Isotopic composition of silicon in meteorites     

Carol Molinivelsko  Toshiko K. Mayeda  Robert N. Clayton   《Geochimica et cosmochimica acta》1986,50(12):2719-2726

Samples of bulk meteorites show only mass-dependent fractionation of silicon isotopes. No isotopic anomalies were found. The variation of the ratios ²⁹Si/²⁸Si and ³⁰Si/²⁸Si over the meteorite classes is small; 1%. per mass unit difference. The average Si isotopic composition for each class of meteorites is identical, within analytical uncertainties. This is quite unlike O, whose anomalous isotopic abundances in bulk samples differentiate among the classes of meteorites. The overlapping abundance ranges of Si isotopes among many classes of meteorites suggest closed-system behavior for this element prior to meteorite accretion and allow calculation of an average solar system Si isotope composition.  相似文献   

Pyrolysis-GC characterization of whole rock and kerogen-concentrate samples of immature Jurassic source rocks from NW-Germany     

Carol Arnosti  Peter J. Müller   《Organic Geochemistry》1987,11(6)

Nine rock samples from three Jurassic stratigraphic units of a shallow core from NW Germany were analyzed by pyrolysis-gas chromatography. The units contain a mixed Type-II/III kerogen (Dogger-α), a hydrogen-rich Type-II kerogen (Lias-), and a hydrogen-poor Type-III kerogen (Lias-δ). All of the kerogen was immature (R_o = 0.5%). Two sets of kerogen concentrates (“AD”: HCl/HF followed by a density separation, and “A”: only acid treatment) prepared from the rock samples were also analyzed to make a detailed comparison of the pyrolysates of rock and corresponding kerogen-concentrates.Hydrogen-index (HI) values of the kerogen concentrates prepared from organic-carbon poor rock were nearly 200% higher than HI values of the rock samples. Changes in HI were minimal for the samples containing Type-II kerogen. The A and AD samples from the C_org-poor rock yielded pyrolysates with n-alkane series of very different molecular lengths. Pyrograms of the rock samples had n-alkane series extending to n-C₁₄; the chromatograms of the A samples reached the n-C₁₄-nC₂₀ range. The AD samples from C_org-poor rock and all three sample types from the C_org-rich rock had n-alkane series up to n-C₂₉. The benzene/hexane and toluene/heptane ratios for the C_org-poor rock and A samples were far higher than for the AD samples, which had ratios similar to those of all three sample types from the C_org-rich rocks. These results indicate that choice of kerogen preparation method is critical when C_org-poor samples are analyzed.  相似文献   

Book reviews     

Carol Stoker  S. K. Sinha  David Pimentel 《Climatic change》1984,6(1):99-102

  相似文献   

The Geochemical Evolution of Riparian Ground Water in a Forested Piedmont Catchment   总被引：2，自引：0，他引：2  

Douglas A. Burns  L. Niel Plummer  Jeffrey J. McDonnell    Eurybiades Busenberg  Gerolamo C. Casile  Carol Kendall  Richard P. Hooper  James E. Freer  Norman E. Peters  Keith Beven  Peter Schlosser 《Ground water》2003,41(7):913-925

  相似文献   

ENVIRONMENTAL DEGRADATION IN BRAZILIAN AMAZONIA: PERSPECTIVES IN US NEWS MEDIA*     

Jacob Bendix  Carol M. Liebler 《The Professional geographer》1991,43(4):474-485

While news media play a major role in shaping public opinion and government policy, existing literature suggests that coverage of both the third world and environmental issues is superficial and crisis-oriented. This study uses the example of Amazonian deforestation to explore the quantity and content of coverage in influential American newspapers. We found that coverage included a wide range of (sometimes) contradictory theories regarding the causes of deforestation, and that the amount, but not the nature, of the coverage changed in response to a “crisis.”  相似文献   

An ensemble climate projection for Africa     

Carlo Buontempo  Camilla Mathison  Richard Jones  Karina Williams  Changgui Wang  Carol McSweeney 《Climate Dynamics》2015,44(7-8):2097-2118

  相似文献   

Comparison of Enterococcus density estimates in marine beach and bay samples by real-time polymerase chain reaction, membrane filtration and defined substrate testing     

Ferretti JA  Tran HV  Cosgrove E  Protonentis J  Loftin V  Conklin CS  Grant RN 《Marine pollution bulletin》2011,62(5):1066-1072

Currently, densities of Enterococcus in marine bathing beach samples are performed using conventional methods which require 24 h to obtain results. Real-time PCR methods are available which can measure results in as little as 3 h. The purpose of this study was to evaluate a more rapid test method for the determination of bacterial contamination in marine bathing beaches to better protect human health. The geometric mean of Enterococcus densities using Enterolert® defined substrate testing and membrane filtration ranged from 5.2 to 150 MPN or CFU/100 mL and corresponding qPCR results ranged from 6.6 to 1785 CCE/100 mL. The regression analysis of these results showed a positive correlation between qPCR and conventional tests with an overall correlation (r) of 0.71. qPCR was found to provide accurate and sensitive estimate of Enterococcus densities and has the potential to be used as a rapid test method for the quantification of Enterococcus in marine waters.  相似文献   

Organic carbon amendments for passive in situ treatment of mine drainage: Field experiments     

Matthew B.J. Lindsay  David W. BlowesPeter D. Condon  Carol J. Ptacek 《Applied Geochemistry》2011,26(7):1169-1183

A field-scale experiment was conducted to evaluate various organic C sources as amendments for passive treatment of tailings pore water. Varied mixtures of peat, spent-brewing grain (SBG) and municipal biosolids (MB) were assessed for the potential to promote dissimilatory sulfate reduction (DSR) and metal-sulfide precipitation. Five amended cells and one control were constructed in the vadose zone of a sulfide- and carbonate-rich tailings deposit, and the geochemistry, microbiology and mineralogy were monitored for 4 a. Increases in pore-water concentrations of dissolved organic C (DOC) and decreases in aqueous SO₄ concentrations of >2500 mg L⁻¹ were observed in cells amended with peat + SBG and peat + SBG + MB. Removal of SO₄ was accompanied by shifts in δ³⁴S-SO₄ values of >+30‰, undersaturation of pore water with respect to gypsum [CaSO₄·2H₂O], and increased populations of SO₄-reducing bacteria (SRB). Decreases in aqueous concentrations of Zn, Mn, Ni, Sb and Tl were observed for these cells relative to the control. Organic C introduction also supported growth of Fe-reducing bacteria (IRB) and increases in Fe and As concentrations. Enhanced Fe and As mobility occurred in all cells; however, maximum concentrations were observed in cells amended with MB. Subsequent decreases in Fe and As concentrations were attributed to DSR and metal-sulfide precipitation. The common presence of secondary Zn-S and Fe-S phases was observed by field emission-scanning electron microscopy (FE-SEM) and energy dispersive X-ray (EDS) spectroscopy. Selective extractions indicated that large decreases in water-soluble SO₄ occurred in cells that supported DSR. Furthermore, amendments that supported DSR generally were characterized by slight decreases in solid-phase concentrations of extractable metal(loid)s. Amendment of tailings with organic C amendments that supported ongoing DOC production and DSR was essential for sustained treatment.  相似文献   

GSFC optical ozonesonde results during the Gap,France, intercomparisons,June 1981     

Arlin J. Krueger  Peter Simeth  Carol A. Fry  Krishna Tewari 《Planetary and Space Science》1983,31(7):749-759

A GSFC Super Loki optical ozonesonde instrument was flown as part of the ozone sensor intercomparison balloon campaign at Gap, France, in June 1981. A primary objective was to confirm biases between external absorption techniques, such as the GSFC sonde, and in situ techniques, which include ECC, Mast-Brewer, and DASIBI sondes. Ozone distributions were obtained with the GSFC sonde on three of the four ascent-descent legs of the first flight on 19 June. Ozone densities were measured redundantly over altitudes from 22 to 32 km using filters centered at 303 and 300 nm. The three profiles obtained by averaging the data from the two channels are in close agreement with an average S.E. of 1.4%. However, small but consistent differences were found between the ozone densities measured at the two wavelengths. The average difference is 5% using Vigroux cross sections and 4% using preliminary Bass cross sections. The integral ozone amount above the first ceiling altitude of 32.85 km was determined by the Langley plot method to be 45 D.U. The total ozone derived by integrating the optical ozonesonde and ECC profiles is within 2% of the Chiran Dobson Spectrophotometer observation based on a pre-campaign calibration but is 9% greater than the amount derived using a post-campaign calibration.  相似文献   

On zero-thickness interface elements for diffusion problems     

J. M. Segura  I. Carol 《国际地质力学数值与分析法杂志》2004,28(9):947-962

The present study focuses on the hydraulic behaviour of joints, and, specially, on its numerical implementation in terms of the FEM analysis using a discrete fracture flow approach. Fluid flow through discontinuities has traditionally been modelled using special elements of zero-thickness, which we can classify into single, double and triple-nodded. Single node elements are the simplest and consist of ‘line’ or ‘pipe’ elements which are superimposed onto the standard continuum mesh and that can only model the longitudinal conductivity through the discontinuity. On the other hand, some authors have included the influence of a transversal conductivity, and the subsequent localized potential drop, by using triple node interface elements. In those, the two nodes of the adjacent continuum elements represent the potentials in the pore system on each side of the interface, and a third node in the middle represents the average potential of the fluid in the channel represented by the discontinuity. Finally, double node interface elements have also been proposed, which have the advantage of making it possible to use the same FE mesh for both mechanical and flow analysis. In some cases the influence of a transversal conductivity is not considered and, therefore, although geometrically double-nodded, these elements belong to the single node type and when time comes to solve the system the two nodes must have the same potential, which can only be obtained by the ‘trick’ of prescribing the equivalence of these two d.o.f. before solving the global system of equations. This limitation may, however, be avoided by assuming that the potential in the channel is the average of the two sides of the interface. Based in this simple assumption, an alternative flow interface model has been recently developed and implemented, which preserves both longitudinal and transversal conductivities. An application example is developed and solved with the three types of interfaces described. The results offer useful information regarding the range of applicability and limitations of the new double-nodded interface element proposed. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献