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21.
Frédéric Angeli Marina Gaillard Thibault Charpentier 《Geochimica et cosmochimica acta》2006,70(10):2577-2590
A multinuclear solid-state NMR investigation of the structure of the amorphous alteration products (so called gels) that form during the aqueous alteration of silicate glasses is reported. The studied glass compositions are of increasing complexity, with addition of aluminum, calcium, and zirconium to a sodium borosilicate glass. Two series of gels were obtained, in acidic and in basic solutions, and were analyzed using 1H, 29Si, and 27Al MAS NMR spectroscopy. Advanced NMR techniques have been employed such as 1H-29Si and 1H-27Al cross-polarization (CP) MAS NMR, 1H double quantum (DQ) MAS NMR and 27Al multiple quantum (MQ) MAS NMR. Under acidic conditions, 29Si CP MAS NMR data show that the repolymerized silicate networks have similar configuration. Zirconium as a second nearest neighbor increases the 29Si isotropic chemical shift. The gel porosity is influenced by the pristine glass composition, modifying the silicon-proton interactions. From 1H DQ and 1H-29Si CP MAS NMR experiments, it was possible to discriminate between silanol groups (isolated or not) and physisorbed molecular water near Si (Q2), Si (Q3), and Si (Q4) sites, as well as to gain insight into the hydrogen-bonding interaction and the mobility of the proton species. These experiments were also carried out on heated samples (180 °C) to evidence hydrogen bonds between hydroxyl groups on molecular water. Alteration in basic media resulted in a gel structure that is more dependent on the initial glass composition. 27Al MQMAS NMR data revealed an exchange of charge compensating cations of the [AlO4]− groups during glass alteration. 1H-27Al CP MAS NMR data provide information about the proximities of these two nuclei and two aluminum environments have been distinguished. The availability of these new structural data should provide a better understanding of the impact of glass composition on the gel structure depending on the nature of the alteration solution. 相似文献
22.
First experimental investigation of dual-reciprocating drilling in planetary regoliths: Proposition of penetration mechanics 总被引：1，自引：0，他引：1
Thibault P. Gouache Yang Gao Pierre Coste Yves Gourinat 《Planetary and Space Science》2011,59(13):1529-1541
The search for life in the solar system requires sub-surface exploration capabilities of extra-terrestrial bodies like the Moon and Mars. To do so different techniques are being developed: from the classical rotary drilling techniques widely used on Earth to more original techniques like ultrasonic drilling. Dual-reciprocating drilling (DRD) is a bio-mimetic drilling principle inspired by the manner wood-wasps drill into wood to lay its eggs. It was proposed as an efficient extra-terrestrial drilling technique requiring low over-head force. To deepen the understanding of this novel drilling technique, DRD has been tested for the first time in planetary regolith simulants. These experiments are reported here. To do so a new test bench was built and is presented. The soil forces on the drill bit are analysed and the final depth reached by the DRD system is compared to the final depth reached by static penetration. The experiments have shown very high levels of slippage (defined here specifically for DRD). The observations of the surface deformations and the importance of slippage lead to the proposal of DRD penetration mechanics in regoliths. Finally a re-evaluation of previous DRD experiments conducted on low compressive strength rocks also show the high levels of slippage during DRD. 相似文献
23.
Stephane Descloux Thibault Datry Pierre Marmonier 《Aquatic Sciences - Research Across Boundaries》2013,75(4):493-507
Streambed colmation by fine sediment, e.g. the deposition, accumulation and storage of fines in the substrate, is a major environmental concern throughout the world. Nevertheless, the ecological effects of streambed colmation on both benthic and hyporheic invertebrate assemblages have rarely been considered simultaneously. We studied a continuum of a naturally increasing percentage of fine sediment in three temperate rivers and hypothesized that the increasing percentage of fine sediment would decrease both benthic and hyporheic invertebrate densities and diversities, and reduce the similarities between them. To test these hypotheses, we first compared heavily, moderately and lightly clogged reaches located in downwelling areas and sampled invertebrates in the benthic zone and at 3 different depths (10, 30 and 50 cm) in the hyporheic zone. Secondly, we modified the sediment grain size distribution experimentally by increasing the percentage of fine sediment and using artificial substrates. The increasing colmation halved the hyporheic taxonomic richness and reduced benthic and hyporheic densities to a third. Some taxa were found in both zones, mainly in high colmation (e.g. Baetidae) or low colmation contexts (e.g. Orthocladiinae, Cyclopoida and Harpacticoida). The dissimilarity between benthic and hyporheic fauna (only at ?50 cm) was significantly higher in heavily clogged reaches than in moderately and lightly clogged ones, suggesting reduced vertical exchange of invertebrates or differential impacts between zones. The total abundance, taxonomic richness, percentage of EPT taxa and densities of most organisms observed using the artificial substrates decreased linearly with the increasing percentage of fine sediment in the experiment. Only the Ephemeroptera Caenis spp. and Heptageniidae disappeared above 30 and 50 % of fine sediment, respectively, suggesting that the response to increasing colmation are strongly taxon-specific. High amount of fine sediments within the substrate significantly decreased habitat quality for benthic and hyporheic invertebrates and thus limit the production of streams and their capacity to recover after disturbance. Moreover, the use of hyporheic invertebrates seems more relevant than benthic invertebrates to assess the effect of colmation and thus could be tested in future research as indicators. 相似文献
24.
Thibault Datry R. Corti C. Claret M. Philippe 《Aquatic Sciences - Research Across Boundaries》2011,73(4):471-483
The inputs and breakdown of terrestrial leaf litter in streams is a fundamental ecological process that sustains in-stream
foodwebs and secondary production. In temporary rivers, litter breakdown is reduced during dry phases, but the long-term effect
of alternating drying and wetting cycles on litter breakdown is still poorly understood. We tested the hypothesis that leaf
litter breakdown (LLB) in temporary rivers is primarily controlled by flow permanence (the number of flowing days over a given
period expressed in %), and that drying events affect LLB during leaf fall periods through reduction of microbial activity
and the modification of aquatic invertebrate assemblages. LLB rates (k), microbial activity and invertebrate assemblages were determined in winter at ten cross-sections scattered along a flow
permanence gradient on the temporary Albarine River, France. Results demonstrated that summer drying events affected the breakdown
process for up to 6 months after flow has resumed in the river. LLB rates decreased exponentially with decreasing flow permanence,
and with increasing drying event duration and frequency. These exponential relationships were observed for flow permanence
variables calculated for the river for both 24-years and 1-year time periods prior to the experiment. A decrease in flow permanence
from 100 to 85% led to a four-fold decrease in leaf litter breakdown rate. Microbial activity, which typically did not differ
between cross-sections, failed to explain the between-cross-section differences in k. By contrast, invertebrate assemblages and, shredders, in particular, decreased exponentially with decreasing flow permanence
and with increasing drying event duration and frequency. 相似文献
25.
Jiwei Liang Rongxi Li Shaoni Zhang Baoyun Chen Lizhi Duan Pierre Thibault 《中国地球化学学报》2012,31(4):441-448
Gold-bearing quartz veins of the Taihua Group consisting of Archean metavolcanic rocks are a main gold deposit type in the Xiao Qinling area,one of the three biggest gold production areas in China.The quartz veins experienced strong alteration characterized by a typical mesothermal hydrothermal altered mineral assemblage.The grade of gold is affected by the contents of sulphides,e.g.galena,pyrite and chalcopyrite.Results of minor elements analysis for the of gold-bearing quartz veins indicate higher contents of Au and high contents of Ag,Pb,Cu,Cd,W,and Mo.Abundant fluid inclusions were found in the gold-bearing quartz veins.Three types of fluid inclusions were identified:(1) aqueous inclusions;(2) CO 2-bearing inclusions;and(3) daughter crystal-bearing fluid inclusions.Homogenization temperatures ranged from 110 to 670℃ with low and high peaks appearing at 160 180℃ and 280 300℃,respectively.The salinity of aqueous inclusions varies between 1.8 wt% and 38.2 wt% NaCl.The homogenization temperature and salinity show a positive correlation.The H and O isotopes of fluid inclusions in the gold-bearing quartz veins indicate that magmatic solution and metamorphic hydrothermal solution,together with meteoric water,were involved in the formation of gold-bearing fluid.Mesozoic magma activities related to granite intrusions should be the main source of CO 2 fluid with higher temperature and salinity. 相似文献
26.
We present a chemical and mineralogical explanation, derived from powder X-ray diffraction and Mössbauer spectroscopy measurements of synthetic samples, of the P:Fe = 1:2 limiting ratio of P incorporation (as PO4) that was previously observed in natural aquatic oxic iron precipitates. The 57Fe Mössbauer hyperfine parameters are interpreted with the help of state-of-the-art ab initio electronic structure calculations. We find that there is a strong tendency for solid solution P-Fe mixing in the P-bearing hydrous ferric oxide (P-HFO) aqueous coprecipitate system, interpreted as occurring between the P-free (ferrihydrite) end-member and an inferred P:Fe = 1:2 end-member beyond which P is not incorporated in the structure of the P-HFO solid. Up to and somewhat beyond the limiting end-member P:Fe ratio, all available P is scavenged by the coprecipitation reaction, suggesting strong P-Fe complexation in the precipitation-precursor dissolved species. The P-HFO solids are more stable (i.e., have stronger chemical bonds) than the P-free ferrihydrite end-member. We show that in coprecipitation the P specifically incorporates within the nanoparticle structure rather than complexing to the nanoparticle surface. Our results are relevant to the question of the mechanisms of coupling between the Fe and P cycles in natural aqueous environments and highlight a strong affinity between Fe and P in aqueous environments. 相似文献
27.
Scott T. Larned Thibault Datry Christopher T. Robinson 《Aquatic Sciences - Research Across Boundaries》2007,69(4):554-567
Inundation marks the shift from a terrestrial ecosystem to an aquatic ecosystem in ephemeral rivers. The forms and rates of
responses by aquatic invertebrates and sediment microbes to inundation depend on desiccation resistance during preceding dry
periods. We assessed invertebrate and microbial responses to inundation over a range of preceding dry periods in an ephemeral
reach of the Selwyn River, New Zealand. Microbial response variables were dissolved oxygen consumption and non-specific esterase
activity. Sampling sites along the reach had been continuously dry for 1–592 d prior to sample collection. The onset of flow
simulated by an experimental inundation led to the appearance of aquatic invertebrates in all samples, but the assemblages
varied with the length of the preceding dry period. Taxon richness decreased linearly with dry period length while density
decreased exponentially. These patterns indicate that a large number of individuals from desiccation-sensitive taxa were eliminated
soon after flow ceased, and a low-density assemblage composed of a small number of desiccation-resistant taxa persisted during
prolonged dry periods. As with invertebrate density, sediment respiration and nonspecific esterase activity decreased with
length of dry period, and were characterized by exponential decay functions. The results of the inundation experiments suggest
that a temporal ecotone exists for about one week after the disappearance of flowing water, and before the terrestrial system
stabilizes. 相似文献
28.
The African continent has afforded a wealth of evidence bearing on the early evolution of Hominidae and the development of capacities for culture. However, until recently there has been scant documentation of the time of dispersal of hominids from tropical into north temperate latitudes. Human populations were certainly well established in Europe by Mindel Glacial times, rather less than 0.7 my ago, to judge from known occupation places in France and Hungary. Recently several localities in southern France and southern Spain have afforded artifactual evidence to suggest the presence of human populations in the preceding Cromerian interglacial, and even very probably in the preceding glacial stage, the “Gunz” (of authors). The identity of these first Europeans still remains unknown. 相似文献
29.
Estanislao Pujades Thibault Willems Sarah Bodeux Philippe Orban Alain Dassargues 《Hydrogeology Journal》2016,24(6):1531-1546
Underground pumped storage hydroelectricity (UPSH) plants using open-pit or deep mines can be used in flat regions to store the excess of electricity produced during low-demand energy periods. It is essential to consider the interaction between UPSH plants and the surrounding geological media. There has been little work on the assessment of associated groundwater flow impacts. The impacts on groundwater flow are determined numerically using a simplified numerical model which is assumed to be representative of open-pit and deep mines. The main impact consists of oscillation of the piezometric head, and its magnitude depends on the characteristics of the aquifer/geological medium, the mine and the pumping and injection intervals. If an average piezometric head is considered, it drops at early times after the start of the UPSH plant activity and then recovers progressively. The most favorable hydrogeological conditions to minimize impacts are evaluated by comparing several scenarios. The impact magnitude will be lower in geological media with low hydraulic diffusivity; however, the parameter that plays the more important role is the volume of water stored in the mine. Its variation modifies considerably the groundwater flow impacts. Finally, the problem is studied analytically and some solutions are proposed to approximate the impacts, allowing a quick screening of favorable locations for future UPSH plants. 相似文献
30.