Pre-equating: a simulation study based on a large scale assessment model

Although post-equating (PE) has proven to be an acceptable method in the scaling and equating of items and forms, there are times when the turn-around period for equating and converting raw scores to scale scores is so small that PE cannot be undertaken within the prescribed time frame. In such cases, pre-equating (PrE) could be considered as an acceptable alternative. Assessing the feasibility of using item calibrations from the item bank (as in PrE) is conditioned on the equivalency of the calibrations and the errors associated with it vis a vis the results obtained via PE. This paper creates item banks over three periods of item introduction into the banks and uses the Rasch model in examining data with respect to the recovery of item parameters, the measurement error, and the effect cut-points have on examinee placement in both the PrE and PE situations. Results indicate that PrE is a viable solution to PE provided the stability of the item calibrations are enhanced by using large sample sizes (perhaps as large as full-population) in populating the item bank.     

On a mesh optimization method based on a minimization of interpolation error

In this article a new mesh optimization technique for finite element methods is presented. The mesh modification strategy is based on a minimization of an interpolation error estimate and can be viewed as a generalization of existing conformai map-type mesh generators. The new mesh results in an essential improvement of finite element approximation which is illustrated in numerical examples.     

Dual-reciprocity BEM based on global interpolation functions

Several global shape functions are introduced to interpolate the body-force term in the dual-reciprocity boundary-element method. These global-interpolation functions, which include polynomial, trigonometric, and hyperbolic series, can be used in place of the locally based radial shape function. For the several examples presented, the global functions have demonstrated superior convergence properties.     

POD‐based model reduction with empirical interpolation applied to nonlinear elasticity

The constantly rising demands on finite element simulations yield numerical models with increasing number of degrees‐of‐freedom. Due to nonlinearity, be it in the material model or of geometrical nature, the computational effort increases even further. For these reasons, it is today still not possible to run such complex simulations in real time parallel to, for example, an experiment or an application. Model reduction techniques such as the proper orthogonal decomposition method have been developed to reduce the computational effort while maintaining high accuracy. Nonetheless, this approach shows a limited reduction in computational time for nonlinear problems. Therefore, the aim of this paper is to overcome this limitation by using an additional empirical interpolation. The concept of the so‐called discrete empirical interpolation method is translated to problems of solid mechanics with soft nonlinear elasticity and large deformations. The key point of the presented method is a further reduction of the nonlinear term by an empirical interpolation based on a small number of interpolation indices. The method is implemented into the finite element method in two different ways, and it is extended by using different solution strategies including a numerical as well as a quasi‐Newton tangent. The new method is successfully applied to two numerical examples concerning hyperelastic as well as viscoelastic material behavior. Using the extended discrete empirical interpolation method combined with a quasi‐Newton tangent enables reductions in computational time of factor 10 with respect to the proper orthogonal decomposition method without empirical interpolation. Negligibly, orders of error can be reached. Copyright © 2015 John Wiley & Sons, Ltd.     

Discovering communities based on mention distance

Scientometrics - Scholarly community detection has important applications in various fields. Current studies rely heavily on structured scholar networks, which have high computational complexity...     

Substructured macro elements based on locally blended interpolation

In this paper we describe a new class of locally refined macro finite elements which are especially amenable to the use of substructuring techniques for the efficient solution of the resulting idealization. The tools and guidelines illustrated by the examples of modelling crack tips, point load singularities and singularities at re-entrant corners should enable an analyst to construct other such blended macro elements specifically tailored to his particular class of problems. The use of such substructured macro elements in finite element calculations permits substantial reduction in the manual effort of data preparation and the computational cost of numerical solution.     

基于B样条插值的局部均值分解方法研究

局部均值分解(Local Mean Decomposition,LMD)方法是一种较新的自适应信号分析方法。LMD算法的核心思想是将原始信号分解为多个乘积函数(Production Function,PF),其中每个PF都是一个包络函数和一个纯调频函数的乘积。在LMD算法中需要提取信号的局部均值函数和包络估计,然而常规的提取方法会带来局部误差且分解速度慢。为了解决此问题,提出了利用三次B样条对信号上、下极值点进行插值得到上、下包络线,进而获取信号局部均值和包络估计的新方法。对仿真信号和机械振动信号的对比实验验证了该方法的优越性。     

利用二维插值核的高分辨力图像重构

利用连续图像采样及其内插公式,提出了一种基于二维插值核重建高分辨力图像的新算法。该算法先使一般低分辨力序列图像具有标准位移关系,再根据高、低分辨力图像之间的关系重构高分辨力图像。同时利用正则化技术导出了一套重复迭代算法,以提高算法的处理效果和克服病态问题。实验表明,该算法使图像的细节和清晰度大大增强,分辨力大幅度提高,明显优于零阶保持插值算法的处理结果,其峰值信噪比提高8-9dB。     

Goodnes-of-fit tests for location and scale families based on a weighted L<Subscript>2</Subscript>-Wasserstein distance measure

In two recent papers del Barrio et al. (1999) and del Barrio et al. (2000) consider a new class of goodness-of-fit statistics based on theL ₂-Wasserstein distance. They derive the limiting distribution of these statistics and show that the normal distribution is the only location-scale family for which this limiting distribution has the “loss of degrees of freedom” property, due to the estimation of the unknown parameters. In this paper a weightedL ₂-Wasserstein distance is considered and it is proven that these statistics retain the loss of degrees of freedom property for general classes of distributions if applied separately to the location family and to the scale family and if the “right” weight function is used. These weight functions are such that the corresponding minimum distance estimators for the location parameter and the scale parameter are asymptotically efficient. Examples are discussed for both location and scale families.     

Self-mixing interferometry based on a double-modulation technique for absolute distance measurement

A new, to the best of our knowledge, method for the measurement of the absolute distance of a remote target based on the laser diode self-mixing interferometry is presented. A double-modulation technique is introduced to improve the measurement resolution. Wavelength modulation of the laser beam is obtained by modulating the injection current of the laser diode. Phase modulation of the laser beam is obtained by an electro-optic crystal in the external cavity. Absolute distance of the external target is determined by the Fourier analysis method. Theoretical analysis and numerical simulations are given. Experimental results show that a resolution of +/-0.3 mm can be achieved for absolute distance ranging from 277 to 477 mm.     

基于等效源法插值的声场重放方法

声场重放旨在保留声音内容与声场空间特性,创造或再现一个真实的空间声学环境.一套在真实"听音室"实现的声场重放听音系统,需要对扬声器阵列的声传递函数进行多次测量,这个过程繁琐且耗时.文章提出一种等效源法插值重放方法,在传声器采样率较低的情况下,实现了扬声器阵列声传递函数在整个目标重放空间内的插值.对比传统的声压匹配法,所...     

Precise integration methods based on Lagrange piecewise interpolation polynomials

This paper introduces two new types of precise integration methods for dynamic response analysis of structures, namely, the integral formula method and the homogenized initial system method. The applied loading vectors in the two algorithms are simulated by the Lagrange piecewise interpolation polynomials based on the zeros of the first Chebyshev polynomial. Developed on the basis of the integral formula and the Lagrange piecewise interpolation polynomial and combined with the recurrence relationship of some key parameters in the integral computation suggested in this paper with the solving process of linear algebraic equations, the integral formula method has been set up. On the basis of the Lagrange piecewise interpolation polynomial, and transforming the non‐homogenous initial system into the homogeneous dynamic system, the homogenized initial system method without dimensional expanding is presented; this homogenized initial system method avoids the matrix inversion operation and is a general homogenized high‐precision direct integration scheme. The accuracy of the presented time integration schemes is studied and is compared with those of other commonly used schemes; the presented time integration schemes have arbitrary order of accuracy, wider application and are less time consuming. Two numerical examples are also presented to demonstrate the applicability of these new methods. Copyright © 2008 John Wiley & Sons, Ltd.     

基于Hausdorff距离的工件焊缝接头类型识别

提出了一种以Hausdorff距离为度量准则的工件焊缝接头类型识别方法.通过激光结构光视觉方法,CCD摄像机采集被焊工件焊缝接头的激光图像,并提取出激光条纹中心线.根据焊缝接头图像特点,提出6种焊缝接头条纹形状基准模型.以Hausdorff距离度量激光条纹图形与基准模型库之间的匹配程度,当条纹形状与基准模型的距离具有最小容差时,认为与相对应的焊缝接头类型相匹配.为实现算法加速,采用Hough变换和Hotelling变换来标准化图形,并利用图像特征对搜索空间进行了降维.实验结果验证了该识别方法的有效性.     

基于B样条插值的图像边缘检测的硬件实现

为了能高速、高质量地进行图像边缘检测,提出了一种新的基于B样条插值的边缘检测方法.该方法采用了三次B样条插值原理,对图像的像素点灰度值进行插值运算,提出了基于B样条插值的一阶和二阶微分算子,并引入数字滤波技术加以实现.还利用B样条的可分离特性,实现了2维空间中基于B样条插值的连续图像的重构函数,在此基础上提出了用于边缘检测的基于3次B样条的一阶微分模板和二阶微分模板.设计出一套基于DSP FPGA的实时图像处理和显示系统.     

基于ARMA模型和时空kriging插值联合模拟大跨结构的脉动风速时程

采用ARMA模型模拟具有时间和空间相关性的大跨结构的随机风速时程。并对Whittle递推算法进行了改进,求解出自回归系数和滑动回归系数矩阵。利用MATLAB软件编制了模拟大跨桥梁的风速时程模拟程序,运行结果表明: 改进的方法计算效率高,模拟精度符合要求。然后又利用时空Kriging插值法对控制点区域内节点的脉动风速时程进行模拟,其模拟精度较好且求解过程快,可用于大跨空间结构、超高层建筑等含有大量节点的结构风场模拟。