CLUSEL Maxime
Organisme : CNRS
Chargé de Recherche
Maxime.Clusel
univ-montp2.fr
0467144933
Bureau: 273, Etg: 2, Bât: 13 - Site : Campus Triolet
Domaines de Recherche: - Physique/Matière Condensée/Mécanique statistique
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Productions scientifiques :
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Generalised Extreme Statistics and Sum of Correlated Variables 
Auteur(s): CLUSEL M.
Conférence invité: Aggregation, Inference and Rare Events in the Natural and Socio-Economic Sciences (Warwick, GB, 2012-05-17)
Ref HAL: hal-00755545_v1
Résumé: So-called "generalised extreme value distributions" have become popular fitting functions for fluctuations observed in many correlated systems. We show that generalised extreme value statistics --the statistics of the $k^\mathrm{th}$ largest value among a large set of random variables-- can be mapped onto a problem of random sums. This allows us to identify classes of non-identical and (generally) correlated random variables with a sum distributed according to one of the three ($k$-dependent) asymptotic distributions of extreme value statistics, namely the Gumbel, Fréchet and Weibull distributions. These classes, as well as the limit distributions, are naturally extended to real values of $k$, thus providing a clear interpretation to the onset of Gumbel distributions with non-integer index $k$ in the statistics of global observables. This is one of the very few known generalisations of the central limit theorem to non-independent random variables. Finally, in the context of a simple physical model, we relate the index $k$ to the ratio of the correlation length to the system size, which remains finite in strongly correlated systems. I will conclude by presenting possible extension of this approach to extreme value statistics of correlated random variables.
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Temperature Can Enhance Coherent Oscillations at a Landau-Zener Transition
Auteur(s): Whitney Robert, CLUSEL M., Ziman Timothy
(Article) Publié:
Physical Review Letters, vol. 107 p.210402 (2011)
Ref HAL: hal-00641711_v1
DOI: 10.1103/PhysRevLett.107.210402
Résumé: We consider sweeping a system through a Landau-Zener avoided crossing, when that system is also coupled to an environment or noise. Unsurprisingly, we find that decoherence suppresses the coherent oscillations of quantum superpositions of system states, as superpositions decohere into mixed states. However, we also find an effect we call "Lamb-assisted coherent oscillations," in which a Lamb shift exponentially enhances the coherent-oscillation amplitude. This dominates for high-frequency environments such as super-Ohmic environments, where the coherent oscillations can grow exponentially as either the environment coupling or temperature are increased. The effect could be used as an experimental probe for high-frequency environments in such systems as molecular magnets, solid-state qubits, spin-polarized gases (neutrons or He3), or Bose condensates.
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Unfolding protein with an atomic force microscope: Force-fluctuation induced non-exponential kinetics
Auteur(s): CLUSEL M., Corwin Eric
(Article) Publié:
Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, vol. 84 p.041920 (2011)
Ref HAL: hal-00617317_v2
Ref Arxiv: 1108.5701
DOI: 10.1103/PhysRevE.84.041920
Résumé: We show that in experimental atomic force microscopy studies of the lifetime distribution of mechanically stressed folded proteins the effects of externally applied fluctuations can not be distinguished from those of internally present fluctuations. In certain circumstances this leads to artificially non-exponential lifetime distributions which can be misinterpreted as a signature of protein complexity. This work highlights the importance of fully characterizing and controlling external sources of fluctuation in mechanical studies of proteins before drawing conclusions on the physics at play on the molecular level.
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