Prédire l’occurrence des espèces adventices : quelles échelles de temps et d’espace ?

Comprendre la distribution spatiale des communautés végétales et les processus écologiques sous-jacents constituent un enjeu majeur en particulier pour la gestion intégrée de la flore adventice. Le projet européen PURE ("Pesticide Use-and-risk Reduction in European farming systems with Integrated Pest Management") vise à concevoir, à partir d’études empiriques identifiant les déterminants locaux et régionaux de la distribution d’espèces nuisibles, des paysages qui leur soient défavorables. Les déterminants de la distribution des adventices sont généralement étudiés à l’échelle de la parcelle or, de récentes études suggèrent qu’il est également nécessaire de tenir compte du contexte paysager. Par ailleurs, les paysages agricoles constituent des systèmes dynamiques dans lesquels les cultures et les pratiques se succèdent. Nous faisons l’hypothèse que la flore adventice qui s’exprime dans une parcelle une année donnée dépend à la fois des pratiques appliquées l’année donnée mais également les années précédentes et des pratiques sur les parcelles voisines. Notre étude vise ainsi à identifier quelles échelles de temps et d’espace sont les plus pertinentes pour prédire l’occurrence des espèces adventices. La flore adventice a été échantillonnée dans 58 parcelles de la zone de Fénay pendant 4 années consécutives. Les pratiques de ces parcelles ont été recensées de 2004 à 2011 par enquêtes auprès des agriculteurs. Nous avons adopté une approche de sélection de modèles basée sur le critère d’AIC, complétée par une validation croisée pour quantifier les capacités prédictives du meilleur modèle. Les premiers résultats montrent que l’intégration d’échelles de temps et d’espace larges améliore la description de la distribution des adventices

Fatigue Crack Propagation in Gaseous Hydrogen Environment in Low Alloy Steel

International audienceFatigue crack propagation in low alloyed steel (3.5Ni-1.5Cr-0.5Mo-V) used for turbine generator of nuclear plant is studied under 4 bar hydrogen atmosphere in comparison to ambient air and high vacuum. Tests are conducted on CT specimens and the variation of the fatigue crack growth rate da/dN with respect to the amplitude of the applied stress intensity factor ΔK is explored in a wide range and especially in the near threshold domain. The propagation behaviour under hydrogen atmosphere is shown similar to that obtained in air in the low rate range, i.e. when the maximum of the stress intensity factor Kmax is lower than a critical level of 16 MPam1/2 with higher crack growth rate than in high vacuum. This environment effect is related to the presence of residual water vapour in both gases. For Kmax higher than 16 MPam1/2, much faster growth rates under hydrogen atmosphere in comparison to air and vacuum are observed and related to hydrogen assisted intergranular propagation combining fatigue and sustained loading damage. The results are discussed on the basis of micrographic observations supporting the involved mechanisms

Central venous O2 saturation and venous-to-arterial CO2 difference as complementary tools for goal-directed therapy during high-risk surgery

International audienceIntroduction: Central venous oxygen saturation (ScvO 2) is a useful therapeutic target in septic shock and high-risk surgery. We tested the hypothesis that central venous-to-arterial carbon dioxide difference (P(cv-a)CO 2), a global index of tissue perfusion, could be used as a complementary tool to ScvO 2 for goal-directed fluid therapy (GDT) to identify persistent low flow after optimization of preload has been achieved by fluid loading during high-risk surgery. Methods: This is a secondary analysis of results obtained in a study involving 70 adult patients (ASA I to III), undergoing major abdominal surgery, and treated with an individualized goal-directed fluid replacement therapy. All patients were managed to maintain a respiratory variation in peak aortic flow velocity below 13%. Cardiac index (CI), oxygen delivery index (DO 2 i), ScvO 2 , P(cv-a)CO 2 and postoperative complications were recorded blindly for all patients. Results: A total of 34% of patients developed postoperative complications. At baseline, there was no difference in demographic or haemodynamic variables between patients who developed complications and those who did not. In patients with complications, during surgery, both mean ScvO 2 (78 ± 4 versus 81 ± 4%, P = 0.017) and minimal ScvO 2 (minScvO 2) (67 ± 6 versus 72 ± 6%, P = 0.0017) were lower than in patients without complications, despite perfusion of similar volumes of fluids and comparable CI and DO 2 i values. The optimal ScvO 2 cutoff value was 70.6% and minScvO 2 < 70% was independently associated with the development of postoperative complications (OR = 4.2 (95% CI: 1.1 to 14.4), P = 0.025). P(cv-a)CO 2 was larger in patients with complications (7.8 ± 2 versus 5.6 ± 2 mmHg, P < 10-6). In patients with complications and ScvO 2 ≥71%, P(cv-a)CO 2 was also significantly larger (7.7 ± 2 versus 5.5 ± 2 mmHg, P < 10-6) than in patients without complications. The area under the receiver operating characteristic (ROC) curve was 0.785 (95% CI: 0.74 to 0.83) for discrimination of patients with ScvO 2 ≥71% who did and did not develop complications, with 5 mmHg as the most predictive threshold value

Generation of Two-Dimensional Plasmonic Bottle Beams

By analogy to the three dimensional optical bottle beam, we introduce the plasmonic bottle beam: a two dimensional surface wave which features a lattice of plasmonic bottles, i.e. alternating regions of bright focii surrounded by low intensities. The two-dimensional bottle beam is created by the interference of a non-diffracting beam, a cosine-Gaussian beam, and a plane wave, thus giving rise to a non-diffracting complex intensity distribution. By controlling the propagation constant of the cosine-Gauss beam, the size and number of plasmonic bottles can be engineered. The two dimensional lattice of hot spots formed by this new plasmonic wave could have applications in plasmonic trapping.Engineering and Applied Science

Histoire et philologie du Japon ancien et médiéval

Programme de l’année 2009-2010 : I. La vie quotidienne dans le Japon médiéval d’après le « Rouleau de peinture des pérégrinations d’Ippen » (1299). — II. Le Iken jûnikajô (914), texte en kanbun

Qualification sanitaire des troupeaux, représentations du risque selon les acteurs et les disciplines

La qualification sanitaire vise à établir de manière objective et fiable le statut sanitaire d'un animal ou d'un ensemble d'animaux au regard d'une maladie infectieuse. Concevoir une qualification sanitaire repose sur des connaissances biologiques concernant l'agent pathogène, ses voies de transmission et les moyens de détection de la maladie. Les modèles mathématiques et les outils statistiques et probabilistes permettent d'intégrer ces connaissances tout en prenant en compte l'incertitude et la variabilité des données biologiques. Les sciences humaines apportent un éclairage sur les enjeux, les perceptions et les logiques des individus et des collectifs, afin d'étudier la demande et l'acceptabilité de la qualification sanitaire. Chaque discipline apporte ainsi son point de vue sur la notion de risque sous-jacente à la démarche de qualification. Cette approche interdisciplinaire nécessite une coconstruction de la recherche, qui doit dépasser les différences culturelles et épistémologiques entre disciplines. Elle n'obéit pas à un seul type de rationalité, scientifique ou juridico-administrative ; elle mobilise nécessairement des connaissances savantes et des savoirs empiriques et dépend de nombreuses décisions pouvant engendrer convergences ou contradictions. (Résumé d'auteur

Dose- and Volume-Limiting Late Toxicity of FLASH Radiotherapy in Cats with Squamous Cell Carcinoma of the Nasal Planum and in Mini Pigs

Purpose: The FLASH effect is characterized by normal tissue sparing without compromising tumor control. Although demonstrated in various preclinical models, safe translation of FLASH-radiotherapy stands to benefit from larger vertebrate animal models. Based on prior results, we designed a randomized phase III trial to investigate the FLASH effect in cat patients with spontaneous tumors. In parallel, the sparing capacity of FLASH-radiotherapy was studied on mini pigs by using large field irradiation. Experimental Design: Cats with T1-T2, N0 carcinomas of the nasal planum were randomly assigned to two arms of electron irradiation: arm 1 was the standard of care (SoC) and used 10 × 4.8 Gy (90% isodose); arm 2 used 1 × 30 Gy (90% isodose) FLASH. Mini pigs were irradiated using applicators of increasing size and a single surface dose of 31 Gy FLASH. Results: In cats, acute side effects were mild and similar in both arms. The trial was prematurely interrupted due to maxillary bone necrosis, which occurred 9 to 15 months after radiotherapy in 3 of 7 cats treated with FLASH-radiotherapy (43%), as compared with 0 of 9 cats treated with SoC. All cats were tumor-free at 1 year in both arms, with one cat progressing later in each arm. In pigs, no acute toxicity was recorded, but severe late skin necrosis occurred in a volume-dependent manner (7–9 months), which later resolved. Conclusions: The reported outcomes point to the caveats of translating single-high-dose FLASH-radiotherapy and emphasizes the need for caution and further investigations. See related commentary by Maity and Koumenis, p. 363