470 research outputs found
Submarine landslides on the upper southeast Australian passive continental margin – preliminary findings
The southeast Australian passive continental margin is narrow, steep and sediment-deficient, and characterized by relatively low rates of modern sedimentation. Upper slope (\u3c1200m) sediments comprise mixtures of calcareous and terrigenous sand and mud. Three of twelve sediment cores recovered from geologically-recent, submarine landslides located offshore New South Wales/Queensland (NSW/QLD) are interpreted to have sampled failure surfaces at depths of between 85 cm and 220 cm below the present-day seabed. Differences in sediment physical properties are recorded above and below the three slide-plane boundaries. Sediment taken directly above the inferred submarine landslide failure surfaces and presumed to be post-landslide, returned radiocarbon ages of 15.8 ka, 20.7 ka and 20.1 ka. The last two ages correspond to adjacent slide features, which are inferred to be consistent with their being triggered by a single event such as an earthquake. Slope stability models based on classical soil mechanics and measured sediment shearstrengths indicate that the upper slope sediments should be stable. However, multibeam sonar data reveal that many upper slope landslides occur across the margin and that submarine landsliding is a common process. We infer from these results that: a) an unidentified mechanism regularly acts to reduce the shear resistance of these sediments to the very low values required to enable slope failure, and/or b) the margin experiences seismic events that act to destabilise the slope sediments
An HST/WFPC Survey of Bright Young Clusters in M31. II. Photometry of Less Luminous Clusters in the Fields
We report on the properties of 89 low mass star clusters located in the
vicinity of luminous young clusters (blue globulars) in the disk of M31. 82 of
the clusters are newly detected. We have determined their integrated magnitudes
and colors, based on a series of Hubble Space Telescope Wide Field/Planetary
Camera 2 exposures in blue and red (HST filters F450W and F814W). The
integrated apparent magnitudes range from F450W = 17.5 to 22.5, and the colors
indicate a wide range of ages. Stellar color-magnitude diagrams for all
clusters were obtained and those with bright enough stars were fit to
theoretical isochrones to provide age estimates. The ages range from 12 Myr to
>500 Myr. Reddenings, which average E(F450 - F814) = 0.59 with a dispersion of
0.21 magnitudes, were derived from the main sequence fitting for those
clusters. Comparison of these ages and integrated colors with single population
theoretical models with solar abundances suggests a color offset of 0.085
magnitudes at the ages tested. Estimated ages for the remaining clusters are
based on their measured colors. The age-frequency diagram shows a steep decline
of number with age, with a large decrease in number per age interval between
the youngest and the oldest clusters detected.Comment: 20 pages, 9 figure
Long-Term V-Band Monitoring of the Bright Stars of M33 at the Wise Observatory
We have conducted a long-term V-band photometric monitoring of M33 on 95
nights during four observing seasons (2000 - 2003). A total number of 6418
lightcurves of bright objects in the range of 14 - 21 mag have been obtained.
All measurements are publicly available. A total of 127 new variables were
detected, of which 28 are periodic. Ten previously known non-periodic variables
were identified as periodic, 3 of which are Cepheids, and another previously
known periodic variable was identified as an eclipsing binary. Our derived
periods range from 2.11 to almost 300 days. For 50 variables we have combined
our observations with those of the DIRECT project, obtaining lightcurves of up
to 500 measurements, with a time-span of ~7 years. We have detected a few
interesting variables, including a 99.3 day periodic variable with a 0.04 mag
amplitude, at the position of SNR 19.Comment: 29 pages, accepted for publication in MNRAS. Additional material is
available at http://wise-obs.tau.ac.il/~shporer/m33
Sedimentology, structure and age estimate of five continental slope submarine landslides, eastern Australia
Sedimentological and accelerator mass spectrometry (AMS) <sup>14</sup>C data provide estimates of the structure and age of five submarine landslides (∼0.4–3 km<sup>3</sup>) present on eastern Australia's continental slope between Noosa Heads and Yamba. Dating of the post-slide conformably deposited sediment indicates sediment accumulation rates between 0.017 m ka<sup>–1</sup> and 0.2 m ka<sup>–1</sup>, which is consistent with previous estimates reported for this area. Boundary surfaces were identified in five continental slope cores at depths of 0.8 to 2.2 m below the present-day seafloor. Boundary surfaces present as a sharp colour-change across the surface, discernible but small increases in sediment stiffness, a slight increase in sediment bulk density of 0.1 g cm<sup>–3</sup>, and distinct gaps in AMS <sup>14</sup>C ages of at least 25 ka. Boundary surfaces are interpreted to represent a slide plane detachment surface but are not necessarily the only ones or even the major ones. Sub-bottom profiler records indicate that: (1) the youngest identifiable sediment reflectors upslope from three submarine landslides terminate on and are truncated by slide rupture surfaces; (2) there is no obvious evidence for a post-slide sediment layer draped over, or burying, slide ruptures or exposed slide detachment surfaces; and (3) the boundary surfaces identified within the cores are unlikely to be near-surface slide surfaces within an overall larger en masse dislocation. These findings suggest that these submarine landslides are geologically recent (<25 ka), and that the boundary surfaces are either: (a) an erosional features that developed after the landslide, in which case the boundary surface age provides a minimum age for the landslide; or (b) detachment surfaces from which slabs of near-surface sediment were removed during landsliding, in which case the age of the sediment above the boundary surface indicates the approximate age of landsliding. While an earthquake-triggering mechanism is favoured for the initiation of submarine landslides on the eastern Australian margin, further evidence is required to confirm this interpretation
The natural science of cosmology
The network of cosmological tests is tight enough now to show that the
relativistic Big Bang cosmology is a good approximation to what happened as the
universe expanded and cooled through light element production and evolved to
the present. I explain why I reach this conclusion, comment on the varieties of
philosophies informing searches for a still better cosmology, and offer an
example for further study, the curious tendency of some classes of galaxies to
behave as island universes.Comment: Keynote lecture at the seventh International Conference on
Gravitation and Cosmology, Goa India, December 201
Respectable Drinkers, Sensible Drinking, Serious Leisure: Single-Malt Whisky Enthusiasts and the Moral Panic of Irresponsible Others
In the public discourse of policy-makers and journalists, drinkers of (excessive) alcohol are portrayed either as irresponsible, immoral deviants or as gullible victims. In other words, the public discourse engenders a moral panic about alcohol-crazed individuals, who become what Cohen [1972. Folk devil and moral panics. London: Routledge] identifies as folk devils: the Other, abusing alcohol to create anti-social disorder. However, alcohol-drinking was, is and continues to be an everyday practice in the leisure lives of the majority of people in the UK. In this research article, I want to explore the serious leisure of whisky-tasting to provide a counter to the myth of the alcohol-drinker as folk devil, to try to construct a new public discourse of sensible drinking. I will draw on ethnographic work at whisky-tastings alongside interviews and analysis of on-line discourses. I show that participation in whisky-tasting events creates a safe space in which excessive amounts of alcohol are consumed, yet the norms of the particular habitus ensure that such drinking never leads to misbehaviour. In doing so, however, I will note that the respectability of whisky-drinking is associated with its masculine, white, privileged habitus – the folk devil becomes someone else, someone Other
Testing The Friedmann Equation: The Expansion of the Universe During Big-Bang Nucleosynthesis
In conventional general relativity, the expansion rate H of a
Robertson-Walker universe is related to the energy density by the Friedmann
equation. Aside from the present day, the only epoch at which we can constrain
the expansion history in a model-independent way is during Big-Bang
Nucleosynthesis (BBN). We consider a simple two-parameter characterization of
the behavior of H during BBN and derive constraints on this parameter space,
finding that the allowed region of parameter space is essentially
one-dimensional. We also study the effects of a large neutrino asymmetry within
this framework. Our results provide a simple way to compare an alternative
cosmology to the observational requirement of matching the primordial
abundances of the light elements.Comment: 18 pages, Final version to be published in Phys. Rev.
Measuring our universe from galaxy redshift surveys
Galaxy redshift surveys have achieved significant progress over the last
couple of decades. Those surveys tell us in the most straightforward way what
our local universe looks like. While the galaxy distribution traces the bright
side of the universe, detailed quantitative analyses of the data have even
revealed the dark side of the universe dominated by non-baryonic dark matter as
well as more mysterious dark energy (or Einstein's cosmological constant). We
describe several methodologies of using galaxy redshift surveys as cosmological
probes, and then summarize the recent results from the existing surveys.
Finally we present our views on the future of redshift surveys in the era of
Precision Cosmology.Comment: 82 pages, 31 figures, invited review article published in Living
Reviews in Relativity, http://www.livingreviews.org/lrr-2004-
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