关于微分几何中可展曲面教学的一些探讨

可展曲面是直纹面的一种类型,在理论和应用上都很重要.一般的教材中先给出可展曲面的定义,然后以命题的形式给出了可展曲面的诸多性质,其中对"可展曲面是单参数平面族的包络"这一性质学生不易理解,总感到茫然.为了帮助学生清晰地理解可展曲面的特征性质,本文给出了直观的例子,并且具体给出了三种可展曲面的切平面族,这样处理教学内容,学生对"可展曲面是单参数平面族的包络"这一特征性质能够有个较深的理解.     

包络曲面(线)的初等求解公式及其应用

设F(x,λ)=0表示单参数曲面(线)族的方程。对F(x,λ)可以表成λ的多项式的情形,得到包络曲面(线)的一组初等求解公式,并讨论了这些公式在微分几何、常微分方程及解析几何中的初步应用。     

包络曲面（线）的初等求解公式及其应用

设Ｆ（x,λ）＝０表示单参数曲面（线）族的方程，对Ｆ（x，λ）可以表成λ的多项式的情形，得到包络曲面（线）的一组初等求解公式，并讲座了这些公式在微分几何、常微分方程及解析几何中的初步应用。     

伪球面上的测地线与测地圆

通常,所谓”伪球面”就是平面上一条曳物线绕其渐近线旋转而成的曲面,它是负常曲率曲面的一个模型.如所知,适当选取这个曲面的参数,那么它的测地线与测地圆就同参数平面上的某些圆弧相对应;尽管如此,但仍然没有象球面上测地线与测地圆的直观性.这个问题在三维欧氏空间E~3中是无法解决的.我们在三维拟欧氏空间F~3中给出了负常收率曲面的模型,从本文讨论中可以看出,F~3中的这一曲面与E~3中的球面确有许多相似之处.因此,我们认为把它叫做伪球面也许更切意些.另外,我们还希望通过对伪球面这个例子的讨论,     

旋转圆锥曲面上的成象理论

作者为物理系傅景礼,全文发表于中国自然科学核心期刊《大学物理》1998年第2期,系国家教委下达世界银行贷款资助项目的子课题．以往的专著和文献,以曲面的曲率中心和曲率半径为参数,研究了光在平面和球面上的反射与折射问题．此文应用焦点和焦点参数,研究光在旋转圆锥曲面上反射与折射的成象问题,建立了其成象理论．研究了光在旋转圆锥曲面上反射与折射的单心性,建立了近轴条件下成象的一般公式,并讨论得到了旋转抛物面、旋转椭球面、旋转双曲面、球面、及平面上的反射与折射的成象公式．发展了几何光学的成象理论．旋转圆锥曲面上…     

直纹曲面是可展曲面的一个充要条件

可展曲面是直纹曲面的一种类型,可展曲面就是沿每一条直母线只有一个切平面．通过几何分析方法,讨论了直纹曲面,给出了直纹曲面是可展曲面的一个充分且必要条件,说明直纹曲面S：r^→（u,v）=ρ^→（u）＋ve^→（u）是可展曲面,其充要条件是：沿准线C：v=0,r^→=ρ^→（u）,曲面S是它的切平面族的包络面．并且给出了这个定理应用的两个例子．     

全脐点弯曲曲面及其上曲线的若干性质

本文论证了全脐点曲面必为球面或平面 ,并讨论了球面曲线的一系列性质 ,揭示了这类曲线的曲率和挠率之间的特殊关系 ,从而刻画出其几何特征。     

单位球面上的Moebius极小子流形

本文给单位球面上的子流形为Moebius极小子流形的一个充要条件,并证明了S3中不含脐点的曲面为极小曲面当且仅当它为常平均曲率的Moebius极小.     

一个积分公式及其在整体曲面论中的应用

§1 引言.三維欧氏空間中的球面可以用各种不同的方法来刻划它;从凸曲面的微分几何性質出发,远在1899年H.Liebmann 就获得了著名的关于球的不可变形性(Unverbiegbarkeit der Kugel)的定理:球面是唯一的高斯曲率为常量的封閉曲面。一年以后,又得到了一个与此相当的关于平均曲率的定理,是即世之所謂Liebmann     

调和映射与极小超曲面以及等参超曲面的几何拓扑

主要项目简介 该项目属于基础数学中的微分几何与拓扑学,对若干基本问题和著名猜想,取得了突破性的研究成果,产生了广泛的国际影响。证明了三维欧氏空间中的完备稳定极小曲面是平面,被公认为Bernstein定理的实质推广;对球面中的极小超曲面,证明了常数量曲率的第二间隙定理,这是关于陈省身猜想的首次突破性进民关于球面或对称空间中等参超曲面的几何拓扑,得到了非常系统的研究结果;构造了球面之间许多新的调和映射,     

卡思卡特城堡

It is worthy of noting that, whilst Crookston Castle witnessed the earlier and happier portion of Mary's variegated life,     

Western and Eastern culture differences in commercial field

The communication of people partially is the communication of cultures. Culture has a direct effect on international commercial activities in all aspects. Different conceptions about time, space, equality, law and the like, lead people to deal with things in different ways. So to know cultures of the counterpart is to facil-itate our enterprises so as to have a smooth and successful communication in commercial activity.     

不同的吃喝玩乐

一、吃和喝吃苹果 eat an apple, 吃药 take medicine,吃糖 have some sweets,吃饭 have one's meals,吃馆子 dine out,吃惊 be surprised/     

漏洞百出的教育

Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help?     

只要努力,不要后悔

There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love.     

浅谈移民问题

Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject.     

风的曲线

Rosco and I wait for the fishermen to return.I sit at a wooden bench near the store at Mt.Baker Resort and watch the clouds change shape. Rosco has my belt around his neck and an eight foot tow chain hooked to a tree. Dogs must be on a leash. Ducks and rabbits are loose.     

团图为数的图中的闭团贯数

Given a graph G,a subgraph C is called a clique of G if C is a complete subgraph of G maximal under inclusion and |C|≥2. A clique-transversal set S of G is a set of vertices of G such that S meets all cliques of G. The clique-transversal number, denoted as TC (G), is the minimum cardinality of a clique-transversal set in G. The clique-graph of G, denoted as K (G), is the graph obtained by taking the cliques of G as vertices, and two vertices are adjacent if and only if the corresponding cliques in G have nonempty intersection. Let F be a class of graphs G such that F={G|K(G) is a tree}. In this paper the graphs in F having independent clique-transversal sets are shown and thus TC (G)/|G|≤1/2 for all G ∈ F.     

Sister Carrie, an Adherent of Desires

Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities.