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991.
M. Hyslop A. Wurl S.A. Brown B.D. Hall R. Monot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):233-236
A beam of Pb clusters is produced with the inert gas aggregation method and probed by electron diffraction. Analysis of the
diffraction patterns indicates that average cluster size can vary between 3 and 7 nm, according to nucleation conditions.
The diffraction patterns from beams with larger average cluster size are very similar to patterns calculated from model decahedron
clusters, while those for smaller cluster size do not appear to have simple geometrical face-centred cubic, decahedral, or
icosahedral structure.
Received 30 November 2000 相似文献
992.
Although it is generally agreed that the singer's formant (FS) is a prerequisite for successful stage performance, the results of this research do not support its presence in the soprano voices of trained female singers. Results are based on a recent investigation testing 10 advanced/professional sopranos in two groups singing sustained vowels at three frequencies: high (932 Hz), mid (622 Hz), and low (261 Hz). Spectrographic analysis shows that the nature of harmonic energy varies in relation to pitch. A resonance band somewhat resembling the tenor FS was usually evident in vowels sung at low and mid pitch. However, unlike the FS of typically less than 1 kHz bandwidth associated with tenors, sopranos singing similar pitches produced corresponding bandwidths which were significantly broader, usually at least 2-kHz wide. Vowels sung by sopranos at high-pitch levels exhibited strong fundamental frequency production with strong reinforcement of adjacent harmonics extending to 5 kHz and beyond. This type of production in essence nullifies the necessity for a typical FS. Absence of the FS in strong soprano voices might also imply the adaptation of a sufficiently different overall vocal tract configuration, so that techniques geared to developing maximal projection should not be the same as those developed to maximize the FS in other voices. 相似文献
993.
Cigang Xu Emmanuel Flahaut Sam R. Bailey Gareth Brown Jeremy Sloan Karl S. Coleman V. Clifford Williams Malcolm L. H. Green * . Inorganic Chemistry Laboratory University of Oxford Oxford OX QR UK 《高等学校化学研究》2002,18(2):130-132
IntroductionSingle walledcarbonnanotubes(SWNTs)havebeensynthesisedbyusingvariousmethods[1— 3] andthechemicalvapourdeposition (CVD )methodhasbeenconsideredasa promisingmethodto produceSWNTsonanindustrialscale[3— 5] .However ,alltheSWNT productssynthesisedtodateco… 相似文献
994.
Andreas Markwitz Geoffrey Vaughan White William Joseph Trompetter Ian William Murray Brown 《Mikrochimica acta》2001,137(1-2):49-56
Thin SiO2 layers were produced by thermal oxidation of Si wafer material. To study the effect of nitridation on the oxide layers, the
specimens were nitrided in a furnace at high temperature. Non-destructive ion beam analysis was performed to determine changes
in the elemental concentrations and depth profiles of the major components. In particular, N and O concentrations were measured
using the non-resonant nuclear reactions 14N(d, α)12C and 16O(d, p)17O, respectively. To obtain depth profiles of the as-prepared and nitrided specimens, the samples were measured with RBS and
heavy ion elastic recoil detection analysis. The ion beam analyses revealed an increase in thickness of the SiO2 layers with temperature. The specimens nitrided at 1200 °C were almost free of N. Surface topology investigations with scanning
electron microscopy revealed concentric annular artificial patterns at the surfaces. In the centre of the pattern, only silicon
was measured. Additionally, a band consisting of Si, O, and N surrounding the pattern was discovered. The findings are in
agreement with specimens prepared at higher temperatures.
Received June 19, 2000. Revision December 9, 2000. 相似文献
995.
Matthew R. Brown 《Journal of Geometry》2000,67(1-2):61-72
It is shown that if a plane of PG(3,q),q even, meets an ovoid in a pointed conic, then eitherq=4 and the ovoid is an elliptic quadric, orq=8 and the ovoid is a Tits ovoid. 相似文献
996.
Helen C. Brown Richard D. Bowen Howell G. M. Edwards Dennis W. Farwell 《Journal of Raman spectroscopy : JRS》2007,38(12):1586-1594
The Raman spectra of 3‐(pent‐1‐enyl) methyl ether (3‐methoxypent‐1‐ene) and four deuterium‐labelled analogues are reported and discussed. Correlations between specific structural features and the associated Raman bands are developed, with a view to enhancing the analytical application of Raman spectroscopy in investigating materials containing an alkenyl group. Particular attention is given to developing means of distinguishing the methyl group attached to the carbon skeleton from that of the methoxy group, to maximize the analytical utility of the signals associated with ν(sp2 CH), ν(sp2 CH2) and ν(CC) stretching vibrations, and to interpreting in more detail certain δ(sp2 CH) and δ(sp2 CH2) vibrations of the atoms of the double bond. These results establish a definitive spectroscopic protocol for differentiating a methoxy group from a methyl substituent attached directly to a carbon atom in unsaturated ethers. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
997.
M. K. Rotich B. D. Glass M. E. Brown 《Journal of Thermal Analysis and Calorimetry》2001,64(2):681-688
The thermal behaviour of various substituted aminobenzoic acids(3-aminobenzoic acid (3-ABA), 4-aminobenzoic acid (4-ABA),
3-aminosalicylic acid(3-ASA), 4-aminosalicylic acid (4-ASA), and 5-aminosalicylic acid (5-ASA), as well as the‘parent’ benzoic
acid (BA) and salicylic acid (SA) as reference substances, and possible decomposition products: 2-aminophenol (2-AP), 3-aminophenol
(3-AP) and 4-aminophenol(4-AP) in the solid state has been examined.
The various sets of isomers studied showed considerable and interesting differences. Most sublimed well before melting, generally
with an increasing rate of mass loss beyond their very different melting points. The differences in behaviour of 4-ASA and
5-ASA were the most remarkable, with 5-ASA being far more stable and apparently not decarboxylating readily, while 4-ASA sublimed
at temperatures below the melting point, becoming less stable and decarboxylating in the liquid form.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
998.
Kellie Brown John Cameron John Stears Wayne Hicky Roger Cormier Xiaoyi Bao Liang Chen 《Fiber and Integrated Optics》2001,20(5):427-442
With OC-192 communications systems being commercially available and higher bit rate systems in development, prudent telecommunications network administrators are testing their installed fibers to determine if they can be successfully used at 10 Gb/s and higher. Together with New Brunswick Telephone (NBTel), the Fiber Optics Group at UNB have tested various installed fibers and cables in the NBTel network for their losses at wavelengths of 1244, 1310, 1550, and 1625 nm, as well as for strain and polarization mode dispersion (PMD). Weather conditions, age, place of installation, and cable types have also been considered. Aging does not seem to affect the performance of the fibers. Although most fibers are high-speed system compatible when looking at attenuation measurements, about 40% of the fibers tested would not meet the 10 Gb/s OC-192 system manufacturer's design guidelines concerning PMD. 相似文献
999.
A short synthesis of tetramethyltetrathiafulvalene quadruply labeled with carbon-13 is described. 相似文献
1000.