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241.
Mitchell S. Craig 《地球表面变化过程与地形》2000,25(3):239-253
Aeolian sand transport was studied at the Lanphere Dunes, a coastal dune complex in northern California, by comparing slipface advance rates with transport predicted based on local wind data. The slipfaces of a 2·5 m high transverse ridge and 10 m high parabolic dune were monitored over a period of three months to estimate sand discharge. The study was performed during the dry season, which has the maximum sand‐driving potential. Over the three month study period, average sand discharge was 12·5 m3 per m width per year at the transverse ridge and 8·8 m3 per m width per year at the parabolic dune. A method was developed for modelling slipfaces that are sinuous and where sediment transport rates are not constant across the width of the slipface. Field measurements were used to generate three‐dimensional representations of dune slipfaces. Periodic measurements over the course of three months were used to compute the volume of displaced sediment. Theoretical sand transport was computed from local wind data using the Bagnold model and compared with the observed transport rates. Predicted rates were substantially lower than observed rates. Wind velocities rarely exceeded the threshold velocity. Discrepancies between the observed and predicted values appear to be caused by a combination of wind data recording procedures and differences between wind velocities at the anemometer location and the site where sand transport was measured. Wind data collected by weather bureaux have been utilized in numerous studies for modelling sediment transport. Such data typically have sample intervals of one hour or greater and are often averaged prior to reporting. The effect of averaging was investigated by comparing sand transport estimates based on daily average wind velocities with those based on the original hourly observations. The daily average data were depleted of high velocity winds and sand transport estimates were accordingly much lower than those based on the hourly data. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
242.
Precise geodesy with the Very Long Baseline Array 总被引:2,自引:2,他引:0
Leonid Petrov David Gordon John Gipson Dan MacMillan Chopo Ma Ed Fomalont R. Craig Walker Claudia Carabajal 《Journal of Geodesy》2009,83(9):859-876
We report on a program of geodetic measurements between 1994 and 2007 which used the Very Long Baseline Array (VLBA) and up
to ten globally distributed antennas. One of the goals of this program was to monitor positions of the array at a 1 mm level
of accuracy and to tie the VLBA into the international terrestrial reference frame. We describe the analysis of these data
and report several interesting geophysical results including measured station displacements due to crustal motion, earthquakes,
and antenna tilt. In terms of both formal errors and observed scatter, these sessions are among the very best geodetic very
long baseline interferometry experiments. 相似文献
243.
James T. Julian John A. Young John W. Jones Craig D. Snyder C. Wayne Wright 《Journal of Geographical Systems》2009,11(1):89-106
We examined whether spatially explicit information improved models that use LiDAR return signal intensity to discriminate
in-pond habitat from terrestrial habitat at 24 amphibian breeding ponds. The addition of Local Indicators of Spatial Association
(LISA) to LiDAR return intensity data significantly improved predictive models at all ponds, reduced residual error by as
much as 74%, and appeared to improve models by reducing classification errors associated with types of in-pond vegetation.
We conclude that LISA statistics can help maximize the information content that can be extracted from time resolved LiDAR
return data in models that predict the occurrence of small, seasonal ponds.
相似文献
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The aim of this paper is to determine whether British and German sea fisheries policies have been shaped by domestic factors or by European Union (EU) institutions. To achieve this aim, British and German perceptions of the EU's Common Fisheries Policy (CFP) were compared using two alternative theories of EU integration: Moravscik's Liberal Intergovernmentalism and Pierson's Historical Institutionalism. The perceptions of three sets of respondents—fisheries scientists, fishers, and politicians—were investigated in each country to determine whether they saw the CFP as a means of attaining their own nation's domestic fisheries agenda (as Liberal Intergovernmentalism would argue), or as an institutional champion of European fisheries as a whole (as might be predicted by Historical Institutionalism). The article concludes that although there were elements of both theories evident in each country's perceptions, British perceptions were more strongly indicative of Historical Institutionalism than Liberal Intergovernmentalism, and German perceptions were more strongly indicative of Liberal Intergovernmentalism than Historical Institutionalism. This difference is exemplified in Britain's euroscepticism (which sees EU institutions as obstacles to British fisheries’ interests), and Germany's environmentalism (which sees EU institutions as synchronising with Germany's national priorities). 相似文献
246.
Fiona A. Harrison Finn E. Christensen William Craig Charles Hailey Wayne Baumgartner C. M. H. Chen James Chonko W. Rick Cook Jason Koglin Kristin-Kruse Madsen Michael Pivavoroff Steven Boggs David Smith 《Experimental Astronomy》2005,20(1-3):131-137
Hard X-ray/soft gamma-ray astrophysics is on the verge of a major advance with the practical realization of technologies capable of efficiently focusing X-rays above 10 keV. Hard X-ray focusing telescopes can achieve orders of magnitude improvements in sensitivity compared to the instruments based on coded apertures and collimated detectors that have traditionally been employed in this energy band. Compact focal planes enable high-performance detectors with good spectral resolution to be employed in efficient, low-background configurations. We have developed multilayer coated grazing incidence optics and solid state Cadmium Zinc Telluride focal plane systems for the High Energy Focusing Telescope (HEFT) balloon-borne experiment, and for the Nuclear Spectroscopic Telescope Array (NuSTAR) Small Explorer satellite. In this paper we describe the technologies, telescope designs, and performance of both experiments. 相似文献
247.
Craig M. White 《Meteoritics & planetary science》1989,24(1):56-56
Abstract— The Wilder chondrite, a single stone of 1970 g, was found in southwestern Idaho in 1982. A classification of H5 is indicated by the mean compositions of olivines (Fa18.4) and orthopyroxenes (Fs16.3), and the narrow range in mineral compositions, recrystallized nature of the matrix, and mean Wo content of the orthopyroxenes (Wo1.34). 相似文献
248.
249.
This paper describes the formulation and application of a coupled unsaturated/saturated model framework developed to investigate the impact of mining on catchment water yield and groundwater dynamics. The model conceptualization was implemented in both a finite‐element (SUSCAT) and finite‐difference (WEC‐C) solution scheme and found to give similar results. The model framework simulates a coupled surface‐water and groundwater system in which a physically based solution scheme was used to simulate one‐dimensional movement through the unsaturated zone, and a distributed model was used to simulate two‐dimensional saturated groundwater flow. Each soil column comprises a series of layers, each layer being connected to adjacent cells. Subsurface lateral flow is considered when any cell within a layer develops a saturated thickness. Simulation results presented are based on a catchment in the Darling Range, Western Australia that was progressively mined and subsequently rehabilitated. The results predicted the groundwater system beneath the mine areas to have a peak rise owing to mining of between 2 and 4 m. Six years after mining, and following vegetation rehabilitation, the groundwater rise had reduced to 1 m above simulated unmined levels. The corresponding streamflow increase as a result of mining was estimated to peak at 21 mm/year and declined to 7·4 mm/year eight years after revegetation of the mined areas. The simulated groundwater response and streamflow results derived from both models were found to be consistent with observed data. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
250.