THE ISM: A FORMAL TOOL FOR MODELLING AND VERIFICATION

This paper addresses the issue of modelling and analysis of systems. The necessity of carrying out verification and/or validation tasks is discussed, the factors which influence the choice of a model are shown, and the differences between simulation tools or formal methods is explained. Within the framework of discrete time modelling of systems, a method for formally analysing the behaviour of a system described by a Finite State Machine permits to prove properties: the method is based on the translation into a formal system which has got a temporal logic interpretation, and the analysis of the sensitivity of the temporal evolution of the system with respect to some events involves the use of the Temporal Boolean Difference. Furthermore, in order to improve the expressiveness power of the model, an extension of the Finite State Machine model, called Interpreted Sequential Machine (lSM) supports the representation of complex data. The verification process has been adapted to t his model

On the influence of microstructural gradients in the fatigue lifetime estimation of a railway axle

This study aims at characterizing the influence of gradients at different scales (loading, geometry, microstructure...) on fatigue strength through a multi-scale finite element modeling associated to several high cycle fatigue criteria. This is a necessary step in the perspective of conducting a relevant experimental campaign on notched specimen exhibiting a gradient of mechanical properties

Caractérisation du comportement mécanique d'un gradient de microstructure

Une démarche pour la caractérisation des métaux à gradients de microstructure s'appuyant sur des mesures de champs cinématiques est proposée. L'application d'un traitement de recristallisation à une éprouvette de traction en fer pur permet l'obtention d'un gradient de taille de grain localisé. Une variation de propriétés élasto-plastique à l'échelle de ce gradient de microstructure est recherchée en comparant la réponse observée aux résultats de calculs éléments finis

Outgassing Behavior of C/2012 S1 (ISON) From September 2011 to June 2013

We report photometric observations for comet C/2012 S1 (ISON) obtained during the time period immediately after discovery (r=6.28 AU) until it moved into solar conjunction in mid-2013 June using the UH2.2m, and Gemini North 8-m telescopes on Mauna Kea, the Lowell 1.8m in Flagstaff, the Calar Alto 1.2m telescope in Spain, the VYSOS-5 telescopes on Mauna Loa Hawaii and data from the CARA network. Additional pre-discovery data from the Pan STARRS1 survey extends the light curve back to 2011 September 30 (r=9.4 AU). The images showed a similar tail morphology due to small micron sized particles throughout 2013. Observations at sub-mm wavelengths using the JCMT on 15 nights between 2013 March 9 (r=4.52 AU) and June 16 (r=3.35 AU) were used to search for CO and HCN rotation lines. No gas was detected, with upper limits for CO ranging between (3.5-4.5)E27 molec/s. Combined with published water production rate estimates we have generated ice sublimation models consistent with the photometric light curve. The inbound light curve is likely controlled by sublimation of CO2. At these distances water is not a strong contributor to the outgassing. We also infer that there was a long slow outburst of activity beginning in late 2011 peaking in mid-2013 January (r~5 AU) at which point the activity decreased again through 2013 June. We suggest that this outburst was driven by CO injecting large water ice grains into the coma. Observations as the comet came out of solar conjunction seem to confirm our models.Comment: 8 pages, 2 figures, 3 table

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Three-dimensional modeling with enriched finite element for the calculation of singularities delamnination and at the junction of anisotropic materials

Il est connu de longue date que les discontinuités matérielles et/ou géométriques peuvent provoquer des concentrations des contraintes, dites "surcontraintes", nocives pour la résistance du matériau qui doit les supporter. En effet, l'état de contrainte dans ces zones peut être singulier et ne peut être modélisé en pratique par éléments finis réguliers tridimensionnels, à moins de mailler très finement. Pour palier cette difficulté, nous proposons une méthode numérique en deux étapes. La première permet de déterminer l'ordre de la singularité et le mode de surcontraintes. La seconde étape consiste à inclure ces résultats dans une description des champs mécaniques régnant dans la structure pour obtenir les informations complètes sur l'amorçage de fissure via une règle de raccordement. Ce raccordement a d'abord été effectué dans une formulation d'éléments finis hybrides "Métis" à double singularité puis dans une formulation en déplacement pur. Cette technique a été étendue au cas général où l'exposant de singularité est quelconque permettant de résoudre des problèmes de bord libre ou d'entaille à la jonction de plusieurs matériaux anisotropes avec une grande précision. L'analyse duale d'un problème grâce aux deux types de formulations fournit une estimation a posteriori de l'erreur. Des applications numériques tant au niveau du calcul d'exposants de singularité que de celui des facteurs d'intensité des contraintes valident la méthode en s'appuyant sur divers exemples issus de la littérature. Les résultats montrent une bonne cohérence et une bonne précision. De plus, ces méthodes ne requièrent qu'un faible temps CPU.Material and/or geometry discontinuities can cause concentrations of stress. This stress can be harmful to the strength of the structure. Indeed, the state of stress in these areas can be singular. This kind of stress, called "overstress", can be modeled in practice by regular three-dimensional finite element, unless very finely meshed. To overcome this difficulty, we propose a numerical method in two steps. The first determines the singularity order and the mode fracture. The second step is to include these results in a description of the mechanical fields prevailing in the structure to obtain complete information on the initiation of the crack via a rule of connection. This connection was implemented in a finite element mixed formulation named "Metis" and a finite element displacement formulation. The proposed technique has been extended for all given singularity order. So, this technique can resolve any problems like free-edge or V-notch at the junction of several anisotropic materials with great precision. The dual analysis of a problem with these two types of formulations provides a posteriori error. Numerical applications for calculation of stress intensity factors and singularity order validate the proposed method on examples from literature. The results show a good consistency and good accuracy. Moreover, these methods require only low CPU time

Prise en charge thérapeutique de la maladie d'Alzheimer en Picardie

Si le traitement anticholinestérasique a montré une efficacité, la prescription ne semble pas encore s'étendre à tous les patients qui pourraient en bénéficier. Afin d'estimer la prise en charge thérapeutique en région Picardie, nous avons mené une enquête recensant les prescriptions en IACE et la prévalence estimée de la maladie. Compte tenu des indications bien codifiées en IACE, ces prescriptions constituent un reflet global de la prise en charge thérapeutique de la MA. D'une part nous avons utilisé les données de l'assurance maladie et des trois laboratoires qui commercialisent les IACE concernant le nombre de patients traités. D'autre part, à l'aide de l'étude EURODEM et du recensement INSEE 1999 nous avons obtenu une estimation de la prévalence de la MA en Picardie. Ce travail a donc donné une estimation de la prévalence de 11 677, une incidence de 3 212, et montre que 22 % des cas prévalents sont traités. Les prescriptions ont progressé de 30.1% entre février 2001 et février 2002, avec 1 798 patients traités la première année et 2 572 la deuxième. Les résultats de l'étude suggèrent que cette pathologie est sous diagnostiquée et que la prise en charge thérapeutique reste très insuffisanteAMIENS-BU Santé (800212102) / SudocSudocFranceF

Modélisation tridimensionnelle de singularités à la jonction de multi-matériaux anisotropes

Dans l'étude de l'endommagement des multicouches, des phénomènes de « surcontraintes » apparaissent. Néanmoins, leur modélisation échappe largement au traitement numérique par éléments finis réguliers à moins de mailler extrêmement finement. Ainsi, pour traiter ce genre de problèmes, nous avons développé une méthode d'éléments finis singuliers 3D. Nous l’avons testé dans différents cas dont celui du bord libre d'un bimatériau. Les résultats montrent une bonne cohérence et une bonne précision

Methodology of porosity modeling for friction pad: Consequence on the squeal instability

International audienceMechanical property is an important parameter of friction material as it influences contact distribution (tribological and thermo-mechanical behavior), dynamic behavior (and then squeal propensity). Due to the process, the percentage of porosity in the volume is near 10%. So, a friction pad has been characterized by a topographical study using X-ray. This step permits to obtain some information concerning the porosity. In a second step, a simplified pin-on-disc is modeled using finite element method considering initially homog-enized friction material and secondly heterogeneous friction material including the pores. The pore distributions are generated using a representative random fields technique. The introduction of pores shows clearly some differences on dynamical behavior between homogenized and heterogeneous materials consideration

Identification des propriétés des matériaux à partir de champs cinématiques via le deep learning

International audienc