16,490 research outputs found
Effect of molecular anisotropy on the intensity and degree of polarization of light scattered from model atmospheres
Computations of the intensity, flux, degree of polarization, and the positions of neutral points are presented for models of the terrestrial gaseous and hazy atmospheres by incorporating the molecular anisotropy due to air in the Rayleigh scattering optical thickness and phase matrix. Molecular anisotropy causes significant changes in the intensity, flux and the degree of polarization of the scattered light. The positions of neutral points do not change significantly. When the Rayleigh scattering optical thickness is kept constant and the molecular anisotropy factor is included only in the Rayleigh phase matrix, the flux does not change and the intensity and positions of neutron points change by a small amount. The changes in the degree of polarization are still significant
Soft-tissue specimens from pre-European extinct birds of New Zealand
We provide the first complete review of soft tissue remains from New Zealand birds that became extinct prior to European settlement (c. AD 1800). These rare specimens allow insights into the anatomy and appearance of the birds that are not attainable from bones. Our review includes previously unpublished records of ‘lost’ specimens, and descriptions of recently discovered specimens such as the first evidence of soft tissues from the South Island goose (Cnemiornis calcitrans). Overall, the soft tissue remains are dominated by moa (with specimens from each of the six genera), but also include specimens from Finsch's duck (Chenonetta finschi) and the New Zealand owlet-nightjar (Aegotheles novaezealandiae). All desiccated soft tissue specimens that have radiocarbon or stratigraphic dates are late Holocene in age, and most have been found in the semi-arid region of Central Otago
A methodology to understand student choice of Higher Education Institutions: the case of the United Kingdom
The need to understand how prospective students decide which Higher Education Institution to attend is becoming of paramount importance as the policy context for Higher Education moves towards market-based systems in many countries. This paper provides a novel methodology by which student preferences between institutions can be assessed, using the UK as a case study. It applies both revealed preference and discrete choice modelling techniques to estimate the priority attributes and potential trade-offs of students choosing between different United Kingdom universities. Whereas the former methodology has the advantage of being based on actual decisions, the latter provides an experimental setting for more nuanced findings to be elicited; the combination of approaches allows for a rich and detailed set of results. This methodology can also be used to ask detailed strategic questions of higher education institutions, and further applied to other international markets
Weakly-bound rare isotopes with a coupled-channel approach that includes resonant levels
The question of how the scattering cross section changes when the spectra of
the colliding nuclei have low-excitation particle-emitting resonances is
explored using a multi-channel algebraic scattering (MCAS) method. As a test
case, the light-mass nuclear target 8Be, being particle-unstable, has been
considered. Nucleon-nucleus scattering cross sections, as well as the spectra
of the compound nuclei formed, have been determined from calculations that do,
and do not, consider particle emission widths of the target nuclear states. The
resonant character of the unstable excited states introduces a problem because
the low-energy tails of these resonances can intrude into the sub-threshold,
bound-state region. This unphysical behaviour needs to be corrected by
modifying, in an energy-dependent way, the shape of the target resonances from
the usual Lorentzian one. The resonance function must smoothly reach zero at
the elastic threshold. Ways of achieving this condition are explored in this
paper.Comment: Contribution presented at INPC 2010, Vancouve
Formation of magnetic minerals at hydrocarbon-generation conditions
In this paper, we report the pyrolysis and formation of magnetic minerals in three source rock samples from the Wessex Basin in Dorset, southern England. The experimental conditions in the laboratory recreated the catagenesis environment of oil source rocks. Magnetic analysis of both the heated and the unheated samples at room temperature and at very low-temperatures (5 K), coupled with transmission electron-microscopy imaging and X-ray analysis, revealed the formation of nanometre-sized (<10 nm), magnetic particles that varied across the rock samples analysed, but more importantly across the pyrolysis temperature range. Magnetic measurements demonstrated the formation of these magnetic minerals peaked at 250 °C for all rock samples and then decreased at 300 °C before rising again at 320 °C. The newly formed magnetic minerals are suggested to be primarily pyrrhotite, though magnetite and greigite are also thought to be present. The sizes of the magnetic minerals formed suggest a propensity to migrate together with oil potentially explaining the magnetic anomalies observed above and within oil fields
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