Radiative transfer and diffusion limits for wave field correlations in locally shifted random media

The aim of this paper is to develop a mathematical framework for opto-elastography. In opto-elastography, a mechanical perturbation of the medium produces a decorrelation of optical speckle patterns due to the displacements of optical scatterers. To model this, we consider two optically random media, with the second medium obtained by shifting the first medium in some local region. We derive the radiative transfer equation for the cross-correlation of the wave fields in the media. Then we derive its diffusion approximation. In both the radiative transfer and the diffusion regimes, we relate the correlation of speckle patterns to the solutions of the radiative transfer and the diffusion equations. We present numerical simulations based on our model which are in agreement with recent experimental measurements

Computing the diffusivity of a particle subject to dry friction with colored noise

This paper considers the motion of an object subjected to dry friction and an external random force. The objective is to characterize the role of the correlation time of the external random force. We develop efficient stochastic simulation methods for computing the diffusivity (the linear growth rate of the variance of the displacement) and other related quantities of interest when the external random force is white or colored. These methods are based on original representation formulas for the quantities of interest which make it possible to build unbiased and consistent estimators. The numerical results obtained with these original methods are in perfect agreement with known closed-form formulas valid in the white noise regime. In the colored noise regime the numerical results show that the predictions obtained from the white-noise approximation are reasonable for quantities such as the histograms of the stationary velocity but can be wrong for the diffusivity unless the correlation time is extremely small

Object Description Based on Spatial Relations between Level-Sets

International audienceObject recognition methods usually rely on either structural or statistical description. These methods aim at describing different types of information such as the outer contour, the inner structure or texture effects. Comparing two objects then comes down to averaging different data representations which may be a tricky issue. In this paper, we introduce an object descriptor based on the spatial relations that structures object content. This descriptor integrates in a single homogeneous representation both shape information and relative spatial information about the object under consideration. We use this description in the context of image retrieval and show results on a butterfly image database compared with both GFD and SIFT descriptors

Comparaison entre quatre solutions pour échanger de l'énergie entre systèmes de forte capacité de stockage

International audienceL'électrification de systèmes toujours plus puissants est habituellement corrélée à de plus grands besoins de fiabilité, continuité de service et échanges d'énergie entre sources. Dans le domaine des systèmes de stockage électrochimique d'énergie, ces besoins sont souvent satisfaits en parallélisant des batteries. La déconnexion de deux batteries en parallèle est un processus simple et bien maîtrisé. En revanche, la connexion est un processus bien plus long et compliqué qui requière de l'électronique de puissance adaptée car cela revient à connecter en parallèle deux sources de tension. Basé sur un cas concret d'application et grâce à des simulations, cet article propose une comparaison entre quatre solutions pour échanger de l'énergie entre systèmes batterie lithium-ion et maitriser la connexion en parallèle de ceux-ci

Influence of dispersal processes on the global dynamics of Emperor penguin, a species threatened by climate change

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Biological Conservation 212 (2017): 63-73, doi:10.1016/j.biocon.2017.05.017.Species endangered by rapid climate change may persist by tracking their optimal habitat; this depends on their dispersal characteristics. The Emperor Penguin (EP) is an Antarctic seabird threatened by future sea ice change, currently under consideration for listing under the US Endangered Species Act. Indeed, a climate-dependent-demographic model without dispersion projects that many EP colonies will decline by more than 50% from their current size by 2100, resulting in a dramatic global population decline. Here we assess whether or not dispersion could act as an ecological rescue, i.e. reverse the anticipated global population decline projected by a model without dispersion. To do so, we integrate de22 tailed dispersal processes in a metapopulation model|specifically, dispersal stages, dispersal distance, habitat structure, informed dispersal behaviors, and density-dependent dispersion rates. For EP, relative to a scenario without dispersion, dispersal can either offset or accelerate climate driven population declines; dispersal may increase the global population by up to 31% or decrease it by 65%, depending on the rate of emigration and distance individuals disperse. By developing simpler theoretical models, we demonstrate that the global population dynamic depends on the global landscape quality. In addition, the interaction among dispersal processes - dispersion rates, dispersal distance, and dispersal decisions - that influence landscape occupancy, impacts the global population dynamics. Our analyses bound the impact of between-colony emigration on global population size, and provides intuition as to the direction of population change depending on the EP dispersal characteristics. Our general model is flexible such that multiple dispersal scenarios could be implemented for a wide range of species to improve our understanding and predictions of species persistence under future global change.S. Jenouvrier acknowledges support from WHOI Unrestricted funds and Mission Blue / Biotherm; J. Garnier and L. Desvillettes acknowledge respectively the NONLOCAL project (ANR-14-CE25-0013) and the Kibord project (ANR-13-BS01-0004) from the French National Research Agency

Biliary cirrhosis and sepsis are two risk factors of failure after surgical repair of major bile duct injury post-laparoscopic cholecystectomy.

International audienceBACKGROUND: Major bile duct injury (MBDI) remains frequent after laparoscopic cholecystectomy (LC) reaching 0.3 to 0.6 % and is associated with a significant mortality rate. The aim of this study was to retrospectively analyze the factors likely to influence the long-term results of surgical repair for MBDI occurring after LC. METHODS: Medical records of patients referred to our referral center from January 1992 to January 2010 for management of bile duct injury following LC were retrospectively analyzed, and patients with MBDI were identified. Clinicopathological factors likely to influence long-term results after surgical repair were assessed by univariate and multivariable analysis. RESULTS: During the study period, 38 patients were treated for MBDI. These 38 patients underwent Roux-en-Y hepaticojejunostomy (HJ) or HJ revision in 25 (66 %) and 13 (34 %) cases, respectively. The median follow-up period was 93 (26-204) months. A Clavien-Dindo post-operative morbidity class >3 occurred in 10 (26 %) cases and was independently associated with a surgical repair performed during a sepsis period (OR = 102.5; IC 95 % [7.12; 11,352], p < 0.007). Long-term results showed that biliary strictures occurred in 5 (13 %) cases and were associated with sepsis (p < 0.006), liver cirrhosis (p < 0.002) and post-operative complications (p < 0.012). Multivariate analysis revealed that only liver cirrhosis remained predictive of stricture (OR = 26.4, 95 % CI [2; 1,018], p < 0.026). CONCLUSION: When MBDI occurs following LC, HJ seems to be the optimal treatment but should not be performed during a sepsis period. Long-term results are significantly altered by the presence of a biliary cirrhosis at time of repair

Effect of interfacial oxidation occurring during the duplex process combining surface nanocrystallisation and co-rolling

International audienceThis paper presents an investigation of the interface quality of nanocristallised 316L stainless steel multilayer structures. They were produced by a duplex process, combining the Surface Mechanical Attrition Treatment (SMAT) and the co-rolling process at two different annealing temperatures (550°C and 650°C). Oxide layers were observed at the interfaces between the sheets and their morphology was characterised by optical microscopy. Their chemical composition was determined by Energy Dispersive X-ray spectrometry. The microstructure near the interfaces was analysed by Transmission Electron Microscopy (TEM). In the laminate co-rolled at 550°C, the presence of ultrafine grains was demonstrated. Additional tensile tests have shown an influence of the annealing temperature on the yield strength, as well as on the resistance of the interfaces of the co-rolled multilayer structures

Evaluation du contenu des rencontres de tutorat et de la fonction enseignante des tuteurs par les internes de médecine générale d'Angers (Etude quantitative auprès d'une promotion d'étudiants en fin de DES)

Le Département de Médecine Générale de la Faculté de médecine d Angers a mis en place le tutorat en 2004. Ce dispositif pédagogique est centré sur les apprentissages dans l objectif d améliorer les compétences des internes à partir de récits de situations cliniques authentiques (RSCA). Le but de notre étude était d analyser le contenu des rencontres tuteur tutoré, du point de vue des internes, au regard des objectifs pédagogiques du tutorat et de recueillir la perception des internes sur la fonction enseignante des tuteurs. Une étude transversale descriptive par questionnaire en ligne a été menée de novembre 2012 à janvier 2013 auprès de 94 Angevins inscrits en 3ème année d internat de médecine générale. 74% des questionnaires ont été analysés. Les rencontres tuteur tutoré étaient structurées par la discussion des RSCA. Les recherches sur les récits et leur discussion n étaient pas systématiques, l analyse de la démarche réflexive améliorait la résolution d une situation similaire. Aborder les compétences en médecine générale améliorait l autoévaluation des internes. Un tiers des internes considérait leur tuteur comme un enseignant, 53 l estimaient comme un formateur compétent. Le tutorat individuel, fragilisé par l augmentation des effectifs, semble évoluer vers un suivi de groupe. En juillet 2013, des experts nationaux ont défini et décrit les compétences génériques transversales et les 11 familles de situations auxquelles les internes doivent être confrontées pendant le DES de médecine générale. Le tutorat devra intégrer ces éléments qui structurent la formation des médecins généralistes.The department of General Medicine of the Faculty of Medicine of Angers set up a tutoring system in 2004. This teaching aid focuses on the learning procedure in order to improve the interns' skills, using stories of authentic clinical situations (RSCA). The aim of our study was to analyze the content of meetings between tutors and interns, from the intern s point of view, concerning the educational targets of the learning procedure and to have the interns perception on the educational skills of their tutor. A descriptive cross study, conducted from November 2012 to January 2013 via an online questionnaire, was submitted to 94 Angers interns in their third year of general practice internship. 74% of the questionnaires have been analyzed. The meetings between the intern and his tutor were based on the discussion of real clinical situations. Research pertaining to these stories and their discussion did not systematically occur. Analyzing the reflexive process has improved the ability to resolve a similar case. Addressing general practice related skills improves the self-evaluation of interns. One in three interns considers their tutor a teacher, 53 consider him a competent trainer. The tutorial system on its own, weakened by the augmentation of its size, seems to evolve to a group support form. In July 2013, national experts defined and described the generic cross skills and the 11 families of situations interns have to face during a general medicine internship. The tutoring must integrate these elements that structure the education of the general practitioners.ANGERS-BU Médecine-Pharmacie (490072105) / SudocSudocFranceF