Energy balance of locomotion with pedal-driven watercraft

In this study, we examined the mechanics and energetics of locomotion with a paddle-wheel boat and a water bike. Power output (Wtot) was measured directly on the water bike by means of an instrumented chain-ring. The simultaneous assessment of oxygen uptake (VO2) allowed the computation of the "overall" efficiency of locomotion (etao = Wtot/VO2). Mean etao was 0.27 (s = 0.02), which was unaffected by the speed, and was assumed to be the same for the two boats as both are semi-recumbent bicycles. For the paddle-wheel boat, Wtot was then obtained from etao and measures of VO2. The power to overcome (passive) drag was calculated as Wd = D x v (where D is the force measured by means of a load cell when towing the boats at given speeds). Propelling efficiency was calculated as etap = Wd/Wtot, which was lower with the paddle-wheel boat (mean 0.35, s = 0.01) than with the water bike (mean 0.57, s = 0.01). The observed differences in etap and Wd explain why at the highest speed tested (approximately 3 m s(-1), the energy required to cover a unit distance with the water bike is similar to that required to move the paddle-wheel boat at 1.3 m s-1).     

失败的发明——便利贴

几乎没有一家公司或个人不曾使用过便利贴。便利贴有多种颜色及规格,用过的人,没有不喜欢的,原因就是太方便了。     

Changes in the prevalence of child sexual abuse, its risk factors, and their associations as a function of age cohort in a Finnish population sample

Objective

We examined (1) the prevalence of childhood sexual abuse (CSA) experiences as a function of cohort and gender, (2) the prevalence of factors associated with CSA as a function of cohort and whether the association of these factors with CSA remained the same irrespective of cohort, and (3) whether any cohort differences could be explainable by cohort differences in reporting bias.

Method

We used the responses of 4,561 men (M = 29, SD = 7 years) and 8,361 female (M = 29, SD = 7 years) Finnish participants who responded to the Childhood Trauma Questionnaire-Short Form as well as questions regarding family structure.

Results

The prevalence of CSA experiences varied between 0.7-4.6% for men and 1.8-7.5% for women depending on the item. Younger cohorts reported less CSA as well as less of the risk factors (physical neglect and abuse, emotional neglect and abuse, parental substances abuse, not growing up with both biological parents) that were positively associated with the likelihood of CSA. The effects of these risk factors did not vary as a function of the cohort. Also, the declining trend was not explainable by social desirability being higher in the younger cohorts.

Conclusions

The results suggest that there is a real decline in the prevalence of CSA and it is associated with a simultaneous decline in factors associated with CSA.     

对美国社区学院课程演变的考察

美国社区学院的课程直接反映了学生们截然不同的目标。纵观其历史，社区学院已经维持着一种去反映学生抱负模式的变化和地方经济模式改变的课程使命。这正反映着社区学院独有的特点并有可能被当成是其最大的力量。     

斯巴达克队准备期的一次训练课

1984年春天莫斯科“斯巴达克”队面临着欧洲足联杯赛的又一轮比赛。摆在教练员面前的任务不轻:要使队员在不习惯的时期达到很高的竞技状态,同时又要根据苏联的训练周期理论,为运动员打好身体训练和机能训练的基础。现在已经可以肯定,这两项实质上相互排斥的目标没有完全达到。在全国甲级联赛第二阶段比赛初期,主教练贝斯科夫     

能力预测的问与答

问:你说在象橄榄球这样一类的运动中,在最后一次力量训练与比赛之间必须要有48小时的休息时间,这么说来,如何能完成赛季中每周有2—3次比赛的篮球训练计划?另外如何安排那些肌肉发达而协调性差的初中学生的训练?是否要减少或停止他们的力量训练? 答:篮球和摔跤是两个强度较大的运动项目,训练中会出现间发性的矛盾,一周内安排两次比赛不会有问题,但三次就不行了,在有三次比赛的星期中,你会     

110米跨栏跑训练的全年计划

运动训练的年度计划是根据竞赛日程和竞技状态的发展规律所确定的。根据田径竞赛日程的特点,运动员的冬季赛程是60米,整个比赛期持续5—6周,夏季比赛距离则是110米,比赛期长达3个丰月。这些特点决定跨栏运动员在训练中具     

解读中国的专利司法保护

中国几乎所有的高层官员都有工科教育背景。用英特尔公司前任首席执行官贝瑞特的话说：“他们懂行”，他们明白科技发展与生产制造、大学教育及基础设施“生态系统”之间的联系。