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1.
B. Ahmed G. J. Alner H. Araujo J. C. Barton A. Bewick M. J. Carson D. Davidge J. V. Dawson T. Gamble S. P. Hart R. Hollingworth A. S. Howard W. G. Jones M. K. Joshi V. A. Kudryavtsev T. B. Lawson V. Lebedenko M. J. Lehner J. D. Lewin P. K. Lightfoot I. Liubarsky R. Lüscher J. E. McMillan B. Morgan G. Nicklin S. M. Paling R. M. Preece J. J. Quenby J. W. Roberts M. Robinson N. J. T. Smith P. F. Smith N. J. C. Spooner T. J. Sumner D. R. Tovey 《Astroparticle Physics》2003,19(6):691-702
The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented. 相似文献
2.
We have used Monte Carlo simulations to investigate the capabilities of a giant air shower observatory designed to detect showers initiated by cosmic rays with energies exceeding 1019 eV. The observatory is to consist of an array of detectors that will characterise the air shower at ground level, and optical detectors to measure the fluorescence light emitted by the shower in the atmosphere. Using these detectors together in a ‘hybrid’ configuration, we find that precise geometrical reconstruction of the shower axis is possible, leading to excellent resolution in energy. The technique is also shown to provide very good reconstruction below 1019 eV, at energies where the ground array is not fully efficient. 相似文献
3.
Antony J. Long Sarah A. Woodroffe Sue Dawson David H. Roberts Charlotte L. Bryant 《第四纪科学杂志》2009,24(4):345-359
In West Greenland, early and mid Holocene relative sea level (RSL) fall was replaced by late Holocene RSL rise during the Neoglacial, after 4–3 cal. ka BP (thousand calibrated years before present). Here we present the results of an isolation basin RSL study completed near to the coastal town of Sisimiut, in central West Greenland. RSL fell from 14 m above sea level at 5.7 cal. ka BP to reach a lowstand of ?4.0 m at 2.3–1.2 cal. ka BP, before rising by an equivalent amount to present. Differences in the timing and magnitude of the RSL lowstand between this and other sites in West and South Greenland record the varied interplay of local and non‐Greenland RSL processes, notably the reloading of the Earth's crust caused by a Neoglacial expansion of the Greenland Ice Sheet (GIS) and the subsidence associated with the collapse of the Laurentide Ice Sheet forebulge. This means that the timing of the sea level lowstand cannot be used to infer directly when the GIS advanced during the Neoglacial. The rise in Late Holocene RSL is contrary to recently reported bedrock uplift in the Sisimiut area, based on repeat GPS surveys. This indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late Holocene, and that there has been a switch from subsidence to uplift at some point in the last thousand years or so. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
4.
In this paper we view the different practices of archaeology, anthropology, environmental reconstruction and geomorphology through the lens of fieldwork on the clitter fields and Bronze Age settlement patterns on Leskernick Hill, Bodmin Moor, southwest Britain. The moor forms one of the best preserved fossil prehistoric landscapes of Europe and has undergone repeated periglacial episodes during the Quaternary. We show that the characterisation of patterned ground by archaeologists and anthropologists can be very different from that generated by geomorphology, particularly with respect to the spatial scales at which culture/nature questions are posed. We argue that the research project at Leskernick is a good example of how multi-disciplinary work is often more fruitful than mono-disciplinary and provides an example of how conversations across the divides of disciplinary practice can be held. 相似文献
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When spatial datasets are overlaid, corresponding features do not always coincide. This may be a result of the datasets having differing quality characteristics, being captured at different scales or perhaps being in different projections or datums. Data integration methods have been developed to bring such datasets into alignment. Although these methods attempt to maintain topological relationships within each dataset, spatial relationships between features in different datasets are generally not considered. The preservation of inter‐dataset topology is a research area of considerable current interest. This research addresses the preservation of topology within a data integration process. It describes the functional models established to represent a number of spatial relationships as observation equations. These are used to provide additional information concerning the relative positions of features. Since many topological relationships are best modelled as inequalities, an algorithm is developed to accommodate such relationships. The method, based on least squares with inequalities (LSI), is tested on simulated and real datasets. Results are presented to illustrate the optimal positioning solutions determined using all of the available information. In addition, updated quality parameters are provided at the level of the individual coordinate, enabling communication of local variation in the resultant quality of the integrated datasets. 相似文献
8.
A continuous/discontinuous Galerkin framework for modeling coupled subsurface and surface water flow
Clint Dawson 《Computational Geosciences》2008,12(4):451-472
We consider conjunctive surface-subsurface flow modeling, where surface water flow is described by the shallow water equations
and ground water flow by Richards’ equation for the vadose zone. Coupling between the models is based on the continuity of
flux and water pressure. Numerical approximation of the coupled model using the framework of discontinuous Galerkin (DG) methods
is formulated. In the subsurface, the local discontinuous Galerkin (LDG) method is used to approximate ground water velocity
and hydraulic head; a DG method is also used to approximate surface water velocity and elevation. This approach allows for
a weak coupling of the models and the use of different approximating spaces and/or meshes within each regime. A simplified
LDG method based on continuous approximations to water head is also described. Numerical results that investigate physical
and numerical aspects of surface–subsurface flow modeling are presented.
This work was supported by National Science Foundation grant DMS-0411413. 相似文献
9.
A preliminary study of the carbon-isotopic content of ambient formic acid and two selected sources: Automobile exhaust and formicine ants 总被引:2,自引:0,他引:2
Relatively large quantities (1 mg) of formic acid have been collected from the atmosphere and subjected to carbon-isotopic analysis, as a means of source discrimination. Ambient formic acid was captured on Ca(OH)2-treated filters using a high-volume sampler. The collection method was not only efficient (>96%), but also appears to have low artifact production.Most of the samples (36 out of 52) were collected over a two-year period at the summit of Mount Lemmon, Arizona, where a strong seasonality in HCOOH mixing ratio was observed (0.2 ppb during winter months to 1.5 ppb in the summer). Other collection sites included the Oregon coast, Colorado Rockies, urban Tucson, and the North Dakota prairie. The carbon-13 content of atmospheric HCOOH was found to be have little variation (–18 to –25), regardless of location or season. This is consistent with a single dominant source of formic acid. The carbon-14 measurements of 6 Mount Lemmon samples showed high levels of modern carbon (93–113% modern).The emissions from formicine ants and automobile combustion were selected as two other potential sources for isotopic analysis. The HCOOH collected from auto exhaust was much more depleted in13C than the atmospheric samples, with a 13C of –28.0 and –48.6 from a leaded and unleaded automobile, respectively. Formicine ants, on the other hand, ranged from –17.2 to –20.6. 相似文献
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