A probabilistic model to predict the formation and propagation of crack networks in thermal fatigue

International audienceA probabilistic model is presented to predict the formation and propagation of crack networks in thermal fatigue. It is based on a random distribution of sites where cracks initiate and on the shielding phenomenon corresponding to the relaxed stress field created around cracks. Currently, the model considers only heterogeneous uniaxial stress loading even if thermal fatigue is multiaxial. However, the first simulations on a uniaxial mechanical loading representative of the stress gradient that appears in thermal fatigue shocks are in qualitative agreement with experimental results. The larger the stress amplitude, the denser the crack network and the smaller the crack sizes

On the formation of crack networks in high cycle fatigue

International audienceA probabilistic model based on an initial distribution of sites is proposed to describe different aspects of the formation, propagation and coalescence of crack networks in thermomechanical fatigue. The interaction between cracks is modeled by considering shielding effects

Orientation-dependent stress relaxation in hetero-epitaxial 3C-SiC films

Residual stresses in epitaxial 3C-SiC films on silicon, for chosen growth conditions, appear determined by their growth orientation. Stress evaluation locally with Raman spectroscopy, and across a 150 mm wafer with curvature measurements, indicate that thin films can be grown on Si(100) with residual tensile stresses as low as 150 MPa. However, films on Si(111) retain a considerably higher stress, around 900 MPa, with only minor decrease versus film thickness. Stacking faults are indeed geometrically a less efficient relief mechanism for the biaxial strain of SiC films grown on Si(111) with 〈111〉 orientation. Residual stresses can be tuned by the epitaxial process temperatures. © 2013 American Institute of Physics

Transient Alteration of Cellular Redox Buffering before Irradiation Triggers Apoptosis in Head and Neck Carcinoma Stem and Non-Stem Cells

Background: Head and neck squamous cell carcinoma (HNSCC) is an aggressive and recurrent malignancy owing to intrinsic radioresistance and lack of induction of apoptosis. The major focus of this work was to design a transient glutathione depleting strategy during the course of irradiation of HNSCC in order to overcome their radioresistance associated with redox adaptation. Methodology/Principal Findings: Treatment of SQ20B cells with dimethylfumarate (DMF), a GSH-depleting agent, and L-Buthionine sulfoximine (BSO), an inhibitor of GSH biosynthesis 4 h before a 10 Gy irradiation led to the lowering of the endogenous GSH content to less than 10 % of that in control cells and to the triggering of radiation-induced apoptotic cell death. The sequence of biochemical events after GSH depletion and irradiation included ASK-1 followed by JNK activation which resulted in the triggering of the intrinsic apoptotic pathway through Bax translocation to mitochondria. Conclusions: This transient GSH depletion also triggered radiation-induced cell death in SQ20B stem cells, a key event to overcome locoregional recurrence of HNSCC. Finally, our in vivo data highlight the relevance for further clinical trials o

2012 Activity Report of the Regional Research Programme on Hadrontherapy for the ETOILE Center

2012 is the penultimate year of financial support by the CPER 2007-2013 for ETOILE's research program, sustained by the PRRH at the University Claude Bernard. As with each edition we make the annual review of the research in this group, so active for over 12 years now. Over the difficulties in the decision-making process for the implementation of the ETOILE Center, towards which all our efforts are focussed, some "themes" (work packages) were strengthened, others have progressed, or have been dropped. This is the case of the eighth theme (technological developments), centered around the technology for rotative beam distribution heads (gantries) and, after being synchronized with the developments of ULICE's WP6, remained so by ceasing its activities, coinciding also with the retirement of its historic leader at IPNL, Marcel Bajard. Topic number 5 ("In silico simulations") has suffered the departure of its leader, Benjamin Ribba, although the work has still been provided by Branka Bernard, a former postdoctoral fellow in Lyon Sud, and now back home in Croatia, still in contract with UCBL for the ULICE project. Aside from these two issues (and the fact that the theme "Medico-economical simulations" is now directly linked to the first one ("Medical Project"), the rest of the teams are growing, as evidenced by the publication statistics at the beginning of this report. This is obviously due to the financial support of our always faithful regional institutions, but also to the synergy that the previous years, the European projects, the arrival of the PRIMES LabEx, and the national France Hadron infrastructure have managed to impulse. The Rhone-Alpes hadron team, which naturally includes the researchers of LPC at Clermont, should also see its influence result in a strong presence in France Hadron's regional node, which is being organized. The future of this regional research is not yet fully guaranteed, especially in the still uncertain context of ETOILE, but the tracks are beginning to emerge to allow past and present efforts translate into a long future that we all want to see established. Each of the researchers in PRRH is aware that 2013 will be (and already is) the year of great challenge : for ETOILE, for the PRRH, for hadron therapy in France, for French hadrontherapy in Europe (after the opening and beginning of treatments in the German [HIT Heidelberg, Marburg], Italian [CNAO, Pavia] and Austrian [MedAustron, Wien Neuerstadt]) centers. Let us meet again in early 2014 for a comprehensive review of the past and a perspective for the future ..

Phenotypic effects of genetic variants associated with autism

While over 100 genes have been associated with autism, little is known about the prevalence of variants affecting them in individuals without a diagnosis of autism. Nor do we fully appreciate the phenotypic diversity beyond the formal autism diagnosis. Based on data from more than 13,000 individuals with autism and 210,000 undiagnosed individuals, we estimated the odds ratios for autism associated to rare loss-of-function (LoF) variants in 185 genes associated with autism, alongside 2,492 genes displaying intolerance to LoF variants. In contrast to autism-centric approaches, we investigated the correlates of these variants in individuals without a diagnosis of autism. We show that these variants are associated with a small but significant decrease in fluid intelligence, qualification level and income and an increase in metrics related to material deprivation. These effects were larger for autism-associated genes than in other LoF-intolerant genes. Using brain imaging data from 21,040 individuals from the UK Biobank, we could not detect significant differences in the overall brain anatomy between LoF carriers and non-carriers. Our results highlight the importance of studying the effect of the genetic variants beyond categorical diagnosis and the need for more research to understand the association between these variants and sociodemographic factors, to best support individuals carrying these variants

Development and characterization of graphene, fluorinated graphene, and graphene/boron nitride heterostructures based devices as a prelude to gas detection

Cette thèse a pour but le développement et l’étude d'un capteur de gaz ultrasensible et sélectif à base de graphène. Nous présentons la technologie utilisée pour la réalisation des capteurs intégrant une monocouche de graphène : photolithographie et transfert de couches. Les techniques de caractérisation globales (microscopie optique, AFM, Raman…) permettant un diagnostic des rubans de graphène et assurent une bonne reproductibilité des procédés technologiques. Nous présentons les résultats de caractérisation sous gaz sur une large gamme de températures et de concentrations, y compris les très faibles concentrations de NO2 et NH3. Nous avons également cherché les moyens de limiter les instabilités liées au substrat et améliorer la sensibilité du capteur par la mise en place d’une hétérostructure « all-CVD » graphène/BN. Enfin, nous avons étudié les possibilités d’accroître la sélectivité du dispositif par une technique de fluoration innovante du graphène avec une étude complète XPS pour tester la stabilité en température et en temps des couches de graphène fluorées et leur sélectivité chimique.This thesis aims at the development and study of a highly sensitive and selective graphene-based gas sensor. We present the technology used for the realization of sensors integrating a single layer of graphene: photolithography and transfer of layers. Characterization techniques (optical microscopy, AFM, Raman, etc.) ensure a diagnosis of graphene ribbons and allow good reproducibility of technological processes. We present the results of gas characterization over a wide range of temperatures and concentrations, including very low NO2 and NH3 concentrations. We also looked at ways to limit substrate instabilities and improve sensor sensitivity through the introduction of a graphene/BN “all-CVD” heterostructure. Finally, we studied the possibilities of increasing the selectivity of the device by an innovative fluorination technique of graphene with a complete XPS study to assess the temperature and time stability of fluorographene layers and their chemical selectivity

Fabrication et caractérisation de dispositifs à base de graphène, graphène-fluoré et d’hétérostructures graphène/nitrure de bore en vue d’applications à des capteurs de gaz

This thesis aims at the development and study of a highly sensitive and selective graphene-based gas sensor. We present the technology used for the realization of sensors integrating a single layer of graphene: photolithography and transfer of layers. Characterization techniques (optical microscopy, AFM, Raman, etc.) ensure a diagnosis of graphene ribbons and allow good reproducibility of technological processes. We present the results of gas characterization over a wide range of temperatures and concentrations, including very low NO2 and NH3 concentrations. We also looked at ways to limit substrate instabilities and improve sensor sensitivity through the introduction of a graphene/BN “all-CVD” heterostructure. Finally, we studied the possibilities of increasing the selectivity of the device by an innovative fluorination technique of graphene with a complete XPS study to assess the temperature and time stability of fluorographene layers and their chemical selectivity.Cette thèse a pour but le développement et l’étude d'un capteur de gaz ultrasensible et sélectif à base de graphène. Nous présentons la technologie utilisée pour la réalisation des capteurs intégrant une monocouche de graphène : photolithographie et transfert de couches. Les techniques de caractérisation globales (microscopie optique, AFM, Raman…) permettant un diagnostic des rubans de graphène et assurent une bonne reproductibilité des procédés technologiques. Nous présentons les résultats de caractérisation sous gaz sur une large gamme de températures et de concentrations, y compris les très faibles concentrations de NO2 et NH3. Nous avons également cherché les moyens de limiter les instabilités liées au substrat et améliorer la sensibilité du capteur par la mise en place d’une hétérostructure « all-CVD » graphène/BN. Enfin, nous avons étudié les possibilités d’accroître la sélectivité du dispositif par une technique de fluoration innovante du graphène avec une étude complète XPS pour tester la stabilité en température et en temps des couches de graphène fluorées et leur sélectivité chimique

Modélisation probabiliste de formation de réseaux de fissures de fatigue thermique

Thermal superficial crack networks have been detected in mixing zone of cooling system in nuclear power plants. Numerous experimental works have already been led to characterize initiation and propagation of these cracks. The random aspect of initiation led to propose a probabilistic model for the formation and propagation of crack networks in thermal fatigue. In a first part, uniaxial mechanical test were performed on smooth and slightly notched specimens in order to characterize the initiation of multiple cracks, their arrest due to obscuration and the coalescence phenomenon by recovery of amplification stress zones. In a second time, the probabilistic model was established under two assumptions: the continuous cracks initiation on surface, described by a Poisson point process law with threshold, and the shielding phenomenon which prohibits the initiation or the propagation of a crack if this one is in the relaxation stress zone of another existing crack. The crack propagation is assumed to follow a Paris' law based on the computation of stress intensity factors at the top and the bottom of crack. The evolution of multiaxial cracks on the surface can be followed thanks to three quantities: the shielding probability, comparable to a damage variable of the structure, the initiated crack density, representing the total number of cracks per unit surface which can be compared to experimental observations, and the propagating crack density, representing the number per unit surface of active cracks in the network. The crack sizes distribution is also computed by the model allowing an easier comparison with experimental results.Des réseaux de fissures superficielles de fatigue thermique ont été détectés dans des conduites de centrales nucléaires, plus précisément dans les zones de mélange du circuit de refroidissement du réacteur à l'arrêt. De nombreux travaux expérimentaux ont d'ores et déjà été menés pour caractériser l'apparition et la propagation de ces fissures. L'aspect aléatoire de l'apparition de celles-ci a conduit à proposer un modèle probabiliste de formation et de propagation de fissures. Dans un premier temps, des essais de fatigue mécanique uniaxiale sur des éprouvettes entaillées ont été réalisés afin de mettre en évidence le multi-amorçage de fissures, leur arrêt par obscurcissement et leur coalescence par recouvrement des zones d'amplification des contraintes. Dans un deuxième temps, le modèle probabiliste a été établi sous deux hypothèses : la germination continue de fissures en surface, grâce à une loi d'amorçage à seuil suivant un processus ponctuel de Poisson, et le processus d'obscurcissement qui interdit l'amorçage ou la propagation d'une fissure si celle-ci se situe dans la zone de relaxation des contraintes d'une autre fissure déjà existante. La propagation des fissures est assurée par une loi de type Paris basée sur des calculs de facteurs d'intensité des contraintes en pointe et en fond de fissure. L'évolution des réseaux de fissures multidirectionnelles en surface peut ainsi être suivi au moyen de trois grandeurs : la probabilité d'obscurcissement, comparable à une variable d'endommagement de la structure, la densité de fissures activées, comparable à la densité de fissure d'un réseau réel, et la densité de fissures actives qui permet de connaître le nombre de fissures qui se propagent toujours dans la zone d'étude. La distribution des tailles de fissures est également accessible permettant une comparaison plus rapide avec les résultats expérimentaux