A numerical study of dispersion of passive scalars in city canyons     

Glenn T. Johnson  Laraine J. Hunter 《Boundary-Layer Meteorology》1995,75(3):235-262

A numerical model which simulates the dispersion of passive scalars within an urban canyon is proposed and some initial verification of the model undertaken. It is then used to investigate three-dimensional characteristics of the concentration field established for flow perpendicular to canyons with emissions released near the floor of the canyon by motor vehicles. In particular, the influence of canyon geometry on the concentration field is studied and some general observations made concerning the location of maximum concentrations.  相似文献   

Age of Sheep Creek Tephra (Pleistocene) in Central Alaska from Thermoluminescence Dating of Bracketing Loess     

Glenn W. Berger  Troy L. Péwé  John A. Westgate  Shari J. Preece 《Quaternary Research》1996,45(3):263-270

The age of the Sheep Creek tephra (SCt), a widespread marker ash bed in eastern Alaska and western Yukon Territory, has been ambiguous and controversial. We have obtained three reliable thermoluminescence age estimates from bracketing loess near Fairbanks that imply a deposition age of about 190,000 ± 20,000 yr for SCt. Three of six loess samples near and closely bracketing the SCt beds near Fairbanks yielded younger age estimates (∼117,000 and ∼135,000 yr), most likely (based on field aspects) because of reworking and contamination by translocated grains. The new, reliable age assignment of 190,000 yr confirms independent stratigraphic evidence of a pre-last interglaciation age, and stratigraphic evidence from one site (Upper Eva Creek) that SCt is older than the more-widespread 140,000-yr-old Old Crow tephra. The SCt age also has implications for regional correlations of glacial and nonglacial deposits. In particular, it supports the stratigraphic and geomorphic interpretation that the Delta Glaciation in the east-central Alaska Range and the Reid Glaciation in western Yukon Territory are older than the last interglaciation (isotope substage 5e).  相似文献   

Neural network methods in hydrodynamic yield estimation     

F. Dowla  R. Leach  L. Glenn  B. Moran  R. Heinle 《Pure and Applied Geophysics》1993,140(3):427-454

Hydrodynamic theory allows us to use the speed of a shock wave front to determine the yield of an explosion. On the basis of this theory we developed a neural network to estimate a yield of underground explosions from the shock wave radius versus time (RVT) data, as measured by continuous reflectometry for radius versus time experiments (CORRTEX). The proposed method not only replaces the subjective elements of conventional algorithms, but produces significantly improved yield estimates. The network was trained with real hydrodynamic data and its performance on unseen test events was studied. A backpropagation network was employed; the architecture consisted of ten input units, a hidden layer with eleven hidden units, and one output unit. The network was trained with thousands of input-output measurement vectors, the feasible input set, derived from the RVT data from only four other training or standard events (selected on the basis of the given RVT data from the unknown event). The feasible input vectors were propagated through the trained network and the network output was used to select the optimum yield estimate. Elements of the input vector were: center of energy (COE) offsets, shock front radii, and time onset and interval of analysis for both the standard and unknown events. We studied the performance of the proposed system using 24 Nevada Test Site (NTS) events that were located in the geologic medium tuff. Sensitivity analysis of the proposed method to the assumed nominal COE offset is discussed. Variations of the proposed system that might lead to further improvements in performance are suggested.  相似文献   

A multivariate approach to the evaluation of the climatic regions and climatic resources of China   总被引：1，自引：0，他引：1  

Glenn R. McGregor 《Geoforum》1993,24(4)

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A self-consistent model of the jovian plasma sheet     

Glenn T. Vickers 《Planetary and Space Science》1978,26(4):381-385

An axially-symmetric, rapidly-rotating magnetosphere containing low-energy plasma is considered. The resulting plasma sheet is presumed isothermal and thin compared with the radius of the sheet. Solutions of the model equations are found which include the effects of centrifugal, pressure and electro-magnetic forces. These solutions show that the sheet has a constant thickness and that the pressure decays exponentially with distance from the equatorial plane. The calculated curves for the magnetic induction field are compared with the observed field of Jupiter.  相似文献   

Does transported seagrass provide an important trophic link in unvegetated, nearshore areas?   总被引：2，自引：0，他引：2  

Glenn A. Hyndes  Paul S. Lavery 《Estuarine, Coastal and Shelf Science》2005,63(4):633-643

The contribution of detritus from seagrass and other primary producers to faunal production in unvegetated nearshore areas was examined primarily using stable isotopes. Fish, macroinvertebrates, meiofauna and primary producers (seagrasses, macroalgae, seston and benthic microalgae) were sampled from sites in south-western Australia. All samples were analysed for δ¹³C and δ¹⁵N values and fish gut contents were determined. δ¹³C values for seagrasses in the region were high compared to other macrophytes, ranging from 49.9 to −8.2‰ compared to −19.8 to −12.6‰ for macroalgae. The δ¹⁵N values ranged between 4.0 and 7.7‰ for the red, brown and green algae, and between 3.2 and 5.9‰ for seagrasses. Seston and benthic microalgae samples had a mean δ¹³C value of −12.8 and −14.0‰, respectively, and their δ¹⁵N values were comparable to the macroalgae. All invertebrate fauna had mean δ¹³C values considerably lower than seagrasses. However, individual samples harpacticoid copepods and polychaetes had a value as high as −11.7‰. δ¹⁵N values for consumers were higher than those of the primary producers, except for copepods and amphipods. The δ¹³C values for fish had a relatively small range, between −16.6 and −13.1‰, and the δ¹⁵N values of fish were elevated compared to the invertebrates and primary producers, ranging mostly between 10.0 and 12.6‰. Mixing model analysis based on δ¹³C values indicated that seagrass ranked low as a likely carbon source for all invertebrates other than harpacticoid copepods at a single site and some samples of polychaetes. The δ¹³C values for fish were similar to those of a combination of harpacticoid and calanoid copepods, amphipods and polychaetes. The consumption of harpacticoid copepods by some fish species indicates that Amphibolis and Posidonia species in south-western Australia can contribute to the food web of unvegetated nearshore areas as detritus, but brown algae is likely to make a greater contribution. At least for the time of year that was sampled, the flow of detrital seagrass material into the foodweb may be mediated by specific detrivores, in this case harpactacoid copepods, rather than by all detritivores.  相似文献   

The drying up of Britain? A national estimate of changes in seasonal river flows from 11 Regional Climate Model simulations     

Christel Prudhomme  Andy Young  Glenn Watts  Tracey Haxton  Sue Crooks  Jennifer Williamson  Helen Davies  Simon Dadson  Stuart Allen 《水文研究》2012,26(7):1115-1118

As climate change may modify the hydrological cycle significantly, understanding the impact on river flow is important because it affects long‐term water resources planning. Here, we describe a high‐resolution British assessment of changes in river flows in the 2050s under 11 different realisations of HadRM3. In winter, river flows may either increase or decrease, with a wide range of possible decreases in summer flow. These results should encourage adaptation that copes with a broad range of future hydrological conditions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Evaluation of a numerical model of the British–Irish ice sheet using relative sea‐level data: implications for the interpretation of trimline observations     

Joseph Kuchar  Glenn Milne  Alun Hubbard  Henry Patton  Sarah Bradley  Ian Shennan  Robin Edwards 《第四纪科学杂志》2012,27(6):597-605

The glacial isostatic adjustment (GIA) of the British Isles is complex due to the interplay between local and non‐local signals. A number of recent studies have modelled the GIA response of the British Isles using relative sea‐level data. This study extends these previous analyses by using output from a numerical glaciological model as input to a GIA model. This is a necessary step towards more realistic GIA models, and although there have been similar studies for the major late Pleistocene ice sheets, this is the first study to do so for the British Isles. We test three reconstructions, classed as ‘minimal’, ‘median’ and ‘maximal’ in terms of their volume at maximum extent, and find it is possible to obtain good data–model fits. The minimal reconstruction is clearly preferred by the sea‐level data. The ice reconstructions tested were not constrained by geomorphological information of past ice extent (lateral and vertical). As a consequence, the reconstructions extend further than much of this information suggests, particularly in terms of ice thickness. It is notable, however, that the reconstructions produce good fits to many sea‐level data from central, mountainous regions (e.g. Scottish highlands), which lends support to the suggestion that trimlines, often used as an constraint on the palaeo ice surface location, are in fact features formed at the transition from warm‐ to cold‐based ice and so mark a minimum constraint on the ice surface altitude. Based on data–model misfits, suggestions are made for improving the ice model reconstructions. However, in many locations, the cause of the misfit could be due to non‐local, predominantly Fennoscandian ice and so interpretation is not straightforward. As a result, we suggest that future analyses of this type consider models and observations for both Fennoscandia and the British Isles. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Understanding soil‐pipe flow and its role in ephemeral gully erosion     

Glenn Wilson 《水文研究》2011,25(15):2354-2364

The role of soil pipeflow in ephemeral gully erosion is not well understood. Experiments were conducted on continuous soil pipes to better understand the role of internal erosion of soil pipes and its relation to ephemeral gully development. Soil beds of 140 cm length, 100 cm width and 20 cm depth had a single soil pipe of different initial sizes (2, 4, 6, 8, and 10 mm diameter) extend from a water reservoir to the outlet. Experiments were run on Providence silt loam and Smithdale loam soils under a constant head of 15 cm established for 30 min. Either the tunnel collapsed or the head could not be maintained. Soil pipes that were initially 2 and 4 mm clogged instantaneously at their mouth and did not exhibit flow, whereas, pipes initially ≥ 6 mm enlarged by 268, 397, and 699% on average for the 6, 8, and 10 mm diameters, respectively. Critical shear stress values were found to be essentially zero, and erodibility values gave erosion indexes that were extremely high. The rapid internal erosion resulted in erratic flow and sediment concentrations with periods of no flow as pipes were temporarily clogged followed by surges of high flow and high sediment concentrations. Tensiometers within 6 cm of the soil pipes did not exhibit pressure increases typically associated with pipe clogging. Flow through 10 mm diameter soil pipes exhibited tunnel collapse for both soils tested. Tunnel collapse typically occurred within minutes of flow establishment suggesting that ephemeral gullies could be misinterpreted as being caused by convergent surface flow if observations were made after the runoff event instead of when flow is first established through soil pipes. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The ultraluminous and hyperluminous infrared galaxies in the Sloan Digital Sky Survey, 2dF Galaxy Redshift Survey and 6dF Galaxy Survey     

Ho Seong Hwang  Stephen Serjeant  Myung Gyoon Lee  Kang Hwan Lee  Glenn J. White 《Monthly notices of the Royal Astronomical Society》2007,375(1):115-127

We present a result of cross-correlating the Infrared Astronomical Satellite Faint Source Catalogue with the spectroscopic catalogues of galaxies in the Fourth Data Release of the Sloan Digital Sky Survey, the Final Data Release of the 2dF Galaxy Redshift Survey (2dFGRS) and the Second Data Release of the 6dF Galaxy Survey. We have identified 324 ultraluminous infrared galaxies (ULIRGs) including 190 newly discovered ULIRGs, and two hyperluminous infrared galaxies. Adding these new ULIRGs, we increase the number of known ULIRGs by about 30 per cent. The reliability of the cross-correlation is estimated using the likelihood ratio method. The incompleteness of our sample introduced by the identification procedure in this study is estimated to be about 5 per cent. Our sample covers the redshift range of   z = 0.037–0.517  with a median redshift of     , which is larger than that     of the sample of previously known ULIRGs.  相似文献