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Rachid Ait Akbour Jamaâ Douch Mohamed Hamdani Philippe Schmitz 《Comptes Rendus Geoscience》2002,334(13):981-985
To evaluate the risk of contaminant transport by mobile colloids, it is necessary to understand how colloids and associated pollutants behave during their migration through uncontaminated soil or groundwater. In this study, we investigated the influence of aggregation induced by Ca2+ and trace metals (Pb2+, Cu2+) concentrations on the transport of humic-coated kaolinite colloids through a natural quartz sand at pH=4. Adsorbed divalent cations reduce the colloids surface charge and thereby induce aggregation and deposition in porous media. To cite this article: R. Ait Akbour et al., C. R. Geoscience 334 (2002) 981–985. 相似文献
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The intertidal zone of an exposed sandy beach on the French coast of the English Channel was sampled with a 1.5 m beam-trawl over five years (2000 and 2003–2006) at weekly intervals. The fish and macrocrustacean catches were analysed to determine the inter-season and interannual variation in community structure and relate these variations to changes in the major environmental variables. Only six species (plaice Pleuronectes platessa, common goby Pomatoschistus microps, sprat Sprattus sprattus, sand eel Ammodytes tobianus, brown shrimp Crangon crangon and shore crab Carcinus maenas) from the 27 species captured can be considered as dominant species of the intertidal zone, and they accounted for >90% of total numbers. Most individuals caught were young-of-the-year or juvenile. Analysis of similarities (ANOSIM) and similarities percentage (SIMPER) indicated that inter-season variability of community structure (mean average similarity = 47%) was more pronounced than interannual variability (mean average similarity = 65%). Canonical correspondence analysis (CCA) indicates that a substantial component (32.2%) of the measured inter-season variation in community structure can be explained by environmental factors (mainly water temperature). The main inter-season changes in the abundance and community structure were due to the variation of the six key species and reflect the different times of their recruitment. During the five years of the study, the structure of the fish and macrocrustacean spring community persisted from year to year, with the dominant species reappearing consistently even though their abundances fluctuated from year to year. This interannual variation probably reflects variable recruitment success influenced by physico-chemical conditions. In spite of the considerable interannual variation (40 times) in the spring bloom of the prymnesiophyte alga Phaeocystis globosa we found no effect of this bloom on either fish and macrocrustacean species densities or diversity index. 相似文献
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Palaeoclimates across Europe for 6000 y BP were estimated from pollen data using the modern pollen analogue technique constrained
with lake-level data. The constraint consists of restricting the set of modern pollen samples considered as analogues of the
fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration (P–E) is consistent with the regional change in moisture balance as indicated by lakes. An artificial neural network was used
for the spatial interpolation of lake-level changes to the pollen sites, and for mapping palaeoclimate anomalies. The climate
variables reconstructed were mean temperature of the coldest month (T
c
), growing degree days above 5 °C (GDD), moisture availability expressed as the ratio of actual to equilibrium evapotranspiration (α), and P–E. The constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies, especially for P–E. The reconstructions indicate clear spatial and seasonal patterns of Holocene climate change, which can provide a quantitative
benchmark for the evaluation of palaeoclimate model simulations. Winter temperatures (T
c
) were 1–3 K greater than present in the far N and NE of Europe, but 2–4 K less than present in the Mediterranean region.
Summer warmth (GDD) was greater than present in NW Europe (by 400–800 K day at the highest elevations) and in the Alps, but >400 K day less
than present at lower elevations in S Europe. P–E was 50–250 mm less than present in NW Europe and the Alps, but α was 10–15% greater than present in S Europe and P–E was 50–200 mm greater than present in S and E Europe.
Received: 3 January 1996 / Accepted: 15 July 1996 相似文献
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Rachid Ouyed Denis Leahy Brian Niebergal Youling Yue 《Monthly notices of the Royal Astronomical Society》2009,396(2):1058-1065
This is the third paper of a series of papers where we explore the evolution of iron-rich ejecta from quark-novae. In the first paper, we explored the case where a quark-nova ejecta forms a degenerate shell, supported by the star's magnetic field, with applications to SGRs. In the second paper, we considered the case where the ejecta would have sufficient angular momentum to form a degenerate Keplerian torus and applied such a system to two AXPs, namely 1E2259+586 and 4U0142+615. Here, we explore the late evolution of the degenerate torus and find that it can remain unchanged for ∼106 yr before it becomes non-degenerate. This transition from a degenerate torus (accretion-dominated) to a non-degenerate disc (no accretion) occurs about 106 yr following the quark-nova, and exhibits features that are reminiscent of observed properties of Rotation RAdio Transients (RRATs). Using this model, we can account for the duration of both the radio bursts and the quiet phase, as well as the observed radio flux from RRATs. We discuss a connection between XDINs and RRATs and argue that some XDINs may be 'dead RRATs' that have already consumed their non-degenerate disc. 相似文献
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Manjari Bagchi Rachid Ouyed Jan Staff Subharthi Ray Mira Dey † Jishnu Dey ‡ 《Monthly notices of the Royal Astronomical Society》2008,387(1):115-120
We study the effects of temperature on strange stars. It is found that the maximum mass of the star decreases with the increase of temperature, as at high temperatures the equations of state become softer. Moreover, if the temperature of a strange star increases, keeping its baryon number fixed, its gravitational mass increases and its radius decreases. This leads to a limiting temperature, where it turns into a black hole. These features are the result of a combined effect of the change of gluon mass and the quark distribution with temperature. We report on a new type of radial oscillation of strange stars, driven by what we call 'chromothermal' instability. We also discuss the relevance of our findings in the astrophysics of core collapse supernovae and gamma-ray bursts. 相似文献
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The most luminous Supernova SN2006gy (more than 100 times brighter than a typical supernova) has been a challenge to explain by standard models. For example, pair-instability supernovae which are luminous enough seem to have too slow a rise, and core-collapse supernovae do not seem to be luminous enough. We present an alternative scenario involving a Quark Nova (an explosive transition of the newly born neutron star to a quark star) in which a second explosion (delayed) occurs inside the ejecta of a normal supernova. The reheated supernova ejecta can radiate at higher levels for longer periods of time primarily due to reduced adiabatic-expansion losses, unlike the standard supernova case. We find an encouraging match between the resulting light curve and that observed in the case of SN2006gy suggesting that we might have at hand the first ever signature of a Quark Nova. Successful application of our model to SN2005gj and SN2005ap is also presented. 相似文献
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Within the framework of the PMIP (Paleoclimate Modelling Intercomparison Project), we have compared mid-Holocene climate
simulations from 16 atmospheric general circulation models (AGCMs) with new pollen-based reconstructions of the European bioclimatic
variables for winter and growing season temperatures as well as annual water budget changes. In winter, some models are able
to simulate the reconstructed northeastern warming, due to an increased heat transport from the ocean, associated with a larger
north-south pressure gradient over the northern Atlantic. Whereas most models are only able to simulate a strong summer warming,
data indicate a shorter and/ or colder growing season in southern Europe and a longer and/or warmer growing season in northwestern
Europe. The reconstructed change in annual water budget indicates drier conditions in northwestern Europe and wetter conditions
in southern Europe. Some models simulate such moisture changes, due to more summer evaporation over Scandinavia during summer,
and more autumn-winter-spring precipitation over southern Europe. To address the PMIP approximation of no change in ocean
and land boundary conditions, we have performed short sensitivity experiments to surface boundary conditions (sea-surface-temperatures,
vegetation) using one single model. The model-data disagreements over Europe are probably due to the local influence of the
surrounding oceans which are not taken into account in the first PMIP simulations. We therefore stress the need for more mid-Holocene
SST reconstructions and further analysis of pollen data in the Mediterranean region.
Received: 23 February 1998 /Accepted: 19 September 1998 相似文献