薄壳非线性变形理论

对薄壳的非线性变形,给出了应变与位移之间的精确关系.经过合理的简化,给出了壳的挠度与厚度同级的大变形基本公式.当薄壳为无限长柱形且作柱形变形时,精确地求得了壳的挠度与长度同级的大变形基本公式.     

调控基本不等式应用中恒等变形方向的若干维度探析

基本不等式是高中数学中为数不多的处理多变量问题强有力的工具.但是在教学实践中,我们发现基本不等式尽管形式简洁优美,但是其应用需要学生对原始条件和多变量目标函数的外在结构进行适时恒等变形,对学生的思维品质(如灵活性,敏捷性和批判性等等)提出了较高的要求.因此基本不等式应用中的恒等变形技巧已经成为学生学习基本不等式和提升能力的瓶颈.为此笔者结合自己的教学实践,通过剖析基本不等式成立的内在机理,从求解问题的内在需要出发探求恒等变形的自然合理性,希望给读者求解类似问题给予一定的启发.1从不等式的方向中寻求恒等变形的方向考虑到基本不等式应用中恒等变形变化莫测,我们无法确定变形的针对性和有效性,因此我们希望能从问题的结构中去突破解决问题的入口以便     

基于精确Cosserat模型的螺旋杆稳定性分析

弹性杆的螺旋线平衡问题在DNA、纤维、海底电缆和输油管线等方面具有应用背景.Kirchhoff动力学比拟是分析弹性细杆平衡稳定性的有效方法.Kirchhoff模型中包括中心线无拉伸变形和截面无剪切变形的基本假定与生物大分子等软物质的实际状况有较大差异.基于精确Cosserat模型,考虑中心线的拉伸压缩变形和截面剪切变形,以及剪切变形引起杆中心线转动导致切线轴相对截面法线轴的偏离,以Euler角表达截面姿态,建立圆截面弹性杆的动力学普遍方程.在静力学范畴内讨论螺旋线平衡状态的Liapunov稳定性和Euler稳定性问题,导出稳定性条件及轴向力和扭矩的Euler临界值.证明螺旋杆平衡的静态Liapunov稳定性和Euler稳定性条件是动态Liapunov稳定性的必要条件.     

圆薄膜在集中力作用下的大变形

利用圆薄膜在中心集中力作用下大变形的基本方程、边界条件和Hercky变换,求解了非线性边值问题,推广了Hencky变换,得到了集中力作用下圆薄膜大变形问题的精确解.     

基本不等式与其他知识的交汇融合

<正>本文中归纳总结了基本不等式与其他知识交汇融合的6种常见题型,并结合具体实例进行分析求解,以引导学生通过总结归纳强化和提升对相关知识、方法的综合运用能力.1常见题型一：基本不等式与函数的交汇求解有关代数式的范围或最值时,往往需要适当构造函数,在数形结合的基础上,利用基本不等式或者基本不等式的变形结论加以灵活求解.     

基于高阶变形理论的硬夹芯夹层板横向载荷条件下的弯曲

考虑面板和夹芯的面内刚度及抗弯刚度,基于高阶变形理论考虑各层的横向抗剪刚度,并根据横向剪应变分布情况给出应力函数,基于广义虚位移原理推导了夹层板的基本方程.详细研究了四边简支受横向载荷条件下的夹层板的弯曲,对比计算了面板与芯层厚度变化对计算结果的影响,并与一阶变形理论计算结果进行对比.研究了厚度方向的剪应变分布情况以及中面法线变形后的形态,给出了横向剪应变引起的附加转角在面内的分布情况.     

因式分解中常用的变形技巧

因式分解是初中代数的重要内容.教材中介绍了四种基本方法.因式分解的题型多、方法灵活,有些是不能直接应用四种基本方法的,而需要适当的恒等变形,改变多项式的原有结构,方能找到奏效方法.下面列举几例,向同学们介绍几类常用的变形技巧.     

2023年北京大学优秀中学生暑期学堂数学测试题赏析

2023年北京大学优秀中学生暑期学堂数学测试题所涉及的知识与方法基本在高中范围之内,较为重视考查代数变形、数学运算与数学推理等能力素养,本文对试题进行赏析,介绍解题方法,剖析问题背景.     

不可压缩弹性固体中的二维应力波分析

本文研究不可压缩弹性固体中的二维应力波.首先对一般的应变能函数给出了分析简单波和激波的基本方程,然后求出了波速和相应的本征向量,证明在一般情况下有两组简单波和两组激波,最后举了平面变形和反平面变形两个例子.在平面变形的情况下,平面激波的斜反射问题一般无解.     

子空间Parseval框架的一个基本恒等式

本文研究了子空间框架的一个基本恒等式.利用算子理论的两个基本结果,得到了子空间Parseval框架的基本恒等式,同时给出了恒等式的几种变形,包括一般子空间框架的情况.     

Archimedean ordered semigroups as ideal extensions

The main result of the paper is a structure theorem concerning the ideal extensions of archimedean ordered semigroups. We prove that an archimedean ordered semigroup which contains an idempotent is an ideal extension of a simple ordered semigroup containing an idempotent by a nil ordered semigroup. Conversely, if an ordered semigroup S is an ideal extension of a simple ordered semigroup by a nil ordered semigroup, then S is archimedean. As a consequence, an ordered semigroup is archimedean and contains an idempotent if and only if it is an ideal extension of a simple ordered semigroup containing an idempotent by a nil ordered semigroup.     

The Turaev genus of an adequate knot

The Turaev genus of a knot is an obstruction to the knot being alternating. An adequate knot is a generalization of an alternating knot. A natural problem is a characterization of the Turaev genus of an adequate knot. In this paper, we show that the Turaev genus of an adequate knot is realized by the genus of the Turaev surface associated to an adequate diagram of the knot using the Khovanov homology. As a result, we obtain the additivity of the Turaev genus of adequate knots, and show that the Turaev genus of an adequate knot is “often” preserved under mutation. We also show that an n-semi-alternating knot is of Turaev genus n. This is the first examples of adequate knots of Turaev genus two or more.     

Excellent扩张和弱维数

在这篇文章里，我们证明了，当环Ｓ是Ｒ的ｅｘｃｅｌｌｅｎｔ扩张，Ｍ是Ｓ－模时，Ｍ做为Ｓ－模的弱维数与Ｍ做为Ｒ－模的弱维数相等。     

Eigenvector method,consistency test and inconsistency repairing for an incomplete fuzzy preference relation

In this paper, we extend the eigenvector method (EM) to priority for an incomplete fuzzy preference relation. We give a reasonable definition of multiplicative consistency for an incomplete fuzzy preference relation. We also give an approach to judge whether an incomplete fuzzy relation is acceptable or not. We develop the acceptable consistency ratio for an incomplete multiplicative fuzzy preference relation, which is simple and similar to Saaty’s consistency ratio (CR) for the multiplicative preference relation. If the incomplete fuzzy preference relation is not of acceptable consistency, we define a criterion to find the unusual and false element (UFE) in the preference relation, and present an algorithm to repair an inconsistent fuzzy preference relation until its consistency is satisfied with the consistency ratio. As a result, our improvement method cannot only satisfy the consistency requirement, but also preserve the initial preference information as much as possible. Finally, an example is illustrated to show that our method is simple, efficiency, and can be performed on computer easily.     

Invariant properties of representations under cleft extensions

The main aim of this paper is to give the invariant properties of representations of algebras under cleft extensions over a semisimple Hopf algebra. Firstly, we explain the concept of the cleft extension and give a relation between the cleft extension and the crossed product which is the approach we depend upon. Then, by making use of them, we prove that over an algebraically closed field k, for a finite dimensional Hopf algebra H which is semisimple as well as its dual H*, the representation type of an algebra is an invariant property under a finite dimensional H-cleft extension . In the other part, we still show that over an arbitrary field k, the Nakayama property of a k-algebra is also an invariant property under an H -cleft extension when the radical of the algebra is H-stable.     

Relations Between Algebras and Their Subalgebras of Invariants

We prove that, if H is a finite-dimensional semisimple Hopf algebra, and A is an FCR H-module algebra over an algebraically closed field, then A is a PI-algebra, provided the subalgebra of invariants is a PI-algebra. We also show that if A is an affine algebra with an action of a finite group G by automorphisms, the subalgebra of the fixed points A^G is in the center of A, and the characteristic of the ground field is either zero or relatively prime to the order of G, then A^G is affine. Analogous results are proved for graded algebras and H-module algebras over a semisimple triangular Hopf algebra over a field of characteristic zero. We prove also that, if A is an H-module algebra with an identity element, and H is either a semisimple group algebra or its dual, then, if A is semiprimitive (semiprime), then so is A^H.     

Determination of the insulated inclusion in conductivity problem and related Eshelby conjecture

In the study of composites, it is important to determine the shape of inclusions. There is an interesting case in conductivity problem that the inclusion is insulated. In present paper, we first obtain the representation formula of the solution to an exterior problem, and then prove that for any uniform loading such solution can be extended into the inclusion as an affine function if and only if the insulated inclusion is an ellipse or an ellipsoid. We also show that an analogous result holds for the elasticity problem, which is related to Eshelby conjecture. The main results in this paper are motivated by Ammari, Kang, Kim and Lee (2013), Ammari, Kang and Lim (2005), Kang and Milton (2008), and Liu (2008).     

Adaptive Wavelet Solution to the Stokes Problem

This paper deals with the design and analysis of adaptive wavelet method for the Stokes problem. First, the limitation of Richardson iteration is explained and the multiplied matrix M0 in the paper of Bramble and Pasciak is proved to be the simplest possible in an appropiate sense. Similar to the divergence operator, an exact application of its dual is shown; Second, based on these above observations, an adaptive wavelet algorithm for the Stokes problem is designed. Error analysis and computational complexity are given; Finally, since our algorithm is mainly to deal with an elliptic and positive definite operator equation, the last section is devoted to the Galerkin solution of an elliptic and positive definite equation. It turns out that the upper bound for error estimation may be improved.     

Self Extending Rings

A ring R is an IPQ (isomorphic proper quotient)-ring if R ? R/A for every proper ideal A ? R. If every ideal A ? R satisfies: either R ? A or R ? R/A, then R is called an SE (self extending)-ring. It is shown that with one exception, an abelian group G is the additive group of an IPQ-ring if and only if G is the additive group of an SE-ring. The one exception is the infinite cyclic group Z. The zeroring with additive group Z is an SE-ring, but a ring with infinite cyclic additive group is not an IPQ-ring. Since the structure of the additive groups of IPQ-rings is known, the structure of the additive groups of SE-rings is completely determined.     

Intermediate buffer analysis for a production system

In this paper, a production system consisting of two serial machines and an intermediate buffer is studied. A shortage cost is incurred when the upstream machine is down and the buffer is exhausted. The practical example for this type of system can be an automated work center or an automobile general assembly.Researches on a similar two-machine system have been done in some articles where maintenance and an intermediate buffer are considered, but the spare parts are not involved. Nevertheless, spare parts are essential for maintenance implementation, and there is interaction between the buffer inventory and the spare parts due to maintenance activity. This paper is aimed to investigate three types of cost related to the intermediate buffer inventory, and obtain their expectations as functions of several decision parameters on maintenance, buffer, and spare parts during a renewal cycle, by using mathematical analysis. The proposed method can be an important basis for further study of system cost calculation and decision making optimization.