Bedform topography and basal conditions beneath a fast-flowing West Antarctic ice stream     

Andy M. Smith  Tavi Murray 《Quaternary Science Reviews》2009,28(7-8):584-596

A grid of seismic reflection lines has been used to image basal topography and infer basal conditions and flow processes beneath ～140 km² of Rutford Ice Stream, West Antarctica. The subglacial topography in this region consists of two troughs flanking a central high and the bed is composed of water-saturated sediments. The two troughs are filled with deforming sediment, whereas the bed in the central region appears to undergo a transition from largely deforming conditions upstream to basal sliding downstream. The deforming bed is very flat along flow, but undulates across flow. Sliding areas show rougher bed topography. Cross-stream bed topography is characterised by streamlined mounds of deforming sediment aligned in the ice flow direction. These bedforms occur superimposed on the bed in regions of both basal sliding and sediment deformation. In places, they form finger-like mounds of material, which extend into the sliding region further downstream. Mean bedform height is 22 m, mean width is 267 m, and many of them extend for at least 1–2 km along flow. We interpret most of these bedforms as drumlins and one as a mega-scale glacial lineation. The juxtaposition of different basal conditions is consistent with models proposed from terrestrial studies in which the glacier bed is a mosaic of stable and deforming bed areas, variable both spatially and temporally. Any theory of subglacial sediment rheology must also be able to account for our conclusion that, at any given time, pervasive deformation extends at least a few metres into the bed and can persist over a considerable area (many km²). Bedform geometry and basal conditions concur with interpretations of former ice streams, with evidence for increasing elongation ratio with distance downstream. However, those studies also identified bedrock cropping out at the ice-bed interface, for which there is no evidence on Rutford Ice Stream.  相似文献   

Consolidation with threshold gradients     

Florica Pascal  Henry Pascal  D. W. Murray 《国际地质力学数值与分析法杂志》1981,5(3):247-261

Evidence for threshold gradients is reviewed. The consolidation problem, with threshold gradient, is properly formulated and solved numerically. An approximate analytical solution is also developed. The influence of a threshold gradient on the time rate of settlement is examined, and it is shown that by modifying the definition of the degree of consolidation a good approximation to the threshold gradient problem can be obtained directly from the Terzaghi solution. It is also shown that threshold gradients will have no influence on odometer testing and their effect is, therefore, to reduce the primary compression below that predicted from standard tests.  相似文献   

An introduction to global environmental issues. Kevin T. Pickering and Lewis A. Owen. Publisher Routledge,London 1994 (390 pp) £50.00 ISBN 0 415 10227 8 (hbk), £15.99 0 415 10228 6 (pbk)     

Murray Gray 《第四纪科学杂志》1995,10(2):186-186

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Three tenuous rings/arcs for three tiny moons     

M.M. Hedman  C.D. Murray  M.S. Tiscareno  M.W. Evans 《Icarus》2009,199(2):378-386

Using Cassini images, we examine the faint material along the orbits of Methone, Anthe and Pallene, three small moons that reside between the orbits of Mimas and Enceladus. A continuous ring of material covers the orbit of Pallene; it is visible at extremely high phase angles and appears to be localized vertically to within ±25 km of Pallene's inclined orbit. By contrast, the material associated with Anthe and Methone appears to lie in longitudinally confined arcs. The Methone arc extends over ∼10° in longitude around the satellite's position, while the Anthe arc reaches ∼20° in length. The extents of these arcs are consistent with their confinement by nearby corotation eccentricity resonances with Mimas. Anthe has even been observed to shift in longitude relative to its arc in the expected manner given the predicted librations of the moon.  相似文献   

Sorted stone circles in Elysium Planitia, Mars: Implications for recent martian climate     

M.R. Balme  C.J. Gallagher  J.B. Murray 《Icarus》2009,200(1):30-38

We have found sorted stone circles and polygons near the equator of Mars, using new 25 cm/pixel NASA HiRISE (High Resolution Imaging Science Experiment) images. The sorted circles occur in geologically recent catastrophic flood deposits in the equatorial Elysium Planitia region, and are diagnostic of periglacial processes: sorted polygons do not form from volcanic activity, as has been suggested for non-sorted polygons in this region. These landforms indicate that (i) a long-lived, geologically recent, active cryoturbation layer of ground ice was present in the regolith, (ii) there was some degree of freeze-thaw, and thus (iii) there were sustained period(s), likely within the last 10 Ma, in which the martian climate was 40 to 60 K warmer than current models predict.  相似文献   

Strategies for spectroscopy on extremely large telescopes – III. Remapping switched fibre systems     

C. L. Poppett  J. R. Allington-Smith  G. J. Murray 《Monthly notices of the Royal Astronomical Society》2009,399(1):443-452

We explore the use of remapping techniques to improve the efficiency of highly multiplexed fibre systems for astronomical spectroscopy. This is particularly important for the implementation of diverse field spectroscopy (DFS) using highly multiplexed monolithic fibre systems (MFS). DFS allows arbitrary distributions of target regions to be addressed to optimize observing efficiency when observing complex, clumpy structures such as protoclusters which will be increasingly accessible to extremely large telescopes. We show how the adoption of various types of remapping between the input and output of an MFS can allow contiguous regions of spatial elements to be selected using only simple switch arrays. Finally, we show how this compares in efficiency with integral-field and multi-object spectroscopy by simulations using artificial and real catalogues of objects. With the adoption of these mapping strategies, DFS outperforms other techniques when addressing a range of realistic target distributions. These techniques are also applicable to biomedical science and were in fact inspired by it.  相似文献   

Carbon catalysed hydrogen exchange in petroleum source rocks     

Robert Alexander  Daniel Dawson  Kieran Pierce  Andrew Murray 《Organic Geochemistry》2009,40(9):951-955

Exchange of carbon bound hydrogen has been observed when alkenes, saturated and aromatic hydrocarbons are heated at moderate temperatures on carbonaceous surfaces (activated carbon and coal). Isomerisation of alkenes and the formation of hydrogenated/dehydrogenated products from the saturated and aromatic reactants resulted. A suite of crude oils from the Carnarvon Basin (Western Australia) have been analysed with a view to comparing their relative abundances of structurally similar hydrocarbons. The consistent relationships between hydrocarbons in crude oils that are chemically related via hydrogenation/dehydrogenation reactions suggest that a hydrogen exchange process similar to that demonstrated in laboratory experiments occurs during crude oil formation in sedimentary rocks.  相似文献   

Youth empowerment and information and communication technologies: a case study of a remote Australian Aboriginal community     

Guy Singleton  Maria Fay Rola-Rubzen  Kado Muir  Deeva Muir  Murray McGregor 《GeoJournal》2009,74(5):403-413

In spite of a ‘digital divide’, Aboriginal groups in Australia, as internationally, are increasingly using information and communication technologies (ICTs) to maintain their cultures, communicate, archive knowledge, empower their communities, develop skills and generate income. Each community uses the technologies differently in accordance with their particular needs and the opportunities available. The use of ICTs in Aboriginal youth empowerment is illustrated through a case study of an initiative undertaken by the Walkatjurra Cultural Centre in Leonora, remote Western Australia. A participatory process was used to engage the Centre’s young people and they were given individual assistance to develop their ICT related capacity. The community conceives this youth empowerment to be part of a broader youth participation process that will contribute to the Centre’s overall objectives.  相似文献   

Paleoclimatic changes in southern Africa during the intensification of Northern Hemisphere glaciation: evidence from ODP Leg 175 Site 1085     

B. A. Christensen  J. L. Kalbas  M. Maslin  R. W. Murray 《Marine Geology》2002,180(1-4):117-131

Pliocene age sediments from Ocean Drilling Program Leg 175, Site 1085-A and B in the Cape Basin were analyzed to investigate the impact of the intensification of Northern Hemisphere glaciation (INHG) on the South Atlantic Benguela Current system from 4 to 2 Ma. Proxies for productivity (concentrations and mass accumulation rates of total organic carbon, carbon to nitrogen ratios, percent calcium carbonate, and percent biogenic silica) as well as weight percent sand (a proxy for preservation or winnowing) peak at 3.2, 3.0, 2.4, and 2.25 Ma. Normative calculations of allied trace and major elemental determinations indicate synchronous increases in productivity peaks, as well as high concentrations and accumulations of terrigenous sediments. Coeval increases in hemipelagic sedimentation and productivity indicators could be the result of enhanced eolian sedimentation resulting from strengthened winds, leading to elevated rates of upwelling and enhanced productivity. However, rapid burial, as indicated by high sedimentation rates, could also enhance preservation. The very high concentrations (>30%) and accumulations (up to 60 g/cm²/kyr) limit the likelihood that eolian sedimentation was the only transport mechanism, invoking an additional fluvial source. Rapid burial by either eolian or fluvial transport links these intervals of enhanced preservation and productivity with continental climate changes resulting from (1) increased winds and/or dust availability due to higher aridity in the Namibia/northern South Africa region; (2) lowered sea-level related to increased ice volume; (3) increased sediment load due to wetter conditions in the continental interior; or (4) some combination. Peaks at 3.2, 2.4 and 2.25 Ma are coincident with maximum precession, suggesting a link between hemipelagic sedimentation and enhanced monsoonal circulation over southern Africa. The Site 1085 sedimentary record during the INHG seems to be controlled by low-latitude processes linked to precession rather than hig-latitude processes.  相似文献   

The Evolution of Sunspot Magnetic Fields Associated with a Solar Flare     

Sophie A. Murray  D. Shaun Bloomfield  Peter T. Gallagher 《Solar physics》2012,277(1):45-57

Solar flares occur due to the sudden release of energy stored in active-region magnetic fields. To date, the precursors to flaring are still not fully understood, although there is evidence that flaring is related to changes in the topology or complexity of an active-region’s magnetic field. Here, the evolution of the magnetic field in active region NOAA 10953 was examined using Hinode/SOT-SP data over a period of 12 hours leading up to and after a GOES B1.0 flare. A number of magnetic-field properties and low-order aspects of magnetic-field topology were extracted from two flux regions that exhibited increased Ca ii H emission during the flare. Pre-flare increases in vertical field strength, vertical current density, and inclination angle of ≈ 8° toward the vertical were observed in flux elements surrounding the primary sunspot. The vertical field strength and current density subsequently decreased in the post-flare state, with the inclination becoming more horizontal by ≈ 7°. This behavior of the field vector may provide a physical basis for future flare-forecasting efforts.  相似文献