ESPCI web site
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 |
| 30 juin | Feedback on the "Vie de labo" activity at CoDoc 2022 |
| 7 juillet | PhD students presentations Yutong Cui |
| juill-août | Summer vacations |
| 1er sept | Amir Porat (PhD student at Tel-Aviv University) On the mechanical origins of waving, coiling and skewing patterns in Arabidopsis thaliana roots We present novel simulations of the well-known waving, coiling and skewing patterns presented by roots of Arabidopsis thaliana when grown on stiff agar substrates that are tilted with respect to gravity. By creating a novel numerical solver based on a quasi-static integration scheme and a Cosserat rod integrator, we are able to investigate in-silico how growing rod-like organs mechanically interact with their environment for the first time. Our simulations confirm previous theories suggesting that waving and coiling result from the combination of active gravitropism and passive interactions between the root and the tilted plane, while skewing is related to an intrinsic twist profile (also known as cell file rotation). Besides successfully replicating many experimental observations, we develop analytic models relating skewing angles, and the transition between waving and coiling patterns, to the tilt angle of the substrate. Furthermore, we compare our simulation results to quantitative data from a number of published experimental papers and find a good agreement. |
| 8 sept | PhD students presentations Anumita Jawahar - Tristan Auregan - Maïka Saint-Jean |
| 15 sept | PhD students presentations Pas de séminaire café - Conférences internationales |
| 22 sept | PhD students presentations Andréa de la Sen - Xavier Mousset |
| 29 sept | PhD students presentations Maud Dobler - Pierre-Ewen Lecoq - Lars Kool |
| 6 oct | PhD students presentations Guillaume Sintes - Magdalena Kopec |
| 13 oct | PhD students presentations Wissem Kathla - Lucile Rabiet - Manon Quiros |
| 20 oct | Elisabeth Bouchaud (La Reine Blanche) Arts et Sciences |
| 27 oct | Post PhD’s adventure trails Charles Duchene - Microfluidic Scientist at Ixaka |
| 3 nov | No coffee seminar (Vacances de la Toussaint) |
| 10 nov | Pablo Cobelli (Professor at the Physics Department (UBA) and researcher at CONICET (Argentina)) Particle transport in turbulent flow |
| 17 nov | Santiago Benavides (Postdoc at Warwick University) Modeling turbulent bands in Plane Couette Flow Despite the success of models capturing the dynamics of turbulent puffs and slugs in pipe flow, the large-scale organization of turbulent structures in extended two-dimensional domains, such as in Plane Couette Flow or Plane Poiseuille Flow, remains a challenge. In this work, we take an important step towards this direction by introducing a one-dimensional model of Plane Couette Flow in the tilted configuration which is able to reproduce the phenomenology of banded turbulent structures. We arrive at the model through a series of approximations and assumptions which we validate using direct numerical simulation results of ’Model Waleffe Flow (stress-free boundary version of Plane Couette Flow). In this talk, I will go through these assumptions, show the resulting model equations, and demonstrate their ability to reproduce all the known phenomena observed in tilted geometry configurations of Plane Couette Flows. Finally, I will discuss the extension to a fully two-dimensional model. |
| 24 nov | Post PhD’s adventure trails Lucie Ducloué - H2E director for energy management and carbon intensity |
| 1 dec | Post PhD’s adventure trails Guillaume Dupeux - Manager at STMicroelectronics |
| 8 dec | PhD Defense of Maika Saint Jean 14h in ESPCI amphitheater |
| 15 dec | Foie Gras Party |
| 22-29 dec | Christmas Holidays |
