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101.
Andrey E. Sheshenev Anna K. Croft Alexandre S. Shashkov Ivan G. Bolesov 《Tetrahedron letters》2006,47(16):2839-2843
1-Trimethylsilyl-3-phenylcyclopropene undergoes a highly stereocontrolled ene-reaction to give a dimer and further reaction leads to one or more trimers derived through two ene-reactions. 相似文献
102.
103.
CFD modelling of ‘real‐life’ thermo‐fluid processes often requires solutions in complex three‐dimensional geometries, which can result in meshes containing aspects that are badly distorted. Cell‐centred finite volume methods (CC‐FV), typical of most commercial CFD tools, are computationally efficient, but can lead to convergence problems on meshes that feature cells with highly non‐orthogonal shapes. The control volume‐finite element method (CVFE) uses a vertex‐based approach and handles distorted meshes with relative ease, but is computationally expensive. A combined vertex‐based—cell‐centre technique (CFVM), detailed in this paper, allows solutions on distorted meshes where purely cell‐centred solutions procedures fail. The method utilizes the ability of the vertex‐based approach to resolve the flow field on a distorted mesh, enabling well established cell‐centred physical models to be employed in the solution of other transported quantities. The vertex‐based flow code is verified against a manufactured 3D solution and error norms are compared on meshes with various degrees of distortion. The CFVM method is validated with benchmark solutions for thermally driven flow and turbulent flow. Finally, the method is illustrated on three‐dimensional turbulent flow over an aircraft wing on a distorted mesh where purely cell‐centred techniques fail. The CFVM is relatively straightforward to embed within generic CC based CFD tools allowing it to be employed in a wide variety of processing applications. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
104.
The relative rates of H-transfer between partners in ion-neutral complexes were compared with those in intramolecular rearrangements using results of first differential photoionization mass spectrometry measurements. Complex-mediated H-transfers are inferred to have rates of the same order as those for intramolecular hydrogen rearrangements, suggesting a similar range of motion of the reactive sites in both types of reactions. It is also concluded that at their fastest H-transfers take place between the partners in ion-neutral complexes within at most the time of several rotations of the partners in the complexes. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
105.
The number of students continuing with their mathematics educationpost GCSE level has declined in recent years and hence studentsentering Engineering degrees are reducing. The University ofBirmingham recognized this problem and introduced the Suiteof Technology programme (STP) which no longer requires studentsto have A-level mathematics. Therefore lecturers at universityare now faced with teaching A-level mathematics in order togive the students the mathematical skills for their technologydegree. With little experience of teaching at this level, lecturersfrequently face the challenge of choosing the most appropriatelevel for a lecture that encourages students to engage withand learn a subject that they are novices in. It turned outthat some students have a mathematics anxiety and hence thebiggest challenge for a lecturer is supporting the studentsovercoming this fear of mathematics. Choosing the appropriatestarting level for any lecture and the fear of mathematics wasacknowledged during a peer learning group meeting as part ofthe Post Graduate Certificate in Learning and Teaching in HigherEducation (PGCLTHE) at the University of Birmingham. In orderto explore this further, a session of mathematics was taughtby a Civil Engineering lecturer to fellow peers who do not havean engineering background. This article describes the mathematicsteaching session, reflections from the lecturer and the learners,and the impact that this had on teaching mathematics to undergraduates.Further, the article explores the difficulties and challengesexperienced by lecturers when teaching mathematics as a servicesubject. 相似文献
106.
Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co2+Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed. 相似文献
107.
K.J. Peach W. Cameron P. Capiluppi P. Croft E. Flaminio G. Kalmus P. Lugaresi-Serra G. Mandrioli V. Moggi W. Morton A.M. Rossi B. Saitta W. Venus 《Nuclear Physics B》1977,127(3):399-412
The results are presented of an analysis of 4709 fully reconstructed KL0 → π+π?π0, observed in a hydrogen bubble chamber. The data fit to a linear π0 energy spectrum to give a slope parameter g = 0.610 ± 0.022. 相似文献
108.
Fluoroalkylthio substituted five-membered ring aromatic heterocycles were prepared by direct substitution with fluoroalkylsulfenyl chlorides. 相似文献
109.
110.
The condensation of fluoroacetones with oxalyl fluoride in the presence of potassium fluoride has been shown to yield 2,2-di(fluoroalkyl)-5,5-difluoro-1,3-dioxolan-4-ones. 相似文献