Calculations of plastic collapse load of pressure vessel using FEA

This paper proposes a theoretical method using finite element analysis （FEA） to calculate the plastic collapse loads of pressure vessels under internal pressure, and compares the analytical methods according to three criteria stated in the ASME Boiler Pressure Vessel Code. First, a finite element technique using the arc-length algorithm and the restart analysis is developed to conduct the plastic collapse analysis of vessels, which includes the material and geometry non-linear properties of vessels. Second, as the mechanical properties of vessels are assumed to be elastic-perfectly plastic, the limit load analysis is performed by employing the Newton-Raphson algorithm, while the limit pressure of vessels is obtained by the twice-elastic-slope method and the tangent intersection method respectively to avoid excessive deformation. Finally, the elastic stress analysis under working pressure is conducted and the stress strength of vessels is checked by sorting the stress results. The results are compared with those obtained by experiments and other existing models. This work provides a reference for the selection of the failure criteria and the calculation of the plastic collapse load.     

谈正楔运动的增压效应

变质岩中的金刚石是在地壳还是在地幔中形成的,是地学中争议很大的问题.分析认为地壳中存在楔块和楔块运动,正楔块运动应有增压效应,能使地壳底部一定区域内的压力成倍增加.正楔底部的增压效应与其厚度成正比,与其下底面积成反比.正软楔的运动则是保持下底面积不变、岩石不断增厚的过程,能导致增压效应不断加强.因此造山带（正软楔运动）地壳的底部是形成高压变质岩和金刚石等高压变质矿物的有利部位.     

人民币汇率制度选择与改革路径——基于升值压力条件下的分析

本文讨论升值压力条件下的人民币汇率制度改革及调整路径。文章分析了人民币升值压力产生的根源以及升值预期对经济的影响,讨论了应对升值预期的对策,并对改革的路径选择和相关制度安排提出了政策建议。人民币升值压力的根本原因在于中国作为国际生产分工的"世界工厂"地位和各贸易伙伴国之间不平衡的储蓄率,解决贸易摩擦需要贸易政策调整和汇率政策改革的配合;升值预期引起的资本内流引发了流动性过剩、通货膨胀和资产泡沫等诸多严重问题;短期内解决升值预期的对策在于采用货币政策配合升值幅度消除资本流入的套利机会;而改革结售汇制度为市场形成汇率的机制,是中长期缓解人民币升值压力的关键所在。     

中国耕地压力指数时空规律分析

耕地压力指数是指最小人均耕地面积与实际人均耕地面积之比。文章通过对改革开放以来我国耕地压力指数的测算，发现耕地压力指数在1981年～1996年间呈下降趋势，主要原因是由于期间最小人均耕地面积减少速度大于实际人均耕地面积的减少速度；1996年后耕地压力指数整体处于上升趋势，这主要是由于期间实际人均耕地面积急剧减少所致。通过对2004年各省份压力指数的测算，发现有21个省份的耕地压力指数大于1，其中上海的耕地压力指数达到了2.84；即便是在无明显压力的5个省份中，其压力指数也均在0.78以上，区域耕地压力非常明显。导致各省份耕地压力指数过大的主要原因有3个：一是由于耕地大量被占用，实际人均耕地面积偏小而导致的压力指数过大；二是因单产水平过低而导致最小人均耕地面积偏大，从而使压力指数偏大；三是粮食主产区由于要承担国家商品粮任务，使区域粮食自给率过高，导致最小人均耕地面积过大，从而使耕地压力指数偏大。通过控制耕地面积减少速度、提高农业科技水平可以有效缓解耕地压力状况。     

水电站调速系统用油压装置的容量选择计算

针对景洪电站接力器的大小及机组的运行要求,对整个调速系纯的用油量进行准确计算,以设计出满足要求的油压装置。     

压力报警传感器校验后的设计

压力报警传感校验台利用气压系统来实现零件的装卸,压力的校验和报警以及模拟汽车行驶时的振动。为了达到准确控制系统压力值的目的,校验部分的手动阀为自制阀;为了保护精密压力表,系统采用了改装减压阀。     

Inspiratory muscle fatigue in swimmers after a single 200 m swim

Inspiratory muscle fatigue may occur in as little as 6 min during high-intensity spontaneously breathing exercise. The aims of this study were to determine whether inspiratory muscle fatigue occurs during swimming exercise and whether inspiratory muscle strength differs between the supine and standing body positions. Seven competitive swimmers were recruited to perform a single 200 m front-crawl swim, corresponding to 90-95% of race pace. Inspiratory muscle strength was measured at residual volume using a hand-held mouth pressure meter that measured maximal inspiratory pressure in the upright and supine positions. At baseline, maximal inspiratory pressure in the supine position was significantly lower than maximal inspiratory pressure in the upright position (112±20.4 and 133±16.7 cmH₂O, respectively; P?0.01). Post-exercise maximal inspiratory pressure in the supine position (80±15.7 cmH₂O) was significantly lower than baseline maximal inspiratory pressure in the supine position (P?0.01). The results indicate that a single 200 m front-crawl swim corresponding to 90-95% of race pace was sufficient to induce inspiratory muscle fatigue in less than 2.7 min. Furthermore, although diaphragm muscle length is optimized when supine, our results indicate that the force output of the diaphragm and inspiratory accessory muscles is greater when upright than when supine.     

基于压力传感器的气体比热容比的测定

为提高气体比热容比的测量精度,提出一种新颖的检测方法及实验检测装置。该方法通过测定物体在特定容器中的振动周期来计算气体比热容比,采用压力传感器检测气体的压力和振动周期。实验表明,该方法方便、准确,空气的比热容比测量结果为1.39。     

不同等级青少年男子网球运动员循环机能指标的选择与分析

采用问卷调查法、专家访谈法调查访谈了在第六届城运会比赛网球项目成绩排名前五名省市,包括湖北、河南、天津、安徽、北京等的一线优秀网球运动员和教练员,并运用单因素方差分析与独立样本T检验对我国青少年男子网球运动员的身体机能特征中的循环机能指标进行深入而系统的分析,得出不同等级网球运动员身体机能特征中的循环机能中有显著差异指标,旨在为促进我国网球运动后备人才选材以及建立机能评价标准提供可操作性的依据。     

高瓦斯矿井底抽巷区域消突技术实践研究

为解决河南大峪沟煤业集团有限责任公司华泰煤矿工作面上隅角瓦斯浓度超限的问题,在12采区12030和12070工作面下部开展底板抽放巷、底板抽放巷穿层钻孔、并对底板抽放巷穿层钻孔进行水力冲孔卸压增透等措施。通过分析底抽巷区域消突工程可以从物理力学性质上增大二1煤层的孔隙率、透水性和润湿性。较大程度的提高了瓦斯抽采率,较好的解决了工作面和上隅角瓦斯浓度过大,为多构造突出矿井的安全高效生产提供了实践经验和理论参考。