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SUMMARY:Active Lèvy matter: Hydrodynamic description and linear stability
analysis
DTSTART;VALUE=DATE-TIME:20180904T074500Z
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UID:indico-contribution-39-204@zakopane.if.uj.edu.pl
DESCRIPTION:Speakers: Andrea Cairoli (Imperial College London)\nCollective
ordered motion can emerge spontaneously in many biological systems\, such
as bird flocks\, insect swarms and tissue under dynamic re-organization.
This phenomenon is typically modelled under the active fluid formalism. Ho
wever\, anomalous diffusion\, characterizing particles whose position mean
-square displacement scales non-linearly in time\, is also widespread in b
iology. For instance\, Lèvy walks exhibiting super-diffusion can represen
t an optimal foraging strategy under specific environmental conditions. Su
rprisingly\, the emergence of collective motion in systems displaying such
anomalous diffusive behaviour has not yet been discussed. Here\, we will
investigate a system of active particles performing Lèvy flights and endo
wed with alignment interactions. We will derive the model equation in the
hydrodynamic limit and investigate the stability of its ordered and disord
ered phases. This analysis aims at developing a framework integrating both
anomalous diffusive motility and inter-particle interactions\, thus pavin
g the way for the definition of more realistic active matter models.\n\nht
tps://zakopane.if.uj.edu.pl/event/6/contributions/204/
LOCATION:
URL:https://zakopane.if.uj.edu.pl/event/6/contributions/204/
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SUMMARY:Robust Active Force Detection with the Overdamped Langevin Equatio
n
DTSTART;VALUE=DATE-TIME:20180904T080500Z
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UID:indico-contribution-39-190@zakopane.if.uj.edu.pl
DESCRIPTION:Speakers: Alexander S. Serov (Decision and Bayesian Computatio
n Group\, Department of Neuroscience\, CNRS\, UMR 3571\, Institut Pasteur\
, Paris\; C3BI\, USR 3756\, Institut Pasteur\, CNRS - Paris)\nThe Overdamp
ed Langevin equation describes the inertialess motion of a particle under
deterministic drift and thermal noise. The deterministic drift is the resu
lt of the combined action of active forces and the diffusivity gradient (t
he “spurious” force). For biological applications\, it is important to
distinguish between the two components\, because the former indicates spe
cific interactions\, while the latter is due to a heterogeneous environmen
t\, in which these interactions take place. The spurious force is always p
roportional to the diffusivity gradient\, but the proportionality coeffici
ent is only known for equilibrium systems. This leads to a range of possib
le spurious force values in out-of-equilibrium systems and leads to ambigu
ity in the interpretation of the observed drift. This ambiguity is known a
s the Itô-Stratonovich dilemma. \n\nIn this work\, we do not try to resol
ve the dilemma\, but analyze the information that can be extracted about t
he active forces in an *a priori* unknown out-of-equilibrium system. To th
is end\, we propose a Bayesian method that marginalizes over all possible
values of the spurious force and allows robust identification of active fo
rces in both equilibrium and out-of-equilibrium setups. Under certain assu
mptions\, the main result can be obtained in an analytical form. The metho
d has a significantly decreased false positive rate of active force detect
ion as compared to conventional approaches. We illustrate the practical va
lue of the method by integrating it into an open-source software project a
nd applying it to both numerical trajectories and experimental single-biom
olecule tracks recorded on the cell membrane.\n\nhttps://zakopane.if.uj.ed
u.pl/event/6/contributions/190/
LOCATION:
URL:https://zakopane.if.uj.edu.pl/event/6/contributions/190/
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SUMMARY:Anomalous diffusion\, ergodicity\, ageing\, and non-gaussianity
DTSTART;VALUE=DATE-TIME:20180904T070000Z
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UID:indico-contribution-39-170@zakopane.if.uj.edu.pl
DESCRIPTION:Speakers: Ralf Metzler (University of Potsdam)\nA surging amou
nt of experimental and simulations studies reveals persistent\nanomalous d
iffusion in the membranes and volume of living biological cells\nas well a
s other complex fluids [1]. This anomalous diffusion is observed\nfor micr
on-sized objects down to labelled single molecules such as green\nfluoresc
ent proteins [2].\n\nIn this talk I will present results from large scale
computer simulations\nand stochastic analysis of the motion of lipids and
embedded proteins in\nlipid bilayer model membranes [3]\, indicating that
increased disorder leads\nto longer and longer lasting anomalous diffusion
. In particular\, the motion\nof lipids and proteins can become non-Gaussi
an [3]. In the membranes of living\ncells anomalous diffusion of embedded
protein channels can last over several\nhundreds of seconds [4].\n\nAnomal
ous diffusion inside the volume of cells will be discussed\, as well. In\n
particular\, the emergence of non-Gaussian diffusion patterns for both Fic
kian\nand non-Fickian diffusion will be addressed within the framework of
diffusing\ndiffusivities [5].\n\nThe observed stochastic dynamics may be e
rgodic or not\, depending on the\nexact physical mechanisms governing the
motion of the test particle. The\ntalk will discuss how non-ergodic behavi
our needs to be taken into account\nwhen interpreting data from stochastic
systems. In addition effects of ageing\nwill be explained [6].\n\n\n[1] F
. Hofling and T. Franosch\, Rep Progr Phys 76\, 046602 (2013)\;\n K. No
erregaard\, R. Metzler\, C. M. Ritter\, K. Berg-Soerensen\, and L. B.\n
Oddershede\, Chem. Rev. 117\, 4342 (2017).\n\n[2] C Di Rienzo\, V Piazza\
, E Gratton\, F Beltram\, and F Cardarelli\, Nature Comm\n 5\, 5891 (20
14).\n\n[3] J-H Jeon\, HM-S Monne\, M Javanainen\, and R Metzler\, Phys Re
v Lett 109\,\n 188103 (2012)\; J-H Jeon\, M Javanainen\, H Martinez-Sea
ra\, R Metzler\, and\n I Vattulainen\, Phys Rev X 6\, 021006 (2016).\n\
n[4] AV Weigel\, B Simon\, MM Tamkun\, and D Krapf\, Proc Natl Acad Sci US
A 108\,\n 6438 (2011).\n\n[5] AV Chechkin\, F Seno\, R Metzler\, and IM
Sokolov\, Phys Rev X 7\, 021002 (2017)\;\n TJ Lampo\, S Stylianidou\,
MP Backlund\, PA Wiggins\, AJ Spakowitz\, Biophys J\n 112\, 532 (2017).
\n\n[6] R Metzler\, J-H Jeon\, AG Cherstvy\, E Barkai\, Phys Chem Chem Phy
s 16 24128\n (2014)\; JHP Schulz\, E Barkai\, R Metzler\, Phys Rev X 4\,
011028 (2014).\n\nhttps://zakopane.if.uj.edu.pl/event/6/contributions/170
/
LOCATION:
URL:https://zakopane.if.uj.edu.pl/event/6/contributions/170/
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