Séminaire café 2021

28 janvier Anumita Jawahar (Stagiaire M2 au PMMH)
Article presentation : "Vortex arrays and ciliary tangles underlie the feeding–swimming trade-off in starfish larvae" (Nature, 2016)
4 février Botond Tyukodi (Post-doctorant Brandeis University)
Size control and escape mechanisms in geometrically frustrated assemblies

The self-limited assembly of building blocks into structures with large, but well-defined finite sizes, is an essential capability of biological systems. Developing human-engineered building blocks with a similar ability to undergo self-limited assembly is of great interest in nanotechnology. Recently, it has been theoretically proposed that self-limited assembly can be achieved through ‘geometric frustration’, in which the preferred local packing of subunits is incompatible with their preferred large-scaleassembly structure.
In this talk we describe a computational investigation of geometrically frustrated assembly that is motivated by ongoing experiments in which building blocks are designed from DNA origami. Specifically, we consider triangular subunits that self-assemble into a hexagonal array, but have interaction geometries that favor formation of catenoid structures. The resulting negative Gaussian curvature is incompatible with hexagonal order, leading to geometric frustration. We use dynamic Monte Carlo simulations and free energy calculations to demonstrate that this incompatibility can lead to equilibrium self-limited assembly in some parameter regimes. We also identify mechanisms by which the system can escape self-limitation in other parameter regimes, and we identify two relevant dimensionless parameters controlling the equilibrium behavior. The first parameter controls the self-limited size of the catenoids, whereas the second controls their brittleness.
11 février Pas de séminaire : PC Focus
25 février Adam Anglart (Doctorant au PMMH)
Propagating localized structure in a 1D Faraday experiment
04 mars Pas de séminaire : soutenance de Manon L’Estimé
11 mars Ludovic Bellebon (Doctorant au PMMH)
Characterization of cells acoustic properties
18 mars Julien Lehuen (Doctorant à l’INRAE Montpellier)
Rhéophysique de colonnes granulaires perturbées par un intrus mécanique
01 avril Présentation doctorants première année
08 avril Présentation doctorants deuxième année
15 avril Pas de séminaire café
22 avril Suite présentation doctorants deuxième année
29 avril Présentation doctorants troisième année
6 mai Pas de séminaire café
13 mai Jour Férié
20 mai Benoit Manchon (Doctorant à l’INL, Lyon)
Design and Fabrication of Ferroelectric Artificial Synapse for Neuromorphic Computing
27 mai PMMHouches
3 juin Camille Grange (Ingénieure formulation quantique à la SNCF)
Formulations et Résolutions Quantiques d’un Problème de Conception de plan de transport ferroviaire
10 juin Abel Rangel (Doctorant à l’ISA, Lyon)
Diabetes Research for AI solutions in the Easy wellbeing, Easy prevention and Easy care of hypo and hyperglycemia using state-of-the-art techniques and actual market devices
17 juin Chloé Dupuis & Baptiste Lafoux
Présentation de PMMHouches
24 juin Nathan Jeger-Madiot
Self-organization and culture of Mesenchymal Stromal Cell spheroids in acoustic levitation
1er juillet Manon l’Estimé (Post-doctorante au PMMH)
Presentation of the discussion held in PMMHouches about the lab life
8 juillet Paul Bienvenue (Stagiaire 3A de l’ESPCI)
Experimental study of nonlinear hydrodynamic effects on static buoys ; application to wave energy conversion
Supervised by Gatien Polly (Biomim team)
15 juillet Pas de séminaire café - Pont National
22 juillet Niels Sageaux (Stagiaire 3A de l’ESPCI)
Baromorphic acoustic lens
Supervised by José Bico (Mecawet team)
29 juillet - 9 sept Summer Break
09 sept Sergio Lembo (Post doc at the University of Heidelberg)
Membrane-to-Cortex Attachment regulates cell cortex architecture and mechanics

The plasma membrane and the underlying actomyosin cortex constitute the surface of animal cells, and their mechanical properties are key for a plethora of cell processes. Although they are often studied as independent structures, the plasma membrane and the cortex are physically tethered to each other via linker proteins, globally referred to as membrane-to-cortex attachment (MCA). MCA contributes to membrane tension and regulates biological processes such as cell migration and stem cell differentiation. Nevertheless, it remains the most elusive element of the animal cell surface.
Aiming at investigating MCA in the context of cell surface mechanics, we have developed artificial signaling-inert linker proteins to specifically perturb it. Strikingly, we have found an unforeseen role for MCA in the regulation of cortex mechanics. Specifically, it modulates cortical tension and cortical stiffness in a density-dependent manner. We further employed in-cell cryo-electron tomography to decipher how MCA affects the architecture of the cortex in cells. Finally, we show the relevance of our findings for early mouse embryo cell specification.
16 sept Antoine Gaillard (Post doc at the University of Amsterdam)
What determines the drop size in sprays of polymer solutions ?

The fragmentation of a liquid jet or sheet into droplets is a complex process known as spraying which involves different hydrodynamic instabilities. Understanding how the droplet size distribution depends on external control parameters is of paramount importance in industry (inkjet printing, spray painting), medicine (drug delivery) and agriculture (crop spraying) for instance. More specifically, in agricultural spraying, droplets smaller than 100 micrometers do not reach the target plant as they are blown away by the wind, causing environmental hazards. It has been shown that polymer additives could be used to reduce the amount of these small droplets while also increasing the efficiency of droplet deposition on hydrophobic plants by reducing the amount of bouncing and splashing during droplet impact.

In this fundamental study, we look at how viscoelasticity affects the properties of sprays. We find that polymer addition results in the formation of bigger droplets on average, as well as a broader distribution of sizes compared to the pure Newtonian solvent. We link these changes in droplet sizes to changes in the properties of the spraying sheet extruded from the nozzle, such as the length beyond which the sheet breaks up and the wavelength of the “flapping” instability responsible for the sheet fragmentation.
23 sept Juan Cruz (Intern at PMMH)
Isolated turbulent bands in Couette-Poiseuille flow

Dans les ecoulements cisaillés et pour les nombre de Reynolds intermédiaires, il existe un regime de bandes turbulentes et laminaires alternantes. Une variante de ce régime a été recemment decouverte dans l’écoulement de Poiseuille, dans lequel des bandes sont isolées et leur têtes (en aval) émettent des ondes. Nous avons voulu voir numériquement si ce régime pouvait aussi exister dans l’écoulement hybrid de Couette-Poiseuille qui est étudié expérimentalement au PMMH.

In wall-bounded shear flows at intermediate Reynolds numbers, there exists a regime of alternating turbulent-laminar bands. A variant of this regime was recently discovered in plane Poiseuille flow, in which the bands are isolated and their downstream heads emit waves. We wished to determine numerically whether this regime could also exist in the hybrid Couette-Poiseuille flow, which is studied experimentally at PMMH.
30 sept Moulin d’Andé
07 oct Valentin Laplaud (Post doc at LadX)
Rain dispersal of Marchantia polymorpha gemmae
14 oct Hector Ignacio (PhD student at PMMH)
Bacteria swimming in complex fluids
21 oct Margot (Moulin d’Andé’s Photographer)
28 oct Trailers of APS Division of Fluid Dynamics

- Saurabh Nath (Postdoc at PMMH)
When bubbles don’t die

- Baptiste Lafoux (PhD Student at PMMH)
To see or not to see

- Vincent Stin (PhD Student at PMMH)
Swimming snakes vortices highlighted with volumetric velocimetry
4 nov Training for Presentations at APS Division of Fluid Dynamics (10 min each)

- Sébastien Gomé (PhD student at PMMH)
Wavelength selection in transitional turbulence in shear flows

Transition to turbulence in shear flows is characterized by oblique turbulent bands. In plane Couette flow, a spacing of λ=40h between the bands naturally arises from featureless turbulence. Below 40h, turbulent bands interact too strongly to coexist naturally, but can be produced in periodic domains of restricted lengths and fixed tilt. The stability of such fixed-wavelength patterns is studied as a function of Reynolds number, as well as the mechanisms giving birth to a wavelength selection from featureless turbulence.

- Aliénor Rivière (PhD student at PMMH)
Origin of the sub-Hinze scale bubble production in turbulence
11 nov WWI Armistice Day
18 nov Training for Presentations at APS Division of Fluid Dynamics (10 min each)

- Adithia Jha (PhD student at PMMH)
Coalescence of drops on soft gels - a delay !
25 nov Filippo Agnelli (PhD student at LMS)
Shape-shifting thin panels from 3D printed undulated ribbon lattice

Materials that change their shape in response to external stimuli open up new prospects for efficient and versatile design and shaping of three-dimensional objects. Here, we present a novel class of micro-structures exhibiting an extension-bending coupling (EBC) effect, that can be harnessed as an elementary building block for shape-shifting panels. They are built with a single material as a network of undulated ribbons, parametrised using b-spline surfaces. The undulations feature an asymmetry along the height that is leveraged to obtain the EBC mechanism. The deformations mechanisms of both single and connected undulated ribbons are analysed using the finite element method to explain the main features of the EBC mechanism. While single undulated ribbons do not exhibit specific coupling mechanics, we demonstrate that their interconnection starts the mechanism. For a particular micro-structure of the proposed class, the elastic response is investigated both under small strain assumption combining two-scale homogenization with Kirchhoff-Love plate theory, and at finite strains relying on numerical analysis. The range of achievable EBC ratio is then assessed with respect to the geometric parameters of the unit cell.
Patterned specimens are manufactured using a commercial FFF Ultimaker 3D printer and are mechanically tested at finite strain up to 20%. The displacement measured by point tracking match the predictions from the finite element simulations and indicate that the structure maintain its properties at finite strain. Moreover, a tensile test load with point-like boundary is proposed to highlight exceptional out of plane displacement. The proposed ribbon based architectures can be combined with active materials for the actuation of shape shifting structures, like soft robots, control systems and power devices.
2 dec Pas de séminaire café
9 dec Doron Grossman (Postdoc at LadHyx)
Shape and Function

The shape and function of many many chemical and biological systems are tightly related to each other and to the shapes of the discrete building blocks that form them. In this talk I will give two examples, one chemical, and one biological, showing how a macroscopic continuous description arise in discrete systems. In turn, this description allows us to study the mechanical and statistical behaviour of such systems, and describe their material properties.
16 dec Gabriel Dumy (CEO of Kolibri)
How to create a startup after a PhD

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Informations Pratiques

Laboratoire : 01 40 79 45 22
Directeur : Damien Vandembroucq
Codirecteur : Philippe Petitjeans
Administratrice : Frédérique Auger (01 40 79 45 22)
Gestionnaire : Claudette Barez (01 40 79 58 53)
Courriel : dir (arobase) pmmh.espci.fr