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151.
Delphine Vantelon Rachid Belkhou Isabelle Bihannic Laurent J. Michot Emmanuelle Montargès-Pelletier Jean-Louis Robert 《Physics and Chemistry of Minerals》2009,36(10):593-602
X-PEEM images and XPS were collected on isolated layers of three synthetic swelling clays, one hectorite and two saponites
with various charge, recording the Si(2p), Al(2p) and Mg(2p) core level spectra from the clay sheets. Spectra were fitted
to determine the different components of the core levels. Due to their large full width at half maximum, Si XPS spectra were
fitted using two to three doublets. It appears that, for a given clay mineral, Si, Al and Mg binding energies (BE) were constant,
for all the observed layers. However, variations of the Si BE were observed depending on the nature of the mineral investigated.
The various components obtained from the fit of Si spectra could be assigned to different substitution rates; binding energy
shifting to lower values with substitution increase in the layer. Furthermore, variations in Si BE according to charge location
were assigned to the influence of exchangeable cation. 相似文献
152.
Marwan Alkattan Eric H. Oelkers Jean-Louis Dandurand Jacques Schott 《Chemical Geology》2002,190(1-4):291-302
Dissolution rates of single calcite crystals were determined from sample weight loss using free-drift rotating disk techniques. Experiments were performed at 25 °C in aqueous HCl solutions over the bulk solution pH range −1 to 3 and in the presence of trace concentrations of aqueous NaPO3 and MgCl2. These salts were chosen for this study because aqueous magnesium and phosphate are known to strongly inhibit calcite dissolution at neutral to basic pH. Reactive solutions were undersaturated with respect to possible secondary phases. Neither an inhibition or enhancement of calcite dissolution rates was observed in the presence of aqueous MgCl2 at pH 1 and 3. The presence of trace quantities of NaPO3, which dissociates in solution to Na+ and H2PO4−, decreased the overall calcite dissolution rate at pH≤2. This contrasting behavior could be attributed to the different adsorption behavior of these dissolved species. As calcite surfaces are positively charged in acidic solutions, aqueous Mg2+ may not adsorb, whereas aqueous phosphate, present as either the anion H2PO4− or the neutral species H3PO40, readily adsorbs on calcite surfaces leading to significant dissolution inhibition. 相似文献
153.
The activities of particulate and soluble phosphatase were analyzed monthly for 1 year in the coastal ecosystems of the NW Mediterranean Sea. The mean contribution of the particulate activity increased from 56% at an MUF-P concentration of 30 μM to 77% at 0.04 μM. This particulate activity was negatively correlated with the DIP, DOP and TDP concentrations when the activities were related to the seawater volume, chlorophyll a or the protein concentration. The TDP correlations were highly significant (p: 0.001). The DOP correlations were significant (p: 0.04) and became highly significant (p: 0.009) at low DIP concentrations (<0.13 μM). The DIP correlations were significant (p: 0.04) only at low DOP concentrations (<0.18 μM). Thus, the effects of seawater DIP and DOP were found to be linked. The soluble activity exhibited distinct phosphatase fractions with high (0.5–29.5 μM) and low (0.02–2 μM) Km values, but none exhibited significant correlations with phosphorus compounds. 相似文献
154.
Véronique Bommier Egidio Landi Degl'Innocenti Jean-Louis Leroy Sylvie Sahal-Bréchot 《Solar physics》1994,154(2):231-260
The present paper is devoted to the interpretation of linear polarization data obtained in 14 quiescent prominences with the Pic-du-Midi coronagraph-polarimeter by J. L. Leroy, in the two lines Hei D3 andH quasi-simultaneously. The linear polarization of the lines is due to scattering of the anisotropic photospheric radiation, modified by the Hanle effect due to the local magnetic field. The interpretation of the polarization data in the two lines is able to provide the 3 components of the magnetic field vector, and one extra parameter, namely the electron density, because the linear polarization of H is also sensitive to the depolarizing effect of collisions with the electrons and protons of the medium. Moreover, by using two lines with different optical thicknesses, namely Hei D3, which is optically thin, and H, which is optically thick ( = 1), it is possible to solve the fundamental ambiguity, each line providing two field vector solutions that are symmetrical in direction with respect to the line of sight in the case of the optically thin line, and which have a different symmetry in the case of the optically thick line.It is then possible to determine without ambiguity the polarity of the prominence magnetic field with respect to that of the photospheric field: 12 prominences are found to be Inverse polarity prominences, whereas 2 prominences are found to be Normal polarity prominences. It must be noticed that in 12 of the 14 cases, the line-of-sight component of the magnetic field vector has a Normal polarity (to the extent that the notion of polarity of a vector component is meaningful; no polarity can be derived in the 2 remaining cases); this may explain the controversy between the results obtained with methods based on the Hanle effect with results obtained through the Zeeman effect. A dip of the magnetic field lines across the prominence has been assumed, to which the optically thick H line is sensitive, and the optically thin Hei D3 line is insensitive.For the Inverse prominences, the average field strength is 7.5±1.2 G, the average angle,, between the field vector and the prominence long axis is 36° ± 15°, the average angle, , between the outgoing field lines and the solar surface at the prominence boundary is 29° ± 20°, and the average electron density is 2.1 × 1010 ± 0.7 × 1010 cm–3. For the Normal prominences, the average field strength is 13.2±2.0 G, the average angle,, between the field vector and the prominence long axis is 53° ± 15°, the average angle, , between the outgoing field lines and the solar surface at the prominence boundary is 0° ± 20° (horizontal field), and the average electron density is 8.7 × 109 ± 3.0 × 109 cm–3. 相似文献
155.
Françoise Andrieux-Loyer Afi Azandegbé Florian Caradec Xavier Philippon Roger Kérouel Agnès Youenou Jean-Louis Nicolas 《Aquatic Geochemistry》2014,20(6):573-611
This study aims to compare the impact of oyster cultures on diagenetic processes and the phosphorus cycle in the sediments of the Aber Benoît and the Rivière d’Auray, estuary of Brittany, France. Our results showed clear evidence of the seasonal impact of oyster cultures on sediment characteristics (grain size and organic matter parameters) and the phosphorus cycle, especially in the Aber Benoît. At this site, seasonal variations in sulfide and Fe concentrations in pore waters, as well as Fe–P concentrations in the solid phase, highlighted a shift from a system governed by iron reduction (Reference) to a system governed by sulfate reduction (beneath oyster). This could be partly explained by the increase in labile organic matter (i.e., biodeposits) beneath oysters, whose mineralization by sulfate led to high sulfide concentrations in pore waters (up to 4,475 µmol l?1). In turn, sulfide caused an enhanced release of phosphate in the summer, as adsorption sites for phosphate decreased through the formation of iron–sulfide compounds (FeS and FeS2). In the Aber Benoît, dissolved Fe/PO4 ratios could be used as an indicator of phosphate release into oxic water. Low Fe/PO4 ratios in the summer indicated higher effluxes of phosphate toward the water column (up to 47 µmol m?2 h?1). At other periods, Fe/PO4 ratios higher than 2 mol/mol indicated very low phosphate fluxes. In contrast, in the Rivière d’Auray, the occurrence of macroalgae, stranding regularly all over the site, clearly masked the impact of oyster cultures on sediment properties and the phosphorus cycle and made the use of Fe/PO4 ratios more difficult in terms of indicators of phosphate release. 相似文献
156.
Alexis Hannart Michael Ghil Jean-Louis Dufresne Philippe Naveau 《Climatic change》2013,119(3-4):585-601
How will our estimates of climate uncertainty evolve in the coming years, as new learning is acquired and climate research makes further progress? As a tentative contribution to this question, we argue here that the future path of climate uncertainty may itself be quite uncertain, and that our uncertainty is actually prone to increase even though we learn more about the climate system. We term disconcerting learning this somewhat counter-intuitive process in which improved knowledge generates higher uncertainty. After recalling some definitions, this concept is connected with the related concept of negative learning that was introduced earlier by Oppenheimer et al. (Clim Change 89:155–172, 2008). We illustrate disconcerting learning on several real-life examples and characterize mathematically certain general conditions for its occurrence. We show next that these conditions are met in the current state of our knowledge on climate sensitivity, and illustrate this situation based on an energy balance model of climate. We finally discuss the implications of these results on the development of adaptation and mitigation policy. 相似文献
157.
Lin Li Yi Pan Farshad Amini Kuang Cuiping Jean-Louis Briaud 《Geotechnical and Geological Engineering》2014,32(4):847-857
Post-Katrina investigations revealed that most earthen levee damage occurred on the levee crest and land-side slope as a result of either wave overtopping, storm surge overflow, or a combination of both. This study addresses erosion resistance performance of a levee strengthening technique—high performance turf reinforcement mat under combined wave and surge overtopping conditions using full-scale flume tests as well as erosion function apparatus (EFA) tests. Based on the results of full-scale flume tests, an “upper limit” of soil loss is observed for certain flow conditions. Erosion rate was presented as a function of velocity and freeboard. The effect of duration of overtopping on the erosion depth is also determined. The results of EFA tests indicate that the presence of grass roots substantially improve the critical velocity and soil erodibility. 相似文献
158.
Dmitri?A.?IonovEmail author Ingrid?Chanefo Jean-Louis?Bodinier 《Contributions to Mineralogy and Petrology》2005,150(3):335-353
Lherzolite–wehrlite (LW) series xenoliths from the quaternary Tok volcanic field in the southeastern Siberian craton are distinguished
from the more common lherzolite–harzburgite (LH) series by (a) low Mg numbers (0.84–0.89) at high modal olivine (66–84%) and
(b) widespread replacement of orthopyroxene (0–12%) and spinel by clinopyroxene (7–22%). The LW series peridotites are typically
enriched in Ca, Fe, Mn and Ti, and depleted in Si, Ni and Cr relative to refractory LH series rocks (Mg number ≥0.89), which
are metasomatised partial melting residues. Numerical modelling of Fe–Mg solid/liquid exchange during melt percolation demonstrates
that LW series rocks can form by reaction of host refractory peridotites with evolved (Mg numbers 0.6–0.7), silica-undersaturated
silicate melts at high melt/rock ratios, which replace orthopyroxene with clinopyroxene and decrease Mg numbers. This process
is most likely related to underplating and fractionation of basaltic magma in the shallow mantle, which also produced olivine–clinopyroxene
cumulates found among the Tok xenoliths. 相似文献
159.
Lacoue-Labarthe T Warnau M Oberhänsli F Teyssié JL Jeffree R Bustamante P 《Marine pollution bulletin》2008,57(6-12):826-831
The aim of this study was to provide a first insight on the incorporation of eight metals in the eggs of the cuttlefish Sepia officinalis via maternal transfer, using radiotracer techniques ((110m)Ag, (241)Am, (109)Cd, (60)Co, (134)Cs, (54)Mn, (75)Se and (65)Zn). The cuttlefish was fed daily with radiolabelled crabs for two weeks; it then started to spawn every three days. Among the eight tracers, only (110m)Ag, (75)Se and (65)Zn were significantly transferred to the eggs. The radiotracer distribution among the egg compartments showed that (75)Se and (65)Zn were accumulated mainly in the vitellus whereas (110m)Ag was found in similar proportion in the vitellus and the eggshell. During the embryonic development, (75)Se and (65)Zn contained in the vitellus were progressively transferred to the embryo, likely to supply its metabolic needs in these essential elements. Although it has no known biological functions, Ag contained in both vitellus and eggshell was also transferred to the embryo. Overall, our results showed that transfer of Ag, Se, and Zn does actually occur from a female cuttlefish to its eggs, at least during the last two weeks before spawning. 相似文献
160.
桑沟湾和胶州湾沉积物耗氧率研究 总被引:2,自引:0,他引:2
为评价浅海海域底层在碳元素生物地化循环中的作用,采用现场取样培养法测定了黄海桑沟湾和胶州湾的沉积物耗氧率。桑沟湾5月和8月的沉积物耗氧率分别为15和24 mmol.m-2.d-1;胶州湾8月的沉积物耗氧率为18 mmol.m-2.d-1。回归分析表明,2个湾的沉积物耗氧率分别与沉积物表层的有机碳和总氮含量正相关。取呼吸商为0.8,得到桑沟湾底层对有机碳的矿化率占水层初级生产力的102%(5月)和67%(8月),胶州湾底层对有机碳的矿化率占水层初级生产力的28%(8月)。取桑沟湾颗粒有机碳的生物沉积速率为236 mg.m-2.d-1,得到底层对有机碳的埋置效率为40%(5月)和3%(8月),埋置的有机碳占水层初级生产力的69%(5月)和2%(8月);胶州湾颗粒有机碳的自然沉积速率为251 mg.m-2.d-1,底层对有机碳的埋置效率为32%(8月),埋置的有机碳占水层初级生产力的13%(8月)。 相似文献