HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Inertia-induced power law scaling in martensites
No full textInternational audienceWhile martensites subjected to quasi-static deformation are known to exhibit power law distributed acoustic emission in a broad range of scales the origin of the observed scaling behavior and the mechanism for self-organization towards criticality remains obscure. Here, we argue that the power-law structure of intermittent fluctuations can be at least partially attributed to inertia. We build on the insight that inertial dynamics, evidenced by acoustic emission, can become an important factor if the underlying mechanical system is only marginally stable. We first illustrate the possibility of inertiainduced heavy-tailed avalanche size distributions using a prototypical example of a discrete chain with bi-stable springs. We then explore the effects of inertia in fully realistic two-and three-dimensional continuum models of elastic phase transitions. In particular, we demonstrate that a three-dimensional model of this type can produce not only qualitative but also quantitative agreement with experiment
Protocol for studying GABAA receptor subsynaptic domains in rat hippocampal neurons using single-molecule localization microscopy
No full textInternational audienceProtocol for studying GABA A receptor subsynaptic domains in rat hippocampal neurons using single-molecule localization microscopyThe study of protein organization at synapses and their rearrangement to maintain efficient synaptic transmission is made possible by single-molecule super-resolution imaging. Here, we present a protocol for studying the organization of GABA A R subdomains at inhibitory synapses. We describe steps for cell fixation, immunolabeling, super-resolution acquisition, and data analysis using a MATLAB open-source algorithm. This protocol has potential applications in the study of membrane molecules at synapses, as well as in other cellular compartments.</p
Causality and Instability in Wave Propagation in Random Time-Varying Media
No full textInternational audienceWe develop a theoretical model to investigate wave propagation in media with random time-varying properties, where temporal fluctuations lead to complex scattering dynamics. Focusing on the ensemble-averaged field, we derive an exact expression for the average Green’s function in the presence of finite temporal disorder, and extend the analysis to the thermodynamic limit. In contrast to spatial disorder, causality prevents recurrent scattering, allowing us to achieve a nonperturbative solution. We introduce an effective medium description providing a simple analysis of the propagation regimes. Our findings offer new insights into wave dynamics in temporally disordered media, with potential applications in time-varying metamaterials, dynamic sensing, and imaging in turbulent or chaotic environments
De la transition de percolation à la localisation d'Anderson dans les potentiels speckle unidimensionnels.
No full textClassical particles in random potentials typically experience a percolation phase transition, being trapped in clusters of mean size that diverges algebraically at a percolation threshold. In contrast, quantum transport in random potentials is controlled by the Anderson localization length, which shows no distinct feature at this classical critical point. Here, we present a comprehensive theoretical analysis of the semi-classical crossover between these two regimes by studying particle propagation in a one-dimensional, red speckle potential, which hosts a percolation transition at its upper bound. As the system deviates from the classical limit, we find that the algebraic divergence of continuously connects to a smooth yet non-analytic increase of the localization length. We characterize this behavior both numerically and theoretically using a semi-classical approach. In this crossover regime, the correlated and non-Gaussian nature of the speckle potential becomes essential, causing the standard DMPK description for uncorrelated disorder to break down. Instead, we predict the emergence of a bimodal transmission distribution, a behavior normally absent in one dimension, which we capture within our semi-classical analysis. Deep in the quantum regime, the DMPK framework is recovered and the universal features of Anderson localization reappear
Three-dimensional deformations in single-layer antimonene and interaction with a Au(111) surface from first principles
No full textUsing density functional theory, we investigate the electronic structure of the alpha phase of an antimony monolayer in its isolated form and in contact to the (111) surface of gold. We demonstrate that the isolated single-layer actually displays a slightly modulated puckering that stabilizes the monolayer, not a uniform one as often assumed. Moreover, it has dramatic consequences on the electronic band structure: the material is a semiconductor with low-dispersing bands near the Brillouin zone center. By further application of about 12% strain on the armchair direction, a double-cone features develops wherein an electronic bandgap of about 21~meV is found. When in contact with a Au(111) surface, a strong interaction with gold arises, as it appears clearly from (i) substantial atomic displacements compared to the isolated form, and (ii) hybridization of Sb and Au orbitals. The latter profoundly modifies the electronic band structure by strengthening the spin-orbit splitting of hybridized bands and spoiling the double-cone feature whose manipulation through substrate-induced strain appears therefore questionable, at least in the simulated epitaxial implementation
Collaboration is our most powerful resistance in an increasingly fragmented world: Science is the light that reveals the unity beneath our differences
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Taking Advantage of Multiple Scattering for Optical Reflection Tomography
No full textOptical Diffraction Tomography (ODT) is a powerful non-invasive imaging technique widely used in biological and medical applications. While significant progress has been made in transmission configuration, reflection ODT remains challenging due to the ill-posed nature of the inverse problem. We present a novel optimization algorithm for 3D refractive index (RI) reconstruction in reflection-mode microscopy. Our method takes advantage of the multiply-scattered waves that are reflected by uncontrolled background structures and that illuminate the foreground RI from behind. It tackles the ill-posed nature of the problem using weighted time loss, positivity constraints and Total Variation regularization. We have validated our method with data generated by detailed 2D and 3D simulations, demonstrating its performance under weak multiple scattering conditions and with simplified forward models used in the optimization routine for computational efficiency.In addition, we highlight the need for multi-wavelength analysis and the use of regularization to ensure the reconstruction of the low spatial frequencies of the foreground RI.</div
Nonreciprocal Ising model
No full textInternational audienceSystems with nonreciprocal interactions generically display time-dependent states. These are routinely observed in finite systems, from neuroscience to active matter, in which globally ordered oscillations exist. However, the stability of these uniform nonreciprocal phases in noisy spatiallyextended systems, their fate in the thermodynamic limit, and the critical behavior of the corresponding phase transitions are not fully understood. Here, we address these questions by introducing a nonreciprocal generalization of the Ising model and study its phase transitions by means of numerical and analytical approaches. While the mean-field equations predict three stable homogeneous phases (disordered, ordered and a time-dependent swap phase), our large scale numerical simulations reveal a more complex picture. Static order is destroyed in any finite dimension due to the growth of rare droplets unless the symmetry between the two spin types is broken triggering a stabilizing droplet-capture mechanism. The swap phase is destroyed by fluctuations in two dimensions through the proliferation of spiral defects, but stabilized in three dimensions where nonreciprocity changes the critical exponents from Ising to XY, thus giving rise to a robust spatially-distributed clock.</div
Natural convection in a vertical channel. Part 3. Bifurcations of many (additional) unstable periodic orbits and their dynamical relevance
No full textInternational audienceVertical thermal convection exhibits weak turbulence and spatio-temporally chaotic behaviour. For this configuration, we report seven new equilibria and 26 new periodic orbits. These orbits, together with four previously studied in Zheng et al. ( J. Fluid Mech. , 2024 b , vol. 1000, p. A29) bring the number of periodic-orbit branches computed so far to 30, all solutions to the fully nonlinear three-dimensional Navier–Stokes equations. These new and unstable invariant solutions capture intricate spatio-temporal flow patterns including straight, oblique, wavy, skewed and distorted convection rolls, as well as bursts and defects. These interesting and important fluid mechanical processes in a small flow unit are shown to also appear locally and instantaneously in a chaotic simulation in a large domain. Most of the solution branches show rich spatial and/or spatio-temporal symmetries. The bifurcation-theoretic organisation of these solutions is discussed; the bifurcation scenarios include Hopf, pitchfork, saddle-node, period-doubling, period-halving, global homoclinic and heteroclinic bifurcations, as well as isolas. Furthermore, these orbits are shown to be able to reconstruct statistically the core part of the attractor, so that these results may contribute to a quantitative description of transitional fluid turbulence using periodic orbit theory
High throughput measurement of bubble coalescence times using digital millifluidics
No full textFoams may form in oil mixtures, such as lubricants, as a result of air entrainment. The long lifetimes of those foams significantlyimpair the thermal properties of lubricants and increase power losses by engines [Zhan et al. (2022)]. In order to improve theefficiency of lubricants, we offer here to gain insights in the stability of bubbles in binary mixtures of miscible oils as a function ofbubble size and liquid composition. To do so, using a micro-millifluidic set-up, we control the formation of bubbles in oil mixturesand study variations in their coalescence time. The set-up allows to easily vary the curvature of the bubbles over one decade,perform statistics over a large number of coalescence events and measure coalescence times that span more than three orders ofmagnitude