二维正态随机变量的线性组合的独立性

正态分布是实际生活中应用最广泛的一种概率分布。文章讨论了服从二维正态分布的随机变量(X,Y)的线性组合U=a X+b Y和V=c X+d Y的独立性问题,并基于变换矩阵给出了(U,V)的分布与(X,Y)的分布之间的联系,得到了U和V独立的充要条件,同时,分析了U和V独立的条件下(U,V)的分布。     

WVD的快速计算

The paper proposes a new method for computation of the Wigner-Ville distribution (WVD) taking account of the conjugate symmetry of the WVD kernel function and the periodicity and symmetry of the trigonometric function. The method transfers the computation of WVD into real field from complex field to remove the redundancies in the fast Fourier transform(FFT) computation. The realization of fast cosine operation and fast sine operation considerably reduces the computation cost. Theoretical analysis shows that     

探究图形变换,提高识图能力

新课标在“空间与图形”部分的内容中，要求学生通过探索基本图形的基本性质及其相互关系，进一步丰富对空间图形的认识和感受．如何丰富对空间图形的认识，提高根据识图能力呢?本文通过具体实例对此进行一些探讨．     

巧解长短句变换题

句式变换是考查学生理解能力和操作能力的有效途径之一,近年来颇受出题者的青睐,频频出现在中考、高考的单元训练,仿真模拟,正式试题中,分值看涨。而考生望而生畏,无从着手,失分率较高。长短句变换题更使考生望“题”兴叹,不得要领。下面笔者就此问题结合实例谈谈,以飨考生。例一:将下列短句组成一个长句。①淮河大桥今天举行通车典礼。②这是一座铁路公路两用桥。③它的落成使淮南市到淮北市的路程缩短了几百公里。④省委领导同志参加了这个典礼。分析:要做好这道题,首先要搞清这四个短句的内容;其次,要弄清这四个短句的共同内容,这是将几…     

《搜神记》同义变换修辞的语义分析

运用同义变换分析法,对《搜神记》同义变换修辞的语义特色进行个案研究,可知其主要特色是模糊同义,体现为模糊概念及模糊命题的同义变换两大类型。     

应用拉氏变换中延迟性质时象函数的唯一性问题

举例说明在应用拉氏变换中延迟性质时。出现不同象函数的原因。从理论上论证了象函数的唯一性。并指出正确解法。     

"得"字句句式可变换的原因探析

本文就前人对“得”字句变换已做的研究进行了小小的综述，并对“得”字句一般都可变换为重复动词的“得”字句、“得”后是主谓结构的“得”字句仍可变换为重复动词的“得”字句、“得”字句的“把”“被”的转换、王还(1979)认为的“得”字句的三种基本形式的转换等现象的原因进行了探讨。     

基于修正相似度的微博社会化推荐系统构建方法研究

将影响社会化推荐的三种因素分别量化,建立了与微博社会网络一一映射。然后,基于Karhunen-Loéve(KL)变换方法,计算出了同一主题下积极性和消极性文本平均距离。最后,将社会网络信息与情感相似结合形成修正的情感相似度量方法,利用修正相似度方法构建了新的社会化推荐系统。基于微博数据的实证计算和分析显示:经过变换后的用户相似度可以得到不同程度的提高;利用修正相似度方法构建的微博社会化推荐系统更符合用户心理偏好。     

条件用得巧 全靠变形好

在解分式求值问题时,若能视其特点,对已知条件或待求式进行适当的变形,就可以使问题巧妙获解.例1已知1/p-1/q=1/(p+q),求p~2/q~2+q~2/p~2的值.解由已知,得q~2-p~2=pq,     

WPT-based modal control on distributed structures with MRF-04K damper

The magnetorheological (MR) fluid damper-based semiactive control systems have received considerable attention for protecting structures against natural hazards such as strong earthquakes and high winds. In this paper, a novel modal controller using wavelet packet transform (WPT) is proposed for the vibration control of distributed structures. In the proposed control system, the WPT method is utilized to decompose the acceleration measurement and select the modes containing most of the WPT energy component as the dominant modes. Then, a modal controller is designed to control the dominant modes and the optimal active control force is solved. Finally, Clipped-optimal con- trol law is adopted to determine the voltage applied to each MR damper. A Kalman-filter observer, which estimates the full controlled modal states from local accelerometer feedbacks, is designed for rendering the controller to be more applicable to distributed structures with a large number of degrees of freedom. A numerical example of a stadium roof structure installed with MRF-04K damper is presented. The effectiveness of the controller is evaluated under both Tianjin and El Centro earthquake excitations. The superior performance and adaptability of the controller for versatile loading conditions are demonstrated through the comparison with traditional truncated modal controller.