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Ice-rubber friction mechanisms across scales
No full textInternational audienceRubber-ice friction is governed by the coupled contributions of viscoelastic adhesion and interfacial heating. This work provides unique in situ / in operando insight into the friction mechanisms from the macroscopic to the molecular scale using combined experimental measurements and analytical modelling approches. Simultaneous force and real contact area imaging were used to quantify the real shear stress of SBR-silica elastomers spanning a small-strain, low-frequency shear-modulus range of 1-8 MPa (low glass transition temperature, ∼−60◦C) during pure sliding over 50 µm.s−1-1 m.s−1 and environmental temperatures down to −30◦C. The normalized real contact area exhibited a non-monotonic velocity dependence; together with a bell-shaped shear stress-velocity curve, this revealed three friction regimes: at low velocity, adhesion and viscoelastic dissipation dominated over thermal effects; near the peak, frictional heat generation increased; and at high velocity, thermally driven mechanisms, including advection-dominated heat removal, became more significant, with the possible occurrence of localized interfacial melting. No bulk melting was observed. The novelty of this work relies on bridging the scales in ice-rubber friction mechanisms. At the macroscopic scale, a simple thermal analysis of the rubber-ice sliding interface yielded a dimensionless average contact temperature that collapsed across all compounds and test conditions considered. At the molecular scale, a Chernyak-Leonov kinetics was used to describe elastomer chain attachment/detachment on ice and its temperature dependence. Successfully confronting our experimental results to this multiscale modeling lead to a predictive interfacial shear stress model that, when supplied with measured real contact area, reproduced both the magnitude and shape of the friction response
Tunable polarization-entangled near-infrared photons from orthogonal GaAs nanowires
No full textQuantum entanglement is a fundamental resource for emerging quantum technologies, enabling secure communication and enhanced sensing. For decades, generating polarization entangled states has been mainly achieved using bulk crystals with spontaneous parametric down conversion (SPDC), preventing scalability and on chip integration. Miniaturizing the quantum source provides access to more versatility and tunability while enabling an easier integration to other devices, notably necessary for satellite-based quantum communication, and eventually reducing fabrication costs. This challenging task can be achieved with Zinc Blende GaAs nanowires. They already have shown an efficient photon pairs generation via SPDC at 1550 nm. Here we demonstrate that a pair of orthogonal GaAs nanowires constitutes a new nanoscale platform to control the quantum state at telecommunication wavelength, enabling a transition from polarization entangled to separable states as a function of the pump polarization, with fidelities reaching 90
New insights from old DNA into the colonization of the Pacific: Two case studies
No full textInternational audienceThis paper is based on a keynote lecture given at the Wellcome Trust meeting on Human Evolution: From Fossils to Ancient Genomes in April 2025. After giving some background on the colonization of the Pacific, I describe the results of two of our studies of ancient DNA. The first used ancient DNA from Eastern Indonesia to address questions about the timing of the admixture between indigenous Papuan groups and incoming Austronesian groups, and showed that this admixture likely occurred soon after the arrival of Austronesians in the region. However, there were unexpected differences in the ancestry of ancient samples from northern Eastern Indonesia (i.e., the North Moluccas) vs. southern Eastern Indonesia (i.e., the Nusa Tenggaras): the latter had ancestry from mainland Southeast Asia that was absent in the former. The second study investigated the origin and relationships of the early colonists of Guam, in the Marianas Archipelago, and found that the most probable origin was from the Philippines, in agreement with linguistic evidence and some interpretations of the archaeological (pottery) evidence, but contrary to the results of computer simulations of voyaging. These studies illustrate the power of ancient DNA analyses to address questions about population history, as well as to provide novel insights that were not realized from studies of modern populations
Measurements of the production of W and Z bosons in pp collisions at TeV
No full textInternational audienceMeasurements of the production of the W and Z bosons at midrapidity in pp collisions at TeV with ALICE at the Large Hadron Collider (LHC) are presented. The W and Z bosons are detected via their (di)electronic decay channels, with the electron reconstruction performed in the midrapidity region (). The -integrated and -differential production cross sections of electrons from W decays in the interval GeV/, as well as the -integrated production cross section of Z bosons, are measured. The results are described by perturbative QCD calculations using different sets of parton distribution functions. The production of W bosons and azimuthally correlated associated hadrons is also measured as a function of the charged-particle multiplicity for the first time at the LHC. The former increases approximately linearly with the charged-particle multiplicity, while for the latter, there are hints of a faster-than-linear increase. These observations are compared with theoretical calculations
Lacets dans les surfaces, diagrammes de cordes, graphes d'entrelacement:factorisation de l'opérade et grammaire génératrice
No full textA filoop is a generic immersion of a circle in a closed oriented surface, whose complement is a disjoint union of discs, considered up to orientation preserving diffeomorphisms. It gives rise to a chord diagram C which has an interlace graph G, called a chordiagraph. For a graph G with even degrees, we compute a quantity mg(G) which yields, for every chord diagram C with interlace graph G, the minimal genus of filoops with chord diagram C. If mg(G)=0 then C admits exactly two framings of genus 0, corresponding to spheriloops. After recalling the Cunningham factorisation of connected graphs, we describe a canonical factorisation of filoops into spheric sums followed by toric sums, for which the genus is additive. This is analogous to the factorisation of compact connected 3-manifolds along spheres and tori. We describe unambiguous context-sensitive grammars generating the set of all graphs and with mg(G)=0 and deduce stability properties with respect to spheric and toric factorisations. Similar results hold for chordiagraphs with mg(G) = 0 and their corresponding spheriloops.30 pages, 25 figure
Experimental investigation of passive alternating flow heating strategies for PEMFC cold start
No full textInternational audiencePassive cold start remains a major challenge to Proton Exchange Membrane Fuel Cells (PEMFCs), with thermal imbalance during warm-up being a key challenge. Uneven temperatures can cause startup failure and long-term degradation. This study experimentally evaluates a new passive heating strategy using alternating coolant flow to improve thermal management. Experiments are conducted using a 3-cell thermal-emulation stack (100 cm2 per cell, ≈230 W thermal power), designed to replicate the edge and central-cell thermal behavior of real PEMFC stacks at −10 °C. The proposed method relies on alternating-flow operation, in which the coolant periodically reverses direction inside the cooling channels, enhancing heat retention and redistribution. This configuration is systematically compared with conventional no-flow (no coolant circulation) and unidirectional-flow (constant flow direction) using key thermal metrics, including temperature rise, vertical and horizontal uniformity, and forced-convection losses. Results show that the no-flow configuration enables rapid heating but induces significant inter-cell temperature differences, resulting in poor horizontal uniformity. Unidirectional configuration provides better horizontal uniformity but limits heating capability and leads to vertical temperature stratification at the cell level due to convective heat removal. The proposed alternating-flow strategy outperforms both reference cases, achieving a 32.3 °C temperature rise in 85 s, reducing vertical gradients by 90 %, and decreasing inter-cell temperature dispersion by more than 57 %. Under these conditions, the active surface exceeds 0 °C, enabling safe cold start. An adaptive strategy is proposed, dynamically switching flow modes based on internal thermal monitoring. This scalable approach offers a promising passive solution for cold-start management in PEMFCs
Refined cellular activity expression signatures provide a targeted framework to quantify phenotypic intra-tumor heterogeneity in single-cell data
No full textSingle cell RNA-seq (scRNA-seq) now allows deeper insight into cellular biology at both the individual and population level. Measuring cell-to-cell variations in the population enables quantification of phenotypic heterogeneity in populations in which cell states and identities deviate from healthy transcriptomic profiles. Cellular activities quantifiable using gene set enrichment analyses can provide useful grounds to quantify phenotypic heterogeneity, but the specificity and adequacy of existing molecular signatures for scRNA-seq data is still insufficient. Here we induced 6 activities in vitro, for which we refined existing expression signatures to enhance specificity and detection in scRNA-seq data: epithelial-mesenchymal transition (EMT), DNA repair, responses to interferons α and γ (IFNα and IFNγ, respectively), glycolysis, oxidative phosphorylation (OxPhos). We report new signatures, with much lower redundancy between IFNα and IFNγ, and glycolysis and OxPhos signatures, achieving average AUCs of 0.85 across bootstrapped datasets for each activity. We could use these signatures to quantify phenotypic intra-tumor heterogeneity (ITH) in 20 patient samples and 14 cell lines, observing high correlation with diversity indices in classified healthy cells (p<0.001). Focusing on cancer cells only, we furthermore report higher phenotypic ITH in patients than in cell lines (p<0.001), and in basal tumors (p=0.028)
DEFORMATION-AWARE SIMULATOR FOR HANDHELD ULTRASOUND IMAGING
No full textInternational audienceRealistic ultrasound simulation is essential for training and algorithm development. However, most existing methods generate single-frame images from thin slices of the probe's field of view, neglecting tissue deformation and spatial continuity across frames. We propose a physics-based simulation pipeline, fully compatible with any scatterer-based ultrasound simulator, which employs finite element modeling to update local scatterer maps under large-scale stability constraints, given the probe trajectory and tissue geometry. The framework produces continuous and anatomically accurate ultrasound sequences with physically consistent speckle evolution, providing a practical tool for training, visualization, and the development of freehand ultrasound reconstruction algorithms.</div