Ref HAL: hal-00823864_v1
DOI: 10.1103/PhysRevB.87.195429
Résumé: We develop a nonlocal dielectric-response theory to describe the temperature dependence of exciton lifetime in metal-semiconductor heterostructures. Coupling between excitons and surface plasmons results in a strongly nonmonotonous behavior of exciton decay rate versus temperature, affected by surface plasmons on both sides of the metal layer. Unlike the photons, surface plasmons are not able to escape the sample; hence, the additional decay channel for excitons appears solely due to the plasmon scattering in metal and metal-dielectric interfaces. Tuning the plasmon frequency, one can control the exciton lifetime and under certain conditions emission efficiency

Ref HAL: in2p3-00822639_v1
Ref Arxiv: 1305.2942
Résumé: The distributions of event-by-event harmonic flow coefficients v_n for n=2-4 are measured in sqrt(s_NN)=2.76 TeV Pb+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using charged particles with transverse momentum pT> 0.5 GeV and in the pseudorapidity range |eta|<2.5 in a dataset of approximately 7 ub^-1 recorded in 2010. The shapes of the v_n distributions are described by a two-dimensional Gaussian function for the underlying flow vector in central collisions for v_2 and over most of the measured centrality range for v_3 and v_4. Significant deviations from this function are observed for v_2 in mid-central and peripheral collisions, and a small deviation is observed for v_3 in mid-central collisions. It is shown that the commonly used multi-particle cumulants are insensitive to the deviations for v_2. The v_n distributions are also measured independently for charged particles with 0.51 GeV. When these distributions are rescaled to the same mean values, the adjusted shapes are found to be nearly the same for these two pT ranges. The v_n distributions are compared with the eccentricity distributions from two models for the initial collision geometry: a Glauber model and a model that includes corrections to the initial geometry due to gluon saturation effects. Both models fail to describe the experimental data consistently over most of the measured centrality range.

Commentaires: 41 pages plus author list (62 pages total), 33 figures, submitted to JHEP, All figures including auxiliary figures can be found at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2012-10/; See paper for full list of authors

Ref HAL: hal-00823177_v1
Ref Arxiv: 1302.4868
DOI: 10.1038/nphys2592
Résumé: The glass transition, extensively studied in dense fluids, polymers, or colloids, corresponds to a dramatic evolution of equilibrium transport coefficients upon a modest change of control parameter, like temperature or pressure. A similar phenomenology is found in many systems evolving far from equilibrium, such as driven granular media, active and living matter. While many theories compete to describe the glass transition at thermal equilibrium, very little is understood far from equilibrium. Here, we solve the dynamics of a specific, yet representative, class of glass models in the presence of nonthermal driving forces and energy dissipation, and show that a dynamic arrest can take place in these nonequilibrium conditions. While the location of the transition depends on the specifics of the driving mechanisms, important features of the glassy dynamics are insensitive to details, suggesting that an 'effective' thermal dynamics generically emerges at long time scales in nonequilibrium systems close to dynamic arrest.

Commentaires: 7 pages, 2 figs Journal: Nature Phys. 9, 310 (2013)

Ref HAL: hal-00822680_v1
Ref Arxiv: 1302.1673
DOI: 10.1103/PhysRevE.87.052703
Résumé: The closure of long equilibrated denaturation bubbles in DNA is studied using Brownian dynamics simulations. A minimal mesoscopic model is used where the double-helix is made of two interacting bead-spring freely rotating strands, with a non-zero torsional modulus in the duplex state, $\kappa_\phi=$200 to 300 kT. For DNAs of lengths N=40 to 100 base-pairs (bps) with a large initial bubble in their middle, long closure times of 0.1 to 100 microseconds are found. The bubble starts winding from both ends until it reaches a 10 bp metastable state. The final closure is limited by three competing mechanisms depending on $\kappa_\phi$ and N: arms diffusion until their alignment, bubble diffusion along the DNA until one end is reached, or local Kramers process (crossing over a torsional energy barrier). For clamped ends or long DNAs, the closure occurs via this latter temperature activated mechanism, yielding for the first time a good quantitative agreement with experiments.

Ref HAL: hal-00822944_v1
Résumé: Since 1992 and the apparition of highly dispersible silica as a nanofiller in the green-tire formulation, the structure and dynamics of precipitated silica-SBR nanocomposites produced by solid phase mixing is of a great interest for manufacturers. In this work, we make use of SAXS and TEM to investigate the organization of silica nanoparticles (Rsi 10nm) varying the filler fraction while dynamics is studied by broadband dielectric spectroscopy (BDS) and rheology. The structural analysis of such complex materials revealed a multi-scale filler organization based on a 3D fractal network built up from aggregates made of nanoparticles [1]. The characteristics (size, average aggregation number, compacity…) of such aggregates are extracted from a combined analysis of SAXS and TEM data taking into account the aggregate polydispersity (Nagg50, 35%). Jointly with mechanical experiments, this analysis enables us to estimate the critical aggregation volume fraction at which the network fully percolates (Figure 1a). In the same context, the ionic conductivity () measured by BDS at high temperature displays a jump from 12.7% of silica that we associate with the percolation threshold observed in rheology (Figure 1b). Moreover, at lower temperatures, a Maxwell-Wagner-Sillars process related to the charges blocked at the interface between silica and polymer is observed at temperatures higher than the glass transition in the nanocomposites.

Ref HAL: hal-00822935_v1
Résumé: Since 1992 and the apparition of highly dispersible silica as a nanofiller in the green-tire formulation, the structure and dynamics of precipitated silica-SBR nanocomposites produced by solid phase mixing is of a great interest for manufacturers. In this work, we make use of SAXS and TEM to investigate the organization of silica nanoparticles (Rsi 10nm) varying the filler fraction while dynamics is studied by broadband dielectric spectroscopy (BDS) and rheology. The structural analysis of such complex materials revealed a multi-scale filler organization based on a 3D fractal network built up from aggregates made of nanoparticles [1]. The characteristics (size, average aggregation number, compacity...) of such aggregates are extracted from a combined analysis of SAXS and TEM data taking into account the aggregate polydispersity (Nagg50, 35%). Jointly with mechanical experiments, this analysis enables us to estimate the critical aggregation volume fraction at which the network fully percolates (Figure 1a). In the same context, the ionic conductivity () measured by BDS at high temperature displays a jump from 12.7% of silica that we associate with the percolation threshold observed in rheology (Figure 1b). Moreover, at lower temperatures, a Maxwell-Wagner-Sillars process related to the charges blocked at the interface between silica and polymer is observed at temperatures higher than the glass transition in the nanocomposites.

Ref HAL: hal-00822746_v1
DOI: 10.1007/s10867-013-9320-1
Résumé: Compared to organisms such as bacteria and eukaryotic cells, viruses have such a low level of complexity that they were at first regarded as being proto-organisms, at the borderline between living and inanimate matter. This view was gradually superseded by the recognition that viruses are highly efficient organisms which have evolved in order to hijack the "active" biological machinery of the infected cells. Recent studies revealed how physical mechanisms are used by the viruses for guiding all salient steps of their "life cycle" This fact has also strongly motivated the recent upsurge of theoretical and experimental studies addressing the molecular basis of the key problems in virology. Specifically, the topics that are presently investigated most intensively include the following: the self-assembly and maturation of viral capsids, the functioning of the molecular motors that loads the viral genome inside preformed capsids, the conformational arrangement of the DNA or RNA inside capsids, the physical forces at play during the ejection of the viral DNA into the host cell, and the electrostatic interactions between the nucleic acids and coat proteins and virus-based nano-composites. The abovementioned efforts in characterizing the key molecular aspects of single viral particles are complemented by the very active research in the modeling of viral epidemics where, again, physics-based statistical mechanical approaches are widely used. A "physical virology" topical conference held at the ICTP in 2012 provided a timely state-of-the art perspective on the subject that is rapidly progressing because of the ongoing advancements in experimental techniques (cryo-EM imaging and single-molecule manipulation) and theoretical ones (large-scale simulations). It came at a very timely junction as the first Gordon conference on physical virology was held in 2009 in Galveston, Texas, and the latest one in Ventura, California, in 2013, which could be taken as the defining events in the establishment of the whole field of physical virology. This special issue of the Journal of Biological Physics is entirely dedicated to physical virology and aims to present a broad overview of the current state of the art in various subtopics of physical virology and stimulate additional activity in this rapidly developing field.