Reactions of Cl Atoms with Selected VOCs: Kinetics, Products and Mechanisms   总被引：1，自引：0，他引：1  

Gaia Fantechi  Niels R. Jensen  Ole Saastad  Jens Hjorth  Jozef Peeters 《Journal of Atmospheric Chemistry》1998,31(3):247-267

The reactions of isoprene, MBO (2-methyl-3-buten-2-ol) and toluene with chlorine atoms have been studied at 298 ± 5 K and 740 ± 5 Torr with the use of FTIR spectroscopy. Major products of the isoprene-Cl reaction and of the MBO-Cl reaction have been identified and quantified, and reaction mechanisms have been tentatively proposed in order to explain the products formed. The reaction between isoprene and Cl atoms yields mainly HCl, formyl chloride, formic acid, methylglyoxal (pyruvic aldehyde), CO and CO2, while the MBO-Cl reaction forms acetone, HCl, formyl chloride, formic acid, CO, CO2. As products from the reaction between toluene and Cl we identified and quantified HCl and benzaldehyde. The rate constants for the reactions of isoprene and toluene with Cl atoms have also been determined using a relative rate method. The measured values are: kisoprene = (5.5 ± 1.0) × 10–10 cm3 molecule–1 s–1 and ktoluene = (5.6 ± 1.3) × 10–11 cm3 molecule–1 s–1. Atmospheric lifetimes have been estimated from these values.  相似文献   

Diffusive and total oxygen uptake of deep-sea sediments in the eastern South Atlantic Ocean:in situ and laboratory measurements     

Ronnie Nhr Glud  Jens K. Gundersen  Bo Barker Jrgensen  Niels Peter Revsbech  Horst D. Schulz 《Deep Sea Research Part I: Oceanographic Research Papers》1994,41(11-12)

Total O₂ uptake rates were measured by the benthic flux chamber lander ELINOR, and O₂ microprofiles were measured by the profiling lander PROFILUR in the eastern South Atlantic. Diffusive O₂ fluxes through the diffusive boundary layer and the depth distribution of O₂ consumption rates within the sediment were calculated from the obtained microprofiles. The depth integrated O₂ consumption rate agreed closely with the diffusive O₂ uptake at all stations. Total O₂ uptake was 1.2–4.2 times the diffusive O₂ uptake, and the difference correlated with the abundance of macrofauna in the sediment. Diffusive O₂ uptake and O₂-penetration depths correlated with the organic content of the sediments and exhibited an inverse correlation with water depth. Total and diffusive rates of in situ O₂ uptake were higher than previously published data for shelf and abyssal sediments in the Atlantic, but were comparable to rates from upwelling areas in the eastern Pacific. Laboratory measurements on recovered sediment cores showed lower O₂ penetration depths and higher diffusive uptake rates than in situ measurements. The differences increased with increasing water depth. We primarily ascribe this compression of O₂ profiles to a transiently increased temperature during recovery and enhanced microbial activity in decompressed sediment cores. Total O₂ uptake rates measured in the laboratory on macrofauna-rich stations were, in contrast, lower than those measured in situ because of underrepresentation and disturbance of the macrofauna.  相似文献   

Changes in abundance of demersal fish species in the North Sea between 1906-1909 and 1990-1995   总被引：4，自引：0，他引：4  

Rijnsdorp  Adriaan D.; van Leeuwen  Piet I.; Daan  Niels; Heessen  Henk J. L. 《ICES Journal of Marine Science》1996,53(6):1054-1062

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The Importance of Posidonia oceanica and Cymodocea nodosa as Contributors of Free Amino Acids in Water and Sediment of Seagrass Beds     

Niels O. G.  Jørgensen  T. Henry  Blackburn  Kai  Henriksen Daniel  Bay 《Marine Ecology》1981,2(2):97-112

Abstract. Dissolved free amino acids (DFAA) were measured in sediment porewater and overlying sea water in seagrass beds of Posidonia oceanica and Cymodocea nodosa at a water depth of 8–10 m in Corsica, France. In the sea water, DFAA concentrations from 0.5 to 1.9μM were found. Lowest concentrations occurred in the afternoon in surface water samples, while higher concentrations were measured in morning surface samples and in all bottom samples. The most abundant amino acids were serine, glycine, and alanine. In the sediment, the upper 4cm contained the highest concentrations of DFAA (177nmol cm^-3 or 367 μM), while lower concentrations (<50nmol cm^-3 or 104 μM) prevailed deeper in the sediment. Glycine, glutamic acid, alanine, and β-alanine were the major components of the DFAA. The photosynthetic activity of the seagrasses influenced sediment porewater pools of DFAA. When a Posidonia bed was covered with a black polyethylene shield, the interstitial amino acids were reduced at a rate of 16nmol cm^-2 h^-1 (0-10cm depth). Conversely, extended daylight (floodlight) increased the DFAA pool in sediment depths below 4 cm. Free amino acids were released to the overlying sea water from both seagrass sediment and individual shoots, the rates being highest in the dark. The present investigation indicates that a substantial portion of the N-cycling of the seagrass sediment includes free amino acids.  相似文献   

Status and trends of the major roundfish, flatfish, and pelagic fish stocks in the North Sea: thirty-year overview     

Serchuk  Fredric M.; Kirkegaard  Eskild; Daan  Niels 《ICES Journal of Marine Science》1996,53(6):1130-1145

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An Afterthought: Ecosystem Metrics and Pressure Indicators   总被引：2，自引：2，他引：2  

Daan  Niels 《ICES Journal of Marine Science》2005,62(3):612-613

Editing the symposium contributions has been an interestingand instructive experience, because they provide a broad overviewof the well-nigh unlimited creativity of marine scientists totry and find building blocks for an ecosystem approach to fisherymanagement. A wealth of ideas appears to be emerging on howdifferent aspects of the state of exploited marine ecosystemscan be measured. Although the metrics produced are commonlyreferred to as "ecosystem indicators", however, it is generallyless clear what they actually indicate. The concept that management must take the wider ranging  相似文献   

Using modular 3D digital earth applications based on point clouds for the study of complex sites     

Oscar Martinez-Rubi  Maurice de Kleijn  Stefan Verhoeven  Niels Drost  Jisk Attema  Maarten van Meersbergen 《International Journal of Digital Earth》2016,9(12):1135-1152

This article discusses the use of 3D technologies in digital earth applications (DEAs) to study complex sites. These are large areas containing objects with heterogeneous shapes and semantic information. The study proposes that DEAs should be modular, have multi-tier architectures, and be developed as Free and Open Source Software if possible. In DEAs requiring high reliability in the 3D measurements, point clouds are proposed as basis for the 3D Digital digital earth representation. For the development of DEAs, we propose to follow a workflow with four components: data acquisition and processing, data management, data analysis and data visualization. For every component, technological challenges of using 3D technologies are identified and solutions applied for a case study are presented. The case study is a modular 3D DEA developed for the archaeological project Mapping the Via Appia. The 3D DEA allows archaeologists to virtually analyze a complex study area.  相似文献   

A palaeomagnetic experiment on crustal uplift in West Greenland     

George E.J. Beckmann  Niels Ø. Olesen  Kai Sørensen 《Earth and Planetary Science Letters》1977,36(2):269-279

In the Nordre Strømfjord shear zone of central West Greenland it is believed that the gneisses exposed at the coast reached a maximum depth of burial about 10 km deeper than those now adjacent to the inland ice. This theory was tested palaeomagnetically. Further sampling up the mountain K?llingeh?tten was carried out to ascertain changes of direction of magnetization with height.The magnetic susceptibility ellipsoids were determined for each specimen and were used to correct their directions of magnetization for the effects of anisotropy. Complicated but compact polar wander paths were derived for both the fjord and mountain traverses. The path for the fjord is consistent with the geological model but does not support it. This inconclusive result may be the consequence of a low rate of polar wander. The mean palaeomagnetic poles are 27.7°N, 276.6° E (dp = 13.8°,dm = 17.3°) for Nordre Strømfjord and 25.3°N, 300.4°E (dp = 11.5°,dm = 14.1°) for K?llingeh?tten.  相似文献   

Design rainfall in Qatar: sensitivity to climate change scenarios     

Abdullah Al Mamoon  Niels E. Joergensen  Ataur Rahman  Hassan Qasem 《Natural Hazards》2016,81(3):1797-1810

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Strontium-isotope studies of “brown water” (organic-rich groundwater) from Denmark     

Niels Oluf Jørgensen  Jørn Morthorst  Paul Martin Holm 《Hydrogeology Journal》1999,7(6):533-539

 Groundwater from some Quaternary and upper Tertiary aquifers in western Jutland, Denmark, is heavily influenced by "brown water", i.e., groundwater with a high content of naturally occurring dissolved organic matter. Stable-isotope analyses (¹⁸O/¹⁶O and D/H) indicate that both Quaternary and upper Tertiary aquifers are dominated by meteoric water. However, strontium-isotope analyses make it possible to distinguish between water samples from Quaternary and Miocene aquifers. Relatively low ⁸⁷Sr/⁸⁶Sr ratios, i.e., ∼0.7083, in Sr-rich water samples indicate that the majority of dissolved Sr in groundwater from Miocene as well as Quaternary strata is probably derived from Miocene marine skeletal carbonate matter in the subsurface. This situation is probably the result of Quaternary glacial reworking of upper Tertiary material and/or hydraulic contact between Quaternary and Miocene aquifers. A positive correlation between Sr contents and non-volatile organic carbon indicates that the remarkably high contents of organic matter recorded in these aquifers almost certainly are derived from Miocene sources as well. Received, February 1999 / Revised, July 1999 / Accepted, July 1999  相似文献