ESPCI web site
Le séminaire hebdomadaire du laboratoire PMMH a lieu tous les vendredis à 11h, au premier étage Barre Cassan, campus Jussieu (plan).
Stéphane Perrard
Etienne Reyssat
Virgile Thiévenaz
PMMH
BARRE CASSAN
BAT A 1ER ETAGE CASE 18
7 QUAI SAINT BERNARD
75005 PARIS
France
Tel : (33) 1 40 79 45 22
Séminaire PMMH – Daniel Tam (TU Delft)
Fluid mechanics at biological interfaces : from membranes to motile organisms
Biology is wet and active. On the micron-scale, the complex interactions at the interfaces between fluids and soft, deformable biological matter give rise to unexpected fluid mechanics. We use recently developed optical tools, from optical tweezers to multiview microscopy to unravel surprising fluid mechanics at biological interfaces, from biological membranes to motile organisms.
1. Starting at the smallest scale, we will first discuss the fluid mechanics of biological membranes. A cell's interactions with the environment are mediated by its cellular membrane. This nanometer-thick, liquid crystalline structure is mostly composed of a lipid bilayer, which serves as a scaffold for embedded proteins and other macromolecules. In this study, we use optical tweezers to both apply and measure local forces on free-standing lipid bilayers within microfluidic channels. These measurements give insight into the boundary conditions at an interface between a fluid and a lipid bilayer.
2. We will then consider the fluid mechanics around motile ciliated cells. There, Stokes equations are commonly used to model the hydrodynamic flow around cilia. Using a new velocimetry methods, combining optical trapping and Kalman filtering, we investigate the validity of the zero Reynolds number approximation. We find that beating cilia generate a flow, which fundamentally differs from the stokeslet field predicted by Stokes equations. This indicates that the quasisteady approximation and use of Stokes equations for unsteady ciliary flow are not always justified and the finite timescale for vorticity diffusion cannot be neglected.
3. Considering interactions between motile unicellular organisms swimming through complex environments, they often interacting with solid surfaces. Their swimming is influenced by the proximity to solid substrates, through hydrodynamic and steric interactions. These interactions directly influence the cell population density distribution and the residence time in the vicinity of the surface. Swimming cells are recorded simultaneously by four separate cameras and triangulated in three-dimensions. Our results provide evidence of the existence of a long-range hydrodynamic interaction, which induces orbiting behaviour in the near-surface region.
4. If time allows, I will discuss recent rheological measurements of active suspensions. The shear viscosity of contractile suspensions of several volume fractions has been experimentally measured at different temperatures and shear rates. We show that temperature affects the rheology through the motility of the particles. As a result, the suspension shows unexpected rheological response to temperature such as `heat-thickening, whereby the stresses in the system increase with temperature. We find that motility of the particles can trigger a glass-like transition in the suspension due to the emergence of motility induced stresses that resembles a yield stress. Our study suggests that the emergence of this yield-like stress induced by motility is at the origin of the different rheological properties of the active suspension.
- Archives des anciens séminaires
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Séminaires récents (6)
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Séminaire PMMH – Vincent Bertin (IUSTI, U. Aix-Marseille)
Vendredi 6 juin de 11h00 à 12h00 - Salle réunion PMMH 1
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Séminaire PMMH – Vincent Bertin (IUSTI, U. Aix-Marseille)
Vendredi 6 juin de 11h00 à 12h00 - Salle réunion PMMH 1
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Séminaire PMMH - José Halloy (LIED, Univ. Paris Cité)
Vendredi 23 mai de 11h00 à 12h00 - Salle réunion PMMH 1
Energy Transition and Earth System Dynamics : Quantifying Long-Term Sustainability Trajectories for Human Societies
This talk explores how current industrial technologies - linear, extractive, and ecologically disruptive - must be replaced by systems designed in harmony with the Earth's living metabolism. Framing the planet as a dynamic, interdependent system rather than a passive resource pool leads to a fundamental rethinking (…) -
Séminaire PMMH - José Halloy (LIED, Univ. Paris Cité)
Vendredi 23 mai de 11h00 à 12h00 - Salle réunion PMMH 1
Energy Transition and Earth System Dynamics : Quantifying Long-Term Sustainability Trajectories for Human Societies
This talk explores how current industrial technologies - linear, extractive, and ecologically disruptive - must be replaced by systems designed in harmony with the Earth's living metabolism. Framing the planet as a dynamic, interdependent system rather than a passive resource pool leads to a fundamental rethinking (…) -
Séminaire PMMH - Julien Scheibert (LTDS, EC Lyon)
Vendredi 16 mai de 11h00 à 12h00 - Salle réunion PMMH 1
Metainterfaces : how to design a rough contact that obeys a specific friction law ?
Many devices, including touchscreens and robotic hands, involve frictional contacts. Optimizing those devices requires fine control of the interface's friction law. We lack systematic methods to create dry contact interfaces whose frictional behaviour satisfies preset specifications. In this seminar, I will present (…) -
Séminaire PMMH - Julien Scheibert (LTDS, EC Lyon)
Vendredi 16 mai de 11h00 à 12h00 - Salle réunion PMMH 1
Metainterfaces : how to design a rough contact that obeys a specific friction law ?
Many devices, including touchscreens and robotic hands, involve frictional contacts. Optimizing those devices requires fine control of the interface's friction law. We lack systematic methods to create dry contact interfaces whose frictional behaviour satisfies preset specifications. In this seminar, I will present (…)
Instructions générales pour les conférenciers
Le public du séminaire est très hétérogène (rien qu’au PMMH nous travaillons sur des thématiques très diverses, mécanique des fluides, des milieux granulaires, des solides, physique statistique, physique du mouillage, micro-fluidique, biophysique,...) l’objectif est donc de ne pas faire un séminaire trop spécialiste : au moins la première moitié du séminaire à un niveau accessible pour celui qui ne connaît rien sur le sujet.
Le séminaire a lieu à 11h. rendez-vous 15 minutes avant pour installer et tester la projection.
Le séminaire dure environ 45 minutes pour laisser un peu de temps pour discuter à la fin.
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- Séminaire de Mécanique d’Orsay (page web FAST)
- Séminaire de Mécanique d’Orsay (page web LIMSI)
- Séminaire de Mécanique des Fluides de l’Institut Jean le Rond d’Alembert
- Séminaires du laboratoire MSC, Paris VII
- Séminaires Gulliver
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