浅谈教学中钻头的刃磨缺陷分析与技巧     

彭红萍 《科教文汇》2013,(15):76-77

钻孔加工在机械加工领域中是一项重要的技术,也是当今机械加工中应用最广的一个技术工种。在金属切削加工中,孔加工的工作量约占据了三分之一的量。在实际加工时,钻头的刃磨质量直接关系到钻孔的质量与效率。  相似文献   

Correlation between architectural variables and torque in the erector spinae muscle during maximal isometric contraction     

Antonio Cuesta-Vargas  Manuel González-Sánchez 《Journal of sports sciences》2013,31(19):1797-1804

Abstract

This study analysed whether a significant relationship exists between the torque and muscle thickness and pennation angle of the erector spinae muscle during a maximal isometric lumbar extension with the lumbar spine in neutral position. This was a cross-sectional study in which 46 healthy adults performed three repetitions for 5 s of maximal isometric lumbar extension with rests of 90 s. During the lumbar extensions, bilateral ultrasound images of the erector spinae muscle (to measure pennation angle and muscle thickness) and torque were acquired. Reliability test analysis calculating the internal consistency (Cronbach's alpha) of the measure, correlation between pennation angle, muscle thickness and torque extensions were examined. Through a linear regression the contribution of each independent variable (muscle thickness and pennation angle) to the variation of the dependent variable (torque) was calculated. The results of the reliability test were: 0.976–0.979 (pennation angle), 0.980–0.980 (muscle thickness) and 0.994 (torque). The results show that pennation angle and muscle thickness were significantly related to each other with a range between 0.295 and 0.762. In addition, multiple regression analysis showed that the two variables considered in this study explained 68% of the variance in the torque. Pennation angle and muscle thickness have a moderate impact on the variance exerted on the torque during a maximal isometric lumbar extension with the lumbar spine in neutral position.  相似文献   

The influence of electrostimulation on mechanical and morphological characteristics of the triceps surae     

L. Martin  G. Cometti  M. Pousson  B. Morlon 《Journal of sports sciences》2013,31(4):377-381

The present study assessed the effects of training using electrostimulation of muscle (EMS) on the torque‐angular velocity and torque‐angle relationships, and the cross‐sectional area (CSA) of the triceps surae. Twelve physical education students, divided into two groups (6 control, 6 experimental), participated in the experiment. The EMS sessions were undertaken using a ‘Compex‐type’ stimulator. Flexible elastomer electrodes were used. The current used discharged pulses lasting for 200 μs at a frequency of 70 Hz. The durations of contraction and rest were 5 and 15 s, respectively. The session lasted for 10 min for each muscle. The training regimen was three sessions per week for 4 weeks. Biomechanical tests were performed with the Biodex (Biodex Corporation, Shirley, NY, USA) isokinetic ergometer. Plantar flexions of the ankle over a concentric range of voluntary contractions were performed at different angular velocities (1.05, 2.10, 3.14, 4.20, 5.23 and 6.28 rad s^‐1) and maximum voluntary isometric contractions were held for 5 s at several ankle flexion angles (–30°, –15°, 0° and 15°; 0° corresponds to foot flexion of 90° relative to the leg axis). The peak value of the torque was recorded. Morphological tests consisted of measuring the CSA of the triceps surae on the right leg, 15 cm below the tibial protuberance, by a computerized tomography technique. The torque‐velocity relationship was seen to shift significantly upwards after EMS training. The increase in the isometric torque observed after EMS training was greater in dorsiflexion than in plantarflexion. No change was noted in the CSA of the muscle. It appears that the increase in strength following EMS training is not related to an increase in the contractile matter. These observations show that EMS training for 4 weeks develops dynamic and static contractile properties of the muscle. Neural mechanisms may account for these adaptations.  相似文献   

基因视角的中国画研究     

张云翼  何敏 《衡阳师范学院学报》2012,(1):153-155

在生物学上,遗传是生物的一种属性,基因是生命的密码,是基因决定了中国画、油画的"物种"特质。"生命的密码"互相制约、相互提携共同打造了东方艺术的"中国"品牌。"中国"基因的变异与消失正是中国画的"中国"性逐步消解、中国画面临被逐步异化危险的关键所在。诸多的忧思与呼吁正是我们系统研究中国画基因问题、加固中国画本体精神的必要性之所在。  相似文献   

水准仪“i”角误差的快速检验方法     

杨旭江  张养安  邱晓波 《杨凌职业技术学院学报》2012,11(2):40-41

水准仪是通过其望远镜的视准轴和水准管的水准轴的相互平行,来获得水平视线。若二者在竖直面上的投影不平行,两投影线的交角称为“i”角误差。对水准测量而言,如果“i”角误差为零,表明水准管的水准轴水平后,望远镜的视准轴也是水平的,从而可提供水平视线,满足水准测量基本原理的要求。可见在水准测量中“i”角误差对观测结果影响很大,必须在测量工作前快速、准确地检验出“i”角误差大小,并加以校正。本文中水准仪“i”角误差的快速检验方法是在常规的检验方法的基础上,通过在距水准尺特定距离上的不同的地方安置两次水准仪,分别测出同两点间的两次高差。根据所设定的特定距离简化计算“i”角误差的公式,无须结合计算器等计算工具,可在现场直接口算出该水准仪的“i”角误差的大小及距水准仪最远水准尺上的正确读数。从而比常规检验方法更快速、方便地实现对水准仪“i”角误差的检验和校正。  相似文献   

管理学理论的视角、参照系和分析工具     

孙博  谭力文 《武汉职业技术学院学报》2012,11(1):52-56

经济基础决定上层建筑,实务中利润往往被列为管理的第一视角。管理追求1＋1〉2的效果,其间暗含着一种互动的视角。由利润的视角来透视管理,免不了要以经济为参照系。权力进入商业企业领域,则体现为公司政治和市场政治。“和谐社会的构建”暗示从和谐的视角来考量管理,更多地是选取了社会作为参照的标准。本位主义是与互动相矛盾的管理现象,应对它要求以整个或更大的系统为参照,即系统观。建立在一般均衡之上的经济学分析是管理者重要的日常工具。管理实务中要形成权力上的牵制,不可出现极化一这就要诉诸政治学分析来实现。格局的合理搭配,即“衡平”,是贯穿于管理各个环节的考量依据。为达到“互动”或“他动”的目的,把管理对象放在系统内考察,“系统动力学”就成为了此时的分析工具。  相似文献   

理工类院校英语专业人才培养模式新探究     

周雪婷  孙奉怡 《北京城市学院学报》2012,(6):16-19,24

从培养"厚基础、懂科技、晓国际、勇创新"高素质人才的目标出发,以长沙理工大学为例,在课程体系和实践能力培养等方面进行了探索,并指出理工科院校英语专业人才培养应利用其优势资源,建立"国际化创新型"英语专业人才的培养模式。  相似文献   

从“角”看数学课程内容的关联性     

郜舒竹  刘莹  王智秋 《课程.教材.教法》2012,(5):62-69

角概念的特殊性使得这一概念及其相关内容在数学课程中显示出孤立的特征。通过历史的考察,挖掘出角概念的主要作用在于描述方向的改变,由此进一步了解到凡与方向有关的内容均与角相关联。从历史和文化的视角审视角的度量和角的定义,还可以清晰地发现其中蕴涵着的人文因素以及认知难点,对更好地实现数学史融入数学课程有所裨益。  相似文献   

太阳能光伏电池板倾角优化研究     

徐婧 《江苏广播电视大学学报》2012,23(5):56-58

对于固定式太阳电池方阵,不同倾角直接影响到太阳能电池方阵接收到的太阳辐射量。为使光伏方阵效率最大化,需要对太阳能光伏电板的倾角进行设计及优化,选择太阳电池方阵的最佳倾角。在前人的简化模型基础上提出更精确的太阳能光伏电池板倾角优化算法,并在使用《天文算法》中的复杂算法得出的高精度太阳位置的基础上自建模型加入晴雨时长系数修正,通过对直接辐射时长的比较提高算法精度。实践证明,经过优化的方法为太阳能设备效率优化提高了精确度。  相似文献   

柯氏力引起的导弹弹着点偏差的近似计算     

王志刚  王庆禄  王志广 《唐山师范学院学报》2001,23(5):55-57

考虑地球自转时，定量讨论了导弹在柯氏力作用下，弹着点的偏差与纬度及发射角的关系。  相似文献