什么是浑沌

神话和现实盘古从鸡蛋样的浑沌(或混沌)开天辟地,这是古老的中国神话,最早见宋代《太平御览》转引三国时徐整的《三五历纪》,而"浑沌"一词本身,在战国时期的《庄子》中已有。古希腊类似的记载更早,声名仅次于荷马(Homer)的诗人赫西俄德(Hesiod,约公元前8世纪)对天上众神排了个"家谱",在他的《神谱》(Theogony)中写道:"首先来到的是Xaog,然后有宽胸的'大地',有'地狱'爱...     

《力学名词》已定稿付印

经过7年的工作,《力学名词》(第一批)已审定、定稿付印,将在1993年公布.这次公布的名词,共2500多条,分成5个部分:通用词(普通物理中力学部分、理论力学和材料力学),一般力学,固体力学,流体力学,以及其他(交叉,应用学科和新分支).除了委员会成员的工作外,学会一些专业会议(如“三流”专业会议)和个人(如梅凤翔)提供了不少有用的材料.定     

《力学名词》已定稿付印

<正> 经过7年的工作,《力学名词》(第一批)已审定、定稿付印,将在1993年公布.这次公布的名词,共2500多条,分成5个部分:通用词(普通物理中力学部分、理论力学和材料力学),一般力学,固体力学,流体力学,以及其他(交叉,应用学科和新分支).除了委员会成员的工作外,学会一些专业会议(如“三流”专业会议)和个人(如梅凤翔)提供了不少有用的材料.定     

声音辨

名词不统一,对学术工作带来一些不便.力学界目前没有统一的词汇,往往从相邻学科的名词汇编假借.但是,仅以《英汉物理词汇》(1978科学版,下简称《物》)和《英汉数学词汇》(1978科学版,下称《数》)而言,同一个英文词在好多处却有不同的译名.如果涵义不同,译名不同是可以的,如 annihilation,《物》《数》分别译为"湮灭"和"零化".然而,有些却是同义异译,如 covariant(《物》译"协变",《数》译"共变")critical value(中肯值,临界值)dyad(并向量,并矢)iteration(叠代,迭代)metric tensor(度规张量,度量张量)Normal coordinates(简正坐标,正规坐标或法坐标)pseudo(赝,伪)quasi(准、拟)random vibration(无规运动,随机运动)steady(稳[恒],定常)vertical(竖直,垂直)等.至于人名,本刊编辑部一般采用原文(牛顿等最常见的除外),但在不得不用汉译名时,即使常见的人名也有困难.仍以《物》《数》两词汇的规定为例,不同译法有 Cauchy(科希,科西)D'Alembert(达朗伯,达朗贝尔)Euler(欧勒,欧拉)Green(格临,格林)Hermite(厄密,埃尔密特)Hilbert(希尔伯,希尔伯特)Kronecker(克朗内克,克罗内克)Jacobi(雅科毕,雅可此)Liouville(刘维,刘维尔)Lorentz(洛伦兹,洛伦茨)Neumann(诺埃曼,诺伊曼)Schwartz 或 Schwarz(薛华兹,许尔瓦兹)等.至于数学、物理界和工程技术界的名词不统一处也有很多(如湍流,紊流).下面刊登《声音辨》这篇短文,希望引起读者的注意与讨论,让我们大家一起来解决名词的"约定俗成"问题.     

力矩析微

力矩是力学教学中最重要的基础概念之一,但教材中一般会同时给出力对点之矩和力对轴之矩两种定义,这在概念上容易引起学习者的困惑,尤其是空间问题中的力对点之矩,从物理意义的角度讲更是不易理解.本文在利用杠杆原理阐述力矩定义起源的基础上明确指出:力矩本质上即力对轴之矩,是力使刚体绕特定轴转动效应的一种度量,是滑动矢量;而力对点之矩是力对轴之矩的一种抽象的等价表述,是定位矢量,是力矩概念在复杂应用中的进一步发展.这种解释理清了力对点之矩与力对轴之矩两种定义之间的关系,物理意义明确直观,更有利于教学和实践中对力矩概念的清晰理解和准确应用.     

力学和数学中的“调和”释义

力学的教学过程中经常涉及"调和"这个概念,其与数学基础理论和力学应用紧密联系,了解该概念的本义与延伸,可以帮助学生更恰当准确地理解和掌握相关知识点。本文将力学学习过程中经常遇到的多个与"调和"有关的名词联系起来,给出了详细的解释,并示例应用,有助于相关知识点的教学活动。     

浅谈《流体力学》教学中的智慧教育

在《流体力学》教学中,不仅要让学生学习到西方科学的精神,更要让学生学习到中国文化的智慧.围绕这一目的,作者在《流体力学》课堂教学方法上进行了一些探索.比如:彰显《流体力学》中的西方科学精神;在《流体力学》课堂中融入礼乐的氛围;适当地采用文学化的语言讲解流体力学的概念.     

航空遥感用三轴惯性稳定平台不平衡力矩前馈补偿方法

航空遥感用三轴惯性稳定平台用于稳定成像载荷,获取高分辨的遥感数据。但是由于稳定平台承载大且存在质量偏心,在载机加速度的作用下平台产生幅值较大的不平衡力矩,导致平台的稳定精度下降和相机成像质量退化。为了有效抑制不平衡力矩产生的影响,提高平台的稳定精度,提出了一种基于不平衡力矩观测器的惯性稳定平台不平衡力矩前馈补偿方法。首先设计一种不平衡力矩观测器,实时估计出平台的不平衡力矩;然后通过前馈补偿的方法抑制不平衡力矩的作用,从而达到提高平台的稳定精度的目的。仿真结果显示,平台的稳定精度得到大幅度提高,基于不平衡力矩观测器的惯性稳定平台不平衡力矩前馈补偿方法有显著补偿效果。     

“黏”和“粘”用法区别

古人原先造了个“黏”(读nián)字,又造了个“粘”(亦读nián)(见《四角号码新词典》1950年出版;《康熙字典》1958年出版),1955年《第一批异体字整理表》把“黏”作为“粘”的异体字淘汰了,废除了“黏”字．于是见诸报端和学术刊物(包括《力学名词》第1版)的“黏”均被“粘”字取而代之了(见《中华词典》1990年版)．1988年3月国家语言文     

大众力学丛书《趣味流体力学》前言

正《诗情画意谈力学》2008年在高等教育出版社出版以来,笔者在《力学与实践》、《自然杂志》等期刊上又发表了一些力学科普文章(主要涉及流体力学),现结集为《趣话流体力学》,以飨读者.与《诗情画意谈力学》一样,内容仍大致可分为"力学诗话"和"力学趣谈"两部分,"力学诗话"的文章,力图从唐宋诗词中对力学现象观察和描述的佳句入手,将诗情画意与近代力学的发展交融在一起阐述;"力     

On the L_p intersection body

In this paper,by using the Brunn-Minkowski-Firey mixed volume theory and dual mixed volume theory,associated with L_p intersection body and dual mixed volume,some dual Brunn-Minkowski inequalities and their isolate forms are established for L_p intersection body about the normalized L_p radial addition and L_p radial linear combination.Some properties of operator Lp are given.     

Preparation and characterization of LiAl_xCo_yNi_1-x-yO₂ particles

Lithium-aluminum-cobalt-nickel oxide LiAlxCoyNi1xyO2 particles, generally used as cathode of lithium battery, were prepared by chemical coprecipitation from an aqueous solution of LiOH, Al(NO3)3, Co(NO3)2 and Ni(NO3)2 with NH4OH. XRD, SEM and FTIR were used to examine the effect of nickel content on the product. FTIR patterns showed that increase in nickel content decreased the absorption strength of the peak of spinel structure of the product, attributed to the occupation by nickel in the aluminum sites. Particle size and electrical properties of the lithium-aluminum-cobalt-nickel oxide (abbreviated as LACNO) particles were also determined.     

Reduction of<Emphasis Type="Italic">K</Emphasis><Subscript>I</Subscript> and<Emphasis Type="Italic">K</Emphasis><Subscript>II</Subscript> by the shape-memory effect in a TiNi shape-memory fiber-reinforced epoxy matrix composite

Shape-memory TiNi fiber-reinforced/epoxy matrix composites have been fabricated, and the suppression of crack-tip stress intensity and the change in fracture toughness have been systematically investigated. Stress-strain data for these composite specimens with notches at various angles and different crack lengths in the transverse direction have been measured in tensile tests. The stress intensity factor at the crack tip is experimentally determined from photoelastic fringe patterns. The decreases inK values are attributed to the compressive stress field in the matrix induced when the pre-strains of the TiNi fiber contract to their initial length upon heating above the austenitic final temperature. We present the influences of the pre-strain of TiNi fibers and the compressive domain size between a crack tip and fiber on theK value.     

Inequalities relating to Lp-version of Petty＇s conjectured projection inequality

Petty＇s conjectured projection inequality is a famous open problem in the theory of convex bodies. In this paper, it is shown that an inequality relating to Lp-version of the Petty＇s conjectured projection inequality is developed by using the notions of the Lp-mixed volume and the Lp-dual mixed volume, the relation of the Lp-projection body and the geometric body Г-pK, the Bourgain-Milman inequality and the Lp-Bnsemann-Petty inequality. In addition, for each origin-symmetric convex body, by applying the Jensen inequality and the monotonicity of the geometric body Г-pK, the reverses of Lp-version of the Petty＇s conjectured projection inequality and the Lp-Petty projection inequality are given, respectively.     

Differential Independence of <Emphasis Type="Italic">Γ</Emphasis> and <Emphasis Type="Italic">ζ</Emphasis>

In a celebrated theorem H?lder proved that the Euler Γ-function is differential transcendental, i.e. Γ(z) is not a solution of any (non-trivial) algebraic ordinary differential equation with coefficients that are complex numbers; and we extend his methods to the Riemann ζ-function. Moreover, we conjecture that Γ and ζ are differential independent, i.e. Γ(z) is not a solution of any such algebraic differential equation—even allowing coefficients that are differential polynomials in ζ(z). However, we are able to demonstrate only the partial result that Γ(z) and ζ(sin 2πz) are differential independent.     

HAMILTON OPERATORS AND HOMOTHETIC MOTIONS IN R^3

Quaternion is a division ring. It is shown that planes passing through the origin can be made a field with the quaternion product in R3. The Hamiltonian operators help us define the homothetic motions on these planes. New characterizations for these motions are investigated.     

MAXIMAL ELEMENTS FOR GB-MAJORIZED MAPPINGS IN PRODUCT G-CONVEX SPACES AND APPLICATIONS (Ⅰ)

A new family of set-valued mappings from a topological space into generalized convex spaces was introduced and studied. By using the continuous partition of unity theorem and Brouwer fixed point theorem, several existence theorems of maximal elements for the family of set-valued mappings were proved under noncompact setting of product generalized convex spaces. These theorems improve, unify and generalize many important results in recent literature. Contributed by DING Xie-ping Foundation items: the National Natural Science Foundation of China (19871059); the Natural Science Foundation of Education Department of Sichuan Province of China ([2000]25) Biography: DING Xie-ping (1938∼)     

MAXIMAL ELEMENTS FOR G-B-MAJORIZED MAPPINGS IN PRODUCT G-CONVEX SPACES AND APPLICATIONS (Ⅱ)

By applying existence theorems of maximal elements for a family of G_B-majorized mappings in a product space of G-convex spaces, some coincidence theorem, Fan-Browder type fixed point theorem and some existence theorems of solutions for a system of minimax inequalities are proved under noncompact setting of G-convex spaces. These theorems improve and generalize many important known results in literature. Contributed by Duping Xie-ping Foundation items: the National Natural Science Foundation of China (19871059); the Natural Science Foundation of Education Department of Sichuan Province ([2000]25) Biography: Duping Xie-ping (1938∼), Professor (E-mail: dingxip@sichu.edu.cn)     

Electrorheological response of SnO<Subscript>2</Subscript> and Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in silicon oil

The electrorheological properties (ER) of some fluids containing particles change extensively under the external electrical field. This phenomenon is applicable in many industries and equipments, such as clutches and motor driven rotor, which would transfer the spin to a drive shaft through a thin layer of electrorheological fluid. In this investigation, the effects of external electrical field on ER properties of non-Newtonian fluids (silicon oil) with the addition of SnO₂ and Y₂O₃ nanoparticles were studied. The ER properties were measured for a wide range of SnO₂ and Y₂O₃ nanoparticle concentrations and DC electrical voltages using concentric cylinder rotary rheometer. Based on the results, ER properties of nanofluids, e.g., apparent viscosity, shear stress, and yield stress, were enhanced by applying electrical field and increasing SnO₂ and Y₂O₃ concentrations.