THE LOOP CHONDRITE: PETROLOGY,MINERAL CHEMISTRY,AND OPAQUE MINERALOGY     

Nabil Z. Boctor  Gunnar Kullerud 《Meteoritics & planetary science》1981,16(1):61-68

The Loop meteorite was found in 1962 in Gaines County, Texas, at a location very close to that where the Ashmore chondrite was found in 1969. The two specimens were assumed to be fragments of the same meteorite. The Loop meteorite is a type L6 chondrite composed of olivine (Fo_75.4Fa_24.6), orthopyroxene (En_77.6Wo_1.5Fs_20.9), clinopyroxene (En_47.5Wo_45.1Fs_7.4), plagioclase (Ab_84.3Or_5.5An_10.2), Fe-Ni metal, troilite, and chromite. Fe-Ni metal is represented by kamacite (5.8-6.4 wt % Ni, 0.88-1.00 wt % Co), taenite (30.0–52.9 wt % Ni, 0.16-0.34 wt % Co), and plessite (16.8–28.5 wt % Ni, 0.38-0.54 wt % Co). Native copper occurs as rare inclusions in Fe-Ni metal. Both chondrules and matrix have similar mineral compositions. The mineral chemistry of the Loop meteorite is quite different from that of the Ashmore, which was classified as an H5 chondrite by Bryan and Kullerud (1975). Therefore, the Ashmore and Loop meteorites are two different chondrites, even though they were recovered from the same geographic location.  相似文献   

Temperature/flow statistics and thermomechanics of low-temperature geothermal systems in Iceland     

Gunnar Bodvarsson 《Journal of Volcanology and Geothermal Research》1983,19(3-4)

A survey of low-temperature geothermal activity in Iceland shows that there is a strong positive correlation between the temperature and the mass flow of the systems. The relation is very clearly displayed by the thermal systems in Central Northern Iceland. Subdividing the temperature interval from 20/dgC to 100°C into 8 intervals of equal length and plotting the average system flow in each interval against the average temperature of the interval we find that the mass flow increases with the temperature. At the lower end this relation is the result of a conductive cooling of the thermal water as it ascends to the surface. At temperatures above 50°C convective effects appear to be the dominant cause. A very simple lumped element analysis of the low-temperature systems results in reasonable estimates of important flow parameters. The convective downward migration of fracture spaces along the walls of mafic dikes appears to be a dominant thermomechanical process in the development of the low-temperature systems in Northern Iceland.  相似文献   

Laboratory determination of strength properties of frozen salt marine clay   总被引：2，自引：0，他引：2  

Gunnar Aas 《Engineering Geology》1981,18(1-4):67-78

In connection with the building of a railway tunnel through the City of Oslo, temporary improvement of the soft clay by freezing was considered in order to reinforce the tunnel ceiling in an area where the rock cover was insufficient. The same solution was also considered for another part of the tunnel where the problem was to prevent bottom heave failure in a deep excavation.

As this marine clay deposit has a very high salt content (about 25 g/l pore liquid), it was reasonable to believe that the strength of the frozen clay would be relatively low compared to previously published data concerning fresh clay soils. To investigate the stress—strain properties of frozen Oslo clay, a fairly comprehensive research programme was carried out; including two different temperature levels and using different testing techniques. The clay was tested in compression, tension, bending and shear, respectively. The tests were run very slowly, time to failure was normally 70–100 days.

This paper presents the main test results, which indicate that there exists a fairly well defined critical shear stress level for a given freezing temperature. As long as the stresses do not exceed this stress level, the creep deformations are small and the creep rates are constant or decreasing with time. On the other hand, higher shear stresses lead to very extensive deformations or failure.  相似文献   

A three-dimensional numerical sea model with eddy viscosity varying piecewise linearly in the vertical     

Gunnar Furnes 《Continental Shelf Research》1982,2(4):231-241

The solution of the three-dimensional linear hydrodynamic equations which describe wind-driven flow in a homogeneous sea are solved using the eigenfunction method. The eddy viscosity is taken to vary piecewise linearly in the vertical over an arbitrary number of layers. Using this formulation the eigenfunctions are given in terms of Bessel functions. The coefficients of integration as well as the eigenvalues are determined accurately such that the boundary conditions are satisfied. Values of the eigenfunctions at any depth can then be determined very fast and to a high degree of accuracy.Current profiles at any position can hence be computed accurately. The expansion of the horizontal component of current converges very fast at all depths.  相似文献   

Correlation of dispersant effectiveness and toxicity of oil dispersants towards the alga Chlamydomonas reinhardti     

Gunnar Bratbak  Mikal Heldal  Gjert Knutsen  Torleiv Lien  Svein Norland 《Marine pollution bulletin》1982,13(10):351-353

Using synchronous cultures of the unicellular green alga Chlamydomonas reinhardti, the toxicities of mixtures of Ekofisk crude oil and oil dispersants were measured. Sixteen so-called concentrates and 10 solvent-based dispersants were tested. The dispersing effectiveness of these compounds with respect to the Ekofisk crude oil was also measured. The concentrates were tested undiluted as well as diluted using algal growth medium (2‰ salinity) and artificial sea water (33‰ salinity) as dispersing liquid. The solvent-based compounds were tested in algal medium. For all compounds we found significant correlations between their toxicity and their effectiveness in dispersing the Ekofisk oil, such that the more effective the compound, the more toxic it was.  相似文献   

Fate of pharmaceutical micro-pollutants in Lake Tegel (Berlin,Germany): the impact of lake-specific mechanisms     

Sebastian Schimmelpfennig  Georgiy Kirillin  Christof Engelhardt  Uwe Dünnbier  Gunnar Nützmann 《Environmental Earth Sciences》2016,75(10):893

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Performance of EVA-Based Membranes for SCL in Hard Rock     

Karl Gunnar Holter 《Rock Mechanics and Rock Engineering》2016,49(4):1329-1358

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Implications of weak near-term climate policies on long-term mitigation pathways     

Gunnar?LudererEmail author  Christoph?Bertram  Katherine?Calvin  Enrica?De?Cian  Elmar?Kriegler 《Climatic change》2016,135(1):127-141

While the international community has agreed on the long-term target of limiting global warming to no more than 2 °C above pre-industrial levels, only a few concrete climate policies and measures to reduce greenhouse gas (GHG) emissions have been implemented. We use a set of three global integrated assessment models to analyze the implications of current climate policies on long-term mitigation targets. We define a weak-policy baseline scenario, which extrapolates the current policy environment by assuming that the global climate regime remains fragmented and that emission reduction efforts remain unambitious in most of the world’s regions. These scenarios clearly fall short of limiting warming to 2 °C. We investigate the cost and achievability of the stabilization of atmospheric GHG concentrations at 450 ppm CO₂e by 2100, if countries follow the weak policy pathway until 2020 or 2030 before pursuing the long-term mitigation target with global cooperative action. We find that after a deferral of ambitious action the 450 ppm CO₂e is only achievable with a radical up-scaling of efforts after target adoption. This has severe effects on transformation pathways and exacerbates the challenges of climate stabilization, in particular for a delay of cooperative action until 2030. Specifically, reaching the target with weak near-term action implies (a) faster and more aggressive transformations of energy systems in the medium term, (b) more stranded investments in fossil-based capacities, (c) higher long-term mitigation costs and carbon prices and (d) stronger transitional economic impacts, rendering the political feasibility of such pathways questionable.  相似文献   

Genetic studies of redfish (Sebastes spp.) from Icelandic and Greenland waters     

Nedreaas  Kjell; Johansen  Torild; Naevdal  Gunnar 《ICES Journal of Marine Science》1994,51(4):461-467

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Assessing coupling between lakes and layered aquifers in a complex Pleistocene landscape based on water level dynamics     

Gunnar Lischeid  Marco Natkhin  Jörg Steidl  Ottfried Dietrich  Ralf Dannowski  Christoph Merz 《Advances in water resources》2010

The biosphere reserve Schorfheide-Chorin is a scenic region with many lakes. Hydraulic coupling between lakes and groundwater is difficult to assess due to the very heterogeneous Pleistocene deposits with a complex layering of different aquifers, part of them being confined. Thus, a principal component analysis of time series of groundwater and lake water levels was performed. The first two principal components provided a quantitative measure of damping of the input signal, i.e., the extent to which time series of groundwater pressure heads or lake water levels are smoothed and delayed with respect to the input signal, i.e., groundwater recharge or precipitation minus evapotranspiration, respectively. The lakes differed substantially with respect to damping behaviour, indicating different impacts of deep groundwater contribution. For most of the groundwater wells, damping increased linearly with mean depth to water table. In contrast, some wells exhibited nearly identical behaviour independent of depth. High-pass filtered data of water table level from these wells were strongly and inversely correlated with those of barometric pressure fluctuations, pointing to a confined aquifer which was evidently not connected to the adjacent lake.  相似文献