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991.
Synthesis of refractory metal nuggets and constraints on the thermal histories of nugget‐bearing Ca,Al‐rich inclusions
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Tiny refractory metal nuggets are mainly observed inside Ca, Al‐rich inclusions (CAIs) from chondritic meteorites and are commonly assumed to be condensates from a solar composition gas. However, recent detailed studies of metal nugget compositions and their comparison with predictions from condensation show that the observed abundance patterns are extremely difficult to achieve in this way. As a test for the proposed alternative, precipitation from a silicate liquid, we conducted melting experiments, in which nine different refractory metals (nugget components) were equilibrated with each other along with a CAI‐like liquid at reducing conditions. When quenched, minerals similar to those in CAIs formed from such liquids including refractory metal nuggets exhibiting compositions and appearances similar to those of the meteoritic nuggets. The run products and their comparison with a meteoritic nugget‐bearing CAI is evidence for formation of refractory metal nuggets during cooling of Ca, Al‐rich liquids at rates about 1000°/40 s (in the interval from 1900 to 900 °C). To achieve the formation of refractory metal nuggets and the textures observed in the host inclusions, during cooling the rate probably changed. Refractory metal nuggets apparently formed during quenching before spinel crystallized. 相似文献
992.
993.
Strid A Jörundsdóttir H Päpke O Svavarsson J Bergman A 《Marine pollution bulletin》2007,54(9):1514-1522
The Greenland shark (Somniosus microcephalus) is a high-trophic fish species present in Arctic waters. The present study aimed to determine concentrations of polychlorinated dibenzo-p-dioxins and furans (PCDDs/Fs), dioxin-like (DL) PCBs and six non-dioxin-like (NDL) PCBs in muscle and liver from 10 female Greenland sharks collected between 2001 and 2003 from Icelandic waters. The mean total concentrations of PCDDs/Fs were 13 and 530pg/g fat for muscle and liver, respectively, and show enrichment in the liver. Concentrations of DL-non-ortho PCBs were also higher in liver compared to muscle with mean concentrations of 7.8 and 0.36ng/g fat, respectively. No enrichment in the liver was found for DL-mono-ortho- and NDL-PCBs. No correlation was found between the size range studied and total concentrations of the compounds analyzed. Total WHO-TEQs (PCDDs/Fs and DL-PCBs) ranged between 7.1-70 and 54-1500pg/g fat in muscle and liver, respectively. 相似文献
994.
The BEEP project in the Baltic Sea: overview of results and outline for a regional biological effects monitoring strategy 总被引:1,自引:0,他引:1
Lehtonen KK Schiedek D Köhler A Lang T Vuorinen PJ Förlin L Barsiene J Pempkowiak J Gercken J 《Marine pollution bulletin》2006,53(8-9):523-537
Field studies in the framework of the EU funded BEEP project (Biological Effects of Environmental Pollution in Marine Coastal Ecosystems, 2001-2004) aimed at validating and intercalibrating a battery of biomarkers of contaminant exposure and effects in selected indicator species in the Mediterranean, the North Atlantic and the Baltic Seas. Major strategic goals of the BEEP project were the development of a sensitive and cost-efficient biological effects monitoring approach, delivery of information and advice to end-user groups, and the implementation of a network of biomarker researchers around Europe. Based on the main results obtained in the Baltic Sea component of the BEEP the present paper summarises and assesses the applicability of biomarkers for different regions and species in this sea area. Moreover, a general strategy and some practical considerations for the monitoring of biological effects in the Baltic Sea are outlined. 相似文献
995.
Pregnant eelpout were collected for several years at German and Swedish Baltic coastal stations with different impact of pollutants and the prevalence of fry abnormalities compared between sites. Mortality of apparently normal developed larvae was observed with high variability in both German and Swedish sites. Malformation of larvae was a prominent disorder at all German stations with a prevalence ranging from about 50% up to a maximum of 90% in almost all analysed samples. At the Swedish stations malformation rates were significantly lower (range: 0-6%). Growth retardation of fry was clearly more prominent in eelpout from German coastal waters as well. Taken together the field data suggests that impaired larval development was associated with the state of environmental pollution at the sampling locations. 相似文献
996.
Barsiene J Schiedek D Rybakovas A Syvokiene J Kopecka J Förlin L 《Marine pollution bulletin》2006,53(8-9):469-478
Frequency of micronuclei (MN) and other nuclear abnormalities (nuclear buds, bi-nucleated and fragmented-apoptotic cells) was analysed in gill cells of the blue mussel (Mytilus spp.) from selected coastal sites in the Baltic Sea--Kv?d?fj?rden (Sweden), Klaipeda-Būtinge zone (Lithuania), Gulf of Gdansk (Poland) and Wismar Bay (Germany). Samples were collected from 650 specimens during bi-annual sampling campaigns in 2001 and 2002. The lowest frequency of MN (0.37 MN/1000 cells) was found in blue mussels from the reference site (Kv?d?fj?rden). The highest MN values (up to 6.7 MN/1000 cells) were registered in blue mussels from the Gulf of Gdansk in autumn 2001 and 2002, and at Wismar Bay in spring 2001 (up to 5.06 MN/1000 cells). Gradients of MN incidences were observed when comparing the three studied locations in Wismar Bay, and at the Lithuanian coast before the crude oil spill in the Būtinge oil terminal. Moreover, significant seasonal and inter-location differences in the responses were documented (P<0.0001). Nuclear abnormalities were observed most frequently in blue mussels from the Gulf of Gdansk. 相似文献
997.
To decipher the thermal structure of the sedimentary veneer in southern Israel, new values of thermal conductivity and porosity as well as of the radiogenic heat budget are provided. Thermal conductivity is measured for lithotypes and scaled up for geological formations. The new data are higher than most of the previously measured values, in particular for sandstones and siltstones, whose mean values are 5.0 and 2.9 W m?1 K?1. Mean values of the most abundant lithotypes, which are dolomites and limestones, are on the order of 4.1 and 2.7 W m?1 K?1, respectively. The total radiogenic heat production of the sedimentary cover varies slightly over southern Israel, due to variable lithology and total sediment thickness, yielding a maximum heat flow on the order of 4 mW m?2 where the sedimentary section is thickest (ca. 7 km). A temperature prognosis was made by calculating temperature profiles to the top of the crystalline basement at five well locations applying the new thermal‐conductivity data set and three scenarios of surface heat flow (50, 55 and 60 mW m?2). The calculated temperatures best match with measured drillstem‐test temperatures by using heat‐flow values close to the upper bound of range. Surface heat flow on the order of 55–60 mW m?2 is supported by a reevaluation of an existing temperature log and the application of thermal conductivity from this study. The temperature prediction for southern Israel shows values of 100–120°C at 3500–4500 m depth, indicating a geothermal potential that can be used for heating as well as electricity production. 相似文献
998.
H. Lammer J. H. Bredehöft A. Coustenis M. L. Khodachenko L. Kaltenegger O. Grasset D. Prieur F. Raulin P. Ehrenfreund M. Yamauchi J.-E. Wahlund J.-M. Grießmeier G. Stangl C. S. Cockell Yu. N. Kulikov J. L. Grenfell H. Rauer 《Astronomy and Astrophysics Review》2009,17(2):181-249
This work reviews factors which are important for the evolution of habitable Earth-like planets such as the effects of the
host star dependent radiation and particle fluxes on the evolution of atmospheres and initial water inventories. We discuss
the geodynamical and geophysical environments which are necessary for planets where plate tectonics remain active over geological
time scales and for planets which evolve to one-plate planets. The discoveries of methane–ethane surface lakes on Saturn’s
large moon Titan, subsurface water oceans or reservoirs inside the moons of Solar System gas giants such as Europa, Ganymede,
Titan and Enceladus and more than 335 exoplanets, indicate that the classical definition of the habitable zone concept neglects
more exotic habitats and may fail to be adequate for stars which are different from our Sun. A classification of four habitat
types is proposed. Class I habitats represent bodies on which stellar and geophysical conditions allow Earth-analog planets
to evolve so that complex multi-cellular life forms may originate. Class II habitats includes bodies on which life may evolve
but due to stellar and geophysical conditions that are different from the class I habitats, the planets rather evolve toward
Venus- or Mars-type worlds where complex life-forms may not develop. Class III habitats are planetary bodies where subsurface
water oceans exist which interact directly with a silicate-rich core, while class IV habitats have liquid water layers between
two ice layers, or liquids above ice. Furthermore, we discuss from the present viewpoint how life may have originated on early
Earth, the possibilities that life may evolve on such Earth-like bodies and how future space missions may discover manifestations
of extraterrestrial life. 相似文献
999.
We describe the application of the implicit midpoint integrator to the problem of attitude dynamics for low-altitude satellites without the use of quaternions. Initially, we consider the satellite to rotate without external torques applied to it. We compare the numerical solution with the exact solution in terms of Jacobi’s elliptic functions. Then, we include the gravity-gradient torque, where the implicit midpoint integrator proves to be a fast, simple and accurate method. Higher-order versions of the implicit midpoint scheme are compared to Gauss–Legendre Runge–Kutta methods in terms of accuracy and processing time. Finally, we investigate the performance of a parameter-adaptive Kalman filter based on the implicit midpoint integrator for the determination of the principal moments of inertia through observations. 相似文献
1000.
Christoph Zöckler Lera Miles Lucy Fish Annett Wolf Gareth Rees Fiona Danks 《Climatic change》2008,87(1-2):119-130
Climate change is expected to alter the distribution of habitats and thus the distribution of species connected with these
habitats in the terrestrial Barents Sea region. It was hypothesised that wild species connected with the tundra and open-land
biome may be particularly at risk as forest area expands. Fourteen species of birds were identified as useful indicators for
the biodiversity dependent upon this biome. By bringing together species distribution information with the LPJ-GUESS vegetation
model, and with estimates of future wild and domestic reindeer density, potential impacts on these species between the present
time and 2080 were assessed. Over this period there was a net loss of open land within the current breeding range of most
bird species. Grazing reindeer were modelled as increasing the amount of open land retained for nine of the tundra bird species. 相似文献