多元化与公司风险研究

文章研究了公司的系统风险、债务风险和经营风险与公司的多元化程度的相关性。本文的实证结果表明,公司的系统风险与公司的多元化程度是正相关的;公司的债务风险与公司的多元化程度是正相关的;公司的经营风险与公司的多元化程度是负相关的。随着公司多元化程度加深,公司的经营风险会变小,但是公司面临的宏观的资本市场的系统风险和企业自身的债务风险,会随着变大。     

几何学概论（三）

（四）罗氏几何的光辉照亮了科学前进的道路我们来分析他的学说的哲学意义．住罗氏的时代,哲学中占统治地位的思想足康德的“不可知论”,按照这批人的说法,客观世界是存在的,但是不可知的,时间空间是人心的创造,是人心给经验安排的秩序,我们所确实知道的世界的规律性是人心按先天的原则所创造出来的,先天就是与经验无关的,     

极小圈模对与二元域拟阵的特征

研究极小圈模对与二元域拟阵的特征.首先给出拟阵M的极小圈模对,模对的并的秩与相应的超平面的交的秩三者的等价关系.在两个极小圈不等的条件下,证明了满足极小圈消去公理的极小圈是唯一的并且极小圈模对的对称差包含在其中,结合极小圈的对称差的表示,证明了极小圈与基的差的绝对值大于等于2.后面两个证明都把原来的必要条件推广为充要条件.最后,用M上不相同的极小圈,极小圈模对,极小圈的对称差表示,M上不相等的超平面,超平面的并不等于E及满足的秩等式极简单地刻划了二元域拟阵M的特征.     

科学计算用数字电子计算机的若干问题

数字电子计算机的发明与发展的主要动力是大型科学计算.计算机是应科学计算的需要而发明的,应科学计算的不断追求而迅速发展的.科学计算课题的要求是无限的,而计算机的解题能力是有限的,装备计算机的技术也是有限的.因此如何处处“节约”技术,最“经济”地使用技术,以当前有限的技术研制出计算能力尽可能大的计算机是科学计算工作者很关心的问题.     

关于无公度线段的问题

八年级的学生应当获得关于无公度线段(作为无公度的量的具体例子)的清晰概念,因为用数表示和度量单位无公度的量的需要,对引入无理数的必要性来说是一个主要的论据.事实上,仅以正方形的对角线和它的一边的无公度性为例,学生就能通晓无公度的量的存在的证明.     

关于非独立随机变量序列部分和的一个不等式及其应用

本文讨论的是一般随机变量部分和的处理方法,得到了非独立随机变量部分和的分布的一个不等式并给出了它的应用,证明了非负有界随机变量序列的部分和的收敛与它的相应的条件期望序列的部分和的收敛等价。     

不可压MHD系统的零耗散极限中的边界层

本文研究通常的Dirichlet物理边界条件下带有小而变化的黏性和磁扩散系数的不可压磁流体(MHD)方程组的初边值的极限问题;发现了一类非平凡的初值,对于这类初值能建立其Prandtl型边界层的一致稳定性,并且严格证明了理想的MHD方程组的解和Pandtl型边界层矫正子的叠加是黏性扩散不可压MHD方程的解的一致逼近.这里的主要困难是处理和控制由耗散的MHD系统和理想MHD系统边界条件差异产生的Prandtl型的奇异边界层.关键的观察是对于本文研究的初值,其解的速度场和磁场的边界层的主要奇异项存在有抵消现象.这使得我们能基于精细的能量方法来使用这个特殊结构带来的好处,从而克服在研究这类问题中通常不能解决的困难.此外,在黏性系数为固定的正常数情形,对于一般初值,也能建立磁场的扩散边界层的稳定性以及零磁扩散极限中解的一致收敛性.     

分段函数与初等函数关系及表达的讨论与进展

依据历史的延革、认知的进展,提出了关于初等函数的一个比较系统的概念;给出的限制域、存在域、定义域的概念,使函数的表达、相关的判断得以扩展,给出了分段函数初等性的一个简明的充分性判断;对于分段函数初等性主要的、广传的文献作了综述与评析,指出了存在的与需要研讨的问题.     

关于椭圆,双曲线及抛物线离心率的几何性质

平面解析几何中关于椭圆、双曲线及抛物线的离心率的定义分别是这样给出的：椭圆的焦距与长轴长的比ｅ＝ｃａ,叫做椭圆的离心率．双曲线的焦距与实轴长的比ｅ＝ｃａ,叫做双曲线的离心率,抛物线上的点与焦点的距离和准线的距离的比,叫做抛物线的离心率,用ｅ表示,按抛...     

数学课堂有效导入的实践

现在二期课改的核心理念是“以学生的学为主体,老师的教为辅”,但如何激发学生的主体学习？怎样让学生积极主动地参与学习？这是每个教育工作者应该积极思考与研究的课题．笔者认为一节课的有效的导入便成了激发学生主体去学的基本点之一．应该精心设计课堂的导入,能在较短的时间内吸引学生的注意力,激发其浓厚的学习兴趣,为课堂教学营造活跃和愉悦的学习氛围,对教学任务的顺利实现,教学目标的顺利达成能起到很好的辅助作用．如果仅仅是千篇一律的导入模式肯定是不行的,不同的教学内容常常需要不同的教学导入理念和导入方法．如何根据不同的教学内容实现数学课堂的有效导人呢？     

Self-triggered filter design for a class of nonlinear stochastic systems with Markovian jumping parameters

This paper is concerned with the self-triggered filtering problem for a class of Markovian jumping nonlinear stochastic systems. The event-triggered mechanism (ETM) is employed between the sensor and the filter to reduce unnecessary measurement transmission. Governed by the ETM, the measurement is transmitted to the filter as long as a predefined condition is satisfied. The purpose of the addressed problem is to synthesize a filter such that the dynamics of the filtering error is bounded in probability (BIP). A sufficient condition is first given to ensure the boundedness in probability of the filtering error dynamics, and the characterization of the desired filter gains is then realized by means of the feasibility of certain matrix inequalities. Furthermore, a self-triggered mechanism is designed to guarantee the filtering error dynamics to be BSP with excluded Zeno phenomenon. In the end, numerical simulation is carried out to illustrate the usefulness of the proposed self-triggered filtering algorithm.     

Non-Convex Strong Duality Via Subdifferential

In this article, the strong duality is treated. It is shown that the strong duality is equivalent to the non-emptiness of the subdifferential of a sort map involving the constraint functions. It is also noted that this technique is useful to verify the Assumption S. Indeed, the linearity of a constraint function h is not required as usually seen in the literature. Moreover, it is shown that this condition is easer to verify in the applications. We apply this new principle to the bi-obstacle problem, to the elastic-plastic torsion problem and to the continuum model of transportation.     

Torsional oscillations in symmetrical structures

A two-time perturbation technique is used to study the lateral and torsional motions of a nonlinear symmetrical structure subject to a lateral sinusoidal ground motion. It is shown that when the ground acceleration frequency is about one-third of or three times the natural frequency of the lateral motion, the symmetrical structure is particularly susceptible to torsional oscillations even when the natural frequency of torsion is not close to the natural frequency of the lateral motion. The implication of this type of nonlinear coupling between the lateral and torsional motions in real structures subject to earthquakes is also discussed.     

AR（p）模型中的缺失数据估计

运用EM算法,对含有缺失数据的AR（p）模型进行参数估计,通过最大似然准则就非左端缺失的情况进行插补.最后,用蒙特卡洛方法给出实验分析,表明如下结果：（i）误差与AR模型的阶数正相关,与缺失比例正相关;（ii）当AR模型的特征根模长相对较小时,误差与数据长度负相关,且误差被控制在了标准差的30％以内;（iii）当模长中等时,误差基本控制在1个标准差左右;（iv）当模长较大时,误差与数据长度正相关,而且误差也相对较大.     

Discrete dynamic programming with outcomes in random variable structures

Multiobjective approach is the common way of generalization single-criterion dynamic programming models. Another way is to consider partially ordered criteria structures. That approach is rather rare. The aim of the paper is to present such a model. Generalization of Bellman’s principle of optimality is employed to create a forward procedure to find the set of all maximal elements. As this set is usual large, the second problem under consideration is to find its subsets. To reduce the number of solutions presented to decision maker we propose to apply a family of narrowing relations. That approach is similar to scalarization in multiobjective programming. Ordered structures of random variables based on mean–variance, stochastic dominance and inverse stochastic dominance are considered. Numerical illustration is given at the end of the paper.     

二项线性随机效应模型的拟蒙特卡罗估计

讨论了如何运用拟蒙特卡罗方法对二项线性随机效应模型进行参数估计.首先写出观测数据的边缘对数似然函数,然后用拟蒙特卡罗方法将函数中的积分写成求和的形式,接着利用Newton-Raphson算法计算参数的极大似然估计.以一组种子数据为例,说明该方法是简单可行的.     

The wavelet multiscale method for inversion of porosity in the fluid-saturated porous media

In this paper, the wavelet multiscale method is applied to the inversion of porosity in the fluid-saturated porous media. The inverse problem is decomposed to multiple scales with wavelet transform and hence the original inverse problem is re-formulated to be a set of sub-inverse problem corresponding to different scales and is solved successively according to the size of scale from the smallest to the largest. On each scale, regularization Gauss–Newton method is carried out, which is stable and fast, until the optimum solution of original inverse problem is found. The results of numerical simulations demonstrate that the method is a widely convergent optimization method and exhibits the advantages of conventional regularization Gauss–Newton method methods on computational efficiency and precision.     

基于熵的群决策专家选择研究

群决策是研究多人如何做出统一的有效抉择.在群决策中专家决策水平直接反应到决策结论上,是影响事业的成败关键,因此专家的选择对于群决策而言是至关重要的.建立了评价群决策专家的指标集,从专家选择角度定义了理想专家,给出了专家选择的熵模型,并通过一个例子说明该模型的有效性.     

B-Spline Collocation Method for Nonlinear Singularly-Perturbed Two-Point Boundary-Value Problems

A B-spline collocation method is presented for nonlinear singularly-perturbed boundary-value problems with mixed boundary conditions. The quasilinearization technique is used to linearize the original nonlinear singular perturbation problem into a sequence of linear singular perturbation problems. The B-spline collocation method on piecewise uniform mesh is derived for the linear case and is used to solve each linear singular perturbation problem obtained through quasilinearization. The fitted mesh technique is employed to generate a piecewise uniform mesh, condensed in the neighborhood of the boundary layers. The convergence analysis is given and the method is shown to have second-order uniform convergence. The stability of the B-spline collocation system is discussed. Numerical experiments are conducted to demonstrate the efficiency of the method.     

A defense of indeterminism

My goal is to defend the indeterminist approach to vagueness, according to which a borderline vague utterance is neither true nor false. Indeterminism appears to contradict bivalence and the disquotational schema for truth. I agree that indeterminism compels us to modify each of these principles. Kit Fine has defended indeterminism by claiming that ordinary ambiguous sentences are neither true nor false when one disambiguation is true and the other is false. But even if Fine is right about sentences, his point does not seem to generalize to utterances. What the indeterminist needs -- and what ordinary ambiguity does not provide -- is an ambiguous utterance where what is being said is indeterminate between two different propositions. I will show that such cases exist. These cases imply that the modifications that indeterminism makes to bivalence and the disquotational schema are required independently of indeterminism, in fact independently of vagueness.