Séminaire café 2022

6 jan Florence Elias (Professeure à l’Université Paris Diderot)
The physics and physical chemistry of marine foam

Very stable marine foams are regularly observed on some coastlines, as a result of the correlation of high wind events and phytoplankton bloom in the water. The role played by these foams in the ecosystem is still unknown, while a significant drop in phytoplankton biomass and biodiversity is observed in seawater when these marine foams appear. We address these issues from a physical and physico-chemical perspective through two questions. Firstly, as liquid foams are known to concentrate many types of particles due to the particle hydrophobicity or size, is it conceivable that phytoplankton, seen as a community of active particles, is also concentrated and therefore retained in the foam ? This question raises the more general question of the transport of active particles in complex environments (confined and potentially non-Newtonian). Secondly, what are the physico-chemical mechanisms at the origin of the high stability of these foams, even though the presence of a high ionic concentration, as is the case in seawater, is known to inhibit the stabilisation of foams ?
In this talk I will present recent results obtained on model systems, ongoing and planned work on this topic.
13 jan Lucia Mandon (Postdoc at LESIA (Meudon))
One year of Martian exploration : news from the Perseverance rover

On the 18th of February 2021, the Perseverance rover of the Mars 2020 mission (NASA) landed at the "Octavia E. Butler" site, on the floor of the 45 km diameter Jezero crater, an ancient Martian lake that once hosted liquid water. The goals of the mission are to characterize past environments at Jezero and search for biosignatures. These objectives will be achieved through the collection of samples to be returned to Earth by the MSR (Mars Sample Return, NASA/ESA) mission and the investigation of the rocks of the crater and beyond using the rover payload. We will present the results of nearly one year exploring the crater floor of Jezero, in particular through the “eyes” of the rover, the SuperCam instrument, which plays a critical role in the exploration strategy as it combines various remote-sensing techniques to investigate the elemental and mineralogical composition of surfaces.
20 jan Laurette Tuckerman (Research Director at PMMH)
Overview of french presidential election
27 jan Pas de séminaire café (PhD defense of Tao)
3 fév Discussion about Tandems
10 fév Antoine Allard (Postdoctoral Researcher at Warwick University)
Towards Artificilia
16 fév Charlie Duclut
Nonlinear and active rheology of cell tissues

Summary : Tissues are assemblies of large numbers of cells, which form a soft active material. Their dynamics are governed by chemical signals between cells, which both coordinate active mechanical processes. In my talk, using vertex-model simulations and a continuum description, I will show how cell-cell rearrangements and active fluctuations make tissues behave as nonlinear viscoelastic fluids. In particular, I will briefly discuss the energetics of cell rearrangements and how chemical work shapes tissues.
17 fév PC Focus
24 fév Jean-Baptiste Gorce (Postdoctoral Researcher at Université de Paris)

Turbulence hydrodynamique 3D générée par des agitateurs magnétiques
Les écoulements turbulents se développent dans différentes situations : vents atmosphériques, courants océaniques ou dans l’industrie. Bien qu’il existe une grande diversité d’écoulements turbulents, ils présentent des similitudes et nécessitent une compréhension approfondie. Nous présentons ici une technique de génération d’écoulement turbulent utilisant des agitateurs magnétiques immergés dans un fluide. Un champ magnétique vertical oscillant transmet de l’énergie cinétique aux agitateurs magnétiques en leur imposant un moment angulaire. L’énergie cinétique des agitateurs magnétiques est ensuite transférée au fluide de manière aléatoire dans l’espace et le temps. L’écoulement généré est statistiquement homogène, stationnaire, isotrope et satisfait les hypothèses de la théorie de Kolmogorov. Les mesures de champ de vitesses montrent que l’énergie cinétique injectée dans le fluide est dissipée par un mécanisme de cascade turbulente auto-similaire.
3 mars Marie Tani

Liquid pinching off from a foamy droplet
Putting some foam on a vertical surface is a ubiquitous situation, for example, when we shave or when we clean a wall. Some animals or insects also use foam in egg-laying or making nests. In such a situation, it seems preferable that the foam stays in the initial position. Moreover, it is not desirable to lose the solution via liquid pinch-off from the bottom of the foam. To address the pinching off condition and mechanism, we conducted model experiments : we confined an amount of foam in a Hele-Shaw cell and observed how the foam behaves under gravity. Two slide-down modes were found, with and without a liquid pinch-off. Furthermore, the onset of the pinch-off mode was theoretically clarified.
10 mars Mathieu Lerouge (PhD Student at Centrale Paris)
Conception de méthode d’explication des solutions produites par des systèmes d’optimisation.
Dans les secteurs de l’industrie et des services, mais également dans la vie quotidienne, nous sommes régulièrement confrontés à des problèmes dits d’optimisation combinatoire (e.g. déterminer le meilleur itinéraire entre deux lieux, planifier les tournées de techniciens mobiles devant réaliser le plus de tâches de maintenance possible en un horizon de temps donné) : afin de résoudre ces problèmes, nous avons recours à des outils numériques qui intègrent des algorithmes d’optimisation. Nous pouvons ensuite prendre des décisions sur la base des résultats fournis par ces systèmes, sans pour autant connaître ou comprendre leur fonctionnement algorithmique.
L’objectif des travaux menés est de concevoir des méthodes afin de générer des explications en réponse aux questions des utilisateurs des systèmes d’optimisation. Pour cette présentation, le problème d’optimisation choisi est la planification de techniciens mobiles. La méthode présentée permet de traiter une question d’un utilisateur parmi une liste de questions possibles et de lui retourner une explication sous forme de texte dans un langage et un vocabulaire accessible.
21 avril PhD students presentations
Benjamin - Joseph Vermeil - Sauraubh Nath
28 avril PhD students presentations
Wu Changsong - Baptiste Lafoux - Chloé Dupuis
5 mai Maxime Guerbois (PIMM, ENSAM Paris)
Application du grenaillage par choc laser aux acier à haute limite d’élasticité

In the frame of transmission components features, gear teeth root load-carrying capacity is one of the key factors in gear design. That is why state of the art on such component regarding materials / processes are thermochemical treatments, enhanced eventually by shot peening post-treatment to enhance fatigue lifetime. Because of the high hardness of nitrided surface introducing additional compressive residual stresses with conventional shot peening request specific conditions and shots. Laser Shock Peening (LSP) technology generate very high pressure on material surface and so introduce higher and deeper compressive residual stress. Today, most of study about laser peening are performed on aluminium or titanium alloys. In this study, samples were 32-CrMoV-13 deep Nitrided steel. The study aim was to identify material behaviour regarding laser peening parameters. This study is performed in the frame of IRT-M2P TRANSFUGE project, which aims to study innovative material and treatment for gear parts.
12 mai PhD students presentations
Camille Aracheloff - Samantha Kucher - Li Zhibo
19 mai PhD students presentations
Aliénor Rivière - Renaud Baillou - Dheeraj Kumar
2 juin Zacchari Ben Meriem (PostDoc at LAAS in Toulouse)
Towards complete mechano-chemical control in Tumor-on-a-Chip

The increasing need for new in vitro technologies to mimick functional pathologies and organs has led to the developpement of new micro-physiological devices. One of these pathology is pancreatic ductal adenocarcinoma cancer (PDAC), a particularly aggressive cancer, with a death toll of 99% after 5 years. As of today, there is no efficient treatment or targeted therapy. The rapid proliferation of the cancerous cells in a confined environment, along with the remodeling of the extracellular matrix, leads to growth-induced mechanical compressive stresses that eventually accumulate in PDAC. Although mechanical stresses alter cellular physiology and cancer treatments, we further hypothesize that cancer cells could modulate their response to chemical signals in presence of mechanical stresses. In this context, it is not known if specific mechanical stresses can either promote or restrain tumor progression.
To address these questions, we are developing one of the first experimental platform based on microfluidics that permits the study of cancer cells in a perfectly controlled environment. More specifically, we can include a population of cells (whether separated or agregated) in a extracellular matrix (ECM) of our chosing and confine the total in our device. We can then subjugate this ensemble to a single or a gradient of mechanical compressions on several locations, therefore altering the intensity of the ECM and compressing the cells. Our microfluidic platform also enables a dynamical control of the chemical environment. This allows us to perform operations such as chemical gradients or the coupling between mechanical and biochemical signals. Moreover, innovative microfabrication approaches even allow us to recover the sample of interest (such as patient-derived organoid) to perform subsequent analysis. We are currently using this experimental platform to determine how a cellular biological response is altered following a mechanical environments.
Altogether, our work can bridge the biochemical, genetic and mechanical characteristics of cancer cells. Our device can eventually be used to understand cancer progression and explore novel therapeutic strategies incorporating mechanics.
9 juin PhD students presentations
Juan Pimienta - Sébastien Gomé - Mathieu Letrou
16 juin Sylvain Patinet’s HDR
23 juin PhD students presentations
Peixin Zhang - Gatien Polly - Federigo Ceraudo

Haut de page

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