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排序方式: 共有145条查询结果,搜索用时 468 毫秒
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Evaluating fishery impacts using metrics of community structure 总被引:8,自引:14,他引:8
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Organic pollutants associated with macromolecular soil organic matter: Mode of binding 总被引:2,自引:0,他引:2
H. H. Richnow R. Seifert J. Hefter M. Link W. Francke G. Schaefer W. Michaelis 《Organic Geochemistry》1997,26(11-12)
A study of ether-linked moieties in macromolecular bound residues of polycyclic aromatic hydrocarbons (PAH) generated in bioremediation experiments was performed using high temperature hydrolysis degradation with subsequent analysis of the products by GC-MS. This hydrolysis reaction was specifically designed to cleave ether bonds including relatively stable diarylether structures. Among the reaction products, aromatic alcohols representing typical microbiologically derived metabolites of PAH were found in addition to natural compounds. Thus, parts of the bound residues appeared to be linked within the macromolecular material by ether bonds. Model experiments with an oxidoreductase enzyme and aromatic alcohols indicate the formation of these ether bonds to be an enzyme-catalysed process. 相似文献
5.
Jean-Pierre Berger Bettina Reichenbacher Damien Becker Matthias Grimm Kirsten Grimm Laurent Picot Andrea Storni Claudius Pirkenseer Andreas Schaefer 《International Journal of Earth Sciences》2005,94(4):711-731
We present a general stratigraphic synthesis for the Upper Rhine Graben (URG) and the Swiss Molasse Basin (SMB) from Eocene to Pliocene times. The stratigraphic data were compiled both from literature and from research carried out by the authors during the past 6 years ; an index of the stratigraphically most important localitites is provided. We distinguish 14 geographical areas from the Helvetic domain in the South to the Hanau Basin in the North. For each geographical area, we give a synthesis of the biostratigraphy, lithofacies, and chronostratigraphic ranges. The relationships between this stratigraphic record and the global sea-level changes are generally disturbed by the geodynamic (e.g., subsidence) evolution of the basins. However, global sea-level changes probably affected the dynamic of transgression–regression in the URG (e.g., Middle Pechelbronn Beds and Serie Grise corresponding with sea-level rise between Ru1/Ru2 and Ru2/Ru3 sequences, respectively) as well as in the Molasse basin (regression of the UMM corresponding with the sea-level drop at the Ch1 sequence). The URGENT-project (Upper Rhine Graben evolution and neotectonics) provided an unique opportunity to carry out and present this synthesis. Discussions with scientists addressing sedimentology, tectonics, geophysics and geochemistry permitted the comparison of the sedimentary history and stratigraphy of the basin with processes controlling its geodynamic evolution. Data presented here back up the palaeogeographic reconstructions presented in a companion paper by the same authors (see Berger et al. in Int J Earth Sci 2005). 相似文献
6.
Luke Daly Phil A. Bland Svetlana Tessalina David W. Saxey Steven M. Reddy Denis Fougerouse William D.A. Rickard Lucy V. Forman Alexandre La Fontaine Julie M. Cairney Simon P. Ringer Bruce F. Schaefer Daniel Schwander 《Geostandards and Geoanalytical Research》2018,42(3):279-299
Atom probe microscopy (APM) is a relatively new in situ tool for measuring isotope fractions from nanoscale volumes (< 0.01 μm3). We calculate the theoretical detectable difference of an isotope ratio measurement result from APM using counting statistics of a hypothetical data set to be ± 4δ or 0.4% (2s). However, challenges associated with APM measurements (e.g., peak ranging, hydride formation and isobaric interferences), result in larger uncertainties if not properly accounted for. We evaluate these factors for Re‐Os isotope ratio measurements by comparing APM and negative thermal ionisation mass spectrometry (N‐TIMS) measurement results of pure Os, pure Re, and two synthetic Re‐Os‐bearing alloys from Schwander et al. (2015, Meteoritics and Planetary Science, 50, 893) [the original metal alloy (HSE) and alloys produced by heating HSE within silicate liquid (SYN)]. From this, we propose a current best practice for APM Re‐Os isotope ratio measurements. Using this refined approach, mean APM and N‐TIMS 187Os/189Os measurement results agree within 0.05% and 2s (pure Os), 0.6–2% and 2s (SYN) and 5–10% (HSE). The good agreement of N‐TIMS and APM 187Os/189Os measurements confirms that APM can extract robust isotope ratios. Therefore, this approach permits nanoscale isotope measurements of Os‐bearing alloys using the Re‐Os geochronometer that could not be measured by conventional measurement principles. 相似文献
7.
The absence of a production rate calibration experiment on Greenland has limited the ability to link 10Be exposure dating chronologies of ice‐margin change to independent records of rapid climate change. We use radiocarbon age control on Holocene glacial features near Jakobshavn Isbræ, western Greenland, to investigate 10Be production rates. The radiocarbon chronology is inconsistent with the 10Be age calculations based on the current globally averaged 10Be production rate calibration data set, but is consistent with the 10Be production rate calibration data set from north‐eastern North America, which includes a calibration site nearby on north‐eastern Baffin Island. Based on the best‐dated feature available from the Jakobshavn Isbræ forefield, we derive a 10Be production rate value of 3.98 ± 0.24 atoms g a?1, using the ‘St’ scaling scheme, which overlaps with recently published reference 10Be production rates. We suggest that these 10Be production rate data, or the very similar data from north‐eastern North America, are used on Greenland. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
Jake Hancock 《Cretaceous Research》2001,22(6):677
The Aptian/Albian boundary, as currently placed, presents problems which have not yet been solved and possibly never will be. No detailed definition of recent years can be applied on a world-wide scale, which will be needed for any definition acceptable to the Subcommission on Cretaceous Stratigraphy. The only satisfactory and workable solution is to choose a completely new position. It is suggested that this should be at the base of the Zone of Lyelliceras lyelli. This would change the start of the Albian from appproximately 112 Ma to 109 Ma but it would be a standard which should be recognizable on all five continents. 相似文献
9.
Dr. Vincent J. Schaefer 《Pure and Applied Geophysics》1956,34(1):211-220
Summary An exploration of the electrical properties of the atmosphere on and above the island of Hawaii, as indicated by a portable corona current unit, is described. A 30 foot telescopic mast having a radioactive probe mounted on an insulated bushing and connected by shielded cable to a sensitive microammeter was used. Corona currents were measured at a number of geographic locations ranging from sea level under conditions of heavy surf to the 10,000 foot level on Mauna Kea several thousand feet above the exchange layer, and over the land and ocean in a light plane. Observations were made under clear, cloudy and rainy conditions. Fair weather and cloudy conditions gave currents from air to earth of positive sign. With warm rain falling the currents had a negative sign and increased in value with intensity of precipitation. In several instances indications of incipient discharges similar to that observed in mild lightningstorms were noted.The island of Hawaii has many desirable features to recommend it for an extensive research program in atmospheric electricity. A simple and inexpensive approach to inaugurating such a program is suggested. 相似文献
10.
We propose that the europium excess in Precambrian sedimentary rocks, relative to those of younger age is derived from volcanic rocks of ancient island arcs, which were the source materials for the sediments. Precambrian sedimentary rocks and present-day volcanic rocks of island arcs have similar REE patterns, total REE abundances and excess Eu, relative to the North American shale composite. The present upper crustal REE pattern, as exemplified by that of sediments, is depleted in Eu, relative to chondrites. This depletion is considered to be a consequence of development of a grandioritic upper crust by partial melting in the lower crust, which selectively retains europium. 相似文献