基于欧氏距离平方的机械振动故障识别研究

在机械设备运行过程中,经常发生振动过大而影响设备正常运行,因此,应用有效的方法对振动故障进行及时判别具有重要意义。本文采集实际中的某齿轮箱的振动故障与正常运行时候的振动偏移量,应用欧氏距离平方算法对不同运行状态的数据进行计算,分别统计出所得到的欧氏距离平方值的范围,观察是否振动两种情况下计算得到欧氏距离平方值的范围。经过对大量的机械振动故障情况进行计算统计,发现在机械振动的情况下,计算得到的欧氏距离平方值明显大于正常运行的值。同时,该算法简单,计算速度快,能快速、准确的识别机械设备是否发生了振动故障。     

基于最小相位差全局搜索的高压输电线路故障测距

在本文中笔者将分析并提出了一种针对目前高压线路中,与两相接地故障相关的单端故障测距算法。这种故障测距法的基本原理就是利用电力系统保护安装为止的电压、电流大小,搜集并估算在运行线路上的残压以及故障线路的故障电流情况,进一步通过故障发生点的残压和故障分量电流的相位差最小特征进行实际的定位。为了可以正确、精准地考虑与研究线路上分布电容产生的影响,也可以采用贝瑞隆模型来计算全线上的电压分布情况。最终通过相模变换方法,建立了一套基于线路模空间的输电线路计算方程,设定出故障发生点的为止后,通过其相模反变换方法有效地还原出假设故障发生点的相电压残压数值。在实践中为了真正克服与超越方程求解计算中的困难,笔者还进一步提出了运用全局一维的搜索与计算方法,对线路全体的电压数值、电流分布状况进行分析与估算,最终找出其中的相位差最小电压以及电流,那么与其相对应的距离也就是实际的线路故障距离。通过大量数据验证,经过该算法的计算后均能够非常准确地测量出故障实际距离,并且最大的测距误差均保持在0．5％以内。     

三相短路开断等效电路模型建立及仿真计算

短路故障是电力系统运行中的一种常见故障,计算系统中发生短路故障时的电流和电压参数具有重要的意义。本文以对称分量法的正序、负序、零序分量为基础,合并正序、负序分量为相序分量,然后在中性点与地之间引入零序接地阻抗得出简化的等效电路。针对中性点有效接地和非有效接地的电力系统在三相对称短路的情况下,使用等效电路计算了两种情况下的电流及电压参数,并用PSCAD软件的仿真结果验证了计算结果的正确性。     

基于协方差-自回归模型的气缸压力故障检测

在实际生产中,压缩气缸如果发生故障,将对生产及经济带来很大影响。对此,本文提出应用自回归(AR)模型对压缩气缸的压力进行数据采集、统计分析。在该过程中,首先对正常情况下的压缩机气缸压力进行数据采集并作为基准,建立二阶自回归(AR)模型,再利用协方差方法对压力值提取相关的参数,然后对取得的参数进行绝对值后做和。其次,对故障时刻的压力以正常情况为基准再进行同样计算,最终对正常情况下和故障时刻的绝对值之和进行比较。结果表明,是否发生故障的两种情况下,绝对值之和差别明显,能够很容易区分出是否发生了故障。因此,为相关工作提供了理论基础,并相应的提高了经济效益。     

基于瞬时dq变换的电压暂降检测方法

本文对现有的电压暂降检测算法进行研究,详细分析了基于瞬时dq分解法和单相坐标变换法在电压暂降幅值和相位跳变检测方法,并在Matlab中建立模型进行了仿真验证,对比分析了瞬时dq变换检测算法用于电压暂降检测的优劣。     

典型敏感设备运行状态评估软件

正在发生电压暂降事件时,及时知晓敏感设备的运行状态尤为重要。本文针对电压暂降事件对敏感设备的影响设计了典型敏感设备运行状态评估软件。本软件确定了变频器暂降耐受曲线、交流接触器暂降耐受曲线、PC机暂降耐受曲线、可编程逻辑控制器暂降耐受曲线以及典型敏感设备综合暂降耐受曲线,当发生电压暂降事件时计算出敏感设备的故障概率,对敏感设备的运行状态作出评估。本软件作为电能质量监测系统的一部分,实用性和正确性都得到了很好的验证。     

基于单片机的智能电力系统故障录波仪浅析

智能电力系统故障录波仪是一种数据采集记录装置,它可以记录系统非正常和正常状况下系统电压、电流、频率的变化。在电力系统正常运行情况下记录的数据,对于分析电力系统正常运行下电能的应用情况起着重要的作用;而故障阶段记录的数据,对于分析电力系统故障发生的原因,以及帮助寻找故障发生点,从而迅速处理相关故障事故起着关键的作用。     

基于欧氏距离的人工免疫算法的研究

针对基于信息熵的人工免疫算法速度慢的原因,提出了基于欧氏距离的人工免疫算法,通过进行数值仿真比较,证明了基于欧氏距离的人工免疫算法在全局收敛、计算速度、收敛次数等方面的优越性。     

电力系统中继电保护隐性故障分析与改进措施

电力系统的安全性是指系统在发生故障情况下,系统能保持稳定运行和正常供电的风险程度。传统的电力系统安全性主要是在发生故障情况下,研究电力系统本身的动态特性,包括系统的功角稳定性、电压稳定性、频率稳定性、系统解列、热过载等。它们的研究一般是针对单一故障,但大面积停电事故一般是连锁事件的复杂序列。本文将主要探讨电力系统中继电保护隐性故障与改进措施。     

基于分段曲线拟合的故障录波器采样精度优化方法

在电力系统中,故障录波器不可缺少的测量元件是互感器。互感器在不同的测量范围内其误差不同,直接影响着故障录波器的采集精度。为提高测量精度,消除不同测量范围内的误差影响,文章提出了针对互感器不同测量范围内的误差进行分段曲线拟合的实际校正算法。该方法首先对电压互感器0～120V电压测量范围进行32等份分段,然后对所有分段内信号进行实际测量,并与故障录波器后台读入数据进行分析比较,得出不同分段范围内的曲线拟合参数,写入采集系统中。实际使用中,算法首先判断输入电压的范围,并选取相应范围内的分段曲线拟合参数进行计算,得出符合实际值的采集结果。该方法简单实用,在故障录波器的现场运行中,采集误差控制在了0.3%以内,表明了该方法的正确性与有效性。     

To serve and promote science development via innovation

CAS should stick to the principle of rendering service to, and giving impetus for, the development of China＇s science enterprise by making S＆T innovations, said CAS President LU Yongxiang. The CAS president made the remarks in a recent talk to communicate the gist of the winter session of the Party＇s Leading-member Group at CAS, which was held from 7 to 11 January in Beijing.     

Students' Reactions to the Introduction of Videoconferencing for Classroom Instruction

This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors.     

Tracing the origin and early radiation of birds——Paleornithologist ZHOU Zhonghe

With great care, Dr. ZHOU Zhonghe takes out a package wrapped by cotton tissue from a drawer and says: "This is the gem of our collections: the fossil of a bird that lived 125 million years ago!" Then, pointing at a tiny mound, he explains: "Look, this is the claw and that is the head. It was in the egg shell and ready to hatch ... The species fell into a family of waterside inhabitants."     

Cooler temperatures inductive to locust outbreaks

Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China＇s projected climate warming could decrease the pest＇s numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007.     

Exploring Multiplexity: Social Network Structures in a Computer-Supported Distance Learning Class

A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction.     

The Role of Intermediating Institutions in the Diffusion of Electronic Data Interchange (EDI): How Industry Associations Intervened in Denmark, Finland, and Hong Kong

Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies.     

How Electronic Publishers are Protecting Against Piracy: Doubts About Technical Systems of Protection

The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means.     

Rough Justice: A Statistical Assessment of ICANN's Uniform Dispute Resolution Policy

Long-standing conflict between domain name registrants and trademark holders prompted the Internet Corporation for Assigned Names and Numbers (ICANN) to create a global, mandatory arbitration procedure known as the Uniform Dispute Resolution Policy (UDRP). The UDRP has been used in 2166 cases involving 3938 domain names as of 1 November 2000. The policy gives the initiator of a complaint, generally a trademark holder, the right to choose which ICANN-accredited dispute resolution service provider (RSP) will handle the case. During the preparation of the UDRP,some feared that complainant selection would lead to "forum shopping" that might bias the results. This article performs a statistical assessment of the forum-shopping thesis and finds support for it. There are statistically significant differences in the various RSPs' propensity to take away names from defendants; there are also major differences in the number of cases brought to each RSP. RSPs who take away names have the larger share of cases. The study examines other variables that might explain differences in market share, such as price, the plaintiff's nationality, or the time taken to decide a case. It finds that nationality and time also are correlated with market share. The study concludes that shopping for a favorable outcome is an important factor in the UDRP.     

Prevalence of soft neurological signs in Chinese people

Prof. Raymond C.K. Chen, a neuropsychologist with the CAS Institute of Psychology, has made novel progress in his studies of schizophrenia. His work has been reported by a recent issue of Behavioural Neurology.     

Stern-Gerlach effect goes chiral

Prof. SUN Changpu from the CAS Institute of Theoretical Physics and coworkers from University of Basel in Switzerland have worked out a way --at least in theory --to split a beam of molecules according to their chirality. The technique involves passing the molecules through three different laser beams and is similar to the famous Stern-Gerlach effect, whereby a beam of atoms passing through a magnetic field is split in two according to the atoms＇ spin states （Phys. Rev. Lett. 99 130403）.