Jeudi 29 Novembre 2012 à 14h, Salle 114, bât. 210 (LPT)
Hiroki OHTA (LPTMS)
Lane formation in a lattice model for oppositely driven binary particles
I will introduce a two-dimensional lattice model for oppositely driven binary
particles with purely repulsive interactions
where some classes of steady states have been constructed in systematic ways.
Using such constructions, I will discuss nonequilibrium phase transitions in this
lattice model [1].
Also, I would like to discuss those relevance to lane formations in colloidal
suspensions [2] [3].
References :
[1] H. Ohta, Europhys. Lett. 99, 40006 (2012).
[2] J. Dzubiella, G. P. Hoffmann, H. Löwen, Phys. Rev. E 65, 021402 (2002).
[3] T. Vissers, A. Wysocki, M. Rex, H. Löwen, C. P. Royall, A. Imhof, A.
van Blaaderen, Soft Matter 7, 2352 (2011).
Jeudi 25 Octobre 2012 à 14h, Salle 114, bât. 210 (LPT)
Joel STAVANS (Dpt Physics of Complex Systems, Weizmann Institute of Science, Israel)
Effects of Post-Transcriptional Regulation on Phenotypic Noise in Bacteria
Cell-to-cell variations in protein abundance or noise give rise to phenotypic
variability between isogenic cells. Studies of noise have focused on stochasticity
introduced at transcription, yet the effects of post-transcriptional regulatory
processes on noise remain unknown. We study the effects of RyhB, a small-RNA of E.
coli produced upon iron stress, on the phenotypic variability of two of its
down-regulated target proteins, using dual chromosomal fusions to fluorescent
reporters and measurements in live individual cells. Remarkably, the total noise of
each of the target proteins is robust over a wide range of RyhB production rates
despite cells being in stress, and that coordinate down-regulation of the two target
proteins by RyhB reduces the mutual correlation between their levels. Hence an
increase in phenotypic variability under stress is achieved by decoupling the
expression of different target protein in the same cell, rather than by an increase
in the total noise of each. Extrinsic noise provides the dominant contribution to
the total protein noise over the same range of RyhB production rates. No evidence of
a theoretically-predicted peak in noise at finite RyhB production rates is found.
Stochastic simulations incorporating extrinsic and intrinsic noise sources reproduce
qualitatively key features of our observations.
Jeudi 18 Octobre 2012 à 14h, Salle 201, bât. 100A (LPTMS)
Sara JABBARI-FAROUJI (LPTMS - Orsay)
Interplay of anisotropy and interactions in charged colloidal disks
Charged plate-like colloidal suspensions such as gibbsite and some clays exhibit interesting and
rich phase behavior including liquid-crystalline and arrested gel-like states. The anisotropic
shape of such particles suggests that these materials could form liquid crystalline phases due to
the competition between positional and orientational entropy. In some cases, however,
isotropic-nematic transition is hindered by formation of a gel-like viscoelastic phase. The
question that arises is how the electrostatic interactions influence the liquid crystal
formation. Motivated by these experimental findings, we have investigated the structure and
dynamics of charged disks by means of Monte-Carlo simulations. In this talk, I will clarify the
the role of anisotropic nature of screened electrostatic interactions on the formation of
liquid-crystalline phases and arrested states. Finally, I will compare the results of our
simulations with experiments.
Jeudi 27 Septembre 2012 à 14h, Salle 114, bât. 210 (LPT)
Ellen SAADA (Laboratoire MAP5, Université Paris Descartes)
Comportement hydrodynamique de systèmes de particules
attractifs en milieu aléatoire ;
applications à des modèles de misanthropes et de trafic.
Travaux en collaboration avec
C. Bahadoran (Clermont-Ferrand), H. Guiol (Grenoble),
T. Mountford (Lausanne), K. Ravishankar (SUNY, New Paltz).
Nous avons obtenu la limite hydrodynamique trempee (’quenched’)
sous un changement d’echelle hyperbolique pour des systemes de
particules attractifs sur Z dans un environnement aleatoire
ergodique. La limite est donnee par la solution entropique
d’une loi de conservation scalaire avec une fonction de flux
macroscopique lipschitzienne. Notre resultat est une loi forte
des grands nombres, nous le demontrons par une methode constructive.
Nous illustrons notre resultat sur plusieurs exemples, comme des
generalisations du processus de misanthropes, et de processus de
K-exclusion a k etapes, avec differents types d’environnement
aleatoire. Nous detaillerons un modele de trafic et un modele
de file d’attente.
Accès / Find us
Séminaire commun LPT/LPTMS 2012-2013