Saint-Gobain (France)

scikit-image is an image processing library that implements algorithms and utilities for use in research, education and industry applications. It is released under the liberal Modified BSD open source license, provides a well-documented API in the Python programming language, and is developed by an active, international team of collaborators. In this paper we highlight the advantages of open source to achieve the goals of the scikit-image library, and we showcase several real-world image processing applications that use scikit-image. More information can be found on the project homepage, http://scikit-image.org.

Individual, organizational, and contextual variables were found to be much better predictors of hospital adoption of technological innovations than of administrative innovations. The two different ...

ABSTRACT We study the investment analyses of 67 portfolio investments by 11 venture capital (VC) firms. VCs describe the strengths and risks of the investments as well as expected postinvestment actions. We classify the risks into three categories and relate them to the allocation of cash flow rights, contingencies, control rights, and liquidation rights between VCs and entrepreneurs. The risk results suggest that agency and hold‐up problems are important to contract design and monitoring, but that risk sharing is not. Greater VC control is associated with increased management intervention, while greater VC equity incentives are associated with increased value‐added support.

If deposited on a hydrophobic rough substrate, a small drop of water can look like a pearl, with a contact angle close to 180°. We examine the conditions for observing such a phenomenon and show practical achievements where the contact angle can be predicted and thus quantitatively tuned by the design of the surface microstructure.

Abstract: The current state of the art of digital image correlation, where displacements can be determined for values less than one pixel, enables one to better characterise the behaviour of materials and the response of structures to external loads. A general presentation of the extraction of displacement fields from pictures taken at different instants during an experiment is given. Different strategies can be followed to determine subpixel displacements. New identification procedures are then devised making use of full‐field measurements. A priori or a posteriori routes can be followed. They are illustrated on the analysis of a Brazilian disk test.

Tally's Corner est devenu un texte-cle dans l'analyse et la comprehension des phenomenes urbains lies a la pauvrete. Alors que les revoltes urbaines s'intensifient et que les habitants des grandes villes du Nord des Etats-Unis, des populations immigrees, connaissent un fort taux de chomage, une situation sanitaire difficile et la desagregation de leur cellule familiale, Elliot Liebow procede au compte rendu detaille des actes ordinaires de la fraction masculine la plus pauvre de la population noire d'une de ces grande villes. En suivant au jour le jour quelques-uns des hommes qui trainent regulierement, apparemment sans rien faire, au coin d'une rue, l'auteur, Elliot Liebow, montre comment ces hommes s'organisent afin de surmonter les difficultes sans fin auxquelles ils sont confrontes, comment ils fondent des familles, tentent de subvenir a leurs besoins et de conserver leur dignite. Si Tally's Corner a traverse les annees et est devenu un classique de la sociologie, c'est que tant par son sujet que par son mode de collecte et de restitution des donnees, l'ouvrage constitue un modele d'enquete ethnographique et de remise en question des theories dominantes sur la pauvrete. C'est aussi parce que son style simple et clair en fait un ouvrage romanesque qui emporte le lecteur au cœur d'histoires de vies permettant d'apprehender l'Amerique contemporaine en general et la vie des Noirs americains, en particulier.

Abstract Direct ink writing of dense and strong ceramic objects remains an important open challenge. We develop a universal dimensionless criterion for printing such objects. Boehmite, an Al 2 O 3 precursor, was used to assess the rheological properties leading to dense structures in ceramics manufactured by direct ink writing. Boehmite suspensions undergo time dependent gelation, thus providing a rheological laboratory of flow behaviours that can be correlated with printability requirements. We measured the evolution of rheological properties over several days and quantified the deformation of simple printed shapes at different aging times. We then identified the relevant physical parameters leading to printable suspensions. We defined a dimensionless number, Ξ, based on measured rheological properties, that predicts deformation of the printed object and determines the printability criterion. An important difference with this criterion is that Ξ necessarily accounts for capillary forces and gravitational slumping. We show that boehmite inks reach a printed shape fidelity > 90% when Ξ > 1, and that Al 2 O 3 bars printed under these conditions can be sintered to 97% density, without printing defects, and have flexural strengths (500–600 MPa) competitive with commercial aluminas. Using Ξ, researchers can rationally design inks for printing dense materials by tailoring their rheological properties such that Ξ ≈ 1.

Nanometric particles of titania, brookite and rutile polymorphs were synthesised by thermolysis of TiCl4 in concentrated HCl solutions. The Cl∶Ti molar ratio seems to be the key factor in determining the crystalline phases and their relative proportions as well as the particle size and a large proportion of brookite can be obtained under specific conditions. The complex Ti(OH)2(Cl)2(OH2)2 seems to be the precursor of the brookite phase. The presence of chloride ions is also necessary to stabilise brookite in suspension. Depending on the acidity and the ageing conditions, different morphologies of brookite nanoparticles are obtained, namely spheroidal particles or platelets. Stable sols of pure brookite are obtained by peptization of the solid phase.

Large and good-optical-quality crystals of gadolinium and calcium oxoborate, Ca4GdO(BO3)3 (GdCOB) have been grown from a melt by the Czochralski pulling method. The crystal is absolutely insensitive to moisture. Linear- and quadratic nonlinear-optical properties of this new monoclinic biaxial borate crystal are reported. The crystal is transparent in the visible and the near IR (from 0.32 to 2.7 µm), with favorable phase matching conditions for second-harmonic generation. Experimental phase-matching results, measured with a femtosecond broadband pulse parametric generator source tunable from 0.8 to 2.100 µm, are compared with theoretical predictions. The effective nonlinear coefficients are determined, leading to deff=1 pm/V for type I crystals in the ZX plane. The damage threshold is as high as 1 GW/cm2 at 0.532 µm. The second-harmonic generation conversion efficiency of a Q-switched Nd:YAG laser with a 15-mm long crystal is greater than 50%. These values together with the possibility of growing large crystals make GdCOB an excellent candidate for the next generation of crystals for frequency conversion and parametric processes.

Bismuth-based oxides have attractive photocatalytic properties under visible light. A better understanding of the origin of that good photocatalytic activity should allow its control and its optimization. In this Article, we have studied the impact of surface properties on photocatalytic activity for three bismuth-based oxides Bi2O3, BiVO4, and Bi2WO6. The surface acidity of particles was investigated by pyridine adsorption using infrared spectroscopy and the photocatalytic activity was investigated by the degradation of an aqueous solution of rhodamine B (RhB) and of stearic acid deposited on films under visible light. From the results obtained for the three bismuth-based oxides, we established a relation between surface acidity and photocatalytic mechanism of RhB degradation. The best photocatalytic efficiency for RhB and stearic acid degradation has been obtained with Bi2WO6 that also exhibits the highest surface acidity. The most acid sites promote a strong interaction with the pollutant, implying a short distance between the pollutant and the photocatalyst. Consequently, the photogenerated electrons, holes, and radicals can reach more easily the pollutant, leading to an efficient degradation under visible light. The development of strong acid solids such as Bi2WO6 emerged as promising materials for the degradation of pollutants. Because the good photocatalytic properties are related to the high acidity of Bi2WO6, we are interested in its origin using the multi site complexation model (MUSIC model). We found high acidity sites that are located on the lateral faces of the Bi2WO6 platelets (crystallographic planes (101), (101̅), (100), and (001)).

We compare different finite-difference schemes for two-dimensional (2-D) acoustic frequencydomain forward modelling. The schemes are based on staggered-grid stencils of various accuracy and grid rotation strategies to discretize the derivatives of the wave equation. A combination of two O( x 2 ) staggered-grid stencils on the classical Cartesian coordinate system and the 45 rotated grid is the basis of the so-called mixed-grid stencil. This method is compared with a parsimonious staggered-grid method based on a fourth-order approximation of the first derivative operator. Averaging of the mass acceleration can be incorporated in the two stencils. Sponge-like perfectly matched layer absorbing boundary conditions are also examined for each stencil and shown to be effective.

The freeze-casting of porous materials has received a great deal of attention during the past few years. This simple process, where a material suspension is simply frozen and then sublimated, provides materials with unique porous architectures, where the porosity is almost a direct replica of the frozen solvent crystals. This review focuses on the recent results on the process and the derived porous structures with regards to the biomaterials applications. Of particular interest is the architecture of the materials and the versatility of the process, which can be readily controlled and applied to biomaterials applications. A careful control of the starting formulation and processing conditions is required to control the integrity of the structure and resulting properties. Further in vitro and in vivo investigations are required to validate the potential of this new class of porous materials.

The freezing of concentrated colloidal suspensions is a complex physical process involving a large number of parameters. These parameters provide unique tools to manipulate the architecture of freeze‐cast materials at multiple length scales in a single processing step. However, we are still far from developing predictive models to describe the growth of ice crystals in concentrated particle slurries. In order to exert reliable control over the microstructural formation of freeze‐cast materials, it is necessary to reach a deeper understanding of the basic relationships between the experimental conditions and the microstructure of the growing solid. In this work, we explore the role of several processing variables (e.g., composition of the suspension, freezing rate, and patterning of the freezing surface) that could affect the formulation strategies for the architectural manipulation of freeze‐cast materials. We also demonstrate, using freeze‐cast lamellar structures, that reducing the lamellar thickness by less than half increases the compressive strength by more than one order of magnitude.

http://stacks.iop.org/0022-3727/41/163001

Several phosphides with the chemical formula M2P crystallize in a hexagonal structure: Mn2P, Fe2P, and Ni2P. The structure of Co2P is orthorhombic. These two structures are related via an identical elementary subcell consisting of a tetrahedral-site and a pyramidal-site M-atom pair. This investigation shows that solid solutions between two hexagonal end members, such as Fe2P or Ni2P with Mn2P, may exhibit orthorhombic structures at intermediate compositions. Fe2P shows complete solid solubility with Ni2P. Curiously, hexagonal and orthorhombic symmetries alternate with decreasing number of 3d electrons, Ni2P(hex) -Co2P(ortho) -Fe2P(hex) -FeMnP(ortho) -Mn2P(hex). Lattice parameter variations with composition and Mössbauer studies reveal atomic ordering in the mixed systems, Mn and Cr substituting for pyramidal-site iron in FeMnP and FeCrP while Ni and Co substitute preferentially for tetrahedralsite iron in FeCoP and FeNiP. While neither Co2P nor Mn2P are ferromagnetic, intermediate phases are, the Curie temperature and magnetization reaching the maximum values 310°C and 3.03 μB/molecule for MnCoP. Metamagnetism appears for a range of compositions about (Mn0.7Co0.3)2P. The Co2P-Fe2P system is also ferromagnetic with a maximum Curie temperature near FeCoP. This system shows a sharp discontinuity in magnetization, but only a small discontinuity in Curie temperature, across the phase transition. Sensitivity to stoichiometry in the magnetization of Fe2-εP is attributed to an electron/atom ratio near that for the appearance of metamagnetism.

Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2(1-x)</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2x</sub> SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> :Ce (10 at% Y) single crystals co-doped with Ca <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> and Mg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> were prepared by the Czochralski technique. It is shown that co-doping leads to significant improvements of the scintillation performances. Afterglow following X-ray excitation is reduced down to 200 ppm after 20 ms and light yield is increased from 28,000 ph/MeV up to 34,000 ph/MeV under <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs-662 keV excitation. X-ray Absorption Near Edge Spectroscopy (XANES) was used to demonstrate that a significant part of the Ce ions are stabilized in the Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> oxidation state in co-doped crystals. A new scintillation mechanism involving Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> is proposed.

Le secteur de la construction a souvent défrayé la chronique économique ou judiciaire, mais le quotidien des chantiers demeure obscur. C’est ce quotidien qu’explore ce livre. L’auteur, qui s’est immergé durant une année dans le monde du béton armé parisien, en tant qu’ouvrier, retrace ici l’itinéraire de son enquête. Au fil des expériences et des rencontres, il expose les conditions d’emploi et de travail liées au recours croissant à la sous-traitance et à l’intérim : division des collectifs ouvriers, infériorisation et culpabilisation des sous-traitants et des intérimaires, pratiques illégales d’employeurs, contradictions pesant sur la sécurité au travail, recours massif à une main-d’œuvre étrangère fragilisée et parfois sans papiers, racisme et discriminations… L’enquête ébranle au passage certaines idées reçues et témoigne également des résistances des travailleurs concernés. S’ils s’affrontent rarement à leurs employeurs, ils entretiennent en revanche une révolte souterraine qui peut menacer à l’occasion les constructions et contraindre les employeurs à mettre en œuvre des aménagements. L’implication physique de l’auteur dans son enquête permet une restitution fine des situations rencontrées et offre une immersion impressionnante dans cet univers méconnu du bâtiment.

We analyze particle velocity fluctuations in a simulated granular system subjected to homogeneous quasistatic shearing. We show that these fluctuations share the following scaling characteristics of fluid turbulence in spite of their different physical origins: (i) scale-dependent probability distribution with non-Gaussian broadening at small time scales; (ii) spatial power spectrum of the velocity field showing a power-law decay, reflecting long-range correlations and the self-affine nature of the fluctuations; and (iii) superdiffusion of particles with respect to the mean background flow.

Abstract The methodology of eXtended finite element method is applied to the measurement of displacements through digital image correlation. An algorithm, initially based on a finite element decomposition of displacement fields, is extended to benefit from discontinuity and singular enrichments over a suited subset of elements. This allows one to measure irregular displacements encountered, say, in cracked solids, as demonstrated both in artificial examples and experimental case studies. Moreover, an optimization strategy for the support of the discontinuity enables one to adjust the crack path configuration to reduce the residual mismatch, and hence to be tailored automatically to a wavy or irregular crack path. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Abstract It is proposed to determine damage parameters in two dimensions (surface of a material) or three dimensions (in the bulk of a solid) by using full‐field displacement measurements. A finite‐element approach is developed to evaluate piece‐wise constant elastic parameters modeled by an isotropic damage variable. Two sets of examples are discussed. The first series deals with mechanical fields obtained by finite element simulations to assess the performance of the approach. The second series is concerned with displacement measurements performed during a biaxial test on a composite material. Copyright © 2004 John Wiley &amp; Sons, Ltd.