正螺面的两个特征

通过对曲线主法线面的研究,得到了正螺面的两个特征.     

有理Béziter曲线面中权因子的性质研究

有理Bezier(或有理B样条)方法越来越广泛地应用于自由曲线面的设计,并在一些商业 CAD软件中起作用. 有理Bezier(或有理B样条)曲线面不仅继承了Bezier(或B样条)曲线面的凸包性、包络性、剖分性等许多优良性质,而且还把普通多项式曲线面与圆锥曲线面在形式上有机地统一起来,大大方便了程序的实现,并使得曲线面造型在权因子的作用下更灵活、更自由。     

优选法在自动聚集中的应用

调焦判别函数随焦距分布的曲线是一个单峰曲线 ,因此我们可以运用优选法来确定最佳像面的位置 .     

空间曲线绕任意轴的旋转面面积

利用向量和定积分的知识,解决了空间曲线绕任意轴旋转所得旋转面的面积计算问题,给出了旋转面面积的简明计算公式,并借助实例进行说明.     

一类直纹面的研究

本给出了过任意空间C^k(k≥3)类光滑曲线的直纹面是可展曲面的充要条件．同时得到了该空间曲线为相应直纹面的曲率线,测地线和渐近曲线的充要条件。     

任意多边形匀面重心的计算方法

我们都知道 ,当一闭曲线所围几何图形Ω是一均匀薄片时 ,其重心计算公式是ｘ0 =1Ｍ Ωｘｄｘｄｙｙ0 =1Ｍ Ωｙｄｘｄｙ其中Ｍ= Ωｄｘｄｙ为薄片质量(设密度为 1 )但在作具体计算时我们都清楚 ,计算的难度完全取决于Ω的形状 ,而即使是像多边形这样的简单图形 ,当边数稍稍多一点 .运算量就颇大 .本文的目的在于寻找一种计算任意多边形(凸凹不限 )均匀薄片重心的方法 .为叙述方便 ,后文我们把多边形围成的均匀薄片的重心简称为多边形匀面重心 .定理 1　设Ω1 ,Ω2 ,… ,Ωｎ是对均匀薄片Ω的一个几何剖分 ,每个Ωｉ的面积记为Ｓｉ,∑ｎｉ=1…     

圆环面上测地线的稳定性

通过讨论圆环面上的测地线,研究在纤维缠绕时测地线的稳定性问题,按传统观点,测地线在曲面上是最稳定的,其意为一条弹性柔软的细线,在给定曲面上拉紧时,其形状应是测地线,且不会使曲线变形,上述提法仅在局部领域中成立,从整体角度分析,当拉紧弹性柔软细线时,将有两类不稳定测地线,第一类不稳定产生于过两点可以有多条测地线,另一类是缠绕的测地线位于曲面的凹侧,此时就会产生搭桥现象,这两类不稳定性在纤维缠绕中有着现实的意义,文章将对圆环面的测地线进行具体讨论。     

二阶曲线间的射影映射

平面上的射影变换,将二阶曲线变为另一二阶曲线,这个射影变换也可以称为这两个二阶曲线间的射影映射.若两个二阶曲线相切,则存在以切点为射影中心的两个二阶曲线间的射影映射;若两个二阶曲线相离,则存在以两个二阶曲线公切线交点为射影中心的射影映射;若两个二阶曲线相交,则存在以其中一交点为射影中心的两个二阶曲线间的射影映射.     

有理曲线的多项式逼近

利用曲线摄动的思想给出了用多项式曲线逼近有理曲线的一种新方法．其基本步骤是对有理曲线的控制顶点进行摄动，使之产生一多项式曲线，并使摄动误差在某种范数意义之下达到最小．同时，通过适当控制摄动曲线的顶点，使逼近多项式曲线与有理曲线在两端点保持一定的连续性．这一结果可以与细分（ｓｕｂｄｉｖｉｓｉｏｎ）技术结合给出有理曲线的整体光滑的分片多项式逼近．实例表明，在某些情况下本文中的方法要优于传统的Ｈｅｒｍｉｔｅ插值方法及Ｔ．Ｗ．Ｓｅｄｅｒｂｅｒｇ和Ｍ．Ｋａｋｉｍｏｔｏ（１９９１）提出的杂交曲线逼近算法．     

Pythagorean Bézier速端曲线及其等距线

１．引言 工业领域里的许多ＣＡＤ／ＣＡＭ系统,往往需要建立有关几何模型的连续、自动的数控刀具轨迹．例如,数控加工机床的刀具中心轨迹的计算,在纺织和制鞋业中,缝纫机械和自动化工业中铣床的数据控制,以及汽车外形设计,机器人的运动轨迹等都涉及到等距线和等距面的有效设计和计算［１,３,４,１０］ 一般地,具有给定函数类形式的曲线（面）的等距线（面）,常常不能被精确地表示为同类函数形式．例如,有理函数形式的参数曲线（面）的等距线（面）通常不再是有理的曲线（面）,而是参数 ｔ的无理向量函数形式［３,４,１０］…     

Quasi-planar graphs have a linear number of edges

A graph is calledquasi-planar if it can be drawn in the plane so that no three of its edges are pairwise crossing. It is shown that the maximum number of edges of a quasi-planar graph withn vertices isO(n).Work on this paper by Pankaj K. Agarwal, Boris Aronov and Micha Sharir has been supported by a grant from the U.S.-Israeli Binational Science Foundation. Work on this paper by Pankaj K. Agarwal has also been supported by NSF Grant CCR-93-01259, by an Army Research Office MURI grant DAAH04-96-1-0013, by an NYI award, and by matching funds from Xerox Corporation. Work on this paper by Boris Aronov has also been supported by NSF Grant CCR-92-11541 and by a Sloan Research Fellowship. Work on this paper by János Pach, Richard Pollack, and Micha Sharir has been supported by NSF Grants CCR-91-22103 and CCR-94-24398. Work by János Pach was also supported by Grant OTKA-4269 and by a CUNY Research Award. Work by Richard Pollack was also supported by NSF Grants CCR-94-02640 and DMS-94-00293. Work by Micha Sharir was also supported by NSF Grant CCR-93-11127, by a Max-Planck Research Award, and by grants from the Israel Science Fund administered by the Israeli Academy of Sciences, and the G.I.F., the German-Israeli Foundation for Scientific Research and Development. Part of the work on this paper was done during the participation of the first four authors in the Special Semester on Computational and Combinatorial Geometry organized by the Mathematical Research Institute of Tel Aviv University, Spring 1995.     

带干扰的Erlang(2)过程

本篇论文主要讨论带干扰的E rlang(2)过程,首先通过指数分布的可加性来推得生存概率所满足的积分微分方程,进而得到破产概率(由干扰引起和由索赔引起)所满足的积分微分方程,最后得到破产概率的拉氏变换所满足的方程.     

A five facets frame for the design of heuristics

The author suggested to distinguish between the ‘engineering approach’ and the ‘mathematical approach’ in connection with the design of heuristics. Stainton and Papoulias extended the scope by suggesting the ‘relational approach’. Based upon this extension, a five facets frame is presented here which is suggested to precede and accompany the ‘technical’ design of the heuristic. The facets are: coverage by participation, experience by doing, abstraction by structuring, extension by comparison, exploration by creativity.     

A New Characterization of the Mathieu Groups and Alternating Groups with Degrees Primes

In the past thirty years, several kinds of quantitative characterizations of finite groups especially finite simple groups have been investigated by many mathematicians. Such as quantitative characterizations by group order and element orders, by element orders alone, by the set of sizes of conjugacy classes, by dimensions of irreducible characters, by the set of orders of maximal abelian subgroups and so on. Here the authors continue this topic in a new area tending to characterize finite simple groups with given orders by some special conjugacy class sizes, such as largest conjugacy class sizes, smallest conjugacy class sizes greater than 1 and so on.     

Symmetry Reductions of the Combined KdV—mKdV Equation

ＳｙｍｍｅｔｒｙＲｅｄｕｃｔｉｏｎｓｏｆｔｈｅＣｏｍｂｉｎｅｄＫｄＶ－ｍＫｄＶＥｑｕａｔｉｏｎＺｈａｎｇＪｉｅｆａｎｇ（张解放）；ＸｕＸｕｅｊｕｎ（许学军）；ＣｈｅｎｇＤｅｓｈｅｎｇ（程德声）（ＤｅｐａｒｔｍｅｎｔｏｆＰｈｙｓｉｃｓ，Ｚｈｅｊｉａｎｇ...     

Adaptive robot under fuzzy control

This paper deals with the problem of ranking n fuzzy subsets of the unit interval. A number of methods suggested in the literature is reviewed and tested on a group of selected examples, where the fuzzy sets can be nonnormal and/or nonconvex.The ranking is obtained from: (i) the index of strict preference defined by Watson, (ii) three indexes proposed by Yager, (iii) the algorithm used by Chang, (iv) three versions of the a-preference index suggested by Adamo, (v) the index defined by Baas and Kwakernaak, (vi) three modified versions used by Baldwin and Guild, (vii) the method proposed by Kerre, (viii) three forms of the index suggested by Jain, (ix) the four grades of dominance studied by Dubois and Prade.In simple cases the results are good for all the methods, with some exceptions. In questionable cases, where the decision must be probably modelled in accordance with the context in which it is imbedded, the best indexes seem to be the dominances suggested by Dubois and Prade. These indexes do not force any particular choice, but clearly describe the situation, hence allowing the decision-maker himself to make his ‘best’ choice.     

Intrinsic regular submanifolds in Heisenberg groups are differentiable graphs

We characterize intrinsic regular submanifolds in the Heisenberg group as intrinsic differentiable graphs. G. Arena is supported by MIUR (Italy), by INDAM and by University of Trento. R. Serapioni is supported by MIUR (Italy), by GALA project of the Sixth Framework Programme of European Community and by University of Trento.     

插补空间的逼近外推定理

本文建立了拟模Abelian群上双参数算子族逼近的外推定理,所得的结果包含了DeVoreR．等人对正规逼近族之最佳逼近所建立的外推定理,且所需的条件更弱．同时从本文的结果立即可以建立起算子逼近的外推定理．     

Approximate Gradient Projection Method with Runge-Kutta Schemes for Optimal Control Problems

We consider an optimal control problem for systems governed by ordinary differential equations with control constraints. The state equation is discretized by the explicit fourth order Runge-Kutta scheme and the controls are approximated by discontinuous piecewise affine ones. We then propose an approximate gradient projection method that generates sequences of discrete controls and progressively refines the discretization during the iterations. Instead of using the exact discrete directional derivative, which is difficult to calculate, we use an approximate derivative of the cost functional defined by discretizing the continuous adjoint equation by the same Runge-Kutta scheme and the integral involved by Simpson's integration rule, both involving intermediate approximations. The main result is that accumulation points, if they exist, of sequences constructed by this method satisfy the weak necessary conditions for optimality for the continuous problem. Finally, numerical examples are given.     

Well-posedness by perturbations of mixed variational inequalities in Banach spaces

In this paper, we consider an extension of the notion of well-posedness by perturbations, introduced by Zolezzi for a minimization problem, to a mixed variational inequality problem in a Banach space. We establish some metric characterizations of the well-posedness by perturbations. We also show that under suitable conditions, the well-posedness by perturbations of a mixed variational inequality problem is equivalent to the well-posedness by perturbations of a corresponding inclusion problem and a corresponding fixed point problem. Also, we derive some conditions under which the well-posedness by perturbations of a mixed variational inequality is equivalent to the existence and uniqueness of its solution.