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41.
R.J. Grant C.G. Johnson D.H. Wilkinson 《International Journal of Heat and Fluid Flow》1983,4(4):239-245
A single stage model turbine has been provided with a set of three special inlet sections which include backward facing steps to produce casing separations of varying size upstream of the stator blades. In addition each inlet section is equipped so as tc be able to emit a swirling jet which simulates the tip leakage jet from a preceeding stage. It is demonstrated that there is a substantial efficiency penalty associated with the stepped casing and its attendant separation and that a small mitigation is brought about by the tip leakage jet, by re-energising the fluid in the separation zone 相似文献
42.
We discuss the relative speeds DeltaV of inertial particles suspended in a highly turbulent gas when the Stokes number, a dimensionless measure of their inertia, is large. We identify a mechanism giving rise to the distribution P(DeltaV) approximately exp(-C|DeltaV|(4/3)) (for some constant C). Our conclusions are supported by numerical simulations, and by the analytical solution of a model equation of motion. The results determine the rate of collisions between suspended particles. They are relevant to the hypothesized mechanism for formation of planets by aggregation of dust particles in circumstellar nebula. 相似文献
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D.P.A. Hardwick S.L. Naylor S. Bujkiewicz T.M. Fromhold D. Fowler A. Patan L. Eaves A.A. Krokhin P.B. Wilkinson M. Henini F.W. Sheard 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):285
We study the effects of inter-miniband electron tunneling and electric field domains on the current–voltage and conductance–voltage curves of biased semiconductor superlattices under the action of a magnetic field that is tilted relative to the plane of the layers. For this geometry, electrons in the superlattice minibands exhibit a unique type of stochastic semiclassical motion. At certain critical values of the electric field within the superlattice layers, the stochastic trajectories change abruptly from fully localized to completely unbounded, and map out an intricate web-like mesh of conduction channels in phase space. Delocalization of the electron paths produces a series of strong resonant peaks in the electron drift velocity versus electric field curves. We use these drift velocity characteristics to make self-consistent drift-diffusion calculations of the current–voltage and differential conductance–voltage curves of the superlattices, which reveal strong resonant features originating from the sudden delocalization of the stochastic single-electron paths. We show that this delocalization has a pronounced effect on the distribution of space charge and electric field domains within the superlattices. Inter-miniband tunneling greatly reduces the amount of space-charge buildup, thus enhancing the domain structure and both the strength and number of the current resonances. 相似文献
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If an ex situ programme for the conservation of rare and threatened bryophytes is to succeed, a method of long-term, basal storage is required. The aim of this study was to determine the effectiveness of sucrose, ABA and sucrose/ABA combined, as cryoprotectant pretreatments, for the long-term storage of protonemata of the endangered Cornish path moss, Ditrichum cornubicum. This work is a prelude to the in vitro conservation of rare and endangered UK bryophytes. The addition of sucrose and/or ABA in the pre-culture medium, reduced protonemal growth rate. However, pretreatment afforded a high level of protection against tissue damage during dehydration and freezing, with 100 % regeneration of pretreated plants after thawing, compared to 53 % regeneration of controls. Sucrose combined with ABA in the pre-culture medium gave the most effective cryoprotection, with protonemata having fewer necrotic tissues and rapid recovery of growth. 相似文献
47.
Kwok W. Chiu David Lyons Geoffrey Wilkinson Mark Thornton-Pett Michael B. Hursthouse 《Polyhedron》1983,2(8):803-810
The reduction of WCl4(PMe3)3 by sodium amalgam in presence of phenylacetylene gives W(PMe3)(PhCCH)3 (A). Reduction in presence of methylisocyanide gives W(PMe3)2(MeNC)4 (B), while in presence of excess PMe3 in tetrahydrofuran under hydrogen, WH2Cl2(PMe3)4 (C) is formed. The reaction of WCl2(PMe3)4 with methanol in tetrahydrofuran gives mixtures of WH2Cl2(PMe3)4 and WOC12(PMe3)3 (D).The structures of A, B, and D have been determined by X-ray diffraction. 相似文献
48.
A numerical solution of the developing non-isothermal flow of a generalised power-law fluid in a slightly converging slit is presented, a problem which is relevance to some polymer processing operations.The results are presented in graphical form. They indicate that inertia forces and kinetic energy increases along the slit and these factors affect the development of the velocity and stress distributions. The effect of other parameters on the process is also brought out. 相似文献
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