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- SourceAvailable from: Robert Pyle[Show abstract] [Hide abstract]
ABSTRACT: Narrow-bore instruments are commonly perceived to be brighter than wide-bore models of the same kind of instrument. This effect is closely related to the effect of the bore profile of a brass instrument on the potential for non-linear propagation of sound within the tube. This paper reports on practical tests with trumpets of different bore diameters, experiments with loudspeaker excitation of instruments, and simulations. The brassiness curves of a range of low instruments with similar Brassiness Potential but differing in their absolute bore diameters are compared. The relative importance of the two effects is explored.
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ABSTRACT: Quasars that allow the study of intergalactic medium (IGM) He ii are very rare, since they must be at high redshift along sightlines free of substantial hydrogen absorption, but recent work has dramatically expanded the number of such quasars known. We analyze two dozen higher-redshift (z = 3.1–3.9) low-resolution He ii quasar spectra from the Hubble Space Telescope and find that their He ii Gunn–Peterson troughs suggest exclusion of very early and very late reionization models, favoring a reionization redshift of z ∼ 3. Although the data quality is not sufficient to reveal details such as the expected redshift evolution of helium opacity, we obtain the first ensemble measure of helium opacity at high redshift averaged over many sightlines: τ = 4.90 at z ∼ 3.3. We also find that it would be very difficult to observe the IGM red wing of absorption from the beginning of He ii reionization, but depending on the redshift of reionization and the size of ionization zones, it might be possible to do so in some objects with the current generation of UV spectrographs.The Astrophysical Journal 08/2015; 726(2). DOI:10.1088/0004-637X/726/2/111
- LISTA Endinburgh 2012; 06/2015