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51.
52.
John A. Steele Allan T. Dolovich 《International journal for numerical methods in engineering》2000,48(5):721-730
The vector epsilon algorithm (VEA) is a non‐linear sequence‐to‐sequence transformation which has been in use for over 35 years to determine the limits (antilimits) of convergent (divergent) vector sequences. Recently, it has been used in a variety of engineering applications to accelerate iterative solution processes, including iterative finite element techniques. The VEA has been shown to give the limiting value of many sequences. However, an expression describing the kernel of the VEA, the set of all sequences { v n} which the VEA extrapolates successfully to the sequence's limit (antilimit) vector v , remains elusive. Here, this question is addressed with a simple proof giving the kernel of the first‐order VEA with some comments about the kernel for higher orders. We prove that the first‐order VEA assumes that each term of the related sequence { v n‐ v } is rotated by a fixed angle and scaled in length by a constant factor with respect to the preceding term. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
53.
Jiun‐Shyan Chen Cheng‐Tang Wu Sangpil Yoon Yang You 《International journal for numerical methods in engineering》2001,50(2):435-466
Domain integration by Gauss quadrature in the Galerkin mesh‐free methods adds considerable complexity to solution procedures. Direct nodal integration, on the other hand, leads to a numerical instability due to under integration and vanishing derivatives of shape functions at the nodes. A strain smoothing stabilization for nodal integration is proposed to eliminate spatial instability in nodal integration. For convergence, an integration constraint (IC) is introduced as a necessary condition for a linear exactness in the mesh‐free Galerkin approximation. The gradient matrix of strain smoothing is shown to satisfy IC using a divergence theorem. No numerical control parameter is involved in the proposed strain smoothing stabilization. The numerical results show that the accuracy and convergent rates in the mesh‐free method with a direct nodal integration are improved considerably by the proposed stabilized conforming nodal integration method. It is also demonstrated that the Gauss integration method fails to meet IC in mesh‐free discretization. For this reason the proposed method provides even better accuracy than Gauss integration for Galerkin mesh‐free method as presented in several numerical examples. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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55.
Hu‐Chuan Lu Ying‐Jie Huang Yen‐Wei Chen 《International journal of imaging systems and technology》2010,20(3):253-260
PCA, ICA, and Gabor wavelet are considered as the important and powerful face representation methods. In this article, we propose a new approach for face representation, which is called a pixel‐pattern‐based texture feature (PPBTF) and apply it to the real‐time facial expression recognition. A gray scale image is transformed into a pattern map where edges and lines are used for characterizing the facial texture information. Based on the pattern map, a feature vector is comprised of the numbers of the pixels belonging to each pattern. We use the image basis functions obtained by principal component analysis as the templates for pattern matching. Adaboost and Support Vector Machine are adopted to classify facial expression. Extensive experiments on the Cohn‐Kanade Database, PIE Database, and DUT Database illustrate that the PPBTF is quite effective and insensitive to illumination. The comparison with Gabor show the PPBTF is speedy. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 253–260, 2010 相似文献
56.
容积效应和伪影现象是MR影像处理中的重要影响因素,单模态处理方法易受两者影响。提出一种改进的基于多模态局部转向核的方法来检测大脑中的多发性硬化。该方法利用多模态脑MR影像和大脑近似轴对称的先验知识来进行大脑情况的变化检测。局部转向核能够度量像素与其周围环境的相似程度,因此该方法将局部转向核作为特征,用余弦相似性来衡量差异性。实验结果表明,多模态的引入减少了容积效应和伪影现象,改善了检测效果。 相似文献
57.
本文研究了以微波辅助法提取向日葵仁中的绿原酸,在单因素的基础上,探究了料液比、乙醇体积分数、微波时间、微波温度、微波功率对绿原酸提取率的影响,并通过正交试验对影响绿原酸提取率的参数进行优化。在最佳条件下:料液比1∶20(g/mL)、乙醇体积分数70%、微波时间4 min、微波温度80℃、微波功率400 W,向日葵仁中绿原酸提取率可达到3.5764%。 相似文献
58.
Kernel deconvolution of stochastic volatility models 总被引:2,自引:0,他引:2
Fabienne Comte 《时间序列分析杂志》2004,25(4):563-582
Abstract. In this paper, we study the problem of the nonparametric estimation of the function m in a stochastic volatility model h t = exp( X t /2λ) ξ t , X t = m ( X t −1 ) + η t , where ξ t is a Gaussian white noise. We show that the model can be written as an autoregression with errors-in-variables. Then an adaptation of the deconvolution kernel estimator proposed by Fan and Truong [ Annals of Statistics , 21, (1993) 1900] estimates the function m with the optimal rate, which depends on the distribution of the measurement error. The rates vary from powers of n to powers of ln( n ) depending on the rate of decay near infinity of the characteristic function of this noise. The performance of the method are studied by some simulation experiments and some real data are also examined. 相似文献
59.
通过适当变换,将一类含多个核的非线性奇异积分方程归结为一个与之等价的积分方程组,组中的每个方程仅含一个核。于是通过研究方程组来讨论原方程的诸多可解性问题,例如给出解的存在和唯一性定理。 相似文献
60.
《国际聚合物材料杂志》2012,61(14):1091-1101
The melt flow behavior and thermal properties of low-density polyethylene (LDPE)/palm kernel shell (PKS) composites were studied. Polyethylene acrylic acid (PEAA) was used as a compatibilizer in the composites. The results showed that the increasing of PKS loading had decreased MFI values of LDPE/PKS composites. The presence of PEAA increased the MFI values of the LDPE/PKS composites. The apparent viscosity of the composites was found to exhibit a linear relationship with the reciprocal of the temperature. Thermal properties showed that higher filler loading tended to reduce the onset temperature as the PKS possessed lower degradation temperature compared to the LDPE. The presence of the PKS in the LDPE polymeric matrix improved the thermal stability of the composites. The addition of PEAA into the composites provided better interfacial bonding between the LDPE matrix and PKS filler, while higher onset temperature and lower total weight loss were observed of LDPE/PKS composites. The activation energy of the LDPE/PKS composites was increased with increasing filler loading. At similar filler loading, the presence of PEAA increased the activation energy of the LDPE/PKS composites. 相似文献