A general threshold stress hybrid hazard model for lifetime data

In this paper we propose a hybrid hazard regression model with threshold stress which includes the proportional hazards and the accelerated failure time models as particular cases. To express the behavior of lifetimes the generalized-gamma distribution is assumed and an inverse power law model with a threshold stress is considered. For parameter estimation we develop a sampling-based posterior inference procedure based on Markov Chain Monte Carlo techniques. We assume proper but vague priors for the parameters of interest. A simulation study investigates the frequentist properties of the proposed estimators obtained under the assumption of vague priors. Further, some discussions on model selection criteria are given. The methodology is illustrated on simulated and real lifetime data set.

INFERENCES FOR THE CHANGE-POINT OF THE EXPONENTIATED WEIBULL HAZARD FUNCTION

In many applications of lifetime data analysis, it is important to perform inferences about the change-point of the hazard function. The change-point could be a maximum for unimodal hazard functions or a minimum for bathtub forms of hazard functions and is usually of great interest in medical or industrial applications. For lifetime distributions where this change-point of the hazard function can be analytically calculated, its maximum likelihood estimator is easily obtained from the invariance properties of the maximum likelihood estimators. From the asymptotical normality of the maximum likelihood estimators, confidence intervals can also be obtained. Considering the exponentiated Weibull distribution for the lifetime data, we have different forms for the hazard function: constant, increasing, unimodal, decreasing or bathtub forms. This model gives great flexibility of fit, but we do not have analytic expressions for the change-point of the hazard function. In this way, we consider the use of Markov Chain Monte Carlo methods to get posterior summaries for the change-point of the hazard function considering the exponentiated Weibull distribution.

UV-Ozone Generation from Modified High Intensity Discharge Mercury Vapor Lamps for Treatment of Indium Tin Oxide Films

In a homemade UV-Ozone generator, different ignition tubes extracted from HID mercury vapor lamps were investigated, namely: 80, 125, 250 and 400 watts. The performance of the generator in function of the type of the ignition lamp was monitored by the measurements of the ozone concentration and the temperature increment. The results have shown that the 400 W set up presented the highest ozone production, which was used in the treatment of indium tin oxide (ITO) films. Polymer light emitting diodes were assembled using ITO films, treated for 10, 20 and 30 min, as an anode. The overall results indicate improvement of the threshold voltage (reduction) and electroluminescence of these devices.

Nuts and seed: A natural yet dangerous foreign body

Rationale and aim: This paper has the object to present the impact of nuts' and seeds' injuries withdrawing data from the Susy Safe registry, highlighting that as for other foreign bodies the main item efficiently and substantially susceptible to changes to decrease the accidents' rates is the education of adults and children, that can be shared with parents both from pediatricians and general practitioners. Indeed labeling and age related warnings have also a fundamental relevance in prevention. Methods: The present study draws its data from the Susy Safe registry. Details on injuries are entered in the Susy Safe Web-registry through a standardized case report form, that includes information regarding: children age and gender, features of the object, circumstances of injury (presence of parents and activity) and hospitalization's details (lasting, complications and removal details). Cases are prospectively collected using the Susy Safe system from 06/2005; moreover, also information regarding past consecutive cases available in each centre adhering to the project have been entered in the Susy Safe registry. Results: Nuts and seeds are one of the most common food item retrieved in foreign bodies injuries in children. In Susy Safe registry they represent the 38% in food group, and almost the 10% in general cases. Trachea, bronchi and lungs were the main location of FB's retrieval, showing an incidence of 68%. Hospitalization occurred in 83% of cases, showing the major frequency for foreign bodies located in trachea. This location was also the principal site of complications, with a frequency of 68%. There were no significant associations between these outcomes and the age class of the children. The most common complications seen (22.4%) was bronchitis, followed by pneumonia (19.7%). Adult presence was recorded as positive in 71.2% of cases, showing an association (p value 0.009) between the adult supervision and the hospitalization outcome. On the contrary there was a non significant association between adult presence and the occurrence of complications. In 80.7% of cases, the incident happened while the child was eating. Among those cases, 88.6% interested trachea, lungs and bronchi. Conclusions: Food-related aspiration injuries are common events for young children, particularly under 4 years of age, and may lead to severe complication. There is a need to study in more depth specific characteristics of foreign bodies associated with increased hazard, such as size, shape, hardness or firmness, lubricity, pliability and elasticity, in order to better identify risky foods, and more precisely described the pathogenetic pathway. Parents are not adequately conscious and aware toward this risk; therefore, the number and severity of the injuries could be reduced by educating parents and children. Information about food safety should be included in all visits to pediatricians in order to make parents able to understand, select, and identify key characteristics of hazardous foods and better control the hazard level of various foods. Finally, preventive measures including warning labels on high-risk foods could be implemented. (C) 2012 Elsevier Ireland Ltd. All rights reserved.

Facilitatory effects of an auditory warning stimulus in a visual location identification task and a visual shape identification task

The occurrence of a weak auditory warning stimulus increases the speed of the response to a subsequent visual target stimulus that must be identified. This facilitatory effect has been attributed to the temporal expectancy automatically induced by the warning stimulus. It has not been determined whether this results from a modulation of the stimulus identification process, the response selection process or both. The present study examined these possibilities. A group of 12 young adults performed a reaction time location identification task and another group of 12 young adults performed a reaction time shape identification task. A visual target stimulus was presented 1850 to 2350 ms plus a fixed interval (50, 100, 200, 400, 800, or 1600 ms, depending on the block) after the appearance of a fixation point, on its left or right side, above or below a virtual horizontal line passing through it. In half of the trials, a weak auditory warning stimulus (S1) appeared 50, 100, 200, 400, 800, or 1600 ms (according to the block) before the target stimulus (S2). Twelve trials were run for each condition. The S1 produced a facilitatory effect for the 200, 400, 800, and 1600 ms stimulus onset asynchronies (SOA) in the case of the side stimulus-response (S-R) corresponding condition, and for the 100 and 400 ms SOA in the case of the side S-R non-corresponding condition. Since these two conditions differ mainly by their response selection requirements, it is reasonable to conclude that automatic temporal expectancy influences the response selection process.