Séminaires


Conférence Chen-li SUN : « On the locomotion of planktonic micro-organisms in a microfluidic environment »

DATE : le jeudi 15 juin de 11h00-11h45 dans la Salle des Thèses, Bât. 2A Université Rennes 1, Campus Beaulieu

Intervenante : Chen-li SUN
professeure au Department of Mechanical Engineering, National Taiwan University

Abstract

Planktonic micro-organisms play an important role in marine ecology, fishery, and the ocean carbon cycle. As the foundation of the oceanic food chain, phytoplankton and zooplankton form a complex food web, and their trophic interaction is vital to the prosperity of other marine life.
In this talk, I will demonstrate how microfluidic devices can be employed to gain a better understanding of marine ecosystem in a single-cell level.

Focusing on studying the locomotion of plankton K. veneficum (CCMP426), we design amicrocavity device to investigate the effects of different microflow conditions: stationary f/2-Si medium, steady flow, and oscillatory flow. After measuring the local flow field, we are able to determine the absolute and relative velocities of individual plankton cells, from which their rheotaxis can be derived. The probability density function, the expected value and the standard deviation are calculated in order to statistically represent the locomotion of the planktonic community. The experimental results show that when the plankton reside in stationary and homogeneous nutrient medium, the swimming velocity and the acceleration are 52.7±43.5 μ m s -1 and 878±820 μ m s -2 , respectively. In addition, K. veneficum is capable of maneuvering in a flow speed up to 150 μ m s -1 . Once the current is too strong, their locomotion is dominated by the flow.

Under the condition of oscillatory flow, K. veneficum exhibits positive rheotaxis. In the strong flow field region, planktonic cells can not directly cross the streamlines. Rather, they tend to cut through streamlines with small angle in order to reach the weak flow field region. The outcome of this study helps us clarify the interaction between the behavior of plankton and the microfluidic environment.

Biography

Chen-li Sun is Professor of Mechanical Engineering at National Taiwan University (NTU). She teaches in the areas of thermodynamics, heat transfer, energy engineering, two-phase flow, and thermal management for electronic devices. She is Visiting Professor at l’École normale supérieure de Rennes (Summer 2017) and l’Université Paris-Sud (Winter 2016). Prior to joining NTU, she was on the faculty of National Taiwan University of Science and Technology from 2003 to 2011. Prof. Sun received her B.S. degree from National Central University, Taiwan in 1994, M.S. from Stanford University in 1996, and Ph.D. from the University of California at Berkeley in 2002, all in Mechanical Engineering. In 2002-03, she was a postdoctoral researcher for Prof. Al P. Pisano in the Berkeley Sensor and Actuator Center (BSAC). Prof. Sun is the 2012 recipient of the Ta-You Wu Memorial Award, which recognizes young Taiwanese PIs dedicated to long-term outstanding research work. She is also the 2014 recipient of the Distinguished Young Scholar Award from the Society of Theoretical and Applied Mechanics. Dr. Sun’s research interest focuses on near-interface microscale transport phenomena and phase-change heat transfer in energy systems. Specifically, she is interested in exploring innovative measurement techniques for studying microscale transport in microfluidics.

Contacts:

martinus.werts@ens-rennes.fr
janine.emile@univ-rennes1.fr

 

 

 

 

 

 

 

 

 

 

Conférence
On the locomotion of planktonic micro-organisms
in a microfluidic environment
par
Chen-li SUN
professeure au
Department of Mechanical Engineering, National Taiwan University
le jeudi 15 juin de 11h00-11h45
dans la Salle des Thèses, Bât. 2A
Université Rennes 1, Campus Beaulieu
Abstract
Planktonic micro-organisms play an important role in marine ecology, fishery, and the ocean
carbon cycle. As the foundation of the oceanic food chain, phytoplankton and zooplankton form
a complex food web, and their trophic interaction is vital to the prosperity of other marine life.
In this talk, I will demonstrate how microfluidic devices can be employed to gain a better
understanding of marine ecosystem in a single-cell level.
Focusing on studying the locomotion of plankton
K. veneficum
(CCMP426), we design a
microcavity device to investigate the effects of different microflow conditions: stationary f/2-Si
medium, steady flow, and oscillatory flow. After measuring the local flow field, we are able to
determine the absolute and relative velocities of individual plankton cells, from which their
rheotaxis can be derived. The probability density function, the expected value and the standard
deviation are calculated in order to statistically represent the locomotion of the planktonic
community. The experimental results show that when the plankton reside in stationary and
homogeneous nutrient medium, the swimming velocity and the acceleration are 52.7±43.5
μ
m s
-1
and 878±820
μ
m s
-2
, respectively. In addition,
K. veneficum
is capable of maneuvering in a flow
speed up to 150
μ
m s
-1
. Once the current is too strong, their locomotion is dominated by the flow.
Under the condition of oscillatory flow,
K. veneficum
exhibits positive rheotaxis. In the strong
flow field region, planktonic cells can not directly cross the streamlines. Rather, they tend to cut
through streamlines with small angle in order to reach the weak flow field region. The outcome
of this study helps us clarify the interaction between the behavior of plankton and the
microfluidic environment.
Biography
Chen-li Sun is Professor of Mechanical Engineering at National Taiwan University (NTU). She
teaches in the areas of thermodynamics, heat transfer, energy engineering, two-phase flow, and
thermal management for electronic devices. She is Visiting Professor at l’École normale
supérieure de Rennes (Summer 2017) and l’Université Paris-Sud (Winter 2016). Prior to joining
NTU, she was on the faculty of National Taiwan University of Science and Technology from
2003 to 2011. Prof. Sun received her B.S. degree from National Central University, Taiwan in
1994, M.S. from Stanford University in 1996, and Ph.D. from the University of California at
Berkeley in 2002, all in Mechanical Engineering. In 2002-03, she was a postdoctoral researcher
for Prof. Al P. Pisano in the Berkeley Sensor and Actuator Center (BSAC). Prof. Sun is the 2012
recipient of the Ta-You Wu Memorial Award, which recognizes young Taiwanese PIs dedicated
to long-term outstanding research work. She is also the 2014 recipient of the Distinguished
Young Scholar Award from the Society of Theoretical and Applied Mechanics. Dr. Sun’s research
interest focuses on near-interface microscale transport phenomena and phase-change heat
transfer in energy systems. Specifically, she is interested in exploring innovative measurement
techniques for studying microscale transport in microfluidics.
Contact:
martinus.werts@ens-rennes.fr
,
janine.emile@univ-rennes1.fr

Publié dans Physique des milieux divisés et verres, Séminaires | Commentaires fermés sur Conférence Chen-li SUN : « On the locomotion of planktonic micro-organisms in a microfluidic environment »

Séminaire A. TURCHI : Density Functional Theory and Thermodynamics Applied to Complex Materials – Is there still a need for Ab Initio-aided alloy theory?

DATE : 19 juin 2017 – 11h00
              Pièce 007 – RdC du Bât 10B ISCR

Intervenant : A. Turchi, turchi1@llnl.gov
Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551, USA

 Ab initio methodologies provide, despite limitations that will be briefly commented on, fundamental insight on materials behavior and properties. This will be illustrated with a few ab initio-based predictions on phase stability, ordering trends, and thermodynamic properties. Examples will include the case of FeSi2, and of bcc-based transition metal alloys. In addition, ab initio output plays an important role in supplementing in two ways CALPHAD that is the most versatile and preferred method for assessing the thermodynamics of complex multi-component alloys: either by direct input of ab initio energetics in thermodynamic databases, or, more challenging, by assessing ab initio-based thermodynamics à la CALPHAD. These two applications will be briefly discussed in the context of phase diagram determination for selected transition metal and actinide-based alloys. Finally, a few comments on prospects in the alloy theory field, of critical importance for advancing our fundamental knowledge of materials performance, will conclude this presentation.

Publié dans Départements, Nanosciences, Séminaires Matériaux-Nanosciences | Commentaires fermés sur Séminaire A. TURCHI : Density Functional Theory and Thermodynamics Applied to Complex Materials – Is there still a need for Ab Initio-aided alloy theory?

Séminaire Etienne Mangaud : « Quantum dynamics of electron transfer in strongly coupled environments »

DATE : 13 juin 2017 à 10h00 en salle 120

Etienne MANGAUD,  Laboratoire de Chimie Physique, UMR8000, Université Paris-Sud, ORSAY

Experiments of time-resolved bidimensional spectroscopy carried out in complex
systems, such as photosynthetic systems (FMO)[1] or conjugated polymers[2], showed that quantum coherences amongst electronic excited states can persist for long times, comparable to the electron or excitation energy transfer times.
In order to investigate these phenomena from a theoretical point of view, one needs to
study the quantum motion of the nuclei and its influence onto the transfer. In the systems at stake, photo-induced electron transfer are studied in an oligothiophene-fullerene heterojunction[3] and a chromoprotein cryptochrome[4] as shown on Fig. 1 with a realistic environment.

Figure 1 Photo-induced electron transfer systems under study: On the left (Panel (a)), oligothiophene (OT4) –fullerene (C60) heterojunction. On the right (Panel (b)), chromoprotein cryptochrome with a flavin-adenosin-diphosphate (FAD) chromophore and a chain of three tryptophan molecules (W400, W377 and
W324)
For the heterojunction (Fig. 1 (a)), a reference Hamiltonian[5] describing a
donor-acceptor electronic system coupled to a bath of harmonic oscillators has been used. For the cryptochrome (Fig. 1 (b)), a three electronic states Hamiltonian has been parameterized using QM/MM trajectories based on constrained DFT (cDFT).[6,7]
Based on these parametrized Hamiltonians, time propagations have been carried out
using methods of dissipative quantum dynamics. However, since these systems exhibit a strong system-bath coupling that cannot be handled with traditional perturbation theory, one has to resort to exact computations such as the hierarchical equation of motion method.[8] A special care has also been taken to evaluate the quantum memory effects which prove to be significant in these systems.[9] To catch a glimpse of the physical movement at stake in the transfer, we perform a coordinate transformation used to define an effective mode[10], which is included into
the system, and which itself is coupled to a secondary bath. S H H 4 (a) (b)

As main results, we show and explain the dynamical behavior of various cases leading to an easy delocalization or to a trapping of the charge and assess the time scales of the transfer.
In the cases considered, the proposed methodology is well suited to analyze the subtle interplay between charge transfer and nuclear deformations, a prototype situation for many important processes in chemical and biological systems.
Acknowledgement: We acknowledge I. Burghardt for providing the heterojunction Hamiltonian data and F. Cailliez for fruitful discussions.

References:
[1] G. S. Engel et al, Nature, 2007, 446, 78
[2] E. Collini and G. Scholes, Science, 2009, 323, 369
[3] A. Chenel, E. Mangaud, I. Burghardt, C. Meier, M. Desouter-Lecomte, J. Chem. Phys., 2014, 140, 044104
[4] T. Firmino, E. Mangaud, F. Cailliez, A. Devolder, D. Mendive-Tapia, F. Gatti, C. Meier, M. Desouter-Lecomte, A. de la Lande, Phys. Chem. Chem. Phys., 2016, 18, 21442
[5] H. Tamura, I. Burghardt, and M. Tsukada, J. Phys. Chem. C, 2011, 115, 10205
[6] J. Řezáč, B. Lévy, I. Demachy, A. de la Lande, J. Chem. Theory Comput., 2012, 8,418
[7] Q. Wu, T. Van Voorhis, J. Chem. Theory Comput., 2006, 2,765
[8] Y. Tanimura, R. Kubo, J. Phys. Soc. Jpn., 1989, 58, 101
[9] H.-P. Breuer, E.M. Laine, J. Piilo and B. Vacchini, Rev. Mod. Phys., 2016, 88, 021003
[10] A. Pereverzev, E. R. Bittner, I. Burghardt, J. Chem. Phys., 1999, 131, 034104

Publié dans Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Séminaire Etienne Mangaud : « Quantum dynamics of electron transfer in strongly coupled environments »

Séminaire Théorie et Simulation : Laurent JOLY « Molecular views on surface-driven flows »

DATE : 23 Mai 2017 à 14h00
Salle 120 – IPR

Intervenant : Laurent JOLY / Institut Lumière Matière – Université Lyon 1

Surface-driven flows (also called osmotic flows) are generated at interfaces by various thermodynamic gradients (e.g. electric potential gradient: electro-osmosis, solute concentration gradient: diffusio-osmosis, temperature gradient: thermos-osmosis). They represent powerful tools to manipulate liquids in micro and nanofluidic systems, and play a key role in living systems, in sustainable energies, or in water treatment and desalination processes. Osmotic flows arise from the coupling between hydrodynamics and liquid-wall interactions in the nanometric vicinity of the interface, and yet standard descriptions are usually based on continuum models and liquid-wall interactions only. During this talk I will illustrate with recent work how molecular dynamics simulations can be used to investigate the mechanisms underlying surface-driven flow, and in particular to explore the role of interfacial hydrodynamics.

[1] L. Joly, F. Detcheverry, A.-L. Biance: “Anomalous zeta potential in foam films”, Phys. Rev. Lett. 113, 088301 (2014) [2] A. Barbosa de Lima, L. Joly, “Electro-osmosis at surfactant-laden liquid-gas interfaces: beyond standard models”, Soft Matter, Advance article (2017) [3] C. Lee, C. Cottin-Bizonne, R. Fulcrand, L. Joly, C. Ybert: “Nanoscale Dynamics versus Surface Interactions: What Dictates Osmotic Transport”, J. Phys. Chem. Lett. 8, 478 (2017) [4] L. Fu, S. Merabia, L. Joly, in preparation

Publié dans Départements, Nanosciences, Séminaires Matériaux-Nanosciences | Commentaires fermés sur Séminaire Théorie et Simulation : Laurent JOLY « Molecular views on surface-driven flows »

Séminaire MMC: Antoine Bérut « Gravisensing in plant cells is controlled by an active granular material »

DATE :  vendredi 12 mai 2017 à 11h salle 120

« Plants are able to sense gravity, so that the roots grow downward and the shoots upward. This gravitropism has been widely studied by biologists, and the commonly accepted hypothesis states that the gravity detection is mediated by the movement of starch-accumulating amyloplasts (statoliths), that sediment toward gravity in gravity sensing cells (statocytes), as show in figure a.
By performing microscopic observations of statocytes in wheat coleoptiles cuts, we have shown that a pile of statoliths flows easily, even in response to small inclination angles, contrary to what is expected for a classical granular material. This flowability ensures a high sensitivy for gravity detection, and might be explained by the agitation that statoliths undergo in plant cells. To identify the origin of the observed agitation, we have used a “biomimetic” microfluidic chambers filled with silica micro-particles of same dimension than statoliths in plant cells, but only submitted to thermal agitation (shown in figure b). The direct comparison of avalanche dynamics in the biological and physical systems suggests that the high flowability of statoliths cannot be explained by thermal motion, but is rather due to biological activity in plant cells such as cytoskeleton activity. This obervation is also supported by the difference between single trajectories of statoliths and silica particles at the top of a pile at rest: the amplitude of statoliths motion in wheat cell exceed by a factor ∼10 those of an inert particle of the same weight. Therefore gravisensing in plant cells relies on an active granular material. »

Publié dans Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire MMC: Antoine Bérut « Gravisensing in plant cells is controlled by an active granular material »

Séminaire MMC : Julien Husson « Single-cell leukocyte mechanics: force generation, viscoelasticity, and rupture mechanics « 

DATE : Vendredi 28 Avril 2017 à 11h00 en salle 120

Julien Husson
Hydrodynamics laboratory (LadHyX), Ecole polytechnique, CNRS UMR 7646, Palaiseau, France
https://cellmechanics.jimdo.com/

Résumé :
Leukocytes are very soft cells that perform many diverse functions: they adhere, crawl, transmigrate, kill, phagocytose or interact with other cells. During their activation, leukocytes both generate mechanical forces and change their viscoelastic properties (i.e. they stiffen/soften, get more or less viscous). We have developed micropipette-based setups to quantify single-leukocyte mechanical properties and monitor them over time while a leukocytes gets activated by a relevant stimulus. We further quantify rupture properties of cell membrane, as these help us better understand cell structure and dynamics.

We use this approach in diverse contexts involving leukocytes: activation of T lymphocytes, phagocytosis of a target by a neutrophil, or transmigration of a lymphoblast across an endothelial monolayer. We perform microrheology experiments with a profile microindentation setup1,2, measure forces generated by T lymphocytes3,4, characterize cell-substrate adhesion5 or establish a rupture criteria for membrane rupture2,6(Figure 1). These mechanical measurements shed a new light on how cell mechanical properties evolve over a short period of time (seconds), how they adapt to the stiffness of their environment, and how intracellular signaling is involved.

 

Publié dans Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire MMC : Julien Husson « Single-cell leukocyte mechanics: force generation, viscoelasticity, and rupture mechanics « 

Conférence IPR Françoise COMBES : « Les trous noirs super-massifs trop gloutons »

DATE : Mardi 02 Mai 2017- 12h15 – Le Diapason

Lien vers la vidéo Youtube : https://www.youtube.com/watch?v=7m13uWHhvfs

Toutes les galaxies abritent en leur centre un trou noir super-massif, de masse
comprise entre un million et quelques milliards de masses solaires. Il existe un rapport de proportionnalité entre la masse de ces trous noirs et la masse du bulbe des galaxies, ce qui fait penser que la formation des étoiles et l’alimentation des trous noirs se produit simultanément, en quelque sorte les galaxies et leurs trous noirs croissent en symbiose.

Lorsque du gaz tombe vers le centre de la galaxie, le trou noir en avale le plus possible,
mais la masse qu’il peut absorber est limitée. La chute de matière sur le trou noir
libère une quantité considérable d’énergie, sous forme de rayonnement, et aussi
sous forme d’énergie cinétique. Le noyau de la galaxie devient actif, soit
un noyau de Seyfert, soit un quasar. Les vents et jets de plasma émis par le trou
noir entraînent le gaz interstellaire environnant. Des flots de gaz moléculaire ont
récemment été détectés autour des noyaux actifs, emportant tellement de masse qu’ils peuvent avoir un impact significatif sur l’évolution de la galaxie hôte, enrégulant ou stoppant même l’approvisionnement en gaz pour la formation des étoiles.

Les trous noirs gloutons en recrachant leur nourriture, régulent la formation des étoiles.
Nous détaillerons ces phénomènes, peut-être à l’origine de la proportionnalité entre masses des trous noirs et des bulbes.

Publié dans Actualités, Conferences IPR | Commentaires fermés sur Conférence IPR Françoise COMBES : « Les trous noirs super-massifs trop gloutons »

Séminaire Théorie et Simulation: Patrice Malfreyt « Simulation moléculaire des interfaces »

DATE : le vendredi 28 avril 2017 à 14h en salle 50 (bat. 11B)

Les premières simulations de systèmes interfaciaux ont débuté en 1974 sur une interface plane de fluide Lennard-Jones (LJ). En 2017, des travaux sont encore publiés sur la méthodologie de simulation des interfaces planes. Il a fallu attendre plus de quarante ans et l’arrivée de calculs intensifs pour mettre au point les protocoles de simulations de systèmes hétérogènes.

Des illustrations de quelques effets de dépendances du calcul de la tension superficielle de fluide Lennard-Jones vous seront présentées (effets de taille, de troncature, importance des corrections à longue distance due à la troncature du potentiel, potentiel à deux corps) sur des interfaces liquide vapeur de corps purs. Quelle est la température maximale que l’on peut simuler proche du point critique avec des méthodes qui modélisent l’interface ? La réponse à cette question passe par le développement de simulations de tailles de systèmes importantes. On peut désormais apporter une réponse et approcher le point critique, zone où l’interface fluctue énormément. Des exemples de simulations vous seront présentées dans cette région critique.

Des simulations de systèmes binaires permettront de montrer le caractère prédictif de ces simulations sur la dépendance en pression de la tension interfaciale sur des systèmes eau-gaz acides, eau-alcanes, alcanes-gaz acides. Un potentiel polarisable a été testé sur la capacité à rendre compte de l’évolution de la tension interfaciale de solutions saline en concentration de sels. 

On complétera cette présentation sur le calcul de la tension superficielle d’interfaces cylindriques et sur l’utilisation de potentiels gros grains pour la modélisation d’interfaces plus complexes de type eau-huile-tensio-actifs.

Intervenant :
Patrice Malfreyt, Professeur à l’Institut de Chimie de Clermont-Ferrand (ICCF UMR CNRS 6296)

 

Publié dans Actualités, Départements, Nanosciences, Séminaires Matériaux-Nanosciences | Commentaires fermés sur Séminaire Théorie et Simulation: Patrice Malfreyt « Simulation moléculaire des interfaces »

Séminaire Roman BERTONI : Experiment triggered by theory vs Theory triggering experiment.

DATE : 24 avril 2017 à 14h00 – Salle 120

The interaction between experimental physics and theory is rather complex, but when in gear they can open up entire research fields. I will discuss two opposite cases of scientific work where theory and experiment were interacting and showing that scientific coherence can emerge from these duals works. In the first case, the experiment was performed as a verification of a complex ab-initio modelization. Indeed, time resolved electron diffraction was used to investigate the complex electron lattice interactions in metals and compared the extracted values to the ab-initio calculations. In the second case, simulation was used to support an experimental result. We recently demonstrate the occurrence of self-amplification in prototypical molecular materials upon photo-excitation. Thanks to a recently developed Monte-Carlo model solving mechano-elastic interactions, the main experimental result was reproduced leading to the clear identification of the main parameters at play.

Publié dans Départements, Nanosciences, Séminaires Matériaux-Nanosciences | Commentaires fermés sur Séminaire Roman BERTONI : Experiment triggered by theory vs Theory triggering experiment.

Séminaire DPM : Philippe BODUCH « Des ions lourds et des glaces pour l’astrophysique »

DATE :27 AVRIL 2017 – 10H00 – Salle 050 , Bât 11B

INTERVENANT : Philippe BODUCH
Université de Caen Normandie – CIMAP/GANIL

Depuis 2008, une équipe du CIMAP-GANIL se concentre sur l’irradiation de glaces d’intérêt astrophysique avec des ions lourds. Ces glaces sont composées de molécules simples telles que H2O, CO, CO2, NH3… Elles sont présentes sur les comètes, les satellites de certaines planètes (lunes joviennes par ex.) et sur les grains composant les nuages denses. Ces glaces sont soumises à différentes radiations présentes dans l’espace : UV, vents stellaires, rayons cosmiques… Les irradiations aux protons et aux UV ont fait l’objet de nombreuses études. Avec les ions lourds, seules quelques études ont été réalisées à basse énergie. Il nous a donc paru important de simuler en laboratoire les interactions entre des ions lourds rapides et les glaces présentes dans l’espace afin de comprendre le rôle des rayons cosmiques dans l’évolution de ces glaces. Ces ions déposent localement une très grande quantité d’énergie. Ils peuvent alors générer des effets non observables avec des particules plus légères. Dans ce cadre, je présenterai l’étude de glaces simples et des mélanges à une température de 15 K irradiées par des ions lourds produits par le GANIL (Grand Accélérateur National d’Ions Lourds, Caen, France). Les effets d’irradiations sont analysés in situ par spectroscopie photonique (infra-rouge par transformée de Fourier et UV-Visible). Les résultats présentés lors de ce séminaire porteront sur les effets induits sur la structure de la glace, sur les modifications chimiques et sur le rôle de l’implantation. Les perspectives seront aussi abordées, notamment sur l’utilisation d’un nouveau dispositif ultravide IGLIAS financé par l’ANR ainsi que les travaux sur les molécules plus complexes (molécules aromatiques hétérocycliques, par ex.).

Publié dans Départements, Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Séminaire DPM : Philippe BODUCH « Des ions lourds et des glaces pour l’astrophysique »