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排序方式: 共有432条查询结果,搜索用时 31 毫秒
131.
132.
Comparative major ion geochemistry of Piedmont streams in the Atlanta,Georgia region: possible effects of urbanization 总被引:3,自引:0,他引:3
S. Rose 《Environmental Geology》2002,42(1):102-113
133.
A.F. Lotter P.G. Appleby R. Bindler J.A. Dearing J.-A. Grytnes W. Hofmann C. Kamenik A. Lami D.M. Livingstone C. Ohlendorf N. Rose M. Sturm 《Journal of Paleolimnology》2002,28(1):111-127
Sediment cores spanning the last two centuries were taken in Hagelseewli, a high-elevation lake in the Swiss Alps. Contiguous 0.5 cm samples were analysed for biological remains, including diatoms, chironomids, cladocera, chrysophyte cysts, and fossil pigments. In addition, sedimentological and geochemical variables such as loss-on-ignition, total carbon, nitrogen, sulphur, grain-size and magnetic mineralogy were determined. The results of these analyses were compared to a long instrumental air temperature record that was adapted to the elevation of Hagelseewli by applying mean monthly lapse rates.During much of the time, the lake is in the shadow of a high cliff to the south, so that the lake is ice-covered during much of the year and thus decoupled from climatic forcing. Lake biology is therefore influenced more by the duration of ice-cover than by direct temperature effects during the short open-water season. Long periods of ice-cover result in anoxic water conditions and dissolution of authigenic calcites, leading to carbonate-free sediments.The diversity of chironomid and cladoceran assemblages is extremely low, whereas that of diatom and chrysophyte cyst assemblages is much higher. Weak correlations were observed between the diatom and chrysophyte cyst assemblages on the one hand and summer or autumn air temperatures on the other, but the proportion of variance explained is low, so that air temperature alone cannot account for the degree of variation observed in the paleolimnological record.Analyses of mineral magnetic parameters, spheroidal carbonaceous particles and lead suggest that atmospheric pollution has had a significant effect on the sediments of Hagelseewli, but little effect on the water quality as reflected in the lake biota. 相似文献
134.
Even with the flow of water over a soil surface in which roughness elements are well inundated, and in less erosive situations where erosional bed forms are not pronounced, the magnitude of resistance coefficients in equations such as those of Darcy–Weisbach, Chezy or Manning vary with flow velocity (at least). Using both original laboratory and field data, and data from the literature, the paper examines this question of the apparent variation of resistance coefficients in relation to flow velocity, even in the absence of interaction between hydraulics and resulting erosional bed forms. Resistance equations are first assessed as to their ability to describe overland flow velocity when tested against these data sources. The result is that Manning's equation received stronger support than the Darcy–Weisbach or Chezy equations, though all equations were useful. The second question addressed is how best to estimate velocity of overland flow from measurements of slope and unit discharge, recognizing that the apparent flow velocity variation in resistance coefficients is probably a result of shortcomings in all of the listed resistance equations. A new methodology is illustrated which gives good agreement between estimated and measured flow velocity for both well-inundated sheet and rill flow. Comments are given on the predictive use of this methodology. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
135.
An improved age framework for late Quaternary silicic eruptions in northern Central America 总被引:1,自引:0,他引:1
William I. Rose F. Michael Conway Carlos R. Pullinger Alan Deino William C. McIntosh 《Bulletin of Volcanology》1999,61(1-2):106-120
Five new stepwise-heating 40Ar/39Ar ages and one new high-sensitivity 14C date of ash-fall and ash-flow deposits from late Quaternary silicic volcanoes in northern Central America document the eruption
rates and frequencies of five major rhyodacite and rhyolite calderas (Atitlán, Amatitlán, Ayarza, Coatepeque, and Ilopango)
located north of the basalt, andesite, and dacite stratovolcanoes of the Central American volcanic front. These deposits form
extensive time-stratigraphic horizons that intercalate regionally, and knowledge of dates and stratigraphy provides a valuable
framework for age determinations of more localized volcanic and nonvolcanic events. The new data, especially when integrated
with previous stratigraphic and dating work, show that all five calderas erupted several times in the past 200 ka and, despite
a lack of historic activity, should be considered as active centers that could produce highly explosive eruptions again. Because
of their locations near the highly vulnerable economic hearts of Guatemala and El Salvador, the risks of eruptions from these
calderas should be carefully considered along with risks of major earthquakes and volcanic front volcanoes, which are much
more frequent but inflict less severe and extensive damage. This investigation also includes some examples of dating efforts
that failed to produce reasonable results.
Received: 15 May 1998 / Accepted: 18 January 1999 相似文献
136.
137.
138.
Taichiro Okazaki Masayoshi Nakashima Keiichiro Suita Tomohiro Matusmiya 《地震工程与结构动力学》2007,36(1):35-53
Interaction between the external wall cladding and the seismic load resisting frame was examined in a full‐scale cyclic loading test of a three‐storey steel building structure. The building specimen had Autoclaved Lightweight Concrete (ALC, also designated as Autoclaved Aerated Concrete) panels installed and anchored to the structural frame as external wall cladding, using a standard Japanese method developed following the 1995 Kobe earthquake. ALC panelling is among the most widely used material for claddings in Japan. In the test, the ALC panel cladding contributed little to the stiffness and strength of the overall structure, even under a very large storey drift of 0.04 rad. No visible damage was noted in the ALC panels other than minor cracks and spalling of the bottom of the panels in the first storey. Consequently, in a Japanese steel building with properly installed ALC panel cladding, the structural frame is likely to be little affected by its cladding, and the ALC panels are capable of accommodating the maximum storey drift generally considered in structural design without sustaining discernible damage. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
139.
140.
Andrew L. Rose 《Geochimica et cosmochimica acta》2006,70(15):3869-3882
We have conducted a series of laboratory studies to investigate the generation of ferrous iron and reactive oxygen species when solutions of seawater containing natural organic matter (NOM) and ferric iron are exposed to simulated sunlight. Total ferrous iron and hydrogen peroxide were measured at nanomolar concentrations with high temporal resolution using chemiluminescence-based methods. In all cases, ferrous iron concentrations rapidly peaked at several nanomoles per litre after a few minutes, and then declined over time, while hydrogen peroxide concentrations increased in a non-linear manner. Although concentrations of both species depended on the concentration of NOM, hydrogen peroxide concentrations were only minimally affected by the presence of iron. Increasing the NOM concentration while the total iron concentration was maintained constant led to an increase in the maximum ferrous iron concentration, suggesting that superoxide-mediated reduction of iron may be a major pathway for ferrous iron formation. This was supported by measurements of superoxide production from irradiation of NOM in the absence of iron and kinetic calculations, as well as an experiment in which superoxide dismutase was added. Further analysis of the data suggested that dissolved oxygen and photo-produced hydrogen peroxide were the primary oxidants of the Fe(II) formed. Thus we propose that superoxide and ferrous iron may be intricately coupled in the system, and that their generation is determined by the supply of NOM available to harvest light and donate electrons. 相似文献