Direct numerical simulation of the dynamics of sliding rough surfaces

The noise generated by the friction of two rough surfaces under weak contact pressure is usually called roughness noise. The underlying vibration which produces the noise stems from numerous instantaneous shocks (in the microsecond range) between surface micro-asperities. The numerical simulation of this problem using classical mechanics requires a fine discretization in both space and time. This is why the finite element method takes much CPU time. In this study, we propose an alternative numerical approach which is based on a truncated modal decomposition of the vibration, a central difference integration scheme and two algorithms for contact: The penalty algorithm and the Lagrange multiplier algorithm. Not only does it reproduce the empirical laws of vibration level versus roughness and sliding speed found experimentally but it also provides the statistical properties of local events which are not accessible by experiment. The CPU time reduction is typically a factor of 10.Comment: 16 pages, 16 figures, accepted versio

A neurotoxic peripherin splice variant in a mouse model of ALS

Peripherin, a neuronal intermediate filament (nIF) protein found associated with pathological aggregates in motor neurons of patients with amyotrophic lateral sclerosis (ALS) and of transgenic mice overexpressing mutant superoxide dismutase-1 (SOD1G37R), induces the selective degeneration of motor neurons when overexpressed in transgenic mice. Mouse peripherin is unique compared with other nIF proteins in that three peripherin isoforms are generated by alternative splicing. Here, the properties of the peripherin splice variants Per 58, Per 56, and Per 61 have been investigated in transfected cell lines, in primary motor neurons, and in transgenic mice overexpressing peripherin or overexpressing SOD1G37R. Of the three isoforms, Per 61 proved to be distinctly neurotoxic, being assembly incompetent and inducing degeneration of motor neurons in culture. Using isoform-specific antibodies, Per 61 expression was detected in motor neurons of SOD1G37R transgenic mice but not of control or peripherin transgenic mice. The Per 61 antibody also selectively labeled motor neurons and axonal spheroids in two cases of familial ALS and immunoprecipitated a higher molecular mass peripherin species from disease tissue. This evidence suggests that expression of neurotoxic splice variants of peripherin may contribute to the neurodegenerative mechanism in ALS

Modelling VARTM process induced variations on bending performance of composite Omega beams

Finite element simulation with cohesive contact is presented, to correlate the vacuum assisted RTM process and the bending performance of Omega beams. The model considers the process induced variations, including part thickness, resin rich pockets and voids. The bending performance prediction relies on cohesive contact to model delamination initiation and propagation. Computing efficiency is achieved by mesh scaling. The modelling approach applies to three variations of Omega beams with the different mode-mixture ratios. The finite element predictions result in a high degree of agreement with the experimental measurements

L’Intelligence Collective dans la Conception et le Déploiement d’une Unité d’Enseignement Transversale et Interdisciplinaire à Grande Échelle : l’UE CATI

L’Unité d’Enseignement (UE) CATI est basée sur l’apprentissage par projets, la transversalité et l’interdisciplinarité de sa conception jusqu’à sa valorisation. Expérimentées pour la première2fois en 2020-2021 pour les 1086 étudiants de 1ʳᵉ année de licence inscrits au sein de l’institut sciences et techniques de CY Cergy Paris Université (CY), la construction et la réalisation en apprentissage par projet d’une UE interdisciplinaire de cette envergure ont été rendues possibles par l’implication de plusieurs acteurs, en mobilisant les principes de l’intelligence collective.Dans cet article, nous indiquerons comment l’intégration des principes de l’intelligence collective à toutes les étapes a permis d’engager et de mettre en mouvement ces différents acteurs : la conception de l’UE par 15 enseignants issus de 8 départements disciplinaires, sa mise en oeuvre/animation par 44 étudiants-tuteurs, eux-mêmes accompagnés par deux services distincts de l’université, a permis au millier d’étudiants de 1ʳᵉ année organisés en 143 groupes autonomes, de travailler en apprentissage par projet, de produire dans les délais imposés des livrables ancrés dans des problématiques sociétales et territoriales

Hidden attractors in fundamental problems and engineering models

Recently a concept of self-excited and hidden attractors was suggested: an attractor is called a self-excited attractor if its basin of attraction overlaps with neighborhood of an equilibrium, otherwise it is called a hidden attractor. For example, hidden attractors are attractors in systems with no equilibria or with only one stable equilibrium (a special case of multistability and coexistence of attractors). While coexisting self-excited attractors can be found using the standard computational procedure, there is no standard way of predicting the existence or coexistence of hidden attractors in a system. In this plenary survey lecture the concept of self-excited and hidden attractors is discussed, and various corresponding examples of self-excited and hidden attractors are considered

Live. Tell. Resist.

This edition of First-Gen Voices features the stories and work of 24 first-generation college students at multiple higher education institutions. The aim is to disseminate a story about us, for us, and consequently, the dominant cultures that have yet to learn from our power

Thermal Imaging of Nanostructures by Quantitative Optical Phase Analysis

International audienceWe introduce an optical microscopy technique aimed at characterizing the heat generation arising from nanostructures, in a comprehensive and quantitative manner. Namely, the technique permits (i) mapping the temperature distribution around the source of heat, (ii) mapping the heat power density delivered by the source, and (iii) retrieving the absolute absorption cross section of light-absorbing structures. The technique is based on the measure of the thermal-induced refractive index variation of the medium surrounding the source of heat. The measurement is achieved using an association of a regular CCD camera along with a modified Hartmann diffraction grating. Such a simple association makes this technique straightforward to implement on any conventional microscope with its native broadband illumination conditions. We illustrate this technique on gold nanoparticles illuminated at their plasmonic resonance. The spatial resolution of this technique is diffraction limited, and temperature variations weaker than 1 K can be detected

Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS: Evidence for Strong Stellar Contamination in the Transmission Spectra

TRAPPIST-1 is a nearby system of seven Earth-sized, temperate, rocky exoplanets transiting a Jupiter-sized M8.5V star, ideally suited for in-depth atmospheric studies. Each TRAPPIST-1 planet has been observed in transmission both from space and from the ground, confidently rejecting cloud-free, hydrogen-rich atmospheres. Secondary eclipse observations of TRAPPIST-1 b with JWST/MIRI are consistent with little to no atmosphere given the lack of heat redistribution. Here we present the first transmission spectra of TRAPPIST-1 b obtained with JWST/NIRISS over two visits. The two transmission spectra show moderate to strong evidence of contamination from unocculted stellar heterogeneities, which dominates the signal in both visits. The transmission spectrum of the first visit is consistent with unocculted starspots and the second visit exhibits signatures of unocculted faculae. Fitting the stellar contamination and planetary atmosphere either sequentially or simultaneously, we confirm the absence of cloud-free hydrogen-rich atmospheres, but cannot assess the presence of secondary atmospheres. We find that the uncertainties associated with the lack of stellar model fidelity are one order of magnitude above the observation precision of 89 ppm (combining the two visits). Without affecting the conclusion regarding the atmosphere of TRAPPIST-1 b, this highlights an important caveat for future explorations, which calls for additional observations to characterize stellar heterogeneities empirically and/or theoretical works to improve model fidelity for such cool stars. This need is all the more justified as stellar contamination can affect the search for atmospheres around the outer, cooler TRAPPIST-1 planets for which transmission spectroscopy is currently the most efficient technique.Comment: 26 pages, 11 figures, accepted for publication in The Astrophysical Journal Letter