
BibTeX:
@article{Barbier2015, author = {Barbier, A. and Aghavnian, T. and Badjeck, V. and Mocuta, C. and Stanescu, D. and Magnan, H. and Rountree, C. L. and Belkhou, R. and Ohresser, P. and Jedrecy, N.}, title = {Antiferromagnetic longrange spin ordering in Fe and NiFe2doped BaTiO3 multiferroic layers}, journal = {Physical Review B}, publisher = {American Physical Society}, year = {2015}, volume = {91}, pages = {035417}, url = {http://link.aps.org/doi/10.1103/PhysRevB.91.035417}, doi = {10.1103/PhysRevB.91.035417} } 

Abstract: This study investigates the mechanical response of sodium borosilicate (SBN) glasses as a function of their chemical composition. Vickers's indentation tests provide an estimate of the material hardness (HV) and indentation fracture toughness (K_C^VIF) plus the amount of densification/shear flow processes. Sodium content significantly impacts the glass behavior under a sharp indenter. Low sodium glasses maintain high connected networks and low Poisson's ratios ($). This entails significant densification processes during deformation. Conversely, glasses with high sodium content, i.e. large $, partake in a more depolymerized network favoring deformation by shear flow. As a consequence, indentation patterns differ depending on the processes occurring. Densification processes appear to hinder the formation of halfpenny medianradial cracks. Increasing ? favors shear flow and residual stresses enhance the development of halfpenny medianradial cracks. Hence, K_C^VIF decreases linearly with $. 
BibTeX:
@article{Barlet2015, author = {Marina Barlet and JeanMarc Delaye and Thibault Charpentier and Mickael Gennisson and Daniel Bonamy and Tanguy Rouxel and Cindy L. Rountree}, title = {Hardness and toughness of sodium borosilicate glasses via Vickers's indentations }, journal = {Journal of NonCrystalline Solids }, year = {2015}, volume = {417418}, pages = {66  79}, url = {http://www.sciencedirect.com/science/article/pii/S0022309315000538}, doi = {10.1016/j.jnoncrysol.2015.02.005} } 

BibTeX:
@article{Baudet2015, author = {C. Baudet and M. Bon Mardion and P. Bonnay and A. Braslau and B. Castaing and F. Chillà and L. Chevillard and F. Daviaud and P. Diribarne and B. Dubrulle and D. Durì and D. Faranda and B. Gallet and M. Gibert and A. Girard and B. Hébral and I. Moukharski and J.M. Poncet and J.P. Moro and P.E. Roche and B. Rousset and E. Rusaouën and B. SaintMichel and J. Salort and EW. Saw and K. Steiros and C. WiertelGasquet}, title = {Local Velocity Measurements in the Shrek Experiment at High Reynolds Number}, booktitle = {European Journal of Mechanics}, journal = {European Journal of Mechanics}, year = {2015} } 

Abstract: Zeropoint quantum fluctuations of the electromagnetic vacuum create the widely known Londonvan der Waals attractive force between two atoms. Recently, there has been a revived interest in the interaction of rotating matter with the quantum vacuum. Here, we consider a rotating pair of atoms maintained by Londonvan der Waals forces and calculate the frictional torque they experience due to zeropoint radiation. Using a semiclassical framework derived from the fluctuation dissipation theorem, we take into account the full electrostatic coupling between induced dipoles. Considering the case of zero temperature only, we find a braking torque proportional to the angular velocity and to the third power of the fine structure constant. Although very small compared to Londonvan derWaals attraction, the torque is strong enough to induce the formation of dimers in binary collisions. This new friction phenomenon at the atomic level should induce a paradigm change in the explanation of irreversibility. 
BibTeX:
@article{Bercegol2015, author = {Bercegol, Herve and Lehoucq, Roland}, title = {Vacuum Friction on a Rotating Pair of Atoms}, journal = {Physical Review Letters}, year = {2015}, volume = {115}, number = {9}, pages = {090402}, doi = {10.1103/PhysRevLett.115.090402} } 

Abstract: Considering systems of selfpropelled polar particles with nematic interactions ("rods"), we compare the continuum equations describing the evolution of polar and nematic order parameters, derived either from Smoluchowski or Boltzmann equations. Our main goal is to understand the discrepancies between the continuum equations obtained so far in both frameworks. We first show that, in the simple case of pointlike particles with only alignment interactions, the continuum equations obtained have the same structure in both cases. We further study, in the Smoluchowski framework, the case where an interaction force is added on top of the aligning torque. This clarifies the origin of the additional terms obtained in previous works. Our observations lead us to emphasize the need for a more involved closure scheme than the standard normal form of the distribution when dealing with active systems. 
BibTeX:
@article{Bertin2015, author = {Bertin, Eric and Baskaran, Aparna and Chate, Hugues and Marchetti, M. Cristina}, title = {Comparison between Smoluchowski and Boltzmann approaches for selfpropelled rods}, journal = {Physical Review E}, year = {2015}, volume = {92}, number = {4}, pages = {042141}, doi = {10.1103/PhysRevE.92.042141} } 

Abstract: A thermally chargeable capacitor containing a binary solution of 1ethyl3methylimidazolium bis(trifluoromethylsulfonyl)imide in acetonitrile is electrically charged by applying a temperature gradient to two ideally polarisable electrodes. The corresponding thermoelectric coefficient is 1.7 mV/K for platinum foil electrodes and 0.3 mV/K for nanoporous carbon electrodes. Stored electrical energy is extracted by discharging the capacitor through a resistor. The measured capacitance of the electrode/ionicliquid interface is 5 mu F for each platinum electrode while it becomes four orders of magnitude larger, approximate to 36 mF, for a single nanoporous carbon electrode. Reproducibility of the effect through repeated chargingdischarging cycles under a steadystate temperature gradient demonstrates the robustness of the electrical charging process at the liquid/electrode interface. The acceleration of the charging by convective flows is also observed. This offers the possibility to convert wasteheat into electric energy without exchanging electrons between ions and electrodes, in contrast to what occurs in most thermogalvanic cells. (C) 2015 AIP Publishing LLC. 
BibTeX:
@article{Bonetti2015a, author = {Bonetti, Marco and Nakamae, Sawako and Huang, Bo Tao and Salez, Thomas J. and WiertelGasquet, Cecile and Roger, Michel}, title = {Thermoelectric energy recovery at ionicliquid/electrode interface}, journal = {Journal of Chemical Physics}, year = {2015}, volume = {142}, number = {24}, pages = {244708}, doi = {10.1063/1.4923199} } 

Abstract: Fish schools are able to display a rich variety of collective states and behavioural responses when they are confronted by threats. However, a school's response to perturbations may be different depending on the nature of its collective state. Here we use a previously developed datadriven fish school model to investigate how the school responds to perturbations depending on its different collective states, we measure its susceptibility to such perturbations, and exploit its relation with the intrinsic fluctuations in the school. In particular, we study how a single or a small number of perturbing individuals whose attraction and alignment parameters are different from those of the main population affect the longterm behaviour of a school. We find that the responsiveness of the school to the perturbations is maximum near the transition region between milling and schooling states where the school exhibits multistability and regularly shifts between these two states. It is also in this region that the susceptibility, and hence the fluctuations, of the polarization order parameter is maximal. We also find that a significant school's response to a perturbation only happens below a certain threshold of the noise to social interactions ratio. 
BibTeX:
@article{Calovi2015, author = {Calovi, Daniel S. and Lopez, Ugo and Schuhmacher, Paul and Chate, Hugues and Sire, Clement and Theraulaz, Guy}, title = {Collective response to perturbations in a datadriven fish school model}, journal = {Journal of the Royal Society Interface}, year = {2015}, volume = {12}, number = {104}, pages = {20141362}, doi = {10.1098/rsif.2014.1362} } 

BibTeX:
@article{Cambonie2015, author = {Cambonie, T. and Bares, J. and Hattali, M. L. and Bonamy, D. and Lazarus, V. and Auradou, H.}, title = {Effect of the porosity on the fracture surface roughness of sintered materials: From anisotropic to isotropic selfaffine scaling}, journal = {Physical Review E}, publisher = {American Physical Society}, year = {2015}, volume = {91}, pages = {012406}, url = {http://link.aps.org/doi/10.1103/PhysRevE.91.012406}, doi = {10.1103/PhysRevE.91.012406} } 

Abstract: We present a spatiotemporal analysis of a statistically stationary rotatingturbulence experiment, aiming to extract a signature of inertial waves and to determine the scales and frequencies at which they can be detected. The analysis uses twopoint spatial correlations of the temporal Fourier transform of velocity fields obtained from timeresolved stereoscopic particle image velocimetry measurements in the rotating frame. We quantify the degree of anisotropy of turbulence as a function of frequency and spatial scale. We show that this spacetimedependent anisotropy is well described by the dispersion relation of linear inertial waves at large scale, while smaller scales are dominated by the sweeping of the waves by fluid motion at larger scales. This sweeping effect is mostly due to the lowfrequency quasitwodimensional component of the turbulent flow, a prominent feature of our experiment that is not accounted for by waveturbulence theory. These results question the relevance of this theory for rotating turbulence at the moderate Rossby numbers accessible in laboratory experiments, which are relevant to most geophysical and astrophysical flows. 
BibTeX:
@article{Campagne2015, author = {Campagne, Antoine and Gallet, Basile and Moisy, Frederic and Cortet, PierrePhilippe}, title = {Disentangling inertial waves from eddy turbulence in a forced rotating turbulence experiment}, journal = {Physical Review E}, year = {2015}, volume = {91}, number = {4}, pages = {043016}, doi = {10.1103/PhysRevE.91.043016} } 

BibTeX:
@article{Charignon2015, author = {Charignon, T. and Lloveras, P. and Chatain, D. and Truskinovsky, L. and Vives, E. and Beysens, D. and Nikolayev, V. S.}, title = {Criticality in the sloweddown boiling crisis at zero gravity}, journal = {Physical Review E}, publisher = {American Physical Society}, year = {2015}, volume = {91}, pages = {053007}, url = {http://link.aps.org/doi/10.1103/PhysRevE.91.053007}, doi = {10.1103/PhysRevE.91.053007} } 

Abstract: Atmospheric midlatitude circulation is dominated by a zonal, westerly flow. Such a flow is generally symmetric, but it can be occasionally broken up by blocking anticyclones. The subsequent asymmetric flow can persist for several days. In this paper, we apply new mathematical tools based on the computation of an extremal index in order to reexamine the dynamical mechanisms responsible for the transitions between zonal and blocked flows. We discard the claim that midlatitude circulation features two distinct stable equilibria or chaotic regimes, in favor of a simpler mechanism that is well understood in dynamical systems theory: we identify the blocked flow as an unstable fixed point (or saddle point) of a single basin chaotic attractor, dominated by the westerlies regime. We also analyze the North Atlantic Oscillation and the Arctic Oscillation atmospheric indices, whose behavior is often associated with the transition between the two circulation regimes, and investigate analogies and differences with the bidimensional blocking indices. We find that the Arctic Oscillation index, which can be thought as a proxy for a hemispheric average of the TibaldiMolteni blocking index, tracks unstable fixed points. On the other hand, the North Atlantic Oscillation, representative only for local properties of the North Atlantic blocking dynamics, does not show any trace of the presence of unstable fixed points of the dynamics. 
BibTeX:
@article{Faranda2015, author = {D. Faranda and G. Masato and N. Moloney and Y. Sato and F. Daviaud and B. Dubrulle and P. Yiou}, title = {The switching between zonal and blocked midlatitude atmospheric circulation: a dynamical system perspective}, journal = {Climate Dynamics}, year = {2015}, pages = {113}, url = {http://dx.doi.org/10.1007/s0038201529216}, doi = {10.1007/s0038201529216} } 
Abstract: Abstract We address the problem of defining early warning indicators of financial crises. To this purpose, we fit the relevant time series through a class of linear models, known as autoregressive movingaverage (ARMA(p, q)) models. By running such a fit on intervals of the time series that can be considered stationary, we first determine the typical ARMA( p Â¯ , q Â¯ ). Such a model exists over windows of about 60 days and turns out to be an AR(1). For each of them, we estimate the relative parameters, i.e. Ïi and Î¸i on the same running windows. Then, we define a distance Ï from such typical model in the space of the likelihood functions and compute it on short intervals of stocks indexes. Such a distance is expected to increase when the stock market deviates from its normal state for the modifications of the volatility which happen commonly before a crisis. We observe that Ï computed for the Dow Jones, Standard and Poorâs and EURO STOXX 50 indexes provides an effective early warning indicator which allows for detection of the crisis events that showed precursors. 
BibTeX:
@article{Faranda2015a, author = {D. Faranda and F. M. E. Pons and E. Giachino and S. Vaienti and B. Dubrulle}, title = {Early warnings indicators of financial crises via auto regressive moving average models}, journal = {Communications in Nonlinear Science and Numerical Simulation}, year = {2015}, volume = {29}, number = {1â3}, pages = {233239}, url = {http://www.sciencedirect.com/science/article/pii/S1007570415001653} } 

Abstract: We consider the flow of a Newtonian fluid in a threedimensional domain, rotating about a vertical axis and driven by a vertically invariant horizontal body force. This system admits vertically invariant solutions that satisfy the 2D NavierStokes equation. At high Reynolds number and without global rotation, such solutions are usually unstable to threedimensional perturbations. By contrast, for strong enough global rotation, we prove rigorously that the 2D (and possibly turbulent) solutions are stable to vertically dependent perturbations. We first consider the 3D rotating NavierStokes equation linearized around a statistically steady 2D flow solution. We show that this base flow is linearly stable to vertically dependent perturbations when the global rotation is fast enough: under a Reynoldsnumberdependent threshold value Ro(c)(Re) of the Rossby number, the flow becomes exactly 2D in the longtime limit, provided that the initial 3D perturbations are small. We call this property linear twodimensionalization. We compute explicit lower bounds on Ro(c)(Re) and therefore determine regions of the parameter space. (Re, Ro) where such exact twodimensionalization takes place. We present similar results in terms of the forcing strength instead of the rootmeansquare velocity: the global attractor of the 2D NavierStokes equation is linearly stable to vertically dependent perturbations when the forcingbased Rossby number Ro((f)) is lower than a Grashofnumberdependent threshold value Ro(c)((f))(Gr). We then consider the fully nonlinear 3D rotating NavierStokes equation and prove absolute twodimensionalization: we show that, below some threshold value Ro(abs)((f))(Gr) of the forcingbased Rossby number, the flow becomes twodimensional in the longtime limit, regardless of the initial condition (including initial 3D perturbations of arbitrarily large amplitude). These results shed some light on several fundamental questions of rotating turbulence: for arbitrary Reynolds number Re and small enough Rossby number, the system is attracted towards purely 2D flow solutions, which display no energy dissipation anomaly and no cycloneanticyclone asymmetry. Finally, these results challenge the applicability of wave turbulence theory to describe stationary rotating turbulence in bounded domains. 
BibTeX:
@article{Gallet2015a, author = {Gallet, Basile}, title = {Exact twodimensionalization of rapidly rotating largeReynoldsnumber flows}, journal = {Journal of Fluid Mechanics}, year = {2015}, volume = {783}, pages = {412447}, doi = {10.1017/jfm.2015.569} } 

Abstract: We investigate the behaviour of flows, including turbulent flows, driven by a horizontal body force and subject to a vertical magnetic field, with the following question in mind: for a very strong applied magnetic field, is the flow mostly twodimensional, with remaining weak threedimensional fluctuations, or does it become exactly 2D, with no dependence along the vertical direction? We first focus on the quasistatic approximation, i. e. the asymptotic limit of vanishing magnetic Reynolds number, Rm << 1: we prove that the flow becomes exactly 2D asymptotically in time, regardless of the initial condition and provided that the interaction parameter N is larger than a threshold value. We call this property absolute twodimensionalization: the attractor of the system is necessarily a (possibly turbulent) 2D flow. We then consider the full magnetohydrodynamic (MHD) equations and prove that, for low enough Rm and large enough N, the flow becomes exactly 2D in the longtime limit provided the initial vertically dependent perturbations are infinitesimal. We call this phenomenon linear twodimensionalization: the (possibly turbulent) 2D flow is an attractor of the dynamics, but it is not necessarily the only attractor of the system. Some 3D attractors may also exist and be attained for strong enough initial 3D perturbations. These results shed some light on the existence of a dissipation anomaly for MHD flows subject to a strong external magnetic field. 
BibTeX:
@article{Gallet2015, author = {Gallet, Basile and Doering, Charles R.}, title = {Exact twodimensionalization of lowmagneticReynoldsnumber flows subject to a strong magnetic field}, journal = {Journal of Fluid Mechanics}, year = {2015}, volume = {773}, pages = {154177}, doi = {10.1017/jfm.2015.232} } 

Abstract: In field theory, particles are waves or excitations that propagate on the fundamental state. In experiments or cosmological models, one typically wants to compute the outofequilibrium evolution of a given initial distribution of such waves. Wave turbulence deals with outofequilibrium ensembles of weakly nonlinear waves, and is therefore well suited to address this problem. As an example, we consider the complex KleinGordon equation with a Mexicanhat potential. This simple equation displays two kinds of excitations around the fundamental state: massive particles and massless Goldstone bosons. The former are waves with a nonzero frequency for vanishing wave number, whereas the latter obey an acoustic dispersion relation. Using waveturbulence theory, we derive wave kinetic equations that govern the coupled evolution of the spectra of massive and massless waves. We first consider the thermodynamic solutions to these equations and study the wave condensation transition, which is the classical equivalent of BoseEinstein condensation. We then focus on nonlocal interactions in wavenumber space: we study the decay of an ensemble of massive particles into massless ones. Under rather general conditions, these massless particles accumulate at low wave number. We study the dynamics of waves coexisting with such a strong condensate, and we compute rigorously a nonlocal KolmogorovZakharov solution, where particles are transferred nonlocally to the condensate, while energy cascades towards large wave numbers through local interactions. This nonlocal cascading state constitutes the intermediate asymptotics between the initial distribution of waves and the thermodynamic state reached in the longtime limit. 
BibTeX:
@article{Gallet2015b, author = {Gallet, Basile and Nazarenko, Sergey and Dubrulle, Berengere}, title = {Waveturbulence description of interacting particles: KleinGordon model with a Mexicanhat potential}, journal = {Physical Review E}, year = {2015}, volume = {92}, number = {1}, pages = {012909}, doi = {10.1103/PhysRevE.92.012909} } 

Abstract: This work addresses the question of the stability of stratified, spatially periodic shear flows at low Peclet number but high Reynolds number. This littlestudied limit is motivated by astrophysical systems, where the Prandtl number is often very small. Furthermore, it can be studied using a reduced set of "lowPecletnumber equations" proposed by Lignisres ["The smallPecletnumber approximation in stellar radiative zones," Astron. Astrophys. 348, 933939 (1999)]. Through a linear stability analysis, we first determine the conditions for instability to infinitesimal perturbations. We formally extend Squire's theorem to the lowPecletnumber equations, which shows that the first unstable mode is always twodimensional. We then perform an energy stability analysis of the lowPecletnumber equations and prove that for a given value of the Reynolds number, above a critical strength of the stratification, any smooth periodic shear flow is stable to perturbations of arbitrary amplitude. In that parameter regime, the flow can only be laminar and turbulent mixing does not take place. Finding that the conditions for linear and energy stability are different, we thus identify a region in parameter space where finiteamplitude instabilities could exist. Using direct numerical simulations, we indeed find that the system is subject to such finiteamplitude instabilities. We determine numerically how far into the linearly stable region of parameter space turbulence can be sustained. (C) 2015 AIP Publishing LLC. 
BibTeX:
@article{Garaud2015, author = {Garaud, Pascale and Gallet, Basile and Bischoff, Tobias}, title = {The stability of stratified spatially periodic shear flows at low Peclet number}, journal = {Physics of Fluids}, year = {2015}, volume = {27}, number = {8}, pages = {084104}, doi = {10.1063/1.4928164} } 

Abstract: We present an experimental study on the statistical properties of the injected power needed to maintain an inelastic ball bouncing constantly on a randomly accelerating piston in the presence of gravity. We compute the injected power at each collision of the ball with the moving piston by measuring the velocity of the piston and the force exerted on the piston by the ball. The probability density function of the injected power has its most probable value close to zero and displays two asymmetric exponential tails, depending on the restitution coefficient, the piston acceleration, and its frequency content. This distribution can be deduced from a simple model assuming quasiGaussian statistics for the force and velocity of the piston. 
BibTeX:
@article{GarciaCid2015, author = {GarciaCid, Alfredo and Gutierrez, Pablo and Falcon, Claudio and Aumaitre, Sebastien and Falcon, Eric}, title = {Statistics of injected power on a bouncing ball subjected to a randomly vibrating piston}, journal = {Physical Review E}, year = {2015}, volume = {92}, number = {3}, pages = {032915}, doi = {10.1103/PhysRevE.92.032915} } 

Abstract: Among the many fascinating examples of collective behavior exhibited by animal groups, some species are known to alternate slow group dispersion in space with rapid aggregation phenomena induced by a sudden behavioral shift at the individual level. We study this phenomenon quantitatively in large groups of grazing Merino sheep under controlled experimental conditions. Our analysis reveals strongly intermittent collective dynamics consisting of fast, avalanchelike regrouping events distributed on all experimentally accessible scales. As a proof of principle, we introduce an agentbased model with individual behavioral shifts, which we show to account faithfully for all collective properties observed. This offers, in turn, an insight on the individual stimulus/response functions that can generate such intermittent behavior. In particular, the intensity of sheep allelomimetic behavior plays a key role in the group's ability to increase the per capita grazing surface while minimizing the time needed to regroup into a tightly packed configuration. We conclude that the emergent behavior reported probably arises from the necessity to balance two conflicting imperatives: ( i) the exploration of foraging space by individuals and ( ii) the protection from predators offered by being part of large, cohesive groups. We discuss our results in the context of the current debate about criticality in biology. 
BibTeX:
@article{Ginelli2015, author = {Ginelli, Francesco and Peruani, Fernando and Pillot, MarieHelene and Chate, Hugues and Theraulaz, Guy and Bon, Richard}, title = {Intermittent collective dynamics emerge from conflicting imperatives in sheep herds}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, year = {2015}, volume = {112}, number = {41}, pages = {1272912734}, doi = {10.1073/pnas.1503749112} } 
BibTeX:
@article{Gutierrez2015, author = {P. Gutierrez and S. Aumaître}, title = {Experimental study on the clustering of floaters on the free surface of a turbulent flow}, journal = {Physical Review E}, year = {2015}, volume = {Submitted}, note = {http://arxiv.org/abs/1410.7824} } 

Abstract: We revisit the Kuramoto model to explore the finitesize scaling (FSS) of the order parameter and its dynamic fluctuations near the onset of the synchronization transition, paying particular attention to effects induced by the randomness of the intrinsic frequencies of oscillators. For a population of size N, we study two ways of sampling the intrinsic frequencies according to the same given unimodal distribution g(omega). In the ldquo randomrdquo case, frequencies are generated independently in accordance with g(omega), which gives rise to oscillator number fluctuation within any given frequency interval. In the ldquo regularrdquo case, the N frequencies are generated in a deterministic manner that minimizes the oscillator number fluctuations, leading to quasiuniformly spaced frequencies in the population. We find that the two samplings yield substantially different finitesize properties with clearly distinct scaling exponents. Moreover, the hyperscaling relation between the order parameter and its fluctuations is valid in the regular case, but it is violated in the random case. In this last case, a selfconsistent meanfield theory that completely ignores dynamic fluctuations correctly predicts the FSS exponent of the order parameter but not its critical amplitude. 
BibTeX:
@article{Hong2015, author = {Hyunsuk Hong and Chate, H. and LeiHan Tang and Hyunggyu Park}, title = {Finitesize scaling, dynamic fluctuations, and hyperscaling relation in the Kuramoto model}, journal = {Physical Review E (Statistical, Nonlinear, and Soft Matter Physics)}, year = {2015}, volume = {92}, number = {2}, pages = {022122 (8 pp.)022122}, doi = {10.1103/PhysRevE.92.022122} } 

Abstract: The Seebeck and Soret coefficients of ionically stabilized suspension of maghemite nanoparticles in dimethyl sulfoxide are experimentally studied as a function of nanoparticle volume fraction. In the presence of a temperature gradient, the charged colloidal nanoparticles experience both thermal drift due to their interactions with the solvent and electric forces proportional to the internal thermoelectric field. The resulting thermodiffusion of nanoparticles is observed through forced Rayleigh scattering measurements, while the thermoelectric field is accessed through voltage measurements in a thermocell. Both techniques provide independent estimates of nanoparticle's entropy of transfer as high as 82 meV K 1. Such a property may be used to improve the thermoelectric coefficients in liquid thermocells. 
BibTeX:
@article{Huang2015a, author = {Huang, B. T. and Roger, M. and Bonetti, M. and Salez, T. J. and WiertelGasquet, C. and Dubois, E. and Cabreira Gomes, R. and Demouchy, G. and Meriguet, G. and Peyre, V. and Kouyate, M. and Filomeno, C. L. and Depeyrot, J. and Tourinho, F. A. and Perzynski, R. and Nakamae, S.}, title = {Thermoelectricity and thermodiffusion in charged colloids}, journal = {Journal of Chemical Physics}, year = {2015}, volume = {143}, number = {5}, pages = {054902 (5 pp.)054902}, doi = {10.1063/1.4927665} } 

Abstract: Abstract We investigate a possibility to regularize the hydrodynamic contact line singularity in the configuration of partial wetting (liquid wedge on a solid substrate) via evaporationcondensation, when an inert gas is present in the atmosphere above the liquid. The noslip condition is imposed at the solidliquid interface and the system is assumed to be isothermal. The mass exchange dynamics is controlled by vapor diffusion in the inert gas and interfacial kinetic resistance. The coupling between the liquid meniscus curvature and mass exchange is provided by the Kelvin effect. The atmosphere is saturated and the substrate moves at a steady velocity with respect to the liquid wedge. A multiscale analysis is performed. The liquid dynamics description in the phasechangecontrolled microregion and viscocapillary intermediate region is based on the lubrication equations. The vapor diffusion is considered in the gas phase. It is shown that from the mathematical point of view, the phase exchange relieves the contact line singularity. The liquid mass is conserved: evaporation existing on a part of the meniscus and condensation occurring over another part compensate exactly each other. However, numerical estimations carried out for three common fluids (ethanol, water and glycerol) at the ambient conditions show that the characteristic length scales are tiny. 
BibTeX:
@article{Janecek2015, author = {V. Janecek and F. Doumenc and B. Guerrier and V.S. Nikolayev}, title = {Can hydrodynamic contact line paradox be solved by evaporationcondensation?}, journal = {Journal of Colloid and Interface Science}, year = {2015}, volume = {460}, pages = {329  338}, url = {http://www.sciencedirect.com/science/article/pii/S0021979715301570}, doi = {10.1016/j.jcis.2015.08.062} } 

Abstract: In this paper, we investigate the relations between global and local energy transfers in a turbulent von Karman flow. The goal is to understand how and where energy is dissipated in such a flow and to reconstruct the energy cycle in an experimental device where local as well as global quantities can be measured. In order to do so, we use particle image velocimetry (PIV) measurements and we model the Reynolds stress tensor to take subgrid scales into account. This procedure involves a free parameter that is calibrated using angular momentum balance. We then estimate the local and global mean injected and dissipated powers for several types of impellers, for various Reynolds numbers, and for various flow topologies. These PIV estimates are then compared with direct injected power estimates provided by torque measurements at the impellers. The agreement between PIV estimates and direct measurements depends on the flow topology. In symmetric situations, we are able to capture up to 90% of the actual global energy dissipation rate. However, our results become increasingly inaccurate as the shear layer responsible for most of the dissipation approaches one of the impellers and cannot be resolved by our PIV setup. Finally, we show that a very good agreement between PIV estimates and direct measurements is obtained using a new method based on the work of Duchon and Robert ["Inertial energy dissipation for weak solutions of incompressible Euler and NavierStokes equations," Nonlinearity 13, 249225 (2000)] which generalizes the KarmanHowarth equation to nonisotropic, nonhomogeneous flows. This method provides parameterfree estimates of the energy dissipation rate as long as the smallest resolved scale lies in the inertial range. These results are used to evidence a welldefined stationary energy cycle within the flow in which most of the energy is injected at the top and bottom impellers and dissipated within the shear layer. The influence of the mean flow geometry and the Reynolds number on this energy cycle is studied for a wide range of parameters. (C) 2015 AIP Publishing LLC. 
BibTeX:
@article{Kuzzay2015, author = {Kuzzay, Denis and Faranda, Davide and Dubrulle, Berengere}, title = {Global vs local energy dissipation: The energy cycle of the turbulent von Karman flow}, journal = {Physics of Fluids}, year = {2015}, volume = {27}, number = {7}, pages = {075105}, doi = {10.1063/1.4923750} } 

Abstract: We show that memory, in the form of underdamped angular dynamics, is a crucial ingredient for the collective properties of selfpropelled particles. Using Vicsekstyle models with an OrnsteinUhlenbeck process acting on angular velocity, we uncover a rich variety of collective phases not observed in usual overdamped systems, including vortex lattices and active foams. In a model with strictly nematic interactions the smectic arrangement of Vicsek waves giving rise to global polar order is observed. We also provide a calculation of the effective interaction between vortices in the case where a telegraphic noise process is at play, explaining thus the emergence and structure of the vortex lattices observed here and in motility assay experiments. 
BibTeX:
@article{Nagai2015, author = {Nagai, Ken H. and Sumino, Yutaka and Montagne, Raul and Aranson, Igor S. and Chate, Hugues}, title = {Collective Motion of SelfPropelled Particles with Memory}, journal = {Physical Review Letters}, year = {2015}, volume = {114}, number = {16}, pages = {168001}, doi = {10.1103/PhysRevLett.114.168001} } 

BibTeX:
@article{Nikolayev2015a, author = {Nikolayev, V. and Garrabos, Y. and Lecoutre, C. and Charignon, T. and Hitz, D. and Chatain, D. and Guillaument, R. and Marre, S. and Beysens, D.}, title = {Boiling Crisis Dynamics: Low Gravity Experiments at High Pressure}, journal = {Microgravity Science and Technology}, publisher = {Springer Netherlands}, year = {2015}, pages = {18}, url = {http://dx.doi.org/10.1007/s1221701594478}, doi = {10.1007/s1221701594478} } 

Abstract: Abstract The direct conversion of solar light into chemical energy or fuel through photoelectrochemical water splitting is promising as a clean hydrogen production solution. Tidoped hematite (Ti:Î±Fe2O3) is a potential key photoanode material, which despite its optimal band gap, excellent chemical stability, abundance, nontoxicity and low cost, still has to be improved. Here we give evidence of a drastic improvement of the water splitting performances of Tidoped hematite photoanodes upon a HCl wetetching. In addition to the topography investigation by atomic force microscopy, a detailed determination of the local electronic structure has been carried out in order to understand the phenomenon and to provide new insights in the understanding of solar water splitting. Using synchrotron radiation based spectromicroscopy (XPEEM), we investigated the Xray absorption spectral features at the L3 Fe edge of the as grown surface and of the wetetched surface on the very same sample thanks to patterning. We show that HCl wet etching leads to substantial surface modifications of the oxide layer including increased roughness and chemical reduction (presence of Fe2 +) without changing the band gap. We demonstrate that these changes are profitable and correlated to the drastic changes of the photocatalytic activity. 
BibTeX:
@article{Rioult2015, author = {M. Rioult and R. Belkhou and H. Magnan and D. Stanescu and S. Stanescu and F. Maccherozzi and C. Rountree and A. Barbier}, title = {Local electronic structure and photoelectrochemical activity of partial chemically etched Tidoped hematite }, journal = {Surface Science}, year = {2015}, volume = {In Press}, pages = { }, url = {http://www.sciencedirect.com/science/article/pii/S0039602815000059}, doi = {10.1016/j.susc.2015.01.002} } 

Abstract: Recently, CEA Grenoble SBT has designed, built and tested three liquid helium facilities dedicated to turbulence studies. All these experiments can operate either in HeI or HeII within the same campaign. The three facilities utilize moving parts inside liquid helium. The SHREK experiment is a von KÃ¡rmÃ¡n swirling flow between 0.72 m diameter counterrotating disks equipped with blades. The HeJet facility is used to produce a liquid helium free jet inside a 0.200 m I.D., 0.47 m length stainless steel cylindrical testing chamber. The OGRES experiment consists of an optical cryostat equipped with a particle injection device and an oscillating grid. We detail specific techniques employed to accommodate these stringent specifications. Solutions for operating these facilities without bubbles nor boiling/cavitation are described. Control parameters as well as Reynolds number and temperature ranges are given. 
BibTeX:
@article{Rousset2015, author = {B Rousset and C Baudet and M Bon Mardion and M Bourgoin and A Braslau and F Daviaud and P Diribarne and B Dubrulle and Y Gagne and B Gallet and M Gibert and A Girard and T Lehner and I Moukharski and F Sy}, title = {Cryogenic turbulence test facilities at CEA/SBT}, journal = {IOP Conference Series: Materials Science and Engineering}, year = {2015}, volume = {101}, number = {1}, pages = {012187}, url = {http://stacks.iop.org/1757899X/101/i=1/a=012187} } 

Abstract: We study in detail the hydrodynamic theories describing the transition to collective motion in polar active matter, exemplified by the Vicsek and active Ising models. Using a simple phenomenological theory, we show the existence of an infinity of propagative solutions, describing both phase and microphase separation, that we fully characterize. We also show that the same results hold specifically in the hydrodynamic equations derived in the literature for the active Ising model and for a simplified version of the Vicsek model. We then study numerically the linear stability of these solutions. We show that stable ones constitute only a small fraction of them, which, however, includes all existing types. We further argue that, in practice, a coarsening mechanism leads towards phaseseparated solutions. Finally, we construct the phase diagrams of the hydrodynamic equations proposed to qualitatively describe the Vicsek and active Ising models and connect our results to the phenomenology of the corresponding microscopic models. 
BibTeX:
@article{Solon2015a, author = {Solon, Alexandre P. and Caussin, JeanBaptiste and Bartolo, Denis and Chate, Hugues and Tailleur, Julien}, title = {Pattern formation in flocking models: A hydrodynamic description}, journal = {Physical Review E}, year = {2015}, volume = {92}, number = {6}, pages = {062111}, doi = {10.1103/PhysRevE.92.062111} } 

Abstract: We show that the flocking transition in the Vicsek model is best understood as a liquidgas transition, rather than an orderdisorder one. The full phase separation observed in flocking models with Z(2) rotational symmetry is, however, replaced by a microphase separation leading to a smectic arrangement of traveling ordered bands. Remarkably, continuous deterministic descriptions do not account for this difference, which is only recovered at the fluctuating hydrodynamics level. Scalar and vectorial order parameters indeed produce different types of number fluctuations, which we show to be essential in selecting the inhomogeneous patterns. This highlights an unexpected role of fluctuations in the selection of flock shapes. 
BibTeX:
@article{Solon2015, author = {Solon, Alexandre P. and Chate, Hugues and Tailleur, Julien}, title = {From Phase to Microphase Separation in Flocking Models: The Essential Role of Nonequilibrium Fluctuations}, journal = {Physical Review Letters}, year = {2015}, volume = {114}, number = {6}, pages = {068101}, doi = {10.1103/PhysRevLett.114.068101} } 
BibTeX:
@article{Soulier2015, author = {A. Soulier and S. Aumaître}, title = {Friction of spheres on a rotating parabolic support}, journal = {American Journal of Physics}, year = {2015}, volume = {To be submitted}, note = {arxiv.org/abs/1411.0694} } 

Abstract: In the present paper, recent experimental results on largescale coherent steady states observed in experimental von KÃ¡rmÃ¡n flows are revisited from a statistical mechanics perspective. The latter is rooted on two levels of description. We first argue that the coherent steady states may be described as the equilibrium states of wellchosen lattice models, which can be used to define global properties of von KÃ¡rmÃ¡n flows, such as their temperatures. The equilibrium description is then enlarged, in order to reinterpret a series of results about the stability of those steady states and their susceptibility to symmetry breaking, in the light of a deep analogy with the statistical theory of ferromagnetism. 
BibTeX:
@article{Thalabard2015, author = {S. Thalabard and B. SaintMichel and E. Herbert and F. Daviaud and B. Dubrulle}, title = {A statistical mechanics framework for the largescale structure of turbulent von Kármán flows}, journal = {New Journal of Physics}, year = {2015}, volume = {17}, number = {6}, pages = {063006}, url = {http://stacks.iop.org/13672630/17/i=6/a=063006}, doi = {10.1088/13672630/17/6/063006} } 

BibTeX:
@article{PhysRevE.92.063015, author = {Varela, J. and Brun, S. and Dubrulle, B. and Nore, C.}, title = {Role of boundary conditions in helicoidal flow collimation: Consequences for the von Kármán sodium dynamo experiment}, journal = {Physical Review E}, publisher = {American Physical Society}, year = {2015}, volume = {92}, pages = {063015}, url = {http://link.aps.org/doi/10.1103/PhysRevE.92.063015}, doi = {10.1103/PhysRevE.92.063015} } 
Maj : 07/02/2017 (2611)