Possible transformation of zinc dissolved in mediterranean coastal sea water     

R. Fukai  L. Huynh-Ngoc  C. N. Murray 《Journal of Oceanography》1973,29(1):44-45

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Distinct side-scan sonar, RADARSAT SAR, and acoustic profiler signatures of gas and oil seeps on the Gulf of Mexico slope   总被引：4，自引：0，他引：4  

S. M. De Beukelaer  I. R. MacDonald  N. L. Guinnasso Jr.  J. A. Murray 《Geo-Marine Letters》2003,23(3-4):177-186

We examined bubble streams from four natural seep sites on the upper continental slope of the Gulf of Mexico. Synthetic aperture radar images verified surface oil slicks over sites with oily bubbles but not over those with non-oily bubbles. Non-oily bubbles produced high backscatter on side-scan sonar records, but were difficult to detect with acoustic profilers. Oily bubbles produced clear signatures extending from the seafloor to the near-surface on acoustic profiles and produced acoustic shadows on side-scan sonar records. We hypothesize that the bubbles oily coating causes the different signatures, since all bubbles were resonant at the tested frequencies.  相似文献   

Comments on the origins of coronal mass ejections     

Murray Dryer 《Solar physics》1996,169(2):421-429

Explicit delineation of the cause (or causes) of coronal mass ejections (CMEs) has eluded our understanding for several decades. More recently, their extension into interplanetary space has also attracted attention, particularly since the faster CMEs have been inferred to be associated with the more severe, non-recurrent, geomagnetic storms. Understanding the linkage of one phenomenon to the other requires improved monitoring of the manifestations of CMEs so that post-launch tracking via remote-sensing (interplanetary scintillations) and/or in situ observations will be meaningful. A critical examination is made here of recent claims that the single cause of CMEs lies in their close connection with large-scale, closed magnetic structures in the corona. Proponents of this position generally disregard or minimize an earlier, proposed suggestion that the cause is to be found in the small-scale, complex activity within eruptive flares with or without eruptive prominences. It is proposed here that equal weight to a bimodal set of causes should be considered. We also revisit a number of comments, pro and con, on the proposed solar flare myth paradigm.Dedicated to Cornelis de Jager  相似文献   

Devensian glacial events in Buchan (NE Scotland): A progress report on new OSL dates and their implications     

Alastair M.D. Gemmell  Andrew S. Murray  E.R. Connell 《Quaternary Geochronology》2007,2(1-4):237-242

Optically stimulated luminescence (OSL) dating of a series of glaciofluvial/glaciodeltaic sediments in central Buchan and Aberdeen has recently been undertaken. The aims of this project are to test the chronological model proposed by the most recent regional review and the suggestion that parts of Buchan may have remained ice-free during the last glacial maximum (late marine isotope stage (MIS) 3 and MIS 2 29–15 ka). The preliminary results indicate that during the Devensian (ca. 116–12 ka), extensive areas of Buchan may have been glaciated earlier than previously believed (possibly during MIS 4, 72–60 ka), but parts of the region show no depositional evidence of later glaciation. Some waterlain sediments from the Ugie Valley have yielded OSL ages indicating deposition during MIS 5d to MIS 5a (116–72 ka). We discuss whether the absence of overlying glaciogenic sediments at these locations raises questions about the reliability of the OSL ages or about existing models of the Devensian glaciation of Buchan.  相似文献   

Investigation of river network evolution using luminescence dating and heavy mineral analysis of Late-Quaternary fluvial sands from the Great Hungarian Plain     

Edit Tham-Bozs  Andrew S. Murray  Annamria Ndor  rpd Magyari  Edit Babinszki 《Quaternary Geochronology》2007,2(1-4):168-173

To reconstruct the evolution of Late-Quaternary river network in the southeastern part of the Great Hungarian Plain, we have used optically stimulated luminescence (OSL) and heavy mineral analysis of 25 sand samples from the upper 2–8 m of the fluvial units, complemented by four radiocarbon ages. The estimated OSL depositional ages vary between 10 and 47 ka. The heavy mineral composition of the OSL samples was compared to the compositional data of recent river sediments using cluster analysis. The new OSL and heavy mineral data show that from 47 to 10 ka ago the sediments were transported mainly from the northeast direction into the southeastern part of the Great Hungarian Plain by the ancestor of the Tisza river and its northern tributaries, and probably by another large river which also flowed northeast–southwest, parallel to the modern Tisza. Between 23 and 14 ka sediments periodically came from the east and reached the eastern part of our study area. Between 15 and 12 ka ago, sands transported from the southeast also occur in the southeastern and central part of the study area. These data suggest that the modern rivers occupied their present courses only in the last 10 ka.  相似文献   

Resetting of sediments mobilised by the LGM ice-sheet in southern Norway   总被引：3，自引：0，他引：3  

Anne-Grete Be  Andrew Murray  Svein Olaf Dahl 《Quaternary Geochronology》2007,2(1-4):222-228

Former geological field investigations in the Rondane area, east-central southern Norway, have proposed that the maximum Fennoscandian ice-sheet coverage occurred during the Late Weichselian Glacial Maximum (LGM, ca. 20 ka) and that subsequent glaciofluvial sediments were first deposited in the early Holocene (after 10 ka). However, recent field investigations with ages from three internally consistent quartz optically stimulated luminescence (OSL) age series show an apparent deglaciation of northern Rondane in the period 20.0–13.8 ka. We examine here the possibility that these ages are too old because the sediment was not completely zeroed prior to deposition. Our investigations of incomplete bleaching use modern analogues, small aliquots, and single grains of quartz. First, the symmetric shape of small aliquot equivalent dose distributions suggests that the sediment was probably well bleached at deposition. This is supported by 5 modern analogue equivalent doses (D_e) of 0.6 Gy, 1.5% of the typical D_e from the deglaciation sediments. Finally, from single grain studies on three samples, we conclude that there is no evidence for poor bleaching in these samples; thus the weighted mean gives the best estimates of D_e, and these are completely consistent with both large and small aliquot estimates for these samples. These comparisons between large aliquots, modern analogues, small aliquots and single-grain analyses help to validate the OSL ages and confirm the complete resetting of these sediments prior to deposition.  相似文献   

A comparison of methods for evaluating soil redistribution in the severely eroded Stavropol region, southern European Russia   总被引：3，自引：1，他引：3  

V.R. Belyaev  P.J. Wallbrink  V.N. Golosov  A.S. Murray  A.Yu. Sidorchuk 《Geomorphology》2005,65(3-4):173-193

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Simulations of superhumps and superoutbursts     

Murray 《Monthly notices of the Royal Astronomical Society》1998,297(1):323-333

We numerically study the tidal instability of accretion discs in close binary systems using a two-dimensional SPH code. We find that the precession rate of tidally unstable, eccentric discs does not only depend upon the binary mass ratio q . Although the (prograde) disc precession rate increases with the strength of the tidal potential, we find that increasing the shear viscosity ν also has a significant prograde effect. Increasing the disc temperature has a retrograde impact upon the precession rate.   We find that motion relative to the binary potential results in superhump-like, periodic luminosity variations in the outer reaches of an eccentric disc. The nature and location of the luminosity modulation are functions of ν. Light curves most similar to observations are obtained for ν values appropriate for a dwarf nova in outburst.   We investigate the thermal–tidal instability model for superoutburst. A dwarf nova outburst is simulated by instantaneously increasing ν, which causes a rapid radial expansion of the disc. Should the disc encounter the 3: 1 eccentric inner Lindblad resonance and become tidally unstable, then tidal torques become much more efficient at removing angular momentum from the disc. The disc then shrinks and M _d increases. The resulting increase in disc luminosity is found to be consistent with the excess luminosity of a superoutburst.  相似文献   

Using an approximation of the three-point Gauss–Hermite quadrature formula for model prediction and quantification of uncertainty     

Jonathan Levy  Murray K. Clayton  Gordon Chesters 《Hydrogeology Journal》1998,6(4):457-468

 Computer models are commonly used by regulators and managers to make predictions regarding groundwater flow and contaminant concentrations at various locations and times. However, the uncertainty associated with those predictions is often overlooked, despite the fact that an assessment of such uncertainty is critical in the formulation of policy decisions. One method of quantifying the uncertainty of model predictions, based on the collective uncertainties of the model parameter input values, is to use an approximation of the three-point Gauss–Hermite quadrature formula. The Gauss–Hermite approximation is a convenient substitute for simple Monte Carlo sampling, because it requires fewer model runs and provides an immediate sensitivity analysis of parameter main effects and two-way interactions. For example, a model with four parameters, each with its own associated uncertainty, needs to be run only 33 times to complete the Gauss–Hermite analysis. For an application to a contaminant-transport model, the Gauss–Hermite approximation compares well to the full method, with considerable savings in computing effort. By comparison, Latin hypercube sampling can be more flexible, but it is more complex to use in some circumstances and cannot as easily generate the detailed sensitivity analysis that the Gauss–Hermite approach offers. Received, October 1997 Revised, August 1998 Accepted, August 1998  相似文献   

Multiple Sources for Sea-Rafted Loisels Pumice, New Zealand     

Phil Shane  Paul Froggatt  Ian Smith  Murray Gregory 《Quaternary Research》1998,49(3):271-279

Sea-rafted Loisels Pumice is one of the few stratigraphic markers used to correlate late Holocene coastal deposits in New Zealand. Along with underlying sea-rafted products of the local Taupo eruption of ca. 1800 yr B.P., these events have been used to bracket the first arrival of humans at New Zealand. Loisels Pumice is dacitic to rhyolitic (SiO₂63–78 wt%) in composition, but individual clasts are homogeneous (SiO₂range ± 1 wt%). Characteristics include very low K₂O (0.5–1.75 wt%) and Rb (<25 ppm) and a mineralogy dominated by calcic and mafic xenocrysts. Similar features are shared by pumices of the Tonga–Kermadec arc, suggesting a common tholeiitic oceanic source. Interclast diversity of Loisels Pumice suggests that it is the product of several eruptive events from different volcanoes. The differences in glass and mineral compositions found at various sites can be explained if the deposits are from different events. A multisource origin can also partially explain the discrepancy in reported¹⁴C ages (ca. 1500–600 yr B.P.) from different localities. Therefore, the value of Loisels Pumice as a stratigraphic marker is questionable, and it does not constrain the arrival of humans. The predominant westward drift of historic Tonga–Kermadec arc pumices and prevailing ocean currents suggest a long anticlockwise semicircular transport route into the Tasman Sea before sea-rafted pumice arrival in New Zealand. The diversity of the pumices indicates that silicic eruptions frequently occur from the predominantly basic oceanic volcanoes.  相似文献