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排序方式: 共有6459条查询结果,搜索用时 31 毫秒
31.
本文研究并比较了分别以8-羟基喹啉和巯基苯骈噻唑为萃取剂,以活性硅胶为载体的柱式萃取色谱法对环境水中Zn、Cu、Pb、Cd、Fe、Co、Ni和Mn的最佳富集和洗脱条件。实验证明,后者明显优于前者。以巯基苯骈噻唑为萃取剂的色谱柱对金属元素的吸附具有快速、完全、寿命长和重现性好等特点。在pH=7~8之间回收率可达98%以上,富集倍数为200倍。 相似文献
32.
A. E. Chmel’ 《Journal of Applied Spectroscopy》1997,64(4):566-568
Using Raman spectroscopy, a quantitative analysis of the distribution of OH− ions on the boundary between a bearing pipe and a glass layer deposited from chlorides in billets for quartz fiber light
guides is carried out. Water penetrated into the light-reflecting shell to a depth of several tenths of a millimeter, depending
on the composition of the doping layer (i.e., ultimately on the temperature of the depsoition process).
A. F. Ioffe Physical-Technical Institute, Academy of Sciences of Russia, 26, Politekhnicheskaya St., St. Petersburg, 194021,
Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 548–550, July–August, 1997. 相似文献
33.
转动喇曼散射截面的群论计算 总被引:1,自引:1,他引:0
本文利用群链U(4)U(3)O(3)描述双原子分子N_2和O_2振转谱的对称性质,并利用群论方法计算了N_2和O_2分子转动喇曼散射的跃迁矩阵元,给出了它们的转动喇曼散射的截面。结果与实验较好地符合。 相似文献
34.
35.
Zi‐Cai Li Tzon‐Tzer Lu Hung‐Tsai Huang Alexander H.‐D. Cheng 《Numerical Methods for Partial Differential Equations》2007,23(1):93-144
In this article we survey the Trefftz method (TM), the collocation method (CM), and the collocation Trefftz method (CTM). We also review the coupling techniques for the interzonal conditions, which include the indirect Trefftz method, the original Trefftz method, the penalty plus hybrid Trefftz method, and the direct Trefftz method. Other boundary methods are also briefly described. Key issues in these algorithms, including the error analysis, are addressed. New numerical results are reported. Comparisons among TMs and other numerical methods are made. It is concluded that the CTM is the simplest algorithm and provides the most accurate solution with the best numerical stability. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献
36.
Francisco‐Javier Sayas 《Numerical Methods for Partial Differential Equations》2003,19(5):555-570
This article presents and analyzes a simple method for the exterior Laplace equation through the coupling of finite and boundary element methods. The main novelty is the use of a smooth parametric artificial boundary where boundary elements fit without effort together with a straight approximate triangulation in the bounded area, with the coupling done only in nodes. A numerically integrated version of the algorithm is also analyzed. Finally, an isoparametric variant with higher order is proposed. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 555–570, 2003 相似文献
37.
Block-diagonalization of sparse equivariant discretization matrices is studied. Such matrices typically arise when partial
differential equations that evolve in symmetric geometries are discretized via the finite element method or via finite differences.
By considering sparse equivariant matrices as equivariant graphs, we identify a condition for when block-diagonalization via
a sparse variant of a generalized Fourier transform (GFT) becomes particularly simple and fast.
Characterizations for finite element triangulations of a symmetric domain are given, and formulas for assembling the block-diagonalized
matrix directly are presented. It is emphasized that the GFT preserves symmetric (Hermitian) properties of an equivariant
matrix.
By simulating the heat equation at the surface of a sphere discretized by an icosahedral grid, it is demonstrated that the
block-diagonalization is beneficial. The gain is significant for a direct method, and modest for an iterative method.
A comparison with a block-diagonalization approach based upon the continuous formulation is made. It is found that the sparse
GFT method is an appropriate way to discretize the resulting continuous subsystems, since the spectrum and the symmetry are
preserved.
AMS subject classification (2000) 43A30, 65T99, 20B25 相似文献
38.
Anton Deitmar 《数学年刊B辑(英文版)》2007,28(4):463-474
Abstract In this paper, Lefschetz formulae for torus actions on p-adic groups are proven. These are similar to comparable formulae for real Lie groups. Applications lie in the realm of dynamical
zeta functions. 相似文献
39.
Two methods for sampling and concentration of volatile organic compounds are reported. In the first method, traps coated with a very thick film (ca. 100 μm) of cross-linked silicone stationary phase are employed. Such thick films can be prepared with a modified dynamic coating procedure, which is briefly described. The low phase ratio traps can be utilized for enrichment of volatiles from gaseous as well as aqueous matrices. The second technique is based on chromatographic evaporation of a solvent in a capillary tube, where the process is sustained by a repeated sample injection and a cyclic flow reversal. In this way, large solvent volumes can be handled by a small volume system. Under optimal conditions, when using a solvent barrier, quantitative recovery is possible even for compounds of comparatively high volatility. Another important application of the technique is extraction of trace components from gases such as headspace samples, polluted air, etc. 相似文献
40.
Zhangxin Chen 《Numerical Methods for Partial Differential Equations》2002,18(2):203-217
In this article we prove uniform convergence estimates for the recently developed Galerkin‐multigrid methods for nonconforming finite elements for second‐order problems with less than full elliptic regularity. These multigrid methods are defined in terms of the “Galerkin approach,” where quadratic forms over coarse grids are constructed using the quadratic form on the finest grid and iterated coarse‐to‐fine intergrid transfer operators. Previously, uniform estimates were obtained for problems with full elliptic regularity, whereas these estimates are derived with less than full elliptic regularity here. Applications to the nonconforming P1, rotated Q1, and Wilson finite elements are analyzed. The result applies to the mixed method based on finite elements that are equivalent to these nonconforming elements. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 203–217, 2002; DOI 10.1002/num.10004 相似文献