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691.
Eric H. Oelkers Sergey V. Golubev Claire Chairat Oleg S. Pokrovsky Jacques Schott 《Geochimica et cosmochimica acta》2009,73(16):4617-6554
The surface chemistry of natural wollastonite, diopside, enstatite, forsterite, and albite in aqueous solutions was characterized using both electrokinetic techniques and surface titrations performed for 20 min in batch reactors. Titrations performed in such reactors allow determination of both proton consumption and metal release from the mineral surface as a function of pH. The compositions, based on aqueous solution analysis, of all investigated surfaces vary dramatically with solution pH. Ca and Mg are preferentially released from the surfaces of all investigated divalent metal silicates at pH less than ∼8.5-10 but preferentially retained relative to silica at higher pH. As such, the surfaces of these minerals are Si-rich and divalent metal poor except in strongly alkaline solutions. The preferential removal of divalent cations from these surfaces is coupled to proton consumption. The number of protons consumed by the preferential removal of each divalent cation is pH independent but depends on the identity of the mineral; ∼1.5 protons are consumed by the preferential removal of each Ca atom from wollastonite, ∼3 protons are consumed by the preferential removal of each Mg or Ca atom from diopside or enstatite, and ∼4 protons are consumed by the preferential removal of each Mg from forsterite. These observations are interpreted to stem from the creation of additional ‘internal’ adsorption sites by the preferential removal of divalent metal cations which can be coupled to the condensation of partially detached Si. Similarly, Na and Al are preferentially removed from the albite surface at 2 > pH > 11; mass balance calculations suggest that three protons are consumed by the preferential removal of each Al atom from this surface over this entire pH range. Electrokinetic measurements on fresh mineral powders yield an isoelectric point (pHIEP) 2.6, 4.4, 3.0, 4.5, and <1, for wollastonite, diopside, enstatite, forsterite, and albite, respectively, consistent with the predominance of SiO2 in the surface layer of all of these multi-oxide silicates at acidic pH. Taken together, these observations suggest fundamental differences between the surface chemistry of simple versus multi-oxide minerals including (1) a dependency of the number and identity of multi-oxide silicate surface sites on the aqueous solution composition, and (2) the dominant role of metal-proton exchange reactions on the reactivity of multi-oxide mineral surfaces including their dissolution rate variation with aqueous solution composition. 相似文献
692.
Joshua Olund Alan Cardini Paul D''Attilio Eric Feldblum John DeWolf 《地震工程与工程振动(英文版)》2008,7(4):427-437
A joint effort between the Connecticut Department of Transportation and the University of Connecticut has been underway for more than 20 years to utilize various structural monitoring approaches to assess different bridges in Connecticut. This has been done to determine the performance of existing bridges, refine techniques needed to evaluate different bridge components, and develop approaches that can be used to provide a continuous status of a bridge's structural integrity. This paper briefly introduces the background of these studies, with emphasis on recent research and the development of structural health monitoring concepts. This paper presents the results from three different bridge types: a post-tensioned curved concrete box girder bridge, a curved steel box-girder bridge, and a steel multi-girder bridge. The structural health monitoring approaches to be discussed have been successfully tested using field data collected during multi-year monitoring periods, and are based on vibrations, rotations and strains. The goal has been to develop cost-effective strategies to provide critical information needed to manage the State of Connecticut's bridge infrastructure. 相似文献
693.
Eric?G.?Potter Roger?H.?MitchellEmail author 《Contributions to Mineralogy and Petrology》2005,150(2):212-229
The Proterozoic Deadhorse Creek volcaniclastic breccia complex was emplaced in Archean metasedimentary and metavolcanic rocks
of the Schreiber-White River greenstone belt adjacent to the Proterozoic Coldwell alkaline complex. The western sub-complex
of the Deadhorse Creek breccia consists of metasomatically-altered breccia, a U-Be-Zr-rich main mineralized zone and a Zr-Y-Th-rich
carbonate vein. The main mineralized zone is enriched in beryllium, thorium, uranium, first and second row transition elements,
and rare earth elements. The major minerals present include: albite; potassium feldspar; quartz; calcite; apatite; and phenakite.
Accessory minerals include: aegirine-jervisite; aegirine-natalyite; allanite; barite; barylite; coffinite; Ca-Mn-silicate;
magnetite; monazite-(Ce); niobian vanadian rutile; pyrite; thorite; thorogummite; thortveitite; uraninite; vanadian crichtonite;
xenotime-(Y); zircon and hydrated zircon; and zircon-thorite-coffinite solid solutions. The carbonate vein consists of dolomite-ankerite
and calcite with accessory zircon, xenotime, and monazite. Barite, baotite and Ba-rich feldspars, were formed during metasomatism
of the earlier-formed and genetically-unrelated volcaniclastic breccia adjacent to the main mineralized zone. The complex
mineral assemblage of the fault-controlled main mineralized zone is considered to have formed in three stages. An initial
emplacement of a “granitic” melt/fluid was followed by introduction of CO2-bearing Cr-Nb-V-Ti-enriched alkaline fluids. The latter reacted with minerals which had crystallized from the “granitic”
melt/fluid to produce the exotic V-, Sc- and Nb-bearing mineral assemblage. Subsequently, a supergene suite of minerals, consisting
principally of calcite, thorogummite, hollandite and tyuyamanite, formed during post-Pleistocene alteration was superimposed
onto the pre-existing Proterozoic age mineral assemblage. The major mineralogy of the main mineralized zone is essentially
‘granitic” and the melts/fluids are considered to be derived from an A-type granite source. However, the Deadhorse Creek mineralization
is older (1129±6 Ma) than the A-type quartz syenites of the adjacent Coldwell complex (1108±1 Ma) which are the nearest potential
sources of such melts. Thus, the source of the “granitic” melt together with that of the Cr-Nb-V-Ti-bearing alkaline fluids
remains enigmatic. 相似文献
694.
Assessing the importance of seepage and springs to nitrate flux in a stream network in the Wisconsin sand plains 下载免费PDF全文
Evaluating the flow paths that contribute to solute flux in stream networks can lead to greater understanding of the linkages between biogeochemistry and hydrology. We compared the contributions of groundwater in spring brooks and in seepage through the streambed to nitrate flux in the Emmons Creek network in the Wisconsin sand plains. We predicted that spring brooks would contribute disproportionately to nitrate flux due to the presumed higher advection rates in springs and less opportunity for nitrate removal relative to seeps. Nitrate flux was measured in 15 spring brooks that entered Emmons Creek. Nitrate flux from seepage was measured at the locations of 30 piezometers, based on Darcy's Law, and by a reach‐scale injection of Rhodamine water tracing (RWT). When seepage discharge was estimated from the RWT release, groundwater inputs from seepage and springs accounted for the discharge gain in the Emmons Creek channel. Springs brooks and seepage (based on the RWT release) contributed 37% and 63%, respectively, to nitrate flux inputs in the study reach. Contrary to our prediction, seeps contributed disproportionately to nitrate flux relative to their discharge. Relatively high rates of seepage discharge and higher than anticipated nitrate concentrations in the shallow pore water at seepage locations contributed to the unanticipated result. 相似文献
695.
Eric Fossat 《Solar physics》1991,133(1):1-12
IRIS (International Research on the Interior of the Sun) is the name of a worldwide network of 8 observing stations for full disk helioseismology. The IRIS scientific community is organizing a yearly workshop in one of the 8 sites. This paper is the introduction to the proceedings of the second IRIS workshop, held at Tashkent, Uzbekistan SSR. It presents a brief history, the structure of the international cooperation, the membership rule, the list of sites and members, the scientific working teams additional structure and, as an appendix, the report of the first meeting of the IRIS Scientific Committee. 相似文献
696.
Vidicon data for the intensities of Balmer and Paschen lines for n = 11 to 18 indicate a line ratio within 1σ of the theoretical value of 3.27, calculated with the assumptions of an optically thin atmosphere and angular momentum substates populated according to their statistical weights. The observed value is not consistent with the value of 8 reported in some early work, or with the model that higher angular momentum states have low populations. 相似文献
697.
Malcolm L. Spaulding Mark Reed Eric Anderson Tatsusaburo Isaji J.Craig Swanson Saul B. Saila Ernesto Lorda Henry Walker 《Estuarine, Coastal and Shelf Science》1985,20(1):41-53
An oil spill fishery impact assessment model system has been applied to the Georges Bank-Gulf of Maine region to assess the sensitivity of probable impact on several key fisheries to spill location and timing. Simulations of the impact on the fishery of tanker spills (20 million gallons released over 5 days), at two separate locations for each season of the year, and blowout spills (68 million gallons released over 30 days) at one location, with monthly releases and at six other locations with seasonal spills have been studied. Atlantic cod has been employed as the principal fish species throughout the simulations. Impacts on Atlantic herring and haddock have also been investigated for selected cases. All spill sites are located on Georges Bank with the majority in the general region of OCS leasing activity.The results of these simulations suggest a complex interaction among spill location and timing, the spatial and temporal distribution of spawning, the population dynamics of the species under study, and the hydrodynamics of the area. For the species studied, spills occurring during the winter and spring have the largest impact with cod being the most heavily impacted followed by haddock and herring. In all cases, the maximum cumulative loss to the fishery of a one time spill event never exceeded 25% of the annual catch with the exact value depending on the number of ichthyoplankton impacted by the spill and the compensatory dynamics of the population. 相似文献
698.
Initial results of round-the-clock observations of solar oscillations at the South Pole are briefly summarized by describing the Figures 1 to 4.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands. 相似文献
699.
The phase-mixing mechanism first proposed as a coronal heating mechanism by Heyvaerts and Priest (1983) is examined using a length-scale analysis adapted from Cally (1991). This allows parameter ranges other than those studied by Heyvaerts and Priest (1983) to be described, together with a detailed examination of the transfer of energy to both longer and shorter length-scales as the Alfvén wave front evolves in the solar corona. The results of Heyvaerts and Priest (1983) are largely confirmed, but with some notable differences. Energy initially at smaller length-scales decays faster than their rate, because the plasma is more strongly dissipative at smaller length-scales. The full inclusion of diffusion across field lines also leads to smoother Alfvén wavefronts. 相似文献
700.
Richard G. West Karen L. Knudsen David N. Penney Richard. C. Preece J. Eric Robinson 《第四纪科学杂志》1994,9(4):357-366
Assemblages of foraminifers, ostracods and molluscs from temperate Ipswichian Stage (last temperate stage) sediments and overlying cold Devensian Stage (last cold stage) sediments at Somersham in the southern Fenland of Cambridgeshire have been analysed. The Ipswichian sediments contain faunas consistent with temperate brackish water conditions under tidal influence. The Devensian assemblages were recovered from a series of sands and gravels laterally accreting in a channel cutting into Ipswichian sediments. In contrast to the Ipswichian faunas, the faunas of particular Devensian samples show a complex mixture of temperate freshwater, brackish and marine taxa. The molluscs are mainly freshwater, with few land snails; they occur together with foraminifers and ostracods. Freshwater, brackish water and marine ostracods are present with foraminifers. A sample of Devensian fine laminated sediment in the channel was analysed for pollen; only abundant pre-Quaternary spores were present, with abundant foraminifers in the same sample. The taphonomy of the assemblages and the difficulties of their interpretation in environmental terms are discussed. The importance of taphonomy in assessing environments, climate, range of taxa and dating is stressed. 相似文献