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The distribution of Fe atoms within the octahedral sheet of a series of trioctahedral micas has been investigated by polarized Fe K-edge EXAFS spectroscopy. Single crystals have been oriented in the X-ray beam with the layer plane at 35° with respect to the electric field vector. At this “magic angle”, contributions to the EXAFS spectrum of nearest cation shells are equal to those recorded on a completely disoriented powder. The average number of Fe and Mg cations surrounding each Fe atom has been determined and compared with those deduced from NMR spectra. It is shown that the distribution of Fe atoms is not random, the deviation from this distribution depending on the fluorine content. The agreement between these independent results proves the reliability of the structural information deduced from EXAFS and NMR spectra as well as the usefulness of these two methods in analyzing the local distribution of cations in minerals. 相似文献
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Dominique Bonnin Georges Calas Hélène Suquet Henri Pezerat 《Physics and Chemistry of Minerals》1985,12(1):55-64
New data on the structure of Garfield nontronite have been produced by the use of different spectroscopic techniques: Mössbauer spectroscopy, optical spectroscopy, X-ray absorption edges and EXAFS and NMR. The tetrahedral iron content is found to be no higher than 1 percent. All iron atoms belong to the octahedral sheet excluding the possibility of the presence of non crystallized phases. Some ambiguities remain about the coherence of the octahedral sheet because of the presence of two doublets in the Mössbauer spectrum and at least two lineshapes in NMR spectra of OH which correspond to different environments. 相似文献
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Bruno Malaizé Elsa Jullien Amandine Tisserand Charlotte Skonieczny E. Francis Grousset Frédérique Eynaud Catherine Kissel Jérôme Bonnin Svenja Karstens Philippe Martinez Aloys Bory Vivianne Bout-Roumazeilles Thibaut Caley Xavier Crosta Karine Charlier Linda Rossignol José-Abel Flores Ralph Schneider 《Quaternary Research》2012,77(1):182-191
A high resolution analysis of benthic foraminifera as well as of aeolian terrigenous proxies extracted from a 37 m-long marine core located off the Mauritanian margin spanning the last ~ 1.2 Ma, documents the possible link between major continental environmental changes with a shift in the isotopic signature of deep waters around 1.0–0.9 Ma, within the so-called Mid-Pleistocene Transition (MPT) time period. The increase in the oxygen isotopic composition of deep waters, as seen through the benthic foraminifera δ18O values, is consistent with the growth of larger ice sheets known to have occurred during this transition. Deep-water mass δ13C changes, also estimated from benthic foraminifera, show a strong depletion for the same time interval. This drastic change in δ13C values is concomitant with a worldwide 0.3‰ decrease observed in the major deep oceanic waters for the MPT time period. The phase relationship between aeolian terrigeneous signal increase and this δ13C decrease in our record, as well as in other paleorecords, supports the hypothesis of a global aridification amongst others processes to explain the deep-water masses isotopic signature changes during the MPT. In any case, the isotopic shifts imply major changes in the end-member δ18O and δ13C values of deep waters. 相似文献
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J. Bonnin S. Heussner A. Calafat J. Fabres A. Palanques X. Durrieu de Madron M. Canals P. Puig J. Avril N. Delsaut 《Continental Shelf Research》2008
In the framework of the European project Eurostrataform, an array of six near-bottom mooring lines was deployed in the heads of the major submarine canyons incising the continental slope of the Gulf of Lions (NW Mediterranean). All moorings were equipped with sediment traps, current meters and turbidity Optical Backscatters Sensors (OBS) situated at few meters above the bottom. Particulate mass fluxes were recorded weekly by the sediment traps between November 2003 and May 2004 and compared with horizontal export fluxes obtained from the turbidity and current meters. 相似文献
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In the northern uplands of the Socialist Republic of Vietnam the state is taking dramatic steps to (re)configure agricultural production through the introduction and subsidisation of hybrid rice and maize seeds. These require yearly cash investments and access to state supplied inputs, a far cry from earlier upland ethnic minority livelihood strategies. In this paper we develop a conceptual framework that brings together an actor-oriented livelihoods approach with concepts from everyday politics and resistance, to examine the relations now at play as ethnic minorities, namely Hmong and Yao households in Lào Cai province, react to the introduction of these hybrid seeds, negotiate with the state over their use, and contest and subtly resist the wholesale adoption of this programme. Our framework takes us beyond an investigation into financial benefits and yields, to focus upon the social, cultural and political aspects inherent in upland farmer decision-making regarding state interventions. Our findings reveal that such agricultural programmes have resulted in new food insecurities and vulnerabilities overlaying more established concerns. Yet in turn, ethnic minority households evaluate these innovations according to their own terms, and have responded by negotiating, accommodating, and also contesting the state’s initiatives using creative and innovative everyday politics and livelihood strategies. In so doing, they have worked to maintain autonomy over choices and decision-making vis-à-vis the economic, social and cultural reproduction of their household units; a delicate balancing act in a socialist state. 相似文献
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A relational database has been developed which permits the storage and retrieval of waveforms, together with essential parameters of events. The capability of the method is tested by applying it to broad-band records from the Geoscope Noumea station (New Caledonia). 相似文献
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We present a new method to automatically track filaments over the solar disk. The filaments are first detected on Meudon Spectroheliograph Hα images of the Sun, applying the technique developed by Fuller, Aboudarham, and Bentley (Solar Phys. 227, 61, 2005). This technique combines cleaning processes, image segmentation based on region growing, and morphological parameter extraction, including the determination of filament skeletons. The coordinates of the skeleton pixels, given in a heliocentric system, are then converted to a more appropriate reference frame that follows the rotation of the Sun surface. In such a frame, a co-rotating filament is always located around the same position, and its skeletons (extracted from each image) are thus spatially close, forming a group of adjacent features. In a third step, the shape of each skeleton is compared with its neighbours using a curve-matching algorithm. This step will permit us to define the probability [P] that two close filaments in the co-rotating frame are actually the same one observed on two different images. At the end, the pairs of features, for which the corresponding probability is greater than a threshold value, are associated using tracking identification indices. On a representative sample of filaments, the good agreement between automated and manual tracking confirms the reliability of the technique to be applied on large data sets. This code is already used in the framework of the Heliophysics Integrated Observatory (HELIO) to populate a catalogue dedicated to solar and heliospheric features (HFC). An extension of this method to other filament observations, and possibly sunspots, faculae, and coronal-holes tracking, can also be envisaged. 相似文献
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