Un article issu d’une collaboration entre l’équipe Théorie de la Matière Condensée, l’Université de Twente et l’ESPCI a fait l’objet d’une publication dans Physical Review Letters (19 janvier 2023). L’article s’intéresse à la dispersion de particules sous l’effet combiné du mouvement Brownien et d’un écoulement au voisinage d’une paroi solide. Cette étude met en évidence le rôle crucial joué par les surfaces dans le processus de dispersion. En particulier, il est montré que la répulsion électrostatique et la perte de particules survenant aux parois réduisent drastiquement la dispersion des nanoparticules.

Référence de l’article :
Nanoparticle Taylor Dispersion Near Charged Surfaces with an Open Boundary
Alexandre Vilquin, Vincent Bertin, Elie Raphaël, David S. Dean, Thomas Salez, and Joshua D. McGraw
Phys. Rev. Lett. (2023)

Edward Laird
Professor, Physics Department | Lancaster University
https://www.lancaster.ac.uk/physics/about-us/people/edward-laird

“A coherent mechanical oscillator pumped by a suspended quantum dot”

Suspended carbon nanotubes are mechanical resonators with low mass, high compliance, and high quality factor, which make them sensitive detectors for tiny forces and masses. The most sensitive way to measure such a resonator is by defining a quantum dot in the suspended segment and monitoring the displacement via the current through the dot. However, the force exerted by individual electrons tunnelling through the dot also creates strong electrical backaction. We have measured an extreme limit of this backaction, in which the current excites spontaneous mechanical oscillations.

Our device consists of a vibrating carbon nanotube spanned across a trench. A pair of tunnel barriers defines a quantum dot, whose conductance depends on the displacement. With low coupling, the quantum dot is a sensitive transducer of driven mechanical vibrations. At intermediate coupling, electrical back-action damps the vibrations. However, at strong coupling, the resonator can enter a regime where the damping becomes negative; it becomes a self-excited oscillator.

This electromechanical oscillator has many similarities to a laser, with the population inversion provided by the electrical bias and the resonator acting as a phonon cavity. We characterize the resulting coherence and demonstrate other laser characteristics, including injection locking and classical squeezing.

Reference:
A coherent nanomechanical oscillator driven by single-electron tunnelling, Y. Wen et al., Nature Physics 16 75 (2020)

Référence de l’article :
Hydrodynamic Synchronization of Chiral Microswimmers
Sotiris Samatas and Juho Lintuvuori
Phys. Rev. Lett. (2023)

Référence de l’article :
Anomalous Diffusion of Deformable Particles in a Honeycomb Network
Zaiyi Shen, Franck Plouraboué, Juho S. Lintuvuori, Hengdi Zhang, Mehdi Abbasi, and Chaouqi Misbah
Phys. Rev. Lett. (2023)

I obtained a PhD in Physics from Université Paris-Saclay, studying on the role of actin cytoskeleton on lipid membrane nanotubes. This work was developed in collaboration with Clément Campillo in Laboratoire Analyse, Modélisation, Matériaux pour la Biologie et l’Environnement (LAMBE), in Évry and with Cécile Sykes in Laboratoire Physico-Chimie Curie (PCC), Curie Institute, in Paris. This work is freely available online.

For this work, I have been awarded two PhD prices:

• C’Nano 2020, in the Interdisciplinary category (interview here)
• Groupe d’Études des Membranes (GEM 2021)

I then joined Marco Polin‘s group at the Physics Department at University of Warwick, in England, where I worked on understanding how the model swimming organism Chlamydomonas reinhardtii, a biflagellated microalgae, responds to light stimulus.

My current research interests, in collaboration with an interdisciplinary network, are focused on the understanding of photosynthesis adaptation to environmental cues, such as complex mechenical and/or light environments. I currently teach undergraduate courses in Physics, and “teaching degree” courses.

Arnaud Casteigts
Professeur, LABRI, Université de Bordeaux
https://www.labri.fr/perso/acasteig/

“Introduction to computational complexity and distributed algorithms”

In this talk, I will give a brief introduction to two areas of theoretical computer science. The first is computational complexity, where the goal is to understand how much resources (in time or space) are needed to solve a given problem. The most famous question in this area is certainly the P versus NP question. The second part will briefly present the field of distributed algorithms, which studies how several entities may interact in order to solve a common problem in absence of central authority. Covering each of these fields in less than half an hour is of course impossible, the goal is merely to give some ideas of the type of questions computer scientists study in such fields, some of which are certainly related to questions in physics.

Matthieu Raoux
Associate Professor, HDR
University of Bordeaux, Institute of Chemistry & Biology of Membranes & Nano-objects, CBMN, UMR 5248 CNRS
http://www.cbmn.u-bordeaux.fr/26-biologie-et-biotechnologie-mecanismes-et-regulation-du-transport-de-vesicules.html#trombinoscope
https://sts.u-bordeaux.fr/actualites/matthieu-raoux-laureat-prix-auguste-loubatieres-2022

“Decoding microorgan function with transdisciplinary tools for biomedical applications”

Better understanding and curing living organs requires the combination of transdisciplinary expertise. The islets of Langerhans in the pancreas are fascinating, vital and complex microorgans, ~100 µm in diameter, which regulate blood glucose, nutrient metabolism and are involved in diabetes, the most common chronic metabolic disease. In this talk, I will present our transdisciplinary works since 2008 between biology, microelectronics, polymer chemistry, electrochemistry, material science, microfluidics, control theory and clinics to develop high resolution sensors with automatic real-time analysis of islet function. Our approaches have already provided major advances in understanding the physiology and pathophysiology of these microorgans and open biomedical applications in the field of diabetes.

REFERENCES

Abarkan et al. (2022) Vertical organic electrochemical transistors and electronics for low amplitude micro-organ signals. Advanced Science. 9:e2105211.
Fischer KL et al. (2021) Pancreatic α and β cells: Best enemies or partners for life? Med Sci. 37(8-9):752-758.
Jaffredo et al. (2021) Dynamic uni- and multicellular patterns encode biphasic activity in pancreatic islets. Diabetes. 70(4):878-888.
Olcomendy et al. (2022) Integrating an islet-based biosensor in the artificial pancreas: in silico proof-of-concept. IEEE Trans Biomed Eng. 69(2):899-909.
Perrier R et al. (2018) Bioelectronic organ-based sensor for microfluidic real-time analysis of the demand in insulin. Biosens Bioelectron. 117:253-259.a

Karim Ramdani
Directeur de recherches à l’INRIA, Institut Elie Cartan, Université de Lorraine
Mathématicien, Membre du Collège “Publications” du Comité pour la Science Ouverte
https://karim-ramdani.perso.math.cnrs.fr/
https://iecl.univ-lorraine.fr/membre-iecl/ramdani-karim/

“Edition scientifique : un rapide survol des évolutions en cours”

Durant cet exposé, je présenterai les différents modèles économiques en vigueur dans l’édition scientifique et dresserai un panorama des évolutions en cours. Je m’intéresserai notamment au libre accès dans toutes ses versions : dépôts en archives ouvertes (voie verte) ou publications en libre accès (voie dorée et voie diamant). J’insisterai plus particulièrement sur les risques que présente l’émergence du modèle auteur-payeur. Enfin, je conclurai en évoquant quelques pistes de solutions possibles à l’échelle individuelle et institutionnelle.

Référence de l’article :
Near-critical spreading of droplets
Raphael Saiseau, Christian Pedersen, Anwar Benjana, Andreas Carlson, Ulysse Delabre, Thomas Salez et Jean-Pierre Delville
Nature Communications (2022)

Sebastian Volz
Laboratory for Integrated Micro Mechatronic Systems, CNRS-IIS,
The University of Tokyo, Tokyo 153-8505, Japan
https://limms-tokyo.org/

“Surface Phonon-Polaritons as Efficient Heat Carriers”

Recent studies showed that surface phonon-polaritons, i.e. evanescent electromagnetic waves propagating along the surface of polar dielectric materials [1] [2], may potentially serve as novel heat carriers to enhance the thermal performance in micro- and nanoscale devices. This seminar will expose the significant contribution of these carriers to thermal conductivity in ultra-thin (<100nm) films [3], but also to radiation, yielding SuperPlanckian emission and absorption between surfaces of larger scales (10mm).

Acknowledgements: This work is supported by CREST JST, Grant JPMJCR19Q3 and JPMJCR19I1.

References
[1] D.-Z Chen, A. Narayanaswamy, and G. Chen, Phys. Rev. B 72, 155435 (2005).
[2]J. Ordonez-Miranda, L. Tranchant, T. Tokunaga, B. Kim, B Palpant, Y. Chalopin, T. Antoni, and S. Volz, J. Appl. Phys. 113, 084311 (2013).
[3] Y. Wu, J. Ordonez-Miranda, S. Gluchko, R. Anufriev, D. De Sousa Meneses, L. Del Campo, S. Volz, and M. Nomura, Science Advances 6(40):eabb4461, (2020).

Etienne Rolley
Professeur à l’Université Paris Cité, Laboratoire de Physique de l’ENS
https://scholar.google.com/citations?user=CNR_IbYAAAAJ

“Cavitation in nanopores”

Cavitation is the mechanism by which a liquid breaks under tension. It occurs in engineering (ultrasonic cleaning, erosion of ship propellers…) as well as in the natural sciences (gas embolism in trees, pistol shrimp…).
In the cavities of a saturated porous material, the liquid is also submitted to tension when the liquid evaporates. In this case, it was long considered that evaporation occurs by recession of the menisci defining the saturated region. It has been realized recently that the liquid can also cavitate inside the pores, for example during the drying of concrete. But distinguishing recession and cavitation is tricky if the topography of the pore network is complex.
We first used porous alumina, which has independent cylindrical pores, and developed a simple technique to reduce the pore opening to promote cavitation evaporation. This allowed us to obtain a direct proof of the existence of cavitation in nanopores. Paradoxically, this system, which has a very large specific surface area, proved to be a system of choice for studying homogeneous cavitation. When the pore diameter is larger than 10 nm, the nucleation rate measurements are in perfect agreement with the classical theory of nucleation provided that the surface tension is corrected to take into account the curvature of the interface. Using this correction, it is therefore possible to use a simple capillary model for a liquid-vapor interface with a curvature radius as small as 1 nm.
We have also studied porous silicon, for which recent experiments seemed to indicate that evaporation takes place by heterogeneous cavitation. We show that, as for alumina, homogeneous cavitation and meniscus recession are sufficient ingredients but that the evaporation scenario is very dependent on the disordered structure of the pore network.

Christophe Humbert
CNRS, Université Paris-Saclay, Institut de Chimie Physique
http://www.lcp.u-psud.fr/spip.php?page=fiche_identite&prenom=Christophe&nom=Humbert

“Nonlinear vibrational and electronic spectroscopy at interfaces: a probe traveling from the atom to complex systems”

Surfaces and interfaces play a vital role in Physics and Chemistry because they are the place where fundamentals reactions occur between molecules when two materials differing by their nature and/or their physical phase are in interaction. Vibrational spectroscopies such as IR and Raman are nondestructive analysis tools of in situ chemistry at interfaces but when considering monolayers or less, they may suffer from their lack of sensitivity to discriminate between “bulk” and “surface-adsorbed” molecules. Nonlinear optics and especially Two-Colour Sum-Frequency Generation (2C-SFG) spectroscopy offers a solution to overcome this issue. As showed in this presentation, after establishing the main principles governing this specific technique, we will see that 2C-SFG can be applied to address fundamental questions related to heterogeneous chemistry, interfacial electrochemistry, catalysis and more recently metal and semiconducting nanomaterials [1] within an original theoretical framework based on Feynman loop diagrams unifying Optics and Condensed Matter Physics [2]. In fact, the particular selection rules of this vibro-electronic spectroscopy gives access to unique and complementary information with respect to the traditional optical investigation probes.