功的定义式中的(?)是力的作用点的位移吗?

功是物理学中最基本的概念之一,也是力学教学的重要课题,但学生对机械运动范围内功的定义和功的计算常有疑问。一、问题的提出力学中功的定义可表为dA=F·dr或A=∫F·dr或A=∫F·dr,有些力学教材把式中的dr表述为力的作用点的位移。这在当受力物体可视为质点时,表述不会发生问题,但当受力物体不能被视为质点时,就产生了疑问。     

对功的一般表达式的讨论

《物理教学》1985年第11期所刊登的《关于功的一般表达式》一文(以下简称<功>)提出F·dr不是功的一般表达式的论点,本人认为是不妥当的。在牛顿力学中,功的一般表达式被定义为在牛顿力学中,功的一般表达式被定义为dW=F·dr(l)式所定义的是机械功,dr是力的作用点(以下简称为力点)的位移。     

机械阻抗在振动分析中的一些应用

系统的机械网络中,由机械阻抗 Z 将力 F 与速度 V 相连系:Z=F/V。本文讨论2个特殊情况:(1)Z=0,由此可得系统的频率方程,并就工程中常见的实例作了分析;(2)Z=∞,这是动力减振器的设计原理。     

_1g_0的收敛性

球面稳定同伦群的研究是同伦论中的一个重要课题,Smith-Toda谱V(n)的同伦群与球谱S的同伦群有极其紧密的联系.主要利用May谱序列证明珓g0在Adams谱序列中是永久循环且不是dr边缘,从而收敛到πp2q+3pq+2q-5(V(1))中的非零元,其中n=1,2,p≥11,q=2(p-1).     

水力学中Sobolev方程组的极限振幅定理

Sobolev 方程组是(V)/(t)-[V,ω]+Δp=F(x,t)(1)divV=0 (x∈R~3,t≥0).且满足 V(x,t)丨_(r=0)=V~0(x),div V~0=0 (2)其中 V(x,t)是速度向量,其分量为 v_1、v_2、v_3.p 是标量函数表压力.ω=(0,0,ω)表 coriolis 参数(柯里奥利),w 是不为零的常数.[·,·]表矢积.由解的结构理论知研究     

谱V(1)同伦群中一些元素的存在性

利用May谱序列以及一些代数和数论的方法，证明了当p≥7时，b1h1，b1g0在Adams谱序列中是永久循环且不是dr边缘，从而分别收敛到同伦群π*V(1)中相应的非零元，其中V(1)是Toda-Smith谱.     

关于域上的方阵环

设F是任意一个域,V为F上任意一个n维线性空间.若取定V的一基α_1,α_2,…α_n,再取F中n~3个元素c_(ij)~t,(i,j,t=1,…,n) 满足     

奖励收集顶点覆盖问题的一个2-近似算法

给定图G、点赋权函数c和边惩罚费用w,对于图中任一顶点子集FV,F的权重可定义为其包含的顶点权重之和加上图G中未被其覆盖的边的费用之和。如何寻找一个权重最小的顶点子集F是近年来研究者广泛关注的问题之一。这一问题被称作奖励收集顶点覆盖问题。本文采用迭代松弛方法给出了这一问题的一个近似算法,并证明了该算法的近似度为2。     

JET装置中的离散阿尔芬本征模探讨

当前的磁约束聚变装置常常运行在先进托卡马克区域内,先进托卡马克区域内存在负磁剪切,s<0(s=rdq/dr)。在JET(Joint European Torus)装置中探讨了一种新型的离散阿尔芬本征模式——αTAE(α-induced to-roidal Alfvén eigenmode),研究其模式随s或α变化的特性,α=-q2Rdβ/dr。这里,q是安全因子,β是等离子体压力与磁压力之比,R和r分别代表托卡马克的大半径和小半径。     

大统一的混合网络模型中的相称性系数转变新特点

首先建立了大统一的混合网络模型(LUHNM),并在总混合比dr基础上,引入了两个新的混合比:随机性混合比gr和确定性混合比fd,用这3个混合比控制整个网络生长和特性变化。通过调控dr,gr和fd,不仅再现了无权网络中不同类型网络的特性(如BA模型,ER模型,HUHPM模型和BPRA模型等),而且发现在无权的大统一的混合网络模型中出现了若干新现象和新特点:随着3个混合比的变化,相称性系数rc可以在一个(-1,1)较大范围内变化,在dr=1/1附近存在一个阈值fd=0.9/1,随着fd的增加,rc实现从负值到正值大范围的转变;当dr→1/0时,在fd～1/1附近存在一个阈值(相变点),相称性系数rc数值将从零附近迅速增加到较大的正值;特别是随着fd→1/1,rc出现了多峰现象(多极值情形)。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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