共查询到20条相似文献，搜索用时 140 毫秒
1.
Ioannis Papadopoulos 《Science & Education》2014,23(1):61-77
This paper describes a classroom experiment where students use techniques found in the history of mathematics to learn about an important mathematical idea. More precisely, sixth graders in a primary school follow Archimedes’s method of exhaustion in order to compute the number π. Working in a computer environment, students inscribe and circumscribe regular polygons inside and around a circle in order to find the approximate area of the circle. They then compute the ratio of that approximation to the area of a square with side-length equal to the radius of the circle. This ratio indicates how many times larger the area of the circle is than the area of the square. Mirroring Archimedes’s findings, students discover that as they increase the number of sides in their polygons, the numerical results they obtain convince them that this number is almost equal to 3.14. 相似文献
2.
Torus bifurcation is a relatively complicated bifurcation caused by a pair of complex conjugate Floquet multipliers coming out of unit circle on the Poincare section. A three-bus system is employed to reveal the relationship between torus bifurcation and some complex dynamics. Based on theoretical analysis and simulation studies, it is found that torus bifurcation is a typical route to chaos in power system. Some complex dynamics usually occur after a torus bifurcation, such as self-organization, deep bifurcations, exquisite structure, coexistence of chaos and divergence. It is also found that chaos has close relationship with various instability scenarios of power systems. Studies of this paper are helpful to understand the mechanism of torus bifurcation in power system and relationship of chaos and power system instabilities. 相似文献
3.
Study on power systemchaotic phenomena is oneimportant aspect in power system stability stu-dies[1—3]. Early studies, such as Lee[4], Chiang[5],Wang[6]and Tan[7], mainly focused on interpretingthe behavior of chaotic oscillations. Later researches,such as Wu[8], Rajesh[9], Jia[10,11], Srivastava[12]and Abed[13]began to concern the following topics,such as interaction of chaotic motion and system dy-namics, the relationship of power system stability re-gion and chaos, and the methods to eli… 相似文献
4.
肖海华 《十堰职业技术学院学报》2000,13(2):72-76
本用定积分的元素法,归纳出含有内切圆的多边形的面积与周长间、含内切球的几何体的体积与表面积间的微积分关系,并给出计算旋转体体积的一般公式。 相似文献
5.
林杰 《廊坊师范学院学报(自然科学版)》2011,11(6)
根据100张血管切片图像,提出搜索最大内切圆的优化算法。搜索范围限制在每张图像边界的外接长方形内的一块长方形区域,从而精确、高效地求出圆心坐标和半径。接着用三次B样条曲线逼近血管的中心点列,并重建出三维血管模型。结果表明,B样条曲线逼近效果良好,重建出的三维血管模型能够反映血管原状。 相似文献
6.
武汉城市圈作为＂两型社会＂建设综合配套改革的试验区,是武汉1＋8城市圈经济发展的新机遇。以湖北省黄冈市为例,探讨城市圈试验区应把握好经济与金融关系,应对试验区建设中产业结构调整和转移的相关问题。 相似文献
7.
8.
王珍娥 《雁北师范学院学报》2007,23(1):75-76,87
若一元函数存在导数，则可推得函数在某点连续，曲线呈光滑状态．而对多元函数来说，自变量在平面区域、空间区域甚至n维空间区域内变化，导数概念相对复杂．本文就导数概念的推广略加探讨． 相似文献
9.
王珍娥 《雁北师范学院学报》2007,(4)
若一元函数存在导数,则可推得函数在某点连续,曲线呈光滑状态.而对多元函数来说,自变量在平面区域、空间区域甚至n维空间区域内变化,导数概念相对复杂.本文就导数概念的推广略加探讨. 相似文献
10.
11.
Dimitris Chassapis 《Educational Studies in Mathematics》1998,37(3):275-293
This study focuses on the process by which children develop a formal mathematical concept of the circle by using various instruments
to draw circles within the context of a goal-directed drawing task. Particular attention was given to the transition from
using tracers and templates to using a compass for drawing circles and to the extent to which the use of different drawing
instruments may contribute to the formation of a formally defined mathematical concept of the circle. The critical difference
considered in the study is that the compass, in contrast to circle-drawing tracers or templates, induces by its physical structure
and its functional use the generative features of formal mathematical concepts of the circle, that is, the centre and the
radius. Analysis of the empirical data indicates that the use of the compass in circle drawing structures the circle-drawing
operation in a radically different fashion than circle tracers and templates, and brings into play an action-bound practical
thinking. Such thinking has an overall positive influence on the construction of analytical concepts by children that are
analogous to the formally defined mathematical concepts of the circle.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
王仁定 《内蒙古师范大学学报(哲学社会科学版)》2004,33(4):73-75
继长江三角洲经济圈建立之后，在地跨蒙西、晋北、陕北、宁北的这一大片地域，为煤、石油、天然气和电力等资源极为富集的地区，完全有条件建立一个北方能源经济圈。建立这样一个经济圈．既有其资源条件、地理条件、交通条件、工业基础、旅游资源等方面的依据，又有在本经济圈充分发挥其产业网络化和经贸一体化的独特的经济功能和社会功能。这对于推进西部大开发和相关省区经济大发展。都有不可估量的作用。 相似文献
13.
首先利用小尺度高斯低通滤波器对虹膜图像进行预处理,去除可能存在的眼睑和睫毛干扰;然后用Canny边缘检测算子得到虹膜的内边缘,通过自适应选取非极大值抑制的高阈值,并对不连续边缘进行修整,得到比较理想的虹膜内边缘;最后利用圆周上任意不共线的3点可以确定一组圆心及半径的参数的性质得到虹膜内边缘的圆心及半径,完成虹膜内边缘定位。实验结果表明,该算法可以比较准确地定位出虹膜的内边缘。 相似文献
14.
用无穷小数法和增量极限法重新定义了空间光滑曲线在某点处的密切面、密切圆、切线、法线、副法线、曲率、曲率半径、曲率中心、曲率半径矢量以及自然坐标系.证明了质点沿空间光滑曲线运动的方向为该空间光滑曲线的切线方向. 相似文献
15.
The National Science Education Standards emphasize teaching unifying concepts and processes such as basic functions of living organisms, the living environment, and scale (NRC 2011). Scale includes understanding that different characteristics, properties, or relationships within a system might change as its dimensions are increased or decreased (NRC 2011). One such relationship involves surface area to volume which is a pervasive concept that can be found throughout different sciences. This concept is important for students to not only understand the association of the two, but to also be able to apply this relationship in science contexts. The purpose of this study is to investigate the factors that influence the understanding surface area to volume relationships. This study examined middle school students’, high school students’, and science teachers’ logical thinking skills (including proportional reasoning), visual-spatial skills, and understandings of surface area to volume relationships. Regression results indicated that participants’ reasoning abilities and components of visual-spatial skills could be possible predictors for one’s ability to understand surface area to volume relationships. Implications for teaching scale concepts such as surface area to volume relationships in the science classroom are discussed. 相似文献
16.
基于解析几何法导出的最大压力角表达式,导出了偏心凸轮机构和对心凸轮机构的基圆半径和偏距的计算公式。只要从动件为常用的运动规律以及不超过3次的多项式运动规律,在满足许用压力角的前提下,采用该解析法确定凸轮基圆半径和偏距,比其它解析法简捷方便。 相似文献
17.
用Java程序计算圆内随机点的点数与正方形内随机点数之比，得到正方形和其内切圆的面积比，计算出圆周率。 相似文献
18.
飞船跟踪测控中的球面区域覆盖 总被引：1，自引：0，他引：1
朱文辉 《南通职业大学学报》2010,24(1):64-66
飞船绕地球飞行,因地球自转,其飞行轨迹呈网状分布于运行球面的某个区域,需用多个测控站的测控区域予以全域覆盖．以实现全程跟踪测控。为此建立了测控圆的立体角计算公式和测控圆的经纬度方程,设计出无空隙的多层覆盖方案及精确计算覆盖纬度的公式。以神州7号的数据为例。给出了测控站数目最少的、能达到全域覆盖的最优方案,并对最优性进行了论证。 相似文献
19.
江新喜 《江西师范大学学报(哲学社会科学版)》2012,45(4):114-123
本文对大学经营诱发的衍生经济圈形成和发展规律做了初步探究。大学经营中伴随着特异的经济外部性,其主要原因在于大学具有的强大现金流而导致的经营资源凝聚效用。而且,由于大学在经营机制上存在着制度的漏逸、文化需求的共谋、知识演替的受容、母校情结和角色扎堆、科技文化产业的强化等促进衍生经济圈的诱因,为大学经营的可持续发展提供了广泛的扩展空间。其中资本流运动是衍生经济圈形成中最为活跃的经营资源演替,是值得广泛研究的学术领域之一。而正向诱导和反向孵化的衍生经济圈形成方式则是大学经营者可以有效利用的实践手法。 相似文献
20.
The National Science Education Standards emphasise teaching unifying concepts and processes such as basic functions of living organisms, the living environment, and scale. Scale influences science processes and phenomena across the domains. One of the big ideas of scale is that of surface area to volume. This study explored whether or not there is a correlation between proportional reasoning ability and a student's ability to understand surface area to volume relationships. Students' knowledge of surface area to volume relationships was assessed pre and post to a one‐week instructional intervention involving investigations about surface area to volume as a limiting factor in biological and physical systems. Results showed that proportional reasoning scores of middle school students were correlated to pre‐test and post‐test assessment scores, and a paired‐sample t‐test found significant differences from pre‐test to post‐test for the surface area to volume assessment. Relationships between proportional reasoning, visualisation abilities and success in solving surface to volume problems are discussed. The implications of the results of this study for learning concepts such as magnitudes of things, limits to size, and properties of systems that change depending on volume and surface are explored. 相似文献