Microbial narrow-escape is facilitated by wall interactions

Cells have evolved efficient strategies to probe their surroundings and navigate through complex environments. From metastatic spread in the body to swimming cells in porous materials, escape through narrow constrictions – a key component of any structured environment connecting isolated micro-domains – is one ubiquitous and crucial aspect of cell exploration. Here, using the model microalgae Chlamydomonas reinhardtii, we combine experiments and simulations to achieve a tractable realization of the classical Brownian narrow escape problem in the context of active confined matter. Our results differ from those expected for Brownian particles or leaking chaotic billiards and demonstrate that cell-wall interactions substantially modify escape rates and, under generic conditions, expedite spread dynamics. More from PRResearch: 2022-Souzy-PRResearch

Winner of the MESA + Photo Contest

This beautiful picture « Path of an evaporative drop », won the 2020 – 4th Quarter MESA+ Photo contest!

It is a visualization of the inner flow pathlines of a self-propelled evaporating droplet of ethanol on a hot substrate. Passive Fluorescent PIV tracers excited by a laser spot reveal there chaotic pathlines (in blue) while flowing in the evaporating droplet. The evaporation process generates strong inner flow and self-propulsion of the droplet, which rapidly translates from the top-left part of the image to the right-bottom part, while the droplet diameter simultaneously decreases as evaporation is ongoing.

1st Price of the Porous media visualization and data reuse challenge

The introduction video to Pore Aventura was awarded the 1st price of the Visualization and Data Reuse Challenge from the Digital Rock Portal of the National Science Foundation! It’s a great pleasure, as it highlights how useful Porous Media Visualization tools are to get a better understanding of porous media, and also to point out the educational assets of such tools!

Note that this video was generated from 3D experimental measurements of the fluid velocity field within a random stack of spherical particles [data are available here and corresponding paper here]. This data has been used to develop Pore Aventura, a 3D velocity field explorer. More details about it on GitHub.

Transition from clogging to continuous flow in constricted particle suspensions

When suspended particles are pushed by liquid flow through a constricted channel, they might either pass the bottleneck without trouble or encounter a permanent clog that will stop them forever. However, they may also flow intermittently with great sensitivity to the neck-to-particle size ratio D/d. These different behaviours can be directly visualize from the above spatio-temporals diagrams (at the neck constriction). In this Rapid Communication, we experimentally explore the limits of the intermittent regime for a dense suspension through a single bottleneck as a function of the neck-to-particle size ratio D/d. More from Phys. Rev E. :2020-Souzy-PRE

Velocity distributions, dispersion and stretching in three-dimensional porous media

Using index-matching and particle tracking, we measure the three-dimensional velocity field in an isotropic porous medium composed of randomly packed solid spheres. In addition to the velocity distributions, this dataset provides new insights into the dynamics of dispersion and stretching in porous media. These results confirm the chaotic nature of advection within three-dimensional porous media. By providing the laws of dispersion and stretching, the present study opens the way to a complete description of mixing in porous media. More from J. Fluid Mech. : 2020-Souzy-JFM

Mesa+ Day 2019 : David Reinhoudt Poster Price

Thanks to the jury and to the people who voted for my poster during the 2019 edition of the Mesa+ Day in Enschede, as I was awarded with the David Reinhoudt Poster Price! The poster is available here



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Release of Pore Aventura : a 3D velocity field explorer

Pore Aventura, an open source 3D velocity field explorer is now available on GitHub. It aims at visualizing and investigating the kinematic properties of any steady 3D velocity field, which can contain solid stationary boundaries. It was initially developped in collaboration with Nicolas Barret to investigate dispersion and mixing in porous media.

Among its features, Pore Aventura allows :

  • 3D motion through the velocity field
  • Local injection of passive advective tracers
  • Upstream injection grid
  • Streamlines visualization
  • Roller-coaster mode

Find here a teaser (0:50) or an introduction video (3:53) ?

Intermittent bursts in constricted particulate suspensions

When people, animals, or particles are forced through a constriction, they either flow continuously, intermittently, or even not at all when a clogging arch is formed. Here, we focus on non-adhesive colloidal particles in suspension flowing through a constriction following intermittent bursts, in a strikingly similar way as dry non-cohesive granular systems do (sheep herds, assembling of grains, pedestrian crowds).

We experimentally investigate the time distribution of the intermittent bursts and the distribution of escaped particles per burst, using image analysis particle tracking. More from here.

Injection of a blob of dye in a porous media

When a blob of dye is injected in the bulk of a porous media, we can directly visualize the complex topology constituted of sheets. These experiments are performed to measure how the concentration level homogenize in porous media.

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