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71.
Uranyl adsorption onto montmorillonite: Evaluation of binding sites and carbonate complexation 总被引:2,自引:0,他引:2
The fate and transport of uranium in contaminated soils and sediments may be affected by adsorption onto the surface of minerals such as montmorillonite. Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to investigate the adsorption of uranyl (UO22+) onto Wyoming montmorillonite. At low pH (∼4) and low ionic strength (10−3 M), uranyl has an EXAFS spectrum indistinguishable from the aqueous uranyl cation, indicating binding via cation exchange. At near-neutral pH (∼7) and high ionic strength (1 M), the equatorial oxygen shell of uranyl is split, indicating inner-sphere binding to edge sites. Linear-combination fitting of the spectra of samples reacted under conditions where both types of binding are possible reveals that cation exchange at low ionic strengths on SWy-2 may be more important than predicted by past surface complexation models of U(VI) adsorption on related montmorillonites. Analysis of the binding site on the edges of montmorillonite suggests that U(VI) sorbs preferentially to [Fe(O,OH)6] octahedral sites over [Al(O,OH)6] sites. When bound to edge sites, U(VI) occurs as uranyl-carbonato ternary surface complexes in systems equilibrated with atmospheric CO2. Polymeric surface complexes were not observed under any of the conditions studied. Current surface complexation models of uranyl sorption on clay minerals may need to be reevaluated to account for the possible increased importance of cation exchange reactions at low ionic strengths, the presence of reactive octahedral iron surface sites, and the formation of uranyl-carbonato ternary surface complexes. Considering the adsorption mechanisms observed in this study, future studies of U(VI) transport in the environment should consider how uranium retardation will be affected by changes in key solution parameters, such as pH, ionic strength, exchangeable cation composition, and the presence or absence of CO2. 相似文献
72.
Sabine K.J. Cochrane Stanislav G. Denisenko Paul E. Renaud Christopher S. Emblow William G. Ambrose Jr. Ingrid H. Ellingsen Jofrid Skarhamar 《Journal of Sea Research》2009,61(4):222-233
Benthic faunal assemblages were analysed from 47 stations in the central and southern parts of the Barents Sea, together with sedimentary and water column parameters, daily ice records and modelled integrated primary productivity. Sampling spanned areas influenced by Atlantic Water (AW) to those lying under Arctic Water (ArW), and included stations with mixed water masses. Ice cover suppressed water column productivity in the northern areas. Three main faunal groups were identified, based on similarity of numerical faunal composition. The northern and southern faunal groups were separated by the northernmost penetration of AW in the bottom water and the third group, the Hopen group, was influenced by modified bank water. Faunal abundances were significantly higher within the southern faunal group relative to the northern group, but the numbers of taxa present were similar. The particularly rich fauna of the Hopen group reflected sediment heterogeneity and tight pelagic–benthic coupling. These results suggest that a retreat and thinning of the ice cover in the Barents Sea likely will result in the northern parts of the Barents Sea becoming more Atlantic in character, with a higher productivity at the sea floor. 相似文献
73.
基于开放互操作标准的分布式地理空间模型共享研究 总被引:1,自引:0,他引:1
传统的单机环境和封闭式网络环境由于有限的资源利用能力, 难以充分支持分散地学数据、模型等资源的共享与应用集成。基于网络环境的信息交换特点, 提出了分布式地理空间模型共享的服务体系。该体系以数据、模型、元数据等互操作要素为核心, 通过网络将数据、模型等网络节点进行开放式耦合。针对地理空间模型服务的互操作问题, 提出了分布式环境下的模型共享服务交互接口, 该接口定义了模型服务元数据、模型服务的交互操作、模型服务的通讯方式等交互规则, 尽可能地降低模型服务与模型终端之间在数据交换、功能调用等方面的互操作困难。为了降低将模型共享为模型服务的实现难度, 设计和开发了地理空间模型共享平台, 并介绍了在该平台上发布地理空间模型的2种方法。最后介绍了研究成果在Prairie生态模型共享方面的应用实践。 相似文献
74.
James R. Ledwell Dennis J. McGillicuddy Jr. Laurence A. Anderson 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1139
An intense deep chlorophyll layer in the Sargasso Sea was reported near the center of an anticyclonic mode-water eddy by McGillicuddy et al. [2007. Eddy–wind interactions stimulate extraordinary mid-ocean plankton blooms, Science, accepted]. The high chlorophyll was associated with anomalously high concentrations of diatoms and with a maximum in the vertical profile of 14C primary productivity. Here we report tracer measurements of the vertical advection and turbulent diffusion of deep-water nutrients into this chlorophyll layer. Tracer released in the chlorophyll layer revealed upward motion relative to isopycnal surfaces of about 0.4 m/d, due to solar heating and mixing. The density surfaces themselves shoaled by about 0.1 m/d. The upward flux of dissolved inorganic nitrogen, averaged over 36 days, was approximately 0.6 mmol/m2/d due to both upwelling and mixing. This flux is about 40% of the basin wide, annually averaged, nitrogen flux required to drive the annual new production in the Sargasso Sea, estimated from the oxygen cycle in the euphotic zone, the oxygen demand below the euphotic zone, and from the 3He excess in the mixed layer. The observed upwelling of the fluid was consistent with theoretical models [Dewar, W.K., Flierl, G.R., 1987. Some effects of wind on rings. Journal of Physical Oceanography 17, 1653–1667; Martin, A.P., Richards, K.J., 2001. Mechanisms for vertical nutrient transport within a North Atlantic mesoscale eddy. Deep-Sea Research II 48, 757–773] in which eddy surface currents cause spatial variations in surface stress. The diapycnal diffusivity at the base of the euphotic zone was 3.5±0.5×10−5 m2/s. Diapycnal mixing was probably enhanced over more typical values by the series of storms passing over the eddy during the experiment and may have been enhanced further by the trapping of near-inertial waves generated within the eddy. 相似文献
75.
Open coast storm surge water levels consist of wind setup due to wind shear at the water surface; a wave setup component caused by wind induced waves transferring momentum to the water column; an atmospheric pressure head component due to the atmospheric pressure deficit over the spatial extent of the storm system; a Coriolis forced setup or setdown component due to the effects of the rotation of the earth acting on the wind driven alongshore current at the coast; a possible seiche component due to resonance effects initiated by moving wind system, and, if astronomical tides are present, an astronomical tide component (although the tide is typically considered to be a forced astronomical event and not really a direct part of the external wind-driven meteorological component of storm surge). Typically the most important component of a storm surge is the wind setup component, especially on the U.S. East Coast and the Gulf of Mexico shorelines. In many approaches to storm surge modeling, a constant depth approximation is invoked over a limited step size in the computational domain. The use of a constant depth approximation has received little attention in the literature although can be very important to the resulting magnitude of the computed storm surge. The importance of discrete step size to the wind setup storm surge component is considered herein with a simple case computation of the wind setup component on a linear slope offshore profile. The present study findings show that the constant depth approximation to wind setup storm surge estimation is biased on the low side (except in extremely shallow water depths) and can provide large errors if discrete step size is not sufficiently resolved. Guidance has been provided on the error that one might encounter for various step sizes on different slopes. 相似文献
76.
S.A. Barboza R. Alway T. Akpulat W.L. Esch P.J. Hicks Jr. M.L. Gerdes 《Marine and Petroleum Geology》2009
Hydrocarbon top seal analyses are particularly difficult in fluvial and marginal marine settings. Although these settings often contain beds comprised of a low-permeability, clay-rich lithology associated with high quality seals, their presence does not guarantee an effective seal because individual beds within the stratal unit may be laterally discontinuous. Lateral facies changes, truncation of fine-grained beds, or the presence of crevasse splays may provide cross-stratal migration pathways, reducing the effective sealing capacity to a magnitude less than the closure height. 相似文献
77.
Harry Y. McSween Jr. Joshua P. Emery Andrew S. Rivkin Michael J. Toplis Julie C. Castillo‐Rogez Thomas H. Prettyman M. Cristina De Sanctis Carle M. Pieters Carol A. Raymond Christopher T. Russell 《Meteoritics & planetary science》2018,53(9):1793-1804
The mineralogy and geochemistry of Ceres, as constrained by Dawn's instruments, are broadly consistent with a carbonaceous chondrite (CM/CI) bulk composition. Differences explainable by Ceres’s more advanced alteration include the formation of Mg‐rich serpentine and ammoniated clay; a greater proportion of carbonate and lesser organic matter; amounts of magnetite, sulfide, and carbon that could act as spectral darkening agents; and partial fractionation of water ice and silicates in the interior and regolith. Ceres is not spectrally unique, but is similar to a few other C‐class asteroids, which may also have suffered extensive alteration. All these bodies are among the largest carbonaceous chondrite asteroids, and they orbit in the same part of the Main Belt. Thus, the degree of alteration is apparently related to the size of the body. Although the ammonia now incorporated into clay likely condensed in the outer nebula, we cannot presently determine whether Ceres itself formed in the outer solar system and migrated inward or was assembled within the Main Belt, along with other carbonaceous chondrite bodies. 相似文献
78.
Deposition in the New Jersey Pinelands was very acidic (pH=4.17) and contained high levels of SO2
−2 based on bulk deposition measurementsfrom July 1984–July 1986. Streamwater over the same interval in undisturbed watersheds
was less acidic (pH =4.52) and had proportionately less SO4
−2. A preliminary alkalinity budget for undisturbed watersheds suggested that SO4
−2 retention within Pinelands watersheds accounted for a large portion of the total alkalinity generated and thereby lessened
the impact of acidic deposition on surface waters. The only process capable of explaining the retention of SO4
−2 was microbial sulfate reduction in the extensive wetlands surrounding Pinelands streams which occurred at high rates. 相似文献
79.
J. F. Abel Jr. 《Geotechnical and Geological Engineering》1988,6(3):215-248
Summary Soft rock pillars can be designed by several methods available in the mining literature. All of these methods include the effect of shape, or geometry, on the average strength of specimens and pillars. All of the pillar design methods include some measurement of the strength of specimens of the pillar rock. The most common rock specimen strength property measured is the unconfined compressive strength. However, the average strength of triaxially confined rock specimens is much greater than the unconfined specimen strength, which can be more important to pillar strength. The estimation of the strength of a pillar is complicated by the decrease in rock specimen strength with increase in specimen size.Editor's note: In common with North American engineering practise, the paper uses English units throughout, where feasible conversions are included in the text. Where not, the following factors may be used: 1 inch=25.4 mm; 1 ft=0.3048 m; 1 lbf/in.–2=6.895 kn/m–2; 1Tonf.=8.896 kN. 相似文献
80.
M. J. Bickle S. M. Wickham H. J. Chapman H. P. Taylor Jr. 《Contributions to Mineralogy and Petrology》1988,100(4):399-417
Nd, Sr, and O isotope analyses have been made on metamorphic and igneous rocks and minerals from a 310–340 Ma Hercynian-age metamorphic terrane in the Pyrenees, France. Lower Paleozoic shales and phyllites have 87Sr/86Sr values of 0.707–0.717 at 310 Ma, but model values at 310 Ma of 0.709–0.736 (based on assumed depositional age of 450 Ma and an initial 87Sr/86Sr=0.707). On a regional scale, 87Sr/86Sr was homogenized to about 0.713 to 0.717 in the higher-grade pelitic schists during metamorphism. Much of this 87Sr/86Sr exchange occurred at very low grades (below the biotite isograd), but significant changes also accompanied the δ 18O lowering of the phyllites (+13 to +16) during their transformation to andalusite- and sillimanite-grade schists (δ 18O=+11 to +12); all of these effects are attributed to pervasive interactions with hydrothermal fluids (Wickham and Taylor 1985). The data also show that a syn-metamorphic plutonic complex, dominated by a biotite granite body, was derived by mixing of a relatively mafic magmatic end-member (87Sr/86Sr~ 0.7025–0.7050 and δ 18O~ +7.5 to +8.0) with two metasedimentary sources, both having 87Sr/86Sr~0.715 and δ 18O~ +10.0 to +12.0, but with one being more homogeneous than the other. The more homogeneous component and the (mantle-derived?) magmatic end-member dominate at low structural levels within the complex. The less homogeneous end-member that dominates at high levels is clearly derived from the local Paleozoic pelitic schists. A Rb-Sr age of 330±20 Ma was obtained on hornblende from a deep level within the complex, which fixes this age for the regional metamorphism, as well. Although a post-metamorphic granodiorite magma body at Trois Seigneurs also displays heterogeneities in δ 18O and 87Sr/86Sr (and thus does not give a clear-cut Rb-Sr isochron), the data are consistent with an emplacement age between 260 and 310 Ma, similar to ages of other late granodiorites in the Pyrenees. 143Nd/ 144Nd is very uniform within the Hercynian crust, both at Trois Seigneurs (? Nd=?3 to ?7) and elsewhere in the Pyrenees; almost all igneous lithologies have depleted-mantle, mid-Proterozoic model ages, consistent with efficient recycling of crustal material following original crustal accretion in this area at about 1600 Ma or earlier. Rb-Sr mineral ages exhibit a complex cooling history reflecting late Hercynian and Mesozoic thermal events. Our results show that profound homogenization of the 87Sr/86Sr and 18O/16O ratios of large volumes of the crust can occur during regional metamorphism and crustal anatexis, particularly in regions undergoing extensional tectonics. Such processes can significantly modify the isotopic compositions of the protoliths of granitic magmas; this may explain why many peraluminous Hercynian granitoids of Western Europe have anomalously low (87Sr/86Sr) initial values compared to their probable sedimentary parent rocks. 相似文献