Damage quantification in aluminium alloys using in situ tensile tests in X-ray tomography

This paper presents results obtained using in situ tensile experiments allowing the observation of damage nucleation, growth and coalescence. Three different aluminium alloys (2024, 7449 and 5754) exhibiting various mechanical properties were chosen to produce a wide data base. Smooth and notched axisymetric samples were cut out of the raw materials to introduce different levels of initial stress triaxiality using the geometry of the samples. In the different cases, the damage steps (initiation, growth and coalescence) were clearly visualised during interrupted and continuous in situ tensile tests in synchrotron X-ray tomography. The imaging was performed with a voxel size of 1.6 μm. The X-ray tomography method also gives a precise image of the outer shape of the sample and its change during deformation can then be analysed. This allows to calculate precisely the true strain vs true stress curve and also an approximation of the stress triaxiality using the Bridgman formula. The results show that damage can be visualised but also quantified precisely in the different cases in terms of nucleation and growth, coalescence being also evident in the results but still hard to quantify so far. Finally, a previously developed model for damage growth during ductile straining based on the Rice and Tracey approach can be fitted to the results.     

Vademecum‐based GFEM (V‐GFEM): optimal enrichment for transient problems

This paper proposes a generalized finite element method based on the use of parametric solutions as enrichment functions. These parametric solutions are precomputed off‐line and stored in memory in the form of a computational vademecum so that they can be used on‐line with negligible cost. This renders a more efficient computational method than traditional finite element methods at performing simulations of processes. One key issue of the proposed method is the efficient computation of the parametric enrichments. These are computed and efficiently stored in memory by employing proper generalized decompositions. Although the presented method can be broadly applied, it is particularly well suited in manufacturing processes involving localized physics that depend on many parameters, such as welding. After introducing the vademecum‐generalized finite element method formulation, we present some numerical examples related to the simulation of thermal models encountered in welding processes. Copyright © 2016 John Wiley & Sons, Ltd.     

A computational model of bounded developable surfaces with application to image‐based three‐dimensional reconstruction

Developable surfaces have been extensively studied in computer graphics because they are involved in a large body of applications. This type of surfaces has also been used in computer vision and document processing in the context of three‐dimensional (3D) reconstruction for book digitization and augmented reality. Indeed, the shape of a smoothly deformed piece of paper can be very well modeled by a developable surface. Most of the existing developable surface parameterizations do not handle boundaries or are driven by overly large parameter sets. These two characteristics become issues in the context of developable surface reconstruction from real observations. Our main contribution is a generative model of bounded developable surfaces that solves these two issues. Our model is governed by intuitive parameters whose number depends on the actual deformation and including the “flat shape boundary”. A vast majority of the existing image‐based paper 3D reconstruction methods either require a tightly controlled environment or restricts the set of possible deformations. We propose an algorithm for reconstructing our model's parameters from a general smooth 3D surface interpolating a sparse cloud of 3D points. The latter is assumed to be reconstructed from images of a static piece of paper or any other developable surface. Our 3D reconstruction method is well adapted to the use of keypoint matches over multiple images. In this context, the initial 3D point cloud is reconstructed by structure‐from‐motion for which mature and reliable algorithms now exist and the thin‐plate spline is used as a general smooth surface model. After initialization, our model's parameters are refined with model‐based bundle adjustment. We experimentally validated our model and 3D reconstruction algorithm for shape capture and augmented reality on seven real datasets. The first six datasets consist of multiple images or videos and a sparse set of 3D points obtained by structure‐from‐motion. The last dataset is a dense 3D point cloud acquired by structured light. Our implementation has been made publicly available on the authors' web home pages. Copyright © 2012 John Wiley & Sons, Ltd.     

Somatic mutations of the beta-catenin gene are frequent in mouse and human hepatocellular carcinomas

Hepatocellular carcinoma (HCC) is the major primary malignant tumor in the human liver, but the molecular changes leading to liver cell transformation remain largely unknown. The Wnt-beta-catenin pathway is activated in colon cancers and some melanoma cell lines, but has not yet been investigated in HCC. We have examined the status of the beta-catenin gene in different transgenic mouse lines of HCC obtained with the oncogenes c-myc or H-ras. Fifty percent of the hepatic tumors in these transgenic mice had activating somatic mutations within the beta-catenin gene similar to those found in colon cancers and melanomas. These alterations in the beta-catenin gene (point mutations or deletions) lead to a disregulation of the signaling function of beta-catenin and thus to carcinogenesis. We then analyzed human HCCs and found similar mutations in eight of 31 (26%) human liver tumors tested and in HepG2 and HuH6 hepatoma cells. The mutations led to the accumulation of beta-catenin in the nucleus. Thus alterations in the beta-catenin gene frequently are selected for during liver tumorigenesis and suggest that disregulation of the Wnt-beta-catenin pathway is a major event in the development of HCC in humans and mice.     

Le développement de la notion de vitesse relative.

Administered a modified version of a Piagetian test on the concept of relative velocity (including questions on the duration of relative displacements) to 96 children placed in age groups of 7, 9, 11, and 13 yr. It was found that (a) the developmental stages of the concept were comparable to those observed by Piaget except for formal operations which seem to evolve later; (b) the combination of 2 movements of same direction but unequal velocity is more difficult to synthesize than any other; (c) success on the problem of durations is not a prerequisite of at least partial success on the problem of velocities; and (d) complete success on the problem of velocities is not necessarily verbalized in spatio-temporal terms. To explain the difficulty observed in synthesizing velocities, the importance of the instructions (e.g., specifying the speed of each mobile) and of changes in the spatial order of the mobiles was emphasized. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Le r?le du surplombement dans l'estimation perceptive des longueurs de deux horizontales a extrémités decalées.

Asked a total of 84 children and adults in 4 age groups (means = 5.11, 7.8, 9.8, 11.5, and 24.4 yrs) to match, by the method of adjustment, the lengths of 2 horizontal lines staggered so as to form 2 sides of a parallelogram under 2 main conditions (variable over the standard or standard over the variable) and a control condition (variable and standard in prolongation). Results show that the variable was generally overestimated, this overestimation did not differ significantly from 1 condition to another, and this overestimation decreased significantly with age. Results suggest that this systematic error would not be attributed to the top positioning but rather to the movement of the variable, which would be a source of overestimation by drawing the relative frequency of S's perceptive centrations. The decrement of the error with age could be explained by the development of perceptual activity, allowing a more balanced centration on the standard and the variable. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Life-threatening asthma with dramatic resolution

The speed of onset of an asthma attack can be highly variable. Recent studies have tried to characterize a subgroup of patients with life-threatening asthma that occurs suddenly but often regresses very rapidly under treatment. We had the opportunity to observe the evolution of two asthmatic women hospitalized with extremely severe respiratory acidosis. One of them required immediate orotracheal intubation and mechanical ventilation during 13 h. The results of her pulmonary function tests were normal 35 h after admission. The second woman's condition improved so rapidly under treatment that she did not require intubation and mechanical ventilation. These observations suggest that bronchospasm might play an important role in the pathophysiology of transient life-threatening asthma.     

Scanning electrochemical microscopy. Hydrodynamics generated by the motion of a scanning tip and its consequences on the tip current

The motion of a SECM tip above a substrate generates a flow of the surrounding fluid. Finite element calculations show that this flow is a simple linear-shear flow (Couette flow) for small tip-substrate separations and deviates from Couette's law at larger ones. The effect of fluid flow on the tip current response was determined numerically. Different mass-transfer regimes are observed depending on the insulating or conducting nature of the substrate, the tip speed (or fluid velocity), and the tip-substrate separation. Those observations are tested experimentally, and good agreement is obtained between numerical and experimental results.     

Relations entre la notion et la perception de la vitesse relative chez l'enfant.

Administered 2 tasks bearing on the perception and concept of relative velocity to 7-, 9-, 11-, and 13-yr-old children (24 at each age level). The perceptual task presented an illusion created by the movement of a target on a moving background, while the conceptual task was a modified version of Piaget's technique. In each task the 2 movements involved were either in the same (MS) or in the opposite direction. It was found that the illusion appeared earlier than the corresponding concept under the MS condition. The possibility of a retroactive effect of the concept on the percept is suggested. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neuropsychological examinations in childhood

Three groups of children aged 8-12 years have been investigated by a test battery to gain insight into the problems surrounding the relationship between cerebral and behavioral development. One group was of children with circumscribed cortical lesions, one was a group of dyslexics with neurologic anomalies, and the third was a control group of children without brain lesions. General test intelligence did not differ significantly in the three groups. Marked differences between the various lesion groups are observable in some tests but not in others. For example, the results of children with left temporal lesions in the verbal part of the intelligence test and in fresh language memory were inferior to those of all other lesion groups and the controls, while the dyslexics showed a similar if less marked deficit. Non-linguistic (figural) memory did not differ as between groups. On the other hand, children with right frontal lesions were notable for inferior results in a visual learning test and a classification test. In a linguistic-dichotic test all the groups of brain lesions and the dyslexics differed from the control group, a fact which suggests retarded development of hemispheric dominance for speech functions. From these provisional results it can be concluded that the brain areas do not all specialize simultaneously, and that compensation of cerebral lesions in relation to different functions probably results in retardation of overall brain development and anatomico-functional specialization.