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

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.     

欧拉公式在电梯曳引力计算中的应用

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。     

性出于气 有善有恶——王廷相的气质人性论

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。     

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

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.     

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

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.     

图书馆管理者与图书馆凝聚力

What is called the force of cohesion in the library is both the library's attractive force to the staff and the staff's centripetal force to the library.Once the force of cohesion is formed,it well produce benefits of the whole.The formation of it is subjected to many different factors,among which,the most important ones are the library administrator's instruction,persuasion and cultivation.A good and qualified library administrator should be able to judge the hour and size up the situation,do his utmost to strengthen the force of cohesion in the library and try to stablilize his own contigent of staff.4 refs.     

发现题材与培育人品——中学作文教学侧议

无话可说是中学生写作文普遍碰到的困难，是作文能力的主要障碍。解决这个问题必须明确作文题材不等于客观事物这一基本事实，并充分认识到题材的实质是主客观的统一体，是写作主体本质力量的对象化，从而在教学中努力贯彻教书育人的方针，切实抓好学生的人品建设，使他们真正走出作文“下笔无言”的困境。     

广州工人与商团事变

因广州商团事变引发的工商阶级对抗,不仅是国共合作“扶助劳工”的政治动员的产物,而且在很大程度上是孙中山政府为挽救其危亡而刻意实施的权宜之策,并不意味着国民党已步入“阶级斗争”的理念正轨。随着商团的覆灭,此种阶级意识亦即呈弱化态势,这与国民党“工商协调”的劳资政策有着密切关联。     

语文课堂教学的新异向——轻分析重实践

语文新课程的实施。教师注重了学生的主体地位。但过分教给固定方法。我们的语文新课程更应“轻分析重实践”。在读、演、听、说中发挥学生的主体性和学习潜能。     

无为与养气——《文心雕龙》“养气”说与魏晋玄学

本文试图详细考察《文心雕龙》中的“养气”说与魏晋玄学的关系。本文认为 ,《文心》的“养气”说与由孟子“知言养气”而来的文气说完全不同 ,它不是从精神方面而是从生理方面立论的 ;《养气》篇的基本宗旨是创作过程应该因任自然而不要强作妄为 ;这种以无为论养气的主张 ,显然受到王弼、郭象等玄学家“无为而无不为”观念以及嵇康“养生论”的影响。