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排序方式: 共有6067条查询结果,搜索用时 31 毫秒
961.
V.G.Yakhno 《计算机、材料和连续体(英文)》2011,21(1):1-16
Homogeneous non-dispersive anisotropic materials, characterized by a positive constant permeability and a symmetric positive definite conductivity tensor, are considered in the paper. In these anisotropic materials, the electric and magnetic dyadic Green's functions are defined as electric and magnetic fields arising from impulsive current dipoles and satisfying the time-dependent Maxwell's equations in quasi-static approximation. A new method of deriving these dyadic Green's functions is suggested in the paper. This method consists of several steps: equations for electric and magnetic dyadic Green's functions are written in terms of the Fourier modes; explicit formulae for the Fourier modes of dyadic Green's functions are derived using the matrix transformations and solutions of some ordinary differential equations depending on the Fourier parameters; the inverse Fourier transform is applied to obtained formulae to find explicit formulae for dyadic Green's functions. 相似文献
962.
部分二值逻辑中Sheffer函数的构造与判定算法 总被引:4,自引:2,他引:2
在深入研究部分二值逻辑中Sheffer函数的基础上,根据部分二值逻辑中准完备集的最小覆盖,提出了一种高效地构造部分二值逻辑中Sheffer函数的算法,此算法能够构造出部分二值逻辑中的全部Sheffer函数,在构造算法的基础上,进一步提出了一种部分二值逻辑中Sheffer函数的判定算法,此算法和传统判定算法相比,避免了繁琐的计算,可以说是一种较简单的判定算法。 相似文献
963.
分别讨论了不同的统计分析方法和预测模型在腐蚀研究中的应用,这其中包括多元线性回归分析、灰色模型GM(1,1)与灰色关联性分析、人工神经网络分析以及剂量响应函数模型。在此基础上,引入了一种源于社会科学的全新的分析方法--多层线性模型(HLM),并对多层线性模型在腐蚀研究中的应用尤其是腐蚀纵向研究进行了可行性的讨论。 相似文献
964.
Antonín Mikš Jiří Novák Pavel Novák 《International journal for numerical methods in engineering》2010,82(4):525-536
The quadrature of general, highly oscillatory integrals is a relatively complicated computational problem that occurs in a wide range of practical applications, e.g. in physics, chemistry, and image analysis. It is often necessary to use a high number of nodal points with classical quadrature formulas in order to achieve a required accuracy of numerical integration of rapidly oscillating functions. However, an increase in integration points leads to a larger computational time. Our work describes and analyses a method for numerical integration of rapidly oscillating functions, which enables to obtain the required accuracy with a smaller number of nodal points than classical integration rules and with a relatively simple integration formula. The proposed method is generally suitable for integration of rapidly oscillating functions in various applications. The method is demonstrated in examples of calculation of the diffraction integral in optics, where the integrand is often a rapidly oscillatory function. The results can be readily adapted to similar problems from other fields. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
965.
F. Szelecsényi C. Vermeulen Z. Kovács T.N. van der Walt 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(20):3306-3314
Cross sections of proton-induced nuclear reactions on highly enriched 192Os were measured up to 66 MeV by using the stacked-foil irradiation technique. Excitation functions are presented for the reactions 192Os(p,n)192Ir, 192Os(p,3n)190Ir, 192Os(p,4n)189Ir, 192Os(p,5n)188Ir, 192Os(p,6n)187Ir and 192Os(p,7n)186Ir. No earlier experimental cross-section data could be found in the literature except for the 192Os(p,n)192Ir process. Our new experimental results are compared with theoretical predictions by means of the theoretical model code ALICE/ASH. Integral thick-target yield calculations were also performed for the 192Os(p,n)192Ir and 192Os(p,3n)190Ir reactions to evaluate the 190Ir contamination level, as a function of energy, in the case of 192Ir productions. 相似文献
966.
Although visuospatial short-term memory tasks have been found to engage more executive resources than do their phonological counterparts, it remains unclear whether this is due to intrinsic differences between the tasks or differences in participants’ experience with them. The authors found 11-year-olds’ performances on both visual short-term and working memory tasks to be more greatly impaired by an executive suppression task (random number generation) than were those of 8-year-olds. Similar findings with adults (e.g., Kane & Engle, 2000) suggest that the imposition of a suppression task may have overloaded the older children’s executive resources, which would otherwise be used for deploying strategies for performing the primary tasks. Conversely, the younger children, who probably never had the capacity or know-how to engage these facilitative strategies in the first place, performed more poorly in the single task condition but were less affected in the dual task condition. These findings suggest that differences in the children’s ability to deploy task-relevant strategy are likely to account for at least part of the executive resource requirements of visual memory tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
967.
The development of cognitive skills and gains in academic school readiness for children from low-income families. 总被引:1,自引:0,他引:1
Welsh Janet A.; Nix Robert L.; Blair Clancy; Bierman Karen L.; Nelson Keith E. 《Canadian Metallurgical Quarterly》2010,102(1):43
This study examined developmental associations between growth in domain-general cognitive processes (working memory and attention control) and growth in domain-specific skills (emergent literacy and numeracy) across the prekindergarten year and their relative contributions to kindergarten reading and math achievement. One hundred sixty-four Head Start children (44% African American or Latino; 57% female) were followed longitudinally. Path analyses revealed that working memory and attention control predicted growth in emergent literacy and numeracy skills during the prekindergarten year and that growth in these domain-general cognitive skills made unique contributions to the prediction of kindergarten math and reading achievement, controlling for growth in domain-specific skills. These findings extend research highlighting the importance of working memory and attention control for academic learning, demonstrating the effects in early childhood, prior to school entry. Implications of these findings for prekindergarten programs are discussed, particularly those designed to reduce the school readiness gaps associated with socioeconomic disadvantage. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
968.
航空磁探中,将潜艇目标以磁偶极子模型代替。针对目标信号信噪比较低的情况,利用正交基分解检测算法,大幅提高了水中磁性目标信号的信噪比,有效地检测到磁性目标。采用双L型航空磁探方法,确定磁性目标的运动位置、航向和航速。仿真试验表明,该方法具有一定的工程应用价值。 相似文献
969.
为了克服常规希尔伯特—黄变换(HHT)的缺陷,消除常规经验模态分解(EMD)产生的本征模态函数分量(IMF)中混叠的振荡模式,本文运用改进HHT,即通过引进小波包变换,首先将信号分解成-系列窄带信号,然后对这些窄带信号进行EMD获得-些IMF分量,再根据相关系数法,保留需要的IMF分量,去除虚假的IMF分量,最后进行HHT求取瞬时频率,得到改进HHT谱。改进HHT摆脱了小波变换中的海森堡测不准原理的限制,以及常规HHT模态混叠对分析的干扰。虽然改进HHT谱高频成分存在跳跃现象,但都围绕在真实频率值周围,并且较小波时频图的频带窄很多,能够反映信号的真实频率特性。数值模拟与实际地震记录处理结果证明了改进HHT的可行性。 相似文献
970.