共查询到16条相似文献，搜索用时 218 毫秒
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从法曲率和测地曲率着手,对R^3中一般曲面上曲线的曲率、挠率以及曲面的两类基本量之间的关系进行探究,并得到了相应的结论。 相似文献
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通过解向量微分方程组的特解的方法，给出了曲率函数和挠率函数为常数的空间曲线的方程，并通过分析说明具有该特征的曲线就是圆柱螺线，在此基础上进一步探讨了曲率和挠率为非常数但它们的比值为常数的空间曲线的方程． 相似文献
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主要研究了柱面曲线的曲率与挠率所满足的方程,并利用该方程讨论柱面曲线的性质.研究了当底曲线的曲率为常数时的柱面曲线的曲率与挠率的性质. 相似文献
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韦煜 《黔南民族师范学院学报》1999,(3)
本文将半径为Ｒ的球面上闭曲线（ｃ）作相似变换映射到单位球面（ｓ）上,从而证明了两个结论：（１）球面上正规闭曲线的总挠率等于零。（２）对于球面上任意闭曲线,有ｆ（τ／ｋ）ｄｓ＝０其τ是曲线的挠率,ｋ是曲线的曲率。 相似文献
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借助于可展曲面的分类方法,寻找到空间曲线的一种分类新方法,并对每一类曲线的曲率及挠率的特征进行研究,给出且证明了相应类型曲线用曲率及挠率的关系式表示的充要条件。 相似文献
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举例证实了经典的Frenet公式所定义的曲线的三个曲率不能唯一确定曲线到一个运动;借助于四维空间中三个向量的向量积运算在正则曲线上构造右手Frenet标架并重新定义曲线的第三曲率;据此证明四维空间中的运动保持曲线的曲率和挠率不变,但第三曲率当运动含有反射时会改变符号,并证明结论的逆也成立。 相似文献
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杨泉康 《南京晓庄学院学报》2002,18(4):49-51
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。 相似文献
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郑雪芳 《温州职业技术学院学报》2008,8(2):47-49
根据微分几何基本理论,对圆柱螺线的性质进行探讨,证明了圆柱螺线的切线与Z轴相交于定角,圆柱螺线的曲率与挠率都是常数,且曲率与挠率都是常数的曲线必是圆柱螺线,圆柱螺线必是Bertrand曲线,圆柱螺线是其所在圆柱面的测地线等性质。 相似文献
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三维欧氏空间中曲线的曲率在三维空间的运动下是不变的,但挠率却可以相差一个符号。类似地,曲面的第一基本形式在运动下是不变的,但第二基本形式却可以相差一个符号;尽管如此,高斯曲率却是运动不变的。 相似文献
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Lynn S. Liben Lauren J. Myers Adam E. Christensen Corinne A. Bower 《Child development》2013,84(6):2047-2063
Researchers have shown that young children solve mapping tasks in small spaces, but have rarely tested children's performance in large, unfamiliar environments. In the current research, children (9–10 years; N = 40) explored an unfamiliar campus and marked flags' locations on a map. As hypothesized, better performance was predicted by higher spatial‐test scores, greater spontaneous use of map–space coordinating strategies, and participant sex (favoring boys). Data supported some but not all hypotheses about the roles of specific spatial skills for mapping performance. Data patterns were similar on a computer mapping task that displayed environmental‐scale videos of walks through a park. Patterns of children's mapping errors suggested both idiosyncratic and common mapping strategies that should be addressed in future research and educational interventions. 相似文献
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闫焱 《西安文理学院学报》2006,9(4):45-47
通过对一般曲线的切向量的球面像的曲率和挠率的计算,得出了圆柱螺线的三个基本向量的球面像都是球面上的平面曲线,并且是圆弧的结论.用不同的方法证明了圆柱螺线是它所在圆柱面上的测地线.说明了圆柱螺线是Bertrand曲线,同时曲率和挠率都是常数的空间曲线一定是圆柱螺线. 相似文献
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Meghan McCormick Christina Weiland JoAnn Hsueh Mirjana Pralica Amanda K. Weissman Lillie Moffett Catherine Snow Jason Sachs 《Child development》2021,92(4):e599-e620
This study examines whether associations between enrollment in public and non-public PreK and children’s (N = 508; Mage = 5.60 years in fall of kindergarten) math and language and literacy outcomes were more likely to be sustained through the spring of kindergarten for unconstrained versus constrained skills. Associations between public PreK and language, literacy, and math outcomes were more strongly sustained through the spring of kindergarten for unconstrained skills, relative to constrained skills. Only associations between non-public PreK and unconstrained language skills were sustained through the spring of kindergarten. Associations in the fall of kindergarten differed by family income and dual language learner (DLL) status but there was no subgroup variation by the spring of kindergarten. Implications for policy and practice are discussed. 相似文献
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Creating a “third space” in student teaching: Implications for the university supervisor’s status as outsider 总被引：1，自引：0，他引：1
Alexander Cuenca Mardi Schmeichel Brandon M. Butler Todd Dinkelman Joseph R. Nichols Jr. 《Teaching and Teacher Education》2011,27(7):1068-1077
The work of teacher education during student teaching typically takes place in two distinct “spaces”: placement sites and college/university settings. The program featured in this article is structured in ways that clearly mark out those two spaces. Yet this configuration led our university supervisors, whose work primarily took place in the field, to feel like “outsiders.” To redress this concern, a third learning space was incorporated into our student teaching seminar. We suggest that “third spaces” in combination with return-to-campus courses not only mitigates the peripherality of university supervisors, but also amplifies the influence of a teacher preparation program. 相似文献
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邓国栋 《江西师范大学学报(哲学社会科学版)》2012,45(3):140-144
通过整合认知语言学的概念合成理论和认知语用学的关联理论,得出了新的理论——概念合成关联理论,并以其为理论框架分析了两则仿拟的生成与阐释机制,提出促成概念产生关联的重要因素是认知语境。认为在解读仿拟的过程中,仿拟的仿体空间和本体空间总是相互作用,在认知语境的作用下,促成各个空间概念产生关联,这些关联成为人类解读话语时认知推理的基础,在合成空间里形成层创结构,即仿拟话语的隐含意义。因此,受认知语境制约的多空间概念合成关联理论可揭示人类语言使用和理解过程中概念映现的动态本质。 相似文献