Analyse thermographique du comportement en fatigue d'une tôle d'acier

Depuis plusieurs années de nombreuses équipes de recherche ont misé sur les mesures d'autoéchauffement pour développer des méthodes de détermination rapide de la limite de fatigue. L'évolution de la température n'étant pas intrinsèque au matériau, nous avons choisi de travailler en terme de sources de chaleur plutôt qu'en terme de température. Nous présentons ici une méthode 2D de détermination des sources de chaleur accompagnant la fatigue et s'appuyant sur la mesure de champs de température obtenus à l'aide d'une caméra infrarouge. Ces sources de chaleur peuvent avoir, au moins, deux origines. Les premières sont induites par la thermodilatabilité du matériau et correspondent au couplage thermoélastique. Les secondes entraînent des échauffements de nature dissipative associés aux transformations microstructurales irréversibles. La difficulté majeure du traitement d'images pour estimer séparément ces deux types de sources vient du fait que l'amplitude des sources thermoélastiques est le plus souvent très grande devant la puissance moyenne dissipée durant un cycle (rapport souvent entre 100 et 1000). Du point de vue expérimental, les amplitudes des sources thermoélastiques estimés sont en bon accord avec ce que prévoit la théorie thermoélastique linéaire et isotrope. Pour un niveau de chargement donné, des distributions spatialement hétérogènes mais temporellement constantes de la dissipation moyenne par cycle ont été mises en évidence. L'analyse calorimétrique encore que cette dissipation évolue de façon linéaire en fonction de la fréquence de sollicitation pour un niveau de charge donné et ce quelle que soit la zone étudiée. Il a enfin été montré que ces effets dissipatifs hétérogènes sont bien associés aux caractéristiques locales du matériau

Spécial Environnement

Bulletin d'information de l'IGN N°66Ce rapport rassemble les contributions de I'IGN dans le domaine de l'environnement et de l'information géographique. Il dresse un bilan pluriannuel et aborde de nombreux thèmes de la géographie numérique : cartographie, images spatiales, système d'information géographique (SIG}, géodésie . . . De façon transversale, les sujets environnementaux sont tout aussi variés : protection des paysages, hydrologie, risques technologiques majeurs, effet de serr

Evolution of Retinoid and Steroid Signaling: Vertebrate Diversification from an Amphioxus Perspective

Although the physiological relevance of retinoids and steroids in vertebrates is very well established, the origin and evolution of the genetic machineries implicated in their metabolic pathways is still very poorly understood. We investigated the evolution of these genetic networks by conducting an exhaustive survey of components of the retinoid and steroid pathways in the genome of the invertebrate chordate amphioxus (Branchiostoma floridae). Due to its phylogenetic position at the base of chordates, amphioxus is a very useful model to identify and study chordate versus vertebrate innovations, both on a morphological and a genomic level. We have characterized more than 220 amphioxus genes evolutionarily related to vertebrate components of the retinoid and steroid pathways and found that, globally, amphioxus has orthologs of most of the vertebrate components of these two pathways, with some very important exceptions. For example, we failed to identify a vertebrate-like machinery for retinoid storage, transport, and delivery in amphioxus and were also unable to characterize components of the adrenal steroid pathway in this invertebrate chordate. The absence of these genes from the amphioxus genome suggests that both an elaboration and a refinement of the retinoid and steroid pathways took place at the base of the vertebrate lineage. In stark contrast, we also identified massive amplifications in some amphioxus gene families, most extensively in the short-chain dehydrogenase/reductase superfamily, which, based on phylogenetic and genomic linkage analyses, were likely the result of duplications specific to the amphioxus lineage. In sum, this detailed characterization of genes implicated in retinoid and steroid signaling in amphioxus allows us not only to reconstruct an outline of these pathways in the ancestral chordate but also to discuss functional innovations in retinoid homeostasis and steroid-dependent regulation in both cephalochordate and vertebrate evolution

Late relapse after hematopoietic stem cell transplantation for acute leukemia: a retrospective study by SFGM-TC.

peer reviewedLate relapse (LR) after allogeneic hematopoietic stem cell transplantation (AHSCT) for acute leukemia is a rare event (nearly 4.5%) and raises the questions of prognosis and outcome after salvage therapy. We performed a retrospective multicentric study between January 1, 2010, and December 31, 2016, using data from the French national retrospective register ProMISe provided by the SFGM-TC (French Society for Bone Marrow Transplantation and Cellular Therapy). We included patients presenting with LR, defined as a relapse occurring at least 2 years after AHSCT. We used the Cox model to identify prognosis factors associated with LR. During the study period, a total of 7582 AHSCTs were performed in 29 centers, and 33.8% of patients relapsed. Among them, 319 (12.4%) were considered to have LR, representing an incidence of 4.2% for the entire cohort. The full dataset was available for 290 patients, including 250 (86.2%) with acute myeloid leukemia and 40 (13.8%) with acute lymphoid leukemia. The median interval from AHSCT to LR was 38.2 months (interquartile range [IQR], 29.2 to 49.7 months), and 27.2% of the patients had extramedullary involvement at LR (17.2% exclusively and 10% associated with medullary involvement). One-third of the patients had persistent full donor chimerism at LR. Median overall survival (OS) after LR was 19.9 months (IQR, 5.6 to 46.4 months). The most common salvage therapy was induction regimen (55.5%), with complete remission (CR) obtained in 50.7% of cases. Ninety-four patients (38.5%) underwent a second AHSCT, with a median OS of 20.4 months (IQR, 7.1 to 49.1 months). Nonrelapse mortality after second AHSCT was 18.2%. The Cox model identified the following factors as associated with delay of LR: disease status not in first CR at first HSCT (odds ratio [OR], 1.31; 95% confidence interval [CI], 1.04 to 1.64; P = .02) and the use of post-transplantation cyclophosphamide (OR, 2.23; 95% CI, 1.21 to 4.14; P = .01). Chronic GVHD appeared to be a protective factor (OR, .64; 95% CI, .42 to .96; P = .04). The prognosis of LR is better than in early relapse, with a median OS after LR of 19.9 months. Salvage therapy associated with a second AHSCT improves outcome and is feasible, without creating excess toxicity

Thermographic analysis of fatigue dissipation properties of steel sheets

This paper presents several properties of heat source fields accompanying the high-cycle fatigue of a dual-phase steel grade. Heat sources were derived from thermal data provided by an infrared focal plane array camera. An especially developed image processing estimates separately the thermoelastic coupling source amplitude and the mean dissipation per cycle. Our experiments underline that dissipation sources are heterogeneous and this forms the beginning of the fatigue test. They also point out a linear evolution of the mean dissipation per cycle as a function of the loading frequency for a given stress range and a given loading ratio

Analyse de la dissipation locale induite par la fatique des aciers

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Champs de source de dissipation et de couplage en fatigue des matériaux

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