Ability to accelerate, decelerate, recover and sprint again, is a crucial ability for team sports, athletes are forced in repeatingthis actions several times during matches. The objective parameters that influence res...Ability to accelerate, decelerate, recover and sprint again, is a crucial ability for team sports, athletes are forced in repeatingthis actions several times during matches. The objective parameters that influence resistance to sprints are their duration and recovery.The aim of this study was to analyze performance of young under 18 football players on high intensity running thresholds with the useof GPS 20 Hz （K-Sport Universal, Montelabbate, Italy）. We have analyzed three football matches of Marche Amateur under 18Championship （Italy） during 2017 season, using 10 GPS, one for each players except the goalkeeper. In order to better define a moreaccurate PPM （players performance model）, the players that have been substituted were removed from analysis, using only data fromfull match to build database. Total of detection is 26, with an average of 8.6 players for match divided by role. Our result according withliterature shows that in total distance, the role that obtained higher value was external midfielder and forward traveled more distance insprint.展开更多
Purpose–This paper aims to study the influence of aerodynamics force of trains passing each other on the dynamic response of vehicle bridge coupling system based on numerical simulation and multi-body dynamics and pu...Purpose–This paper aims to study the influence of aerodynamics force of trains passing each other on the dynamic response of vehicle bridge coupling system based on numerical simulation and multi-body dynamics and put forward the speed threshold for safe running of train under different crosswind speeds.Design/methodology/approach–The computational fluid dynamics method is adopted to simulate the aerodynamic force in the whole process of train passing each other by using dynamic grid technology.The dynamic model of vehicle-bridge coupling system is established considering the effects of aerodynamic force of train passing each other under crosswind,the dynamic response of train intersection on the bridge under crosswind is computed and the running safety of the train is evaluated.Findings–The aerodynamic force of trains’intersection has little effects on the derailment factor,lateral wheel-rail force and vertical acceleration of train,but it increases the offload factor of train and significantly increases the lateral acceleration of train.The crosswind has a significant effect on increasing the derailment factor,lateral wheel-rail force and offload factor of train.The offload factor of train is the key factor to control the threshold of train speed.The impact of the aerodynamic force of trains’intersection on running safety cannot be ignored.When the extreme values of crosswind wind speed are 15 m$s1,20 m$s1 and 25 m$s1,respectively,the corresponding speed thresholds for safe running of train are 350 km$h1,275 km$h1 and 200 km$h1,respectively.Originality/value–The research can provide a more precise numerical method to study the running safety of high-speed trains under the aerodynamic effect of trains passing each other on bridge in crosswind.展开更多
A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flot...A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flotation froth images. Firstly, the proposed method adopts histogram equalization to improve the contrast of the image, and then chooses the upper threshold and lower threshold from grey value of histogram of the image equalization, and complete image segmentation using the level set method. In this paper, the model which integrates edge with region level set model is utilized, and the speed energy term is introduced to segment the target. Experimental results show that the proposed method has better segmentation results and higher segmentation efficiency on the images with under-segmentation and incorrect segmentation, and it is meaningful for ore dressing industrial.展开更多
针对在负压干扰条件下,控制器局域网(Control Area Network,CAN)总线接收器存在工作异常以及传输延时较大的问题,设计了一种超宽共模输入范围的可变速率的CAN(CAN with Flexible Data rate,CAN FD)接收器。该设计通过电平移位与共射级...针对在负压干扰条件下,控制器局域网(Control Area Network,CAN)总线接收器存在工作异常以及传输延时较大的问题,设计了一种超宽共模输入范围的可变速率的CAN(CAN with Flexible Data rate,CAN FD)接收器。该设计通过电平移位与共射级相结合的方式,以减少总线信号对输入级静态工作点影响,拓展接收器的负压输入范围;采用电阻分压的方式衰减总线信号电平,以减轻输入级差分对管的耐压负担;引入低温漂电压,以产生高精度的翻转阈值;在输出级模块增添限幅晶体管,以限制接收器输出摆幅,提升传输速度。芯片采用0.18μm 60 V双极、互补、双扩散金属氧化物半导体工艺进行电路设计。仿真结果表明,在5 V电源电压条件下,设计接收器的共模输入范围为-60~60 V,阈值电压为0.71 V,迟滞门限为120 mV,温漂为0.057 mV/℃,平均传输延时小于55 ns。与相关设计相比,设计的接收器具有较宽的共模输入范围,传输延时较小,符合CAN协议规范。展开更多
文摘Ability to accelerate, decelerate, recover and sprint again, is a crucial ability for team sports, athletes are forced in repeatingthis actions several times during matches. The objective parameters that influence resistance to sprints are their duration and recovery.The aim of this study was to analyze performance of young under 18 football players on high intensity running thresholds with the useof GPS 20 Hz （K-Sport Universal, Montelabbate, Italy）. We have analyzed three football matches of Marche Amateur under 18Championship （Italy） during 2017 season, using 10 GPS, one for each players except the goalkeeper. In order to better define a moreaccurate PPM （players performance model）, the players that have been substituted were removed from analysis, using only data fromfull match to build database. Total of detection is 26, with an average of 8.6 players for match divided by role. Our result according withliterature shows that in total distance, the role that obtained higher value was external midfielder and forward traveled more distance insprint.
基金supported by the National Natural Science Foundation of China(Project no.52078489)and the Fundamental Research Funds for the Central Universities of Central South University(Project no.2021zzts0772)to which the authors are most grateful.
文摘Purpose–This paper aims to study the influence of aerodynamics force of trains passing each other on the dynamic response of vehicle bridge coupling system based on numerical simulation and multi-body dynamics and put forward the speed threshold for safe running of train under different crosswind speeds.Design/methodology/approach–The computational fluid dynamics method is adopted to simulate the aerodynamic force in the whole process of train passing each other by using dynamic grid technology.The dynamic model of vehicle-bridge coupling system is established considering the effects of aerodynamic force of train passing each other under crosswind,the dynamic response of train intersection on the bridge under crosswind is computed and the running safety of the train is evaluated.Findings–The aerodynamic force of trains’intersection has little effects on the derailment factor,lateral wheel-rail force and vertical acceleration of train,but it increases the offload factor of train and significantly increases the lateral acceleration of train.The crosswind has a significant effect on increasing the derailment factor,lateral wheel-rail force and offload factor of train.The offload factor of train is the key factor to control the threshold of train speed.The impact of the aerodynamic force of trains’intersection on running safety cannot be ignored.When the extreme values of crosswind wind speed are 15 m$s1,20 m$s1 and 25 m$s1,respectively,the corresponding speed thresholds for safe running of train are 350 km$h1,275 km$h1 and 200 km$h1,respectively.Originality/value–The research can provide a more precise numerical method to study the running safety of high-speed trains under the aerodynamic effect of trains passing each other on bridge in crosswind.
文摘A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flotation froth images. Firstly, the proposed method adopts histogram equalization to improve the contrast of the image, and then chooses the upper threshold and lower threshold from grey value of histogram of the image equalization, and complete image segmentation using the level set method. In this paper, the model which integrates edge with region level set model is utilized, and the speed energy term is introduced to segment the target. Experimental results show that the proposed method has better segmentation results and higher segmentation efficiency on the images with under-segmentation and incorrect segmentation, and it is meaningful for ore dressing industrial.
