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See detailUnified treatment of microscopic boundary conditions in computational homogenization method for multiphysics problems
Nguyen, Van Dung ULg; Wu, Ling ULg; Homsi, Lina ULg et al

Conference (2016, September 08)

Computational homogenization (so-called FE2) method is an effective tool to model complex behavior of heterogeneous media allowing direct coupling between the structure response and the evolving ... [more â–¼]

Computational homogenization (so-called FE2) method is an effective tool to model complex behavior of heterogeneous media allowing direct coupling between the structure response and the evolving microstructure not only in purely mechanical problems but also in multiphysics problems [1]. The basic idea of this method is to obtain the macroscopic constitutive relationships from the resolution of the microscopic boundary value problem (BVP) defined on a representative volume element. This method does not requires any constitutive assumption at the macroscopic level, but an appropriate microscopic boundary condition has to be defined. Our work focuses on the unified treatment of the microscopic boundary condition in a multiphysics microscopic BVP. In particular, an efficient way to compute the tangent operator is developed for an arbitrary kind of boundary conditions. When considering the FE2method, the homogenized stresses and homogenized tangents at every macroscopic integration points are required. From the energy consistency condition between macroscopic and microscopic problems, the homogenized stresses can be easily computed by the volumetric averaging integrals of the microscopic counterparts. The required homogenized tangents often follows a stiffness condensation from the microscopic stiffness matrix at the equilibrium state [2]. When using the stiffness condensation, the microscopic stiffness matrix needs to be partitioned, and dense matrices based on Schur complements (under a matrix form 𝐊̃ 𝑏𝑏=𝐊𝑏𝑏−𝐊𝑏𝑖𝐊𝑖𝑖−1𝐊𝑖𝑏) have to be estimated. The matrix operations based on Schur complements require a large time consuming and a lot of memory when increasing the number of degrees of freedom of the microscopic BVPs. This work proposes an efficient method allowing to compute the homogenized tangents without significant effort. The microscopic stiffness matrix does not need to be partitioned. The homogenized tangents are computed by solving a linear system, which is based on the linearized system at the converge solution of the microscopic BVP, with multiple right hand sides. With proposed numerical improvements, the FE2 method is used in a fully thermo-mechanically-coupled simulation. The temperature-dependent elastoplastic behavior, thermal conduction as well as the heat conversion from the mechanical deformation are considered in the hyperelastic large strain framework. [1]. Geers, M. G. D., Kouznetsova, V. G., Brekelmans, W. A. M., 2010. J. Comput. Appl. Math. 234 (7), 2175-2182. [2]. Kouznetsova, V., Brekelmans, W. A. M., Baaijens, F. P. T., 2001. Comput. Mech. 27 (1), 37-48. [less â–²]

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See detailL'ENSEIGNEMENT DU FRANÇAIS AUX ANGLOPHONES AU CAMEROUN : ANALYSE ET PROPOSITIONS DIDACTIQUES
Mouto Betoko, Christiane ULg

Doctoral thesis (2016)

Au Cameroun, l’école est la garante de la politique du bilinguisme officiel qui vise à faire de tous les citoyens camerounais des individus parfaitement bilingues, afin de garantir leur intégration sur ... [more â–¼]

Au Cameroun, l’école est la garante de la politique du bilinguisme officiel qui vise à faire de tous les citoyens camerounais des individus parfaitement bilingues, afin de garantir leur intégration sur l’ensemble du territoire national. Les élèves anglophones apprennent donc le français, leur deuxième langue officielle (LO2), comme toutes les autres disciplines, tout au long de leur cursus secondaire. En classes terminales, l’un des objectifs prioritaires de l’enseignement de la LO2 (French) est de préparer les élèves à intégrer les milieux universitaires et/ou socioprofessionnels majoritairement implantés en zone francophone. Néanmoins, dans ce contexte, l’atteinte des objectifs scolaires du bilinguisme constitue une problématique imputable à de nombreuses inadéquations inhérentes au sous-système éducatif anglophone. C’est dans cette optique que nous nous sommes demandé comment allier « objectifs scolaires du bilinguisme » et « méthodologie de l’enseignement du French» pour une préparation effective de notre public cible à son intégration dans son milieu de vie au sortir du secondaire. Ainsi, nous avons inscrit cette étude dans le champ épistémologique de la didactique du français langue étrangère, domaine disciplinaire qui fait de la connaissance des publics le point de départ de tout projet de formation en langues étrangères. Ceci dit, nous défendons la thèse selon laquelle la prise en compte des besoins réels des principaux acteurs devrait constituer l’étape préalable à la mise au point des projets de réforme tels la réforme du système éducatif et par ricochet, des programmes de formation que connaît actuellement l’éducation au Cameroun. Ayant constaté que l’environnement sociolinguistique où se déroulent l’enseignement et l’apprentissage du French n’est pas sans conséquence directe sur la mise en application du bilinguisme scolaire, nous avons jugé nécessaire de comprendre les politiques linguistique et éducative du milieu d’étude. Ainsi, dans la première partie de ce travail, il convenait de s’interroger sur le mode d’emploi réel des langues officielles, particulièrement en ce qui concerne l’usage de la langue française dans la société camerounaise ; de comprendre la problématique de la formation bilingue au Cameroun ; de questionner la place des langues maternelles à l’école ; d’analyser les failles du sous-système éducatif anglophone en matière d’enseignements des langues officielles ; et enfin, de mener une réflexion didactique sur les programmes de français II. Dans la deuxième partie de ce travail, nous avons mis en exergue l’importance de la prise en compte des caractéristiques des principaux acteurs de la salle de classe dans l’élaboration des programmes de formation. Les profils de ces acteurs étant absents des directives institutionnelles, nous les avons questionnés pour mettre leurs caractéristiques au grand jour. Pour ce faire, nous avons mené une enquête de terrain dans les deux régions qui constituent la zone anglophone (Nord-Ouest et Sud-Ouest) et, dans une région de la zone francophone (Centre). La récolte des données s’est faite par le biais de deux questionnaires (un pour les enseignants et un pour les élèves en classes terminales) et d’une grille d’observation des pratiques de classe. La méthode utilisée est l’analyse quantitative et descriptive des données statistiques. À travers la discussion des résultats obtenus sur la terrain d’enquête, nous avons validé l’hypothèse générale émise au départ, stipulant qu’il y a actuellement une inadéquation entre les objectifs scolaires du bilinguisme et la méthodologie mise en œuvre pour les atteindre en classes terminales du sous-système éducatif anglophone. À travers cette démonstration, nous avons tout simplement touché du doigt la réalité selon laquelle l’atteinte des objectifs visés dans le cadre du bilinguisme ne peut se faire sans avoir établie, au préalable, les besoins réels des principaux acteurs de la salle de classe. [less â–²]

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See detailMeasurement of Innovation: Where Do We Stand?
Artige, Lionel ULg

Conference (2016, September 08)

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See detailLa tête en l'air, les pieds sur Terre
Stiepen, Arnaud ULg

Conference given outside the academic context (2016)

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See detailGCxGC-HRMS with Soft Ionization for Petroleum Analyses
Giri, Anupam ULg; Focant, Jean-François ULg

Scientific conference (2016, September 08)

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See detailConséquences de la structure fédérale, régionale ou décentralisée de l’État sur les procédures référendaires
Miny, Xavier ULg

Scientific conference (2016, September 08)

La décentralisation politique, poussée à l'extrême dans le cadre du fédéralisme, amène souvent une complexification de la mise en œuvre des mécanismes de démocratie directe (référendum, consultation ... [more â–¼]

La décentralisation politique, poussée à l'extrême dans le cadre du fédéralisme, amène souvent une complexification de la mise en œuvre des mécanismes de démocratie directe (référendum, consultation populaire) car elle implique la participation des citoyens qui relèvent d’entités subétatiques différentes. Or, dans un contexte parfois multinational et multi-identitaire, la décentralisation poussée – fédéralisme, régionalisme – rentre bien souvent en contradiction avec la dynamique majoritaire pure et simple. La recherche entend s'intéresser, par le droit comparé, à la prise en compte des phénomènes régionaux dans le recours aux instruments référendaires. [less â–²]

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See detailSeroprevalence of Borrelia burgdorferi in horses in the southern part of Belgium: a “one health” driven study
Meersschaert, Carole; Cerri, Simona ULg; Houben rosa, Rosa et al

Conference (2016, September 08)

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See detailApplication of GRACE to the assessment of model-based estimates of monthly Greenland Ice Sheet mass balance (2003–2012)
Schlegel, N.; Wiese, D.; Larour, E. et al

in Cryosphere (The) (2016), 10

Quantifying the Greenland Ice Sheet's future contribution to sea level rise is a challenging task that requires accurate estimates of ice sheet sensitivity to climate change. Forward ice sheet models are ... [more â–¼]

Quantifying the Greenland Ice Sheet's future contribution to sea level rise is a challenging task that requires accurate estimates of ice sheet sensitivity to climate change. Forward ice sheet models are promising tools for estimating future ice sheet behavior, yet confidence is low because evaluation of historical simulations is challenging due to the scarcity of continental-wide data for model evaluation. Recent advancements in processing of Gravity Recovery and Climate Experiment (GRACE) data using Bayesian-constrained mass concentration ("mascon") functions have led to improvements in spatial resolution and noise reduction of monthly global gravity fields. Specifically, the Jet Propulsion Laboratory's JPL RL05M GRACE mascon solution (GRACE_JPL) offers an opportunity for the assessment of model-based estimates of ice sheet mass balance (MB) at ∼ 300 km spatial scales. Here, we quantify the differences between Greenland monthly observed MB (GRACE_JPL) and that estimated by state-of-the-art, high-resolution models, with respect to GRACE_JPL and model uncertainties. To simulate the years 2003–2012, we force the Ice Sheet System Model (ISSM) with anomalies from three different surface mass balance (SMB) products derived from regional climate models. Resulting MB is compared against GRACE_JPL within individual mascons. Overall, we find agreement in the northeast and southwest where MB is assumed to be primarily controlled by SMB. In the interior, we find a discrepancy in trend, which we presume to be related to millennial-scale dynamic thickening not considered by our model. In the northwest, seasonal amplitudes agree, but modeled mass trends are muted relative to GRACE_JPL. Here, discrepancies are likely controlled by temporal variability in ice discharge and other related processes not represented by our model simulations, i.e., hydrological processes and ice–ocean interaction. In the southeast, GRACE_JPL exhibits larger seasonal amplitude than predicted by the models while simultaneously having more pronounced trends; thus, discrepancies are likely controlled by a combination of missing processes and errors in both the SMB products and ISSM. At the margins, we find evidence of consistent intra-annual variations in regional MB that deviate distinctively from the SMB annual cycle. Ultimately, these monthly-scale variations, likely associated with hydrology or ice–ocean interaction, contribute to steeper negative mass trends observed by GRACE_JPL. Thus, models should consider such processes at relatively high (monthly-to-seasonal) temporal resolutions to achieve accurate estimates of Greenland MB. [less â–²]

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See detailDroits de l'homme - Recueil de jurisprudence belge, européenne et internationale - 3e édition
Bouhon, Frédéric ULg

Learning material (2016)

Ce dossier rassemble les extraits de dizaines de décisions prononcées par de hautes juridictions nationales et internationales. Une grande partie d'entre elles sont des arrêts de la Cour européenne des ... [more â–¼]

Ce dossier rassemble les extraits de dizaines de décisions prononcées par de hautes juridictions nationales et internationales. Une grande partie d'entre elles sont des arrêts de la Cour européenne des droits de l'homme. Les étudiants qui suivent le cours de "Droits de l'homme" sont invités à lire le dossier au fur et à mesure du quadrimestre, en appui du cours ex cathedra. [less â–²]

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See detailDroits de l'homme - Plan général du cours 2016-17
Bouhon, Frédéric ULg

Learning material (2016)

Ce document constitue le plan général du cours de "Droits de l'homme" pour l'année académique 2016-2017. Il indique la structure du cours ainsi que les principales références à la jurisprudence étudiée ... [more â–¼]

Ce document constitue le plan général du cours de "Droits de l'homme" pour l'année académique 2016-2017. Il indique la structure du cours ainsi que les principales références à la jurisprudence étudiée dans le cadre du cours. [less â–²]

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See detailGeneralized Pascal triangle for binomial coefficients of words : an overview
Stipulanti, Manon ULg

Conference (2016, September 07)

We introduce a generalization of Pascal triangle based on binomial coefficients of finite words. These coefficients count the number of times a finite word appears as a subsequence of another finite word ... [more â–¼]

We introduce a generalization of Pascal triangle based on binomial coefficients of finite words. These coefficients count the number of times a finite word appears as a subsequence of another finite word. Similarly to the Sierpiński gasket that can be built as the limit set, for the Hausdorff distance, of a convergent sequence of normalized compact blocks extracted from Pascal triangle modulo 2, we describe and study the first properties of the subset of [0, 1] × [0, 1] associated with this extended Pascal triangle modulo a prime p. Then we create a new sequence from this extended Pascal triangle that counts, on each row of this triangle, the number of positive binomial coefficients. We study some properties of this sequences. To be precise, we investigate some properties regarding the regularity of the sequence. To extend our work, we construct a Pascal triangle using the Fibonacci representations of all the nonnegative integers and we define the corresponding sequence of which we study the regularity. This regularity is an extension of the classical k-regularity of sequences. [less â–²]

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See detailHow do droplets form?
Van Loo, Stéphanie ULg; Stoukatch, Serguei ULg; Kraft, Michael ULg et al

Poster (2016, September 07)

In microfluidics, flow focusing is widely used to produce water-in-oil droplets in microchannels at high frequency. We here report an experimental study of droplet formation in a microfluidic cross ... [more â–¼]

In microfluidics, flow focusing is widely used to produce water-in-oil droplets in microchannels at high frequency. We here report an experimental study of droplet formation in a microfluidic cross-junction with a minimum number of geometrical parameters. We mostly focus on the squeezing regime, which is com- posed of two distinct steps : filling and pinching. The duration of each step (and corresponding volumes of each liquid phase) are analyzed. They vary according to both water and oil flow rates. These variations provide several insights about the fluid flows in both phases. We propose several scaling laws to relate the droplet volume and frequency to the flow rate of both phases. We also discuss the influence of surfactant and channel compliance on droplet formation. [less â–²]

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See detailBetween bovine milk production and reproduction : the challenge.
Hanzen, Christian ULg; Nguyen Kien, Cuong

in Vo Thi Tra; Ho Thi Kim, Hoa; Le Thanh, Hien (Eds.) et al Proceedings of the 19th Federation of Asian Veterinary Association Congress (2016, September 07)

Huge differences in dairy milk production can be observed around the world. They can be explained by differences in genetic, nutritional resources and management including the capacities of the farmers ... [more â–¼]

Huge differences in dairy milk production can be observed around the world. They can be explained by differences in genetic, nutritional resources and management including the capacities of the farmers and veterinarian to prevent and treat the different pathologies inducing of the wellbeing of the animals. According to the world market of milk production, the challenge of each farm is not only to produce a milk of quality but also to reduce the costs of milk production by improving reproductive performances. Anywhere in the world we are responsible to encourage and develop a sustainable approach of milk production and agriculture development according to his three pillars: environment, economic and social. Our presentation will present (1) the mains figures about the milk production in the world, (2) the definitions and prevalences of the different periods involved in the reproductive life of a cow, (3) the nutritional, genetic and pathological factors involved in the milk production on general and more specifically in reproduction (dystocia, placental retention, uterine infections, postpartum anoestrus), the relationships between these factors, (‘) the state of art of the definition, methods of diagnostic state of art of the main reproduction pathologies (dystocia,) affecting the dairy cows during the waiting and reproduction periods. [less â–²]

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See detailPertes et Reconstructions Identitaires des Foyers Post-Divorce
Bullens, Quentin ULg

Doctoral thesis (2016)

La présente étude s’intéresse au parcours des foyers post-divorce via deux objectifs. Premièrement, nous voulons mettre en avant les éléments organisateurs permettant à ces foyers de passer d’un état à un ... [more â–¼]

La présente étude s’intéresse au parcours des foyers post-divorce via deux objectifs. Premièrement, nous voulons mettre en avant les éléments organisateurs permettant à ces foyers de passer d’un état à un autre. Pour ce faire, nous recourons à la méthode par théorisation ancrée, bien qu’en nous en écartant partiellement. Deuxièmement, nous cherchons à savoir quels sont les champs lexicaux qui peuvent être extraits des transcriptions d’entretiens avec ces foyers. Pour ce second objectif, nous recourons à la méthode Alceste, via le logiciel Iramuteq. Celui-ci nous permet un croisement des données d’entretiens avec des métadonnées issues notamment du FACES-III et du Jeu du Pique-Nique. Tous ces éléments sont discutés au regard des apports de la littérature scientifique. Mais aussi, au regard de la clinique du deuil, à laquelle il est fait appel pour éclairer ces parcours. En outre, nous contextualisons les notions de famille, mariage et divorce dans une perspective historique prenant ses bases au Moyen Âge. [less â–²]

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See detailGPS, Galileo and BeiDou inter-system biases estimation in relative positioning with code and phase pseudoranges
Deprez, Cécile ULg; Warnant, René ULg

Conference (2016, September 07)

The recent increase in the number of Global Navigation Satellite Systems (GNSS) opens new perspectives in the field of high precision positioning. Particularly, the Chinese BeiDou satellite system and the ... [more â–¼]

The recent increase in the number of Global Navigation Satellite Systems (GNSS) opens new perspectives in the field of high precision positioning. Particularly, the Chinese BeiDou satellite system and the European Galileo program have experienced major progress in 2015 and 2016 with the launch of 7 and 8 satellites respectively. Associated with the ongoing GPS modernization, many more frequencies and satellites are now available. Therefore, multi-GNSS relative positioning based on overlapping frequencies should entail better accuracy and reliability in position estimations. However, the differences between satellite systems induce inter-system biases (ISBs) inside the multi-GNSS equations of observation. The combined use of L1 and L5 from GPS with E1 and E5a from Galileo, B2 from BeiDou and E5b from Galileo in zero baseline double differences (ZB DD) based on a unique pivot satellite is employed to resolve ISBs. This model removes all the satellite- and receiver-dependent error sources by differentiating and the zero baseline configuration allows atmospheric and multipath effects elimination. An analysis of the long-term stability of ISBs (GPS- Galileo and Galileo - BeiDou) is conducted onvariouspairsof receiversover large timespans. Thepossibleinfluenceof temperature variations inside the receivers over ISB values is also investigated. Our study is based on the 6 multi-GNSS receivers (2 Septentrio PolaRx4, 1 Septentrio PolaRxS, 1 Septentrio PolaRx5 and 2 Trimble NetR9) installed on the roof of our building in Liege. The estimated ISBs are then used as corrections in the multi-GNSS observation model and the resulting accuracy of multi-GNSS positioning is compared to GPS, Galileo and BeiDou standalone solutions. [less â–²]

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See detailProbabilistic prediction of the quality factor of micro-resonator using a stochastic thermo-mechanical multi-scale approach
Wu, Ling ULg; Lucas, Vincent ULg; Golinval, Jean-Claude ULg et al

Conference (2016, September 07)

As the size of the device is only one or two orders of magnitude higher than the size of the grains, the structural properties, such as the thermo-elastic quality factor (Q), of micro-electro-mechanical ... [more â–¼]

As the size of the device is only one or two orders of magnitude higher than the size of the grains, the structural properties, such as the thermo-elastic quality factor (Q), of micro-electro-mechanical systems (MEMS) made of poly-crystalline materials exhibit a scatter, due to the existing randomness in the grain size, grain orientation, surface roughness... In order to predict the probabilistic behavior of micro-resonators, the authors extend herein a previously developed stochastic 3-scale approach [1] to the case of thermoelastic damping [2]. In this method, stochastic volume elements (SVEs) [3] are defined by considering random grain orientations in a tessellation. For each SVE realization, the mesoscopic apparent elasticity tensor, thermal conductivity tensor, and thermal dilatation tensor can be obtained using thermo-mechanical computational homogenization theory [4]. The extracted mesoscopic apparent properties tensors can then be used to define a spatially correlated meso-scale random field, which is in turn used as input for stochastic finite element simulations. As a result, the probabilistic distribution of the quality factor of micro-resonator can be extracted by considering Monte-Carlo simulations of coarse-meshed micro-resonators, accounting implicitly for the random micro-structure of the poly-silicon material. [1] V. Lucas, J.-C. Golinval, S. Paquay, V.-D. Nguyen, L. Noels, L. Wu, A stochastic computational multiscale approach; Application to MEMS resonators. Computer Methods in Applied Mechanics and Engineering, 294, 141-167, 2015. [2] L. Wu, V. Lucas, V.-D. Nguyen, J.-C. Golinval, S. Paquay, L. Noels, A Stochastic Multiscale Approach for the Modeling of Thermoelastic Damping in Micro-Resonators. Submitted. [3] M. Ostoja-Starzewski, X.Wang, Stochastic finite elements as a bridge between random material microstructure and global response, Computer Methods in Applied Mechanics and Engineering, 168, 35--49, 1999. [4] I. Özdemir, W. A. M. Brekelmans, M. G. D. Geers, Computational homogenization for heat conduction in heterogeneous solids, International Journal for Numerical Methods in Engineering 73, 185-204, 2008. [less â–²]

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See detailRôle du climat et de la compétition interspécifique dans la limitation de l'aire d'invasion d'Ambrosia artemisiifolia L. en Europe de l'Ouest
Ortmans, William ULg

Doctoral thesis (2016)

The invasion process is classically described from a temporal point of view, where a species overcomes a defined number of barriers. First, a species has to get through the geographical barrier, i.e., be ... [more â–¼]

The invasion process is classically described from a temporal point of view, where a species overcomes a defined number of barriers. First, a species has to get through the geographical barrier, i.e., be introduced in the new area. Once introduced, the species has to survive new environmental conditions and reproduce successfully. When the environmental barrier is overcome, i.e. when the species is able to reproduce and its populations are self-sufficient, it is considered as naturalized. To finally be considered as invasive, the species has to overcome the dispersal barrier and spread across landscapes. Within a given continent, a species could have overcome a variable number of barriers depending on the considered area. At a given moment, depending on the geographical area, one can observe non-naturalized populations, naturalized populations that are not invasive, and invasive populations. This geographical variation may be the result of an environmental variation across the continent. The common ragweed (Ambrosia artemisiifolia L.) invasion in Western Europe is a good opportunity to study this aspect of invasion biology. The invasion history and the species distribution are well documented, and highlight a geographical variation of the invasion dynamics. This is particularly clear in Western Europe, where there is a contrast between the highly invaded zone of the Rhône valley in France, and more northern areas such as the North of France, Belgium, and the Netherlands. In this work, we tested the hypothesis that the current invasion area is limited northwards, because of an unfavorable local climate or a too strong interspecific competition. In order to answer this general objective, four different questions were asked: 1) Is the climate and/or the interspecific competition causing a variation in plant performances across Western Europe?; 2) In an agricultural context north to the current invaded range, is the local climate allowing the establishment and the reproduction of newly introduced populations?; 3) What is the role of seed morphological variability in the invasion of areas with rigorous climatic conditions?; and 4) What is the role of the priority effect in the species establishment within a ruderal community? No clear limit to the colonization of areas beyond the current invaded range was found in this study. The local climate and the interspecific competition did not appear to limit the naturalization or spread of the species north to the current invaded range, be it in agricultural or ruderal situations. Results showed that once introduced in an agricultural habitat outside the current invaded range, the species was able to establish self-sustaining populations. On average, each plant produced a number of descendants equal to 273 ± 18.4 (mean ± standard error). In ruderal habitats, populations already exist in Belgium and in Southern Netherlands, and are able to produce a high quantity of seeds: on average, the measured plants carried 222 ± 32.0 seeds. The measured plant performances were similar to those measured within the invaded area. The findings of this work are consistent with those of other authors that questioned the “non-naturalized” species status in Belgium, and illustrate how temporally dynamic invasions are. The results showed the importance of the timing in the colonization of disturbed habitats. When the species started its development a few weeks before the rest of the community, its performance gain was higher than that of other ruderal Asteraceae species: its above ground biomass was 30.5 ± 1.94 times higher, and the number of flower heads 570 ± 160 times more important. The high variability of the species observed all along this work is probably playing an important role in the invasion success. The high morphological variability of the seeds seems to widen the range of environmental conditions the species is able to colonize. This study suggests a great invasion potential north to the current invaded area in Western Europe. In this uncertain situation, it appears critical to create an early detection system of the species in Belgium. Early detection may allow the eradication of the species before the invasion becomes as problematic as in France. Awareness campaigns should be encouraged in Belgium in order to avoid that new occurrences of the species remain unnoticed. [less â–²]

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See detailSimulations of composite laminates inter and intra-laminar failure using on a non-local mean-field damage-enhanced multi-scale method
Wu, Ling ULg; Adam, Laurent; Bidaine, Benoît et al

Conference (2016, September 07)

The failure of carbon fiber reinforced composite laminates is studied using a multiscale method. A non-local mean-field homogenization (MFH) method accounting for the damage evolution of the matrix phase ... [more â–¼]

The failure of carbon fiber reinforced composite laminates is studied using a multiscale method. A non-local mean-field homogenization (MFH) method accounting for the damage evolution of the matrix phase of the composite material [1] is considered in each ply in order to capture the intra-laminar failure. In that formulation, an incremental-secant MFH approach is used to account for the elastic unloading of the fibers during the strain softening of the matrix. In order to avoid the strain/damage localization caused by the matrix material softening, the damage enhanced MFH was formulated in an implicit non-local way [2]. Accurate predictions of the composite softening behavior and of the different phases response is then achieved. The delamination process is modeled by recourse to a hybrid discontinuous Galerkin (DG)/ extrinsic cohesive law approach. An open-hole composite laminate with a quasi-isotropic sequence ([90/45/-45/90/0]S) is then studied experimentally and using the multiscale method [3]. The numerical model is found to predict the damage bands along the fiber directions in agreement with the experimental samples inspected by X-ray computed tomography (XCT). Moreover, the predicted delamination pattern is found to match the experimental observations. Finally, with a view to stochastic analysis, the effect of the volume fraction and orientation variations on the failure is studied by defining them as random variables. REFERENCES [1] L. Wu, L. Noels, L. Adam, I. Doghri, An implicit-gradient-enhanced incremental-secant mean- field homogenization scheme for elasto-plastic composites with damage, International Journal of Solids and Structures, 50, 3843-3860, 2013. [2] R. Peerlings, R. de Borst, W. Brekelmans, S. Ayyapureddi, Gradient-enhanced damage for quasi-brittle materials. International Journal for Numerical Methods in Engineering, 39, 3391-3403, 1996. [3] L. Wu, F. Sket, J.M. Molina-Aldareguia, A. Makradi, L. Adam, I. Doghri, L. Noels, A study of composite laminates failure using an anisotropic gradient-enhanced damage mean-field homogenization model, Composite Structures, 126, 246–264, 2015. [less â–²]

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