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排序方式: 共有271条查询结果,搜索用时 15 毫秒
61.
62.
We develop a new method for the efficient calculation of solenoidal vector fields on general regions. The method takes advantage of fast direct methods and uses boundary integral equations to satisfy boundary conditions. For the latter we give an effective scheme for computing far-field boundary influences (based on discrete charges). Examples and numerical results are given. The method is applicable to incompressible Navier-Stokes calculations. 相似文献
63.
A. Resta J. Blomquist J. Gustafson H. Karhu A. Mikkelsen E. Lundgren P. Uvdal J.N. Andersen 《Surface science》2006,600(24):5136-5141
The catalytic cracking of ethanol on clean and oxygen precovered Rh(1 1 1) surfaces has been studied by a combination of synchrotron based high-resolution core level spectroscopy and surface infrared spectroscopy. On the clean surface the decomposition of ethanol occurs without any formation of atomic oxygen. The presence of oxygen on the surface changes the reactivity significantly and acetate (CH3COO) was identified as an important surface intermediate in the ethanol oxidation. 相似文献
64.
Sven-Åke Gustafson 《BIT Numerical Mathematics》1984,24(4):510-519
In this paper we study the problem of evaluating the sum of a power series whose terms are given numerically with a moderate accuracy. For a large class of divergent series a sum may be defined using analytic continuation. This sum may be estimated using the values of a finite number of terms. However, it is established here that the accuracy of this estimate will generally deteriorate if we use an ever-growing number of terms. A result on the stability of product quadrature is also obtained as a corollary of our main stability theorem.Dedicated to professor Germund Dahlquist, on the occasion of his 60th birthday 相似文献
65.
Karl Gustafson 《Linear and Multilinear Algebra》1994,37(1):139-159
The purpose of the present paper is to survey, from a historical perspective and including some new results, a theory which I will call operator trigonometry. This theory, which is little known, is closely associated with the numerical range W(A) of an operator A. Among the new results is a beautiful connection to numerical linear algebra, in which gradient descent and conjugate gradient convergence rates are shown to be trigonometric. 相似文献
66.
We describe a balanced heterodyne detection method for a Sagnac interferometer that uses a polarization-dependent beam splitter. The signal and the local oscillator are orthogonally polarized components of a single laser beam, permitting the detection of the signal by subtraction of two photocurrents produced in appropriate polarization projections. Using this scheme, we experimentally demonstrate a phase measurement with a sensitivity of 9x10(-10) rad/ radicalHz. The measurement is robust in the presence of laser frequency noise, as a result of preserving the common-path nature of the Sagnac interferometer, and of laser-amplitude noise, as a result of balanced detection. 相似文献
67.
Ed Ash Brian Eaton Karl Gustafson 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1990,41(4):558-578
Summary Computational methods and comparison theory enable, when combined, an enhanced capability for counting the number of solutions in combustion equations. Very good lower bounds for the last turning point reveal a stable high temperature explosion branch for very small positive exothermicity. 相似文献
68.
Stierle A Kasper N Dosch H Lundgren E Gustafson J Mikkelsen A Andersen JN 《The Journal of chemical physics》2005,122(4):44706
The oxidation of Pd(100) and the formation of PdO was studied in situ using surface x-ray diffraction. A bulklike, epitaxial PdO film is formed at oxygen partial pressures beyond 1 mbar and sample temperatures exceeding 650 K. The main orientation is PdO(001)/Pd(001), based upon bulk reflections from the PdO film. By comparing with measurements from the Pd crystal truncation rods, we estimate an rms surface roughness of 6 A, in good agreement with previous high pressure scanning tunneling microscopy measurements. Finally, we observed the transformation from the (radical5 x radical5) surface oxide to PdO bulk oxide at 675 K and 50 mbar O(2) pressure. 相似文献
69.
70.
Mikael Borg Catherine Stampfl Anders Mikkelsen Johan Gustafson Edvin Lundgren Matthias Scheffler Jesper N Andersen 《Chemphyschem》2005,6(9):1923-1928
The structural phases of Al(x)Na(1-x) surface alloys have been investigated theoretically and experimentally. We describe the system using a lattice-gas Hamiltonian, determined from density functional theory, together with Monte Carlo (MC) calculations. The obtained phase diagram reproduces the experiment on a quantitative level. From calculation of the (configurational) density of states by the recently introduced Wang-Landau MC algorithm, we derive thermodynamic quantities, such as the free energy and entropy, which are not directly accessible from conventional MC simulations. We accurately reproduce the stoichiometry, as well as the temperature at which an order-disorder phase transition occurs, and demonstrate the crucial role, and magnitude, of the configurational entropy. 相似文献