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271.
The internal organization within electrochemically polymerized films of the conducting polymers polypyrrole p-toluene sulphonate and polypyrrole sulphate has been examined by scanning electron microscopy (SEM) following transverse fracture and permanganic etching of microtomed cross sections. X-ray scattering studies have shown these two materials to exhibit very different internal ordering: polypyrrole p-toluene sulphonate is thought as being anisotropic, with the counter ions and polypyrrole chains lying down preferentially in the plane of the work electrode, whereas polypyrrole sulphate is considered to be isotropic. Comparison of the internal textures following the two different preparative techniques shows significant differences. Whereas the morphology revealed in transverse fracture surfaces correlates closely with x-ray scattering data, etched surfaces exhibit a morphology that is in good agreement with the direct examination of sections prepared by ultramicrotomy. Despite the apparent contradiction in these two sets of data, a consistent picture of the true morphology (as revealed by permanganic etching) can be deduced and reconciled with the fracture surface micrographs. © 1996 John Wiley & Sons, Inc. 相似文献
272.
Aaron J. Celestian John B. Parise Akhilesh Tripathi ke Kvick Gavin M. B. Vaughan 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(8):i74-i76
The title compound, lithium potassium dialuminium digermanium octaoxide dihydrate, (K,Li)‐(Al,Ge)‐GIS (GIS is gismondine), is the result of a 50% Li+ exchange into the K‐(Al,Ge)‐GIS structure. The (K,Li)‐(Al,Ge)‐GIS structure was determined from a 4 × 4 × 2 µm octahedral single crystal at the ESRF synchrotron X‐ray source. The ion exchange results in a symmetry transformation from I2/a for K‐(Al,Ge)‐GIS to C2/c for (K,Li)‐(Al,Ge)‐GIS. The structural change is due to disordering of K+ ions with Li+ ions along the [001] channel and ordering of water molecules in the [101] channels. The distance between sites partially occupied by K+ ions increases from 2.19 (3) Å in K‐(Al,Ge)‐GIS to 2.94 (3) Å in (K,Li)‐(Al,Ge)‐GIS. The Li+ ions occupy positions along the twofold axis at the intersection of the eight‐membered‐ring channels in a twofold coordination with water molecules. For the four closest framework O2− anions, the Li⃛O distances are 3.87 (4) Å. 相似文献
273.
D. Vaughan 《Journal of sound and vibration》1980,69(1):119-138
The result of a basic warm string tone in a concert hall is that the whole orchestra not only sounds extremely well balanced, but the individual instruments outside the string family sound warmer and richer, and no attention is drawn to their extraneous noises. On the basis of orchestral conducting, performing, recording, and listening experience, some conclusions are reached, and suggestions made, concerning the physical conditions that are likely to be necessary, or conductive, to attainment of warm string tone. Among the physical factors considered are the acoustic and vibratory properties of the stage itself, hall volume, shape and reverberation time, and surface materials. Emphasis is placed, in discussion of the physical and musical factors, on the ways in which the musicians themselves, during performance, interact with “the acoustics”. 相似文献
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277.
Dr. Lucia Amidani Dr. Gavin B. M. Vaughan Dr. Tatiana V. Plakhova Dr. Anna Yu. Romanchuk Evgeny Gerber Dr. Roman Svetogorov Stephan Weiss Dr. Yves Joly Prof. Dr. Stepan N. Kalmykov Prof. Dr. Kristina O. Kvashnina 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(1):252-263
The structural characterisation of actinide nanoparticles (NPs) is of primary importance and hard to achieve, especially for non-homogeneous samples with NPs less than 3 nm. By combining high-energy X-ray scattering (HEXS) and high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD XANES) analysis, we have characterised for the first time both the short- and medium-range order of ThO2 NPs obtained by chemical precipitation. By using this methodology, a novel insight into the structures of NPs at different stages of their formation has been achieved. The pair distribution function revealed a high concentration of ThO2 small units similar to thorium hexamer clusters mixed with 1 nm ThO2 NPs in the initial steps of formation. Drying the precipitates at around 150 °C promoted the recrystallisation of the smallest units into more thermodynamically stable ThO2 NPs. HERFD XANES analysis at the thorium M4 edge, a direct probe for f states, showed variations that we have correlated with the breakdown of the local symmetry around the thorium atoms, which most likely concerns surface atoms. Together, HEXS and HERFD XANES are a powerful methodology for investigating actinide NPs and their formation mechanism. 相似文献
278.
D. Vaughan Griffiths David M. Benoit Yuen-Ki Cheong Philip Duncanson Xiao Han 《Phosphorus, sulfur, and silicon and the related elements》2014,189(7-8):1013-1027
AbstractThe reactions of trivalent phosphorus esters, including trialkyl phosphites, dialkyl phosphonites, and alkyl phosphinites, with 3-halo- and 3,4-dihalo-furan-2,5-diones has been shown to lead to the formation of novel phosphorus ylides possessing additional phosphoryl-containing groups. For the reaction of 3,4-dihalo-furan-2,5-diones with trialkyl phosphites, the products are trialkoxyphosphonium ylides containing an adjacent geminal bisphosphonate unit. These can be used to provide a convenient route to novel 2,3,3-tris(dialkoxyphosphoryl)-substituted propionate esters which can be hydrolyzed to give the corresponding novel trisphosphonic monocarboxylic acid. 相似文献
279.
Emmanuelle Alanvert Claire Doherty Thomas S. Moody Nicholena Nesbit Andrew S. Rowan Stephen J.C. Taylor Fatima Vaughan Tony Vaughan Jonathan Wiffen Ian Wilson 《Tetrahedron: Asymmetry》2009,20(21):2462-2466
The use of recombinant carbonyl reductase biocatalysts for the reduction of alpha-halo ketone intermediates to their corresponding alpha-halo alcohols has been investigated. The alpha-halo alcohol is obtained in good yield from the corresponding ketone in a stereoselective manner. 相似文献
280.
E. Dooryhée M. Anne I. Bardiès J.-L. Hodeau P. Martinetto S. Rondot J. Salomon G.B.M. Vaughan P. Walter 《Applied Physics A: Materials Science & Processing》2005,81(4):663-667
The history and the properties of materials are deduced not only from their elemental and molecular signatures, but also from their exact phase compositions, and from the structures and the defects of their constituents. Here we implement a non-destructive synchrotron X-ray based method, which combines both the quantitative structural content of diffraction and the imaging mode. As a demonstration case, the pigments of a Roman wall painting are examined. The joined elemental and mineral maps mimic the major features of the painting. Different structural phases made of common atomic elements are differentiated. Textures and graininess are measured and related to the artist’s know-how. PACS 07.85.Qe; 61.10.Nz; 83.85.Hf 相似文献