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Production scientifique
Mécanique statistique des systèmes désordonnés, en particulier inspirés par des systèmes à l'interface avec la biologie
(2) Production(s) de l'année 2020
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Stochastic modelling of collective motor protein transport through a crossing of microtubules
Auteur(s): Raguin A., Kern N., Parmeggiani A.
(Article) Publié:
Journal Of Theoretical Biology, vol. 505 p.110370 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02957556_v1
DOI: 10.1016/j.jtbi.2020.110370
Exporter : BibTex | endNote
Résumé: The cytoskeleton in eukaryotic cells plays several crucial roles. In terms of intracellular transport, motor proteins use the cytoskeletal filaments as a backbone along which they can actively transport biological cargos such as vesicles carrying biochemical reactants. Crossings between such filaments constitute a key element, as they may serve to alter the destination of such payload. Although motor proteins are known to display a rich behaviour at such crossings, the latter have so far only been modelled as simple branching points. Here we explore a model for a crossing between two microtubules which retains the individual tracks consisting of protofilaments, and we construct a schematic representation of the transport paths. We study collective transport exemplified by the Totally Asymmetric Simple Exclusion Process (TASEP), and provide a full analysis of the transport features and the associated phase diagram, by a generic mean-field approach which we confirm through particle-based stochastic simulations. In particular we show that transport through such a compound crossing cannot be approximated from a coarse-grained structure with a simple branching point. Instead, it gives rise to entirely new and counterintuitive features: the fundamental current-density relation for traffic flow is no longer a single-valued function, and it furthermore differs according to whether it is observed upstream or downstream from the crossing. We argue that these novel features may be directly relevant for interpreting experimental measurements.
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Determining the Mesh Size of Polymer Solutions via the Pore Size Distribution
Auteur(s): Sorichetti V., Hugouvieux Virginie, Kob W.
(Article) Publié:
Macromolecules, vol. 53 p.2568-2581 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02540128_v1
Ref Arxiv: 1908.01484
DOI: 10.1021/acs.macromol.9b02166
WoS: 000526399500029
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
1 Citation
Résumé: In order to determine in polymeric systems the geometrical mesh size ξ, we simulate a solution of coarse-grained polymers with densities ranging from the dilute to the concentrated regime and for different chain lengths. We determine the monomer density fluctuation correlation length ξc from the monomer structure factor as well as the radial distribution function, showing that the identification ξ = ξc is not justified outside of the semidilute regime. In order to better characterize ξ, we compute the pore size distribution (PSD) following two different definitions, one by Torquato et al. and one by Gubbins et al. We find that the mean values of the two distributions, ⟨r⟩T and ⟨r⟩G, display the behavior predicted for ξ by scaling theory, and argue that ξ can be identified with either one of these quantities. This identification allows to interpret the PSD as the distribution of mesh sizes, a quantity which conventional methods cannot access. Finally, we show that it is possible to map a polymer solution on a system of hard or overlapping spheres, for which Torquato’s PSD can be computed analytically and reproduces accurately the PSD of the solution. We give an expression that allows ⟨r⟩T to be estimated with high accuracy in the semidilute regime by knowing only the radius of gyration and the density of the polymers.
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