JDB-80型电动机综合保护器

<正> 目前我国煤矿广泛使用QC83-80型防爆开关,而此开关不能对电动机实行断线、过载、漏电闭锁保护。为此,我们设计JDB-80型电动机综合保护器,该保护器安装在QC83-80型防爆开关的主腔内,实现电动机断线、过载和漏电闭锁保护。本保护器于1984年11月通过了鉴定。     

异步电动机正常运行和起动时漏电流的回归分析

异步电动机在正常运行时的漏电流I和起动时漏电流Ist有显著的规律性。以部分异步电动机漏电流I和Ist的数据为基础,用数理统计的方法,得出了漏电流I、Ist与电机功率之间的回归方程,从而可在已知电机功率的条件下,利用文中公式,对不同功率电机的漏电流进行点预测和区间预测,为选择漏电保护设备提供参考。     

异步电动机故障保护在采煤机中的应用与研究

分析了异步电动机的常见故障特征和现有采煤机电动机保护方法;针对采煤机截割电动机恒功率保护及阶段式定时限保护未考虑电动机过载承受能力和电流动态性以及断相故障保护中故障判据不准确的问题,应用对称分量法理论,提出了连续型和离散型反时限过载保护方法及基于负序、零序电流检测的不对称故障保护方法,进一步提高了采煤机的运行可靠性。     

电机烧毁原因及一款缺相保护器设计

一、电动机烧毁的原因分析1、电动机发热电机烧毁时的主要特征是发热,因此有人认为电机烧毁的原因是由于定子绕组发热,认为只要采取测量定子温度来进行保护就可以保护电机不被烧毁。其实不然,电机的升温和降温是一个相当缓慢的变化过程,因此,只有对大、中型重要的电动机预埋温度传感器,才能实行有效的过热保护。对于小型电机则相当不经济。2、电动机过载有些使用场合电机负载几乎恒定不变,似乎没有必要安装过流保护。但有时会发生堵转使电机过载而烧毁。因此需对电机过载实施反时限特性的保护,一般由过流继电器或热继电器完成。     

基于PLC的三相鼠笼式异步机控制系统设计

本设计为plc控制的三相鼠笼式异步电动机控制系统设计。主电路采用断路器、接触器、热继电器等元件组成,采用继电器、并关及西门子S7200完成控制部分设计。实现对电机的过流及过载保护,并通过PLC编程实现电动机的正反转、星角启动、延时自启动等功能。本设计操作简单,易编程,实用性强。     

带差动保护高压电动机更换电机的方法

分析异步电动机差动保护原理,提出带差动保护的电动机更换电机的方法。     

SolidWorks仿真同步机偏心磁极压板车胎的研究

在正常运行条件下增安型电动机安全可靠、维护方便,在工业上应用较为广泛,磁极压板零件是其运行重要部件,加工精度与设计合理性关乎整个设备的使用安全.通过对同步电动机结构进行概述,分析了同步电动机磁极压板特点与加工工艺,从定位装置设计、夹紧装置设计、偏心结构设计等方面详细介绍了偏心磁极压板车胎的设计.最后引入SolidWor...     

基于TMS320F2812的电机保护器的研制

结合电动机在实际运行中存在的多种故障问题,本文从硬件设计和软件设计等方面介绍了以TMS320F2812为核心的电机保护器的研制.实践表明,该保护器较好地解决了三相异步电动机运行中的多种故障监测,从而实时、可靠地保护了电动机的正常运行.     

异步电动机微机保护装置的研制

文中分析高压异步电动机热过载保护原理和不平衡故障时负序电流热效应，并用８０９８单片机构成微机保护装置。     

电动机过载和单相运转保护

一、概述关于煤矿电动机过载和单相运转的保护问题,很多单位作了大量的工作,大大减少了电机烧毁事故。我区在这方面仍比较落后,电机因过载和单相运转损坏的现象仍较严重。针对这个情况我们试制了一种保护电路,从试验室试验的情况来看,这种保护电路既可充分发挥电机的效能,     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).