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151.
Guangxin Wu Jieyu Zhang Yongquan Wu Qian Li Kuochih Chou Xinhua Bao 《Applied Physics A: Materials Science & Processing》2011,102(3):739-745
With density-functional theory, the dissociative chemisorptions and diffusion processes of hydrogen on both pure and La-doped
Mg(0001) surfaces are studied. Calculation results show that the energy barrier obtained for hydrogen dissociation on the
La-doped Mg(0001) surface is smaller due to back-donated bonding between molecular H2 and doped La atom. The obtained diffusion barriers (0.8–0.22 eV) imply a fast motion of atomic H on La-doped Mg(0001) surface. 相似文献
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153.
Apparent correlations are found between the N-H chemical shifts of congeneric series of compounds and the dipole moments of the molecules, such as lactams and thiolactams, cyclic ureas and thioureas. When there is a high degree of correlation, either the N-H chemical shift or the dipole moment of the molecule can be used as an electronic parameter in correlating the biological activity with the chemical structure. In a series of substituted salicylaldehydes the Hammett σ constant gives better correlation with the biological activity than the O-H chemical shift. This is probably due to the anisotropic effect of the substituent besides the electronic effect. Other factors affecting the N-H chemical shift, e.g. intramolecular hydrogen-bonding of nitrosoureas and the deshielding effect of a benzene ring, in o-phenyleneureas are also presented. In spite of the limitations, the chemical shifts of many compounds can be obtained very easily, therefore, their uses in structure-activity correlations deserve further investigation. 相似文献
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157.
Summary. We analyze V–cycle multigrid algorithms for a class of perturbed problems whose perturbation in the bilinear form preserves the convergence
properties of the multigrid algorithm of the original problem. As an application, we study the convergence of multigrid algorithms
for a covolume method or a vertex–centered finite volume element method for variable coefficient elliptic problems on polygonal
domains. As in standard finite element methods, the V–cycle algorithm with one pre-smoothing converges with a rate independent of the number of levels. Various types of smoothers
including point or line Jacobi, and Gauss-Seidel relaxation are considered.
Received August 19, 1999 / Revised version received July 10, 2000 / Published online June 7, 2001 相似文献
158.
Two novel systems are proposed to perform the electro-optic (EO) mapping of the electric-field strength close to electrode structure using CW laser diodes. By these systems, mappings of both static (DC) and high-frequency electric-field can be obtained. For the static field, the field is chopped to increase the sensitivity performance. For the high-frequency field, an intensity modulation laser, instead of a pulse laser, is used to perform the mapping measurement in frequency domain, instead of in time domain. This approach greatly simplifies the system. An experiment set-up using a vertical cavity surface emitted laser diode (VCSEL) of a wavelength 850 nm and its mapping results for a coplanar waveguide (CPW) with the signal frequency around 1 GHz are reported. 相似文献
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Using the notations of convergent series of sets and convergent products of relations, general open mapping theorems are presented which encompass classical results of Banach, Ptak, Khanh, and others. 相似文献