Rayleigh-Taylor instability: experiments with image analysis     

Stuart B. Dalziel 《Dynamics of Atmospheres and Oceans》1993,20(1-2)

Rayleigh-Taylor instability is investigated in the laboratory using a simple apparatus of novel design to set up the unstable initial conditions. Visualisation techniques give a qualitative view of the development of the instability. Quantitative measurements are obtained through digital image analysis. Of primary interest is the evolution of the velocity field. Measurements are made over a two dimensional slice of the flow using an efficient, high-resolution particle tracking technique. This technique is described and its strengths and limitations are discussed in comparison with traditional measurement techniques. The visualisations and velocity measurements are compared with the experimental and numerical results of previous workers.  相似文献   

Stick-Nest Rat Middens as Sources of Paleoecological Data in Australian Deserts     

Stuart Pearson  John R. Dodson 《Quaternary Research》1993,39(3)

The existing paleoenvironmental data from the Australian arid zone lack sensitivity and come from only a few sites. Macrofossils and pollen from four dated middens of the stick-nest rat (Leporillus spp.) were analyzed from two sites in Western Australia. Animal and plant macrofossil remains were well preserved and provided evidence of change in species distribution within the last 1150 yr. Brush-tail possum and golden bandicoot have contracted their ranges in the recent past, possibly since the introduction of cats into Australia. An undescribed lacewing was also a significant find. Pollen preserved in parts of the same midden and in middens from different sites indicates that records are sensitive to the composition of the local vegetation when the midden was built. Pollen spectra are quite different from playa lakes, which record largely regional vegetation. Pollen preserved in the fecal pellets, desiccated urine, and grass mat nesting material provided similar information but some differences were apparent, suggesting dietary preferences were reflected in the fecal component. The pollen record suggested a trend to less-wooded vegetation cover in central Australia between 900 and 300 yr B.P.  相似文献   

A Ground Water Monitoring Study for Pesticides and Nitrates Associated with Golf Courses on Cape Cod     

Stuart Z. Cohen  Susan Nickerson  Robert Maxey  Aubry Dupuy Jr.  Joseph A. Senita 《Ground Water Monitoring & Remediation》1990,10(1):160-160

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Physical processes determining the chromospheric temperature distribution     

Stuart D. Jordan 《Solar physics》1977,51(1):51-59

Calculations performed with several models of the solar chromosphere support Ulmschneider's conclusion that relatively short period acoustic waves heat the low chromosphere in the region just above the temperature minimum. However, these same short period waves (10 period P80 s) are not able to maintain chromospheric temperatures at heights where _5000Å(normal) < 10^-6. The calculations also show that an earlier conjecture stating that the H₂ population might influence the non-LTE chromospheric H^- population is probably not correct, due to lower values of the ratio n _e/n _H inferred from more recent observations. Finally, the calculations support Athay's contention that the Cayrel mechanism alone cannot produce the observed temperature rise, because the magnitude of the radiative cooling in the lines is too great.  相似文献   

A synthesis of the early life history of the anglerfish, Lophius piscatorius (Linnaeus, 1758) in northern British waters   总被引：1，自引：0，他引：1  

Hislop  John R.G.; Gallego  Alejandro; Heath  Michael R.; Kennedy  Fiona M.; Reeves  Stuart A.; Wright  Peter J. 《ICES Journal of Marine Science》2001,58(1):70-86

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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   

Assessment of rainfall‐runoff models based upon wavelet analysis     

Stuart N. Lane 《水文研究》2007,21(5):586-607

A basic hypothesis is proposed: given that wavelet‐based analysis has been used to interpret runoff time‐series, it may be extended to evaluation of rainfall‐runoff model results. Conventional objective functions make certain assumptions about the data series to which they are applied (e.g. uncorrelated error, homoscedasticity). The difficulty that objective functions have in distinguishing between different realizations of the same model, or different models of the same system, is that they may have contributed in part to the occurrence of model equifinality. Of particular concern is the fact that the error present in a rainfall‐runoff model may be time dependent, requiring some form of time localization in both identification of error and derivation of global objective functions. We explore the use of a complex Gaussian (order 2) wavelet to describe: (1) a measured hydrograph; (2) the same hydrograph with different simulated errors introduced; and (3) model predictions of the same hydrograph based upon a modified form of TOPMODEL. The analysis of results was based upon: (a) differences in wavelet power (the wavelet power error) between the measured hydrograph and both the simulated error and modelled hydrographs; and (b) the wavelet phase. Power difference and wavelet phase were used to develop two objective functions, RMSE(power) and RMS(phase), which were shown to distinguish between simulated errors and model predictions with similar values of the commonly adopted Nash‐Sutcliffe efficiency index. These objective functions suffer because they do not retain time, frequency or time‐frequency localization. Consideration of wavelet power spectra and time‐ and frequency‐integrated power spectra shows that the impacts of different types of simulated error can be seen through retention of some localization, especially in relation to when and the scale over which error was manifest. Theoretical objections to the use of wavelet analysis for this type of application are noted, especially in relation to the dependence of findings upon the wavelet chosen. However, it is argued that the benefits of localization and the qualitatively low sensitivity of wavelet power and phase to wavelet choice are sufficient to warrant further exploration of wavelet‐based approaches to rainfall‐runoff model evaluation. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Editorial     

Finlay M. Stuart  Tibor J. Dunai 《Quaternary Geochronology》2009,4(6):435-436

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Development of guidelines for ammonia in estuarine and marine water systems   总被引：1，自引：0，他引：1  

Graeme E. Batley  Stuart L. Simpson 《Marine pollution bulletin》2009,58(10):1472-1476

The water quality guideline trigger value for ammonia in estuarine and marine waters has been revised with the addition of 38 new results to the data set of 21 used in earlier guideline derivations. Using species sensitivity distributions, a new trigger value of 460 μg total NH₃-N/L was derived for slightly to moderately disturbed systems (95% protection concentration, PC95), with a value of 160 μg total NH₃-N/L applying to waters of high conservation value (PC99). For sediment pore waters, a guideline trigger value of 3.9 mg total NH₃-N/L, derived from the 80th percentile of background data from Sydney Harbour, is recommended. This value is likely to be exceeded in degraded sediments subject to dredging; however, ocean disposal of such sediments results in rapid decreases in porewater ammonia and a guideline trigger value for dissolved ammonia during disposal of dredged sediments of 1550 μg total NH₃-N/L is proposed.  相似文献   

Suspended sediment transport and deposition over a dune: Río Paraná, Argentina     

Ray Kostaschuk  Dan Shugar  Jim Best  Dan Parsons  Stuart Lane  Rich Hardy  Oscar Orfeo 《地球表面变化过程与地形》2009,34(12):1605-1611

Field data from the Rio Paraná, Argentina, are used to examine patterns of suspended sediment transport over a sand dune. Measurements of three‐dimensional velocity are made with an acoustic Doppler current profiler whilst suspended sediment concentration and particle size have been quantified using a laser in situ sediment scattering transmissometer. Suspended sediment concentration and streamwise and vertical sediment flux are highest close to the bed, with an upward vertical flux over the stoss side of the dune and downward flux over the lee side. Suspended sediment concentrations are higher over the crest compared with the trough and suspended sediment is coarsest near the bed. About 17% of the suspended‐load transported over the crest is deposited in the lee side before it reaches the trough. Most of this deposited sand is coarser sediment that originates close to the bed over the crest, a result consistent with simulations based on the model of Mohrig and Smith (Water Resources Research 1996; 32: 3207–3217) for the excursion lengths of sediment dispersed in the lee side of a dune. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献