Preface: Insights from environmental tracers in groundwater systems   总被引：2，自引：2，他引：0  

Ward E. Sanford  Werner Aeschbach-Hertig  Andrew L. Herczeg 《Hydrogeology Journal》2011,19(1):1-3

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Differences in pathogen indicators between proximal urban and rural karst springs,Central Kentucky,USA     

Thomas M. Reed  Alan E. Fryar  Gail M. Brion  James W. Ward 《Environmental Earth Sciences》2011,64(1):47-55

Because of their architecture, karst aquifers are susceptible to contamination by fecal-derived pathogens. Previous studies have examined the behavior of bacterial indicators such as total coliforms (TC) and fecal coliforms (FC) in karst aquifers, but simple techniques for discriminating between human and non-human inputs are still needed. This study examines concentrations of TC, FC, atypical colonies (AC, which grow on the same media as TC), male-specific coliphage virus (MSP, an indicator of human feces), and nitrate at two springs in the Inner Bluegrass region of Kentucky (USA). Blue Hole Spring primarily drains the city of Versailles, whereas spring SP-2 drains pasture. Baseflow was monitored, usually biweekly, from December 2002 to March 2004, while storm flow was monitored in September 2003 and March 2004. At each spring, bacterial concentrations were highest in storm flow and lowest in “normal” baseflow (for which 72-h antecedent precipitation was negligible). Concentrations in baseflow tended to be highest during late spring and summer and lowest during autumn and winter. FC concentrations exceeded regulatory (contact) standards in storm-flow samples. For both storm flow and baseflow, AC concentrations were greater than TC, which in turn were greater than FC. Median AC and TC concentrations were greater in baseflow at Blue Hole than at SP-2. MSP was detected in most samples from Blue Hole but never at SP-2. The AC/TC ratio was typically <15 except for normal baseflow samples at Blue Hole, which is probably impacted by leakage from sanitary sewers, as suggested by MSP and nitrate results. Mobilization of sessile bacteria appears to reduce the AC/TC ratio during storm flow. Consequently, this ratio shows promise as a screening tool to identify sewage inputs in karst groundwater basins under baseflow conditions.  相似文献   

Avalanche prediction in Scotland: II. Development of a predictive model   总被引：1，自引：0，他引：1  

R.G.W. Ward 《Applied geography (Sevenoaks, England)》1984,4(2):109-133

The paper presents a method for predicting avalanche activity from meteorological data which is suitable for Scottish snow conditions. Two main types of avalanche are distinguished. Direct-action avalanches are the result of fresh snow accumulation and may release after approximately 200 mm of fresh snow has fallen over a period of a few days. They become extremely likely if a further 100 mm falls in a single day. Climax avalanches are the result of strength loss in the snow cover, due either to thawing or persistent cold. Thaws may produce an avalanche after only three or four days with maximum temperatures around 2°C. Alternatively, if maximum temperatures remain below ?4°C for over a week, and especially if cold weather persists for two weeks, slab avalanches of dry snow are likely to occur. Between these two types are several possible avalanche situations in which fresh snow accumulation is combined with high or low temperatures. Topography plays a passive role, and determines where avalanche activity is most likely. Free faces, smooth surfaces and slopes in the lee of major storms respond most rapidly to the onset of avalanche conditions.  相似文献   

Short-Term Plume Containment: Multiobjective Comparison     

Richard C. Peralta  Robert L. Ward 《Ground water》1991,29(4):526-535

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The unusual supernova remnant surrounding the ultraluminous X-ray source IC 342 X-1   总被引：1，自引：0，他引：1  

T. P. Roberts  M. R. Goad  M. J. Ward  R. S. Warwick 《Monthly notices of the Royal Astronomical Society》2003,342(3):709-714

We report the results of an observation of a large-diameter (110 pc) supernova remnant (SNR) found to encircle the position of the ultraluminous X-ray source (ULX) IC 342 X-1. The inferred initial energy input to the SNR is at least 2–3 times greater than the canonical energy for an 'ordinary' SNR. Two regions on the inside of the shell are bright in [O iii ]λ5007 emission, possibly as the result of X-ray photoionization by the ULX. If this is the case, then the morphology of this nebulosity implies that the X-ray emission from the ULX is anisotropic. The presence of the ULX, most probably a black hole X-ray binary, within an unusually energetic SNR suggests that we may be observing the aftermath of a gamma-ray burst, although other origins for the energetic nebula are discussed.  相似文献   

Chandra observations of five ultraluminous X-ray sources in nearby galaxies   总被引：1，自引：0，他引：1  

T. P. Roberts  R. S. Warwick  M. J. Ward  M. R. Goad 《Monthly notices of the Royal Astronomical Society》2004,349(4):1193-1210

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SAVONOSKI CRATER,ALASKA: A POSSIBLE METEORITE IMPACT STRUCTURE     

Bevan M. French  Ernest H. Muller  Peter L. Ward 《Meteoritics & planetary science》1972,7(2):97-107

Savonoski Crater, a small basin about 1700 feet in diameter, is located on a ridge of gently-dipping Jurassic sandstone in Katmai National Monument, southwestern Alaska. Reconnaisance geological, geophysical, and petrographic studies suggest that it was formed either by volcanic processes or meteorite impact prior to the end of the latest glaciation in the region. Surface ejecta, if originally present, apparently have been removed by glaciation. No distinctive shock-metamorphic effects were observed in the few rock specimens collected. Final determination of the crater's origin will require more extensive field studies or drilling in the center of the crater.  相似文献   

Chandra HRC and HST observations of NGC 6240: resolving the active galactic nucleus and starburst     

P. Lira  M. J. Ward  A. Zezas  S. S. Murray 《Monthly notices of the Royal Astronomical Society》2002,333(3):709-714

We present high spatial resolution X-ray Chandra HRC and HST WFPC2 H α observations of the prototypical infrared-luminous galaxy NGC 6240. The central region of this system shows a remarkably complex morphology, with filaments and loops observed in the optical and X-rays. The total X-ray luminosity is dominated by the extended emission. Both nuclei are clearly detected in the HRC image and both appear to be extended. The energetics of the nuclei imply that the southern nucleus is the more plausible counterpart to the obscured active galactic nucleus. The overall spectral energy distribution of the galaxy is in good agreement with a blend of starburst and AGN components that have similar bolometric luminosities,   L _bol∼5×10⁴⁵ erg s^-1  , with the starburst dominating the observed continuum in the near-infrared ( K band), optical and soft X-ray bands.  相似文献   

GROUND-WATER QUALITY MONITORING - WHAT INFORMATION IS TO BE OBTAINED?     

Robert C. Ward 《Ground water》1981,19(2):130-132

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The role of megatides and relative sea level in controlling the deglaciation of the British–Irish and Fennoscandian ice sheets          下载免费PDF全文

J. D. Scourse  S. L. Ward  A. Wainwright  S. L. Bradley  K. Uehara 《第四纪科学杂志》2018,33(2):139-149

Key external forcing factors have been proposed to explain the collapse of ice sheets, including atmospheric and ocean temperatures, subglacial topography, relative sea level and tidal amplitudes. For past ice sheets it has not hitherto been possible to separate relative sea level and tidal amplitudes from the other controls to analyse their influence on deglaciation style and rate. Here we isolate the relative sea level and tidal amplitude controls on key ice stream sectors of the last British–Irish and Fennoscandian ice sheets using published glacial isostatic adjustment models, combined with a new and previously published palaeotidal models for the NE Atlantic since the Last Glacial Maximum (22 ka BP). Relative sea level and tidal amplitude data are combined into a sea surface elevation index for each ice stream sector demonstrating that these controls were potentially important drivers of deglaciation in the western British Irish Ice Sheet ice stream sectors. In contrast, the Norwegian Channel Ice Stream was characterized by falling relative sea level and small tidal amplitudes during most of the deglaciation. As these simulations provide a basis for observational field testing we propose a means of identifying the significance of sea level and tidal amplitudes in ice sheet collapse.  相似文献