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981.
胡晓群 《数学的实践与认识》2007,37(6):18-23
从实证的角度,采用协整分析方法研究了1985~2004年人民币实际有效汇率变动对我国机电产品进出口的影响.实证研究结果表明,人民币实际有效汇率对我国机电产品进出口均有显著影响,但是对进口的影响作用更大;相比汇率弹性,我国机电产品的出口对国外实际收入变化的敏感性要强,而其进口对人民币实际有效汇率变化的敏感性要强于对国内实际收入变化的敏感性. 相似文献
982.
V. Lensky V. Baru J. Haidenbauer C. Hanhart A. E. Kudryavtsev U. -G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2006,27(1):37-45
We study the production amplitude for the reaction NN → NNπ up to next-to-leading order in chiral perturbation theory using a counting scheme that takes into account the large scale
introduced by the initial momentum. In particular, we investigate a subtlety that arises once the leading loop contributions
are convoluted with the NN wave functions as demanded by the non-perturbative nature of the NN interaction. We show how to properly identify the irreducible contribution of loop diagrams in such type of reaction. The
net effect of the inclusion of all next-to-leading-order loops is to enhance the leading rescattering amplitude by a factor
of 4/3, bringing its contribution to the cross-section for pp → dπ+ close to the experimental value. 相似文献
983.
The problem of determining the effective incremental responseof nonlinearly elastic composite materials given some initialprestress is of interest in numerous application areas. In particular,the case when small-amplitude elastic waves pass through a prestressedinhomogeneous structure is of great importance. Of specificinterest is how the initial finite deformation affects the microstructureand thus the subsequent response of the composite. Modellingthis effect is in general extremely difficult. In this article,we consider the simplest problem of this type where the materialis a one dimensional composite bar consisting of two distinctphases periodically distributed. Neglecting lateral contractions,the initial deformation is thus piecewise homogeneous and wecan therefore determine the incremental behaviour semi-analytically,given the constitutive behaviour (strain energy function) ofthe phases in question. We apply asymptotic homogenization theoryin the deformed configuration in order to find the effectiveresponse of the deformed material in the low-frequency limitwhere the wavelength of the propagating waves is much longerthan the characteristic length scale of the microstructure.We close by considering the arbitrary frequency case and illustratehow the initial deformation affects the location of stop bandsand pass bands of the material. Work is under way to confirmthese results experimentally. 相似文献
984.
Virtual material design is the microscopic variation of materials in the computer, followed by the numerical evaluation of
the effect of this variation on the material’s macroscopic properties. The goal of this procedure is an in some sense improved
material. Here, we give examples regarding the dependence of the effective elastic moduli of a composite material on the geometry
of the shape of an inclusion. A new approach on how to solve such interface problems avoids mesh generation and gives second
order accurate results even in the vicinity of the interface. The Explicit Jump Immersed Interface Method is a finite difference
method for elliptic partial differential equations that works on an equidistant Cartesian grid in spite of non-grid aligned
discontinuities in equation parameters and solution. Near discontinuities, the standard finite difference approximations are
modified by adding correction terms that involve jumps in the function and its derivatives. This work derives the correction
terms for two dimensional linear elasticity with piecewise constant coefficients, i.e. for composite materials. It demonstrates
numerically convergence and approximation properties of the method.
相似文献
985.
986.
An effective medium method is developed for the slightly compressible elastic media permeated with air-filled bubbles, according
to the nonlinear oscillation of the bubble, which happens when compressional wave travels through the porous media. The effective
Lame coefficients of the porous medium and the nonlinear elastic wave equation are deduced, based on the fact that the micro-unit
of the effective medium should have the same stress and strain as the micro-unit of the porous media. The linearized properties
obtained by this method are in good agreement with the results of Gaunaurd’s classic theory [Gaunaurd G.C. and überall H.,
J. Acoust. Soc. Am., 1978, 63: 1699–1711]. Furthermore, the nonlinear coefficient, which is an important property of the porous
media, can also be acquired by this method.
__________
Translated from Acta Acustica, 2006 (in Chinese) (in press) 相似文献
987.
Vasco Brattka 《Mathematical Logic Quarterly》2005,51(1):19-44
The investigation of computational properties of discontinuous functions is an important concern in computable analysis. One method to deal with this subject is to consider effective variants of Borel measurable functions. We introduce such a notion of Borel computability for single‐valued as well as for multi‐valued functions by a direct effectivization of the classical definition. On Baire space the finite levels of the resulting hierarchy of functions can be characterized using a notion of reducibility for functions and corresponding complete functions. We use this classification and an effective version of a Selection Theorem of Bhattacharya‐Srivastava in order to prove a generalization of the Representation Theorem of Kreitz‐Weihrauch for Borel measurable functions on computable metric spaces: such functions are Borel measurable on a certain finite level, if and only if they admit a realizer on Baire space of the same quality. This Representation Theorem enables us to introduce a realizer reducibility for functions on metric spaces and we can extend the completeness result to this reducibility. Besides being very useful by itself, this reducibility leads to a new and effective proof of the Banach‐Hausdorff‐Lebesgue Theorem which connects Borel measurable functions with the Baire functions. Hence, for certain metric spaces the class of Borel computable functions on a certain level is exactly the class of functions which can be expressed as a limit of a pointwise convergent and computable sequence of functions of the next lower level. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
988.
入射电子被中性原子散射过程中的库仑波描述 总被引:1,自引:0,他引:1
在前期工作的基础上,给出了有效电荷Zeff的解析形式.研究发现:有效电荷Zeff与入射电子的能量和散射角有关.我们早期工作的一个重要缺陷是:对于初、末通道,分别使用了解析的平面波和库仑波,而现有的波函数与早期工作之间的一个重要差别在于:在初通道,现有的波函数包含有入射电子与中性原子之间的短程相互作用效应,而早期文章则没有这种效应.这里使用的末态波函数与以前是相同的.当入射电子处在有效电荷库仑场的情形下,我们计算了电子入射离化氦原子的三重微分截面,并发现现有的理论计算与实验结果很好的一致. 相似文献
989.
Study of the relationship between porous ratio and effective index in nanoporous film 总被引:1,自引:0,他引:1
Yang Zhenyu Zhu Daqing Lu Dongsheng Zhao Ming Ning Na Liu Yongjun 《Optical and Quantum Electronics》2003,35(12):1133-1141
In this paper, a theory model called 'composite media in parallel' is proposed to explain the connection between the porous ratio and effective index of the nanoporous film. This model comes from theory of composite media's effective dielectric constant in solid material field. From this model, a function relationship between the porous ratio and effective index of the nanoporous film is obtained. And the Finite Difference Time Domain (FDTD) method is used to construct the model of nanoporous film, simulate the propagation of lightwave in the film and calculate some effective indices according to different ratios of pore. Compared with Maxwell Garnett theory model and Bruggeman theory model, it is found that the function curve based on the composite media in parallel model is most consistent with the results simulated by FDTD method. 相似文献
990.
CW/COIL照射LF 6M铝合金板热耦合效应研究 总被引:5,自引:1,他引:4
用热电偶计和热象仪探测靶升温,积分球-光电转换放大测量反射率,金相显微图象数据处理和电子天平称量获得激光照射质量和熔融质量等诊断技术,对连续波(波长1.315μm)氧碘化学激光(CW/COIL),与LF6M板相互作用的有效热耦合系数α_(eff)和热耦合率α_a,进行了实验测量。当照射靶面激光强度I≈(0.60~1.13)kW/cm ̄2和发生熔融时,α_(eff)≈0.16~0.18和α_a≈0.20~0.25(工业商品铝表面);α_(eff)≈0.11和α_a≈0.12~0.14(表面加工粗糙度16μm)。当I≈0.07~0.11kw/cm ̄2和表面不发生熔融时,α_a≈0.09~0.10(工业商品铝表面),α_a≈0.02~0.03(表面加工粗糙度1.6μm)。 相似文献