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一、专题的背景与分析
1. 背景
闵行区的沪闵路─春申路口是交通特别拥挤的交叉路口之一.家住莘庄地区的同学有一个共同的感受,在他们到校或回家路上必经的沪闵路─春申路口时常遇到塞车现象.…… 相似文献
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"牛吃草"问题又称为消长问题,是17世纪英国伟大的科学家牛顿提出来的.典型牛吃草问题的条件是假设草的生长速度固定不变,不同头数的牛吃光同一片草地所需的天数各不相同,求若干头牛吃这片草地可以吃多少天.由于吃的天数不同,草又是天天在生长的,所以草的存量随吃的天数不断地变化.…… 相似文献
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一道以群的定义为背景的高考试题赏析 总被引:2,自引:0,他引:2
每一年的高考数学试卷中都有一些以高等数学背景立意的好题目,如2006年四川卷理科第16题,是一道以近世代数中群的定义为背景立意的填空题,这样的试题能够有效考查学生的学习能力、思维能力和数学创新意识,这为高校选拔学习潜质好的学生创造了条件.…… 相似文献
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导数作为大学的重要内容,进入中学数学教材后,给传统的内容注入了生机与活力,为中学数学命题的研究提供了新视角,新方法.由于导数是研究函数性质的一个很好的工具,它的用途十分广泛,它在解决函数、不等式、解析几何等问题有独到的功能.因此,近几年的高考正逐年加大对导数问题的考查力度,本文通过对07年全国各地高考题的整理和分析寻找命题规律,希望能对今后的教学提供一点复习思路.…… 相似文献
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本文首先介绍基于垂直概率密度表示的,给定密度函数的随机数生成的通用方法;然后介绍球面及球体上均匀随机向量的生成算法。 相似文献
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C. Sánchez-Sellero W. González-Manteiga R. Cao 《Annals of the Institute of Statistical Mathematics》1999,51(1):51-70
A plug-in type bandwidth selector is presented for density estimation with truncated and censored data. It is based on a representation of the MISE function obtained in the paper. Rate of convergence and limit distribution are derived for this selector. A bootstrap method is introduced to estimate the MISE whose minimizer is an alternative bandwidth selector. A simulation study was carried out to assess the behavior with small samples. This methodology is applied to a real-data problem consisting of reporting delay of AIDS cases. The almost sure representation of the product-limit estimator is a key tool in our proofs. 相似文献
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We consider a functional on the Wiener space which is smooth and not degenerated in Malliavin sense and we give a criterion for the strict positivity of the density, that we can use to state lower bounds as well. The results are based on the representation of the density in terms of the Riesz transform introduced in Malliavin and Thalmaier (2006) and on the estimates of the Riesz transform given in Bally and Caramellino (Stoch Process Their Appl 121:1332–1355, 2011). 相似文献
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In this note, we provide a nontrivial example of a differential equation driven by a fractional Brownian motion with Hurst parameter 1/3<H<1/2 whose solution admits a smooth density with respect to Lebesgue measure. The result is obtained through the use of an explicit representation of the solution when the vector fields of the equation are nilpotent, plus a Norris-type lemma in the rough paths context. 相似文献
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针对斜井中顶替流体密度差及套管偏心引起的顶替界面突进两相流体掺混严重的问题,考虑斜井密度差引起的驱动力沿周向角和半径的变化,建立了斜井偏心环空稳定顶替界面形状模型,利用该模型分析了密度差对顶替界面形状的影响,得到了不同井斜角及套管偏心条件下顶替流体的最优密度差及变化规律:斜井中顶替界面突进的位置及程度取决于套管偏心与密度差的相对作用,存在合理的密度差使得顶替界面长度最短;最优顶替流体密度差随套管偏心度的增加而增大,随井斜角的增大而减小;固井顶替时在满足压稳防漏的条件下直井所选用的密度差越大越好,水平井所选用的密度差应相对最小。 相似文献
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In this paper we provide rather weak conditions on a distribution which would guarantee that the t-statistic of a random vector of order n follows the t-distribution with n-1 degrees of freedom. The results sharpen the earlier conclusions of Mauldon [Characterizing properties of statistical distributions, Quart. J. Math. 2(7) (1956) 155-160] and the more recent advances due to Bondesson [When is the t-statistic t-distributed, Sankhyā, Ser. A 45 (1983) 338-345]. The basic tool involved in the derivations is the vertical density representation originally suggested by Troutt [A theorem on the density of the density ordinate and an alternative interpretation of the Box-Muller method, Statistics 22(3) (1991) 463-466; Vertical density representation and a further remark on the Box-Muller method, Statistics 24 (1993) 81-83]. Several illustrative examples are presented. 相似文献
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Mats Ehrnström 《Journal of Mathematical Analysis and Applications》2008,339(1):636-643
We consider steady symmetric gravity water waves on finite depth with constant vorticity and a monotone surface profile between crests and troughs. The problem is transformed into one concerning the vertical velocity. A representation formula for the stream function in terms of the surface and the vorticity is presented, and we show that the surface can be determined from the vertical velocity. 相似文献
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Ion Nechita 《Annales Henri Poincare》2007,8(8):1521-1538
We investigate random density matrices obtained by partial tracing larger random pure states. We show that there is a strong
connection between these random density matrices and the Wishart ensemble of random matrix theory. We provide asymptotic results
on the behavior of the eigenvalues of random density matrices, including convergence of the empirical spectral measure. We
also study the largest eigenvalue (almost sure convergence and fluctuations).
Submitted: February 9, 2007. Accepted: March 3, 2007. 相似文献