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31.
Axially symmetric space-time is considered in the presence of cosmic string source and thick domain walls in the frame work
of a scale-covariant theory of gravitation. A relation between metric potential is assumed to get a determinate solution of
the field equations of this theory. In this particular case, it is observed that the geometric (Nambu) string p-string (Takabayasi
string) and Reddy string do not survive. It is also seen that the stiff (self-gravitating) domain walls do not exist in this
theory. 相似文献
32.
Direct observation of the antiferro (AF) magnetic domain structures of a NiO (0 0 1) surface is found to be possible using a spectroscopy photoelectron low-energy electron microscope (SPELEEM) and a commercial UV Hg excitation light source without using any polarizers. The principle is based on the magnetic linear dichroism (MLD) effect, where different domain contrasts are produced according to the relative angle between the antiferromagnetic axis and the linearly polarized light. The observed AF magnetic domain structures are strongly affected by both bulk AF magnetic domain structures and the stresses induced during the sample cleaving process. Moreover, the AF magnetic domain structures are found to be irreversible when the sample is heated to over its Néel temperature and then cooled. The possibility of imaging AF magnetic domain structures without using synchrotron radiation or a polarizer is attractive. 相似文献
33.
The stability and convergence rate of coupled atomistic-continuum methods are studied analytically and numerically. These methods couple a continuum model with molecular dynamics through the exchange of boundary conditions in the continuum-particle overlapping region. Different coupling schemes, including velocity–velocity, flux–velocity, velocity–flux and flux–flux, are studied. It is found that the velocity–velocity and flux–velocity schemes are stable. The flux–flux scheme is weakly unstable. The stability of the velocity–flux scheme depends on the parameter Tc which is the length of the time interval between successive exchange of boundary conditions. It is stable when Tc is small and unstable when Tc is large. For steady-state problems, the flux–velocity scheme converges faster than the other coupling schemes. 相似文献
34.
Omar Ramadan 《International Journal of Infrared and Millimeter Waves》2005,26(12):1757-1770
Unconditionally stable formulations of the anisotropic perfectly matched layer (APML) are presented for truncating double
negative (DNG) meta-material finite difference time domain (FDTD) grids. In the proposed formulations, the Z-transform theory
is employed in the alternating direction implicit FDTD (ADI-FDTD) scheme to obtain update equations for the field components
in the DNG meta-material domains. Numerical examples carried out in one dimensional Lorentzian type DNG meta-material domains
are included to show the validity of the proposed formulations. 相似文献
35.
36.
As a leading statistician in extreme value theory, Professor Laurens de Haan has made significant contribution in both probability
and statistics of extremes. In honor of his 70th birthday, we review testing issues in extremes, which include research done
by Professor Laurens de Haan and many others. In comparison with statistical estimation in extremes, research on testing has
received less attention. So we also point out some practical questions in this direction.
相似文献
37.
38.
本研究首先利用先本体预聚后溶液扩散链聚合的两步法合成了基于MDl,乙二胺和聚已二酸丁二醇酯(分子量1975和1228)的两系列嵌段聚酯型聚脲氨酯(PUU)弹性体,接着用元素分析,力学试验,GPC,IR,WAXD和SEM等技术对样品进行了全面表征.结果表明:PUU材料具有优异的力学性能.由WAXD和SEM研究发现:PUU中的软、硬段都是部分结晶的,晶体的尺寸依赖于硬段含量和软段分子量的变化.认为:PUU中存在着软、硬段两相微区,硬段微区被分散在由软段形成的基体中充当物理交联作用使材料表现出橡胶弹性性质. 相似文献
39.
This paper deals with the shape reconstruction of a viscous incompressible fluid driven by the Stokes flow. For the approximate solution of the ill-posed and nonlinear problem we propose a regularized Newton method. A theoretical foundation for the Newton method is given by establishing the differentiability of the initial boundary value problem with respect to the interior boundary curve in the sense of a domain derivative. The numerical examples show that our theory is useful for practical purpose and the proposed algorithm is feasible. 相似文献
40.
Ping Luo 《计算数学(英文版)》2001,(2)
1. IlltroductionA nonconforming domain decomposition method with Lagrangian multipliers was proposedin [13]. The basic idea of this method is to deal with the nonconforming of nonmatching gridsby illtroducing the Lagrangian multipliers on interfaces of subdomains and its advalltages arethat it allows not only the incompatibility of the internal variables on the interface betweensubdomains, but also the discolltinuity of the boundary variables on the common venices ofsubdomains. Thus one can c… 相似文献