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211.
Since the early 1960s, the application of aluminum alloy sacrificial anodes to mitigate marine corrosion has been well known. The aim of this work was to study aluminum bioconcentration in Mytilus edulis by an in vitro test performed in two tanks: the first containing non-contaminated water (NCW) and the second containing aluminum-contaminated water (CW) (530 μg L−1) released by sacrificial anode. The mussels were collected and examined over a period of 8 weeks. A comparison between the aluminum concentrations in the digestive glands of mussels from the CW and NCW tanks shows that the highest value (1700 mg/kg d.w.) was found in the CW mussels collected after 13 days. In NCW, the mean aluminum concentration in digestive glands during the test was 281 mg/kg d.w. The rapid concentration decrease in digestive glands is probably due to the inhibition of filtering activity due to valve closure at the high concentration as well as the induction of the detoxification response. 相似文献
212.
Cassandra R. Fenton Reginald L. Hermanns Lars H. Blikra Peter W. Kubik Charlotte Bryant Samuel Niedermann Anette Meixner Mirjam M. Goethals 《Quaternary Geochronology》2011,6(5):437-452
Two rock avalanches in Troms County – the Grøtlandsura and Russenes – were selected as CRONUS-EU natural cosmogenic 10Be production-rate calibration sites because they (a) preserve large boulders that have been continuously exposed to cosmic irradiation since their emplacement; (b) contain boulders with abundant quartz phenocrysts and veins with low concentrations of naturally-occurring 9Be (typically < 1.5 ppb); and (c) have reliable minimum radiocarbon ages of 11,424 ± 108 cal yr BP and 10,942 ± 77 cal yr BP (1σ), respectively. Quartz samples (n = 6) from these two sites contained between 4.28 × 104 and 5.06 × 104 at 10Be/g using the 1.387 Myr 10Be half-life. Determination of these concentrations accounts for topographic and self-shielding, and effects on nuclide production due to isostatic rebound are shown to be negligible. Persistent, constant snow and moss cover cannot be proven, but if taken into consideration they may have reduced 10Be concentrations by 10%. Using the 10Be half-life of 1.387 Myr and the Stone scaling scheme, and accounting for snow- and moss-cover, we calculate an error-weighted mean total 10Be production rate of 4.12 ± 0.19 at/g/yr (1σ). A corresponding error-weighted mean spallogenic 10Be production rate is 3.96 ± 0.16 at/g/yr (1σ), respectively. These are in agreement within uncertainty with other 10Be production rates in the literature, but are significantly, statistically lower than the global average 10Be production rate. This research indicates, like other recent studies, that the production of cosmogenic 10Be in quartz is lower than previously established by other production-rate calibration projects. Similarly, our findings indicate that regional cosmogenic production rates should be used for determining exposure ages of landforms in order to increase the accuracy of those ages. As such, using the total 10Be production rate from our study, we determine an error-weighted mean surface-exposure age of a third rock avalanche in Troms County (the Hølen avalanche) to be 7.5 ± 0.3 kyr (1σ). This age suggests that the rock avalanche occurred shortly after the 8.2 kyr cooling event, just as the radiocarbon ages of the Grøtlandsura and Russenes avalanches confirm field evidence that those rock-slope failures occurred shortly after deglaciation. 相似文献
213.
Terrence Blackburn Samuel A. Bowring Blair Schoene Kevin Mahan Francis Dudas 《Contributions to Mineralogy and Petrology》2011,162(3):479-500
A new approach to U-Pb accessory mineral thermochronology allows high-resolution time-temperature histories to be extracted
from lower crustal xenoliths. The combination of the U-Pb system’s dual decay scheme with the effects of temperature dependent
Pb-diffusion can yield a time sensitive record of Pb production/diffusion within accessory phases. The difference in half-life
for parent isotopes 238U and 235U results in the time-variable production of Pb isotopes 206Pb and 207Pb, while Pb diffusion can result in large variations in the time-scales at which Pb retention occurs between grains of different
sizes. The combined effects of variable production rates between the two systems and diffusion result in data topologies on
a concordia diagram that permit distinction between slow cooling and reheating t-T paths. In slowly cooled systems, the difference
in time for Pb retention for grains of variable size yields a measure of partial retention zone (PRZ) residence time, and
provides a robust measure of cooling rate through the PRZ. In Montana, three lower crustal xenoliths, each from a different
depth, yield U-Pb rutile data that record a prolonged (>1 Ga) and slow cooling history towards a steady state geothermal gradient
following the amalgamation of the terrain onto North America. The shallowest samples record the initial recovery of a conductive
geothermal gradient and cool through the mineral PRZ at rates of <0.25°C/Ma over ~500 Ma. Deeper xenoliths record cooling
at younger times over similar time scales and rates. This multi-depth thermal history provides a long-term record of lithosphere
cooling and stabilization. 相似文献
214.
Tsunamis and intense tropical storms compete as viable mechanisms for catastrophic marine inundations of coastlines, and so
interpretation of deposits laid down by palaeo-events is often problematic. Here, examples are presented from the tropical
South Pacific Islands to demonstrate how indigenous knowledge may provide vital clues supporting sedimentological investigation
and thereby helping to explain the origin of giant boulders emplaced on top of coral reef platforms. 相似文献
215.
Experimental Study of the Brittle Behavior of Clay shale in Rapid Unconfined Compression 总被引:6,自引:3,他引:3
Florian Amann Edward Alan Button Keith Frederick Evans Valentin Samuel Gischig Manfred Blümel 《Rock Mechanics and Rock Engineering》2011,44(4):415-430
The mechanical behavior of clay shales is of great interest in many branches of geo-engineering, including nuclear waste disposal,
underground excavations, and deep well drilling. Observations from test galleries (Mont Terri, Switzerland and Bure, France)
in these materials have shown that the rock mass response near the excavation is associated with brittle failure processes
combined with bedding parallel shearing. To investigate the brittle failure characteristics of the Opalinus Clay recovered
from the Mont Terri Underground Research Laboratory, a series of 19 unconfined uniaxial compression tests were performed utilizing
servo-controlled testing procedures. All specimens were tested at their natural water content with loading approximately normal
to the bedding. Acoustic emission (AE) measurements were utilized to help quantify stress levels associated with crack initiation
and propagation. The unconfined compression strength of the tested specimens averaged 6.9 MPa. The crack initiation threshold
occurred at approximately 30% of the rupture stress based on analyzing both the acoustic emission measurements and the stress–strain
behavior. The crack damage threshold showed large variability and occurred at approximately 70% of the rupture stress. 相似文献
216.
Interannual variability of deep convection in the Northwestern Mediterranean simulated with a coupled AORCM 总被引:2,自引:1,他引:1
A hindcast experiment of the Mediterranean present-day climate is performed using a fully-coupled Atmosphere–Ocean Regional Climate Model (AORCM) for the Mediterranean basin. The new model, called LMDz-NEMO-Med, is composed of LMDz4-regional as atmospheric component and of NEMOMED8 as oceanic component. This AORCM equilibrates freely, without any flux adjustment, neither in fresh water nor in heat. At its atmospheric lateral boundary conditions, it is driven by ERA-40 data from 1958 to 2001, after a spin-up of 40 years in coupled configuration. The model performance is assessed and compared with available observational datasets. The model skill in reproducing mean state and inter-annual variability of main atmospheric and oceanic surface fields is in line with that of state-of-the-art AORCMs. Considering the ocean behaviour, the inter-annual variations of the basin-scale heat content are in very good agreement with the observations. The model results concerning salt content could not be adequately validated. High inter-annual variability of deep convection in the Gulf of Lion is simulated, with 53 % of convective winters, representative of the present climate state. The role of different factors influencing the deep convection and its inter-annual variability is examined, including dynamic and hydrostatic ocean preconditioning and atmospheric surface forcing. A conceptual framework is outlined and validated in linking the occurrence of deep convection to the efficiency of the integrated surface buoyancy fluxes along the winter season to mix the initially stratified averaged water column down to the convective threshold depth. This simple framework (based only on 2 independent variables) is able to explain 60 % (resp. 69 %) of inter-annual variability of the deep water formation rate (resp. maximum mixed layer depth) for the West Mediterranean Deep Water (WMDW) formation process. 相似文献
217.
218.
Immigration has become a leading topic of Italian political discourse and culture over the past decade, but international migrants also play a crucial role in the transformation of political culture at the scale of everyday practices. In the northern Italian industrial city, Turin, migrants from various parts of Africa, Latin America and Southeast Asia bring into relief the deconstruction of postwar labor in Italy, and contribute widely to shifting political practices and identities. Contemporary migrants from diverse ethnic backgrounds are discriminated against in similar ways, and are in the historically peculiar position of building diasporic politics. In Turin, first generation migrants have helped lead newcomers toward active participation in local politics, from the shop floors to the labor unions, and to inter-ethnic and feminist associations. 相似文献
219.
220.
Alexander A. Schekochihin Steven C. Cowley Samuel F. Taylor Jason L. Maron James C. McWilliams 《Astrophysics and Space Science》2004,292(1-4):141-146
We consider the problem of incompressible, forced, nonhelical, homogeneous, isotropic MHD turbulence with no mean magnetic field. This problem is essentially different from the case with externally imposed uniform mean field. There is no scale-by-scale equipartition between magnetic and kinetic energies as would be the case for the Alfvén-wave turbulence. The isotropic MHD turbulence is the end state of the turbulent dynamo which generates folded fields with small-scale direction reversals. We propose that the statistics seen in numerical simulations of isotropic MHD turbulence could be explained as a superposition of these folded fields and Alfvén-like waves that propagate along the folds. 相似文献