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
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
The performance of the skidder Timber jack 450 C was presented in timber skidding of non-coniferous trees in hilly and mountainous conditions. An empirical time study was conducted to evaluate the current skidding sys...The performance of the skidder Timber jack 450 C was presented in timber skidding of non-coniferous trees in hilly and mountainous conditions. An empirical time study was conducted to evaluate the current skidding system in Hyrcanian forest in northern Irma for improving production rate of skidding and finding out the production cost for planning. Based on the identified elements of skidding work phase and 130 recorded cycles, we calculated the models for effective time consumption, total productivity, and unit cost. The validity of the model was tested at 95% confidence interval. The average load volume per cycle was 2.82 m3, average one way skidding distance was 450 m, and the average slope was 18%. The average travel speed of unloaded skidder was 5.8 km.h-1, and the average speed of loaded skidder was 0.1 km.h＂~ higher than the speed of the unloaded ones. The travel speed was pre- dominantly affected by longitudinal slopes and types of strip roads. The average speed of pulling the cable was 1.16 km.h-1, and that of load winching was 0.74 km.hl. The average outputs in skidding was 10.6 m^-3.h^-1 and the unit cost was 12.1 USS per hour. The time consumption and productivity of skidding depends on distances and slope, number of logs per cycle, volume, log length, etc. However, the influence of variables is not the same.展开更多
An empirical time study was cohducted to evaluate the performance of the current felling and tree processing methods used in Northern Iran＇s Hyrcanian forest. Motor-manual felling is done mostly in winter, while tree...An empirical time study was cohducted to evaluate the performance of the current felling and tree processing methods used in Northern Iran＇s Hyrcanian forest. Motor-manual felling is done mostly in winter, while tree processing starts when the felling season ends. We identified the elements of felling and processing work phases, and 142 cycles and 110 cycles were respectively recorded for felling and processing. On the basis of data analysis （time study）, we developed statistical models of effective time consumption in the respective work phase and for its total productivity. The production rate of felling with and without delay time was 9.7 and 11.65 trees per hour （0.17 USD.m^-3 and 0.21 USD-m^-3）, and the average production cost with and without delay was 1.21 USD and 1.45 USD per tree, respectively. The average productivity of processing was 35 m^3 per effective hour and the average unit cost of processing was 0.92 USD.m^-3.展开更多
A water model and a high-speed video camera were utilized in the 300-t RH equipment to study the effect of steel flow patterns in a vacuum chamber on fast decarburization and a superior flow-pattern map was obtained d...A water model and a high-speed video camera were utilized in the 300-t RH equipment to study the effect of steel flow patterns in a vacuum chamber on fast decarburization and a superior flow-pattern map was obtained during the practical RH process. There are three flow patterns with different bubbling characteristics and steel surface states in the vacuum chamber： boiling pattern（BP）, transition pattern（TP）, and wave pattern（WP）. The effect of the liquid-steel level and the residence time of the steel in the chamber on flow patterns and decarburization reaction were investigated, respectively. The liquid-steel level significantly affected the flow-pattern transition from BP to WP, and the residence time and reaction area were crucial to evaluate the whole decarburization process rather than the circulation flow rate and mixing time. A superior flow-pattern map during the practical RH process showed that the steel flow pattern changed from BP to TP quickly, and then remained as TP until the end of decarburization.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
Based on a simulation model of a semiconductor manufacturer, operator-machine ratio （OMR） analysis is made using work study and time study. Through sensitivity analysis, it is found that labor utilization decreases ...Based on a simulation model of a semiconductor manufacturer, operator-machine ratio （OMR） analysis is made using work study and time study. Through sensitivity analysis, it is found that labor utilization decreases with the increase of lot size. Meanwhile, it is able to identify that the OMR for this company should be improved from 1 ： 3 to 1 ： 5. An application result shows that the proposed model can effectively improve the OMR by 33%.展开更多
Acoustic wave time reversal self-focusing in underwater waveguide is studied. The acoustic wave time reversal is theoretically and experimentally investigated in a half-infinite fluid medium and a shallow fluid layer ...Acoustic wave time reversal self-focusing in underwater waveguide is studied. The acoustic wave time reversal is theoretically and experimentally investigated in a half-infinite fluid medium and a shallow fluid layer placed on a hard half-infinite solid medium, respectively. The ray approach method is adopted to study the far field of the acoustic field in theory, and the ultrasonic experiments have been carried out in laboratory to model the underwater waveguide. It is shown by theoretical and experimental results that the focusing gain can be improved by 12 dB or more.展开更多
The normal mode method is adopted to decompose the differences between simulations with SST(sea surface temperature)anomahes over centra-eastern Pacific and normal SST by use of a nine-layer global spec- tral model in...The normal mode method is adopted to decompose the differences between simulations with SST(sea surface temperature)anomahes over centra-eastern Pacific and normal SST by use of a nine-layer global spec- tral model in order to investigate short-range climatic oscillation with various time scales forced by El Nino during the northern summer.Investigation shows that El Nino may have the following influence on atmosphere on various space-time scales.Extra-long wave components of Rossby mode forced by convective anomaly over equatorial western Pacific resulting from El Nino produce climatic oscillation on monthly(sea- sonal)time scale in middle-high latitudes of Southern and Northern Hemispheres;extra-long wave components of Kelvin mode forced by SST anomalies propagate along the equator,resulting in 30—60 day oscillation of tropical and subtropical atmosphere;and its long waves move eastward with westerly,resulting in quasi-biweek oscillation.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 PDS...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 experimenis展开更多
According to the sample survey on 6050 students in Shanghai,there is a low correlation between schoolwork burden and academic achievements.Moreover,schoolwork burden seems to even have some negative effects on test pe...According to the sample survey on 6050 students in Shanghai,there is a low correlation between schoolwork burden and academic achievements.Moreover,schoolwork burden seems to even have some negative effects on test performances.Therefore,it is suggested further studies be conducted regarding ways for students to make the best use of their study time in the hope that examination-oriented teaching could be changed toward the educational system with multi-standards and multi-developments so that heavy burden of schoolwork could thus be alleviated.展开更多
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.
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.
文摘The performance of the skidder Timber jack 450 C was presented in timber skidding of non-coniferous trees in hilly and mountainous conditions. An empirical time study was conducted to evaluate the current skidding system in Hyrcanian forest in northern Irma for improving production rate of skidding and finding out the production cost for planning. Based on the identified elements of skidding work phase and 130 recorded cycles, we calculated the models for effective time consumption, total productivity, and unit cost. The validity of the model was tested at 95% confidence interval. The average load volume per cycle was 2.82 m3, average one way skidding distance was 450 m, and the average slope was 18%. The average travel speed of unloaded skidder was 5.8 km.h-1, and the average speed of loaded skidder was 0.1 km.h＂~ higher than the speed of the unloaded ones. The travel speed was pre- dominantly affected by longitudinal slopes and types of strip roads. The average speed of pulling the cable was 1.16 km.h-1, and that of load winching was 0.74 km.hl. The average outputs in skidding was 10.6 m^-3.h^-1 and the unit cost was 12.1 USS per hour. The time consumption and productivity of skidding depends on distances and slope, number of logs per cycle, volume, log length, etc. However, the influence of variables is not the same.
基金financially supported by Iranian Ministry of Science, Research and Technologies and University of Joensuu
文摘An empirical time study was cohducted to evaluate the performance of the current felling and tree processing methods used in Northern Iran＇s Hyrcanian forest. Motor-manual felling is done mostly in winter, while tree processing starts when the felling season ends. We identified the elements of felling and processing work phases, and 142 cycles and 110 cycles were respectively recorded for felling and processing. On the basis of data analysis （time study）, we developed statistical models of effective time consumption in the respective work phase and for its total productivity. The production rate of felling with and without delay time was 9.7 and 11.65 trees per hour （0.17 USD.m^-3 and 0.21 USD-m^-3）, and the average production cost with and without delay was 1.21 USD and 1.45 USD per tree, respectively. The average productivity of processing was 35 m^3 per effective hour and the average unit cost of processing was 0.92 USD.m^-3.
基金financially supported by the National Natural Science Foundation of China (No.51704203)the PhD Early Development Program of Taiyuan University of Science and Technology (Nos. 20152008, 20152013, and 20152018)+2 种基金Shanxi Province Science Foundation for Youths (No. 201601D202027)Key Project of Research and Development Plan of Shanxi Province (Nos. 201603D111004 and 201603D121010)NSFC-Shanxi Coal Based Low Carbon Joint Fund (No. U1510131)
文摘A water model and a high-speed video camera were utilized in the 300-t RH equipment to study the effect of steel flow patterns in a vacuum chamber on fast decarburization and a superior flow-pattern map was obtained during the practical RH process. There are three flow patterns with different bubbling characteristics and steel surface states in the vacuum chamber： boiling pattern（BP）, transition pattern（TP）, and wave pattern（WP）. The effect of the liquid-steel level and the residence time of the steel in the chamber on flow patterns and decarburization reaction were investigated, respectively. The liquid-steel level significantly affected the flow-pattern transition from BP to WP, and the residence time and reaction area were crucial to evaluate the whole decarburization process rather than the circulation flow rate and mixing time. A superior flow-pattern map during the practical RH process showed that the steel flow pattern changed from BP to TP quickly, and then remained as TP until the end of decarburization.
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Based on a simulation model of a semiconductor manufacturer, operator-machine ratio （OMR） analysis is made using work study and time study. Through sensitivity analysis, it is found that labor utilization decreases with the increase of lot size. Meanwhile, it is able to identify that the OMR for this company should be improved from 1 ： 3 to 1 ： 5. An application result shows that the proposed model can effectively improve the OMR by 33%.
基金This work was supported by the National Natural Science Foundation of China (19634050, 10134020).
文摘Acoustic wave time reversal self-focusing in underwater waveguide is studied. The acoustic wave time reversal is theoretically and experimentally investigated in a half-infinite fluid medium and a shallow fluid layer placed on a hard half-infinite solid medium, respectively. The ray approach method is adopted to study the far field of the acoustic field in theory, and the ultrasonic experiments have been carried out in laboratory to model the underwater waveguide. It is shown by theoretical and experimental results that the focusing gain can be improved by 12 dB or more.
文摘The normal mode method is adopted to decompose the differences between simulations with SST(sea surface temperature)anomahes over centra-eastern Pacific and normal SST by use of a nine-layer global spec- tral model in order to investigate short-range climatic oscillation with various time scales forced by El Nino during the northern summer.Investigation shows that El Nino may have the following influence on atmosphere on various space-time scales.Extra-long wave components of Rossby mode forced by convective anomaly over equatorial western Pacific resulting from El Nino produce climatic oscillation on monthly(sea- sonal)time scale in middle-high latitudes of Southern and Northern Hemispheres;extra-long wave components of Kelvin mode forced by SST anomalies propagate along the equator,resulting in 30—60 day oscillation of tropical and subtropical atmosphere;and its long waves move eastward with westerly,resulting in quasi-biweek oscillation.
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 experimenis
文摘According to the sample survey on 6050 students in Shanghai,there is a low correlation between schoolwork burden and academic achievements.Moreover,schoolwork burden seems to even have some negative effects on test performances.Therefore,it is suggested further studies be conducted regarding ways for students to make the best use of their study time in the hope that examination-oriented teaching could be changed toward the educational system with multi-standards and multi-developments so that heavy burden of schoolwork could thus be alleviated.
