Influence of Wetting Properties on Diffusion in a Confined Fluid

We briefly discuss how the wetting properties of a fluid/solid interface can indirectly influence the diffusion properties of fluid confined between two solid walls. This influence is related to the variability of the hydrodynamic boundary conditions at the interface, which correlates to the wetting properties.Comment: Paper presented at the ILL workshop "Dynamics in confinment", Grenoble, January 2000 (http://www.ill.fr

Universal and non-universal features in coarse-grained models of flow in disordered solids

We study the two-dimensional (2D) shear flow of amorphous solids within variants of an elastoplastic model, paying particular attention to spatial correlations and time fluctuations of, e.g., local stresses. The model is based on the local alternation between an elastic regime and plastic events during which the local stress is redistributed. The importance of a fully tensorial description of the stress and of the inclusion of (coarse-grained) convection in the model is investigated; scalar and tensorial models yield very similar results, while convection enhances fluctuations and breaks the spurious symmetry between the flow and velocity gradient directions, for instance when shear localisation is observed. Besides, correlation lengths measured with diverse protocols are discussed. One class of such correlation lengths simply scale with the spacing between homogeneously distributed, simultaneous plastic events. This leads to a scaling of the correlation length with the shear rate as $\dot{\gamma}^{\frac{-1}{2}}$ in 2D in the athermal regime, regardless of the details of the model. The radius of the cooperative disk, defined as the near-field region in which plastic events induce a stress redistribution that is not amenable to a mean-field treatment, notably follows this scaling. On the other hand, the cooperative volume measured from the four-point stress susceptibility and its dependence on the system size and the shear rate are model-dependent.Comment: 17 page

Enterprise modelling : building a product lifecycle (PLM) model as a component of the integrated vision of the enterprise

Enterprise modelling has proved to be an efficient tool to study organisations structure and facilitate decision making. The enterprise is a complex system that is required to use its processes to generate value in a given environment (concurrent, market, suppliers and humanity). We focus on three management disciplines: Product Lifecycle Management (PLM), Supply Chain Management (SCM) and Customer Relationship Management (CRM). These business processes are so intertwined that the enterprise has to concentrate on the three to attain its economic objectives. To enhance the development of PLM, SCM and CRM models, the enterprise needs to capitalise the knowledge necessary to adapt and apply modelling techniques. Knowledge Management (KM) is a key factor to give a unified enterprise vision. Firstly, we propose an integrated enterprise model depicting the interactions between PLM, SCM, CRM and KM models. But a state of the art showed that PLM models are scarce. Most of the PLM models found depends strongly on the particular case studied and can not be used with other enterprises. After defining the most important components of the PLM vision, we propose to organise these components into a formalised way. The study of SCM and CRM models proved to be helpful to structure these components. Finally the validation methodology that is to be established in our coming research works is not only to be used with the PLM model presented in this paper but with SCM and CRM models also.Product Lifecycle Management (PLM), Enterprise modelling, Enterprise systems

Contribution of shear strains to the vibrational entropy of defect configurations

International audienceCalculating the vibrational entropy of an N-atom assembly in the harmonic approximation requires the diagonalisation of a large matrix. This operation becomes rapidly time consuming when increasing the dimensions of the simulation cell. In the studies of point defects, a widely used shortcut consists in calculating the eigen modes of the atoms contained in an inner region, called the defective region, while the atoms belonging to the outer region are held fixed, and in applying an elastic correction to account for the entropy stored in the distortion of the outer region. A recent paper proposed to base the correction on the local pressure change experienced by each lattice site. The present contribution is an extension in the sense that it includes the shears. We compared the two approximations for configurations which are currently encountered in defect studies, namely those pertaining to defect formation and migration. The studied defects are the single, di- and tri-vacancy as well as the dumbbell interstitial in a host matrix modelled by several empirical potentials mimicking pure copper. It is shown that the inclusion of shears brings a noticeable contribution to the elastic correction for all configurations of low symmetry

Connecting diffusion and dynamical heterogeneities in actively deformed amorphous systems

We present an extensive numerical study of dynamical heterogeneities and their influence on diffusion in an athermal mesoscopic model for actively deformed amorphous solids. At low strain rates the stress dynamics are governed by cooperative regions of plastic events. On the basis of scaling arguments as well as an extensive numerical study of an athermal elasto-plastic model, we show that there is a direct link between the self-diffusion coefficient and the size of cooperative regions at low strain rates. Both depend strongly on rate and on system size. A measure of the mean square displacement of passive tracers in deformed amorphous media thus gives information about the microscopic rheology, such as the geometry of the cooperative regions and their scaling with strain rate and system size

Intrusion and extrusion of water in hydrophobic mesopores

We present experimental and theoretical results on intrusion-extrusion cycles of water in hydrophobic mesoporous materials, characterized by independent cylindrical pores. The intrusion, which takes place above the bulk saturation pressure, can be well described using a macroscopic capillary model. Once the material is saturated with water, extrusion takes place upon reduction of the externally applied pressure; Our results for the extrusion pressure can only be understood by assuming that the limiting extrusion mechanism is the nucleation of a vapour bubble inside the pores. A comparison of calculated and experimental nucleation pressures shows that a proper inclusion of line tension effects is necessary to account for the observed values of nucleation barriers. Negative line tensions of order $10^{-11} \mathrm{J.m}^{-1}$ are found for our system, in reasonable agreement with other experimental estimates of this quantity

HIV-1/M+O INTERGROUP DUAL INFECTIONS AND ASSOCIATED HIV-MO RECOMBINANTS IN FRANCE FROM 2004 TO 2014

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Spontaneous formation of permanent shear bands in a mesoscopic model of flowing disordered matter

This study proposes a coherent scenario of the formation of permanent shear bands in the flow of yield stress materials. It is a well accepted point of view that flow in disordered media is occurring via local plastic events, corresponding to small size rearrangements, that yield a long range stress redistribution over the system. Within a minimalistic mesoscopic model that incorporates these local dynamics, we study the spatial organisation of the local plastic events. The most important parameter in this study is the typical restructuring time needed to regain the original structure after a local rearrangement. In agreement with a recent mean field study [Coussot \textit{et al., Eur. Phys. J. E}, 2010, \textbf{33}, 183] we observe a spontaneous formation of permanent shear bands, when this restructuring time is large compared to the typical stress release time in a rearrangement. The bands consist of a large number of plastic events within a solid region that remains elastic. This heterogeneous flow behaviour is different in nature from the transient dynamical heterogeneities that one observes in the small shear rate limit in flow without shear-banding [Martens \textit{et al., Phys. Rev. Lett.}, 2011, \textbf{106}, 156001]. We analyse in detail the dependence of the shear bands on system size, shear rate and restructuring time. Further we rationalise the scenario within a mean field version of the spatial model, that produces a non monotonous flow curve for large restructuring times. This explains the instability of the homogeneous flow below a critical shear rate, that corresponds to the minimum of the curve. Our study therefore strongly supports the idea that the characteristic time scales involved in the local dynamics are at the physical origin of permanent shear bands.Comment: 10 pages, 9 figure

Appréhender le stock de métal monnayé au ive siècle après J.-C.

Parmi les thématiques abordées en numismatique à l’aide de l’archéométrie, les recherches spécifiques sur le stock de métal monnayé au ive siècle s’avèrent fascinantes mais délicates. Afflux de nouvelles ressources métalliques, refontes volontaires de monnaies : tous ces phénomènes sont de grande conséquence pour les monnayages produits dans les différents ateliers de l’Empire romain tardif. Certaines données de ce type sont mesurables. Les alliages métalliques (donc ici monétaires) contiennent en effet des éléments mineurs ou en traces, constituant la « carte d’identité » de l’approvisionnement des ateliers monétaires. Il y a 10 ans Isabelle Bollard et Jean-Noël Barrandon réunissaient plusieurs analyses de monnaies en alliage cuivreux émises au cours du ive siècle. Nos propres observations, obtenues dans le cadre d’un projet de recherche financé par la région Normandie (intitulé FANUM), sur 14 528 monnaies (nummi) de la période constantinienne contenues dans un trésor découvert fortuitement à Saint-Germain-de-Varreville (Manche), nous ont incités à reprendre, de façon plus approfondie, l’étude des alliages utilisés au cours de cette période, en portant notamment notre attention sur les teneurs en or et en argent. En effet, la grande variété des ateliers représentés au sein du trésor favorisait idéalement une telle enquête. Le choix de la fluorescence X portable a permis d’élaborer un protocole d’analyse précis et adapté à un grand nombre de monnaies. L’exploitation de 774 analyses réalisées sur des nummi frappés dans les ateliers occidentaux a permis de compléter les travaux antérieurs, mais également de mettre en évidence l’utilisation de stocks métalliques différents à partir des années 320.Among the thematics studied in numismatics using archeometry, specific research on the stock of metal struck in the 4th century turns out to be fascinating but complex. Influx of new metallic resources, voluntary recasts of coins: these phenomena have great consequences for the coinage produced in all the workshops throughout the late Roman Empire. Some of these data can be measurable. Metallic alloys (coins in this case) contain minor or trace elements that constitute a kind of “identity card” for the supply of monetary workshops. Ten years ago, Isabelle Bollard and Jean-Noël Barrandon collected several analyzes of bronzes struck during the 4th century. Our own observations, obtained within the FANUM project, funded by the Normandy region, on 14 528 coins (nummi) of the Constantinian period, contained in a fortuitously discovered treasure in Saint-Germain-de-Varreville (Manche) have motivated a thorough new study of the alloys used during this period, focusing on the traces of gold and silver. Indeed, the variety of workshops represented in the treasure has encouraged such an inquiry. The choice of portable X-ray fluorescence has enabled to develop a protocol of analysis adapted to a large number of coins. The use of 774 analyzes carried out on nummi struck in the Western workshops has completed previous works, but also enabled to highlight the use of different metal stocks from the 320s