Subjects: Mechanics >> Solid Mechanics submitted time 2023-06-19 Cooperative journals: 《应用力学学报》
Abstract： The buffering technology based on magnetorheological effect is one of the current research hotspots.This paper reviews the research status of magnetorheological buffering technology for impact conditions in China in the past 20 years.Important research achievements and major problems are systematically analyzed from four aspects:structural design and optimization,mechanical models,control technology,and engineering applications.Combining with the requirements for impact-resistant equipment,materials,intelligent control,and other aspects,this paper also discusses prospects for magnetorheological materials,structural design and optimization,theoretical models,and intelligent control algorithms,aiming to provide ideas and reference for researchers in the field of magnetorheological buffering technology and its related areas.
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2018-04-17 Cooperative journals: 《计算机应用研究》
Abstract： Due to the envelope fitting problem exists in the process of empirical mode decomposition, this paper proposed an improved algorithm which could eliminate the undershoot phenomenon exactly. By introducing "pseudo-extreme points", this algorithm increased the number of extreme points and formed new extreme value sequence. Then it got new envelope by using the new extreme value sequence interpolation. The envelope fitted by this method was closer to the original signal and has better smoothness. Finally, A contrast result between cubic spline interpolation and this algorithm showed that the number of undershoots decreased by about 77.5%, which proved that this algorithm could effectively reduce the number of undershoot points. In addition, fitting the envelope could tightly wrap the original signal and have a better envelope.
Subjects: Medicine, Pharmacy >> Preventive Medicine and Hygienics submitted time 2024-04-15 Cooperative journals: 《中国全科医学》
Abstract： Background Low back pain（LBP）in middle-aged and elderly adults has become a significant public health issue worldwide. Physical activity and sleep are two core components of the 24-hour lifecycle，and maintaining adequate physical activity and good sleep are crucial for health，both of which are associated with LBP. Objective To investigate the prevalence of LBP in middle-aged and elderly adults in China，analyze the independent and combined effects of physical activity and sleep on its occurrence，and provide scientific evidence for behavioral health. Methods Based on the 2018 China Health and Retirement Longitudinal Study，participants without demographic，physical activity，sleep，and LBP data were excluded. A total of 13 496 eligible individuals aged 45 to 69 were included，and their demographic and behavioral information was collected. Binary logistic regression and multiple linear regression were used to examine the relationship between physical activity，sleep duration，and LBP，and a mediation model was constructed to analyze the mediating effect of sleep duration on the association between physical activity and LBP. Results The prevalence of LBP among the 13，496 participants was 39.0%（n=5 269）.Inadequate sleep（<7 hours）was reported by 57.1%（n=7 704）of middle-aged and elderly adults in China，with 11.6%（n=1561）engaging in mild physical activity and 88.4%（n=11 935）engaging in moderate to high-intensity physical activity. The multicollinearity diagnosis results for confounding variables（e.g.，gender，age，alcohol consumption，and smoking） showed that all variance inflation factors were less than 5，indicating no collinearity. Regression analysis revealed a positive correlation between physical activity and LBP（β=0.120，P<0.05），a negative correlation between sleep duration and LBP（β=-0.220，P<0.01），and a negative correlation between physical activity and sleep duration（β=-0.081，P<0.05）. The mediation analysis of categorical variables indicated Z=2.223>1.96，and the path from physical activity to LBP was not significant（β=0.105，P>0.05），suggesting a complete mediating effect of sleep duration on the association between physical activity and LBP. Conclusion Over one-third of middle-aged and elderly adults in China suffer from LBP. Higher levels of physical activity or shorter sleep duration are associated with increased risk of LBP. Sleep duration plays a complete mediating role in the association between physical activity and LBP，where the increased risk of LBP associated with high-intensity physical activity is completely transmitted through reduced sleep duration. Adequate sleep duration plays an important role in reducing the risk of LBP associated with high-intensity physical activity. This study suggests that older adults should adjust their exercise intensity according to their own conditions and maintain adequate sleep duration to reduce the risk of LBP.
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