Showing papers by "ParisTech published in 2008"

Chiral colloidal clusters

Abstract: To advance the use of colloids as building blocks for the fabrication of large-scale complex structures for applications in nanotechnology, it is desirable to give them the functionality and variability found in chemistry. A step in that direction has now been achieved with the development of magnetic colloids that can rapidly self-assemble into a variety of isomeric forms. Depending on the shape of the colloidal blocks relative to their spontaneous direction of magnetization, these colloids self-assemble into structures with controlled helicity. If the size ratio between the colloidal spheres in the assembly is large enough, a single helicity is chosen, right or left. This work opens up a new link between colloidal science and chemistry that could lead to the assembly of a wide variety of nanoparticles and mesopolymers. Chirality is an important element of biology, chemistry and physics. Once symmetry is broken and a handedness is established, biochemical pathways are set. In DNA, the double helix arises from the existence of two competing length scales, one set by the distance between monomers in the sugar backbone, and the other set by the stacking of the base pairs1. Here we use a colloidal system to explore a simple forcing route to chiral structures. To do so we have designed magnetic colloids that, depending on both their shape and induced magnetization, self-assemble with controlled helicity. We model the two length scales with asymmetric colloidal dumbbells linked by a magnetic belt at their waist. In the presence of a magnetic field the belts assemble into a chain and the steric constraints imposed by the asymmetric spheres force the chain to coil. We show that if the size ratio between the spheres is large enough, a single helicity is adopted, right or left. The realization of chiral colloidal clusters opens up a new link between colloidal science and chemistry. These colloidal clusters may also find use as mesopolymers, as optical and light-activated structures2, and as models for enantiomeric separation.

The SAFRAN‐ISBA‐MODCOU hydrometeorological model applied over France

Abstract: The hydrometeorological model SIM consists in a meterological analysis system (SAFRAN), a land surface model (ISBA) and a hydrogeological model (MODCOU). It generates atmospheric forcing at an hourly time step, and it computes water and surface energy budgets, the river ow at more than 900 rivergauging stations, and the level of several aquifers. SIM was extended over all of France in order to have a homogeneous nation-wide monitoring of the water resources: it can therefore be used to forecast flood risk and to monitor drought risk over the entire nation. The hydrometeorologival model was applied over a 10-year period from 1995 to 2005. In this paper the databases used by the SIM model are presented, then the 10-year simulation is assessed by using the observations of daily stream-flow, piezometric head, and snow depth. This assessment shows that SIM is able to reproduce the spatial and temporal variabilities of the water fluxes. The efficiency is above 0.55 (reasonable results) for 66 % of the simulated rivergages, and above 0.65 (rather good results) for 36 % of them. However, the SIM system produces worse results during the driest years, which is more likely due to the fact that only few aquifers are simulated explicitly. The annual evolution of the snow depth is well reproduced, with a square correlation coeficient around 0.9 over the large altitude range in the domain. The stream ow observations were used to estimate the overall error of the simulated latent heat ux, which was estimated to be less than 4 %.

Gamma double prime precipitation kinetic in Alloy 718

Abstract: Gamma double prime (γ′′), precipitation was studied in Alloy 718 using isothermal and isochronal aging heat treatments applied between 943 and 1003 K. It is shown, that the coarsening behavior of γ′′ precipitates follows the coarsening kinetic predictions of the Lifshitz–Slyozov–Wagner (LSW) theory. The activation energy for γ′′ growth has been determined as equal to 272 kJ mol−1 and seems to be controlled by volume diffusion of niobium in the matrix. The energy of the γ′′/matrix interface, Γ, has been found to be 95 ± 17 mJ m−2 by assuming that the γ′′ precipitates adopt a disk shape which minimizes the total energy. This energy includes a volume distortion term calculated from the Eshelby inclusion theory and a surface component which is assumed to be isotropic. This interfacial energy is discussed and compared with the energy of γ′/matrix and γ′′/matrix interfaces in other superalloys. The constant K′′ of the LSW law time dependence has been calculated using the value of interfacial energy and the activation energy of γ′′ precipitates coarsening and is found to be in good agreement with our experimental values.

University spin-off firms: Lessons from ten years of experience in Europe

Abstract: This paper advances our understanding of university spin-off creation and development in environments outside the high-tech cluster of the USA. It adopts a multi-level approach in its examination of this phenomenon in diverse institutional environments. In particular, units of analysis involving universities, technology transfer offices, spin-off firms, finance providers and individual entrepreneurs and teams are analysed. Policy implications are analysed and recommendations are proposed for current policy on university spin-offs.

TapTap and MagStick: improving one-handed target acquisition on small touch-screens

Abstract: We present the design and evaluation of TapTap and MagStick, two thumb interaction techniques for target acquisition on mobile devices with small touch-screens. These two techniques address all the issues raised by the selection of targets with the thumb on small tactile screens: screen accessibility, visual occlusion and accuracy. A controlled experiment shows that TapTap and MagStick allow the selection of targets in all areas of the screen in a fast and accurate way. They were found to be faster than four previous techniques except Direct Touch which, although faster, is too error prone. They also provided the best error rate of all tested techniques. Finally the paper also provides a comprehensive study of various techniques for thumb based touch-screen target selection.

Determining the unsaturated hydraulic conductivity of a compacted sand-bentonite mixture under constant-volume and free-swell conditions

Abstract: Highly compacted sand–bentonite mixtures are often considered as possible engineered barriers in deep high-level radioactive waste disposals. In situ, the saturation of these barriers from their initially unsaturated state is a complex hydro-mechanical coupled process in which temperature effects also play a role. The key parameter of this process is the unsaturated hydraulic conductivity of the barrier. In this paper, isothermal infiltration experiments were conducted to determine the unsaturated hydraulic conductivity according to the instantaneous profile method. To do so, total suction changes were monitored at different locations along the soil specimen by using resistive relative humidity probes. Three constant-volume infiltration tests were conducted showing, unexpectedly, a decrease of the hydraulic conductivity during infiltration. One test performed under free-swell conditions showed the opposite and standard trend. These observations were interpreted in terms of microstructure changes during wetting, both under constant-volume and free-swell conditions.

Flower menus: a new type of marking menu with large menu breadth, within groups and efficient expert mode memorization

Abstract: This paper presents Flower menu, a new type of Marking menu that does not only support straight, but also curved gestures for any of the 8 usual orientations. Flower menus make it possible to put many commands at each menu level and thus to create as large a hierarchy as needed for common applications. Indeed our informal analysis of menu breadth in popular applications shows that a quarter of them have more than 16 items. Flower menus can easily contain 20 items and even more (theoretical maximum of 56 items). Flower menus also support within groups as well as hierarchical groups. They can thus favor breadth organization (within groups) or depth organization (hierarchical groups): as a result, the designers can lay out items in a very flexible way in order to reveal meaningful item groupings. We also investigate the learning performance of the expert mode of Flower menus. A user experiment is presented that compares linear menus (baseline condition), Flower menus and Polygon menus, a variant of Marking menus that supports a breadth of 16 items. Our experiment shows that Flower menus are more efficient than both Polygon and Linear menus for memorizing command activation in expert mode.

Long-time convergence of an adaptive biasing force method

Abstract: We propose a proof of convergence of an adaptive method used in molecular dynamics to compute free energy profiles (see Darve and Porohille 2001 J. Chem. Phys. 115 9169–83, Henin and Chipot 2004 J. Chem. Phys. 121 2904–14, Lelievre et al J. Chem. Phys. 126 134111). Mathematically, it amounts to studying the long-time behaviour of a stochastic process which satisfies a nonlinear stochastic differential equation, where the drift depends on conditional expectations of some functionals of the process. We use entropy techniques to prove exponential convergence to the stationary state.

Experimental Data and Predictions of Dissociation Conditions for Ethane and Propane Simple Hydrates in the Presence of Methanol, Ethylene Glycol, and Triethylene Glycol Aqueous Solutions

Abstract: Experimental dissociation data for ethane and propane simple hydrates in the presence of (0.05 and 0.15) mass fractions of methanol, ethylene glycol, and triethylene glycol aqueous solutions are reported in this work. The experimental data have been measured using an isochoric method. All the experimental data are compared with the predictions of a general correlation (HWHYD correlation) and a thermodynamic model (HWHYD model). The agreements between the experimental and predicted data are generally found acceptable.

Robust Similarity Measures for Named Entities Matching

Abstract: Matching coreferent named entities without prior knowledge requires good similarity measures. Soft-TFIDF is a fine-grained measure which performs well in this task. We propose to enhance this kind of metrics, through a generic model in which measures may be mixed, and show experimentally the relevance of this approach.

Laser-based vehicles tracking and classification using occlusion reasoning and confidence estimation

Abstract: In this paper, we present a robust approach for the detection, tracking and classification of multiple vehicles using a vehicle mounted laser scanner working independently in highways an urban centers. Our classification is based on different criteria: geometrical configuration, occlusion reasoning, sensor specifications and tracking information. The estimated confidence level is thus computed accounting the classification, the geometrical configuration and the tracking duration. Our system has been validated under various conditions (highways, urban centers) with three different laser scanners and proved is robustness on real data and with real time constraints.

Some links between Cosserat, strain gradient crystal plasticity and the statistical theory of dislocations

Abstract: A link is established between a phenomenological Cosserat model of crystal plasticity and recent results obtained in the statistical theory of dislocations. The existence of a back-stress related to the divergence of the couple stress tensor is derived. According to several dislocation-based models of single slip, the kinematic hardening modulus is found to be inversely proportional to the dislocation density. Phenomenological extensions to multislip situations can be proposed based on these generalized continuum approaches.

Experimental Data and Predictions of Dissociation Conditions for Ethane and Propane Simple Hydrates in the Presence of Distilled Water and Methane, Ethane, Propane, and Carbon Dioxide Simple Hydrates in the Presence of Ethanol Aqueous Solutions

Abstract: Experimental gas hydrate dissociation data for ethane + distilled water, propane + distilled water, methane + 0.05 and 0.1 mass fraction ethanol aqueous solution, ethane + 0.05 and 0.1 mass fraction ethanol aqueous solution, propane + 0.05 and 0.1 mass fraction ethanol aqueous solution, and carbon dioxide + 0.05 and 0.1 mass fraction ethanol aqueous solution systems are reported herein. The new experimental data have been measured using an isochoric method. All the experimental data are compared with the predictions of a general correlation and a thermodynamic model. The agreements between the experimental and predicted data are generally found to be acceptable. The hydrate dissociation data for ethane + distilled water and propane + distilled water systems are also compared with some experimental data reported in the literature, and acceptable agreements between the data indicate the reliability of the experimental technique used in this study.

A new method for location selection : A hybrid analysis

Abstract: Site selection is a part of strategic management activities. Location selection decisions involved many factors that may be conflicting in nature. Considering the tangible along with intangible factors in location selection problem, this paper propose a hybrid method of multi criteria decision making (MCDM) that make it possible to select the optimal location that satisfies the decision maker. With the aid of fuzzy AHP, our proposed model considers objective, critical, and subjective factors as the three main common factors in location analysis. The last two factors, critical and subjective factors, are defined by decision maker's judgments for more adoption with the real world problems. Besides, analysis of a numerical example and the sensitivity analysis are discussed to clarify the practicability and effectiveness of the proposed model in the facility location problem.

Dans le « carré de l'activité » : perspectives internationales sur le travail et l'activité

Abstract: Resume Cet article introductif vise a dessiner un espace particulier de recherches sur le travail tel qu’il se fait et qui caracterise la maniere dont les ethnographies des situations de travail se developpent sur le plan international. Cet espace est decrit comme un « carre », borde par quatre perspectives : la cognition distribuee, la « theorie de l’activite », l’ethnomethodologie et les courants qui s’en inspirent et la sociologie des sciences et des techniques. Apres avoir expose leurs principes, l’article se donne pour objet de les confronter et de souligner les tensions et les differences qui se font jour entre elles sur plusieurs points critiques pour l’analyse des situations de travail : la maniere de constituer des donnees de terrain, le role respectif des personnes et des choses, leur posture par rapport a la dialectique de la continuite et du changement. Il aborde enfin la maniere dont le developpement actuel des technologies d’information et de communication constitue un point d’entree permettant de reinterroger ces differentes perspectives et de suggerer des debordements ou des reconfigurations possibles.

Lactate and Amino Acid Catabolism in the Cheese-Ripening Yeast Yarrowia lipolytica

Abstract: The consumption of lactate and amino acids is very important for microbial development and/or aroma production during cheese ripening. A strain of Yarrowia lipolytica isolated from cheese was grown in a liquid medium containing lactate in the presence of a low (0.1×) or high (2×) concentration of amino acids. Our results show that there was a dramatic increase in the growth of Y. lipolytica in the medium containing a high amino acid concentration, but there was limited lactate consumption. Conversely, lactate was efficiently consumed in the medium containing a low concentration of amino acids after amino acid depletion was complete. These data suggest that the amino acids are used by Y. lipolytica as a main energy source, whereas lactate is consumed following amino acid depletion. Amino acid degradation was accompanied by ammonia production corresponding to a dramatic increase in the pH. The effect of adding amino acids to a Y. lipolytica culture grown on lactate was also investigated. Real-time quantitative PCR analyses were performed with specific primers for five genes involved in amino acid transport and catabolism, including an amino acid transporter gene (GAP1) and four aminotransferase genes (ARO8, ARO9, BAT1, and BAT2). The expression of three genes involved in lactate transport and catabolism was also studied. These genes included a lactate transporter gene (JEN1) and two lactate dehydrogenase genes (CYB2-1 and CYB2-2). Our data showed that GAP1, BAT2, BAT1, and ARO8 were maximally expressed after 15 to 30 min following addition of amino acids (BAT2 was the most highly expressed gene), while the maximum expression of JEN1, CYB2-1, and CYB2-2 was delayed (≥60 min).

Inspiration, images and design: an investigation of designers' information gathering strategies

Abstract: Computational tools should efficiently support, and even enhance, designers' creativity. As a ground for such developments, design cognition studies aim at describing designers' mental strategies within the design process. So far, most researches have been focused on the idea generation phases, e.g. sketching activity, which is explicit enough to be observed and described. However, the early stages of design remain incompletely understood, while the informational phase is identified as a crucial step of the design process. In this context, our objective is to identify and evaluate inspirational information used by designers before generating ideas, and to describe how inspirational information is used. In this article, we report a two-part study (interviews and experimental protocol) carried out with professional designers. The main outcomes demonstrate that traditional and electronic resources are not used in the same way by designers. We also show that information gathering strategies are strongly influenced by designers' preference.

A polycrystalline model for the description of ratchetting : effect of intergranular and intragranular hardening

Abstract: In this work, numerical simulations for predicting uni- and multi-axial ratchetting behaviors are carried out, using a polycrystal plasticity model. In this multi-scale modeling, the single crystal behavior is based on crystallographic slip (intragranular scale), whereas the polycrystal behavior is obtained from an explicit transition rule to calculate the local stresses and strains (intergranular scale). A systematic study is performed to show the effect of intergranular and intragranular hardening on the ratchetting behavior. For illustrative purposes, two examples are presented: the model is applied to simulate the experimental results from the literature for a 316 austenitic stainless steel and for a 1026 carbon steel. It was demonstrated that the polycrystalline model was successful in describing the inelastic behavior of the two considered materials adequately.

Measuring the kinetics of biomolecular recognition with magnetic colloids.

Abstract: We introduce a general methodology based on magnetic colloids to study the recognition kinetics of tethered biomolecules. Access to the full kinetics of the reaction is provided by an explicit measure of the time evolution of the reactant densities. Binding between a single ligand and its complementary receptor is here limited by the colloidal rotational diffusion. It occurs within a binding distance that can be extracted by a reaction-diffusion theory that properly accounts for the rotational Brownian dynamics. Our reaction geometry allows us to probe a large diversity of bioadhesive molecules and tethers, thus providing a quantitative guidance for designing more efficient reactive biomimetic surfaces, as required for diagnostic, therapeutic, and tissue engineering techniques.

Context-dependent kernel design for object matching and recognition

Abstract: The success of kernel methods including support vector networks (SVMs) strongly depends on the design of appropriate kernels. While initially kernels were designed in order to handle fixed-length data, their extension to unordered, variable-length data became more than necessary for real pattern recognition problems such as object recognition and bioinformatics. We focus in this paper on object recognition using a new type of kernel referred to as ldquocontext-dependentrdquo. Objects, seen as constellations of local features (interest points, regions, etc.), are matched by minimizing an energy function mixing (1) a fidelity term which measures the quality of feature matching, (2) a neighborhood criteria which captures the object geometry and (3) a regularization term. We will show that the fixed-point of this energy is a ldquocontext-dependentrdquo kernel (ldquoCDKrdquo) which also satisfies the Mercer condition. Experiments conducted on object recognition show that when plugging our kernel in SVMs, we clearly outperform SVMs with ldquocontext-freerdquo kernels.

Indexing of Satellite Images With Different Resolutions by Wavelet Features

Abstract: Space agencies are rapidly building up massive image databases. A particularity of these databases is that they are made of images with different, but known, resolutions. In this paper, we introduce a new scheme allowing us to compare and index images with different resolutions. This scheme relies on a simplified acquisition model of satellite images and uses continuous wavelet decompositions. We establish a correspondence between scales which permits us to compare wavelet decompositions of images having different resolutions. We validate the approach through several matching and classification experiments, and we show that taking the acquisition process into account yields better results than just using scaling properties of wavelet features.

Les coopératives agricoles face à l’internationalisation et à la mondialisation des marchés

Abstract: Les cooperatives agricoles francaises sont confrontees depuis plusieurs decennies a un changement radical de leur environnement, des evolutions de la politique agricole commune en passant par la concentration croissante de la grande distribution. Cet article examine leurs evolutions organisationnelles au regard des strategies qu'elles deploient pour faire face aux contraintes reglementaires et concurrentielles. Les cooperatives ont modifie leur organisation en se complexifiant sous forme de groupes d'entreprises ou en diversifiant leurs activites. Au-dela des strategies de concentration, elles ont developpe des strategies d'integration verticale, de diversification et d'internationalisation. De nouveaux defis se posent alors aux cooperatives agricoles. Si l'essor des cooperatives ne peut desormais plus faire abstraction de la prise en compte du consommateur, l'article montre qu'elles doivent concilier les tensions liees a leur insertion sur les marches et les territoires dans la perspective du maintien du pouvoir de l'adherent proprietaire, de la gestion de la volatilite des marches et du developpement durable.