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Articles
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Séminaire PMMH - Bérengère Abou (MSC, Univ. Paris Cité)
1er marsVendredi 1er mars de 11h00 à 12h00 - Salle réunion PMMH 1Intracellular rheology of red blood cells
The characterisation of erythrocyte stiffness and its heterogeneity in a blood sample is a key parameter for the description of erythrocyte pathologies. I will present a method for investigating the intracellular rheology of red blood cells and the heterogeneity of the population using molecular rotors. These are fluorescent probes that are sensitive to viscosity in viscous fluids. I will illustrate the value of this approach in the context of red cell pathologies such as sickle cell anaemia.
A. Briole, T. Podgorski & B. Abou, Molecular rotors as intracellular probes of red blood cells rigidity, Soft Matter 17, 4525 (2021).
A. Briole & B. Abou, Molecular rotors in haemoglobin and bovine serum albumin proteins, Journal of Royal Society Interface 19 : 20220709 (2022). -
Séminaire PMMH - Bérengère Abou (MSC, Univ. Paris Cité)
25 févrierVendredi 1er mars de 11h00 à 12h00 - Salle réunion PMMH 1Intracellular rheology of red blood cells
The characterisation of erythrocyte stiffness and its heterogeneity in a blood sample is a key parameter for the description of erythrocyte pathologies. I will present a method for investigating the intracellular rheology of red blood cells and the heterogeneity of the population using molecular rotors. These are fluorescent probes that are sensitive to viscosity in viscous fluids. I will illustrate the value of this approach in the context of red cell pathologies such as sickle cell anaemia.
A. Briole, T. Podgorski & B. Abou, Molecular rotors as intracellular probes of red blood cells rigidity, Soft Matter 17, 4525 (2021).
A. Briole & B. Abou, Molecular rotors in haemoglobin and bovine serum albumin proteins, Journal of Royal Society Interface 19 : 20220709 (2022). -
Séminaire PMMH - Jon Otto Fossum (Dept of Physics , NTNU, Trondheim, Norway)
16 févrierVendredi 16 février de 11h00 à 12h00 - Salle réunion PMMH 1Clay minerals as 2D natural nanomaterials for sustainable applications
Clay minerals are among the most abundant and sustainable on earth, and due to this and their low-cost they are found in many traditional applications that exploit their physical and chemical properties, including their mechanical stability, their non-toxicity and in effect their underlying 2D nanoscale character. These traditional applications can for the most part be categorized as low-tech based on empirical knowledge, and they include use of clay mineral particles in bricks and pottery, clay mineral partivles as rheology modifiers, and clay powders or clay nanoporous structures as sorbents or catalysts.
Synthetic clays are of superior quality compared to natural clays, and they have opened up and enabled pathways towards new applications, such as clay minerals for structural coloration, for use in 2D electronic nanodevices, for targeted gas barriers or gas separation, for instance separation of H2 and CO2.
In this lecture such recent developments in natural nanomaterials science, discovered and investigated in our group, will be presented, pointing out that for instance clay minerals are unexploited materials for future sustainable technologies. -
Séminaire PMMH - Alex Hansen (NTNU Norvège)
7 févrierVendredi 29 mars de 11h00 à 12h00 - Salle réunion PMMH 1Séminaire d'Alex Hansen (NTNU, Trondheim, Norvège)
The co-moving velocity, a new concept in immiscible two-phase flow in porous media
Alex Hansen
PoreLab, Department of Physics, NTNU, Trondheim, NorwaySince 1936, relative permeability theory has been the leading description of immiscible two-phase flow in porous media at scales much larger than the pore scale. Central to this theory are the two relative permeabilities, one for each fluid, which measures the reduction of mobility each fluid experiences due to the presence of the other fluid. The theory assumes the two relative permeabilities to be functions of the saturation (i.e., relative concentration) alone. When there are saturation gradients present, a third parameter comes into play, the capillary pressure. This is also assumed to depend on the saturation alone.
Such a theory is clearly quite limited in that it makes many strong assumptions. Yet, it is essentially the only one that is used for practical calculations. Can one do better ? That is, come up with a theory that is closer to the physics that is going on and at the same does not drown in complexity ? My answer is yes [1-7]. The aim of this talk is to describe this new theory. I will focus on a new velocity that pops up, namely the co-moving velocity. This velocity has remarkable properties that hints at something deeper which is yet to be uncovered.
References
[1] A. Hansen, S. Sinha, D. Bedeaux, S. Kjelstrup, M. Aa. Gjennestad and M. Vassvik, Relations between seepage velocities in two-phase flow in homogeneous porous media, Transp. Porous Med. 125, 565 (2018) ; doi:10.1007/s11242-018-1139-6.
[2] S. Roy, S. Sinha, and A. Hansen, Flow-area relations in immiscible two-phase flow in porous media, Front. Phys. 8, 4 (2020) ; doi:10.3389/fphy.2020.00004.
[3] S. Roy, H. Pedersen, S. Sinha, and A. Hansen, The co-moving velocity in immiscible two-phase flow in porous media, Transp. in Porous Media, 143, 69 (2022) ; doi:10.1007/s11242-022-01783-7.
[4] A. Hansen, E. G. Flekkøy, S. Sinha, and P. A. Slotte, A statistical mechanics for immiscible and incompressible two-phase flow in porous media, Adv. Water Res., 171, 104336 (2023) ; doi:10.1016/j.advwatres.2022.104336.
[5] H. Pedersen and A. Hansen, Parametrizations of immiscible two-phase flow in porous media, Front. Phys. 11, 1127345 (2023) ; doi:10.3389/fphy.2023.1127345.
[6] F. Alzubaidi, J. E. McClure, H. Pedersen, A. Hansen, C. F. Berg, P. Mostaghimi and R. T. Armstrong, The impact of wettability on the co-moving velocity of two-fluid flow in porous media, arXiv:2309.0036.
[7] J. Feder, E. G. Flekkøy, and A. Hansen, Physics of Flow in Porous Media, (Cambridge University Press, 2022).
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Séminaire PMMH - Benjamin Guiselin - ENS Lyon
2 févrierVendredi 12 avril de 11h00 à 12h00 - Salle réunion PMMH 1Emergence of spontaneous collective oscillations in dense Human crowds
Massive crowd gatherings form some of the most dangerous and unpredictable environments [1]. However, we lack quantitative characterizations of their dynamics and the heuristic principles used to explain and predict their motion remain elusive. In this talk, I will present our analysis of the dynamics of thousands of packed individuals in a model system, namely, the opening ceremony of the festival of San Fermín in Pamplona, Spain [2]. This analysis reveals that at extreme densities crowds experience self-sustained oscillatory flows, which echo the correlated orbital motion of hundreds of individuals in the absence of any external guidance. I will then detail how the combination of mechanics and symmetry principles has allowed us to establish a robust predictive model of dense crowds inferred from our measurements to elucidate this emergent chiral dynamics. In particular, we establish that the self-organization of crowds into macroscopic oscillators originates from transverse frictional forces between the crowd and the ground.
[1] D. Helbing, A. Johansson, and H. Z. Al-Abideen. ``Dynamics of crowd disasters : An empirical study''. Physical Review E, 75(4), 046109 (2007).
[2] F. Gu*, B. Guiselin*, N. Bain, I. Zuriguel, and D. Bartolo. ``Emergence of collective oscillations powered by odd friction in massive crowds''. Submitted (2024).