Combining the advantages of the stratified sampling and the importance sampling, a stratified importance sampling method （SISM） is presented to analyze the reliability sensitivity for structure with multiple failure...Combining the advantages of the stratified sampling and the importance sampling, a stratified importance sampling method （SISM） is presented to analyze the reliability sensitivity for structure with multiple failure modes. In the presented method, the variable space is divided into several disjoint subspace by n-dimensional coordinate planes at the mean point of the random vec- tor, and the importance sampling functions in the subspaces are constructed by keeping the sampling center at the mean point and augmenting the standard deviation by a factor of 2. The sample size generated from the importance sampling function in each subspace is determined by the contribution of the subspace to the reliability sensitivity, which can be estimated by iterative simulation in the sampling process. The formulae of the reliability sensitivity estimation, the variance and the coefficient of variation are derived for the presented SISM. Comparing with the Monte Carlo method, the stratified sampling method and the importance sampling method, the presented SISM has wider applicability and higher calculation efficiency, which is demonstrated by numerical examples. Finally, the reliability sensitivity analysis of flap structure is illustrated that the SISM can be applied to engineering structure.展开更多
Introduction:Nutrition knowledge(NK)is a key modifiable factor influencing the dietary behavior and nutritional status of children.Currently,nationally representative data assessing NK among Chinese junior high school...Introduction:Nutrition knowledge(NK)is a key modifiable factor influencing the dietary behavior and nutritional status of children.Currently,nationally representative data assessing NK among Chinese junior high school students are unavailable.This study aimed to assess NK levels using recent,nationally representative data from China.Methods:A multistage stratified random cluster sampling method was used to select 28,629 junior high school students from 195 survey sites across 31 provincial-level administrative divisions in China.Data were collected using a standardized questionnaire developed using rigorous scientific procedures.NK awareness rates were described as weighted prevalence rates with 95%confidence intervals(CIs).Subgroup comparisons were performed using the Rao–Scott chisquare test.Results:The overall NK awareness rate among Chinese junior high school students was 40.0%(95%CI:36.5%–43.5%).The rates for the five dimensions,dietary recommendations,nutrient content of foods,food and health,food choices,and food safety,were 20.1%,46.2%,65.3%,65.2%,and 65.2%,respectively.The analysis revealed significant variations in overall and dimension-specific awareness rates across groups.Boys,students from rural and western regions,and students from families with lower socioeconomic status had poorer NK levels than their counterparts.Among the 10 knowledge points with the lowest correct rates,seven belonged to dietary recommendations,two to food safety,and one to food and health.Conclusion:NK awareness rates among junior high school students require improvement,especially regarding dietary recommendations,which remain a key component of students’nutrition education.Boys,students from rural and western regions,and students from families with lower socioeconomic status should be the key populations for NK dissemination in the future.展开更多
基金National Natural Science Foundation of China (10572117,10802063,50875213)Aeronautical Science Foundation of China (2007ZA53012)+1 种基金New Century Program For Excellent Talents of Ministry of Education of China (NCET-05-0868)National High-tech Research and Development Program (2007AA04Z401)
文摘Combining the advantages of the stratified sampling and the importance sampling, a stratified importance sampling method （SISM） is presented to analyze the reliability sensitivity for structure with multiple failure modes. In the presented method, the variable space is divided into several disjoint subspace by n-dimensional coordinate planes at the mean point of the random vec- tor, and the importance sampling functions in the subspaces are constructed by keeping the sampling center at the mean point and augmenting the standard deviation by a factor of 2. The sample size generated from the importance sampling function in each subspace is determined by the contribution of the subspace to the reliability sensitivity, which can be estimated by iterative simulation in the sampling process. The formulae of the reliability sensitivity estimation, the variance and the coefficient of variation are derived for the presented SISM. Comparing with the Monte Carlo method, the stratified sampling method and the importance sampling method, the presented SISM has wider applicability and higher calculation efficiency, which is demonstrated by numerical examples. Finally, the reliability sensitivity analysis of flap structure is illustrated that the SISM can be applied to engineering structure.
基金Approved by the Medical Ethical Review Committee of the National Institute for Nutrition and Health,Chinese Center for Disease Control and Prevention(No.2022-037).
文摘Introduction:Nutrition knowledge(NK)is a key modifiable factor influencing the dietary behavior and nutritional status of children.Currently,nationally representative data assessing NK among Chinese junior high school students are unavailable.This study aimed to assess NK levels using recent,nationally representative data from China.Methods:A multistage stratified random cluster sampling method was used to select 28,629 junior high school students from 195 survey sites across 31 provincial-level administrative divisions in China.Data were collected using a standardized questionnaire developed using rigorous scientific procedures.NK awareness rates were described as weighted prevalence rates with 95%confidence intervals(CIs).Subgroup comparisons were performed using the Rao–Scott chisquare test.Results:The overall NK awareness rate among Chinese junior high school students was 40.0%(95%CI:36.5%–43.5%).The rates for the five dimensions,dietary recommendations,nutrient content of foods,food and health,food choices,and food safety,were 20.1%,46.2%,65.3%,65.2%,and 65.2%,respectively.The analysis revealed significant variations in overall and dimension-specific awareness rates across groups.Boys,students from rural and western regions,and students from families with lower socioeconomic status had poorer NK levels than their counterparts.Among the 10 knowledge points with the lowest correct rates,seven belonged to dietary recommendations,two to food safety,and one to food and health.Conclusion:NK awareness rates among junior high school students require improvement,especially regarding dietary recommendations,which remain a key component of students’nutrition education.Boys,students from rural and western regions,and students from families with lower socioeconomic status should be the key populations for NK dissemination in the future.
