Matière et Systèmes Complexes
Présentation
Le laboratoire « Matière et Systèmes Complexes » (MSC) est une unité mixte de recherche du CNRS et de l’université (UMR 7057). Le laboratoire est installé depuis 2007 sur le nouveau campus de l’Université Paris Diderot, Paris Rive Gauche, dans le bâtiment Condorcet. Il est réparti sur plusieurs étages. La direction et le secrétariat se trouvent au 6e étage. Le directeur actuel en est Laurent Limat, secondé par la directrice adjointe Florence Gazeau.
Le laboratoire MSC a pour sujet d’étude la matière et les systèmes complexes sous toutes leurs formes. Il peut s’agir de fluides montrant des phénomènes complexes non-linéaires (facettages de jets ou de tourbillons, structures et propriétés complexes de mousses, phénomènes de mouillage, propagation de vagues et de tsunamis) ou bien, par exemple, de systèmes proches de la géophysique et de l’environnement (systèmes granulaires tels que les dunes, phénomènes d’érosion, morphogenèse des plantes et même des villes, nage collective d’algues ou de bactéries…). Les études théoriques et expérimentales conduisent à des applications comme par exemple les éoliennes flexibles de haut rendement, l’optimisation de méthodes d’enduisage, le contôle de propriétés de surface ou la récupération de la biomasse (ingénierie verte)...
Le laboratoire étudie également le couplage entre la physique et la biologie des systèmes vivants, avec une approche multi-échelle. Les recherches effectuées vont d’échelles moléculaires ou supra-moléculaires (assemblages des protéines, chromatine, cytosquelette etc.) jusqu’à l’échelle de l’organisme entier (méduses, poulets, vers etc.) en passant par des études plus fondamentales sur des cellules uniques sur lesquelles sont exercées des forces quantifiées, permettant de comprendre les propriétés biophysiques de la matière vivante. Ces études aboutissent à de possibles applications en ingénierie tissulaire ou régénération des tissus avec des transferts dans le domaine médical.
Equipes de recherche
Le laboratoire est structuré en cinq équipes :
- Dynamique des systèmes hors d’équilibre (DSHE), orientée plutôt vers les comportements non-linéaires de fluides, éventuellement actifs ou avec surface libre, et les phénomènes d’auto-organisation en général (morphogenèse des granulaires, systèmes particulaires inspirés de la matière condensée, colloïdes et transition d’encombrement, etc).
- Dynamique et organisation de la matière molle (DOMM), orientée plutôt vers les matériaux mous visco-élastiques aux propriétés rhéologiques complexes (gels, polymères, mousses etc.), milieux caractérisés par une structure hétérogène, et dont l’organisation et les propriétés dépendent de l’échelle d’observation.
- Physique du vivant, orientée plutôt vers l’étude des processus physiques qui sous-tendent les fonctions biologiques, principalement à l’échelle cellulaire, entre la molécule et le tissu.
- Biofluidique, orientée plutôt vers l’étude des systèmes vivants du tissu à l’organisme, avec des applications à visées médicales.
- Une équipe de théoriciens dont les thématiques couvrent un spectre large de questions fondamentales allant de la physique statistique hors équilibre à la neuroscience, en passant par la matière molle et la matière active.
Cependant les activités de ces équipes se recoupent souvent dans des projets communs aux frontières entre les comportements physiques et/ou biologiques (exemple : comportement de mousses marines, mesures de forces dans des tissus reconstitués, etc.)
[hal-00616273] Steady Couette flows of elastoviscoplastic fluids are non-unique
Date: 24 Nov 2011 - 17:07
Desc: The Herschel-Bulkley rheological fluid model includes terms representing viscosity and plasticity. In this classical model, below the yield stress the material is strictly rigid. Complementing this model by including elastic behaviour below the yield stress leads to a description of an elastoviscoplastic (EVP) material such as an emulsion or a liquid foam. We include this modification in a completely tensorial description of cylindrical Couette shear flows. Both the EVP model parameters, at the scale of a representative volume element, and the predictions (velocity, strain and stress fields) can be readily compared with experiments. We perform a detailed study of the effect of the main parameters, especially the yield strain. We discuss the role of the curvature of the cylindrical Couette geometry in the appearance of localisation; we determine the value of the localisation length and provide an approximate analytical expression. We then show that, in this tensorial EVP model of cylindrical Couette shear flow, the normal stress difference strongly influences the velocity profiles, which can be smooth or non-smooth according to the initial conditions on the stress. This feature could explain several open questions regarding experimental measurements on Couette flows for various EVP materials such as emulsions or liquid foams, including the non-reproducibility that has been reported in flows of foams. We then discuss the suitability of Couette flows as a way to measure rheological properties of EVP materials.
[hal-01131346] X chromosome inactivation and active X upregulation in therian mammals: facts, questions, and hypotheses.
Date: 2 Dec 2020 - 14:48
Desc: X chromosome inactivation is a mechanism that modulates the expression of X-linked genes in eutherian females (XX). Ohno proposed that to achieve a proper balance between X-linked and autosomal genes, those on the active X should also undergo a 2-fold upregulation. Although some support for Ohno's hypothesis has been provided through the years, recent genomic studies testing this hypothesis have brought contradictory results and fueled debate. Thus far, there are as many results in favor as against Ohno's hypothesis, depending on the nature of the datasets and the various assumptions and thresholds involved in the analyses. However, they have confirmed the importance of dosage balance between X-linked and autosomal genes involved in stoichiometric relationships. These facts as well as questions and hypotheses are discussed below.
[hal-00604423] Simulating rare events in dynamical processes
Date: 29 Jun 2011 - 09:50
Desc: Untypical, rare trajectories of dynamical systems are important: they are often the paths for chemical reactions, the haven of (relative) stability of planetary systems, the rogue waves that are detected in oil platforms, the structures that are responsible for intermittency in a turbulent liquid, the active regions that allow a supercooled liquid to flow... Simulating them in an efficient, accelerated way, is in fact quite simple.
[hal-00867285] Colloquium: Mechanical formalisms for tissue dynamics
Date: 26 Sep 2015 - 16:50
Desc: The understanding of morphogenesis in living organisms has been renewed by tremendous progressin experimental techniques that provide access to cell-scale, quantitative information both on theshapes of cells within tissues and on the genes being expressed. This information suggests that ourunderstanding of the respective contributions of gene expression and mechanics, and of their crucialentanglement, will soon leap forward. Biomechanics increasingly benefits from models, which assistthe design and interpretation of experiments, point out the main ingredients and assumptions, andultimately lead to predictions. The newly accessible local information thus calls for a reflectionon how to select suitable classes of mechanical models. We review both mechanical ingredientssuggested by the current knowledge of tissue behaviour, and modelling methods that can helpgenerate a rheological diagram or a constitutive equation. We distinguish cell scale (“intra-cell”)and tissue scale (“inter-cell”) contributions. We recall the mathematical framework developpedfor continuum materials and explain how to transform a constitutive equation into a set of partialdifferential equations amenable to numerical resolution. We show that when plastic behaviour isrelevant, the dissipation function formalism appears appropriate to generate constitutive equations;its variational nature facilitates numerical implementation, and we discuss adaptations needed in thecase of large deformations. The present article gathers theoretical methods that can readily enhancethe significance of the data to be extracted from recent or future high throughput biomechanicalexperiments.
[hal-00530995] Non-linear oscillatory rheological properties of a generic continuum foam model: comparison with experiments and shear-banding predictions
Date: 20 Jun 2012 - 17:53
Desc: The occurence of shear bands in a complex fluid is generally understood as resulting from a structural evolution of the material under shear, which leads (from a theoretical perspective) to a non-monotonic stationnary flow curve related to the coexistence of different states of the material under shear. In this paper we present a scenario for shear-banding in a particular class of complex fluids, namely foams and concentrated emulsions, which differs from other scenarii in two important ways. First, the appearance of shear bands is shown to be possible both without any intrinsic physical evolution of the material (e.g. via a parameter coupled to the flow such as concentration or entanglements) and without any finite critical shear rate below which the flow does not remain stationary and homogeneous. Secondly, the appearance of shear bands depends on the initial conditions, i.e., the preparation of the material. In other words, it is history dependent. This behaviour relies on the tensorial character of the underlying model (2D or 3D) and is triggered by an initially inhomogeneous strain distribution in the material. The shear rate displays a discontinuity at the band boundary, whose amplitude is history dependent and thus depends on the sample preparation.
Autres contacts
Université Paris Diderot - Paris 7
U.F.R. Physique
Bâtiment Condorcet
10, rue Alice Domon et Léonie Duquet
75205 PARIS CEDEX 13