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排序方式: 共有354条查询结果,搜索用时 46 毫秒
71.
Michael A. Beswick Nick Choi Alexander D. Hopkins Yvonne G. Lawson Mary McPartlin Alexander Rothenberger Dietmar Stalke Andrew E. H. Wheatley Dominic S. Wright 《Angewandte Chemie (International ed. in English)》1999,38(20):3053-3055
Thermally unstable crystals of the title compound—the first bismuth phosphide complex to be structurally characterized (see picture)—are obtained by the reaction of [Bi(NMe2)3] with [tBuPHLi] (1:3) in THF/hexane. Berry pseudorotation of the pseudo-trigonal-bipyramidal [{(tBuP)3}2Bi]− ion is prevented for steric reasons. 相似文献
72.
Numerical modeling is increasingly becoming an indispensable tool for investigations in many fields of physics. Such modeling is especially useful in today's big science projects as a tool that can provide predictions and design parameters. The reliability of simulation results is thus essential. Code‐to‐code comparisons can help increase our confidence in simulation results, especially when other verification methods – such as comparison to theoretical models or experimental results – are limited or unavailable. In this paper, we describe a code‐to‐code comparison exercise wherein we compare one‐dimensional vacuum arc discharge simulation results from two independent particle‐in‐cell (PIC) codes. As part of our case study, we define a vacuum arc discharge test problem that can be used by other research groups for further comparison. Early disagreement between the two sets of our results motivated us to re‐examine the underlying methods in our codes. After remedying discrepancies, we observe good agreement in vacuum arc discharge time‐to‐breakdown, as well as in the time evolution of particle and current densities. This exercise demonstrates the usefulness of code‐to‐code comparisons and provides an example case study for the benefit of other research groups who may wish to carry out similar code‐to‐code comparisons (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
73.
Neher T Lunner T Hopkins K Moore BC 《The Journal of the Acoustical Society of America》2012,131(4):2561-2564
The relationships between spatial speech recognition (SSR; the ability to understand speech in complex spatial environments), binaural temporal fine structure (TFS) sensitivity, and three cognitive tasks were assessed for 17 hearing-impaired listeners. Correlations were observed between SSR, TFS sensitivity, and two of the three cognitive tasks, which became non-significant when age effects were controlled for, suggesting that reduced TFS sensitivity and certain cognitive deficits may share a common age-related cause. The third cognitive measure was also significantly correlated with SSR, but not with TFS sensitivity or age, suggesting an independent non-age-related cause. 相似文献
74.
J. Scott Parent Darren J. Thom Greg White Ralph A. Whitney William Hopkins 《Journal of polymer science. Part A, Polymer chemistry》2001,39(12):2019-2026
The thermal stability of brominated isobutylene–isoprene rubber (BIIR) was investigated through studies of the elastomer and a model compound that accurately represented the reactive functionality within the polymer. An analysis of commercial BIIR and reaction products of brominated 2,2,4,8,8‐pentamethyl‐4‐nonene (BPMN) by NMR demonstrated that bromination of isobutylene–isoprene rubber by 1,3‐dibromo‐5,5‐dimethylhydantoin yielded a kinetically favored exomethylene substitution product, 3‐bromo‐6,6‐dimethyl‐2‐(2,2‐dimethylpropyl)‐1‐heptene ( 2 ), as opposed to the more stable endo‐isomer, (E,Z)‐4‐(bromomethyl)‐2,2,8,8‐tetramethyl‐4‐nonene ( 3 ). The exposure of BIIR and the brominated model compound BPMN to vulcanization temperatures led to the isomerization of 2 to 3 at a rate strongly dependent on HBr concentration. The elimination of HBr from these allylic bromides to produce exo‐ and endo‐conjugated dienes proceeded concurrently with isomerization, and the kinetics of these processes could be rationalized on the basis of a polar reaction mechanism. The product distributions obtained from both the model system and BIIR were consistent, thereby justifying an extension of the model compound approach to an analysis of BIIR vulcanization chemistry. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2019–2026, 2001 相似文献
75.
Particle image velocimetry measurements in complex geometries 总被引:5,自引:0,他引:5
One of the advantages of Particle Image Velocimetry (PIV) is its ability to determine the instantaneous flow field over two-
or three-dimensional domains. Yet PIV has had limited application to complex flow passages because of the difficulty in replicating
these geometries with optically transparent materials. In this work, we describe a method for overcoming this difficulty using
rapid prototyping techniques. As an illustrative example, the technique has been used to characterize flow in a model of the
human nasal cavity.
Received: 12 January 1999/Accepted: 30 September 1999 相似文献
76.
Carlee A. Montgomery Islam Jameel Fabio Cuzzucoli Tristan Chidley Prof. Dr. W. Scott Hopkins Prof. Dr. Graham K. Murphy 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(71):e202202029
The first systematic evaluation of the electrostatic potential energy maps of iodonium ylides was conducted. We determined that they possess two σ-holes of differing electron deficiencies, with the more electropositive σ-hole located opposite the dative I−C bond to the β-dicarbonyl motif, and the lesser electropositive σ-hole located opposite the iodoarene C−I bond. We also conducted the first systematic evaluation of carboxylic acids, phenols and thiophenols in the O/S-alkylation reaction of iodonium ylides. While carboxylic acids and thiophenols were found to be generally viable, only phenols possessing electron-withdrawing substituents were effective. This high-yielding and highly chemoselective reaction is believed to involve halogen-bond activation of heteroatoms, and nicely complements existing diazo-based methods for alkylation of acidic functional groups. 相似文献
77.
A.J. Kemp A.J. Maclean J.E. Hastie S.A. Smith J.-M. Hopkins S. Calvez G.J. Valentine M.D. Dawson D. Burns 《Applied physics. B, Lasers and optics》2006,83(2):189-194
Finite-element analysis is used to explore the practicalities and power-scaling potential of quasi-monolithic microchip vertical-external-cavity surface-emitting lasers: thermal lensing and its implications for transverse mode control are emphasised. A comparison is made between the use of sapphire and diamond heat spreaders. The experimental characterisation of an InGaAs/sapphire microchip VECSEL is presented as an exemplar system and the factors affecting slope efficiency, threshold and output power roll-over are examined. By comparing experimental measurements with the finite-element model, the key role of thermal lensing in transverse mode control is demonstrated. PACS 42.55.Xi; 42.55.Rz; 42.55.Px 相似文献
78.
An explicit realization of the skew representations of the quantum affine algebra U q (gl n ) is given. It is used to identify these representations in a simple way by calculating their highest weight, Drinfeld polynomials and the Gelfand-Tsetlin character (orq-character). 相似文献
79.
Hutchinson D.A.W. Turner M.M. Doyle R.A. Hopkins M.B. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(4):636-643
A capacitively-coupled RF argon discharge at a pressure of 10 mTorr with a plate separation of 7.5 cm has been studied both experimentally and using a one-dimensional particle in cell simulation with Monte Carlo collisions. A magnetic field of 0 to 60 G is applied in the direction parallel to the capacitor plates. In the simulation it was found that as the magnetic field was increased such that the electron cyclotron orbit radius of the hot electrons became smaller than of the order of the discharge length, the electron heating in the bulk of the discharge increased. The dominant electron heating mechanism was observed to change from a stochastic sheath to a bulk ohmic electron heating mode, with a variation of field from a to 10 G. This was accompanied by a drop in the plasma density at small magnetic fields, which was also observed experimentally. At higher magnetic fields the plasma density was found to increase, A detailed discussion of the simulation results is presented drawing comparisons with the experimental results, with which there is good agreement, and a simple magnetohydrodynamic model for the bulk heating 相似文献
80.