Shape constants for plume models     

B. Henderson-Sellers 《Boundary-Layer Meteorology》1981,21(1):105-114

Two shape profiles are in common use in plume modelling to describe the variation of velocity and buoyancy across the cross-section of a stack plume. Conditions for equivalence of the Gaussian profile and the top hat profile are discussed in detail.  相似文献   

Pumped-storage hydropower schemes: integral plume models for pumpback simulations     

Brian Henderson-Sellers 《Advances in water resources》1983,6(4):224-239

Integral plume rise formulations for submerged jets in reservoirs are analysed for implementation in models of pumped-storage hydropower schemes. Calculations of entrainment require adequate representation of length scales, cross-sectional profiles, the entrainment coefficient and the zone of flow establishment (ZFE). A new method of determining the values of the flux variables at the end of the ZFE is given and recommendations are made for improved representations of the merging of a row of point diffusers.  相似文献   

Upscaling Permeability Measurements Within Complex Heterolithic Tidal Sandstones   总被引：2，自引：0，他引：2  

Matthew D. Jackson  Ann H. Muggeridge  Shuji Yoshida  Howard D. Johnson 《Mathematical Geology》2003,35(5):499-520

We investigate numerically the effect of sample volume on the effective single-phase permeability of heterolithic tidal sandstones, using three-dimensional models reconstructed directly from large rock specimens measuring 45 × 30 × 15 cm. We find that both individual and averaged effective permeability values vary as a function of sample volume, which indicates that permeability data obtained from core-plugs will not be representative at the scale of a reservoir model grid-block regardless of the number of measurements taken. However, the error introduced by averaged data may be minimized using the appropriate averaging scheme for a given facies type and flow direction.  相似文献   

Effects of seawater carbonate ion concentration and temperature on shell U, Mg, and Sr in cultured planktonic foraminifera     

Ann D. Russell  Bärbel Hönisch  Howard J. Spero 《Geochimica et cosmochimica acta》2004,68(21):4347-4361

We investigate the sensitivity of U/Ca, Mg/Ca, and Sr/Ca to changes in seawater [CO₃²⁻] and temperature in calcite produced by the two planktonic foraminifera species, Orbulina universa and Globigerina bulloides, in laboratory culture experiments. Our results demonstrate that at constant temperature, U/Ca in O. universa decreases by 25 ± 7% per 100 μmol [CO₃²⁻] kg⁻¹, as seawater [CO₃²⁻] increases from 110 to 470 μmol kg⁻¹. Results from G. bulloides suggest a similar relationship, but U/Ca is consistently offset by ∼+40% at the same environmental [CO₃²⁻]. In O. universa, U/Ca is insensitive to temperature between 15°C and 25°C. Applying the O. universa relationship to three U/Ca records from a related species, Globigerinoides sacculifer, we estimate that Caribbean and tropical Atlantic [CO₃²⁻] was 110 ± 70 μmol kg⁻¹ and 80 ± 40 μmol kg⁻¹ higher, respectively, during the last glacial period relative to the Holocene. This result is consistent with estimates of the glacial-interglacial change in surface water [CO₃²⁻] based on both modeling and on boron isotope pH estimates. In settings where the addition of U by diagenetic processes is not a factor, down-core records of foraminiferal U/Ca have potential to provide information about changes in the ocean’s carbonate concentration.Below ambient pH (pH < 8.2), Mg/Ca decreased by 7 ± 5% (O. universa) to 16 ± 6% (G. bulloides) per 0.1 unit increase in pH. Above ambient pH, the change in Mg/Ca was not significant for either species. This result suggests that Mg/Ca-based paleotemperature estimates for the Quaternary, during which surface-ocean pH has been at or above modern levels, have not been biased by variations in surface-water pH. Sr/Ca increased linearly by 1.6 ± 0.4% per 0.1 unit increase in pH. Shell Mg/Ca increased exponentially with temperature in O. universa, where Mg/Ca = 0.85 exp (0.096*T), whereas the change in Sr/Ca with temperature was within the reproducibility of replicate measurements.  相似文献   

Magnetic anisotropy of calcite at room-temperature     

Volkmar Schmidt  Detlef Günther  Ann M. Hirt 《Tectonophysics》2006,418(1-2):63

The intrinsic room temperature magnetic properties of pure calcite were determined from a series of natural crystals, and they were found to be highly dependent on the chemical composition. In general, dia-, para-, and ferromagnetic components contribute to the magnetic susceptibility and the anisotropy of magnetic susceptibility (AMS). With a combination of magnetic measurements and chemical analysis these three contributions were determined and related to their mineralogical sources. The intrinsic diamagnetic susceptibility of pure calcite is − 4.46 ± 0.16 × 10^− 9 m³/kg (− 12.09 ± 0.5 × 10^− 6 SI) and the susceptibility difference is 4.06 ± 0.03 × 10^− 10 m³/kg (1.10 ± 0.01 × 10^− 6 SI). These diamagnetic properties are easily dominated by other components. The paramagnetic contribution is due to paramagnetic ions in the crystal lattice that substitute for calcium; these are mainly iron and manganese. The measured paramagnetic susceptibility agrees with the values calculated from the known concentration of paramagnetic ions in the crystals according to the Curie law of paramagnetic susceptibility. Substituted iron leads to an increase in the AMS. The paramagnetic susceptibility difference was found to correlate linearly with the iron content for concentrations between 500 and 10,000 ppm. An empirical relation was determined: (k₁ − k₃)^para (kg/m³) = Fe-content (ppm) × (1 ± 0.1) × 10^− 12 (kg/m³/ppm). The maximum susceptibility difference (Δk = k₁ − k₃) was found to be unaffected by iron contents below 100 ppm. Ferromagnetic contributions due to inclusions of ferromagnetic minerals can dominate the susceptibility. They were detected by acquisition of isothermal remanent magnetization (IRM) and their contribution to the AMS was separated by high-field measurements.  相似文献   

Optimization strategies for sediment reduction practices on roads in steep,forested terrain     

Mary Ann Madej  Elizabeth A. Eschenbach  Carlos Diaz  Rebecca Teasley  Kristine Baker 《地球表面变化过程与地形》2006,31(13):1643-1656

Many forested steeplands in the western United States display a legacy of disturbances due to timber harvest, mining or wildfires, for example. Such disturbances have caused accelerated hillslope erosion, leading to increased sedimentation in fish‐bearing streams. Several restoration techniques have been implemented to address these problems in mountain catchments, many of which involve the removal of abandoned roads and re‐establishing drainage networks across road prisms. With limited restoration funds to be applied across large catchments, land managers are faced with deciding which areas and problems should be treated first, and by which technique, in order to design the most effective and cost‐effective sediment reduction strategy. Currently most restoration is conducted on a site‐specific scale according to uniform treatment policies. To create catchment‐scale policies for restoration, we developed two optimization models – dynamic programming and genetic algorithms – to determine the most cost‐effective treatment level for roads and stream crossings in a pilot study basin with approximately 700 road segments and crossings. These models considered the trade‐offs between the cost and effectiveness of different restoration strategies to minimize the predicted erosion from all forest roads within a catchment, while meeting a specified budget constraint. The optimal sediment reduction strategies developed by these models performed much better than two strategies of uniform erosion control which are commonly applied to road erosion problems by land managers, with sediment savings increased by an additional 48 to 80 per cent. These optimization models can be used to formulate the most cost‐effective restoration policy for sediment reduction on a catchment scale. Thus, cost savings can be applied to further restoration work within the catchment. Nevertheless, the models are based on erosion rates measured on past restoration sites, and need to be updated as additional monitoring studies evaluate long‐term basin response to erosion control treatments. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Dispersion and cost analysis of some finite difference schemes in one-parameter acoustic wave modeling     

Laurent Anné  Quang Huy Tran  William W. Symes 《Computational Geosciences》1997,1(1):1-33

Given a precision threshold to be imposed on the group velocity error and a finite difference scheme for the acoustic wave equation, it is possible to determine time-step and grid-spacing in an optimal manner, i.e., so as to minimize the computational cost. Using this optimal cost as a criterion, it becomes easy to compare schemes for efficiency in homogeneous media. Heterogeneous media with constant density can be accommodated to a certain extent by minimizing the cost over a range of Courant numbers. Such analysis shows that, amongst the second-order Taylor series schemes in time, higher-order schemes are generally more efficient than lower-order schemes. However, this result does not extend to very high order schemes.  相似文献   

Ruptures of deep-focus earthquakes in the north-western Pacific and their implications on seismogenesis   总被引：1，自引：0，他引：1  

Mary Ann Glennon  Wang-Ping Chen 《Geophysical Journal International》1995,120(3):706-720

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Lubbock Lake: Late Quaternary studies on the Southern High Plains : Edited by Eileen Johnson. Texas A&M Univ. Press, College Station, 1987, 179pp., tables, illustrations, $49.50     

Lee Ann Kreutzer 《Quaternary Research》1988,30(3)

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Evaluation of satellite derived land cover characteristics for global climate modelling     

G. Thomas  A. Henderson-Sellers 《Climatic change》1987,11(3):313-347

A preliminary evaluation of the suitability of a currently operational satellite data archive, namely the NOAA global vegetation index (GVI) product, as a basis for providing information on land cover characteristics for global climate modelling has been undertaken by comparing it to several existing data bases of soil and vegetation cover. It is found that temporal composites of GVI values often continue to change beyond the accepted compositing period of three or four weeks. In extreme cases the addition of another week to the compositing period changes over 90% of the pixels. Selection of GVI class boundaries is found to be rather hard and is probably a strong function of the classification technique employed. The resulting GVI classes are generally explicable by reference to other archival material although this study identifies some specific cases of locational divergence from consensus classification. In these locations monitoring with the GVI may prove useful. More importantly GVI values for very similar ecotypes vary widely from region to region thus rendering global classification very dangerous despite the graphic appeal of coloured maps. In its present form the NOAA global vegetation index is not a useful data source for climate modellers.Now at the Institute of Hydrology, Wallingford, U.K.  相似文献