A damage to crack transition model accounting for stress triaxiality formulated in a hybrid nonlocal implicit discontinuous Galerkin‐cohesive band model framework

Modelling the entire ductile fracture process remains a challenge. On the one hand, continuous damage models succeed in capturing the initial diffuse damage stage but are not able to represent discontinuities or cracks. On the other hand, discontinuous methods, as the cohesive zones, which model the crack propagation behaviour, are suited to represent the localised damaging process. However, they are unable to represent diffuse damage. Moreover, most of the cohesive models do not capture triaxiality effect. In this paper, the advantages of the two approaches are combined in a single damage to crack transition framework. In a small deformation setting, a nonlocal elastic damage model is associated with a cohesive model in a discontinuous Galerkin finite element framework. A cohesive band model is used to naturally introduce a triaxiality‐dependent behaviour inside the cohesive law. Practically, a numerical thickness is introduced to recover a 3D state, mandatory to incorporate the in‐plane stretch effects. This thickness is evaluated to ensure the energy consistency of the method and is not a new numerical parameter. The traction‐separation law is then built from the underlying damage model. The method is numerically shown to capture the stress triaxiality effect on the crack initiation and propagation.     

3D Point Cloud Analysis for Detection and Characterization of Defects on Airplane Exterior Surface

Three-dimensional surface defect inspection remains a challenging task. This paper describes a novel automatic vision-based inspection system that is capable of detecting and characterizing defects on an airplane exterior surface. By analyzing 3D data collected with a 3D scanner, our method aims to identify and extract the information about the undesired defects such as dents, protrusions or scratches based on local surface properties. Surface dents and protrusions are identified as the deviations from an ideal, smooth surface. Given an unorganized point cloud, we first smooth noisy data by using Moving Least Squares algorithm. The curvature and normal information are then estimated at every point in the input data. As a next step, Region Growing segmentation algorithm divides the point cloud into defective and non-defective regions using the local normal and curvature information. Further, the convex hull around each defective region is calculated in order to englobe the suspicious irregularity. Finally, we use our new technique to measure the dimension, depth, and orientation of the defects. We tested and validated our novel approach on real aircraft data obtained from an Airbus A320, for different types of defect. The accuracy of the system is evaluated by comparing the measurements of our approach with ground truth measurements obtained by a high-accuracy measuring device. The result shows that our work is robust, effective and promising for industrial applications.     

Participatory Bayesian modelling for sustainable and efficient river restoration projects: Feedback from the case study of the Gave de Pau River,Hautes‐Pyrénées,France

Through the diversity of criteria and stakes, the uncertain nature of the entailed phenomena and the multi‐scale aspects to be taken into account, a river restoration project can be considered as a complex problem. Integrative approaches and modelling tools are thus needed to help river managers make predictions on the evolution of hydromorphological, socio‐economic, safety and ecological issues. Such approach can provide valuable information for handling long‐term management plans that consider the interaction and the balance of stakeholders interests and river system functioning. In this paper, we present a probabilistic participatory modelling (PM) method that assesses the effects of given restoration actions, knowing the hydromorphological modifications that they may induce on the safety, ecological and socio‐economic aspects with the help of local stakeholders through several workshops. To support this strategy, we used Bayesian networks (BNs) as modelling tools as their causal graphs can combine multidimensional knowledge and data from diverse natures. We introduce the causal graphs elaborated with the help of the stakeholders and convert it into BNs that can assist restoration decisions by considering the available decision and utility functions to provide guidance to decision‐makers. This was applied to the “Lac des Gaves” reach in the Hautes‐Pyrénées, France, a reach that has gone through severe sediment extractions for over 50 years. Each network represents possible restoration decisions linked to one of the observed issues. The paper demonstrates how BNs used as a decision support system (DSS) can help to assess the influence of given management strategies on the river system with the consideration of stakeholders’ knowledge and integration in all the modelling process.     

Swelling behavior of polymeric membranes to metalworking fluids

In some working places, such as metal manufacturing or automotive services, mechanical hazards commonly occur along with chemical hazards, particularly metalworking fluids (MWFs). The presence of these chemicals could modify the properties of gloves made from polymeric materials and thus reduce their protective properties against chemical contamination (solvent, MWFs) and mechanical risks (puncture and cutting). This work focused on determining the swelling characteristics and the resistance of six polymeric membranes which were exposed to seven industrial MWFs. We found that the swelling tests can be used to classify the potential of coating polymers in descending order of their resistance to MWFs: nitrile, polyurethane > poly(vinyl chloride), neoprene > butyl, latex. The analysis by multiple linear regression showed, for the first time, that the density or the viscosity‐gravity constant of the fluid and Hansen's solubility parameters of the polymers have a significant impact on the swelling of polymer. For the first time, two new multiple regression models have been proposed, to predict the swelling phenomena of polymers under various MWFs with an accuracy of ≈80%. The effect of temperature on mechanical properties and morphology of material was also examined. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45717.     

Ligand‐Free Synthesis of Aluminum‐Doped Zinc Oxide Nanocrystals and their Use as Optical Spacers in Color‐Tuned Highly Efficient Organic Solar Cells

The color of polymer solar cells using an opaque electrode is given by the reflected light, which depends on the composition and thickness of each layer of the device. Metal‐oxide‐based optical spacers are intensively studied in polymer solar cells aiming to optimize the light absorption. However, the low conductivity of materials such as ZnO and TiO₂ limits the thickness of such optical spacers to tenths of nanometers. A novel synthesis route of cluster‐free Al‐doped ZnO (AZO) nanocrystals (NCs) is presented for solution processing of highly conductive layers without the need of temperature annealing, including thick optical spacers on top of polymer blends. The processing of 80 nm thick optical spacers based on AZO nanocrystal solutions on top of 200 nm thick polymer blend layer is demonstrated leading to improved photocurrent density of 17% compared to solar cells using standard active layers of 90 nm in combination with thin ZnO‐based optical spacers. These AZO NCs also open new opportunities for the processing of high‐efficiency color tuned solar cells. For the first time, it is shown that applying solution‐processed thick optical spacer with polymer blends of different thicknesses can process solar cells of similar efficiency over 7% but of different colors.     

SDS-PAGE under focusing conditions: an electrokinetic transport phenomenon based on charge compensation

A novel method is reported for mass separation of proteins, based on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Unlike conventional SDS-PAGE, in which separation by mass of SDS-laden polypeptide chains is obtained in constant concentration or porosity gradient gels, the present method, called "SDS-PAGE focusing", exploits a "steady-state" process by which the SDS-protein micelles are driven to stationary zones along the migration path against a gradient of positive charges affixed to the neutral polyacrylamide matrix. As the total negative surface charge of such complexes matches the surrounding charge density of the matrix, the SDS-protein complex stops migrating and remains stationary, as typical of steady-state separation techniques. As a result of this mechanism, the proteins are separated in an unorthodox way, with the smaller proteins/peptides staying closer to the application point and larger proteins migrating further down toward the anodic gel end. This results in a positive slope of the Mr vs migration plot, vs a negative slope in conventional SDS-PAGE. Moreover, such a plot is linear (by design), whereas in standard SDS-PAGE it is semi- or even double logarithmic. Particularly advantageous appears the ability of the present method to fine-tune the separation of small-size fragments and tryptic digests, where conventional SDS-PAGE usually fails. Additionally, by exploiting constant plateaus of charges, rather than gradients, it is possible to amplify the separation between species having closely spaced Mr values, down to a limit of approximately 150 Da. This increases the resolution by at least 1 order of magnitude as compared with standard SDS-PAGE, where for a proper separation of two adjacent species, an Mr increment of approximately 3000 Da is needed.     

Optimization of Advanced Live-Cell Imaging through Red/Near-Infrared Dye Labeling and Fluorescence Lifetime-Based Strategies

Fluorescence microscopy is essential for a detailed understanding of cellular processes; however, live-cell preservation during imaging is a matter of debate. In this study, we proposed a guide to optimize advanced light microscopy approaches by reducing light exposure through fluorescence lifetime (τ) exploitation of red/near-infrared dyes. Firstly, we characterized key instrumental elements which revealed that red/near-infrared laser lines with an 86x (Numerical Aperture (NA) = 1.2, water immersion) objective allowed high transmission of fluorescence signals, low irradiance and super-resolution. As a combination of two technologies, i.e., vacuum tubes (e.g., photomultiplier) and semiconductor microelectronics (e.g., avalanche photodiode), type S, X and R of hybrid detectors (HyD-S, HyD-X and HyD-R) were particularly adapted for red/near-infrared photon counting and τ separation. Secondly, we tested and compared lifetime-based imaging including coarse τ separation for confocal microscopy, fitting and phasor plot analysis for fluorescence lifetime microscopy (FLIM), and lifetimes weighting for enhanced stimulated emission depletion (STED) nanoscopy, in light of red/near-infrared multiplexing. Mainly, we showed that the choice of appropriate imaging approach may depend on fluorochrome number, together with their spectral/lifetime characteristics and STED compatibility. Photon-counting mode and sensitivity of HyDs together with phasor plot analysis of fluorescence lifetimes enabled the flexible and fast imaging of multi-labeled living H28 cells. Therefore, a combination of red/near-infrared dyes labeling with lifetime-based strategies offers new perspectives for live-cell imaging by enhancing sample preservation through acquisition time and light exposure reduction.     

Crystallization of poly(butylene terephthalate)

This article provides a thorough analysis of the crystallization process of poly(butylene terephthalate) (PBT). Isothermal crystal growth rates have been experimentally measured between 459 and 491 K, and analyzed according to the Hoffman and Lauritzen theory. A II–III regime transition occurs at 484 K, accompanied by a change in crystal morphology. By means of a non‐linear fitting procedure, precise values of the nucleation constant K_g were obtained. The lateral surface free energy σ was calculated and, from this, the α parameter of the Thomas‐Staveley expression was obtained.     

Complex precipitation pathways in multicomponent alloys

One usual way to strengthen a metal is to add alloying elements and to control the size and the density of the precipitates obtained. However, precipitation in multicomponent alloys can take complex pathways depending on the relative diffusivity of solute atoms and on the relative driving forces involved. In Al-Zr-Sc alloys, atomic simulations based on first-principle calculations combined with various complementary experimental approaches working at different scales reveal a strongly inhomogeneous structure of the precipitates: owing to the much faster diffusivity of Sc compared with Zr in the solid solution, and to the absence of Zr and Sc diffusion inside the precipitates, the precipitate core is mostly Sc-rich, whereas the external shell is Zr-rich. This explains previous observations of an enhanced nucleation rate in Al-Zr-Sc alloys compared with binary Al-Sc alloys, along with much higher resistance to Ostwald ripening, two features of the utmost importance in the field of light high-strength materials.