MUDANCAS CLIMÁTICAS E SECAS: MODELAGEM ESPACIAL E DESAFIOS PARA A AGRICULTURA NA BRETANHA

National audienceABSTRACT. Great droughts of the past (such as 1959, 1976, 1989 or 2003) have had heavy impacts on important socio-economical activities for the economy of the Brittany, such as agriculture. In a climate change context it seems important to evaluate the possible ways of evolution of that risk in this region. These evolutions have been studied by using climate simulations from three IPCC’s scenarios: A1B, A2 and B1. In order to monitor droughts, the methodology used is a soil water balance and the implementation of the evaporation deficit. Results revealed an increase of drought intensity during the 21st century, more specifically in the eastern part of the region. The south coastline would be the most sensitive area in terms of droughts’ intensity and frequency. In that area a similar intensity as the one measured during the 1976 drought, other things being equal, would be frequently reached. Exceptional past droughts could become common in the future, impacting both agriculture and water cycle. This could cause a decreasing in runoff aquifer's levels and force farmers to adapt both crops and cropping methods.RESUME. Les grandes sécheresses du passé (1959, 1976, 1989 ou 2003) ont entrainé des dommages importants sur des activités essentielles pour l’économie de la Bretagne, telles que l’agriculture. Dans un contexte de changement climatique, il apparait donc important d'analyser les évolutions possibles du risque de sécheresse à l’échelle de la région à partir de simulations climatiques du modèle Arpège-Climat pour trois scénarios du GIEC : A1B, A2 et B1. La méthodologie retenue est celle du bilan hydrique et le calcul du déficit d’évaporation. Les résultats montrent une augmentation de l’intensité des sécheresses au cours du 21ème siècle, principalement pour la moitié est de la Bretagne. Le littoral sud serait la région la plus sensible à une augmentation de la fréquence et de l’intensité des sécheresses. En termes d’intensité, on dépasserait ici les valeurs relevées lors de la sécheresse de 1976, toutes choses égales par ailleurs. Ce risque de voir des sécheresses exceptionnelles par le passé devenir communes à moyen terme, impacterait fortement l’agriculture, ainsi que le cycle de l’eau, sur une grande partie de l’année. Cela pourrait entrainer une diminution des écoulements de surface alimentant les nappes phréatiques bretonnes et contraindre les agriculteurs à adapter leurs cultures et leurs pratiques.RESUMO. As grandes secas do passado (1959, 1976, 1989 ou 2003) resultaram em danos significativos às atividades essenciais para a economia da Bretanha, como a agricultura. Por isso, no contexto das mudanças climáticas, parece importante analisar possíveis mudanças quanto ao o risco de seca na escala regional. Essas mudanças são estudadas por meio de simulações climáticas do modelo Arpège-Clima para três cenários do IPCC: A1B, A2 e B1. Para monitorar as secas, a metodologia utilizada é o balanço hídrico e o cálculo do déficit de evaporação. Os resultados mostram um aumento na intensidade das secas durante o século 21, principalmente para a metade oriental da Bretanha. A costa sul seria a região mais sensível para o aumento e a frequência da intensidade das secas. Em termos de intensidade, seriam ultrapassados os valores registrados durante a seca histórica de 1976, inalteradas as circunstâncias. O risco de seca excepcional no passado tornou-se comum em médio prazo e teria um impacto forte sobre a agricultura e o ciclo da água durante uma grande parte do ano. Isso pode causar uma diminuição no escoamento que alimenta o lençol freático na Bretanha e forçar os agricultores a adaptar as suas culturas e práticas agricolas

Polarimetry and photometry of the peculiar main-belt object 7968 = 133P/Elst-Pizarro

133P/Elst-Pizarro is an object that has been described as either an active asteroid or a cometary object in the main asteroid belt. Here we present a photometric and polarimetric study of this object in an attempt to infer additional information about its origin. With the FORS1 instrument of the ESO VLT, we have performed during the 2007 apparition of 133P/Elst-Pizarro quasi-simultaneous photometry and polarimetry of its nucleus at nine epochs in the phase angle range 0 - 20 deg. For each observing epoch, we also combined all available frames to obtain a deep image of the object, to seek signatures of weak cometary activity. Polarimetric data were analysed by means of a novel physical interference modelling. The object brightness was found to be highly variable over timescales <1h, a result fully consistent with previous studies. Using the albedo-polarization relationships for asteroids and our photometric results, we found for our target an albedo of about 0.06-0.07 and a mean radius of about 1.6 km. Throughout the observing epochs, our deep imaging of the comet detects a tail and an anti-tail. Their temporal variations are consistent with an activity profile starting around mid May 2007 of minimum duration of four months. Our images show marginal evidence of a coma around the nucleus. The overall light scattering behaviour (photometry and polarimetry) resembles most closely that of F-type asteroids.Comment: Accepted by Astronomy and Astrophysic

Evolution of the Dust Coma in Comet 67P/Churyumov-Gerasimenko Before 2009 Perihelion

Comet 67P/Churyumov-Gerasimenko is the main target of ESA's Rosetta mission and will be encountered in May 2014. As the spacecraft shall be in orbit the comet nucleus before and after release of the lander {\it Philae}, it is necessary necessary to know the conditions in the coma. Study the dust environment, including the dust production rate and its variations along its preperihelion orbit. The comet was observed during its approach to the Sun on four epochs between early-June 2008 and mid-January 2009, over a large range of heliocentric distances that will be covered by the mission in 2014. An anomalous enhancement of the coma dust density was measured towards the comet nucleus. The scalelength of this enhancement increased with decreasing heliocentric distance of the comet. This is interpreted as a result of an unusually slow expansion of the dust coma. Assuming a spherical symmetric coma, the average amount of dust as well as its ejection velocity have been derived. The latter increases exponentially with decreasing heliocentric distance (\rh), ranging from about 1 m/s at 3 AU to about 25-35 m/s at 1.4 AU. Based on these results we describe the dust environment at those nucleocentric distances at which the spacecraft will presumably be in orbit. Astronomy and Astrophysics, in pressComment: 5 pages, 4 figure

Modèle " de la poubelle " et dynamique du business model

National audienceLe business model est un outil clé de la démarche de légitimation , de création de valeur et de la performance des jeunes entreprises. Lors de son élaboration en situation d'accompagnement, on constate que les entrepreneurs choisissent certaines alternatives relatives aux différentes composantes du business model et à leur articulation, tout en en écartant d'autres. L'impossibilité objective de retenir l'ensemble des alternatives possibles conduit inévitablement à des choix non-optimaux d'un point de vue purement rationnel. " Mettre à la poubelle " des options sans les étudier ou les tester systématiquement semble inévitable. Que se passe-t-il avec les alternatives écartées ? Sont-elles rejetées définitivement ou seulement mises de côté et conservées pour une introduction ultérieure, lors de la phase de développement ? Et quel est le rôle de l'accompagnateur dans l'élaboration et l'évolution du business model ? Afin d'explorer les processus d'élaboration et d'évolution du business model en situation d'accompagnement, nous nous inspirons du " modèle de la poubelle " ou Garbage Can Model (GCM) de Cohen, March et Olsen (1972) . Cet article repose sur une série d'entretiens semi-directifs avec les trois entrepreneurs et leur accompagnateur, ainsi que sur l'analyse des business models de lancement et de développement

Implications of the Small Spin Changes Measured for Large Jupiter-Family Comet Nuclei

Rotational spin-up due to outgassing of comet nuclei has been identified as a possible mechanism for considerable mass-loss and splitting. We report a search for spin changes for three large Jupiter-family comets (JFCs): 14P/Wolf, 143P/Kowal-Mrkos, and 162P/Siding Spring. None of the three comets has detectable period changes, and we set conservative upper limits of 4.2 (14P), 6.6 (143P) and 25 (162P) minutes per orbit. Comparing these results with all eight other JFCs with measured rotational changes, we deduce that none of the observed large JFCs experiences significant spin changes. This suggests that large comet nuclei are less likely to undergo rotationally-driven splitting, and therefore more likely to survive more perihelion passages than smaller nuclei. We find supporting evidence for this hypothesis in the cumulative size distributions of JFCs and dormant comets, as well as in recent numerical studies of cometary orbital dynamics. We added 143P to the sample of 13 other JFCs with known albedos and phase-function slopes. This sample shows a possible correlation of increasing phase-function slopes for larger geometric albedos. Partly based on findings from recent space missions to JFCs, we hypothesise that this correlation corresponds to an evolutionary trend for JFCs. We propose that newly activated JFCs have larger albedos and steeper phase functions, which gradually decrease due to sublimation-driven erosion. If confirmed, this could be used to analyse surface erosion from ground and to distinguish between dormant comets and asteroids

Beginning of activity in 67P/Churyumov-Gerasimenko and predictions for 2014–2015

Context. Comet 67P/Churyumov-Gerasimenko was selected in 2003 as the new target of the Rosetta mission. It has since been the subject of a detailed campaign of observations to characterise its nucleus and activity. Aims. We present previously unpublished data taken around the start of activity of the comet in 2007/8, before its last perihelion passage. We constrain the time of the start of activity, and combine this with other data taken throughout the comet’s orbit to make predictions for its likely behaviour during 2014/5 while Rosetta is operating. Methods. A considerable difficulty in observing 67P during the past years has been its position against crowded fields towards the Galactic centre for much of the time. The 2007/8 data presented here were particularly difficult, and the comet will once again be badly placed for Earth-based observations in 2014/5. We make use of the difference image analysis technique, which is commonly used in variable star and exoplanet research, to remove background sources and extract images of the comet. In addition, we reprocess a large quantity of archival images of 67P covering its full orbit, to produce a heliocentric lightcurve. By using consistent reduction, measurement and calibration techniques we generate a remarkably clean lightcurve, which can be used to measure a brightness-distance relationship and to predict the future brightness of the comet. Results. We determine that the comet was active around November 2007, at a pre-perihelion distance from the Sun of 4.3 AU. The comet will reach this distance, and probably become active again, in March 2014. We find that the dust brightness can be well described by Afρ ∝ r-3.2 pre-perihelion and ∝ r-3.4 post-perihelion, and that the comet has a higher dust-to-gas ratio than average, with log (Afρ/Q(H2O)) = − 24.94 ± 0.22 cm s molecule-1 at r < 2 AU. A model fit to the photometric data suggests that only a small fraction (1.4%) of the surface is active

Foisonnement de l'innovation agricole : quelques exemples d'initiatives en élevage herbivore

Les témoignages rassemblés pour illustrer le foisonnement des innovations agricoles émanent d'acteurs différents (agriculteurs, recherche, développement) mais sont tous caractérisés par des approches plutôt systémiques et des dynamiques de co-conception. Les thèmes abordés concernent la production (valorisation des surfaces avec des cultures dérobées, sélection d'espèce prairiales locales), l'appropriation de résultats de recherche (amélioration de la gestion des prairies), la conception d'itinéraires techniques (solutions pour limiter les pertes d'azote en rotation prairie - prairie), l'évaluation de systèmes (repérer des pratiques innovantes en mobilisant des principes de l'agroécologie) mais aussi l'amélioration des conditions de travail et la formation (communication « intergénérationnelle » entre des paysans herbagers et des élèves)

Rapid Diagnosis of Infection in the Critically Ill, a Multicenter Study of Molecular Detection in Bloodstream Infections, Pneumonia, and Sterile Site Infections

Early identification of causative microorganism(s) in patients with severe infection is crucial to optimize antimicrobial use and patient survival. However, current culture-based pathogen identification is slow and unreliable such that broad-spectrum antibiotics are often used to insure coverage of all potential organisms, carrying risks of overtreatment, toxicity, and selection of multidrug-resistant bacteria. We compared the results obtained using a novel, culture-independent polymerase chain reaction/electrospray ionization-mass spectrometry technology with those obtained by standard microbiological testing and evaluated the potential clinical implications of this technique

Inhibition of KCa2.2 and KCa2.3 channel currents by protonation of outer pore histidine residues

Ion channels are often modulated by changes in extracellular pH, with most examples resulting from shifts in the ionization state of histidine residue(s) in the channel pore. The application of acidic extracellular solution inhibited expressed KCa2.2 (SK2) and KCa2.3 (SK3) channel currents, with KCa2.3 (pIC50 of ∼6.8) being approximately fourfold more sensitive than KCa2.2 (pIC50 of ∼6.2). Inhibition was found to be voltage dependent, resulting from a shift in the affinity for the rectifying intracellular divalent cation(s) at the inner mouth of the selectivity filter. The inhibition by extracellular protons resulted from a reduction in the single-channel conductance, without significant changes in open-state kinetics or open probability. KCa2.2 and KCa2.3 subunits both possess a histidine residue in their outer pore region between the transmembrane S5 segment and the pore helix, with KCa2.3 also exhibiting an additional histidine residue between the selectivity filter and S6. Mutagenesis revealed that the outer pore histidine common to both channels was critical for inhibition. The greater sensitivity of KCa2.3 currents to protons arose from the additional histidine residue in the pore, which was more proximal to the conduction pathway and in the electrostatic vicinity of the ion conduction pathway. The decrease of channel conductance by extracellular protons was mimicked by mutation of the outer pore histidine in KCa2.2 to an asparagine residue. These data suggest that local interactions involving the outer turret histidine residues are crucial to enable high conductance openings, with protonation inhibiting current by changing pore shape

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics