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This paper examines the non-linear dynamic behaviour of a flexible shaft. The shaft is mounted on two journal bearings and the axial load is supported by a defective hydrodynamic thrust bearing at one end. The defect is a levelness defect of the rotor. The thrust bearing behaviour must be considered to be non-linear because of the effects of the defect. The shaft is modelled with typical beam finite elements including effects such as the gyroscopic effects. A modal technique is used to reduce the number of degrees of freedom. Results show that the thrust bearing defects introduce supplementary critical speeds. The linear approach is unable to show the supplementary critical speeds which are obtained only by using non-linear analysis. 相似文献
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We show that using ionic liquids as reagents in conjunction with microwave heating it is possible to prepare primary alkyl halides from the corresponding alcohols rapidly. Using ionic liquids as solvents in conjunction with microwave heating it is possible to prepare aryl nitriles from the corresponding aryl bromides or iodides. The scope and limitations of using microwave-promotion as a tool in these reactions is discussed. 相似文献
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Longitudinal confinement of dark solitons in quasi-one-dimensional Bose-Einstein condensates leads to sound emission and reabsorption. We perform quantitative studies of the dynamics of a soliton oscillating in a tight dimple trap, embedded in a weaker harmonic trap. The dimple depth provides a sensitive handle to control the soliton-sound interaction. In the limit of no reabsorption, the power radiated is found to be proportional to the soliton acceleration squared. An experiment is proposed to detect sound emission as a change in amplitude and frequency of soliton oscillations. 相似文献
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Leadbeater M Winiecki T Samuels DC Barenghi CF Adams CS 《Physical review letters》2001,86(8):1410-1413
By performing numerical simulations based on the Gross-Pitaevskii equation, we make direct quantitative measurements of the sound energy released due to superfluid vortex reconnections. We show that the energy radiated expressed in terms of the loss of vortex line length is a simple function of the reconnection angle. In addition, we study the temporal and spatial distribution of the radiation and show that energy is emitted in the form of a sound pulse with a wavelength of a few healing lengths. 相似文献
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JOSEF MÁLEK JINDŘICH NEČAS K. R. RAJAGOPAL 《Archive for Rational Mechanics and Analysis》2002,165(3):243-269
To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity
of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments.
While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small,
special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place.
Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are
global in time, for a large class of physically meaningful viscosity-pressure relationships.
(Accepted May 1, 2002) Published online November 15, 2002
Communicated by S. S. ANTMAN 相似文献
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A prototype tube-in-tube reactor in which it is possible to load gas and heat simultaneously has been used in a continuous-flow approach to alkoxycarbonylation reactions of aryl iodides. In the stainless steel coil, liquid flows on the outside of a gas-permeable membrane. The coil can be heated and the temperature can be measured accurately via a probe touching the outer steel surface. A range of aryl iodides can be transformed to the corresponding esters in excellent conversion by reaction at 120 °C using 0.5 mol% palladium acetate as the catalyst with no additional ligand required. Small-scale optimization and substrate screening runs were followed by scale-up. 相似文献
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Arvela RK Leadbeater NE Sangi MS Williams VA Granados P Singer RD 《The Journal of organic chemistry》2005,70(1):161-168
We present here a reassessment of our transition-metal free Suzuki-type coupling protocol. We believe that, although the reaction can be run without the need for addition of a metal catalyst, palladium contaminants down to a level of 50 ppb found in commercially available sodium carbonate are responsible for the generation of the biaryl rather than, as previously suggested, an alternative non-palladium-mediated pathway. We present a revised methodology for Suzuki couplings using ultralow palladium concentrations for use with aryl and vinyl boronic acids and discuss the effects of the purity of the boronic acid on the reaction. 相似文献
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