Characterisation of failure in human aortic tissue using digital image correlation

International audienceAn aortic aneurism is a localized dilation of the aorta in a weakened area [1, 2]. The increase of aneurism size may result in rupture, which will be a life threatening emergency. The mechanism of failure in aneurysms is now relatively well understood. However, only limited research has provided quantitative values for the stresses that cause the failure of pathologic arterial tissue. The evaluation of the local failure stress remains an open problem. In this study we apply digital image correlation (DIC) to excised pieces of tissue that we test in a bulge inflation test. The tissue is taken from the ascending aorta in diseased patients requiring an excision for removing an aneurysm. All procedures are carried out in accordance with the guidelines of the Institutional Review Board of the University Hospital of Saint-Etienne, France

La fin d'une étrange lacune de la sociologie des mobilisations:L'étude par sondage des manifestants : fondements théoriques et solutions techniques

Si les formes et les ressorts de l'action collective commencent à être mieux connus, les individus qui manifestent — acteurs des démonstrations de rue — n'ont guère fait l'objet d'études centrées sur les modalités du passage à l'acte. Depuis Barnes et Kaase, il existe de solides études par sondage de la propension des individus à manifester, mais ces études renseignent sur les représentations, et notamment sur la perception de la légitimité de l'action collective, et sur les dispositions à agir, et non sur les comportements effectifs. La plupart des travaux classiques sur la manifestation prennent comme unité d'analyse ces événements que sont les manifestations et constituent des corpus plus ou moins étendus mais toujours riches en informations. Mais d'une part, les conclusions qui s'en dégagent sont le plus souvent non compatibles avec celles issues des études sur la propension à manifester. D'autre part, ces travaux n'aident guère à élucider les mécanismes de la participation des individus à l'action. La solution proposée pour mettre fin à cette étrange lacune de la sociologie des mobilisations est le recours au sondage effectué pendant les manifestations. Mais cette méthode, qui n'a que de rares précédents, soulève des difficultés techniques spécifiques. Trois sondages dans des manifestations effectués à Paris entre février et mai 1994 ont permis d'apporter à ces difficultés des solutions qui font l'objet d'un exposé détaillé. L'apparence antinomie entre cette méthode par construction individualisante qu'est le sondage d'opinion et l'objet par nature collectif (la manifestation de rue) auquel on l'applique ne doit donc plus être considérée comme un obstacle.While the forms and springs of collective action are beginning to be better known, the individuals who demonstrate — the actors in street demonstrations — have not been subjected to studies centered on the modes of the move to action. Since Barnes and Kaase, we have serious survey studies of the propensity of individuals to demonstrate, but they provide data about representations, and in particular on the perception of the legitimacy of collective action and on the willingness to act, not on actual behavior. Most classic works on demonstrations take these as the units of analysis and build up more or less extensive data sets, always rich in information. But on the one hand, their conclusions are often incompatible with those of studies on the propensity to demonstrate. On the other hand, such research does not contribute much to elucidating the mechanisms of individual participation in demonstrations. The solution suggested in order to remedy this strange gap in the sociology of mobilizations is to take sample surveys during demonstrations. Rarely used, this procedure raises specific technical difficulties. Three polls taken during demons-trations in Paris between February and May 1994 provide solutions to these problems, which are here discussed at length. The apparent antinomy between a method of individualizing construction — the opinion poll — and an object of a collective nature — the street demonstration — to which it is applied must therefore no longer be considered an obstacle

Predictive Models with Patient Specific Material Properties for the Biomechanical Behavior of Ascending Thoracic Aneurysms

International audienceThe aim of this study is to identify the patient-specific material properties of ascending thoracic aortic aneurysms (ATAA) using preoperative dynamic gated Computed Tomography (CT) scans. The identification is based on the simultaneous minimization of two cost functions, which define the difference between model predictions and gated CT measurements of the aneurysm volume at respectively systole and cardiac mid-cycle. The method is applied on 5 patients who underwent surgical repair of their ATAA at the University Hospital Center of St. Etienne. For these patients, the aneurysms were collected and tested mechanically using an in vitro bench. For the sake of validation, the mechanical properties found using the in vivo approach and the in vitro bench were compared. We eventually performed finite-element stress analyses based on each set of material properties. Rupture risk indexes were estimated and compared, 2 showing promising results of the patient-specific identification method based on gated CT

Mechanical characterization of the thoracic ascending aortae

International audienceIn this study the digital image correlation technique is used for characterizing the mechanical and fracture properties of aneurysmal tissues. The tissues which have been taken from the thoracic ascending aorta of diseased patients are tested in a bulge inflation test. The approach is original in the sense that it gives access to the local stress fields in the tissue and to local analysis of fracture. Applications to the dynamic behavior and fracture of vascular tissues are envisaged

Sizing of an Electric Power Steering system on dynamic and energetic criteria

International audienceThis paper presents the methodology to size a mechatronic system on dynamic and energetic criteria. The methodology is based on the establishment of the inverse model from the bond graph representation of the system by using the bicausality concept. By means of an automotive example, we illustrate the methodology and we present a solution to extend it to more complex problem

Stability Evaluation of Overtopped Concrete Hydraulic Structures Using Computational Fluid Dynamics

Résumé: L’estimation des pressions hydrodynamiques induites lorsque l’eau à grande vitesse submerge les barrages-poids et les évacuateurs de crues constitue un aspect particulièrement difficile de l’évaluation de la stabilité de ces ouvrages. La dynamique des fluides numérique (CFD) est une alternative attrayante aux modèles physiques pour quantifier les forces hydrodynamiques agissant sur les ouvrages-poids. Dans cet article, les ligne directrices sur la sécurité des barrages pour estimer le poids de la nappe d’eau submergeant les barrages-poids à crête rectangulaire sont tout d’abord examinées. Ensuite, une méthodologie CFD est développée pour améliorer l'estimation simplifiée des champs de pression hydrodynamiques agissant sur les crêtes rectangulaires des ouvrages soumis à la submersion. Les pressions CFD sont utilisées comme données d'entrée dans les analyses de stabilité structurales classiques, basées sur la méthode de la gravité, afin de quantifier de manière plus adéquate la stabilité au glissement des barrages lors d'une submersion. Un retour d’expérience est également effectué sur la stabilité d'un évacuateur vanné, qui a été submergé lors de la crue du Saguenay en 1996. ---------- Abstract: A particularly challenging aspect in gravity dam stability assessment is the estimation of the induced hydrodynamic water pressure when water with significant velocity is overtopping gravity dams and flowing in or over spillway components. The water flow conditions, including the related pressure fields and resultant forces, are difficult to quantify accurately. Herein, existing dam safety guidelines to estimate the weight of the overflowing water nappe on gravity dams with rectangular crests are first reviewed. Then, a CFD methodology is developed to improve the simplified estimation of hydrodynamic pressure fields acting on the rectangular crests of submerged gravity dams. The CFD pressures are used as input data to classical structural stability analyses based on the gravity method to more adequately quantify the dam stability during overtopping. A back analysis is also performed on the stability of an existing gated spillway that was overtopped during the 1996 Saguenay flood in Québec

Techno-economic and Life Cycle Assessment of methane production via biogas upgrading and power to gas technology

International audienceTo decrease the use of fossil fuels and face the energetic demand, the integration of renewable energy is a necessary step. Part of this renewable energy can be supplied by the production of electricity from photovoltaic panels and windfarms. The massive use of these intermittent energies will lead to overproduction periods, and there is consequently a need to convert this surplus of electricity into a storable form of energy. Power-togas (PtG) technology consists in using electricity to convert water into hydrogen by electrolysis, and then to synthetize methane from carbon dioxide and hydrogen. Techno-economic and Life Cycle Assessment of methane production via the combination of anaerobic digestion and PtG technology have been applied to sewage sludge valorization. Process studies and equipment design have been addressed considering already available technologies. Sensitivity analyses have been done on biogas upgrading technologies, electricity prices, annual operation time and composition of the electricity mix with also a comparison between PtG and direct injection. It appears that the more the electricity is expensive, the longer the operation time of the methanation process must be to be competitive with injection of methane from biogas. Reduction of electricity consumption of the electrolysis step decreases production costs. Even if the current context does not feature adapted conditions to ensure an economically viable chain, the evolution of the energetic context in the next few years as well as the expected technological improvements will contribute to overall cost reduction. From an environmental point of view, continuous PtG generates more greenhouse gases than direct injection, but intermittent operation with use of renewable electricity can significantly reduce GHG emissions. From an endpoint impacts perspective, impact from continuous PtG are higher than biogas upgrading, but much lower than fossil energy. Future development of low electricity consumption of the electrolysis process, and integration of renewable credits from CO 2 valorization can increase the competitiveness of this technology

Hybrid treatment of an ascending aortic pseudoaneurysm following multiple sternotomies

Ascending aortic pseudoaneurysm following prior cardiac or aortic surgery is a rare entity that requires reoperation. Surgical repair is a complex procedure associated with high operative mortality. We report the case of a 76-year-old male patient with an ascending aortic pseudoaneurysm developing from distal anastomosis of a Dacron aorto-aortic prosthesis. This high-risk patient had previously undergone multiple cardiovascular operations and was treated by performing an extra-anatomic bypass between the descending thoracic aorta and supra-aortic vessels, followed by endovascular stent graft placement, avoiding median re-sternotomy

Identification of the in vivo elastic properties of common carotid arteries from MRI: a study on subjects with and without atherosclerosis.

International audienceThe stiffness of the arterial wall, which is modified by many cardiovascular diseases such as atherosclerosis, is known to be an indicator of vulnerability. This work focuses on the in vivo quantification of the stiffness of the common carotid artery (CCA) by applying the Magnitude Based Finite Element Model Updating (MB-FEMU) method to 13 healthy and diseased volunteers aged from 24 to 76 years old. The MB-FEMU method is based on the minimisation of the deviation between the image of a deformed artery and a registered image of this artery deformed by means of a finite elements analysis. Cross sections of the neck of each subject at different times of the cardiac cycle are recorded using a Phase Contrast cine-MRI. Applanation tonometry is then performed to obtain the blood pressure variations in the CCA throughout a heart beat. First, a time averaged elastic modulus of each CCA between diastole and systole is identified and a stiffening of the artery with age and disease is observed. Second, four elastic moduli are identified during a single heart beat for each artery, highlighting the nonlinear mechanical behaviour of the artery. A stiffening of the artery is observed and quantified at systole in comparison to diastole