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Juillet 2018 à Marseille : 16th International Workshop on the Physics of Compressible Turbulent Mixing (IWPCTM)

Site web : http://www.iwpctm16.fr/
Evènement organisé par les membres de l’axe de Recherche ECOCI

 

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Séminaire IUSTI – 4 mars 2022 – 11h salle 250

Universality in pipes and landslides

Rory Cerbus – LOMA, Bordeaux

In this seminar I will describe my previous work on the transition to turbulence in pipe flow as well as my current work on landslides. In his seminal work over 130 years ago, Osborne Reynolds observed that as he gradually increased the flow speed of his initially laminar pipe, fluctuating irregular flow invaded the laminar flow creating a patchy combination of the two. These irregular patches have been the subject of intense study ever since, but their internal flow characteristics have largely been ignored. A thorough investigation of these patches has led to a partial solution to the problem of fluid friction in this transition regime, left unsolved by Reynolds, and has also addressed a hallmark of fully turbulent flow, the spatial energy distribution or energy spectrum treated by Kolmogorov. I will show that despite their outward differences, flashes possess the same universal friction laws and energy distributions as fully turbulent flows. Landslides are large mass movements that plague mountainous regions the world over. The feature of landslides of primary concern to both scientists and local inhabitants is the maximum runout distance. A classical result is that the runout correlates with fall height and landslide volume, but the correlation is noisy and the dependence on other parameters is difficult to determine. Using simple laboratory experiments with grains, we determined the runout’s systematic dependence on fall height, landslide size, and grain size, and determined an apparently universal scaling of the normalized runout which applies to both laboratory and natural data, showing that they are connected through their common granular nature.

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Séminaire IUSTI – 7 janvier 2022 – 11h salle 250

Rheologies for the Earth’s brittle crust

Jean-Arthur Olive – ENS, Paris

Most of the brittle, earthquake-generating deformation that shapes mountain ranges takes place in the uppermost ~15 km of the Earth’s crust. On short time scales, the upper crust deforms by slip on frictional faults that delineate elastic blocks. Over millions of years, however, large non-recoverable deformation accumulates both on and off-faults, and distributed brittle strain can localize to form new fault systems. This complex rheological behavior is typically modeled as Mohr-Coulomb elasto-plasticity, with a range of ad-hoc softening parameters that lack a clear micro-mechanical interpretation. I will discuss possible adjustements to this framework aimed at (1) better capturing key properties of crustal rocks inferred from laboratory experiments, and (2) better representing the mineral-scale processes which underlie brittle failure. Improved constitutive laws for the brittle upper crust are a necessary step towards a unified description of geological processes, from mineral to crustal scale, and from seconds to millions of years.

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Soft robots have garnered significant attention in recent years, thanks to their ability to carry out a range of complex tasks such as gripping, crawling or swimming. Joel Marthelot at IUSTI and PT Brun’s team at Princeton University present a new all-in-one methodology for building and programming soft machines. Liquid elastomer is first injected into a mould followed by air. This forms an elongated bubble that rises by gravity and sculpts the internal void of the actuator. By varying the template and flow process, various complex architectures are possible, such as artificial muscles and grippers. The study is featured on the cover of the journal Nature.

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Séminaire IUSTI – 10 déc. 2021 – 11h salle 250

How millions of microscopic active cilia self-organize to protect our airways

Étienne Loiseau – CINAM, Marseille

The respiratory tract is protected by mucus, a complex fluid transported along the epithelial surface by the coordinated beating of millions of microscopic cilia, hence the name of mucociliary clearance. Its impairment is associated with all severe chronic respiratory diseases. Yet, the relationship between ciliary density and the spatial scale of mucus transport, as well as the mechanisms that drive ciliary-beat orientations are much debated. Here, we show on polarized human bronchial epithelia that mucus swirls and circular orientational order of the underlying ciliary beats emerge and grow during ciliogenesis, until a macroscopic mucus transport is achieved for physiological ciliary densities. By establishing that the macroscopic ciliary-beat order is lost and recovered by removing and adding mucus, respectively, we demonstrate that cilia–mucus hydrodynamic interactions govern the collective dynamics of ciliary-beat directions. We propose a two-dimensional model that predicts a phase diagram of mucus transport in accordance with the experiments.

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Pour plus d’informations sur l’agenda: https://jeunesiusti.wordpress.com

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Séminaire exceptionnel – 3 décembre 2021 – 14h salle 250

Impact dynamics of compound drops

Marie-Jean Thoraval – Xi’an Jiaotong Univ, Chine

The impact of a liquid drop has many applications, from combustion to cooling technologies or 3D printing. Additional materials can be loaded into the drop to enhance these applications, such as for the printing of dispersions, biomaterials or polymer foams. The impact dynamics of the resulting complex drops are still not well understood. We focus here on the simplest geometries of compound drops, where either a particle, an immiscible liquid drop or a bubble is added inside the drop. We systematically investigate some of the new dynamics emerging from the impact of these compound drops, including vertical jetting and rebound.

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Séminaire exceptionnel IUSTI – 30 novembre 2021 – 11h amphi Néel

An introduction to Non Imaging Optics, application to Solar Energy Concentration

Manuel Collares-Pereira – Evora, Portugal

An Introduction to Non Imaging Optics is made, from first principles to its application mainly in Solar Energy, but also in other areas as in Illumination, Particle Physics and Astrophysics. The limits to concentration in geometrical optics are explained and different optical configurations will be discussed in comparison with conventional imaging optics.

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Séminaire IUSTI – 26 novembre 2021 – 11h salle 250

Mechanical properties of fiber networks

Mehdi Bouzid – 3SR Lab, Grenoble

Gels of fibrous biopolymers are ubiquitous within cells and their rigidity is crucial for their function [1]. Our current understanding of their elastic response is usually understood as an interplay between the bending and stretching of their filaments [2]. This point of view however fails when applied to the weakly coordinated branched actin networks found throughout the cell [3, 4]. Through experiments and theory, we show that their elasticity crucially involves reversible entanglements between their filaments. Additional entanglements may get locked in during network growth, setting the final properties of the network [5]. These properties could be key to understanding how moving cells dynamically adapt their cytoskeleton to their environment. References [1] G Letort, H Ennomani, L Gressin, M Théry, and L Blanchoin. Dynamic reorganization of the actin cytoskeleton. F1000Research, 4, 2015. [2] C. P Broedersz, X Mao, T C Lubensky, and F. C MacKintosh. Criticality and isostaticity in fibre networks. Nature Physics, 7(12):983, 2011. [3] P Bauer, J Tavacoli, T Pujol, J Planade, J Heuvingh, and O Du Roure. A new method to measure mechanics and dynamic assembly of branched actin networks. Scientific reports, 7(1):15688, 2017. [4] Antoine Allard, Mehdi Bouzid, Timo Betz, Camille Simon, Majdouline Abou-Ghali, Joel Lemiere, Fabrice Valentino, John Manzi, Francoise Brochard-Wyart, Karine Guevorkian, et al. Actin modulates shape and mechanics of tubular membranes. Science Advances, 6(17):eaaz3050, 2020. [5] M Bouzid, C Valencia Gallardo, L Koehler, G Foffi, J Heuvingh, O du Roure, and M Lenz. Elasticity from entanglements in branched actin. In preparation.

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Séminaire exceptionnel – 18 novembre 2021 – 11h salle 357

Active mechanics of living fluids: mucus and tissues

Simon Gsell – IBDM, Marseille

In our body, many physiological processes rely on active soft material flows. To ensure their biological function, these “living fluids” are kept out of mechanical equilibrium through active processes at play within the fluid volume. How active biological processes couple to fluid dynamics to maintain functional spatio-temporal organization remains largely unclear for many of these systems. A first example of living fluid is the mucus protecting bronchial tissue in the lung. This complex fluid is transported along the bronchial tree through active beating of microscopic cilia attached to the tissue. Experiments performed by E. Loiseau and A. Viallat at CINAM (Marseille) on reconstituted in-vitro tissues have shown that directional organization of cilia is coupled to ciliary-driven mucus flow. A minimal hydrodynamic model shows that this self-organization process is controlled by a hydrodynamic length closely connected to the mucus viscosity. The model predicts crucial organizational phase transitions and directional correlation length. Soft cellular tissues can also exhibit fluid-like behavior. During embryonic development, tissue “fluidity” is known to be crucial in several morphogenetic processes. However, the way embryonic tissue flows couple to bio-chemical processes controlling local active cell-cell interactions is generally unknown. This question is currently addressed experimentally in the lab of P.-F. Lenne at IBDM (Marseille) on the basis of embryonic organoids (embryoids). I will present some physical approaches employed to analyze the self-organization dynamics of in-vitro embryoids, as a well as a continuum theoretical/numerical framework that I develop to explore the coupling between advection and cellular organization in such heterogeneous cell aggregates. Finally, I will conclude my talk by presenting potential future works on complex active fluids.

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Séminaire exceptionnel – 19 octobre 2021 – 14h amphi IUSTI

Snap to morph

Lucie Domino – Univ. Amsterdam, Pays-Bas

Creating mechanical structures that have the ability to change shape in a controlled manner is an important challenge nowadays. Many of these so-called morphing structures now exist (they are inflatable, multi material 3D printed, magnetically actuated…), but they always morph into one single shape. Here I will present morphing structures made from bi stable elements (thin elastic shells) embedded in a flat elastic sheet. From the bi stability analysis of a single shell and geometrical frustration arguments I will explain the different stable shapes one can obtain.

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