission due to application of vigabatrin is most pronounced at the level of the thalamic relay nuclei (TC cells). Furthermore, vigabatrin was shown to affect both the SWD starting and stopping mechanisms, as refle...

Abstract. The traditional Cox proportional hazards regression model uses an exponential relative risk function. We argue that under various plausible scenarios, the relative risk part of the model should be bounded, suggesting also that... more

Abstract. The traditional Cox proportional hazards regression model uses an exponential relative risk function. We argue that under various plausible scenarios, the relative risk part of the model should be bounded, suggesting also that the traditional model often might overdramatize the hazard rate assessment for individuals with unusual covariates. This motivates our working with proportional hazards models where the relative risk function takes a logistic form. We provide frequentist methods, based on the partial likelihood, and then go on to semiparametric Bayesian constructions. These involve a Beta process for the cumulative baseline hazard function and any prior with a density, for example that dictated by a Jeffreys-type argument, for the regression coefficients. The posterior is derived using machinery for Lévy processes, and a simulation recipe is devised for sampling from the posterior distribution of any quantity. Our methods are illustrated on real data. A Bernshteĭn–von Mises theorem is reached for our class of semiparametric priors, guaranteeing asymptotic normality of the posterior processes.

An analytical optimization method for preventive maintenance (PM) policy with minimal repair at failure, periodic maintenance, and replacement is proposed for systems with historical failure time data influenced by acurrent PM policy. The... more

An analytical optimization method for preventive maintenance (PM) policy with minimal repair at failure, periodic maintenance, and replacement is proposed for systems with historical failure time data influenced by acurrent PM policy. The method includes a new imperfect PM model based on Weibull distribution and incorporates the current maintenance interval T0 and the optimal maintenance interval T to befound. The Weibull parameters are analytically estimated using maximum likelihood estimation. Based on this model, the optimal number of PM and the optimal maintenance interval for minimizing the expected cost over an infinite time horizon are also analytically determined. A number of examples are presented involving different failure time data and current maintenance intervals to analyze how the proposed analytical optimization method for periodic PM policy performances in response to changes in the distribution of the failure data and the current maintenance interval.

In this work, we show that the Dagum distribution [3] may be a competitive model for describing data which include censored observations in lifetime and reliability problems. Maximum likelihood estimates of the three parameters of the... more

In this work, we show that the Dagum distribution [3] may be a competitive model for describing data which include censored observations in lifetime and reliability problems. Maximum likelihood estimates of the three parameters of the Dagum distribution are determined from samples with type I right and type II doubly censored data. We perform an empirical analysis using published censored data sets: in certain cases, the Dagum distribution fits the data better than other parametric distributions that are more commonly used in survival and reliability analysis. Graphical comparisons confirm that the Dagum model behaves better than a number of competitive distributions in describing the empirical hazard rate of the analyzed data. A probability plot to provide graphical check of the appropriateness of the Dagum model for right censored data is constructed, and the details are given in the appendix. Finally, a simulation study that shows the good performance of the maximum likelihood estimators of the Dagum shape parameters for finite type II doubly censored samples is carried out.

ABSTRACT The purpose of this expository article is to provide greater access to critical values for testing hypotheses about the shape parameter of a gamma distribution. Among the possible tests, we consider tests of exponentiality... more

ABSTRACT The purpose of this expository article is to provide greater access to critical values for testing hypotheses about the shape parameter of a gamma distribution. Among the possible tests, we consider tests of exponentiality against gamma increasing failure rate and/or decreasing failure rate alternatives. Extensive tables of critical values are given for individual sample sizes from 2 to 30, and values of the shape parameter in half-integer increments from 1/2 to 10. Median unbiased estimators are also given for the shape parameter to avoid small-sample complications with maximum likelihood methods. Power curves are given for testing exponentiality against gamma alternatives. These curves illustrate certain advantages of this parametric test oveer nonparametric alternatives.

Improvement factors in hazard rate and age for a sequential preventative maintenance (PM) policy are introduced. Two imperfect PM models are analyzed: (1) PM reduces the hazard rate while it increases with the number of PMs, and (2) PM... more

Improvement factors in hazard rate and age for a sequential preventative maintenance (PM) policy are introduced. Two imperfect PM models are analyzed: (1) PM reduces the hazard rate while it increases with the number of PMs, and (2) PM reduces the age. The PM is done at intervals xk (k=1,2, . . . , N) and is imperfect. The optimal