In the context of the COVID-19 pandemic and under the pressure of high competitiveness for higher education in China,junior high school students’mental health is facing greater challenges.Understanding the time alloc...In the context of the COVID-19 pandemic and under the pressure of high competitiveness for higher education in China,junior high school students’mental health is facing greater challenges.Understanding the time allocation of study and sleep is necessary for developing effective prevention and treatment programs.Based on a survey of 31,057 junior high school students in 47 junior high schools in Gansu Province,China's Mainland,the study analyzed the associations of time spent on study and sleep with anxiety and depressive symptoms among junior high school students through chi-square test,ANOVA,logistic regression model and threshold regression model.It was found that 18.4%–21.1%of junior high school students had mild and above anxiety and depressive symptoms.Female junior high school students were more likely to have anxiety and depressive symptoms.In addition,time spent on study was significantly and positively associated with anxiety and depressive symptoms and time spent on sleep was significantly and negatively associated with anxiety and depressive symptoms.Late sleepers were more likely to suffer from anxiety and depressive tendencies.Reducing after-school study time appropriately and getting more sleep are beneficial in reducing anxiety and depression,but it is more important to ensure time of sleep.For the reduction of anxiety and depressive symptoms,the maximum time spent on study after school should not exceed 1.92 h,the minimum time spent on sleep at night should be more than 7 h and a 40-min lunch break should be guaranteed at noon.展开更多
Motion time study is employed by manufacturing industries to determine operation time.An accurate estimate of operation time is crucial for effective process improvement and production planning.Traditional motion time...Motion time study is employed by manufacturing industries to determine operation time.An accurate estimate of operation time is crucial for effective process improvement and production planning.Traditional motion time study is conducted by human analysts with stopwatches,which may be exposed to human errors.In this paper,an automated time study model based on computer vision is proposed.The model integrates a convolutional neural network,which analyzes a video of a manual operation to classify work elements in each video frame,with a time study model that automatically estimates the work element times.An experiment is conducted using a grayscale video and a color video of a manual assembly operation.The work element times from the model are statistically compared to the reference work element time values.The result shows no statistical difference among the time data,which clearly demonstrates the effectiveness of the proposed model.展开更多
This paper selects some representative regions to obtain their G-R relation curves according to their seismicity characteristics,by using ML≥2.0 microseismicity data(1970~1993)in North China.The annual occurrence rat...This paper selects some representative regions to obtain their G-R relation curves according to their seismicity characteristics,by using ML≥2.0 microseismicity data(1970~1993)in North China.The annual occurrence rate of events of each magnitude can be inferred from the G-R relation.At the same tune,the actual annual occurrence rate of earthquakes of higher magnitudes can be calculated from historical earthquakes(1300-1993)recorded in the same region.It seems that both results are almost the same.Therefore,the rate of events of higher magnitudes can be obtained by using microseismicity data when the proper region is selected.However,two points should be noticed:(1)The method can only give the annual occurrence rate in a seismicity system and estimate the whole situation of the system.(2)When there is a very large earthquake in and near the period in which the microseismicity data are applied,the actual occurrence rate of the system,including this larger earthquake,cannot be obtained by this method.展开更多
The high rate digital acoustic communication technique for horizontal channels has been studied in this article. It is called as "Pattern Time Delay Shift Coding (PDS) communication system." The aim of the P...The high rate digital acoustic communication technique for horizontal channels has been studied in this article. It is called as "Pattern Time Delay Shift Coding (PDS) communication system." The aim of the PDS is to improve the quality of communication in shallow water. The open water experiments shoe that at the condition of 2 kHz bandwidth, the communication rate is more than 300 bit/s and error rate is at the level of 10-4. The details of PDS technique will be shown, including: principle of PDS coding, the model of Anti-multipath illterference and open water展开更多
The fiber properties depending on the coating thickness and long-term time aging were investigated. The coating strip forces of optical fiber were strongly increased with secondary coating thickness. But it did not ch...The fiber properties depending on the coating thickness and long-term time aging were investigated. The coating strip forces of optical fiber were strongly increased with secondary coating thickness. But it did not change with time aging up to 90 days. The tensile strength and stress corrosion parameters of coated fiber were increased with time aging also but the increasing rate was quite different depending on the coating展开更多
文摘In the context of the COVID-19 pandemic and under the pressure of high competitiveness for higher education in China,junior high school students’mental health is facing greater challenges.Understanding the time allocation of study and sleep is necessary for developing effective prevention and treatment programs.Based on a survey of 31,057 junior high school students in 47 junior high schools in Gansu Province,China's Mainland,the study analyzed the associations of time spent on study and sleep with anxiety and depressive symptoms among junior high school students through chi-square test,ANOVA,logistic regression model and threshold regression model.It was found that 18.4%–21.1%of junior high school students had mild and above anxiety and depressive symptoms.Female junior high school students were more likely to have anxiety and depressive symptoms.In addition,time spent on study was significantly and positively associated with anxiety and depressive symptoms and time spent on sleep was significantly and negatively associated with anxiety and depressive symptoms.Late sleepers were more likely to suffer from anxiety and depressive tendencies.Reducing after-school study time appropriately and getting more sleep are beneficial in reducing anxiety and depression,but it is more important to ensure time of sleep.For the reduction of anxiety and depressive symptoms,the maximum time spent on study after school should not exceed 1.92 h,the minimum time spent on sleep at night should be more than 7 h and a 40-min lunch break should be guaranteed at noon.
基金This work is jointly supported by the SIIT Young Researcher Grant,under a Contract No.SIIT 2019-YRG-WP01the Excellent Research Graduate Scholarship,under a Contract No.MOU-CO-2562-8675.
文摘Motion time study is employed by manufacturing industries to determine operation time.An accurate estimate of operation time is crucial for effective process improvement and production planning.Traditional motion time study is conducted by human analysts with stopwatches,which may be exposed to human errors.In this paper,an automated time study model based on computer vision is proposed.The model integrates a convolutional neural network,which analyzes a video of a manual operation to classify work elements in each video frame,with a time study model that automatically estimates the work element times.An experiment is conducted using a grayscale video and a color video of a manual assembly operation.The work element times from the model are statistically compared to the reference work element time values.The result shows no statistical difference among the time data,which clearly demonstrates the effectiveness of the proposed model.
基金This project was sponsored by the National Natural Science Foundation of China under the contract of No. 49574207
文摘This paper selects some representative regions to obtain their G-R relation curves according to their seismicity characteristics,by using ML≥2.0 microseismicity data(1970~1993)in North China.The annual occurrence rate of events of each magnitude can be inferred from the G-R relation.At the same tune,the actual annual occurrence rate of earthquakes of higher magnitudes can be calculated from historical earthquakes(1300-1993)recorded in the same region.It seems that both results are almost the same.Therefore,the rate of events of higher magnitudes can be obtained by using microseismicity data when the proper region is selected.However,two points should be noticed:(1)The method can only give the annual occurrence rate in a seismicity system and estimate the whole situation of the system.(2)When there is a very large earthquake in and near the period in which the microseismicity data are applied,the actual occurrence rate of the system,including this larger earthquake,cannot be obtained by this method.
文摘The high rate digital acoustic communication technique for horizontal channels has been studied in this article. It is called as "Pattern Time Delay Shift Coding (PDS) communication system." The aim of the PDS is to improve the quality of communication in shallow water. The open water experiments shoe that at the condition of 2 kHz bandwidth, the communication rate is more than 300 bit/s and error rate is at the level of 10-4. The details of PDS technique will be shown, including: principle of PDS coding, the model of Anti-multipath illterference and open water
文摘The fiber properties depending on the coating thickness and long-term time aging were investigated. The coating strip forces of optical fiber were strongly increased with secondary coating thickness. But it did not change with time aging up to 90 days. The tensile strength and stress corrosion parameters of coated fiber were increased with time aging also but the increasing rate was quite different depending on the coating
