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Grenoble, France

Gonzalez D.,Aragon Institute of Engineering Research | Ammar A.,CNRS Rheology Laboratory | Chinesta F.,Ecole Centrale Nantes | Cueto E.,Aragon Institute of Engineering Research
International Journal for Numerical Methods in Engineering

Separated representations based on finite sum decompositions constitute an appealing strategy for reducing the computer resources and the calculation costs by reducing drastically the number of degrees of freedom that the functional approximations involve (the number of degrees of freedom scale linearly with the dimension of the space in which the model is defined instead of the exponential growing characteristic of mesh-based discretization strategies). In our knowledge the use of separated representations is the only possibility for circumventing the terrific curse of dimensionality related to some highly multidimensional models involving hundreds of dimensions, as we proved in some of our former works. Its application is not restricted to multidimensional models, obviously separated representation can also be applied in standard 2D or 3D models, allowing for high resolution computations. Because its early life numerous issues persist, many of them attracting the curiosity of many research groups within the computational mechanics community. In this paper we are focusing in two issues never until now addressed: (i) the imposition of non-homogenous essential boundary conditions and (ii) the consideration of complex geometries. © 2009 John Wiley & Sons, Ltd. Source

Chinesta F.,University of Nantes | Ammar A.,CNRS Rheology Laboratory | Cueto E.,University of Zaragoza
International Journal for Numerical Methods in Engineering

In this paper the coupling of a parabolic model with a system of local kinetic equations is analyzed. A space-time separated representation is proposed for the global model (this is simply the radial approximation proposed by Pierre Ladeveze in the LATIN framework (Non-linear Computational Structural Mechanics. Springer: New York, 1999)). The originality of the present work concerns the treatment of the local problem, that is first globalized (in space and time) and then fully globalized by introducing a new coordinate related to the different species involved in the kinetic model. Thanks to the non-incremental nature of both discrete descriptions (the local and the global one) the coupling is quite simple and no special difficulties are encountered by using heterogeneous time integrations. © 2009 John Wiley & Sons, Ltd. Source

Mabrouk A.B.,University of Sfax | Magnin A.,CNRS Rheology Laboratory | Belgacem M.N.,CNRS Structural Engineering | Boufi S.,University of Sfax
Composites Science and Technology

Nanocomposites based on poly(styrene-co-hexylacrylate) copolymer and cellulose whiskers as the nanosize filler were prepared by in situ miniemulsion polymerization and their melt rheological behaviours were investigated under dynamic shear conditions. The effects of γ-methacryloxypropyl triethoxysilane (MPS) content along with the whisker loading were explored. In the absence of whiskers, a transition from a liquid- to a solid-like behaviour was observed when the polymer was synthesized in the presence of MPS. When cellulose nanofiller was added, the storage modulus G' and the dynamic viscosities η of the nanocomposites increased monotonically with whisker content and the resulting materials displayed a solid-like behaviour. Above 2. wt.%. loading, a percolated interconnected whisker-whisker network is built up, producing a jump in the storage modulus and strong shear-thinning behaviour of the viscosity. However, as the nanocomposites were prepared in the presence of 3% of MPS, no enhancement nor in the storage modulus nor in the viscosity was observed up to 5. wt.%. of whisker loading. Such a phenomenon was ascribed to inhibition of build-up of the whisker network. The non-linear viscoelastic behaviour of the nanocomposites was also investigated and analysed in terms of the breakdown of different networks, namely the filler-filler and the polymer-filler networks. © 2011 Elsevier Ltd. Source

Amphiphilic block copolymers autoassemble in water to form either dynamically active micelles or frozen particles at high surface tension. The dynamics of these systems is dominated by an individual process, which involves insertion-expulsion of copolymer chains, and a collective one, which involves fusion and fragmentation of proper micelles. The details of these mechanisms can drastically affect the micelles' morphology and some of their applications (drug delivery, template for mesoscopic structures, etc.). While fusion and fragmentation were found to be important in out-of-equilibrium kinetics such as sphere-to-rod transition, they were reported to be irrelevant at equilibrium by both theories and chain randomization experiments. We show, for the first time, that fusion and fragmentation do in fact take place at equilibrium in triblock copolymer micelles poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide). This was achieved using a fluorescent technique, which probes the randomization of hydrophobic pyrene derivatives between micelles. © 2012 American Chemical Society. Source

Bel Haaj S.,University of Sfax | Magnin A.,CNRS Rheology Laboratory | Petrier C.,CNRS Rheology Laboratory | Boufi S.,University of Sfax
Carbohydrate Polymers

Nano-sized starch particles (NSP) were prepared from starch granules using a purely physical method of high-intensity ultrasonication. Particle size distribution, Field Effect Scanning Electron Microscopy (FE-SEM), Raman spectroscopy, and Wide-Angle X-ray Diffraction (WAXD) were used to characterize the morphology and crystal structure of the ensuing nanoparticles. The results revealed that ultrasound treatment of the starch suspension in water and at low temperature for 75 min results in the formation of starch nanoparticles between 30 and 100 nm in size. An attempt to explain the generation of starch nanoparticles was made on the basis of WAXD, Raman analysis and FE-SEM observation. Compared to acid hydrolysis, which is the most commonly adopted process, the present approach has the advantage of being quite rapid, presenting a higher yield and not requiring any chemical treatment. © 2012 Elsevier Ltd. Source

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