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An attempt is made to find out the suitable entrainment and exit boundary conditions in laminar flow situations. Streamfunction vorticity formulation of the Navier–Stokes equations are solved by ADI method. Two‐dimensional laminar plane wall jet flow is used to test different forms of the boundary conditions. Results are compared with the experimental and similarity solution and the proper boundary condition is suggested. The Kind 1 boundary condition is recommended. It consists of zero first derivative condition for velocity variable and for streamfunction equation, mixed derivative at the entrainment and exit boundaries. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
5.
A. Foussats C. Repetto O. P. Zandron O. S. Zandron 《International Journal of Theoretical Physics》2002,41(6):1053-1082
In order to describe the dynamics of the t–J model, two different families of first-order Lagrangians in terms of the generators of the Hubbard algebra are found. Such families correspond to different dynamical second-class constrained systems. The quantization is carried out by using the path-integral formalism. In this context the introduction of proper ghost fields is needed to render the model renormalizable. In each case the standard Feynman diagrammatics is obtained and the renormalized physical quantities are computed and analyzed. In the first case a nonperturbative large-N expansion is considered with the purpose of studying the generalized Hubbard model describing N-fold-degenerate correlated bands. In this case the 1/N correction to the renormalized boson propagator is computed. In the second case the perturbative Lagrangian formalism is developed and it is shown how propagators and vertices can be renormalized to each order. In particular, the renormalized ferromagnetic magnon propagator coming from our formalism is studied in details. As an example the thermal softening of the magnon frequency is computed. The antiferromagnetic case is also analyzed, and the results are confronted with previous one obtained by means of the spin-polaron theories. 相似文献
6.
C. Waldtmann H.-U. Everts B. Bernu C. Lhuillier P. Sindzingre P. Lecheminant L. Pierre 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):501-507
We study the exact low energy spectra of the spin 1/2 Heisenberg antiferromagnet on small samples of the kagomé lattice of up to N=36 sites. In agreement with the conclusions of previous authors, we find that these low energy spectra contradict the hypothesis
of Néel type long range order. Certainly, the ground state of this system is a spin liquid, but its properties are rather
unusual. The magnetic () excitations are separated from the ground state by a gap. However, this gap is filled with nonmagnetic () excitations. In the thermodynamic limit the spectrum of these nonmagnetic excitations will presumably develop into a gapless
continuum adjacent to the ground state. Surprisingly, the eigenstates of samples with an odd number of sites, i.e. samples with an unsaturated spin, exhibit symmetries which could support long range chiral order. We do not know if these
states will be true thermodynamic states or only metastable ones. In any case, the low energy properties of the spin 1/2 Heisenberg
antiferromagnet on the kagomé lattice clearly distinguish this system from either a short range RVB spin liquid or a standard chiral spin liquid. Presumably
they are facets of a generically new state of frustrated two-dimensional quantum antiferromagnets.
Received: 27 November 1997 / Accepted: 29 January 1998 相似文献
7.
Brian R. Hunt 《Proceedings of the American Mathematical Society》1998,126(3):791-800
The Weierstrass nowhere differentiable function, and functions constructed from similar infinite series, have been studied often as examples of functions whose graph is a fractal. Though there is a simple formula for the Hausdorff dimension of the graph which is widely accepted, it has not been rigorously proved to hold. We prove that if arbitrary phases are included in each term of the summation for the Weierstrass function, the Hausdorff dimension of the graph of the function has the conjectured value for almost every sequence of phases. The argument extends to a much wider class of Weierstrass-like functions.
8.
This paper deals mainly with generalizations of results in finitary combinatorics to infinite ordinals. It is well-known that for finite ordinals ∑bT<αβ is the number of 2-element subsets of an α-element set. It is shown here that for any well-ordered set of arbitrary infinite order type α, ∑bT<αβ is the ordinal of the set M of 2-element subsets, where M is ordered in some natural way. The result is then extended to evaluating the ordinal of the set of all n-element subsets for each natural number n ≥ 2. Moreover, series ∑β<αf(β) are investigated and evaluated, where α is a limit ordinal and the function f belongs to a certain class of functions containing polynomials with natural number coefficients. The tools developed for this result can be extended to cover all infinite α, but the case of finite α appears to be quite problematic. 相似文献
9.
L. K. Aminov I. N. Kurkin D. A. Lukoyanov K. P. Chernov 《Physics of the Solid State》1997,39(8):1184-1186
Results are reported for measurements of the spin-lattice relaxation times of E′1 centers in quartz glass, produced by neutron irradiation, with the measurements made at two frequencies 9.25 and 24.0 GHz
over a wide temperature interval 1.5–300 K. The experimental data are interpreted on the basis of interaction mechanisms of
the spins with two-level systems with excitation energies ∼6, ∼26, and ∼420 cm−1. A small modification of the existing theory allows us to explain a number of features of the observed temperature and frequency
dependence of the relaxation rate. The results are compared with the data available in the literature on spin-lattice relaxation
of irradiation centers in crystalline quartz and quartz glass.
Fiz. Tverd. Tela (St. Petersburg) 39, 1335–1337 (August 1997) 相似文献
10.
J. E. Fischer E. Werwa P. A. Heiney 《Applied Physics A: Materials Science & Processing》1993,56(3):193-196
We have used both reflection-geometry and grazing-incidence-geometry X-ray scattering to study thin films of C60 evaporated onto mica substrates via a hot-wall technique. The growth mode yields close-packed C60 planes, which are parallel to the substrate surface and which exhibit out-of-plane correlation lengths of 850 Å. In the film plane the C60 is at best pseudo-epitaxial, with a 0.9° distribution of crystallite orientations, a 450 Å in-plane correlation length, and a 3.7% lattice mismatch, better than obtained by other thin film techniques but far from the accepted definition of single crystal thin film epitaxy. 相似文献