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导体空腔对电场有屏蔽作用,即导体空腔在电场中电荷重新分布形成了附加电场,附加电场与外电场叠加在腔内形成合场强为零起到了屏蔽作用.在电介质中也有一定的屏蔽作用,即电介质在电场中形成极化电荷,极化电荷形成了附加电场使电场减弱,起到了一定的“屏蔽”作用.在长期的教学过 相似文献
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对于电介质,一般是以“荷”的观点来研究,通过泊松变换,用等效电荷代替电介质来计算电介质对电场的影响.文献[1]通过电介质的类比,文献[2]通过严格的数学证明得到:电介质可类似于磁介质由极化强度(?)引入一个等效电流分布,用此等效电流分布象计算磁感强度一样计算电感应强度(?),从而增加了计算电场的方法,特别是在计算驻极体的电场时更是如此,然而文献[1,2]仅仅是提供了一种方法,对流的物理实质没有作任何解释,为了使这种计算方法满足一定的物理定律,本文给出电介质“流”模型的物理实质,并对流与荷的等效性作一讨论. 相似文献
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本刊编辑部 《数理天地(高中版)》2003,(10)
有些处于静电平衡状态的导体,其边界面上的感应电荷分布复杂.在研究边界外空间的电场时,原则上可以利用点电荷的场强公式和叠加原理求得,但运算繁琐,实际应用并不可取.如果此空间中的电场与某些点电荷产生的电场相同,根据静电场的唯一性原理可知,边界面上的所有感应电荷就可用这些点电荷替代.应用时,可通过空间中电场线或电势的分布情况判断.这些电荷称为像电荷,这种等效替代的方法称为电像法.点电荷形成的电场易于确定,这为处理感应电荷的电场开辟了一条新思路. 相似文献
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秦树艺 《中国远程教育(综合版)》1985,(3)
导体的静电平衡条件是“静电场中的导体与电介质”一章中的重要内容之一。在学习时应深刻理解和掌握下列概念:(1)何谓导体处于静电平衡状态?(2)导体处于静电平衡状态时的条件是什么?为什么会有这些条件?(3)导体处于静电平衡状态时,电荷(导体原来带电或原来不带电)是如何分布的?为什么会有电荷的重新分布?(4)怎样运用导体的静电平衡条件及场强迭加原理求解简单问题中导体的电荷分布,以及场中有导体存在时的场强和电势的分布。 相似文献
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This research investigated students' understanding of electrochemistry following a 7–9-week course of instruction. A list of conceptual and propositional knowledge statements was formulated, and this provided the framework for semistructured interviews that were conducted with 32 students in their final year of high school chemistry, following instruction in electrochemistry. Three misconceptions identified in this study and five which have been reported earlier are incorporated into an alternative framework about electric current. The framework is grounded on the notion that a current always involves drifting electrons, even in solution. Another area where students' misconceptions were prevalent was in relation to the sign of the anode and cathode. Students who thought the anode was negatively charged believed cations would move toward it, and those who thought it was positively charged were unable to explain why electrons move away from it. Electrolytic cells also proved troublesome for students. Many students did not associate the positions of the anode and cathode with the polarity of the applied electromotive force (e.m.f.). Other students attempted to reverse features of electrochemical cells and apply the reversals to electrolytic cells. The implications of the research relate to students' interpretation of the language that is used to describe scientific phenomena and the tendency for students to overgeneralize, due to comments made by teachers or statements in textbooks. 相似文献
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MH-Ni电池充放电性能和贮存性能的研究 总被引：1，自引：0，他引：1
研究了负极材料为Mm0.8La0.2Ni4.0(MnCoAl)1.0贮氢合金的MH-Ni电池的充放电性能,在0.2A电流下的充电电压和放电电压分别为1.4V和1.2V,充电效率为89.1%。电池贮存30天自放电率为22.6%,其原因为电极中氢的解吸和贮氢合金的氧化。 相似文献
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Liu He Cheng Xinbing Zhang Rui Shi Peng Shen Xin Chen Xiaoru Li Tao Huang Jiaqi Zhang Qiang 《天津大学学报(英文版)》2020,26(2):127-134
Lithium(Li) metal anode has received extensive attentions due to its ultrahigh theoretical capacity and the most negative electrode potential. However, dendrite growth severely impedes the practical applications of the Li metal anode in rechargeable batteries. In this contribution, a mesoporous graphene with a high specific surface area was synthesized to host the Li metal anode. The mesoporous graphene host(MGH) has a high specific surface area(2090 m~2/g), which affords free space and an interconnected conductive pathway for Li plating and stripping, thus alleviating the volume variation and reducing the generation of dead Li during repeated cycles. More importantly, the high specific surface area of MGH efficiently reduces the local current density of the electrode, which favors a uniform Li nucleation and plating behavior, rendering a dendritefree deposition morphology at a low overpotential. These factors synergistically boost the Li utilization(90.1% vs. 70.1% for Cu foil) and life span(150 cycles vs. 100 cycles for Cu foil) with a low polarization of MGH electrode at an ultrahigh current of 15.0 m A/cm~2. The as-prepared MGH can provide fresh insights into the electrode design of the Li metal anode operating at high rates. 相似文献
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INTRODUCTION The concept of logic circuits based on quan-tum-dot cellular automata(QCA)has received much attention since it was first proposed by Lent et al.(1993)due to prospects of extremely low-power op-eration and drastic reduction of interconnections.The basic QCA building block is represented by a bistable cell made up of four quantum dots or metallic islands at the vertices of a square and containing two elec-trons that can align along two different diagonals,thus encoding two lo… 相似文献
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程文华 《合肥教育学院学报》2011,(5):63-65,100
负极性词语属于英语词汇-语法模型描写的一个范畴。作为语句的添加成分,负极性词语在使用上呈现不对称性,只能存在于否定性语境中。负极性词语与否定词共现时涉及到句法方面的因素较多,其词汇句法作用的解释理据可以从允许其出现的句法结构以及产生的句法意义这两个层次进行。负极性词语句法意义的形成可以被解释是它们进入句法操作时与允准语否定词发生关系的结果。 相似文献
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程文华 《合肥教育学院学报》2010,(4):66-68
＂极小＂负极性词语属于有量词语,代表的量值为最小,与否定词共现在一起,词汇功能被归入英语语法模型描写的一个范畴。通过对英语＂极小＂负极性词语在语义方面所表现的语言事实简单描述,基于其词汇范畴的改变,解释了＂极小＂负极性词语与否定词之间的关系,揭示了＂极小＂负极性词语和否定词组合等值于全称量词的否定,代表一种质的否定,是极限表达的一种方式。 相似文献
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袁运栋 《内江师范学院学报》2008,23(8):62-65
采用车辆监控系统对输油气管道分布区域及巡检车辆进行实时的动态监控,使管理人员查询方便,对巡检车辆与人员的指挥调度便捷,提高管理人员调度管理的效率,实现油田车辆管理规范化、现代化的管理方法,解决了油田车辆的安全监控问题． 相似文献
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Cultural Coherence and the Schooling for Identity Maintenance 总被引：1，自引：0，他引：1
Michael S. Merry 《Journal of Philosophy of Education》2005,39(3):477-497
An education for cultural coherence tends to the child's well-being through identity construction and maintenance. Critics charge that this sort of education will not bode well for the future autonomy of children. I will argue that culturally coherent education, provided there is no coercion, can lend itself to eventual autonomy and may assist minority children in countering the negative stereotypes and discrimination they face in the larger society. Further, I will argue that few individuals actually possess an entirely coherent identity; rather, most of us possess hybrid identities that lend themselves to multiple, not necessarily conflicting allegiances. 相似文献