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961.
Recently, with the advent of supercomputers, there has been considerable interest in the use of direct numerical simulation to obtain information about turbulent shear flow at low Reynolds number. This paper presents a pseudospectral technique to solve the full three-dimensional time-dependent Navier-Stokes and advection-diffusion equations without the use of subgrid-scale modelling. The technique has not been previously used for fully developed turbulent channel flow simulation and is based on methods applied in other contexts. The emphasis of this paper is to provide a reasonably detailed account of how the simulation is done rather than to present new calculations of turbulence. The details of an algorithm for turbulent channel flow simulation and the grid and time step sizes needed to integrate through transient behaviour to steady state turbulence have not been published before and are presented here. Results from a Cray-2 simulation of fully developed turbulent flow in a channel with heat transfer are presented along with a critical comparison between experiment and computation. The first- and second-order moments agree well with experimental measurements; the agreement is poor for higher-order moments such as the skewness and flatness near the walls of the channel. Detailed information given about the effects of spatial grid resolution on a computed results is important for estimating the size of the computation required to study various aspects of a turbulent flow. 相似文献
962.
B. M. Forster J. M. Bailey G. A. Beer J. L. Beveridge J. H. Brewer W. N. Hardy T. M. Huber K. R. Kendall A. R. Kunselman J. A. Macdonald G. M. Marshall G. R. Mason A. Olin M. Senba J. B. Warren 《Hyperfine Interactions》1991,65(1-4):1007-1013
Muonic hydrogen isotopes (μ− p, μ− d, and μ−t) are simple quantum mechanical systems ideally suited for studies of numerous fundamental phenomena in electroweak and strong
interactions as well as in applied areas such as muon chemistry or muon catalyzed fusion.
Emission of muonic hydrogen isotopes into vacuum helps to overcome the limitations which are normally imposed on conventional
investigations with gaseous and liquid targets. A proof of principle experiment for this new technique was performed at TRIUMF
last year. Negative muons with 30 MeV/c momentum were stopped in a thin film of solid hydrogen and produced very low energy μ−d in vacuum. The distribution center of the normal velocity components of emitted μ−d atoms was measured to be ∼1 cm/μs. The yield of μ−d in vacuum is an increasing function of H2 film thickness δ up to a value of δ≥1 mm. 相似文献
963.
R. Kadono R. F. Kiefl J. H. Brewer G. M. Luke T. Pfiz T. M. Riseman B. J. Sternlieb 《Hyperfine Interactions》1991,64(1-4):635-640
The diffusion rate of muonium in the III–V compound semiconductor GaAs has been determined from measurements of muon spinT
1 relaxation induced by motion in the presence of nuclear hyperfine interactions. It is shown for the first time in a semiconductor
that (a) there is a crossover of the transport mechanism at about 90 K from stochastic to zero-phonon hopping, as evidenced
by a steep rise in the hop rate at lower temperatures, and that (b) the muonium diffuses at the hop rate of 1010 s−1 (corresponding diffusion constantD≈10−6 cm2s−1) at lower temperatures as well as at room temperature. 相似文献
964.
New ferroelectric side-chain liquid-crystalline polymers, a copolymer and a homopolymer, with siloxane backbone and a triaromatic mesogen as the side group have been synthesized. The materials exhibit a chiral smectic C phase over a large temperature range extending to room temperature. They possess high values of spontaneous polarization: 105 nC cm-2 for the homopolymer and 180 nC cm-2 for the copolymer. The electro-optic switching time in the chiral smectic C phase is extremely fast (150 μs). In the smectic A phase, an electroclinic effect with switching times less than 100 μs and with field induced tilt angles of 18° is observed. 相似文献
965.
Mary F. Wheeler J. R. Whiteman 《Numerical Methods for Partial Differential Equations》1994,10(3):271-294
Superconvergent error estimates in l2(H1) and l∞(H1) norms are derived for recovered gradients of finite difference in time/piecewise linear Galerkin approximations in space for linear and quasinonlinear parabolic problems in two space dimensions. The analysis extends previous results for elliptic problems to the parabolic context, and covers problems in regions with nonsmooth boundaries under certain assumptions on the regularity of the solutions. © 1994 John Wiley & Sons, Inc. 相似文献
966.
J P Kiplinger L Contillo W L Hendrick A Grodski 《Rapid communications in mass spectrometry : RCM》1992,6(12):747-752
Derivatization is used to increase both negative-ion sensitivity and positive-ion sequence information in the liquid secondary-ion mass spectra (LSIMS) of a series of peptides. The derivatization method involves acylation with pentafluorobenzoyl fluoride in a single-step reaction, and the reaction mixture is applied directly to the probe tip for analysis. Acylation takes place at the unprotected N-terminus, tyrosine, and lysine. The derivatives exhibit increased signal-to-noise ratio for [M-H]- ions, especially where there is not already an acidic amino acid residue in the peptide. In positive-ion LSIMS, the N-terminal group acts to retain the charge at the N-terminus, simplifying the fragmentation by producing N-terminal fragment ions. It also increases positive-ion fragmentation, sometimes very dramatically, making sequence determination more straightforward. The simplicity of the process, together with the enhancements it provides, make this a generally useful method for obtaining peptide structural information. 相似文献
967.
968.
This paper investigates the applicability and accuracy of existing formulation methods in general purpose finite element programs to the finite strain deformation problems. The basic shortcomings in using such programs in these applications are then pointed out and the need for a different type of formulation is discussed. An arbitrary Lagrangian-Eulerian (ALE) method is proposed and a concise survey of ALE formulation is given. A consistent and complete ALE formulation is derived from the virtual work equation transformed to arbitrary computational reference configurations. Differences between the proposed formulations and similar ones in the literature are discussed. The proposed formulation presents a general approach to ALE method. It includes load correction terms and is suitable for rate-dependent and rate-independent material constitutive law. The proposed formulation reduces to both updated Lagrangian and Eulerian formulations as special cases. 相似文献
969.
P. R. Hageman J. te Nijenhuis M. J. Anders L. J. Giling 《Journal of Crystal Growth》1997,170(1-4):270-275
Doping studies of the incorporation behaviour of three different dopants (Zn, In and Si) versus the misorientation of the (100) surface during MOVPE growth of GaAs have been carried out with diethylzinc, trimethylindium and disilane as precursors. The incorporation of the dopants has been studied as function of the input mole fraction dopant, growth temperature, degree and direction of misorientation. In order to explain the results we discuss the BCF theory and the nature of the steps as function of above mentioned parameters. It appears that the BCF theory alone cannot explain the results, a counteracting mechanism has been introduced based on preferential arsenic desorption from the step edges. 相似文献
970.