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91.
Jianmin Zhou Yulin Yang Lan Zhao Xiaokun Li Renxian Zhou Xiaoming Zheng 《Frontiers of Chemistry in China》2009,4(2):142-148
Using MCM-41 as the supporter, a series of MCM-41 supported amino-palladium complexes has been prepared and characterized
by XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy), etc. The XRD and XPS results indicate that the Pd coordinates
with the -NH2 groups on the MCM-41 surface, and the structure of MCM-41 has been not damaged. Its catalytic performance for Heck arylation
of alkene with aryl iodide shows that the catalysts have high activity and stereoselectivity in 70–90°C. The product of Heck
reaction is in E form. And the effect of the preparation condition of catalyst on the catalytic performance was examined.
Translated form Chinese Journal of Organic Chemistry, 2008, 28(5) (in Chinese) 相似文献
92.
Gregory E. Fasshauer 《Advances in Computational Mathematics》1999,10(1):81-96
We show how conditionally negative definite functions on spheres coupled with strictly completely monotone functions (or functions
whose derivative is strictly completely monotone) can be used for Hermite interpolation. The classes of functions thus obtained
have the advantage over the strictly positive definite functions studied in [17] that closed form representations (as opposed
to series expansions) are readily available. Furthermore, our functions include the historically significant spherical multiquadrics.
Numerical results are also presented.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
93.
G. De Mey G. Verhenne K. Van Oost J. Landuyt 《Applied Physics A: Materials Science & Processing》1987,43(2):93-95
Non-uniform planar resistors are modelled by a small stochastic conductivity pattern superimposed on the constant mean conductivity. At first a theoretical analysis is presented giving the mean square deviation of the resistor current for a given applied voltage. The same problem is then simulated by Monte-Carlo experiments and a good agreement is observed. 相似文献
94.
An implicit function approach to constrained optimization with applications to asymptotic expansions
Robert J. Boik 《Journal of multivariate analysis》2008,99(3):465-489
In this article, an unconstrained Taylor series expansion is constructed for scalar-valued functions of vector-valued arguments that are subject to nonlinear equality constraints. The expansion is made possible by first reparameterizing the constrained argument in terms of identified and implicit parameters and then expanding the function solely in terms of the identified parameters. Matrix expressions are given for the derivatives of the function with respect to the identified parameters. The expansion is employed to construct an unconstrained Newton algorithm for optimizing the function subject to constraints.Parameters in statistical models often are estimated by solving statistical estimating equations. It is shown how the unconstrained Newton algorithm can be employed to solve constrained estimating equations. Also, the unconstrained Taylor series is adapted to construct Edgeworth expansions of scalar functions of the constrained estimators. The Edgeworth expansion is illustrated on maximum likelihood estimators in an exploratory factor analysis model in which an oblique rotation is applied after Kaiser row-normalization of the factor loading matrix. A simulation study illustrates the superiority of the two-term Edgeworth approximation compared to the asymptotic normal approximation when sampling from multivariate normal or nonnormal distributions. 相似文献
95.
Following the general idea of smoothing through convolution, we discuss schemes for smoothing hat functions on the three-directional and the four-directional mesh. The smoothing masks–which in the four-directional case are matrix masks–have the same support as the refinement mask for the hat functions. Several smoothing schemes are presented, and in some cases the smoothness properties of the smoothed functions are analysed. In particular, the results for the four-directional case follow new and original lines of research. 相似文献
96.
In this paper, we present some variants of Cauchy's method for solving non-linear equations. Analysis of convergence shows that the methods have fourth-order convergence. Per iteration the new methods cost almost the same as Cauchy's method. Numerical results show that the methods can compete with Cauchy's method. 相似文献
97.
Stephan Baier 《Advances in Mathematics》2008,219(3):952-985
In this paper, we obtain an unconditional density theorem concerning the low-lying zeros of Hasse-Weil L-functions for a family of elliptic curves. From this together with the Riemann hypothesis for these L-functions, we infer the majorant of 27/14 (which is strictly less than 2) for the average rank of the elliptic curves in the family under consideration. This upper bound for the average rank enables us to deduce that, under the same assumption, a positive proportion of elliptic curves have algebraic ranks equaling their analytic ranks and finite Tate-Shafarevich group. Statements of this flavor were known previously [M.P. Young, Low-lying zeros of families of elliptic curves, J. Amer. Math. Soc. 19 (1) (2005) 205-250] under the additional assumptions of GRH for Dirichlet L-functions and symmetric square L-functions which are removed in the present paper. 相似文献
98.
J. L. López 《Constructive Approximation》2001,17(4):535-559
Symmetric standard elliptic integrals are considered when two or more parameters are larger than the others. The distributional
approach is used to derive seven expansions of these integrals in inverse powers of the asymptotic parameters. Some of these
expansions also involve logarithmic terms in the asymptotic variables. These expansions are uniformly convergent when the
asymptotic parameters are greater than the remaining ones. The coefficients of six of these expansions involve hypergeometric
functions with less parameters than the original integrals. The coefficients of the seventh expansion again involve elliptic
integrals, but with less parameters than the original integrals. The convergence speed of any of these expansions increases
for an increasing difference between the asymptotic variables and the remaining ones. All the expansions are accompanied by
an error bound at any order of the approximation.
January 31, 2000. Date revised: May 18, 2000. Date accepted: August 4, 2000. 相似文献
99.
C. Chisholm 《Journal of Number Theory》2008,128(2):251-262
This paper discusses tetrahedra with rational edges forming a geometric progression, focussing on whether they can have rational volume or rational face areas. We examine the 30 possible configurations of such tetrahedra and show that no face of any of these has rational area. We show that 28 of these configurations cannot have rational volume, and in the remaining two cases there are at most six possible examples, and none have been found. 相似文献
100.
In this paper we analyze the existence of points of a subset S of a linear space X where the shortest distance to a point x of X with respect to an asymmetric norm q is attained (q-nearest points). Since the structure of an asymmetric norm do not provide in general uniqueness of such points—due to the fact that the separation properties in these spaces are in general weaker than in normed spaces—we develop a technique to find particular subsets of the set of q-nearest points—that we call optimal distance points—that are also optimal for the norm qs associated to the asymmetric norm. 相似文献