Optical dating: Recuperation after bleaching   总被引：1，自引：0，他引：1  

M.J. Aitken  B.W. Smith 《Quaternary Science Reviews》1988,7(3-4)

Bleaching by sunlight results in rapid reduction of optically-stimulated luminescence, e.g. by a factor of 300 in 15 min for one of the several samples of quartz so far tried. However, if the bleached sample is stored before measurement the signal partially recovers, suggesting the possibility that the observed natural luminescence from a young sediment sample may contain a significant contribution from this component. Recuperation is accelerated if the sample is warmed during storage: after 5 min at 220°C the recuperation levels in the samples of quartz studied were equivalent to the order of one gray. Recuperative effects are also observed in zircon. We suggest that the effect is associated with phototransfer into shallow light-insensitive traps during bleaching, with subsequent thermal redistribution into the traps responsible for the initial luminescence. Investigation of recuperation gives a useful insight into the mechanisms upon which optical dating relies.  相似文献   

12-μm fine-structure emission line and continuum images of G333.6–0.2     

Takuya Fujiyoshi  Craig H. Smith  Toby J. T. Moore  David K. Aitken  Patrick F. Roche  & Dale E. Quinn 《Monthly notices of the Royal Astronomical Society》1998,296(2):225-230

We present high spatial resolution (∼0.8 arcsec) diffraction-limited 12.8-μm Ne  ii fine-structure emission line and 12.5-μm continuum images of the bright southern compact H  ii region G333.6–0.2, taken with the mid-infrared imaging polarimeter NIMPOL. The two images show remarkably similar, compact, yet asymmetric, flux distributions. The [Ne  ii ] image shows a complex structure near the ionizing source(s) which we interpret in terms of the ionization structure of the H  ii region. It is found that G333.6–0.2 is more likely to be excited by a cluster of O and B stars than by a single star.  相似文献   

A Semicentennial Celebration: Placing The Professional Geographer     

Stuart C. Aitken  Janet Franklin 《The Professional geographer》1998,50(1):1-2

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Mid-infrared polarization studies of SgrA: a three-dimensional study of the central parsec     

David K. Aitken  Craig H. Smith  Toby J. T. Moore  & Patrick F. Roche 《Monthly notices of the Royal Astronomical Society》1998,299(3):743-752

Thermal emission from magnetically aligned dust grains produces the observed mid-infrared polarization in the northern arm and east–west bar of SgrA West; recent arcsecond-resolution imaging polarimetry at 12.5 μm of these ionized filaments is presented, which confirms and extends previous studies. A lower limit ∼2 mG is found for the magnetic field in the northern arm and the IRS16 complex appears to be displaced from the northern arm by ∼ 0.15 pc along the line of sight. It is shown that the physical conditions in the ionized filaments of the central parsec lead to a very uniform grain alignment that is directed along the local magnetic field. The position angle of polarized emission will then be at right angles to the projection of the field direction on the plane of the sky and its amplitude a measure of the component of field along the line of sight; this makes possible a partial reconstruction of the field in three dimensions. We present the first application of the use of polarimetry in this way. This partial reconstruction is compared with the H92α observations of Roberts et al. and the implications are that the northern arm and east–west bar do not define either an orbital path or a spiral arm but rather represent a tidally stretched structure in free fall about SgrA^★ with significant deviations from a single plane, and most likely represent the inner ionized rim of a more extended neutral cloud.  相似文献   

The exaggerated radiocarbon age of deposit‐feeding molluscs in calcareous environments     

John England  Arthur S. Dyke  Roy D. Coulthard  Roger Mcneely  Alec Aitken 《Boreas: An International Journal of Quaternary Research》2013,42(2):362-373

Throughout northern Canada, live‐collected, pre‐bomb, deposit‐feeding marine molluscs from calcareous sediments yield greater apparent radiocarbon ages than do suspension feeders. We explore the size of this effect in a set of 57 paired datings of deposit feeders, mainly Portlandia arctica, and suspension feeders, mainly Hiatella arctica and Mya truncata, collected from both calcareous and non‐calcareous Holocene sediments. Deposit feeders from calcareous sediments are older than their suspension‐feeding counterparts by as much as 2240±130 ¹⁴C years. This is attributed to the uptake of ‘old’ bicarbonate derived from calcareous bedrock. The age discrepancy between suspension and deposit feeders in calcareous terrain is non‐systematic in space and time, thereby invalidating the application of a correction. In contrast, the age comparisons are concordant at sites located on the Precambrian Shield. In terrestrial environments underlain by carbonate, previous acceptance of dates on deposit feeders led to erroneous interpretations of deglaciation and relative sea‐level history, in both the North American and the Eurasian Arctic. This has prompted several researchers to exclude deposit feeders from their late Quaternary reconstructions. The same chronological problem of deposit‐feeding molluscs now needs to be more widely acknowledged by the marine community.  相似文献   

Silicate absorption in heavily obscured galaxy nuclei     

Patrick F. Roche  Christopher Packham  David K. Aitken  Rachel E. Mason 《Monthly notices of the Royal Astronomical Society》2007,375(1):99-104

Spectroscopy at 8–13 μm with T-ReCS on Gemini-S is presented for three galaxies with substantial silicate absorption features, NGC 3094, NGC 7172 and NGC 5506. In the galaxies with the deepest absorption bands, the silicate profile towards the nuclei is well represented by the emissivity function derived from the circumstellar emission from the red supergiant, μ Cephei which is also representative of the mid-infrared absorption in the diffuse interstellar medium in the Galaxy. There is spectral structure near 11.2 μm in NGC 3094 which may be due to a component of crystalline silicates. In NGC 5506, the depth of the silicate absorption increases from north to south across the nucleus, suggestive of a dusty structure on scales of tens of parsecs. We discuss the profile of the silicate absorption band towards galaxy nuclei and the relationship between the 9.7-μm silicate and 3.4-μm hydrocarbon absorption bands.  相似文献   

Spectropolarimetry of the 3-μm water-ice feature towards young stellar objects     

R. P. Holloway  A. Chrysostomou  D. K. Aitken  J. H. Hough  A. McCall 《Monthly notices of the Royal Astronomical Society》2002,336(2):425-435

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Uncertainty, rationality and cooperation in the context of climate change     

Nichola Raihani  David Aitken 《Climatic change》2011,108(1-2):47-55

Climate change represents the largest social dilemma humans have ever faced, where individual actors maximise their personal gain by emitting greenhouse gases into the atmosphere even though this is detrimental to the collective global good. Cooperation on a global scale is urgently required if we are to overcome this problem. However, this is difficult to achieve because cooperators pay the cost of reducing emissions while any benefits are shared between cooperators and free-riders alike. In a risk-free, rational world cooperative behaviour can be promoted through mechanisms that increase the benefit of cooperating relative to free-riding, such as rewards or sanctions. In reality, however, outcomes are seldom certain and humans rarely behave rationally when confronted with risky prospects. Here, we argue that effective policies to mitigate global climate change should incorporate mechanisms to foster cooperation, but also account for both uncertainty and irrational responses that may inhibit collective action.  相似文献   

Street fighting: Placing the crisis of masculinity in David Fincher's Fight Club     

James Craine  Stuart C. Aitken 《GeoJournal》2004,59(4):289-296

Recent writing in geography and its cognate disciplines suggests that the crisis of masculinity is in large part about the marginalization of men. With this paper, we take this spatial metaphor to task using David Fincher's Fight Club as a foil against which we try to pin larger issues of masculinity and urban life. That Flight Club can be viewed as alienated men confronting their homosocial and homoerotic selves through laddish revolutionary pranks detracts from its potential as a commentary on larger social tensions and contradictions. Men are simultaneously in the center and at the margins of what Bourdieu describes as the habitus; they are simultaneously playful and despairing, they are simultaneously alienated and the purveyors of hegemonic order. Fincher's movie engages these spatial metaphors and offers an opportunity to destroy the habitus, to change both masculinity and culture. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Global crises of childhood: rights, justice and the unchildlike child   总被引：1，自引：0，他引：1  

Stuart C. Aitken 《Area》2001,33(2):119-127

This paper traces how the notion of childhood changes as part of other social transformations. Globalization and the disillusion of public and private spheres are related to contemporary crises of childhood. Visible working children and child violence are highlighted as examples of unchildlike behaviour that suggests indeterminacy in the constitution of the global child. Issues of children's rights and new forms of justice are raised as potentially liberatory ways of viewing the crisis.  相似文献