弯曲梁上剪力、弯矩和分布载荷间微分关系

学习梁的弯曲变形必然要分析梁横截面上的内力,最基本的方法是采用截面法进行逐段进行截取分析求出其剪力和弯矩,但是这种方法非常复杂和繁琐。根据多年的教学、研究和分析,找出了一个求解弯曲梁界面剪力图和弯矩图的方法,可以省去繁琐的截面法求解过程,不用列剪力方程和弯矩方程快速画出剪力图和弯矩图。     

基于矩特征和面积特征的二值图像检索方法

在商标图像的检索中,仅凭图像单一的特征很难达到满意的检索效果,文章提出了利用图像矩特征与面积特征相结合的方法进行二值商标图像的检索。实验表明该方法能有效减少虚警和漏检,提高检索的精度。     

关于横向荷载作用下压弯构件的等效弯矩系数的研究

针对横向荷载作用下的压弯构件进行稳定分析,提出了当端弯矩不等时等效弯矩系数的最优解,特别有利于抗风柱等一类构件的稳定分析。     

对速度瞬心的动量矩定理的教学与应用

对速度瞬心的动量矩定理是理论力学教学中的一个难点,应该突出强调速度瞬心的瞬时性。可用“瞬心角色”的概念来表述这个瞬时性,并且指出对速度瞬心的动量矩与对于平常点的动量矩不同,它是对瞬心角色的动量矩。进而据此推导出对速度瞬心的动量矩定理。     

MOMENT EXPLOSIONS AND STATIONARY DISTRIBUTIONS IN AFFINE DIFFUSION MODELS

Many of the most widely used models in finance fall within the affine family of diffusion processes. The affine family combines modeling flexibility with substantial tractability, particularly through transform analysis; these models are used both for econometric modeling and for pricing and hedging of derivative securities. We analyze the tail behavior, the range of finite exponential moments, and the convergence to stationarity in affine models, focusing on the class of canonical models defined by Dai and Singleton (2000) . We show that these models have limiting stationary distributions and characterize these limits. We show that the tails of both the transient and stationary distributions of these models are necessarily exponential or Gaussian; in the non-Gaussian case, we characterize the tail decay rate for any linear combination of factors. We also give necessary and sufficient conditions for a linear combination of factors to be Gaussian. Our results follow from an investigation into the stability properties of the systems of ordinary differential equations associated with affine diffusions.     

Stability of characterizations of normal distributions based on the conditional expected values of the sample skewness and the sample kurtosis

Characterizations of normal distributions given by Nguyen and Dinh (1998) based on conditional expected values of the sample skewness and the sample kurtosis, given the sample mean and the sample variance, are shown to be stable. Received: September 1998     

集中扭矩荷载作用下简支薄壁单室箱梁的约束扭转应力

为研究简支薄壁箱梁横截面参数对扭转应力的影响,以单室箱梁为例,推导出扭转中心、广义主扇性坐标及主扇性静矩等扭转几何特性的实用计算公式。用解析法和ANSYS实体单元计算了简支箱梁算例的翘曲正应力和剪应力,并研究悬臂板宽度和箱室高度变化对广义扇性静矩、二次剪应力及剪应力系数的影响规律。结果表明：按本文方法计算翘曲应力与ANSYS模拟结果吻合较好;悬臂板宽度和底板宽度比值为0.3时,能充分发挥腹板承受剪力的作用;随着悬臂板宽度与顶板宽度的比值和箱室高宽比的增大,顶、底板中点处的广义扇性静矩呈现出完全不同的变化规律。     

单拱肋下承式连续梁拱组合桥梁拱协作机理

以单拱肋下承式连续梁拱组合桥西宁祥瑞街大桥为工程背景,基于吊杆力相等假定和膜张力假定,采用结构力学的方法,推导出梁拱组合体系在均布荷载作用下,拱肋分担荷载比、拱梁弯矩比、拱梁变形比表达式,以此揭示梁拱协作机理。采用四次抛物线对吊杆力进行拟合,通过对公式、有限元计算结果进行误差分析,得出吊杆力修正系数,以此减小吊杆力相等假定带来的误差。同理,采用余弦荷载对吊杆力进行拟合,通过对吊杆力公式、膜张力公式计算结果进行误差分析,得出膜张力修正系数,以此减小膜张力假定带来的误差。最终结合吊杆力修正系数和膜张力修正系数,计算出主梁跨中挠度、拱肋跨中挠度以及吊杆力分担外荷载比例的修正系数分别为1.1、1.2、0.9,以此减小公式误差。