New control charts for monitoring the Weibull percentiles under complete data and Type‐II censoring

In this paper, we propose 3 new control charts for monitoring the lower Weibull percentiles under complete data and Type‐II censoring. In transforming the Weibull distribution to the smallest extreme value distribution, Pascaul et al (2017) presented an exponentially weighted moving average (EWMA) control chart, hereafter referred to as EWMA‐SEV‐Q, based on a pivotal quantity conditioned on ancillary statistics. We extended their concept to construct a cumulative sum (CUSUM) control chart denoted by CUSUM‐SEV‐Q. We provide more insights of the statistical properties of the monitoring statistic. Additionally, in transforming a Weibull distribution to a standard normal distribution, we propose EWMA and CUSUM control charts, denoted as EWMA‐YP and CUSUM‐YP, respectively, based on a pivotal quantity for monitoring the Weibull percentiles with complete data. With complete data, the EWMA‐YP and CUSUM‐YP control charts perform better than the EWMA‐SEV‐Q and CUSUM‐SEV‐Q control charts in terms of average run length. In Type‐II censoring, the EWMA‐SEV‐Q chart is slightly better than the CUSUM‐SEV‐Q chart in terms of average run length. Two numerical examples are used to illustrate the applications of the proposed control charts.     

Prevalence of tobacco use in Eritrea: results from a noncommunicable disease risk factor survey.

The prevalence of noncommunicable diseases in Eritrea is increasing. Tobacco use is a recognized risk factor for most of these diseases, especially cardiovascular disease. No data have been published on tobacco use in Eritrea. The present study sought to establish the prevalence of tobacco smoking in Eritrea. The World Health Organization STEPwise approach was used for the survey, conducted in 2004 on a random national sample size of 2,460 subjects (response rate = 93.7%). The prevalence of tobacco smoking in the general population was 8.1%; the prevalence was 15% among men, compared with 0.6% among women. Prevalence rates were higher in those older than 45 years of age. The prevalence of tobacco smoking was higher among Muslims (11.4%) than Orthodox Christians (5.8%), and among alcohol drinkers (10.2%) than nondrinkers (6.6%). The majority of tobacco users (89.3%) used commercially available cigarettes. A study on knowledge, attitudes, and practices regarding tobacco use is needed to determine the behavioral factors leading to tobacco smoking among the vulnerable groups.     

A field deployable, multiplexed Bragg grating sensor system used in an extensive highway bridge monitoring evaluation tests

A multiplexed optical fiber Bragg grating sensor system with a measurement bandwidth of up to 200 Hz enabling dynamic loading events, e.g., road traffic, to be observed has been designed, installed, and tested over an 18-month period on a 346-m road bridge in Norway, for design verification and structural integrity monitoring purposes. A network of 32 fiber Bragg sensors was surface bonded along with a corresponding set of resistive strain gauges for comparative tests to be made. The wavelength data were calibrated against two thermally stabilized (/spl sim/0.15 pm) reference gratings, which rejected common mode noise and provided absolute wavelength scaling. These data provides independent strain and temperature information. Long-term test results showed good linearity and repeatability of <10 /spl mu//spl epsiv/ over the test period with a precision of /spl plusmn/5 /spl mu//spl epsiv/ and a resolution of /spl plusmn/1 /spl mu//spl epsiv/. The readings from the FBG sensors were comparable to those from the foil gauge sensors to within /spl plusmn/4 /spl mu//spl epsiv/.     

Ah-receptor-dependent modulation of gene expression by aged and diluted sidestream cigarette smoke

Cigarette smoke is known to induce cytochrome P4501A1 expression and activity in a variety of species. Although the elevation of this isozyme is assumed to be associated with the activation of the CYP1A1 gene through a ligand-mediated mechanism involving the Ah-receptor (AhR), this has not been determined. In this study we have examined the mechanism by which an ambient level of aged and diluted sidestream cigarette smoke (ADSS) induces cytochrome P4501A1. Effects of ADSS on C57BL/6N and DBA/ 2N mice were examined. Induction of P4501A1-associated ethoxyresorufin-O-dealkylase (EROD) activity was observed in the lungs of C57BL/6N mice, while there was no induction in DBA/ 2N mice. ADSS also induced EROD in wild-type mouse hepatoma (Hepa1c1c7) cells (hepa1), but not in variant hepa1 cells defective in the AhR nuclear translocator (ARNT) protein. ADSS exposure of recombinant hepa1 cells, stably transfected with a reporter plasmid containing the luciferase gene under control of several dioxin responsive enhancers (DREs), resulted in a time- and exposure-dependent induction of luciferase activity. ADSS-mediated induction of luciferase activity was inhibited by alpha-naphthoflavone (alpha NF), an Ah-receptor antagonist. Gel retardation analysis demonstrated that exposure to ADSS induced transformation and DNA binding of the AhR complex. In summary, our results not only indicate a role for the AhR in mediating the induction of P4501A1 by ADSS, but also demonstrate that environmentally relevant levels of ADSS must contain AhR ligands at sufficient concentrations to activate gene expression in an AhR-dependent manner.     

EWMA chart based on Bayes‐conditional pivotal quantity for Weibull percentiles under complete data and type‐II censoring

Bayes‐conditional control chart has been used for monitoring the Weibull percentiles with complete data and type‐II censoring. Firstly, the Weibull data are transformed to the smallest extreme value (SEV) distribution. Secondly, the posterior median of quantiles is used as a monitoring statistic. Finally, a pivotal quantity based on the monitoring statistic with its conditional distribution function is derived for obtaining the control limits. This control chart is denoted as Shewhart‐SEV‐ . In this study, we extend this work based on an exponential weighted moving average model named exponential weighted moving average‐SEV‐ for monitoring the Weibull percentiles. We provide the statistical properties of the monitoring statistic. The average run length and the standard deviation of run lengths, computed by the integral equation approach, are used as performance measures. The results indicate that the proposed chart performs better than the Shewhart‐SEV‐ . The breaking strength of carbon fibers is used to illustrate the application of the proposed control chart.     

One‐sided control chart based on support vector machines with differential evolution algorithm

The statistical learning classification techniques have been successfully applied to statistical process control problems. In this paper, we proposed a one‐sided control chart based on support vector machines (SVMs) and differential evolution (DE) algorithm to monitor a process with multivariate quality characteristics. The SVM classifier provides a continuous distance from the boundary, and the DE algorithm is used to obtain the optimal parameters of the SVM model by minimizing mean absolute error (MAE). The average run length of the proposed chart is computed using the Monte Carlo simulation approach. Several simulated cases are conducted using a multivariate normal distribution with 10 and 20 dimensions and three different process shift scenarios. In addition, we consider two non‐normal distribution cases. The ARL performance of the proposed chart is better than the distance‐based SVM chart. A real example is used to illustrate the application of the proposed control chart.     

A comparison study of control charts for Weibull distributed time between events

Monitoring decreases in the mean of Weibull time between events data to address process quality deteriorations is an important task in reliability analysis. Two new control charts such as Weibull exponentially weighted moving average and mixed cumulative sum‐exponentially weighted moving average by transforming the Weibull data to the exponential data are proposed and compared with 2 existing control charts such as Weibull cumulative sum and mixed exponentially weighted moving average‐cumulative sum. The performance comparison provides a way to select a specific control chart in a given situation. The average run length and the standard deviation of the run length are used as performance measures. The relative mean index is also utilized to measure the overall performance. The smaller the value of the relative mean index, the better the performance of the control chart and vice versa. Two illustrative examples are provided to show the applications of the proposed control charts.     

A quantitative risk assessment model for Staphylococcus aureus and Salmonella associated with consumption of informally marketed milk products in Tigray,Ethiopia

The aim of this work was to collect relevant input data for integration into Monte-Carlo simulation using 10,000 iterations to obtain quantitative estimates of exposure and associated risk to Staphylococcus aureus and Salmonella. Higher prevalence rates of S. aureus (54.9 vs. 28.3%) and Salmonella (12.9 vs. 11.1%) were observed for raw milk distributed via collection milk collection centers (MCC) compared to those via dairy farms (DF). Prevalence found for S. aureus in traditionally fermented milk averaged only 3.7%. Although the 90% CI estimated probabilities of exposures to S. aureus due to DF and MCC raw milk consumption at levels higher than the D-R value found were 10.6 and 23.5%, respectively, exposures to Salmonella were within the pathogen's tolerable limit. While annual likely of risk of illness by S. aureus due to DF and MCC raw milk consumptions resulted in up to 24.2 and 48.3% estimated illnesses, respectively, traditionally fermented milk consumption was found very much less risky; and resulted only 2.5% estimated illnesses per-serving-per-year. The corresponding values for Salmonella per-serving-per-year estimated illnesses via raw milk sales are, respectively, 5.72 and 11.41% compared to 1.8 and 4.02% when they come in boiled forms.     

Deuterium isotope analysis of methanol oxidation on mixed metal anode catalysts

The widely accepted mechanism for methanol oxidation on Pt based catalyst surfaces has held that the rate determining step is activation of water, and/or oxidation of surface-bound CO to CO₂. In fact on pure Pt, water activation is always rate limiting at potentials negative of 0.6 V. Anode potentials greater than 0.4 V are outside the useful potential window of direct methanol fuel cells when using Nafion 117 at 60 °C. Enhancement of the water activation kinetics on Pt has been effected by the use of oxophilic transition metal promoters including Ru, W and Sn. For decades the search for improved methanol oxidation electrocatalysts has focused on water activation. A systematic deuterium isotope study on Pt black and two active mixed metal catalysts (PtRu and PtRuOsIr) shows that for each catalyst there is a characteristic transition potential above which the primary reaction in the rate-determining step changes from water activation to CH bond activation. On the mixed metal catalysts, this crossover potential is ca. 0.35 V, which is within the direct methanol fuel cell potential window (0-0.400 V). This study confirms that on these active catalysts there is a potential above which further improvements in water activation must be concomitant with acceleration of CH bond activation. Thus the catalyst search strategy involving Pt promoter metals must also consider the kinetic importance of CH bond activation.