Incremental join view maintenance on distributed log-structured storage

Modern database systems desperate for the ability to support highly scalable transactions and efficient queries simultaneously for real-time applications. One solution is to utilize query optimization techniques on the on-line transaction processing (OLTP) systems. The materialized view is considered as a panacea to decrease query latency. However, it also involves the significant cost of maintenance which trades away transaction performance. In this paper, we examine the design space and conclude several design features for the implementation of a view on a distributed log-structured merge-tree (LSMtree), which is a well-known structure for improving data write performance. As a result, we develop two incremental view maintenance (IVM) approaches on LSM-tree. One avoids join computation in view maintenance transactions. Another with two optimizations is proposed to decouple the view maintenance with the transaction process. Under the asynchronous update, we also provide consistency queries for views. Experiments on TPC-H benchmark show our methods achieve better performance than straightforward methods on different workloads.     

Temperature stability and fracture toughness of Nd-Fe-B magnets

Temperature stability and toughness of magnets are very important properties especially for application in motor. In this paper, it is found that temperature stability and toughness of magnets are improved when Fe is substituted with Co andheavy rare earth is substituted for Nd in part and suitable rich B grain-boundary phase is added. In addition, heavy rare earth substitution decreases the remanence temperature coefficient greatly, but has a little effect on Curie temperature of the magnets, which is beneficial to Nd-Fe-B magnets for the application in motor.     

表用步进电机铁芯冲压工艺及模具设计

介绍了几种进口生产线的铁芯冲压工艺和模具结构 ,对进口铁芯的冲压工艺和模具结构进行了分析,给出了适合国内中小企业使用的模具结构和制造工艺     

混凝土输送泵的选择

在水利工程混凝土施工中,施工单位经常用到混凝土输送泵。而在施工当中,往往输送泵用什么型号、功率为多大比较经济适用是每个施工单位必须考虑的事情。文中根据在哈达山水利枢纽输水工程施工中的经验,简要介绍混凝土输送泵的型号,论述了其主要参数及电动机功率的选择方法。     

基于模糊控制的无刷直流电机建模仿真新方法

为提高无刷直流电动机(BLDCM)控制系统的精度,本文根据电机的数学模型,基于Matlab仿真平台构建了BLDCM电流、转速模糊PI复合控制的双闭环控制系统的仿真模型。该模型采用了一种基于分段线性化的思想,利用Simulink中的Look-Up Table对梯形波感应电动势和电磁转矩进行快速建模的方法。仿真结果表明,该模型准确易行、控制精度高,为实际BLDCM控制系统的设计和调试提供了有效的工具。     

一种在线测算交流永磁同步电机定子电感参数的方法

本文介绍了一种采用准电流定向控制在线测算交流永磁同步电机定子电感参数的新方法,该方法利用通用的PWM调制的电压型逆变器在电机定子d轴上施加了一个正负交替的小电压,与d轴上获得的正负交替的小电流一起推算出定子电感参数。该法具有测试时间短和电机无需堵转的特点。它所涉及到的数学计算简单易于数字编程实现。MATLAB仿真结果证明了该方法的可行性和正确性。     

行波型超声电机基于神经网络的逆模型辨识

行波型超声电机的动态特性受定子压电陶瓷迟滞和接触层非线性摩擦力的影响,表现出复杂的多值映射特征.通过引入动态迟滞逆算子,将存在于超声波电机逆系统中的多值映射在新的扩张输入空间上,转换为一一映射;然后使用神经网络建立超声波电机的逆模型,对迟滞和非线性摩擦力的影响进行补偿.所建立的模型结构简单,可以在线调整适应电机参数的非线性变化.实验仿真结果验证了该方法的有效性.     

基于反推法的永磁同步电机全局自适应控制

针对永磁同步电机运行中存在的参数及负载不确定性,研究了基于反推法的非线性全局自适应控制设计方法,分析了闭环系统的稳定性能．仿真结果表明,该控制方法能有效地克服电机运行中参数变化和负载干扰引起的跟踪误差,具有较强的鲁棒性能以及良好的跟踪性能．     

无纺设备的针板停车位控制器设计

根据实际工程背景,为无纺设备设计了基于AT89C4051微处理器的针板停车位控制器。通过控制变频器的输出电压,使设备的上、下针板能够比较准确的分别停靠在上、下支点处。     

永磁同步电机的自适应反演滑模变结构控制

针对永磁同步电机提出一种基于反演的PMSM自适应滑模控制方案.设计基于反演的滑模变结构位置控制器,通过RBF神经网络实现系统参数变化和外部负载扰动等引起的不确定上界值的在线辨识,减小滑模控制器的控制量,并引入饱和函数来减弱系统的"抖动"现象.理论分析和仿真结果对比表明,基于RBF神经网络的自适应反演滑模控制对参数变化和外部负载扰动具有很好的鲁棒性,永磁同步电动机获得了很好的跟踪效果.