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1.
又到开学季! 我怀着沉重的心情来到学校,强装笑脸和大家交流暑假生活.瞧×脸上那由衷绽开的灿烂的微笑,贝卡的心在流泪,啊,别了,我的暑假! 今天是报名日,半天的报到时间,也就意味着暑假只剩下半天时间了. 奇怪的是,今天没看到Lucky,难道这家伙为了逃避上学,胆大到连报名都不来了?  相似文献   

2.
具一步以上的食物链的生态系统的稳定性   总被引:1,自引:0,他引:1  
时,系统(1)有一个坐标皆为正的平衡点x>O,y>0,z>0,w>0. Smith没有研究过这个系统的平衡点(x,y,z,w)的稳定性,但他猜想这个系统该是稳定的。 本文用李雅普诺夫第二方法证明了系统(1)平衡点(x,y,z,w)的稳定性,并把这结果推广到n种捕食者(即任何长度的食物链)的情况。  相似文献   

3.
给出了随机变量 X1,X2 ,X3 ,X4 每三个相互独立 ,但 X1±X2 与 X3 ± X4 不相互独立的例子 ,以及 X1,X2 ,X3 每两个相互独立 ,但 X1± X2 与 X3 不相互独立的例子 .  相似文献   

4.
树的最大特征值的上界的一个注记   总被引:2,自引:2,他引:0  
扈生彪 《数学学报》2007,50(1):145-148
设T是一个树,V是T的顶点集.记dv是υ∈V的度,△是T的最大顶点度.设υ∈V且dw=1.记k=ew+1,这里ew是w的excentricity.设δj′= max{dυ:dist(υ,w)=j},j=1,2,…,k-2,我们证明和这里μ1(T)和λ1(T)分别是T的Laplacian矩阵和邻接矩阵的最大特征值.特别地,记δo′=2.  相似文献   

5.
随机向量的函数的独立性的一个问题   总被引:7,自引:2,他引:5  
陈永义  王炳章 《工科数学》2000,16(2):113-116
给出了随机变量X1,X2,X3,X4每三个相互独立,但X1&;#177;X2与X3&;#177;X4不相互独立的例子,以及X1,X2,X3每两个相互独立,但X1&;#177;X2与X3不相互独立的例子。  相似文献   

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<正> 考虑下述问题R_1=AQ_1-Q_1T_1,其中,A 为 n 阶方阵,T_1为 m 阶方阵 (m相似文献   

7.
n次对称群S_n的元素的阶的集合   总被引:2,自引:0,他引:2  
<正> 我们试图给出 S_n 的元素的阶所构成的集合,为此,要用到下列的基本事实:1°任一个 n 个文字的置换可以分解为不相连的(即彼此无公共文字)循环置换的乘积.2°两个不相连的循环置换可交换.3°k 个文字的循环置换(a_1,a_2,…a_k)的阶为 k.4°群 G 的元素 g_1,g_2,…,g_s 的阶分别为 m_1,m_2,…,m_s,这些元素两两可换,这些阶数两两互质,则积 g_1g_2…g_s 真的阶为 m_1m_2…m_s.5°群 G 的元素 g_1,g_2…,g_s 的阶分别为 t_1,t_2,…,t_s,这些元素两两可换,则积g_1g_2…g_s 真的阶为 t_1,t_2,…t_s 的最小公倍数的因数.  相似文献   

8.
众所周知,数学解题的真正目的不在一个正确答案,主要在解题的思维过程中,培养学生分析和解决问题的能力。因此,如果利用一种错漏的方法,侥幸地得到了问题的正确答案,这对教学工作来讲,不仅是无意义,而是有害的事。以下是出现在本刊有关专栏上的两个例子,提出来供大家讨论。  相似文献   

9.
一元二次方程的根的判别式是初中代数的重要内容之一 ,它在中学数学中有着广泛的应用 ,成为近几年全国各地中考的热点问题 .为了帮助读者更好地掌握好这部分知识内容 ,现对它在初中数学中的应用进行归纳 ,以餮读者 .应用一 :判断一元二次方程 (或二元二次方程组 )的根的情况 ;或已知根的情况 ,求方程 (或组 )中的待定系数的取值范围 .一元二次方程ax2 +bx +c =0 (a≠ 0 )的根的判别式为△ =b2 - 4ac,它与这个方程的根有着十分密切的关系 :( 1)△ >0 方程有两个不等的实数根 ;( 2 )△ =0 方程有两个相等的实数根 .( 3)△ <0 方程…  相似文献   

10.
运用Vakonomic模型导出Lindel f方程 ,表明Lindel f的工作与Vakonomic模型相吻合 ;运用Chetaev模型导出Chaplygin方程 ,表明Chaplygin的工作与Chetaev模型相吻合· 在此基础上 ,通过改进Chaplygin方程和Lindel f方程的表示形式 ,实现了从Lindel f方程向Chaplygin方程的合理过渡和从Chaplygin方程向Lindel f方程的合理的过渡· 最后 ,给出一个典型实例· 结果表明 ,正如Vako nomic模型与Chetaev模型是互补的一样 ,Lindel f的工作与Chaplygin的工作也是互补的·  相似文献   

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We study a class of self-similar processes with stationary increments belonging to higher order Wiener chaoses which are similar to Hermite processes. We obtain an almost sure wavelet-like expansion of these processes. This allows us to compute the pointwise and local Hölder regularity of sample paths and to analyse their behaviour at infinity. We also provide some results on the Hausdorff dimension of the range and graphs of multidimensional anisotropic self-similar processes with stationary increments defined by multiple Wiener–Itô integrals.  相似文献   

13.
It is considered the class of Riemann surfaces with dimT1 = 0, where T1 is a subclass of exact harmonic forms which is one of the factors in the orthogonal decomposition of the spaceΩH of harmonic forms of the surface, namely The surfaces in the class OHD and the class of planar surfaces satisfy dimT1 = 0. A.Pfluger posed the question whether there might exist other surfaces outside those two classes. Here it is shown that in the case of finite genus g, we should look for a surface S with dimT1 = 0 among the surfaces of the form Sg\K , where Sg is a closed surface of genus g and K a compact set of positive harmonic measure with perfect components and very irregular boundary.  相似文献   

14.
张丽娜  吴建华 《数学进展》2008,37(1):115-117
One of the most fundamental problems in theoretical biology is to explain the mechanisms by which patterns and forms are created in the'living world. In his seminal paper "The Chemical Basis of Morphogenesis", Turing showed that a system of coupled reaction-diffusion equations can be used to describe patterns and forms in biological systems. However, the first experimental evidence to the Turing patterns was observed by De Kepper and her associates(1990) on the CIMA reaction in an open unstirred reactor, almost 40 years after Turing's prediction. Lengyel and Epstein characterized this famous experiment using a system of reaction-diffusion equations. The Lengyel-Epstein model is in the form as follows  相似文献   

15.
Schr(o)dinger operator is a central subject in the mathematical study of quantum mechanics.Consider the Schrodinger operator H = -△ V on R, where △ = d2/dx2 and the potential function V is real valued. In Fourier analysis, it is well-known that a square integrable function admits an expansion with exponentials as eigenfunctions of -△. A natural conjecture is that an L2 function admits a similar expansion in terms of "eigenfunctions" of H, a perturbation of the Laplacian (see [7], Ch. Ⅺ and the notes), under certain condition on V.  相似文献   

16.
In this paper, we study the explicit representation and convergence of (0, 1; 0)-interpolation on infinite interval, which means to determine a polynomial of degree ≤ 3n - 2 when the function values are prescribed at two set of points namely the zeros of Hn(x) and H′n(x) and the first derivatives at the zeros of H′n(x).  相似文献   

17.
As early as in 1990, Professor Sun Yongsheng, suggested his students at Beijing Normal University to consider research problems on the unit sphere. Under his guidance and encouragement his students started the research on spherical harmonic analysis and approximation. In this paper, we incompletely introduce the main achievements in this area obtained by our group and relative researchers during recent 5 years (2001-2005). The main topics are: convergence of Cesaro summability, a.e. and strong summability of Fourier-Laplace series; smoothness and K-functionals; Kolmogorov and linear widths.  相似文献   

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