Unsupported lead clusters and electron diffraction

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     

Singer's Formant in Sopranos: Fact or Fiction?

Although it is generally agreed that the singer's formant (F_S) 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 F_S was usually evident in vowels sung at low and mid pitch. However, unlike the F_S 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 F_S. Absence of the F_S 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 F_S in other voices.     

Purification of Single-walled Carbon Nanotubes Grown by a Chemical Vapour Deposition (CVD) Method

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Influence of the Native Oxide Layer on the Silicon Surface During Initial Stages of Nitridation

 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.     

The determination of ovoids of PG(3,q) containing a pointed conic

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.     

Raman spectroscopy of 3‐(pent‐1‐enyl) methyl ether and selected deuterium‐labelled analogues

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(CC) 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.     

Thermal Studies on Some Substituted Aminobenzoic Acids

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.     

Characterization of Fibers in an Existing Network for High Speed System (10Gb/s or Greater) Compatibility

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.     

Synthesis of Quadruply Carbon-13 Labeled Tetramethyltetrathiaful Valene

A short synthesis of tetramethyltetrathiafulvalene quadruply labeled with carbon-13 is described.