A Novel Analytical Modeling Approach for Quality Propagation of Transient Analysis of Serial Production Systems.

Production system modeling (PSM) for quality propagation involves mapping the principles between components and systems. While most existing studies focus on the steady-state analysis, the transient quality analysis remains largely unexplored. It is of significance to fully understand quality propagation, especially during transients, to shorten product changeover time, decrease quality loss, and improve quality. In this paper, a novel analytical PSM approach is established based on the Markov model, to explore product quality propagation for transient analysis of serial multi-stage production systems. The cascade property for quality propagation among correlated sequential stages was investigated, taking into account both the status of the current stage and the quality of the outputs from upstream stages. Closed-form formulae to evaluate transient quality performances of multi-stage systems were formulated, including the dynamics of system quality, settling time, and quality loss. An iterative procedure utilizing the aggregation technique is presented to approximate transient quality performance with computational efficiency and high accuracy. Moreover, system theoretic properties of quality measures were analyzed and the quality bottleneck identification method was investigated. In the case study, the modeling error was 0.36% and the calculation could clearly track system dynamics; quality bottleneck was identified to decrease the quality loss and facilitate continuous improvement. The experimental results illustrate the applicability of the proposed PSM approach.

Online Detection of Surface Defects Based on Improved YOLOV3.

Aiming at the problems of low efficiency and poor accuracy in the product surface defect detection. In this paper, an online surface defects detection method based on YOLOV3 is proposed. Firstly, using lightweight network MobileNetV2 to replace the original backbone as the feature extractor to improve network speed. Then, we propose an extended feature pyramid network (EFPN) to extend the detection layer for multi-size object detection and design a novel feature fusing module (FFM) embedded in the extend layer to super-resolve features and capture more regional details. In addition, we add an IoU loss function to solve the mismatch between classification and bounding box regression. The proposed method is used to train and test on the hot rolled steel open dataset NEU-DET, which contains six typical defects of a steel surface, namely rolled-in scale, patches, crazing, pitted surface, inclusion and scratches. The experimental results show that our method achieves a satisfactory balance between performance and consumption and reaches 86.96% mAP with a speed of 80.96 FPS, which is more accurate and faster than many other algorithms and can realize real-time and high-precision inspection of product surface defects.

Exposure to second hand smoking among middle school students in Beijing in 2019 / 中国学校卫生

Objective@#To understand the exposure to second hand smoking (SHS) and associated factors among middle school students in Beijing, and to provide data support for tobacco control.@*Methods@#The two stage stratified cluster random sampling method were used to select 10 532 students from 370 classes in 48 junior middle schools, 34 senior high schools and 14 vocational high schools in 16 districts of Beijing. The national unified paper questionnaire was used to collect the information.@*Results@#During the past 7 days, 71.5% (95% CI =70.2%-72.7%) of students reported exposure to SHS. The proportion of exposure was highest (60.3%) in outdoor public places, followed by indoor public places (48.9%), at home (34.1%), and public transport (19.1%). About 31.6% of students reported people smoking in the campus in the past 30 days. Risk factors of SHS exposure included one or more parents was smoker( OR =2.62), friends who smoked( OR =2.13), received education on tobacco hazards in school( OR = 0.74 ), and senior high school( OR =0.68-0.73)( P <0.05).@*Conclusion@#High exposure to second hand smoking among middle school students in Beijing is common. Implementation of the regulations and the publicity of tobacco hazards and tobacco control in schools should be strengthened. Smoke free household should be advocated, and middle school students, especially junior middle school students, should be protected from the harm of SHS.