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De Castro J.G.,University of Amsterdam | Zargar R.,University of Amsterdam | Habibi M.,University of Amsterdam | Varol S.H.,Max Planck Institute for Polymer Research | And 4 more authors.
Applied Physics Letters

Polymer composite materials are widely used for their exceptional mechanical properties, notably their ability to resist large deformations. Here, we examine the failure stress and strain of rubbers reinforced by varying amounts of nano-sized silica particles. We find that small amounts of silica increase the fracture stress and strain, but too much filler makes the material become brittle and consequently fracture happens at small deformations. We thus find that as a function of the amount of filler there is an optimum in the breaking resistance at intermediate filler concentrations. We use a modified Griffith theory to establish a direct relation between the material properties and the fracture behavior that agrees with the experiment. © 2015 AIP Publishing LLC. Source

Hekstra D.R.,Rockefeller University | Cocco S.,Institute for Advanced Study | Cocco S.,Laboratoire Of Physique Statistique Of Lecole Normale Superieure | Monasson R.,Institute for Advanced Study | And 3 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics

The dynamical evolution of complex systems is often intrinsically stochastic and subject to external random forces. In order to study the resulting variability in dynamics, it is essential to make measurements on replicate systems and to separate arbitrary variation of the average dynamics of these replicates from fluctuations around the average dynamics. Here we do so for population time-series data from replicate ecosystems sharing a common average dynamics or common trend. We explain how model parameters, including the effective interactions between species and dynamical noise, can be estimated from the data and how replication reduces errors in these estimates. For this, it is essential that the model can fit a variety of average dynamics. We then show how one can judge the quality of a model, compare alternate models, and determine which combinations of parameters are poorly determined by the data. In addition we show how replicate population dynamics experiments could be designed to optimize the acquired information of interest about the systems. Our approach is illustrated on a set of time series gathered from replicate microbial closed ecosystems. © 2013 American Physical Society. Source

Nigues A.,Laboratoire Of Physique Statistique Of Lecole Normale Superieure | Siria A.,Laboratoire Of Physique Statistique Of Lecole Normale Superieure | Verlot P.,University Claude Bernard Lyon 1
Nature Communications

The ability to cool single ions, atomic ensembles, and more recently macroscopic degrees of freedom down to the quantum ground state has generated considerable progress and perspectives in fundamental and technological science. These major advances have been essentially obtained by coupling mechanical motion to a resonant electromagnetic degree of freedom in what is generally known as laser cooling. Here, we experimentally demonstrate the first self-induced coherent cooling mechanism that is not mediated by an electromagnetic resonance. Using a focused electron beam, we report a 50-fold reduction of the motional temperature of a nanowire. Our result primarily relies on the sub-nanometre confinement of the electron beam and generalizes to any delayed and spatially confined interaction, with important consequences for near-field microscopy and fundamental nanoscale dissipation mechanisms. © 2015 Macmillan Publishers Limited. All rights reserved. Source

Ciarletta P.,Laboratoire Of Physique Statistique Of Lecole Normale Superieure | Foret L.,Laboratoire Of Physique Statistique Of Lecole Normale Superieure | Amar M.B.,Laboratoire Of Physique Statistique Of Lecole Normale Superieure
Journal of the Royal Society Interface

Cutaneous melanoma is disproportionately lethal despite its relatively low incidence and its potential for cure in the early stages. The aim of this study is to foster understanding of the role of microstructure on the occurrence of morphological changes in diseased skin during melanoma evolution. The authors propose a biomechanical analysis of its radial growth phase, investigating the role of intercellular/stromal connections on the initial stages of epidermis invasion. The radial growth phase of a primary melanoma is modelled within the multi-phase theory of mixtures, reproducing the mechanical behaviour of the skin layers and of the epidermal-dermal junction. The theoretical analysis takes into account those cellular processes that have been experimentally observed to disrupt homeostasis in normal epidermis. Numerical simulations demonstrate that the loss of adhesiveness of the melanoma cells both to the basal laminae, caused by deregulation mechanisms of adherent junctions, and to adjacent keratynocytes, consequent to a downregulation of E-cadherin, are the fundamental biomechanical features for promoting tumour initiation. Finally, the authors provide the mathematical proof of a long wavelength instability of the tumour front during the early stages of melanoma invasion. These results open the perspective to correlate the early morphology of a growing melanoma with the biomechanical characteristics of its micro-environment. © 2010 The Royal Society. Source

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