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31.
A large amount of interest has recently been expressed pertaining to the quantity of physically adsorbed water by the Martian regolith. Thermodynamic calculations based on experimentally determined adsorption and desorption isotherms and extrapolated to subzero temperatures indicate that physical adsorption of more than one or two monomolecular layers is highly unlikely under Martian conditions. Any additional water would find ice to be the state of lowest energy and therefore the most stable form. To test the validity of the thermodynamic calculations we have measured adsorption and desorption isotherms of sodium montmorillonite at ?5°C. To a first approximation it was found to be valid. 相似文献
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34.
Karen L. Hunter Dewayne A. Fox Lori M. Brown Kenneth W. Able 《Estuaries and Coasts》2006,29(3):487-498
Modification of brackish marshes by nonindigenousPhragmites australis has occurred across a broad geographical area in eastern North America. Among its effects on marsh processes,Phragmites may be increasingly unfavorable to marsh surface fishes as its invasion progresses within an estuary. We assessed the effect
of thePhragmites invasion on resident marsh surface fishes by examining the population response ofFundulus heteroclitus (mummichog, 5–48 mm TL) andF. luciae (spotfin killifish, 5–41 mm TL) to four distinct invasion stages in three estuaries of the U.S. mid Atlantic region (New
Jersey, Delaware, and Maryland). We documented precipitous declines in mean catch per unit effort ofF. heteroclitus in pit traps from natural marsh (51.6), through initial (33.8), early (12.3), and late invasion stages (2.4) across all sites.
A similar pattern was documented forF. luciae, with mean catch per unit effort in pit traps declining from natural marsh (48.9), through initial (39.1), early (9.3), and
late invasion stages (2.7). Population structure of both species also changed somewhat across invasion stages such that we
collected a narrower size range of individuals of both species from late invasion stages. Patterns suggest that as thePhragmites invasion progresses, there is a decline in habitat function for larval and juvenileF. heteroclitus and an increased risk of extirpation ofF. luciae from brackish marshes along the east coast of the U.S. 相似文献
35.
The heterogeneous mantle 总被引:1,自引:0,他引:1
36.
The U.S. and U.K. literatures have discussed “food deserts,” reflecting populated, typically urban, low‐income areas with limited access to full‐service supermarkets. Less is known about supermarket accessibility within Canadian cities. This article uses the minimum distance and coverage methods to determine supermarket accessibility within the city of Edmonton, Canada, with a focus on high‐need and inner‐city neighborhoods. The results show that for 1999 both of these areas generally had higher accessibility than the remainder of the city, but six high‐need neighborhoods had poor supermarket accessibility. We conclude by examining potential reasons for differences in supermarket accessibility between Canadian, U.S., and U.K. cities. 相似文献
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Fred J. Anderson 《Environmental Geology》2006,49(7):1034-1042
Several unfavorable environmental and engineering geologic conditions exist in Fargo, North Dakota. Dominantly, the behavior
of smectitic clays within the proglacial Lake Agassiz sediments of the Sherack and Brenna Formations creates subsoil instability
beneath engineered structures in the Fargo area and slope instability within cutbank meanders of the Red River of the North.
Unfavorable engineering geologic conditions encountered include: the elastic deformation of clayey glaciolacustrine soils,
shrink-swell properties, inadequate bearing capacities, and mass movements. These conditions are responsible for structural
failures including the Fargo Grain Elevator in 1955 and the Northern Pacific railroad grade. Bank failures along the Red River
are common due to the inherent instability of Brenna Formation smectitic clays which are subject to plastic deformation in
the subsurface, with resultant block failure of overlying Sherack Formation. Recent alluvial sediments due to typical fluvial
action and the continued seasonal saturation of cutbank meanders within the floodplain also add to soil instability. 相似文献
39.
Yang Liu Alfred T. Anderson Colin J. N. Wilson Andrew M. Davis Ian M. Steele 《Contributions to Mineralogy and Petrology》2006,151(1):71-87
Large pyroclastic rhyolites are snapshots of evolving magma bodies, and preserved in their eruptive pyroclasts is a record
of evolution up to the time of eruption. Here we focus on the conditions and processes in the Oruanui magma that erupted at
26.5 ka from Taupo Volcano, New Zealand. The 530 km3 (void-free) of material erupted in the Oruanui event is comparable in size to the Bishop Tuff in California, but differs
in that rhyolitic pumice and glass compositions, although variable, did not change systematically with eruption order. We
measured the concentrations of H2O, CO2 and major and trace elements in zoned phenocrysts and melt inclusions from individual pumice clasts covering the range from
early to late erupted units. We also used cathodoluminescence imaging to infer growth histories of quartz phenocrysts. For
quartz-hosted inclusions, we studied both fully enclosed melt inclusions and reentrants (connecting to host melt through a
small opening). The textures and compositions of inclusions and phenocrysts reflect complex pre-eruptive processes of incomplete
assimilation/partial melting, crystallization differentiation, magma mixing and gas saturation. ‘Restitic’ quartz occurs in
seven of eight pumice clasts studied. Variations in dissolved H2O and CO2 in quartz-hosted melt inclusions reflect gas saturation in the Oruanui magma and crystallization depths of ∼3.5–7 km. Based
on variations of dissolved H2O and CO2 in reentrants, the amount of exsolved gas at the beginning of eruption increased with depth, corresponding to decreasing
density with depth. Pre-eruptive mixing of magma with varying gas content implies variations in magma bulk density that would
have driven convective mixing.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献
40.
This paper describes an extension to the Combined Hydrology And Stability Model (CHASM) to fully include the effects of vegetation and slope plan topography on slope stability. The resultant physically based numerical model is designed to be applied to site‐specific slopes in which a detailed assessment of unsaturated and saturated hydrology is required in relation to vegetation, topography and slope stability. Applications are made to the Hawke's Bay region in New Zealand where shallow‐seated instability is strongly associated with spatial and temporal trends in vegetation cover types, and the Mid‐Levels region in Hong Kong, an area subject to a variety of landslide mechanisms, some of which may be subject to strong topographic control. An improved understanding of process mechanism, afforded by the model, is critical for reliable and appropriate design of slope stabilization and remedial measures. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献