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Breakthrough Listen is a 10-yr initiative to search for signatures of technologies created by extraterrestrial civilisations at radio and optical wavelengths. Here, we detail the digital data recording system deployed for Breakthrough Listen observations at the 64-m aperture CSIRO Parkes Telescope in New South Wales, Australia. The recording system currently implements two modes: a dual-polarisation, 1.125-GHz bandwidth mode for single-beam observations, and a 26-input, 308-MHz bandwidth mode for the 21-cm multibeam receiver. The system is also designed to support a 3-GHz single-beam mode for the forthcoming Parkes ultra-wideband feed. In this paper, we present details of the system architecture, provide an overview of hardware and software, and present initial performance results.
The combination of sensitivity and large sky coverage of the ALFALFA HI survey has enabled the detection of difficult to observe low mass galaxies in large numbers, including dwarf galaxies overlooked in optical surveys. Three different, but connected, studies of dwarf galaxies from the ALFALFA survey are of particular interest: SHIELD (Survey of HI in Extremely Low-mass Dwarfs), candidate gas-rich ultra-faint dwarf galaxies, and the (Almost) Dark population. SHIELD is a systematic multiwavelength study of all dwarf galaxies from ALFALFA with MHI < 107.2M⊙ and clear optical counterparts. Candidate gas-rich ultra-faint dwarf galaxies extend the dwarf galaxy population to even lower masses. These galaxies are identified as isolated HI clouds with no discernible optical counterpart but subsequent observations reveal that some are extremely faint, gas-dominated galaxies. Leo P, discovered first as an HI detection, and then found to be an actively star-forming galaxy, bridges the gap between these candidate galaxies and the SHIELD sample. The (Almost) Dark sample consists of galaxies whose optical counterparts are overlooked in current optical surveys but which are clear detections in ALFALFA. This sample includes field gas-rich ultra-diffuse galaxies. Coma P, with a peak surface brightness of only ∼26.4 mag arcsec−2 in g’, demonstrates the sort of extreme low surface brightness galaxy that can be discovered in an HI survey.
The equilibration time
in response to a change in flux from
after an injection period
applied to either a low-Reynolds-number gravity current or one propagating through a porous medium, in both axisymmetric and one-dimensional geometries, is shown to be of the form
, independent of all the remaining physical parameters. Numerical solutions are used to investigate
for each of these situations and compare very well with experimental results in the case of an axisymmetric current propagating over a rigid horizontal boundary. Analysis of the relaxation towards self-similarity provides an illuminating connection between the excess (deficit) volume from early times and an asymptotically equivalent shift in time origin, and hence a good quantitative estimate of
. The case
of equilibration after ceasing injection at time
is a singular limit. Extensions to high-Reynolds-number currents and to the case of a constant-volume release followed by constant-flux injection are discussed briefly.
The ‘voice quality symbols’ (VoQS) transcription system for voice quality was introduced some 20 years ago, and no major revision has been undertaken since then. In this account we describe the first major revision of the VoQS chart, these changes being mostly in the form of additions to the section on phonation types, but include also changes to the layout of the supralaryngeal settings section. These reflect recent developments in the understanding of the physiological underpinnings of sounds produced in the larynx including certain phonation types.
This 1878 account of a scientific tour of Morocco and the Atlas mountains in 1871 was compiled from the journals of Sir Joseph Hooker (1817–1911) and his travelling companion, the geologist John Ball (1818–89). Their plan had been for Hooker to publish their findings soon after the journey, but his work as Director of Kew Gardens and President of the Royal Society, and Ball's frequent absences abroad, as well as his own writing commitments, caused delays. However, they argue that their information is unlikely to be out of date when, from a comparison with earlier accounts, 'no notable change is apparent during the last two centuries'. The botanical and geological interests of both men take centre stage in an engaging narrative which provides interesting details about the government, customs and daily life in an area which even in the late nineteenth century was little visited by Europeans.