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  • 1
    Electronic Resource
    Electronic Resource
    The cell Reynolds number myth (1985)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 5 (1985), S. 305-310 
    Details
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The commonly accepted linear stability analysis for the forward-time centred-space (FTCS) algorithm applied to the transport equation has led to the concept of a cell Reynolds number restriction on the spatial grid size. This paper shows where the commonly accepted original analysis is in error and presents the correct stability restrictions, which are restrictions on the time step, not the spatial grid size. There is no cell Reynolds number restriction. The results are confirmed by numerical computations for the two-dimensional driven cavity problem.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650050402
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    Paper (German National Licenses)
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  • 2
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    Modeling of subglacial hydrological development following rapid supraglacial lake drainage. (2015)
    Wiley
    Details
    Publication Date: 2015-05-15
    Description: The rapid drainage of supraglacial lakes injects substantial volumes of water to the bed of the Greenland Ice Sheet over short timescales. The effect of these water pulses on the development of basal hydrological systems is largely unknown. To address this we develop a lake drainage model incorporating both 1) a subglacial radial flux element driven by elastic hydraulic jacking and 2) downstream drainage through a linked channelized and distributed system. Here we present the model and examine whether substantial, efficient subglacial channels can form during or following lake drainage events and their effect on the water pressure in the surrounding distributed system. We force the model with field data from a lake drainage site, 70 km from the terminus of Russell Glacier in West Greenland. The model outputs suggest that efficient subglacial channels do not readily form in the vicinity of the lake during rapid drainage and instead water is evacuated primarily by a transient turbulent sheet and the distributed system. Following lake drainage, channels grow but are not large enough to reduce the water pressure in the surrounding distributed system, unless pre-existing channels are present throughout the domain. Our results have implications for the analysis of subglacial hydrological systems in regions where rapid lake drainage provides the primary mechanism for surface-to-bed connections.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Persistent flow acceleration within the interior of the Greenland Ice Sheet (2014)
    Wiley
    Details
    Publication Date: 2014-01-16
    Description: [1]  We present surface velocity measurements from a high-elevation site located 140 km from the western margin of the Greenland Ice Sheet, and ~ 50 km into its accumulation area. Annual velocity increased each year from 51.78 ± 0.01 m yr -1 in 2009 to 52.92 ± 0.01 m yr -1 in 2012 – a net increase of 2.2 %. These data also reveal a strong seasonal velocity cycle of up to 8.1 % above the winter mean, driven by seasonal melt and supraglacial lake drainage. Sole et al. (2013) recently argued that ice motion in the ablation area is mediated by reduced winter flow following the development of efficient subglacial drainage during warmer, faster, summers. Our data complement this analysis and reveal a year-on-year increase in annual velocity above the ELA, where despite surface melt increasing, it is still sufficiently low to hinder the development of efficient drainage under thick ice.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed (2014)
    Springer Nature
    Details
    Publication Date: 2014-10-01
    Description: Article The delivery of meltwater to the base of the Greenland Ice Sheet has been shown to regulate ice flow, yet the role of soft basal sediment is unknown. Here, the authors use a three-dimensional ice sheet model to assess the impact of seasonal meltwater delivery on subglacial sediment shear strength and ice flow. Nature Communications doi: 10.1038/ncomms6052 Authors: M. Bougamont, P. Christoffersen, A. L, Hubbard, A. A. Fitzpatrick, S. H. Doyle, S. P. Carter
    Electronic ISSN: 2041-1723
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 5
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    Evidence for sediment eruption on deep sea floor, gulf of Mexico (1989)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1989-01-27
    Description: A large crater has been discovered on the sea floor, Gulf of Mexico, in a water depth of 2176 meters. Deep-tow high-resolution imagery shows that the crater is cut into a low hill surrounded by near-surface concentric faults. Approximately 2 million cubic meters of ejected sediment forms a peripheral debris field. The low hill and faults may be related to mud diapirism or intrusion of gas hydrates into near-surface sediments. A recent eruption evacuated sediments from the crater, apparently because of release of overpressured petrogenic gas.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Prior, D B -- Doyle, E H -- Kaluza, M J -- New York, N.Y. -- Science. 1989 Jan 27;243(4890):517-9.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17799186" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Physical Conditions of Fast Glacier Flow: 3. Seasonally‐Evolving Ice Deformation on Store Glacier, West Greenland (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Temporal variations in ice sheet flow directly impact the internal structure within ice sheets through englacial deformation. Large‐scale changes in the vertical stratigraphy within ice sheets have been previously conducted on centennial to millennial timescales; however, intra‐annual changes in the morphology of internal layers have yet to be explored. Over a period of 2 years, we use autonomous phase‐sensitive radio‐echo sounding to track the daily displacement of internal layers on Store Glacier, West Greenland, to millimeter accuracy. At a site located ∼30 km from the calving terminus, where the ice is ∼600 m thick and flows at ∼700 m/a, we measure distinct seasonal variations in vertical velocities and vertical strain rates over a 2‐year period. Prior to the melt season (March–June), we observe increasingly nonlinear englacial deformation with negative vertical strain rates (i.e., strain thinning) in the upper half of the ice column of approximately −0.03 a−1, whereas the ice below thickens under vertical strain reaching up to +0.16 a−1. Early in the melt season (June–July), vertical thinning gradually ceases as the glacier increasingly thickens. During late summer to midwinter (August–February), vertical thickening occurs linearly throughout the entire ice column, with strain rates averaging 0.016 a−1. We show that these complex variations are unrelated to topographic setting and localized basal slip and hypothesize that this seasonality is driven by far‐field perturbations in the glacier's force balance, in this case generated by variations in basal hydrology near the glacier's terminus and propagated tens of kilometers upstream through transient basal lubrication longitudinal coupling.
    Print ISSN: 2169-9003
    Electronic ISSN: 2169-9011
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    PLOS position on NIH public access policy (2005)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2005-04-16
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gass, Andy -- Doyle, Helen -- New York, N.Y. -- Science. 2005 Apr 15;308(5720):356.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15831740" target="_blank"〉PubMed〈/a〉
    Keywords: Access to Information ; *Biomedical Research ; *Information Dissemination ; Information Storage and Retrieval ; Internet ; *National Institutes of Health (U.S.) ; National Library of Medicine (U.S.) ; Periodicals as Topic ; *Publishing ; Research Support as Topic ; United States
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 8
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    Two distinct overstretched DNA structures revealed by single-molecule thermodynamics measurements [Physics] (2012)
    National Academy of Sciences
    Details
    Publication Date: 2012-05-23
    Description: Double-stranded DNA is a dynamic molecule whose structure can change depending on conditions. While there is consensus in the literature about many structures DNA can have, the state of highly-stretched DNA is still not clear. Several groups have shown that DNA in the torsion-unconstrained B-form undergoes an “overstretching” transition at a stretching force of around 65 pN, which leads to approximately 1.7-fold elongation of the DNA contour length. Recent experiments have revealed that two distinct structural transitions are involved in the overstretching process: (i) a hysteretic “peeling” off one strand from its complementary strand, and (ii) a nonhysteretic transition that leads to an undetermined DNA structure. We report the first simultaneous determination of the entropy (ΔS) and enthalpy changes (ΔH) pertaining to these respective transitions. For the hysteretic peeling transition, we determined ΔS ∼ 20 cal/(K.mol) and ΔH ∼ 7 kcal/mol. In the case of the nonhysteretic transition, ΔS ∼ -3 cal/(K.mol) and ΔH ∼ 1 kcal/mol. Furthermore, the response of the transition force to salt concentration implies that the two DNA strands are spatially separated after the hysteretic peeling transition. In contrast, the corresponding response after the nonhysteretic transition indicated that the strands remained in close proximity. The selection between the two transitions depends on DNA base-pair stability, and it can be illustrated by a multidimensional phase diagram. Our results provide important insights into the thermodynamics of DNA overstretching and conformational structures of overstretched DNA that may play an important role in vivo.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 9
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    How robust are in-situ observations for validating satellite-derived albedo over the dark zone of the Greenland Ice Sheet? (2017)
    Wiley
    Details
    Publication Date: 2017-06-11
    Description: Calibration and validation of satellite-derived ice sheet albedo data require high-quality, in-situ measurements commonly acquired by up- and down-facing pyranometers mounted on automated weather stations (AWS). However, direct comparison between ground and satellite-derived albedo can only be justified when the measured surface is homogeneous at the length-scale of both satellite pixel and in-situ footprint. Here, we use digital imagery acquired by an unmanned aerial vehicle to evaluate point-to-pixel albedo comparisons across the western, ablating margin of the Greenland Ice Sheet. Our results reveal that in-situ measurements overestimate albedo by up to 0.10 at the end of the melt-season because the ground footprints of AWS-mounted pyranometers are insufficient to capture the spatial heterogeneity of the ice surface as it progressively ablates and darkens. Statistical analysis of 21 AWS across the entire Greenland Ice Sheet reveals that almost half suffer from this bias, including some AWS located within the wet snow zone.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Antiquity of the continental slope along the middle-atlantic margin of the United States (1984)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1984-03-02
    Description: A detailed high-resolution geophysical study of part of the continental slope along the mid-Atlantic margin of the United States indicates that it is an ancient, relict landscape largely unmodified by modern slope processes. The slope morphology is heavily influenced by bedrock outcrops, including joints and bedding planes, rather than by any single degradational process. A pelagic drape averaging 3 to 5 meters in thickness blankets the slope. Carbon-14 dates from eight drop cores show that the drape was deposited in late Pleistocene and Holocene times. The Holocene part of the drape, comprising the uppermost 1 meter, was deposited at a continuous rate of 10 centimeters per 1000 years. Most features on the slope predate the drape cover.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Prior, D B -- Coleman, J M -- Doyle, E H -- New York, N.Y. -- Science. 1984 Mar 2;223(4639):926-8.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17781622" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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