小脑在运动学习中的作用

小脑在运动学习中的作用日益引起了人们的重视。小脑是运动学习的初级部位这一假说已得到了在各种运动系统中进行的损毁实验、电刺激记录等研究的支持。目前,对眨眼反射和前庭—眼反射的运动学习的研究表明,神经元可塑性遍布干小脑皮层和小脑深部核团;小脑在运动定时学习中起着特殊作用;小脑皮层对深部核团的学习具指导作用。小脑对这两个不同的运动系统的学习所起的作用极为相似,揭示这两系统学习的小脑机理可能代表了许多运动系统小脑依赖式学习的普遍原理。     

基于空间矢量调制的永磁同步电机无速度传感器直接转矩控制

提出一种基于空间矢量调制的永磁同步电机无速度传感器直接转矩控制策略,并将能实现电机转速辨识的模型参考自适应方法应用于控制中,利用Matlab／Simulink对控制系统进行了仿真研究,同时对该永磁同步电机进行SVM—DTC方法的实验．仿真和实验结果表明,该策略具有良好的稳态和动态性能,能快速动态响应,有效减小转矩和电流的脉动,提高系统的控制性能．     

我国机动车排放与控制的现状及趋势

本文通过大量资料,说明我国城市大气污染已到了非常严重的程度,而机动车排放是这一污染的主要来源。分析了新排放法规对排放控制和机动车制造企业的影响。介绍了当今先进的机动车排放控制技术。分析了燃油质量对排放的影响及对策。     

Identification,design and kinematic analysis of an earthmoving mechanism

Earthmoving mechanisms in motor graders are critical components for earthwork, compaction and re-handling, and yet they have not received much attention by mechanical engineering research in recent times. In this paper, a comprehensive analysis, from mechanism identification and innovative design to kinematic analysis, is presented. First, the mechanism analysis and synthesis method based on multibody system dynamics is carried out through the analysis of the system topology and connectivity. We conclude that the earthmoving multibody system is a spatial hybrid mechanism, which consists of a spatial parallel mechanism and a spatial serial mechanism. Second, a number of new spatial parallel mechanisms, which are advantageous with respect to the original one under certain conditions, are generated. The kinematic characteristics of the parallel mechanism family are investigated in terms of constraint equations formulated in natural coordinates. Third and last, kinematic simulations and optimization processes are carried out to evaluate the advantages of the presented spatial parallel mechanisms. Simulation results show that these mechanisms can provide better kinematic performance.     

变时基技术在汽车实验模态分析中的应用

实验模态分析是了解汽车动态特性的重要工具。文中介绍了用基于变时基技术的冲击激励实验模态分析对某改装汽车进行的分析。利用分析结果,对该汽车动态设计水平进行了评价。     

关于电路分析中参考方向的选取问题

本文旨在介决学生在学习网络理论时碰到的关于如何选取参考方向的疑难问题。提出教师应从帮助学生理介选择参考方向的必要性、任意性和习惯性入手,以使学生明确选择参考方向的重要性。     

基坑深层搅拌桩及超前钢管的施工与质量控制

以广东移动通信枢纽大楼的基坑支护为例，介绍基坑深层搅拌桩和超前钢管的施工及质量控制。     

稀土永磁同步电动机在油田抽油机上的应用与分析

在油田抽油机工况不变的条件下,分别采用稀土永磁同步电动机和Y系列异步电动机拖动抽油机进行现场试验,实测性能数据,计算并分析稀土永磁同步电动机相对Y系列异步电动机的节电率,说明稀土永磁同步电动机具有效率和功率因数高的特点。是一种节能产品,可以解决油田“大马拉小车”的难题。     

Bell-Vol High Volume Sampler

Abstract

Maintenance of a constant flow rate has been a long-standing problem with hi-vol samplers used to collect ambient aerosol. Numerous types of commercially available flow controllers are currently in use. A passive flow controller has now been developed that operates without external power or electrical circuits, and, when coupled with an AC inductive motor and cyclone blower, effectively controls flow rate between 100 and 1500 L/min.

The flow controller described here controls mass flow rate rather than motor speed - the method used in commercially available hot wire anemometer electronic flow controllers - by continuously applying pressure to the outlet air stream. Thus, the controller is unaffected by such problems as brush wear and line voltage variations that are common to hi-vol samplers. In operation, the pressure drop across any constant flow resistance, such as an orifice, elbow, or length of tubing in conjunction with a diaphragm, functions as a servo mechanism to maintain a constant drop across this constant resistance.     

油田丛式抽油机井群集中控制系统的设计

为了解决油田抽油机采油效率和能耗较低等问题,本课题在抽油机单井变频节能控制技术的基础上,研发了丛式抽油机井群单井多模式柔性控制器,并建立丛式机井群一拖四的集中控制方案。通过选择合理的优化算法,实现了单井柔性控制与井组集中优化控制的有机结合,有针对性的提高了井群的整体能效。现场测试效果表明：该丛式抽油机柔性集中控制系统能够适应现场工况条件,实现抽油机井群系统的优化控制,并且能达到较好的控制效果与节能效果。