17 research outputs found

    Avalanches and clusters in planar crack front propagation

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    We study avalanches in a model for a planar crack propagating in a disordered medium. Due to long-range interactions, avalanches are formed by a set of spatially disconnected local clusters, the sizes of which are distributed according to a power law with an exponent τa=1.5\tau_{a}=1.5. We derive a scaling relation τa=2τ1\tau_a=2\tau-1 between the local cluster exponent τa\tau_a and the global avalanche exponent τ\tau. For length scales longer than a cross-over length proportional to the Larkin length, the aspect ratio of the local clusters scales with the roughness exponent of the line model. Our analysis provides an explanation for experimental results on planar crack avalanches in Plexiglas plates, but the results are applicable also to other systems with long-range interactions.Comment: 7 pages, 6 figures, accepted for publication in Physical Review

    Multiscale Stick-Slip Dynamics of Adhesive Tape Peeling

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    Using a high-speed camera, we follow the propagation of the detachment front during the peeling of an adhesive tape from a flat surface. In a given range of peeling velocity, this front displays a multiscale unstable dynamics, entangling two well-separated spatiotemporal scales, which correspond to microscopic and macroscopic dynamical stick-slip instabilities. While the periodic release of the stretch energy of the whole peeled ribbon drives the classical macro-stick-slip, we show that the micro-stick-slip, due to the regular propagation of transverse dynamic fractures discovered by Thoroddsen et al. [Phys. Rev. E 82, 046107 (2010)], is related to a high-frequency periodic release of the elastic bending energy of the adhesive ribbon concentrated in the vicinity of the peeling front.Comment: to appear in Physical Review Letters (2015

    Bursts of activity in collective cell migration

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    Dense monolayers of living cells display intriguing relaxation dynamics, reminiscent of soft and glassy materials close to the jamming transition, and migrate collectively when space is available, as in wound healing or in cancer invasion. Here we show that collective cell migration occurs in bursts that are similar to those recorded in the propagation of cracks, fluid fronts in porous media and ferromagnetic domain walls. In analogy with these systems, the distribution of activity bursts displays scaling laws that are universal in different cell types and for cells moving on different substrates. The main features of the invasion dynamics are quantitatively captured by a model of interacting active particles moving in a disordered landscape. Our results illustrate that collective motion of living cells is analogous to the corresponding dynamics in driven, but inanimate, systems

    Impact of renin-angiotensin system inhibitors on mortality during the COVID Pandemic among STEMI patients undergoing mechanical reperfusion : Insight from an international STEMI registry

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    Background: Concerns have been raised on a potential interaction between renin-angiotensin system inhibitors (RASI) and the susceptibility to coronavirus disease 2019 (COVID-19). No data have been so far reported on the prognostic impact of RASI in patients suffering from ST-elevation myocardial infarction (STEMI) during COVID-19 pandemic, which was the aim of the present study. Methods: STEMI patients treated with primary percutaneous coronary intervention (PPCI) and enrolled in the ISACS-STEMI COVID-19 registry were included in the present sub-analysis and divided according to RASI therapy at admission. Results: Our population is represented by 6095 patients, of whom 3654 admitted in 2019 and 2441 in 2020. No difference in the prevalence of SARSCoV2 infection was observed according to RASI therapy at admission (2.5% vs 2.1%, p = 0.5), which was associated with a significantly lower mortality (adjusted OR [95% CI]=0.68 [0.51 & ndash;0.90], P = 0.006), confirmed in the analysis restricted to 2020 (adjusted OR [95% CI]=0.5[0.33 & ndash;0.74], P = 0.001). Among the 5388 patients in whom data on in-hospital medication were available, in-hospital RASI therapy was associated with a significantly lower mortality (2.1% vs 16.7%, OR [95% CI]=0.11 [0.084 & ndash;0.14], p < 0.0001), confirmed after adjustment in both periods. Among the 62 SARSCoV-2 positive patients, RASI therapy, both at admission or in-hospital, showed no prognostic effect. Conclusions: This is the first study to investigate the impact of RASI therapy on the prognosis and SARSCoV2 infection of STEMI patients undergoing PPCI during the COVID-19 pandemic. Both pre-admission and in-hospital RASI were associated with lower mortality. Among SARSCoV2-positive patients, both chronic and in-hospital RASI therapy showed no impact on survival.Peer reviewe

    Magnetic Janssen effect

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    Abstract A pile of grains, even when at rest in a silo, can display fascinating properties. One of the most celebrated is the Janssen effect, named after the pioneering engineer who explained the pressure saturation at the bottom of a container filled with corn. This surprising behavior arises because of frictional interactions between the grains through a disordered network of contacts, and the vessel lateral walls, which partially support the weight of the column, decreasing its apparent mass. Here, we demonstrate control over frictional interactions using ferromagnetic grains and an external magnetic field. We show that the anisotropic pairwise interactions between magnetized grains result in a radial force along the walls, whose amplitude and direction is fully determined by the applied magnetic field. Such magnetic Janssen effect allows for the fine tuning of the granular column apparent mass. Our findings pave the way towards the design of functional jammed materials in confined geometries, via a further control of both their static and dynamic properties

    ENRICHING A DEVS META-MODEL WITH OCL CONSTRAINTS

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    International audienceThe purpose of this paper is to show how the platform-independent meta-model for DEVS formalism we have been working on can be enriched with Object Constraint Language (OCL) constraints. OCL is a declarative language (without any side effect) and allows us to control both the class attributes and the relationships between classes, in order to facilitate the modeling process and even the code generation towards a DEVS framework. To do so, we chose to follow a MDE, and in particular MDA approach, because OCL 2.0 is now aligned with UML 2.0 and MOF 2.0, which parts of MDA. The implementation of our meta-model with its OCL refinements has been done within Eclipse Modeling Framework (in which OCL 2.0 has been fully implemented) and its meta-meta-formalism Ecore

    From State-Transition Models to DEVS Models - Improving DEVS external interoperability using MetaDEVS: a MDE approach: Improving DEVS external interoperability using MetaDEVS: a MDE approach

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    International audienceIn this paper, the issue of the “external” interoperability of DEVS models is discussed. Scientists often need to simulate non-DEVS models using a DEVS-oriented framework, in order, for instance, to make their DEVS and non-DEVS modes interoperate. The source formalisms we propose to transform onto DEVS models are those which are based on the “family” of states and transitions. A general and model-oriented approach called MetaDEVS is presented in this article. MetaDEVS is also the name given to the DEVS metamodel we use. This metamodel allows creating platform-independent DEVS models. This paper shows how models which belong to the state and transitions “family” can be mapped onto DEVS, and more exactly onto MetaDEVS-based DEVS models, following the MetaDEVS approach. Then, the approach is applied to a concrete case: we transform Finite-State Machine (FSM) models into MetaDEVS models, usingATL, a hybrid language (which mixes both declarative and imperative rules), within the Eclipse Modelling Framework. A metamodel to describe the FSM formalism is also proposed

    Probing the local response of a two-dimensional liquid foam

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    Aqueous foams are viscoelastic yield stress fluids. Due to their complex rheology, foam flow around an obstacle embedded in a 2D Hele-Shaw cell has been widely studied. Typically, in such geometry in the moving flow reference frame the flow field of viscoelastic fluids exhibit a quadrupolar structure characterized by a negative wake. Here, we introduce a measuring geometry, new in this context, whereby instead of flowing the foam around the obstacle, we move the obstacle as an intruder inside the foam. The proposed setup makes it possible to independently control the driving velocity and the liquid foam properties, such as the gas fraction and polydispersity. We show that the liquid foam velocity field around the intruder is similar to the one observed in viscoelastic fluids, in particular the emergence of a negative wake, e.g. a velocity overshoot downstream side of the obstacle. However, surprisingly, the intensity of this velocity overshoot decreases with the number of intruder passes, probably related to the evolution of the local disordered structure of the liquid foam.Peer reviewe

    Interevent Correlations from Avalanches Hiding Below the Detection Threshold

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    Numerous systems ranging from deformation of materials to earthquakes exhibit bursty dynamics, which consist of a sequence of events with a broad event size distribution. Very often these events are observed to be temporally correlated or clustered, evidenced by power-law-distributed waiting times separating two consecutive activity bursts. We show how such interevent correlations arise simply because of a finite detection threshold, created by the limited sensitivity of the measurement apparatus, or used to subtract background activity or noise from the activity signal. Data from crack-propagation experiments and numerical simulations of a nonequilibrium crack-line model demonstrate how thresholding leads to correlated bursts of activity by separating the avalanche events into subavalanches. The resulting temporal subavalanche correlations are well described by our general scaling description of thresholding-induced correlations in crackling noise.Peer reviewe
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