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We report here an optimisation of the demountable direct injection high efficiency nebuliser (d‐DIHEN) for isotopic measurements with a Neptune (ThermoFisher Scientific, Bremen, Germany) multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS) and describe a method for boron isotopic ratio determination. With direct injection nebulisation 100% of the analyte was introduced into the ICP‐MS plasma and wash times were drastically reduced for elements such as boron and thorium. Compared to the classical stable introduction system (SIS: double Scott/cyclonic spray chamber), sensitivity for boron was 2–5 times higher with d‐DIHEN and wash times up to ten times shorter. Repeatability of 11B/10B sample‐calibrator bracketing measurements reached 0.25‰ (2s) for seawater and coral samples. Method accuracy and reproducibility were tested on mixed reference solutions having δ11B values in the ranges ?90 to +40‰ and ?2 to +2.5‰, demonstrating our ability to distinguish δ11B values with differences of only 0.25‰. The international seawater reference material NRCC NASS‐5 (National Research Council, Ottawa, Canada), analysed in different sessions over a 10‐month period, yielded an average δ11B value of +39.89 ± 0.25‰, in the upper range of previously published seawater values. A comparison between δ11B determined by d‐DIHEN MC‐ICP‐MS and positive‐TIMS (P‐TIMS) for four modern corals showed an excellent agreement (with bias of less than 0.4‰).  相似文献   
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European temperatures and their projected changes under the 8.5 W/m2 Representative Concentration Pathway scenario are evaluated in an ensemble of 33 global climate models participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Respective contributions of large-scale dynamics and local processes to both biases and changes in temperatures, and to the inter-model spread, are then investigated from a recently proposed methodology based on weather regimes. On average, CMIP5 models exhibit a cold bias in winter, especially in Northern Europe. They overestimate summer temperatures in Central Europe, in association with a greater diurnal range than observed. The projected temperature increase is stronger in summer than in winter, with the highest summer warming occurring over Mediterranean regions. Links between biases and sensitivities are evidenced in winter, suggesting a potential influence of snow cover biases on the projected surface warming. A brief analysis of daily temperature extremes suggests that the intra-seasonal variability is projected to decrease (slightly increase) in winter (summer). Then, in order to understand model discrepancies in both present-day and future climates, we disentangle effects of large-scale atmospheric dynamics and regional physical processes. In particular, in winter, CMIP5 models simulate a stronger North-Atlantic jet stream than observed and, in contrast with CMIP3 results, the majority of them suggests an increased frequency of the negative phase of the North-Atlantic Oscillation under future warming. While large-scale circulation only has a minor contribution to ensemble-mean biases or changes, which are primarily dominated by non-dynamical processes, it substantially affects the inter-model spread. Finally, other sources of uncertainties, including the North-Atlantic warming and local radiative feedbacks related to snow cover and clouds, are briefly discussed.  相似文献   
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The origin of magmatic layering is still hotly debated. To try to shed some light on this problem, two ultramafic–mafic layered xenoliths from Puy Beaunit (French Massif Central) were investigated in detail. The nodules belong to a stratiform intrusion emplaced in the deep crust during the Permian (257 ± 6 Ma; Féménias, O., Coussaert, N., Bingen, B., Whitehouse, M., Mercier, J.-C., Demaiffe, D., 2003. A Permian underplating event in late- to post-orogenic tectonic setting. Evidence from the mafic–ultramafic layered xenoliths from Beaunit (French Massif Central). Chem. Geol. 199 293–315.). The 3 to 5 cm thick nodules have, in common, a central orthopyroxenite layer; the succession of layers is, respectively, norite–orthopyroxenite–norite (PBN 00-01) and norite–orthopyroxenite–harzburgite (PBN 00-03). The variations of both major (by electron microprobe) and trace, essentially the RE, elements (by LA-ICP-MS) were measured in major mineral phases (orthopyroxene, clinopyroxene, plagioclase, spinel) along cross-section perpendicular to the layering. Strong grain size, chemical and textural variations occur along these sections: they can be continuous or discontinuous, symmetrical or asymmetrical. Such complex variations cannot be solely related to a single magmatic history (fractional crystallisation, mineral sorting). Other processes such as element enrichment by residual liquid channelling along layer boundaries and/or sub-solidus recrystallisation and element redistribution must be invoked. It appears, in particular, that element distribution in the central orthopyroxenite layer could result from the injection of micro-sills of orthopyroxene-rich liquid between previously consolidated layers.  相似文献   
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The archaeological sites in the open-cast mine of Schöningen, Germany, represent outstanding archives for understanding Middle Pleistocene interglacial–glacial transitions and human adaption. Aquatic microfossil and pollen assemblages from the ‘Reinsdorf sequence’, likely correlated to Marine Isotope Stage 9, document environmental changes from a thermal maximum to succeeding glacial conditions recorded in two sequences of excavation sites 12 II and 13 II. Multi-proxy analyses enable detailed reconstruction of lake-shore and landscape developments despite variable microfossil preservation in changing carbonate- and organic-rich deposits. Rich aquatic vegetation with abundant charophytes suggests repeated phases with water depths of 0.5–2 m at site 13 II, while even greater temporary depths are deduced for 12 II DB. Mesorheophilic and mesotitanophilic ostracod species indicate stream inflows with medium–low calcium contents of >18 mg Ca L–1 originating from nearby springs. Diatoms point to meso-eutrophic conditions and an alkaline pH of the lake water. Interglacial conditions with thermophile forests but no aquatic microfossils preserved, suggesting a dry or only temporarily flooded site, mark the beginning of the sequence. Continuous presence of aquatic organisms and overall dominance of small tychoplanktonic diatoms during a subsequent cool steppe phase provide evidence for increased water depths and unstable habitats characterized by erosion and probably prolonged periods of lake ice cover. During the succeeding boreal forest-steppe phase, surface runoff into the productive, shallow lake decreased due to a more extensive vegetation cover. Concurrently, intensified groundwater input in contact with the nearby salt wall caused elevated salinities. Following a lake level drop, stream inflows and lake levels increased again towards the end of the Reinsdorf sequence and promoted development of a diverse fauna and flora at the lake shore; thereby maintaining an attractive living and hunting environment for early humans during a phase of generally cooler temperatures and landscape instability at the transition into a glacial period.  相似文献   
266.
X-ray spectra of accretion discs with dynamic coronae   总被引:1,自引:0,他引:1  
We compute the X-ray spectra produced by non-static coronae atop accretion discs around black holes and neutron stars. The hot corona is radiatively coupled to the underlying disc (the reflector) and generates an X-ray spectrum which is sensitive to the bulk velocity of the coronal plasma, β = v / c . We show that an outflowing corona reproduces the hard-state spectrum of Cyg X-1 and similar objects. The dynamic model predicts a correlation between the observed amplitude of reflection R and the X-ray spectrum slope Γ since both strongly depend on β . A similar correlation was observed and its shape was well fitted by the dynamic model. The scattering of soft radiation in an outflowing corona can also account for the observed optical–UV polarization pattern in active galactic nuclei.  相似文献   
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