纸浆模塑制品热压整形设备的增力机构优化及模具设计

一般纸浆模塑制品热压整形设备采用气液增压系统,工作力小,成本高,维修复杂。为提高效率,减少能耗,选择力增益倍数大的五孔斜排式双曲肘三连杆合模机构,并使用MATLAB软件的多目标最优化函数fgoalattain优化结构尺寸,得到优化参数。为提高设备的适应性,采用PLC控制工艺流程,满足工艺试验要求;得到合理工艺参数,可调节快慢行程时间、保压时间、凸模抽吸时间等工艺参数;根据温度和压力反馈,控制模具温度和合模力。     

Effects of neuromuscular function and split step on reaction speed in simulated tennis response

Abstract

The purpose of this study was to examine whether split step (small hop before step) would be more beneficial than no-split condition in simulated tennis response situation. In addition, it was studied if movement time of the response is related to separately measured force production capabilities and reflex sensitivity of the players. Nine skilled male tennis players participated in this study. Subjects stood on a force plate and reacted to a light signal and moved to appointed direction as fast as possible. With split step the participants were 13.1% faster (P <0.05) than without split step from the start to the distal end of the so called close range movement continuum (2.70 m). This was mainly explained by 43.6% faster time (P <0.05) from the signal to the onset of force production. Greater vertical forces were observed with split step: 15.7% greater F(z) mean force (P <0.05), 60.0% greater F(z) peak force (P<0.01). In split step both mean (r= ? 0.813, P <0.01) and peak (r=?0.765, P <0.05) vertical forces (Fz) correlated negatively with the time from the onset of the force production to the photocell. With split step higher EMGs were observed in muscles responsible for ankle joint movement indicating that different strategies were used. Due to the split step the players were able to start the movement faster which mostly explains the advantages over the no-split step condition. Split step condition may also benefit from stretch shortening type of muscle action.     

Effects of load on ground reaction force and lower limb kinematics during concentric squats

The purpose of this study was to examine the effects of external load on vertical ground reaction force, and linear and angular kinematics, during squats. Eight males aged 22.1?±?0.8 years performed maximal concentric squats using loads ranging from 7 to 70% of one-repetition maximum on a force plate while linear barbell velocity and the angular kinematics of the hip, knee and ankle were recorded. Maximum, average and angle-specific values were recorded. The ground reaction force ranged from 1.67?±?0.20 to 3.21?±?0.29 times body weight and increased significantly as external load increased (P?<?0.05). Bar linear velocity ranged from 0.54?±?0.11 to 2.50?±?0.50?m?·?s^?1 and decreased significantly with increasing external load (P?<?0.05). Hip, knee and ankle angles at maximum ground reaction force were affected by external load (P?<?0.05). The force?–?barbell velocity curves were fitted using linear models with coefficients (r ²) ranging from 0.59 to 0.96. The results suggest that maximal force exertion during squat exercises is not achieved at the same position of the lower body as external load is increased. In contrast, joint velocity coordination does not change as load is increased. The force?–?velocity relationship was linear and independent from the set of data used for its determination.     

抗战时期的中国空军

中国空军的抗战是中国抗日下面战场的一个重要组成部分。但在抗战史研究中,中国空军的抗战是研究中的薄弱环节。本文从抗战前中国空军的发展概况、抗战中中国空军的阶段划分以及中国空军战绩和特点等方面,作了一番初步探讨,可资填补这一方面研究的空白,对当今空军建设也有一定的借鉴意义。     

中国高技能人才开发

高技能人才是劳动力结构中居于决策管理层和操作执行层之间的中间层的称谓。在经济发展过程中，这个承上启下的高技能群体广泛包含了技术型技能、知识型技能和复合型技能的人才。在社会经济活动中开始发挥越来越重要的作用，成为社会生产的主力，社会财富的依托，社会稳定的中坚。中国面临高技能人才严重短缺的形势，推动高技能人才群体发展．是当前中国人才资源开发战略的一项重要任务。     

导出反平方力场中质点运动轨迹方程的一种简易方法

本文介绍了偏心率矢量R(也称Runge-lenz矢量)以及利用矢量R导出反平方有心力场中质点运动轨迹方程的方法,并讨论了有关的问题。     

略论梁启超历史进化论及其动力因

梁启超认为历史是“进化”的，它具有进步性和曲折性，呈无极限之螺旋状而非直线上升。历史“进化”之动力因多种多样，其中最主要的是“革”和“力”。梁的历史进化论，激励着当时中国人救亡保种的斗争活动，具有重要的时代意义。     

“白虎为害”、“夷人射虎”新议

“白虎为害”不仅反映了秦对巴蜀地区的经略与管理，也深刻体现了秦对巴蜀之民的民族政策。它不仅是巴人对秦国统治的一次大起义，也有巴人复国运动的倾向。白虎被射杀导致的四个结果说明“白虎为害”事件对巴人、土家族风俗的深刻影响，它导致巴人分裂，并在某种程度上改变了巴人发展的历史进程。     

湘籍志士与辛亥武昌首义

武昌首义的成功决不是从天而降的"圣果",而是革命的主、客观条件均已成熟使然。武昌首义之成功,革命党人发挥了巨大的主观能动作用是主要原因。由于湖南与湖北在地理位置上同处大湖南北和长江中游地区,晚清末年同属湖广总督管辖范围,又同受荆楚文化的熏陶和影响,因而有着共同的文化心理习惯。两湖革命党人在反清革命斗争实践中,长期合作,并肩战斗,患难与共,生死相依,结下了深厚的革命情谊!毫无疑问,武昌首义的成功自然也记载着湘籍志士的一份劳绩。湘籍志士在首义地点的选择、首义依靠力量的找寻、促成首义之区新军向革命方向转化以及策动各省光复、巩固首义成果等四个方面功勋卓著。     

从庚子自立军起义看清政府的危机应对

自立军起义是继广州起义之后,首次依靠民间会党致力于推翻清政府统治并带有资产阶级革命色彩的运动,可谓是辛亥革命的先声。尽管这次起义历时不长,但却从多个方面暴露了清政府在应对危机时的诸多问题,大致概括为三个方面：社会控制能力的弱化、社会舆论的失控和政府自身资源的内耗。清政府最终走向覆亡,上述因素值得我们深思。