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Estimation of the lifetime distribution from fluctuations in Bellman-Harris processes
No full textInternational audienceThe growth of populations without interactions can often be modeled by branching processes where each individual evolves independently and with the same law. In Bellman–Harris processes, each individual lives a random time and is then replaced by a random number of offspring. We are interested in the estimation of the parameters of this model. Our motivation comes from the estimation of cell division time and we focus on Gamma distribution for lifetime and binary reproduction. The mean of the lifetime is closely related to the growth rate of the population. Going farther and describing lifetime variability from fixed time observations is a challenging task, due to the complexity of the fluctuations of non-Markovian branching processes. Using fine results on these fluctuations, we describe two time-asymptotic regimes and explain how to discriminate between them and estimate the parameters. Then, we consider simulations and biological data to validate and discuss our method. It allows to determine single-cell parameters from time-resolved measurements of populations without the need to track each individual or to know the details of the initial condition. The results can be extended to more general branching processes
MAP-IO: an atmospheric and marine observatory program on board Marion Dufresne over the Southern Ocean
No full textInternational audienc
Utilisation d'indices visuels pour éviter la confusion de mémoire entre le virtuel et le réel dans la réalité augmentée
No full textInternational audienceAs augmented reality technologies advance, the potential for creating hyper-realistic experiences grows, raising concerns about users confusing virtual content with reality. This paper explores ways to mitigate source confusion, a form of false memory where virtual content is misremembered as real and vice-versa. Building on previous studies on source confusion, it proposes a methodological framework for evaluating the capacity of visual cues to reduce source confusion in augmented reality.À mesure que les technologies de réalité augmentée progressent, le potentiel de création d'expériences hyperréalistes augmente, ce qui soulève des inquiétudes chez les utilisateurs qui confondent le contenu virtuel avec la réalité. Cet article explore les moyens d'atténuer la confusion de la source, une forme de fausse mémoire où le contenu virtuel est confondu avec le contenu réel et vice-versa. S'appuyant sur des études antérieures sur la confusion des sources, il propose un cadre méthodologique pour évaluer la capacité des indices visuels à réduire la confusion des sources dans la réalité augmentée
Sustainability in engineering education in Europe over the last 15 years: visions and tendencies among educators as revealed by a literature review
No full textInternational audienceWhile sustainability significantly resonates in engineering education, practices and discussions reveal that what is called sustainability encompasses different realities in terms of objectives and applications. We conducted a review of articles published in the European Journal of Engineering Education between 2008 and 2023. These articles were subject to content analysis with the aim of gaining an understanding of how educators on the ground interpret the need to provide education on both sustainability, and the guiding principles, values, and educational goals that define their initiatives. This study highlights educators' aspirations to contribute to the common good, the pedagogical approaches they develop based on skill and pragmatism, and the significant but limited space that these initiatives occupy within curricula. This review and analysis shed light on the insights, gaps, and trends within the literature, highlighting the need for diverse educational approaches as reflected in these publications, as well as the importance of identifying observable changes in the curricular logic in Europe that shape the representations of knowledge and the social roles of engineers.</div
Efficient boundary integral method to evaluate the acoustic scattering from coupled fluid-fluid problems excited by multiple sources
No full textInternational audienceIn the naval industry many applications require to study the behavior of a penetrable obstacle embedded in water, notably in presence of a turbulent flow. Such configuration is encountered in particular when noise is scattered by two-phase fluids, e.g., turbulent flows with air bubbles. Fast and efficient numerical methods are required to compute this scattering in the presence of realistic 3D geometries, such as bubble curtains. In [1], we have developed a very efficient approach in the case of a rigid obstacle of arbitrary shape, excited by a turbulent flow. It is based on the numerical evaluation of tailored Green's functions. Here we extend this fast method to the case of a penetrable obstacle. It is not a straightforward extension and we propose two main contributions. First, tailored Green's functions for a fluid-fluid coupled problem are derived theoretically and determined numerically. Second, we show the need of a regularized Boundary Integral formulation to obtain these Green's functions accurately in all configurations. Finally, we illustrate the efficiency of the method on various applications related to the scattering by multiple bubbles
Maxwell's equations with hypersingularities at a negative index material conical tip
No full textInternational audienceWe study a transmission problem for the time harmonic Maxwell's equations between a classical positive material and a so-called negative index material in which both the permittivity ε and the permeability µ take negative values. Additionally, we assume that the interface between the two domains is smooth everywhere except at a point where it coincides locally with a conical tip. In this context, it is known that for certain critical values of the contrasts in ε and in µ, the corresponding scalar operators are not of Fredholm type in the usual H^1 spaces. In this work, we show that in these situations, the Maxwell's equations are not well-posed in the classical L^2 framework due to existence of hypersingular fields which are of infinite energy at the tip. By combining the T-coercivity approach and the Kondratiev theory, we explain how to construct new functional frameworks to recover well-posedness of the Maxwell's problem. We also explain how to select the setting which is consistent with the limiting absorption principle. From a technical point of view, the fields as well as their curls decompose as the sum of an explicit singular part, related to the black hole singularities of the scalar operators, and a smooth part belonging to some weighted spaces. The analysis we propose rely in particular on the proof of new key results of scalar and vector potential representations of singular fields
Open Review of "How to introduce an initial crack in phase field simulations to accurately predict the linear elastic fracture propagation threshold?"
No full textOpen Review of "How to introduce an initial crack in phase field simulations to accurately predict the linear elastic fracture propagation threshold?" published in JTCAM.We would like to thank both reviewers for their thoughtful and constructive feedback on our manuscript, "How to introduce an initial crack in phase-field simulations to accurately predict the linear elastic fracture propagation threshold?".We appreciate the time and effort invested in evaluating</div
Magnetic pulse welding of Al-5754 with Al-7075 and MARS 380: Weldability windows and ballistic testing
No full textInternational audienceJoining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible. Magnetic Pulse Welding (MPW) offers a solid-state joining technique that overcomes these issues by using impact to create strong bonds without melting the substrate materials. This study investigates the weldability of aluminum alloy Al-5754 with Al-7075 and MARS 380 steel, used in armouring solutions of defense systems, by the use of MPW. In this work, weldability windows are investigated by varying standoff distances between the coating material and its substrate (0.25-4.5 mm) and discharge energies (5-13 kJ) with both O-shape and U-shape inductors. Mechanical strength of the welded joints were assessed through single lap shear tests, identifying optimal welding parameters. Then, the velocity profiles of the flyer plates were measured using heterodyne velocimetry to understand the dynamics of the impact. Then, substructures assembled with the optimal welding conditions were subjected to ballistic testing using 7.62×51 mm NATO and 9×19 mm Parabellum munitions to evaluate the resilience of the welds under ballistic impact. The outcomes demonstrate that MPW effectively joins Al-5754 with both Al-7075 and MARS 380, producing robust welds capable of withstanding ballistic impacts under certain conditions. This research advances the application of MPW in lightweight ballistic protection of defense systems, contributing to the development of more resilient and lighter protective structures
Self-heating response under cyclic loading of R5 and R6 HSS used for offshore mooring chains: influence of hydrogen on the thermomechanical behavior
No full textInternational audienceSelf-heating response under cyclic loading of R5 and R6 HSS used for offshore mooring chains: influence of hydrogen on the thermomechanical behavio