569 research outputs found
The Discovery and History of the Dalgaranga Meteorite Crater, Western Australia
The Dalgaranga meteorite crater, 100 km northeast of Yalgoo, Western
Australia, was one of the first impact structures identified in Australia, the
smallest isolated crater found in Australia, and the only confirmed crater in
the world associated with a mesosiderite projectile. 17 years passed before the
Dalgaranga meteorites were described in the scientific literature and nearly 40
years passed before a survey of the structure was published. The reasons for
the time-gap were never explained and a number of factual errors about the
discovery and early history remain uncorrected in the scientific literature.
Using historical and archival documents, and discussions with people involved
in Dalgaranga research, the reasons for this time gap are explained by a series
of minor misidentifications and coincidences. The age of the crater has yet to
be determined, but using published data, we estimate the projectile mass to be
500-1000 kg.Comment: Australian Journal of Earth Sciences, accepte
Planetary thermal evolution models with tectonic transitions
Thermal history calculations provide important insights into the interior
evolution of planets, but incorporate simplified dynamics from the systems they
represent. Planetary interiors typical incorporate complex rheologies, viscous
layering, lateral heterogeneities, and time delays in processes, which have not
been traditionally represented by parameterised approaches. Here we develop
numerical models for planetary evolution, incorporating the physical complexity
of Earth's interior, and use them to generate statistically-based Nu-Ra
scalings. These encapsulate the main effects of tectonic transitions, geometry,
and depth-dependent rheology, and time-sensitivity. We find an exponent
of ~0.26 best describes the Nu-Ra relationship for evolving mobile lid systems,
and ~0.12 for stagnant-lid systems. Systems with time dependent
subduction have varying between ~0.26 during the Hadean, when external
factors such as impacts facilitate tectonics, to ~0.12 during the Archaean,
when the system is dominated by long periods of quiescence, and systems driven
by external forcings (eg. due to impacts in the first 100Myr of Earth's
history) may exhibit much higher exponents. We also find a time-lag between Ra
(which primarily depends on mantle temperature) and Nu (normalised surface heat
flow) of around 200-300Myr, suggesting a significant delay between mantle
thermal configuration, and its surface manifestation. These results provide an
approach for the rapid characterisation of tectonic, volcanic, and atmospheric
evolution of terrestrial exoplanets.Comment: Revisions submitted to PS
Lid tectonics. Preface
The idea that plate tectonics may not have operated deep in Earth's Precambrian past has a long legacy. What predated plate tectonics is unknown, and advances in data – from geochemical, geological and tectonic, to paleomagnetic, as well as modelling approaches, and planetary science, have the potential to contribute significantly to the debate. To contrast with the activity of plate tectonics, in this issue we use the term ‘lid tectonics’ to encapsulate a variety of envisaged regimes – from stagnant, sluggish, plutonic-squishy, or heat pipe – which are characterized by comparatively subdued tectonic signatures
A unified framework for trapdoor-permutation-based sequential aggregate signatures
We give a framework for trapdoor-permutation-based sequential aggregate signatures (SAS) that unifies and simplifies prior work and leads to new results. The framework is based on ideal ciphers over large domains, which have recently been shown to be realizable in the random oracle model. The basic idea is to replace the random oracle in the full-domain-hash signature scheme with an ideal cipher. Each signer in sequence applies the ideal cipher, keyed by the message, to the output of the previous signer, and then inverts the trapdoor permutation on the result. We obtain different variants of the scheme by varying additional keying material in the ideal cipher and making different assumptions on the trapdoor permutation. In particular, we obtain the first scheme with lazy verification and signature size independent of the number of signers that does not rely on bilinear pairings.
Since existing proofs that ideal ciphers over large domains can be realized in the random oracle model are lossy, our schemes do not currently permit practical instantiation parameters at a reasonable security level, and thus we view our contribution as mainly conceptual. However, we are optimistic tighter proofs will be found, at least in our specific application.https://eprint.iacr.org/2018/070.pdfAccepted manuscrip
Development of a technology adoption and usage prediction tool for assistive technology for people with dementia
This article is available open access through the publisher’s website at the link below. Copyright @ The Authors 2013.In the current work, data gleaned from an assistive technology (reminding technology), which has been evaluated with people with Dementia over a period of several years was retrospectively studied to extract the factors that contributed to successful adoption. The aim was to develop a prediction model with the capability of prospectively assessing whether the assistive technology would be suitable for persons with Dementia (and their carer), based on user characteristics, needs and perceptions. Such a prediction tool has the ability to empower a formal carer to assess, through a very limited amount of questions, whether the technology will be adopted and used.EPSR
Stability of Sasaki-extremal metrics under complex deformations
We consider the stability of Sasaki-extremal metrics under deformations of
the complex structure on the Reeb foliation. Given such a deformation
preserving the action of a compact subgroup of the automorphism group of a
Sasaki-extremal structure, a sufficient condition is given involving the
nondegeneracy of the relative Futaki invariant for the deformations to contain
Sasaki-extremal structures.
Deformations of Sasaki-Einstein metrics are also considered, where it
suffices that the deformation preserve a maximal torus. As an application, new
families of Sasaki-Einstein and Sasaki-extremal metrics are given on
deformations of well known 3-Sasaki 7-manifolds.Comment: Added the obstruction to the existence of Sasaki structures under
transversal complex deformations. 30 pages and 1 figur
Migrant African women: tales of agency and belonging
This paper explores issues of belonging and agency among asylum seekers and refugee women of African origin in the UK. It discusses the ways these women engendered resistance in their everyday life to destitution, lack of cultural recognition, and gender inequality through the foundation of their own non-governmental organization, African Women’s Empowerment Forum, AWEF, a collective ‘home’ space. The focus of this account is on migrant women’s agency and self-determination for the exercise of choice to be active actors in society. It points to what might be an important phenomenon on how local grassroots movements are challenging the invisibility of asylum seekers’ and refugees’ lives and expanding the notion of politics to embrace a wider notion of community politics with solidarity. AWEF is the embodiment of a social space that resonates the ‘in-between’ experience of migrant life providing stability to the women members regarding political and community identification
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