接地电阻的计算

本文从接地电阻的概念入手,介绍了在直流或工频条件下接地电阻的计算,得出降低接地电阻的基本方法。     

变电所接地技术探讨

接地装置的工频接地电阻是发电厂、变电所以及高压输电线路的一个重要工程指标,降低接地电阻是保护人身安全和设备安全的重要措施.如何合理地设计接地网络,使用恰当的辅助手段来降低接地电阻,是一个重要的研究课题.本文对一些常用接地措施的分析比较做了一些浅显的探讨.     

广播发射台防雷接地电阻值的检测

接地电阻是接地系统的重要技术参数,是衡量防雷装置工程质量的重要指标.本文结合国家相关技术标准,根据广播发射台站测量工作实践,分析了三种接地电阻测试仪的工作原理及适用范围,以及使用手摇电阻测试仪测量铁塔接地电阻的整个过程.     

通过计算确定地线的埋设方法

接地装置的接地电阻有严格的要求,不同埋设地线的方法会产生不同的接地电阻.通过计算表明,水平埋设LCP长效地线产生的接地电阻最小.     

接地电阻的检测方法研究

分析了传统电压降法检测接地电阻的弊端，并详细介绍了检测接地电阻的新零线法。     

山区高速公路供配电工程降低接地电阻的方法与措施

根据笔者工程实践,通过降低高速公路供配电工程接地装置的接地电阻,从接地材料、接地形式、施工管理、技术措施、运行维护等方面进行探讨、研究,找出更为适用的接地电阻措施及方法.     

配电网中性点接地方式探讨

介绍了电网中性点接地方式的沿革和配电网中性点接地方式的要求，简要分析了接地方式，提出经电阻接地是一种比较合理的方式     

电气设备接地的技术要求探讨

在电气设备接地保护系统施工中,土壤特性对接地系统有很大影响,接地电阻测量方法对接地电阻的测试结果也有影响。结合学校机房设备的接地保护安装施工技术要求和电气设备接地保护的意义进行分析,以便为学校师生的学习、生活提供良好的环境。     

配电网中性点接地方式探讨

介绍了电网中性点接地方式的沿革和配电网中性点接地方式的要求，简要分析了接地方式，提出经电阻接地是一种比较合理的方式。     

接地电阻测量仪与兆欧表的比较

接地电阻测量仪与兆欧表的原理和使用是职业高中电工班实践教学的重点和难点。接地电阻测量仪和兆欧表外形相仿 ,都有手摇发电机 ,在使用时都要转动手摇发电机的摇把 ,所以俗称“接地摇表”和“绝缘摇表”。一些学生对这两种“摇表”的概念混淆 ,操作要领未掌握 ,便想当然地将接地电阻测量仪与兆欧表 (俗称“摇表”或“绝缘摇表”)混为一类 ,使用兆欧表的操作方法来操作接地电阻测量仪 ,抓住摇把猛摇一气 ,往往容易造成接地电阻测量仪损坏。实际上这两者的内部构造、电气原理和使用方法都不相同。兆欧表是一种测量电气设备绝缘电阻的专用便…     

试析琵琶演奏中右手触弦技法的运用与音色控制

音色控制的好坏体现了演奏者的艺术能力及修养。文章从琵琶的乐器结构、发音特征出发．阐述合理运用“点”、“面”、“角”、“速”、“力”等右手触弦技法与音色控制的关系．以期对提高琵琶演奏的艺术表现女和感染力奄辑息示。     

Trajectories of child protective services contact among Alaska Native/American Indian and non-Native children

BackgroundContact with child protective services (CPS) functions as an independent marker of child vulnerability. Alaska children are an important population for understanding patterns of CPS contact given high rates of contact overall and among specific demographic groups.ObjectiveWe aimed to identify longitudinal trajectory classes of CPS contact among Alaska Native/American Indian (AN/AI) and non-Native children and examine preconception and prenatal risk factors associated with identified classes.Participants and settingWe used data from the Alaska Longitudinal Child Abuse and Neglect Linkage (ALCANLink) project, a linkage of 2009–2011 Alaska Pregnancy Risk Assessment Monitoring System (PRAMS) births with administrative data including CPS records.MethodsWe conducted growth mixture modeling to identify trajectory classes of CPS contact from birth to age five years. We used Vermunt’s three-step approach to examine associations with preconception and prenatal risk factors.ResultsAmong AN/AI children, we identified three classes: 1) no/low CPS contact (75.4%); 2) continuous CPS contact (19.6%), and 3) early, decreasing CPS contact (5.0%). Among non-Native children, we identified four classes: 1) no CPS contact (81.3%); 2) low, increasing CPS contact (9.5%); 3) early, rapid decline CPS contact (5.8%); and 4) high, decreasing CPS contact (3.3%). Maternal substance use had the largest impact on probabilities of class membership, increasing the probability of membership in classes characterized by CPS contact, among both AN/AI and non-Native children.ConclusionsResults reveal heterogeneity in longitudinal patterns CPS contact across early childhood among Alaska children and identify maternal substance use as an important target for primary prevention.     

新疆高职院校大学生与媒体接触状况调查

文章主要通过调查问卷和深度访谈的方式,调查新疆各民族大学生与媒体接触状况,具体集中在报纸、广播、电视、网络、手机等,从而展现少数民族地区大学生与媒体接触状况。     

Self-reported childhood and adolescent sexual abuse among adult homosexual bisexual men.

From May 1989 through April 1990, 1,001 adult homosexual and bisexual men attending sexually transmitted disease clinics were interviewed regarding potentially abusive sexual contacts during childhood and adolescence. Thirty-seven percent of participants reported they had been encouraged or forced to have sexual contact before age 19 with an older or more powerful partner; 94% occurred with men. Median age of the participant at first contact was 10; median age difference between partners was 11 years. Fifty-one percent involved use of force; 33% involved anal sex. Black and Hispanic men were more likely than white men to report such sexual contact. Using developmentally-based criteria to define sexual abuse, 93% of participants reporting sexual contact with an older or more powerful partner were classified as sexually abused. Our data suggest the risk of sexual abuse may be high among some male youth and increased attention should be devoted to prevention as well as early identification and treatment.     

Effects of Televised Lecture Presentation Styles on Student Learning

College level instructional television (ITV) has been criticised for rigid formats involving little creative or interactive use of the media. Limited budgets and other constraints make it difficult for most ITV operations to introduce innovative communication modes. However, literature suggests other techniques to improve instructional television, specifically the use of interspersed questions and eye contact. This study manipulated these techniques in a television lecture, examining their relevance to student learning and acceptance. In a 2X2 experiment, four sections of an undergraduate course each viewed a different videotape treatment of the same lecture and content. Results yielded four conclusions. (1) Presenter eye contact and inserted questions are perceived as useful learning aids in televised lecture presentations. (2) Student satisfaction with, and interest in, televised courses is relatively low, with various learning difficulties reported. (3) Positive perception of eye contact and inserted questions correlates with higher levels of student interest in and satisfaction with televised courses. (4) Neither eye contact nor inserted questions impact directly on short‐term learning. Further studies would identify ways to more effectively manipulate eye contact and inserted questions in instructional television presentations, exploring how these techniques can enhance student learning motivation and reduce learning difficulties. Long‐term effects of these techniques on learning also should be explored     

Perceiving the Affordance of Contact in Fourand Five-Month-Old Infants

The focus of this study was on the ability of infants to perceive whether an object is positioned at a distance that would make contact possible. As a toy was presented, sometimes within and sometimes beyond reach, the initiation of reaching and leaning forward was scored. Infants were divided into leaning and nonleaning groups. Both leaning and nonleaning 5-month-olds changed their behavior dramatically when the object was placed beyond, as opposed to within, reach. The nonleaners showed a decline in reaching when this boundary for contact was crossed. The "leaners" did not; rather, they began to lean forward. These results suggest that 5-month-olds use information for the affordance of contact. 4-month-olds provided less evidence that arm length regulates reaching. 5-month-old infants acted as if they not only had some sensitivity to the absolute distance of an object but also to the effect that leaning forward has on their ability to make contact with a distant object.     

A tree-shaped motion strategy for robustly executing robotic assembly tasks

An assembly robot needs to be capable of executing an assembly task robustly under various uncertainties.To attain this goal,we use a task sequence tree model originally proposed for manual assembly.This model regards an assembly task under uncertainties as a transformation of the contact state concept.The concept may contain several contact states with probabilities but these are transformed through a series of task elements into the contact state concept having only the goal state at the end.The transformed contact state concept can be classified according to the terminal condition of each task element.Thus,the whole assembly task can be designed as a tree-shaped contingent strategy called a task sequence tree.This paper proposes a systematic approach for reconfiguring a task sequence tree model for application to a robotic assembly task.In addition,by taking a 2D peg-in-hole insertion task to be performed by a robot equipped with a force sensor as an example,we confirm that the proposed approach can provide a robust motion strategy for the task and that the robot can actually execute the task robustly under bounded uncertainty according to the strategy.     

认知结构迁移理论在对日本留学生汉语单元音韵母教学中的应用

母语负迁移对对外汉语语音教学影响尤为明显。本文试图通过对汉日语言中元音的联系与区别的考察,利用奥苏贝尔的认知结构迁移理论,探讨如何在对日本留学生的单元音韵母教学过程中有效利用汉日语音的联系,取得更好的教学效果。     

A systematic review of fantasy driven vs. contact driven internet-initiated sexual offences: Discrete or overlapping typologies?

Within the literature individuals who use the internet to facilitate the sexual abuse of a minor are generally classified as being fantasy or contact driven. Classification is based upon the intended location for sexual climax: fantasy driven individuals aim to reach sexual climax online, whereas contact driven individuals target minors to achieve physical sex offline. This review systematically investigates whether there is an empirical basis for the distinction between these two proposed discrete types. Comparison of tactics and behaviour are considered to examine whether the contact vs. fantasy distinction is useful. A two-stage literature selection process, considered against pre-determined inclusion criteria, identified a total of twenty-two studies. As methodological heterogeneity limited the ability to conduct pooled analysis, a narrative synthesis of data employing an interpretive approach was conducted. This showed that the contact and fantasy distinction is ambiguous, given that both groups engage in online behaviours that provide them with online sexual gratification that can also lead to offline contact. Furthermore, no clear pattern of behaviour was found to define contact and fantasy individuals idiosyncratically. The European Online Grooming Project typology is thus proposed as a better representation of this behaviour; intimacy seeking, adaptable and hypersexualized groups. The distinction between these groups focuses primarily on the intensity of the relationship, acknowledging that sexual abuse can occur with or without offline contact. This review also highlights the need for larger, methodologically robust studies that examine the behaviour of online child sexual offenders.     

How Some Sense Relations Affect Language Use

Ｈｕｍａｎｂｅｉｎｇｓｋｎｏｗｔｈｅｗｏｒｄｓｏｆｔｈｅｌａｎｇｕａｇｅｔｈｅｙｓｐｅａｋａｎｄｋｎｏｗｔｈｅｉｎｆｏｒｍａｔｉｏｎａｂｏｕｔｔｈｅｗｏｒｄｓ .Ｓｐｅａｋｅｒｓｏｆａｌａｎｇｕａｇｅｒａｒｅｌｙｈａｖｅｄｉｆｆｉｃｕｌｔｙｐｉｃｋｉｎｇｏｕｔｔｈｅｗｏｒｄｓｉｎａｓｅｎｔｅｎｃｅｏｆｓｐｅｅｃｈｓｏｕｎｄｓｏｒｌｅａｖｉｎｇｓｐａｃｅｓｆｏｒｗｏｒｄｓｉｎｗｒｉｔｉｎｇ ,ｔｈｅｙｋｎｏｗｈｕｎｄｒｅｄｓｏｒｔｈｏｕ ｓａｎｄｓｏｆｗｏｒｄｓｉｎｃｌｕｄｅｄｉｎｔｈｅｌａｎｇｕａｇ…