Publication

To find out more, take a look at :

• the news published on the CNRS Biologie website,
• the scientific article published in Nature Microbiology.

• Read more about The interaction between macrophages and their environment affects their functioning

This research was funded in whole or in part by the French National Research Agency (ANR) under the COMPLEAT project, coordinated by Didier Mondelain, a CNRS researcher at LIPhy.

To find out more, take a look at the article published in "Focus Sciences" of CNRS Le Journal.

• Read more about Recording the absorption spectra of gaseous molecules with an optical cavity of high finesse

The project was coordinated by Karin John, a CNRS researcher at LIPhy. To find out more, take a look at the article published in "Focus Sciences" of CNRS Le Journal.

• Read more about Scrutinizing the skeleton of our cells, an essential issue for health

We talk about it in Chemistry World, a magazine published by the Royal Society of Chemistry!

The HOT article PCCP can be read here.

• Read more about Hydrogen dimer detected at room temperature at LIPhy

To find out more, take a look at :

• scientific news published on the UGA website and on the CNRS Physique website,
• the scientific article published in Nature Communications

• Read more about Caging bubbles to develop high-resolution microscopes

To find out more, take a look at :

• the news published on the CNRS Biologie website,
• the scientific article published in Nature Microbiology.

• Read more about The secrets of Toxoplasma gondii parasite movement revealed

To find out more, take a look at :

• an explanatory video on the LIPhy Youtube channel,
• the news published on the CNRS Physique website,
• the scientific article published in Physical Review Fluids.

• Read more about When red blood cells go off the beaten track

The full article can be read here.

• Read more about Towards the ultimate precision limits: how information bounds estimation

Fish form schools in a wide variety of environments, from the open sea amid coral reefs to rocky rivers. Some natural environments are obstructed, it is therefore interesting to understand how well the collective structure of a shoal withstands the complexity of the environment. Scientists at LIPhy have demonstrated the existence of a behavioral transition when the environment of zebrafish becomes too crowded.

The study of collective movements provides a better understanding of the dynamic structures resulting from the self-organization of groups of individuals. The study of fish schools is part of this approach. The schooling of fish is remarkable because it occurs in a wide variety of environments, from the open sea to coral reefs. Previous research has focused on the study of schools in simple, unobstructed environments. In this work, a team from LIPhy used an approach combining experiment and modeling to study the impact of a complex environment on the collective organization of a school of fish. To do this, they followed the individual trajectories of a small group of zebrafish in the presence of variable obstacle densities. The structure of the school of fish proved quite resilient to the introduction of obstacles, maintaining an organization similar to that observed in the absence of obstacles. However, when the obstacles reach a critical density, the shoal structure disappears and the fish behave as if they were isolated, aligning themselves with the obstacles and no longer with their fellow fish. This density corresponds to a distance between obstacles close to the typical distance between fish in an undisturbed shoal, i.e. their natural social distance. Using a statistical model, the ingredients of this behavioral transition, from collective to independent, were analyzed in detail. The LIPhy team has shown that a complex environment can have a significant influence on the collective behavior of fish, and that social distance is critical for maintaining collective behavior in a complex environment. These results contribute to the emerging field of active and cognitive matter, and more broadly to the study of animal behavior and swarm robotics through biomimicry.

• Read more about Dissolution of a school of fish in a complex environment

The theoretical description of the rheology of dense suspensions of micrometric soft particles, in which thermal fluctuations are negligible, remains a very open field based mainly on direct numerical simulations of suspensions or on phenomenological macroscopic constitutive models. Starting from a simplified model of a two-dimensional dense suspension, researchers at LIPhy have proposed a statistical physics method to obtain a macroscopic constitutive model from the dynamics of the soft particles constituting the suspension.

The tensor constitutive model derived analytically in this way allows a continuous description of the suspensions in the same way as the already existing phenomenological models, while keeping a link with the scale of the constitutive entities. This constitutive model consists of a nonlinear evolution equation for the deviatoric part of the stress tensor. It allows to reproduce the existence of a threshold stress in the rheology of dense suspensions above the jamming density, and to describe a Bingham-type rheology at low shear rate. The tensor nature of the constitutive equation also allows the prediction of a threshold stress on the difference of the normal stresses.

The approach, which technically includes a number of approximations, is primarily aimed at obtaining a qualitative description of the phenomenology of dense suspensions of soft particles, and at relating the structure of the resulting equation to the ingredients of the microscopic dynamics of the suspension. Interestingly, the obtained constitutive equation also allows to address more complex and time-dependent protocols, such as the start or stop of shearing. In particular, relaxation after shear leads to a lower final stress for a stronger shear, in qualitative agreement with experiments. The model also reproduces the power-law decay of the shear rate in creep experiments, as well as the collapse of the storage modulus measured in parallel superposition protocols, in which a small sinusoidal strain is applied to a dense flowing suspension.

One of the main interests of this approach is that it allows one to link macroscopic rheology with microstructure. In particular, the approach predicts that the orientation of the anisotropy of the microstructure, which is governed by a competition between advection and contact elasticity, plays a key role in the flow properties.

Read more :

 Microscopic Theory for the Rheology of Jammed Soft Suspensions
Nicolas Cuny, Romain Mari, Eric Bertin
Physical Review Letters, Novembre 2021

 Dynamics of microstructure anisotropy and rheology of soft jammed suspensions
Nicolas Cuny, Eric Bertin, Romain Mari
Soft Matter, Janvier 2022

• Read more about Relating rheology to microstructure dynamics in dense suspensions of soft particles