625 research outputs found

    Charcoal does not change the decomposition rate of mixed litters in a mineral cambisol: a controlled conditions study

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    It has been recently shown that the presence of charcoal might promote humus decomposition in the soil. We investigated the decomposition rate of charcoal and litters of different biochemical quality mixed together in a soil incubation under controlled conditions. Despite the large range of organic substrate quality used in this study, we did not find any difference in the decomposition between the average of two individual substrates decomposing separately and the same substrates mixed together. We concluded that charcoal does not always promote other organic matter decomposition and that its particular effect might depend on various factors, for example, soil propertie

    Mineralisation of crop residues on the soil surface or incorporated in the soil under controlled conditions

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    In the present work, we compare the effect of mature crop residues mixed into a ferralitic soil or placed as a single layer on soil surface on the mineralisation of C and N over 55days. As residues, we used dry stems of rice, soybean, sorghum, brachiaria and wheat. There were no significant effects of residue placement on C mineralisation kinetics. Decomposition of the residues on the soil surface slightly increased net N mineralisation for residues having the smallest C/N rati

    Evolution in industrial risk management in France. The agenda concerning LUP, risks and stakeholder perspective on a national level

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    International audienceThis paper will first describe the evolutions of the concepts related to risk management for hazardous installations in France, in particular in the aspects related to the link between risk assessment and land-use planning. Then, the paper will present in details the main novelties introduced by the law of 30th July 2003, and the methods and tools that have been developed to enable its implementation. The results related to the cases studies carried in 2004 on several industrial sites will be presented and analyzed

    Lignin content and chemical characteristics in maize and wheat vary between plant organs and growth stages: consequences for assessing lignin dynamics in soil

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    Assessing lignin turnover in soil on the basis of a 13C natural abundance labeling approach relies on the assumption that chemical characteristics of labeled and control plant inputs are similar and that the 13C content difference between labeled and control plant inputs is constant within the plant parts. We analyzed lignin in soils, roots, stems and leaves of wheat and maize at different stages of growth using the cupric oxide oxidation method. In both plants, lignin concentrations increased with growth, particularly during grain filling. Maize contained more cinnamyl moieties than wheat. Roots had higher lignin contents (especially cinnamyl moieties) than stems and leaves, and seemed to contribute more to the total soil lignin than the aboveground parts. The isotopic differences (∆ ή13C) of lignin phenols were not significantly different (p > 0.05) between plant organs, confirming assumptions underlying the natural abundance 13C labeling approach. Our data show that lignin content and phenol distribution can vary between plant organs and with the time of harvest. Consequently, the amount of annual lignin input may vary as a function of root amount and harvest date, and thus can affect the calculated apparent turnover times of lignin in natural abundance 13C labeling experiment

    L’exemplum : un modĂšle opĂ©ratoire dans la lettre familiĂšre ?

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    Quelle est la fonction du rĂ©cit dans une lettre ? Cette question se pose plus ou moins directement dans tous les traitĂ©s Ă©pistolaires du temps de Mme de SĂ©vignĂ©, oĂč le rĂ©cit fait l’objet d’une Ă©troite surveillance, toujours suspect de longueur excessive ou de digression. L’exemplaritĂ© est, dans les Ă©crits factuels, une des fonctions souvent attribuĂ©e aux sĂ©quences narratives les plus brĂšves pour les lĂ©gitimer. Cette fonction Ă©voque en partie la technique rhĂ©torique de l’exemplum, puisque ce g..

    Studies of climate variability in a simple coupled model

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    Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007.Includes bibliographical references (p. 74-76).The mechanisms of variability of a coupled atmosphere-ocean model are investigated through the study of two coupled configurations: an aquaplanet in which gyres are absent, and an aquaplanet in which a ridge extending from pole to pole supports gyres. Empirical Orthogonal Functions (EOFs) are used to explore the main features of variability exhibited by extended integrations of both configurations. In the aquaplanet a decadal variability is observed in the atmosphere and the ocean. Stochastic driving of the annular modes in the atmosphere generates an anomalous Sea Surface Temperature (SST) dipole through latent heat fluxes and Ekman pumping. A feedback of this SST dipole on the atmosphere enables a damping slow enough for anomalies to persist over decadal time scales. This air-sea feedback combined with a slow advection of the anomalies by mean ocean currents result in the observed decadal oscillation. A simple stochastic model captures the essence of this mechanism. In the ridge decadal variability is absent but centennial variability is observed in the atmosphere and the ocean. Stochastic driving of the annular modes in the atmosphere generates a weak SST tripole due to latent heat fluxes. The weak amplitude of this tripole prevents the existence of any significant air-sea feedback, implies a stronger damping than in the aquaplanet, and ultimately results in the absence of oscillations. The classic stochastic model of Hasselmann [19] explains the evolution of the SST anomaly through time. Within a delay of one year stochastic atmospheric variability additionally generates a baroclinic streamfunction as well as baroclinic Rossby waves at the eastern boundary of the basin. The former is slowly advected by the mean flow while the latter propagates towards the western boundary, inducing a feedback on the atmosphere with a delay of sixty years. A simple model is found to capture the essence of this mechanism. The results of the aquaplanet and the ridge are used to interpret the Drake, a third configuration in which a band of land extends from the North Pole to the line of -45' of latitude. In the northern hemisphere of the Drake mean state and variability are similar to the ones observed in the ridge. The observed centennial oscillation would correspond to a decadal oscillation in the Atlantic. In the southern hemisphere of the Drake, mean state and variability have elements of both the ridge and the aquaplanet.by Claude Abiven.S.M

    Un genre de discours miniature : pour un modùle de l’anecdote

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    L’anecdote est un genre de rĂ©cit courant dont on gagne Ă  Ă©tudier les propriĂ©tĂ©s formelles et les usages discursifs, car elle permet la connaissance de plusieurs fonctions narratives : l’exemplaritĂ© morale ou l’usage pĂ©dagogique des exemples, les processus inductifs dans l’argumentation, la digression, la caractĂ©risation, etc. La compĂ©tence gĂ©nĂ©rique qui permet de reconnaĂźtre l’anecdote et de l’interprĂ©ter repose sur un certain nombre de faits de langue rĂ©currents, qu’on se propose de dĂ©crire ici, en dĂ©finissant un prototype de la sĂ©quence anecdotique. FondĂ© sur un sondage dans de vastes corpus narratifs des XVIIe et XVIIIe siĂšcles (Vies, MĂ©moires, comme ceux de Saint-Simon, recueils d’anecdotes), ce modĂšle sert Ă  dĂ©couper des brĂšves sĂ©quences Ă  l’intĂ©rieur de longs rĂ©cits : cette mĂ©thode, venue de la linguistique textuelle, permet de rendre compte de l’hĂ©tĂ©rogĂ©nĂ©itĂ© des textes (y compris s’ils paraissent tout uniment de type narratif). On insiste ici en particulier sur les procĂ©dĂ©s d’encadrement du micro-rĂ©cit : en ouverture de sĂ©quence, l’entame par « un jour », l’annonce, le rĂ©sumĂ©, et en clĂŽture, la chute et le commentaire

    Le moment discursif des barricades d’aoĂ»t 1648 : quelle interprĂ©tation des rĂ©currences dans le discours sur l’évĂ©nement ?

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    Les barricades d’aoĂ»t 1648 peuvent ĂȘtre considĂ©rĂ©es comme un « moment discursif » au sens oĂč elles donnĂšrent lieu Ă  une abondance de productions langagiĂšres (contemporaines des faits ou non). Il s’agit ici de tirer les consĂ©quences, au niveau empirique, des thĂ©ories sur le « retour de l’évĂ©nement » en histoire, qui font de celui-ci un Ă©vĂ©nement discursif autant qu’un fait historique. À partir de sources hĂ©tĂ©rogĂšnes, on essaie ici de mettre au jour les points communs formels qui ont traversĂ© les diffĂ©rentes pratiques socio-discursives, pour montrer que l’évĂ©nement se constitue aussi par une langue partagĂ©e

    Analyses d'accidents : une nécessité pour les analyses de danger et l'intervention en situation d'urgence ?

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    Lors d'accidents industriels mettant en jeu des explosions, des incendies ou des émissions de produits toxiques ou inflammables dans l'environnement, les effets à prendre en compte s'expriment en termes d'impulsions de pression, de projections de débris, de flux thermiques et de rejets de produits toxiques dans l'air, les eaux et les sols. Dans sa premiÚre partie, le présent article présente les conclusions consécutives à l'analyse de différents types d'accidents survenus en France et met en évidence l'absence de connaissances suffisantes sur le déroulement d'explosions non confinées ou partiellement confinées et sur les modalités d'émissions de produits toxiques lors d'incendies. La prise en considération de ces accidents et de bases de données sur les accidents permettra aux autorités compétentes, aux industriels, aux assureurs et aux centres techniques intéressés par ces questions de partager leurs expériences. La seconde partie aborde la validation des logiciels commerciaux de calcul des conséquences. La comparaison des résultats de l'examen des logiciels CAMEO 3.0, CHARM 6.1, PHAST 3.0 et TRACE 2.5.4. utilisés pour définir tout ou partie des effets mentionnés plus haut a permis de mettre en évidence la nécessité d'un protocole d'évaluation. Pour un tel protocole sont à retenir : la pertinence des modÚles physiques, la convivialité pour l'utilisateur, le caractÚre adapté des bases de données et du manuel opérateur
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