匀强电场中的一个有用结论及其应用

一、结论证明题目:如图所示,水平方向的匀强电场,场强为E,AB∥CD,AB=CD,AB连线与场强方向成θ,试证明UAB=UCD.证明:UAB=E×AB sinθ,UCD=E×CDsinθ,AB=CD.∴UAB=UCD.即在匀强电场中,两长度相等且互相平行的线段的端点间的电势差相等(注意:电势差的下标要同向.)二、结论应用【例1】如图所示,A、B、C、D是匀强电场中一个正方形的四个顶点.已知A、B、C三点电势分别为φA=15V,φB=3V,φC=-3V.由此可得D点电势是多少?解法一∵AB∥DC,AB=CD.∴UAB=UDC即φA-φB=φD-φC.∴φD=9V.灯泡D与滑动解法二∵AD∥BC,AD=…     

浅析摩擦角及其有关现象

物体（质点）沿倾角为θ的斜面下滑，若物体与斜面问的动摩擦因数为μ，当斜面倾角θ满足tanθ=μ时，物体能沿斜面匀速下滑．分析此时物体的受力情况并根据力的平衡条件可得出：N和f的合力F必和mg等大反向，如图1所示．由几何关系得出：φ=θ所以，tanθ=tanφ=f／N=μ，或θ=φ=tan^-1μ．     

一个三角公式的推导及其应用

一、定理:已知二面角的平面角为φ,在二面角的棱上任取一点A分别在两个半平面内作射线,两射线所成的角为θ,两射线与棱为公共边所成的角分别为θ_1和θ_2,则有: cosθ=cosθ_1 cosθ_2+sinθ_1 sinθ_2 coφ 当印φ=90°时,公式为cosθ=cosθ_1 cosθ_2 证明:(设φ,θ_1,θ_2均为锐角) 如图,∠BAC=θ,∠BAQ=θ_1,∠CAQ=θ_2,在PQ上任取一点D,在平面α和β内分别作BD⊥PQ交AB于B,作DC⊥PQ,交AC于C,连BC,则∠BDC=φ,并设AD=a,     

素环上的（θ，φ）-Jordan导子

素环上的(θ，φ)-Jordan导子在特殊的条件下是(θ，φ)一导子．本证明了特征不等于2的素环上的(θ，φ)-Jordan导子就是(θ，φ)-导子。     

三面角公式及应用

在人教版《数学》第二册（下）直线与平面所成的角一节中有一个公式：cosθ=cosθ1cosθ2．如图1，AO是平面α的斜线，A是斜足，OB垂直于α，B为垂足，则直线AB是斜线在平面α内的射影．     

线面角与二面角的关系及应用

如图1,P为平面α外一点,PO⊥α,O为垂足,直线l<α,点P与直线l确定平面为β,点B∈l,设PB与平面α所成的角∠PBO=θ1,与l所成的角∠PBA=θ,二面角α-l-β的平面角∠PAO=φ.下面我们来研究θ1、θ、φ之间的关系.在Rt△POB中,sinθ1=PPBO.在Rt△POA中,sinφ=PPAO.在Rt△PBA中,sinθ=PPBA.因为PPBO=PPAO·PPBA,所以sinθ1=sinφ·sinθ在上述公式中,因为0相似文献   

三角辅助公式的解读

三角辅助公式αsinx＋bcosx=√α^2＋b^2sin（x＋φ）（其中角φ所在象限由α,b符号确定,角φ的值由tanφ=b/a确定）能将一些函数化成y=Asin（ωx＋φ）＋k（其中A,ω,φ为常数,A〉0,x∈R）的形式．在近几年的高考中,三角函数的图象和性质的考查,常常围绕y=Asin（ωx＋φ）的问题展开．下面谈谈辅助公式在解题中的应用．     

一个三角公式的推导和它的应用

一、定理:已知二面角的平面角为φ,在二面角的棱上任取一点分别在两个半平面内作射线,两射线所成的角为θ,两射线与棱所成的锐角分别为θ_1和θ_2且θ_1,θ_2具有公共边,则有: cosθ=cosθ_1cosθ_2 sinθ_1sinθ_2cosφ。当φ=90°时,公式为cosθ=cosθ_1cosθ_2。证明: 如图,∠BAC=θ,∠BAO=θ_1,∠CAQ=θ_2,在PQ上任取一点D,在平面α和β内分别作BD⊥PQ交AB于B,作DC⊥PQ,交AC于C,连BC,则∠BDC=φ,并设AD=α,     

电场中有关电势重要结论的推导及其应用

在高考物理试题中,电学内容和力学内容大约各占50分,电场知识在电学中的地位也非常重要,下面我们围绕电场中有关电势问题进行深入探讨,并总结了四个重要结论,愿与同仁交流.重要结论1如图1所示,在匀强电场中,A、B和C在同一条直线上,C为AB的中点（即AC=CB）,那么C点的电势φ_c等于A点的电势φ_A与B点的电势φ_B之和的一半.即φ_c=φ_A+φ_B/2证明如图1所示,设AB与电场强度之间的方向的夹角为θ,把一个带电量为q的正电荷沿着AB方向从A移到B.设AC=CB=L.则从A移到C,电场力做功为W_AC=qELcosθ=qU_AC=q(φ_A-φ_C)①从C移到B,电场力做功为     

向量与角

1．推导直线的夹角公式设直线l1:A1x B1y C1=0与l2:A2x B2y C2=0,两直线的夹角为α,两直线方向向量的夹角为θ,则α=θ或α=π-θ．因为两直线的方向向量分别为     

价格估计中经验对锚定效应的影响

研究采用语义启动和数值启动的范式进行考察,旨在了解在价格估计中存在的锚定效应,以及个体的消费经验对锚定效应的影响.随机选取54名被试进行2（启动方式：语义启动、数值启动）×2（锚定值：高锚、低锚）×2（熟悉度：熟悉、不熟悉）的混合实验.结果发现：在两种启动条件下,熟悉度对锚定效应均有显著影响;在高锚条件下,语意启动与数值启动之间存在差异,在低锚条件下,语意启动与数值启动之间差异不显著.结论：经验会对价格估计中的锚定效应产生影响.     

A Comparison of Aggregation Rules for Selecting Anchor Items in Multigroup DIF Analysis

This study addresses the topic of how anchoring methods for differential item functioning (DIF) analysis can be used in multigroup scenarios. The direct approach would be to combine anchoring methods developed for two-group scenarios with multigroup DIF-detection methods. Alternatively, multiple tests could be carried out. The results of these tests need to be aggregated to determine the anchor for the final DIF analysis. In this study, the direct approach and three aggregation rules are investigated. All approaches are combined with a variety of anchoring methods, such as the “all-other purified” and “mean p-value threshold” methods, in two simulation studies based on the Rasch model. Our results indicate that the direct approach generally does not lead to more accurate or even to inferior results than the aggregation rules. The min rule overall shows the best trade-off between low false alarm rate and medium to high hit rate. However, it might be too sensitive when the number of groups is large. In this case, the all rule may be a good compromise. We also take a closer look at the anchor selection method “next candidate,” which performed rather poorly, and suggest possible improvements.     

结构胶植筋锚固可靠度分析及设计建议

混凝土结构的粘结锚固问题,不仅在工程实践上很重要（如钢筋的锚固,搭接和细部构造）,而且在理论上也具有重要意义．在承载能力和使用极限状态下,钢筋强度能否得到利用取决于粘结的有效程度,近年来有关地震灾害的调查表明,强震下很多混凝土结构毁于粘结锚固破坏．本文由可靠度分析求得了具有一定可靠度的建筑结构胶植筋锚固长度,并在此基础上提出了与‘混凝土结构设计规范,相一致的、采用计算确定结构胶植筋锚固长度的设计方法,可供工程设计参考．     

钢梁与钢筋混凝土桥墩的新型刚节点联结形式及其静载反复试验

提出了一种新型的桥梁钢梁与钢筋混凝土桥墩的刚节点联结形式．刚节点内部构件间的连接全部采用高强度螺栓连接方式且施工方便，能够较理想地将上部结构弯矩传递到下部结构，剪力传递钢板承受了大部分的水平剪力．通过静荷载反复试验获得了有关这种新型结构性能方面的有效数据，试验结果表明该结构内部应力传递路径明确，并具有良好的抗震性能．有关结构的强度和塑性变形的计算及试验结果均表明，这种结构即使在发生很大变形的情况下，也能保持良好的能量吸收功能且没有出现因应力集中而发生的局部曲屈现象．由于避免使用了价格昂贵的支座，采用这种新型组合结构形式不但具有良好的抗震性能，同时可以降低桥梁的建设成本．     

Not all preconceptions are misconceptions: finding ‘anchoring conceptions’ for grounding instruction on students’ intuitions

This study begins the task of mapping out the domain of valid, potentially helpful beliefs of students and raises the possibility of drawing on these intuitions in teaching conceptual material. Some issues are explored surrounding the identification of such intuitions, referred to as anchoring conceptions or anchors. We attempt to: (1) propose some organizing theoretical and observational definitions of the anchor construct; (2) present some initial findings from a diagnostic test designed to uncover anchors for physics instruction; and (3) provoke an initial discussion of the new methodological issues that arise in this domain.

The results of the diagnostic test indicate that a number of group anchors exist. In addition, some unexpected non‐anchors were identified. Furthermore, evidence was found indicating that some anchoring examples may be ‘brittle’, i.e., evidence that the anchor could not be extended analogically to help a student make sense of a target situation.

Finally, it is suggested that further research is needed to construct a theory of anchoring conceptions that would, for example, specify what characteristics would indicate that an anchoring conception can provide the basis for conceptual change via analogical extension.     

网球运动专项核心力量训练的“花盆模型”

力量训练是其他基本素质训练的基础,而核心力量训练则是专项训练的关键。本研究以运动训练理论为基础,结合网球专项力量训练,初步构建了网球运动专项核心力量训练方法的模型。网球运动专项技能的动作方法、能量代谢特征是其核心力量训练的根本出发点,它是核心力量训练模型的＂花盆和土壤＂,它决定了网球技能动作的运动生物力链和专项力量类型,结合力量训练的原则,进一步决定了核心力量训练的部位、顺序和方式（＂LOM＂）,以及力量训练的最大负荷百分比、每两组练习间的间隔、组内练习重复次数、完成组内重复训练的时间、组数和练习频度（＂PIRTSF＂）,在这些因素的基础上,再选择合适的、具有专项特异性的力量训练方法。     

两种新型的渐开线少齿差传动机构

本文提出了两种新型的渐开线少齿差行星齿轮传动机构,分别称为Ⅰ型机构和Ⅱ型机构。其中,Ⅰ型机构是一种无输出机构的少齿差传动机构,加工方便,成本低廉,只需三个齿轮即可传动。Ⅱ型机构是一种经过变型而派生出来的少齿差传动机构,同样可以采用销轴式或浮动盘式输出机构,具有效率高,承载能力大等特点,可用于中等或中等以上功率的场合。笔者对这种新型机构的传动原理,优越性以及齿形干涉和限制条件进行了详细的论证,并探讨了传动效率、强度计算和参数选择等问题。理论和实践均业已证明这种新型机构是值得推广的。     

When Does Scale Anchoring Work? A Case Study

Providing information to test takers and test score users about the abilities of test takers at different score levels has been a persistent problem in educational and psychological measurement. Scale anchoring, a technique which describes what students at different points on a score scale know and can do, is a tool to provide such information. Scale anchoring for a test involves a substantial amount of work, both by the statistical analysts and test developers involved with the test. In addition, scale anchoring involves considerable use of subjective judgment, so its conclusions may be questionable. We describe statistical procedures that can be used to determine if scale anchoring is likely to be successful for a test. If these procedures indicate that scale anchoring is unlikely to be successful, then there is little reason to perform a detailed scale anchoring study. The procedures are applied to several data sets from a teachers’ licensing test.     

对宝黛钗爱情悲剧背后两种势力的分析

贾宝玉、林黛玉及薛宝钗三人的爱情婚姻悲剧是《红楼梦》一书中最重要的悲剧。本文从文本的角度分析了在爱情婚姻悲剧背后“拥林派”和“拥薛派”双方实力背景,同时指出在双方势均力敌的情况下,宝玉的贴身丫鬟花袭人,有可能成为这出爱情悲剧天平的最后一块砝码。     

Let me Count the Ways. Analysing the Relationship between the Learner and Everyday Technology in Early Childhood

The first part of this paper outlines four ways in which the relationship between the learner and everyday technology might be analysed, using early childhood studies as examples. The four different individual-technology relationships are described as: affording, anchoring, distributing or appropriating. They are associated with four different learning outcomes: skills and problem-solving strategies, working theories or schemas, personal style and abilities, and membership of a learning community. Each succeeding example describes an increasingly complex model of the relationship between a learner and everyday technology that departs from a focus on the individual as the site for learning. The second part of the paper then sets out a fifth example in which the relationship is analysed as a combination of all four processes: affording, anchoring, distributing and appropriating. In this fifth example the learning outcomes are described as learning narratives (a combination of learning dispositions).