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排序方式: 共有383条查询结果,搜索用时 468 毫秒
351.
In this paper, linear and quadratic finite element models are devised for the three- dimensional Helmholtz problem by using a hybrid variational functional. In each element, contin- uous and discontinuous Helmholtz fields are defined with their equality enforced over the element boundary in a weak sense. The continuous field is based on the C° nodal interpolation and the discontinuous field can be condensed before assemblage. Hence, the element can readily be in- corporated seamlessly into the standard finite element program framework. Discontinuous fields constructed by the plane-wave, Bessel and singular spherical-wave solutions are attempted. Nu- merical tests demonstrate that some of the element models are consistently and considerably more accurate than their conventional counterparts. 相似文献
352.
A Comparative Study of Finite Element and Finite Difference Methods for Two-Dimensional Space-Fractional Advection-Dispersion Equation
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Guofei Pang Wen Chen & Kam Yim Sze 《advances in applied mathematics and mechanics.》2016,8(1):166-186
The paper makes a comparative study of the finite element method (FEM)
and the finite difference method (FDM) for two-dimensional fractional advection-dispersion
equation (FADE) which has recently been considered a promising tool in
modeling non-Fickian solute transport in groundwater. Due to the non-local property
of integro-differential operator of the space-fractional derivative, numerical solution of
FADE is very challenging and little has been reported in literature, especially for high-dimensional
case. In order to effectively apply the FEM and the FDM to the FADE
on a rectangular domain, a backward-distance algorithm is presented to extend the
triangular elements to generic polygon elements in the finite element analysis, and a
variable-step vector Grünwald formula is proposed to improve the solution accuracy of the conventional finite difference scheme. Numerical investigation shows that the
FEM compares favorably with the FDM in terms of accuracy and convergence rate
whereas the latter enjoys less computational effort. 相似文献
353.
354.
Chan PY Kwok WM Lam SK Chiu P Phillips DL 《Journal of the American Chemical Society》2005,127(23):8246-8247
Time-resolved resonance Raman spectroscopy was used to directly observe the reaction of the 2-fluorenylnitrenium ion with guanosine to produce a C8 intermediate species. Comparison of the Raman spectra with results of density functional theory calculations indicates the C8 intermediate forms two C=N conjugated bonds in ring 1 of the guanosine moiety. 相似文献
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358.
St. Pekárek 《Czechoslovak Journal of Physics》1973,23(1):153-154
The present paper deals with the influence of a radial magnetic field on different regions of the toroidal glow discharge and with the subsequent changes of the current-voltage characteristics. From the above it is clear that when studying the influence of a transverse magnetic field on the glow discharge it is necessary to understand that the discharge is not a homogeneous unit and the change of current-voltage characteristics involves the total sum of changes of the properties in different regions of the discharge. 相似文献
359.
Conjugate reduction of alkynones by stoichiometric [(Ph(3)P)CuH](6) or catalytic [(Ph(3)P)CuH](6) and polymethyl-hydrosiloxane proceeds to cyclization by an aldol reaction with tethered ketones to generate [small beta]-hydroxyenones with good diastereoselectivity. 相似文献
360.
We propose an ultrafast holographic Stokesmeter using a volume holographic substrate with two sets of two orthogonal gratings to identify all four Stokes parameters of the input beam. We derive the Mueller matrix of the proposed architecture and determine the constraints necessary for reconstructing the complete Stokes vector. The speed of this device is determined primarily by the channel spectral bandwidth (typically 100 GHz), corresponding to a few picoseconds. 相似文献