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Accueil > Équipes > Physique Statistique et Modélisation > Seminaires du groupe

Seminaires du groupe

par Romain Mari - publié le , mis à jour le

Les séminaires du groupe se déroulent habituellement dans la salle de lecture du LIPhy

A venir


- Thursday, November 29, 11:00
Cesare Nardini

Cluster phases and bubbly phase separation in active fluids

Active agents are able to extract non-thermal energy from the environment and dissipate it to self-propel. It is well known that large assemblies of purely repulsive ones, can undergo bulk liquid-vapor phase separation. In experiments and large-scale simulations, however, more complex steady states are often seen, comprising a dynamic population of dense clusters in a sea of vapor, or dilute bubbles in a liquid. 

 

In this talk, we show that these microphase separated states should be expected generically in active matter, without any need to invoke system-specific details. We show this by extending the phi^4 field theory of passive phase separation to allow for all local currents that break detailed balance at leading order in a gradient expansion. Microphase separation is explained by the fact that the classical Ostwald process, that would normally drive bulk phase separation to completion, can be reversed.

We conclude the talk discussing the transition from bulk to microphase separation beyond mean-field level. One loop dynamical renormalization group analysis shows that it probably belongs to a new non-equilibrium universality class.

 

The talk is based on :

- E. Tjhung, C. Nardini, M.E. Cates, Phys. Rev. X 8, 031080, 2018

- F. Caballero, C. Nardini, M.E. Cates, arXiv:1809.10433, 2018


- Thursday, January 10, 11:00
Vivien Lecomte

TBA


- Thursday, February 07, 11:00
Baoshuang Shang

Stretched mechanical response in a supercooled liquid near glass transition, local versus global.

Amorphous materials have a rich relaxation spectrum which is usually described in terms of alpha, beta, and possibly more complex relaxation mechanism. In this work, we investigate the local dynamic modulus spectrum in a model glass just above glass transition temperature by performing a mechanical spectroscopy analysis using molecular dynamics. We find that the spectrum, at the local as well as on the global scale, can be well depicted by Cole-Davidson formula in the frequency range explored with simulations. Surprisingly, the Cole-Davidson stretching exponent does not change with the size of the local region that is probed. The local relaxation time displays a broad distribution, as expected based on dynamic heterogeneity concepts, but the stretching is obtained independently of this distribution. We find that the size dependence of local relaxation time and modulus can be well explained by the elastic shoving model.

Séminaires passés

2018


- Thursday, July 05, 11:00
Marc Joyeux

Role of salt valency in the switch of H-NS proteins between DNA-bridging and DNA-stiffening modes


- Thursday, July 12, 11:00
Victor Purello (Mar del Plata and Bariloche)

Studying the dynamics of massive interfaces

Interfaces are ubiquitous and can be seen in phenomena as large asforest fires, or as small as domain walls in ferromagnetic materials.In our work, we describe the latter by developing models and runninglarge-scale simulations using GPGPU to test our predictions. We havestudied interfaces by modeling them as driven elastic manifolds inquenched random media, where we analyzed the role of the elasticity,the disorder and different thermal effects. Now we are consideringinterfaces with mass, which could play the same role as the memoryeffects induced by the phase in spintronic models. The inertial termis already giving us exciting results as, for instance, a lowercritical force for the depinning transition, or the possible presenceof a critical mass.


- Tuesday, July 17, 14:00
Pinaki Chaudhuri, visitor of the PSM group this month

Thermal and allied transport in glass-forming materials


- Thursday, September 27, 11:00
Takahiro Nemoto (ENS, Paris)

Cloning algorithm to measure large deviation functions of dynamical quantities : principles & applications

Large deviations of non-equilibrium time-extensive quantities have been extensively studied in the last decade in systems ranging from (a)thermally fluctuating particles (Brownian particles, biological motors, Granular particles…), exactly solvable lattice gas models (ASEP, KPZ, KCMs...) as well as high-dimensional chaotic dynamics (FPU chain, climate model,…). By definition, studying large deviations is difficult since the fluctuations leading to their occurrence are hardly observed. In this seminar, I will present an algorithm which allows the observation of these rare events in numerical simulations. The algorithm is based on population dynamics (a.k.a. splitting or diffusion quantum Monte-Carlo method) [1] : an ensemble of copies of the system is simulated and the dynamics of the population includes a selection-mutation process. Namely, rare copies are multiplied (have descendants) but typical ones are killed (become extinct) to select atypical trajectories of interest. After introducing this algorithm in a pedagogical way, I will present recent applications of the algorithm to active Brownian particles, a model of self-propelled particles, which show unexpected dynamical phase transitions to flocking/jammed states in their rare events [2].

[1] Cristian Giardinà, Jorge Kurchan and Luca Peliti, Phys. Rev. Lett. 96, 120603 (2006).
[2] T.N., Étienne Fodor, Michael E. Cates, Robert L. Jack and Julien Tailleur, arXiv:1805.02887 (2018).


- Thursday, October 11, 14:00
Achim Wirth, LEGI / Univ. Grenoble-Alpes

A fluctuation-dissipation relation for the ocean subject to turbulent atmospheric forcing

We establish the fluctuation-dissipation relation for a turbulent fluid layer (ocean) subject to frictional forcing by a superposed lighter fluid layer (atmosphere) in local models of air-sea dynamics. The fluctuation-dissipation relation reflects the fact that air-sea interaction not only injects energy in the ocean but also dissipates it.

Energy injection and dissipation must therefore be related.

The competition between the two processes determines the oceanic energy budget in the idealized dynamics considered here. When applying the fluctuation-dissipation relation to a two-dimensional two-layer Navier-Stokes model with turbulent dynamics, in the atmosphere and the ocean, coupled by a quadratic friction law, the friction parameter is estimated within 8\% of the true value, while the estimation of the mass ratio between the atmosphere and the ocean fails, as the forcing time-scale is not faster than the characteristic time-scale of the atmospheric dynamics.

Link to paper : https://hal.[archives-ouvertes.fr/hal-01769301](http://archives-ouvertes.fr/hal-01769301)


- Thursday, October 25, 11:00
Suman Dutta

TBA


- Thursday, November 08, 10:30
Florent Calvo / LIPhy

The quantum structure of anionic hydrogen clusters