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981.
A note on fast Fourier transforms for nonequispaced grids 总被引:1,自引:0,他引:1
Gabriele Steidl 《Advances in Computational Mathematics》1998,9(3-4):337-352
In this paper, we are concerned with fast Fourier transforms for nonequispaced grids. We propose a general efficient method
for the fast evaluation of trigonometric polynomials at nonequispaced nodes based on the approximation of the polynomials
by special linear combinations of translates of suitable functions ϕ. We derive estimates for the approximation error. In particular, we improve the estimates given by Dutt and Rokhlin [7].
As a practical consequence, we obtain a criterion for the choice of the parameters involved in the fast transforms.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
982.
983.
L. E. Wedgewood 《Rheologica Acta》1993,32(4):405-417
The Gaussian closure method and Brownian dynamics simulations have been used to calculate the shear material properties of a dilute solution of Hookean dumbbells with internal viscosity. Results for the zero-shear-rate material properties and small amplitude oscillatory shear material properties have been found analytically, and numerical results for the steady state shear material properties are also presented. Two interpretations of the stress tensor are investigated and results are compared. Brownian dynamics simulations are used to obtain material properties of the Hookean dumbbell with internal viscosity without approximations. These simulation results are compared with the perturbation solution of Booij and van Wiechen as well as with a new Gaussian closure solution. Also presented are the contracted distribution functions as derived from the Gaussian closure method and from Brownian dynamics simulations. 相似文献
984.
This paper studies the heavy-traffic behavior of a closed system consisting of two service stations. The first station is
an infinite server and the second is a single server whose service rate depends on the size of the queue at the station. We
consider the regime when both the number of customers, n, and the service rate at the single-server station go to infinity while the service rate at the infinite-server station is
held fixed. We show that, as n→∞, the process of the number of customers at the infinite-server station normalized by n converges in probability to a deterministic function satisfying a Volterra integral equation. The deviations of the normalized
queue from its deterministic limit multiplied by √n converge in distribution to the solution of a stochastic Volterra equation.
The proof uses a new approach to studying infinite-server queues in heavy traffic whose main novelty is to express the number
of customers at the infinite server as a time-space integral with respect to a time-changed sequential empirical process.
This gives a new insight into the structure of the limit processes and makes the end results easy to interpret. Also the approach
allows us to give a version of the classical heavy-traffic limit theorem for the G/GI/∞ queue which, in particular, reconciles the limits obtained earlier by Iglehart and Borovkov.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
985.
986.
G. Kjellström 《Journal of Optimization Theory and Applications》1991,69(1):185-187
This contribution to the debate on Monte Carlo optimization methods shows that there exist techniques that may be useful in many technical applications. 相似文献
987.
This paper is the continuation of [1] in which complex symmetries of distributions and their covariance operators are investigated. Here we also study the most general quaternion symmetries of random vectors. Complete classification theorems on these symmetries are proved in terms of covariance operator spectra. 相似文献
988.
J. P. Crenn 《International Journal of Infrared and Millimeter Waves》1993,14(10):1947-1973
The propagation of the HE11 mode and Gaussian beams in hollow oversized circular waveguides is analyzed using optical theories. Different types of waveguides are considered : hollow dielectric or conducting waveguides, dielectric-lined waveguides, corrugated waveguides. General formulas are derived which give the power transmission through these different guides. The best wall materials and structures are determined from a comparison of the waveguide transmissions, at the infrared and millimeter wavelengths. The question of the coupling between the HE11 mode and Gaussian beams is discussed and from a review of coupling coefficients derived before, an optimum value is pointed out. The problem of matching a Gaussian beam into circular waveguides in order to achieve the maximum power transmission is analyzed. These results are of interest for infrared lasers or waveguide applications and for Electron Cyclotron Wave (ECW) systems at the millimeter wavelength. 相似文献
989.
A newly developed semiempirical method, “the INDO-MO model with s-p-d separation” is introduced. Based on the assumption of the equivalent basis functions in the set for each angular-momentum quantum number, the average type electronic repulsion integrals of 3d orbitals are suggested. Similar to our former s-p-d separation CNDO-MO formulation, the proportionality factor K01 for the bonding parameter for each period of the periodic table is proposed for our method of semiempirical calculation. 相似文献
990.
§1.IntroductionandBackground ThedistributiontheoryoverinfinitedimensionalGaussianspacehasbeendevelopedintwodirections:Givenadenselydefinednon-negativeselfadjointoperatorAintheHilbertspaceL2(R),bythewell-knownisomorphismbetween(L2),theHilbertspaceofsquarei… 相似文献