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27 results

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  • Radial-to-axial flows in a scaled pulsed-power scheme for producing outflows resembling YSO jets

  • Part of
  • Hannah R. Hasson, I. Nesli Erez, Matthew Evans, Imani West-Abdallah, James Young, Jay Angel, Chiatai Chen, Euan Freeman, John B. Greenly, David A. Hammer, Bruce R. Kusse, E. Sander Lavine, William M. Potter, Pierre-A. Gourdain
  • Journal:
    Journal of Plasma Physics / Volume 90 / Issue 6 / December 2024
    Published online by Cambridge University Press:
    18 December 2024, 915900601
    • Article
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  • Young stellar objects (YSOs) are protostars that exhibit bipolar outflows fed by accretion disks. Theories of the transition between disk and outflow often involve a complex magnetic field structure thought to be created by the disk coiling field lines at the jet base; however, due to limited resolution, these theories cannot be confirmed with observation and thus may benefit from laboratory astrophysics studies. We create a dynamically similar laboratory system by driving a $\sim$1 MA current pulse with a 200 ns rise through a $\approx$2 mm-tall Al cylindrical wire array mounted to a three-dimensional (3-D)-printed, stainless steel scaffolding. This system creates a plasma that converges on the centre axis and ejects cm-scale bipolar outflows. Depending on the chosen 3-D-printed load path, the system may be designed to push the ablated plasma flow radially inwards or off-axis to make rotation. In this paper, we present results from the simplest iteration of the load which generates radially converging streams that launch non-rotating jets. The temperature, velocity and density of the radial inflows and axial outflows are characterized using interferometry, gated optical and ultraviolet imaging, and Thomson scattering diagnostics. We show that experimental measurements of the Reynolds number and sonic Mach number in three different stages of the experiment scale favourably to the observed properties of YSO jets with $Re\sim 10^5\unicode{x2013}10^9$ and $M\sim 1\unicode{x2013}10$, while our magnetic Reynolds number of $Re_M\sim 1\unicode{x2013}15$ indicates that the magnetic field diffuses out of our plasma over multiple hydrodynamical time scales. We compare our results with 3-D numerical simulations in the PERSEUS extended magnetohydrodynamics code.

Skua and Penguin
  • Predator and Prey
  • Euan Young
  • Published online:
    27 October 2009
    Print publication:
    17 February 1994
  • Areas of barren rock and scree around the edge of Antarctica provide a breeding ground for two of the continent's most well-known species of bird: the south polar skua and the Adélie penguin. This book considers the relationship between these two species, taking as its study site Ross Island. Through detailed observations of the foraging ecology of the skua, the traditional view that skuas are totally dependent on penguin eggs and chicks for food is challenged. In addition, studies of the impact of skuas on penguin breeding and the extent to which the skua breeding cycle is functionally related to that of the penguin provide further evidence to suggest that the two species occur together independently as a consequence of limited breeding space, rather than as a result of a distinct predator-prey relationship.

  • Preface

  • Euan Young, University of Auckland
  • Book:
    Skua and Penguin
    Published online:
    27 October 2009
    Print publication:
    17 February 1994, pp xiii-xvi

  • Summary

    The drama of antarctic bird life is not without its villain. Theft and pillage, murder, cannibalism and infanticide, these crimes are all in the repertory of the South Polar Skua

    Siple and Lindsey, 1937.

    On 16 November 1959 I arrived by helicopter at Cape Royds on Ross Island to make up the second half of a New Zealand team studying penguins and skuas. For the rest of that quite beautiful summer we worked together to unravel as much as we could of the biology of these two extraordinary species. We were living in Shackleton's 1908 hut and working about the local area made so familiar from the photographs and accounts of early expeditions.

    Much of the skua's biology seemed pretty ordinary and they acted as one would have expected of any large gull, with a scavenging–predatory lifestyle. However, there were two surprises.

    First, for some seemingly inexplicable reason the parents allowed the older of the two chicks to harass the younger and chase it from the nest area. Almost none of the younger chicks survived. This problem has since engaged a great deal of research, with a fine study of its causation being undertaken later at Cape Bird by one of the students there. It also set me off on a comparative study of chick behaviour and chick survival of the brown skua among the grasses and shrubs of the benign Chatham Islands environment. The consequences of this decision are still being played out with a long-term study of communal breeding among the skuas there. But that is a separate story.

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