连铸板坯凝固前沿气泡的受力分析     

张影  王晓东  罗志国 《辽宁科技学院学报》2019,21(1):9-12,98

铸坯中与气泡有关的缺陷对于钢的质量有很大的危害,有效去除钢中气泡成为高质量钢的主要任务。文章以吹氩的板坯结晶器为研究内容,运用理论计算对凝固前沿的气泡的受力进行量化。主要结论如下:气泡在钢液中主要受到重力、浮力、虚假质量力、升力、曳力、温度马兰戈尼力、浓度马兰戈尼力的影响。气泡被捕获的时候分为三个阶段,首先是气泡从结晶器主体钢液靠近温度边界层,在这个过程中气泡的运动主要受到曳力、浮力的作用;其次气泡进入温度边界层,在这个阶段气泡主要受到曳力、浮力、以及由温度梯度引起的马兰戈尼力;第三个阶段,气泡穿过温度边界层,到达浓度边界层,受到浓度的马兰戈尼力,其中浓度马兰戈尼力的方向总是朝着凝固前沿的方向。  相似文献   

春小麦外源DNA两次导入和导入后杂交及其后代醇溶蛋白电泳分析     

梁顺祥  许永财  迟德钊  黄居茂 《青海科技》1998,(2)

本文采用A－PAGE方法,对外源DNA导入两次的四个后代变异系、一个后代变异株系的六个单株和导入后代间杂交的四个后代变异系进行了醇溶蛋白电泳分析。结果表明：1．外源DNA两次导入进一步强化了变异;2．A－PAGE方法不仅可用于验证外源DNA导入的变异后代,而且可检测后代变异系的遗传稳定性;3．使外源DNA导入后的变异后代间再进行杂交,能够丰富变异类型。而且导入技术与杂交方法的结合,可以互相补充,对作物育种具有重要意义。  相似文献   

弯曲内力计算的多种方法     

刘永丰 《南通职业大学学报》1999,13(3):43-46

弯曲内力计算的一般方法是截面法,本文给出了另外几种计算方法。这几种方法的特点是不需要先计算支座约束反力,而是由荷载直接计算出梁的内力。  相似文献   

散打运动引入传统武术功力训练的可行性研究     

秦子来  彭云钊  王燕 《哈尔滨体育学院学报》2010,(6):98-102

运用文献资料、专家访谈和逻辑推理等研究方法,以丰富我国现代散打技术训练方法理论体系为研究视点,针对我国散打运动员在多次中外散打对抗赛中所表现出的攻击力薄弱、抗击打能力较差等问题,结合传统武术功力训练的特点和现代散打运动技术训练的实际,提出了将传统武术功力训练的方法有针对性地移植到对散打运动员的拳法、腿法、摔法及步法的训练之中,来最大限度提高散打运动员的攻击力和抗击打能力,有效提高其散打竞技水平。  相似文献   

Organizational resilience and digital resources: Evidence from responding to exogenous shock by going virtual     

《International Journal of Information Management》2023

Recent events have renewed attention to how organizations rely on digital resources in response to exogenous shock. Though the literature on organizational resilience indicates that this is best understood as a process through which organizational actors respond to a specific shock, most IS research attends to resilience as an outcome. Against that backdrop, we present a case study of how a university shifted to virtual teaching in response to a government-imposed lockdown during the COVID-19 pandemic. Adopting a digital resourcing perspective allowed us to reveal the organizational resilience process and the way digital resources shaped it. We found that the resilience process unfolded in stages as educators, assisted by students, managers, and IT personnel pivoted, adapted, and normalized into teaching virtually. Across these stages, digital resources took on specific roles as the resilience process progressed from the organization’s pre-shock accumulation of digital resources into its continued digitalization efforts. Based on these findings, we contribute to existing literature by advancing and empirically substantiating a process view of the role of digital resources in organizational resilience.  相似文献   

纸浆模塑制品热压整形设备的增力机构优化及模具设计     

李雪 《滁州学院学报》2009,11(4):53-55

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。  相似文献   

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

《European Journal of Sport Science》2013,13(4):318-326

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.  相似文献   

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

Eleftherios Kellis  Fotini Arambatzi  Christos Papadopoulos 《Journal of sports sciences》2013,31(10):1045-1055

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.  相似文献   

抗战时期的中国空军     

姜振飞  张伟 《哈尔滨学院学报》2001,22(6):124-128

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。  相似文献   

中国高技能人才开发   总被引：1，自引：0，他引：1  

陈宇 《广东白云职业技术学院广州白云工商高级技工学校学报》2004,11(3):27-31

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。  相似文献