特大桥缆索吊装系统在北盘江大桥施工中的应用     

刘章宇 《贵阳金筑大学学报》2013,(2):41-44

缆索吊装系统主要用来完成加劲梁的空间运送和就位,是整个施工过程的关键工艺之一,也是施工技术中难度较大的一个问题,因此。有必要对缆索吊装系统进行系统的分析与计算。  相似文献   

Three-dimensional joint dynamics and energy expenditure during the execution of a judo throwing technique (Morote Seoï Nage)     

Laurent Blais  Patrick Lacouture 《Journal of sports sciences》2013,31(11):1211-1220

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The impact absorption characteristics of cricket batting helmets     

Richard A. Stretch 《Journal of sports sciences》2013,31(12):959-964

To determine whether the helmets currently used by cricket batsmen offer sufficient protection against impacts of a cricket ball, the impact absorption characteristics of six helmets were measured using the drop test at an impact velocity equivalent to a cricket ball with a release speed of 160 km·h-1 (44.4 m·s -1 ). An accelerometer transducer attached to a 5.0 kg striker was dropped from a height of 3.14 m onto the batting helmets to measure the impact characteristics at the three different impact sites:right temple, forehead and back of the helmet. These data were further expressed as a percentage above (-) or below (+) the recommended safety standard of 300 g . The results indicate that the force absorption characteristics of the helmets showed inter- and intra-helmet variations, with 14 of the 18 impact sites (66.7%) assessed meeting the recommended safety standards. Helmets 1, 2 and 4 succeeded in meeting the safety standards at all impact sites; helmets 5 and 6 both failed at the back and forehead, while helmet 3 failed at all impact sites. These differences were due to the structure and composition of the inner protective layer of the helmets. The helmets that succeeded in meeting the standards were made with a moulded polystyrene insert, a heat-formed ethylene vinyl acetate (EVA) insert, or EVA with a relatively high density that allows a minimal amount of movement of the helmet at ball impact.  相似文献   

Simultaneous measurement of back and front foot ground reaction forces during the same delivery stride of the fast-medium bowler     

P.D. Hurrion  R. Dyson  T. Hale 《Journal of sports sciences》2013,31(12):993-997

Six male cricket bowlers (mean - s x ¥ : age 23.5 - 1.3 years; height 1.83 - 0.04 m; body weight 826 - 20 N) performed their typical bowling action at a set of stumps positioned at standard pitch length (20.1 m). A specially designed force platform rig allowed the correct positioning of two force platforms to be achieved beneath an outdoor polyflex runway (0.017 m depth) for each player's delivery stride pattern. For the back foot, the peak vertical ground reaction force was 1.95 - 0.08 kN (2.37 - 0.14 BW) and the braking force was 0.77 - 0.12 kN (0.94 - 0.16 BW). For the front foot, the peak vertical force was 4.80 - 0.92 kN (5.75 - 0.98 BW) and the braking force was 2.93 - 0.56 kN (3.54 - 0.67 BW). The mean peak vertical loading rate for front foot contact was 205 - 52.8 kN·s -1 (249 - 64 BW·s -1 ) with mean values ranging from 81 to 446 kN·s -1 (98 to 540 BW·s-1). The range for back foot contact was much smaller, 25-70 kN·s -1 (30-85 BW·s -1 ), with a mean of 41.7 - 7.10 kN·s -1 (50.6 - 8.6 BW·s -1 ). Mean peak impact occurred 24 ms after touchdown for the back foot and 16 ms after touchdown for the front foot. At impact, mean peak loading rates were greater for the front foot at 246 kN·s -1 (298 BW·s -1 ), with a range of 80-483 kN·s -1 (98-534 BW·s -1 ), than for the back foot at 65 kN·s -1 (79 BW·s -1 ), with a range of 40-84 kN·s -1 (49-110 BW·s -1 ).  相似文献   

Effects of external loading on power output in a squat jump on a force platform: A comparison between strength and power athletes and sedentary individuals     

Tarak Driss  Tarak Driss  Henry Vandewalle  Jacques Quièvre  Christian Miller  Hugues Monod 《Journal of sports sciences》2013,31(2):99-105

The aim of this study was to determine the effects of external loading on power output during a squat jump on a force platform in athletes specializing in strength and power events (6 elite weight-lifters and 16 volleyball players) and in 20 sedentary individuals. Instantaneous power was computed from time-force curves during vertical jumps with and without an external load (0, 5 or 10 kg worn in a special vest). The jumps were performed from a squat position, without lower limb counter-movement or an arm swing. Peak instantaneous power corresponded to the highest value of instantaneous power during jumping. Average power throughout the push phase of the jump was also calculated. A two‐way analysis of variance showed significant interactions between the load and group effects for peak instantaneous power ( P < 0.01) and average power ( P < 0.001). Peak instantaneous power decreased significantly in sedentary individuals when moderate external loads were added. The peak instantaneous power at 0 kg was greater than that at 5 and 10 kg in the sedentary individuals. In contrast, peak instantaneous power was independent of load in the strength and power athletes. Mean power at 0 kg was significantly lower than at 5 kg in the athletes; at 0 kg it was significantly higher than at 10 kg in the sedentary males and at 5 and 10 kg in the sedentary females. In all groups, the force corresponding to peak instantaneous power increased and the velocity corresponding to peak instantaneous power decreased with external loading. The present results suggest that the effects of external loading on peak instantaneous power are not significant in strength and power athletes provided that the loads do not prevent peak velocity from being higher than the velocity that is optimal for maximal power output.  相似文献   

欧拉公式在电梯曳引力计算中的应用     

刘辉  刘晓红 《孝感职业技术学院学报》2009,12(4):86-89

曳引驱动电梯是由钢丝绳和曳引轮槽之间摩擦而产生曳引力来驱动轿厢作上下运动,钢丝绳对曳引轮的摩擦关系式符合欧拉公式。本文以欧拉公式为基础,推导出曳引力计算公式,并以实际电梯参数为例,计算出电梯在四种工作状况下的曳引力。  相似文献   

性出于气 有善有恶——王廷相的气质人性论     

张立新 《安顺学院学报》2009,11(6):65-68

王廷相是明代中期气学的代表人物,他以元气为世界的本原,将理纳入气中,认为理为气之理,没有超越于气之外的理。在理气论的思想指导下,提出了性出于气,人物之性无非气质所为,离气不能言性,气质之性之外无本然之性;性出于气,有善有恶,人性可通过教化和习行而为善。  相似文献   

An improvement of single-network adaptive critic design for nonlinear systems with asymmetry constraints     

Xiangwei Bu 《Journal of The Franklin Institute》2019,356(16):9646-9664

Traditional approximate/adaptive dynamic programming (ADP) methods can handle a very special class of systems subject to symmetry constraints. In this study, I extend the exiting ADP to a broader class of nonlinear dynamic systems with asymmetry constraints. Firstly, I propose a novel nonquadratic cost function, based on which the developed optimal controller by solving Hamilton–Jacobi–Bellman equation can limit its value to arbitrarily prescribed bound. Then, to avoid “curse of dimensionality”, I approximately implement the addressed controller via single-network adaptive critic design. Fuzzy Hyperbolic Model is introduced to construct the single critic network by approximating optimal cost function, from which I further derive the optimal control law. The potential advantages are that the control structure is simple and the computational load is low. Lyapunov synthesis proves the ultimately uniformly bounded stability of closed-loop control system. Finally, numerical simulation results verify the efficiency and superiority of the proposed approach.  相似文献   

Child maltreatment re-offending in families served by the United States Air Force Family Advocacy Program     

《Child abuse & neglect》2018

The current study examined child maltreatment re-offending in United States Air Force (USAF) families. In a clinical database containing 24,999 child maltreatment incidents perpetrated by 15,042 offenders between the years 1997 and 2013, 13% of offenders maltreated a child on more than one date (i.e., they re-offended). We explored several offender demographic characteristics associated with who re-offended and found that civilians re-offended at a similar rate as active duty members, males re-offended at a similar rate as females, and younger offenders were more likely to re-offend than older offenders. We also explored incident characteristics associated with who re-offended: Re-offending was more likely if the initial maltreatment was neglect or emotional abuse and re-offenders were likely to perpetrate subsequent maltreatment that was the same type and severity as their initial incident. The current data indicate that young offenders and offenders of neglect and emotional maltreatment are the greatest risk of re-offending. These offender and incident characteristics could be used by the USAF to guide their efforts to reduce re-offending.  相似文献   

拳击前手直拳与后手直拳地面支撑反作用力特征比较研究          下载免费PDF全文

史东林 《河北体育学院学报》2015,29(3):68-71

目的:为了区别前手直拳与后手直拳下肢蹬地地面支撑反作用力的特征,进一步细化拳击下肢蹬地发力的特点.方法:运用两块KISTLER三维测力台和VICON MX红外高速摄影系统,让运动员分别以前手直拳和后手直拳全力击打固定目标,采集地面支撑反作用力参数,二者进行对比.结果:运动员后手直拳击打,双脚均主动发力,蹬地发力的时间均在100-200ms;发力50 ms时力值占最大力量峰值的百分比均低于35％,后续发力特征明显.前手直拳击打,前脚起主要作用,蹬地发力时间均在100ms之内,发力50 ms时力值占最大力量峰值的百分比均高于60％.与前手直拳相比,后手直拳下肢发力时长,具有显著性差异(P＜0.01).结论:拳击前手直拳与后手直拳下肢蹬地地面反作用力特征相比存在差异,从发力时长角度比较,前手直拳发力时间短,发力初期力量增长特征明显,表现为起动力量特征;后手直拳下肢蹬地后续发力特征明显,表现为爆发力属性特征.  相似文献