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991.
Jianyuan Tang Lei Wang Gang Liu Yan Liu Yazhuo Hou Wenxiang Zhang Mingjun Jia Werner R. Thiel 《Journal of molecular catalysis. A, Chemical》2009,313(1-2):31-37
A hybrid mesoporous SBA-15 material (2a) containing an oxodiperoxo tungsten complex of the type [WO(O2)2L] (L = pyrazolylpyridine) was synthesized by a post-grafting route. The organic–inorganic hybrid catalyst was characterized by means of XRD, N2 adsorption–desorption and FT-IR. The catalytic property of 2a in the epoxidation of cyclooctene with H2O2 as the oxidant was investigated in comparison with other three kinds of hybrid tungsten containing SBA-15 materials bearing ethylenediamine, imidazole or 4,4′-bipyridine ligands. It was found that all oxodiperoxo tungsten catalysts were active at the reaction temperature of 55 °C with CH3CN as solvent. However, only the catalyst with the pyrazolylpyridine ligand showed good recoverability and relatively high stability against leaching of active tungsten species. Moreover, this catalyst showed very high efficiency for H2O2 utilization, and its catalytic activity could be further improved by using solvent mixtures of CH3CN and CH3COOH. 相似文献
992.
Multiplication operators in weighted Banach (and locally convex) spaces of functions holomorphic in the unit disc are well
known. In this note we investigate the connection between power boundedness, mean ergodicity and uniform mean ergodicity of
such operators.
Received: 13 October 2008, Revised: 18 November 2008 相似文献
993.
This paper analyzes a generic class of two-node queueing systems. A first queue is fed by an on–off Markov fluid source; the
input of a second queue is a function of the state of the Markov fluid source as well, but now also of the first queue being
empty or not. This model covers the classical two-node tandem queue and the two-class priority queue as special cases. Relying
predominantly on probabilistic argumentation, the steady-state buffer content of both queues is determined (in terms of its
Laplace transform). Interpreting the buffer content of the second queue in terms of busy periods of the first queue, the (exact)
tail asymptotics of the distribution of the second queue are found. Two regimes can be distinguished: a first in which the
state of the first queue (that is, being empty or not) hardly plays a role, and a second in which it explicitly does. This
dichotomy can be understood by using large-deviations heuristics.
This work has been carried out partly in the Dutch BSIK/BRICKS project. 相似文献
994.
In this paper, we consider a parallel machine environment when all jobs have the same processing time and arbitrary release dates and deadlines of the jobs are given. We suppose that the available number of machines, which can be used simultaneously, may vary over time. The aim is to construct a feasible schedule in such a way that the maximal number of simultaneously used machines is minimal. We give a polynomial algorithm for this problem. 相似文献
995.
Stephan Dahlke Massimo Fornasier Miriam Primbs Thorsten Raasch Manuel Werner 《Numerical Methods for Partial Differential Equations》2009,25(6):1366-1401
This article is concerned with adaptive numerical frame methods for elliptic operator equations. We show how specific noncanonical frame expansions on domains can be constructed. Moreover, we study the approximation order of best n‐term frame approximation, which serves as the benchmark for the performance of adaptive schemes. We also discuss numerical experiments for second order elliptic boundary value problems in polygonal domains where the discretization is based on recent constructions of boundary adapted wavelet bases on the interval. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009 相似文献
996.
The aim of this paper is the numerical treatment of a boundary value problem for the system of Stokes’ equations. For this we extend the method of approximate approximations to boundary value problems. This method was introduced by Maz’ya (DFG-Kolloquium des DFG-Forschungsschwerpunktes Randelementmethoden, 1991) and has been used until now for the approximation of smooth functions defined on the whole space and for the approximation of volume potentials. In the present paper we develop an approximation procedure for the solution of the interior Dirichlet problem for the system of Stokes’ equations in two dimensions. The procedure is based on potential theoretical considerations in connection with a boundary integral equations method and consists of three approximation steps as follows. In a first step the unknown source density in the potential representation of the solution is replaced by approximate approximations. In a second step the decay behavior of the generating functions is used to gain a suitable approximation for the potential kernel, and in a third step Nyström’s method leads to a linear algebraic system for the approximate source density. For every step a convergence analysis is established and corresponding error estimates are given. 相似文献
997.
This contribution is concerned with mixed finite element formulations for modeling piezoelectric beam and shell structures. Due to the electromechanical coupling, specific deformation modes are joined with electric field components. In bending dominated problems incompatible approximation functions of these fields cause incorrect results. These effects occur in standard finite element formulations, where interpolation functions of lowest order are used. A mixed variational approach is introduced to overcome these problems. The mixed formulation allows for a consistent approximation of the electromechanical coupled problem. It utilizes six independent fields and could be derived from a Hu-Washizu variational principle. Displacements, rotations and the electric potential are employed as nodal degrees of freedom. According to the Timoshenko theory (beam) and the Reissner-Mindlin theory (shell), the formulations account for constant transversal shear strains. To incorporate three dimensional constitutive relations all transversal components of the electric field and the strain field are enriched by mixed finite element interpolations. Thus the complete piezoelectric coupling is appropriately captured. The common assumption of vanishing transversal stress and dielectric displacement components is enforced in an integral sense. Some numerical examples will demonstrate the capability of the presented finite element formulation. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
998.
Smart materials by definition, are solids, fluids or gases which react independently on changing external conditions and modify one or more properties without external stimuli. Sensu lato an external energy can produce the reaction, such as stress, temperature, moisture, pH, magnetic or electric fields. The distinguishing characteristic for electroactive polymers (EAP) is, that they react with a deformation by the application of an electrical field. This contribution presents a nonlinear electro-viscoelastic model for dielectric elastomers and its finite element implementation. This type of smart materials belong to the group of EAP's and consists out of soft elastomer between compliant and conducting electrodes. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
999.
The influence of the complexity of hydromount-models on the results in full vehicle simulation is studied. In particular, a Kelvin-Voigt model, a linear lever model and a non-linear model are assessed with respect to their predictive capabilities as compared to the necessary parameterization and computation efforts. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
1000.
Hans G. Feichtinger Werner Kozek Franz Luef 《Applied and Computational Harmonic Analysis》2009,26(2):230-248
Gabor frames for signals over finite Abelian groups, generated by an arbitrary lattice within the finite time–frequency plane, are the central topic of this paper. Our generic approach covers both multi-dimensional signals as well as non-separable lattices, and in fact the multi-window case as well. Our generic approach includes most of the fundamental facts about Gabor expansions of finite signals for the case of product lattices, as they have been given by Qiu, Wexler–Raz or Tolimieri–Orr, Bastiaans and Van-Leest and others. In our presentation the spreading representation of linear operators between finite-dimensional Hilbert space as well as a symplectic version of Poisson's summation formula over the finite time–frequency plane are essential ingredients. They bring us to the so-called Fundamental Identity of Gabor Analysis. In addition, we highlight projective representations of the time–frequency plane and its subgroups and explain the natural connection to twisted group algebras. In the finite-dimensional setting discussed in this paper these twisted group algebras are just matrix algebras and their structure provides the algebraic framework for the study of the deeper properties of finite-dimensional Gabor frames, independent of the structure theory theorem for finite Abelian groups. 相似文献