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See detailCannabis use initiation among adolescents: the predictive role of peers, alcohol, expectancies and internalizing factors.
Schmits, Emilie ULg; Mathys, Cécile ULg; Quertemont, Etienne ULg

Conference (2014, September 05)

Theoretical background: Cannabis is the most commonly used illicit drug among teenagers. Initiation is influenced by environmental factors and personal characteristics, events or experiences. An early ... [more ▼]

Theoretical background: Cannabis is the most commonly used illicit drug among teenagers. Initiation is influenced by environmental factors and personal characteristics, events or experiences. An early initiation increases the risks of problems related to cannabis use (e.g. negative psychosocial effects, delinquent behaviors, mental disorders). Prevent initiation, through the identification of risk/protective factors and their interaction, seems crucial in terms of public health. Research question and significance: This study aimed to examine the progression of use, to identify protective and risk factors of cannabis initiation (including peers, alcohol, expectancies and internalizing factors) and to specifically focus on the influence of social anxiety and its moderators/mediators. Methods: A questionnaire was administered twice to 877 teenagers (49.94% female, M=15.61) with one year interval. Sex, age, demographic variables, peer cannabis use, cannabis-related variables (lifetime, frequency, problems and expectancies), alcohol use, social anxiety, trait-anxiety and depression were assessed through validated scales. Logistic regressions, mediation and moderation analyzes were performed. Results: During the follow-up period, 12.89% of the young participants initiated cannabis use. Several factors significantly predict initiation: alcohol use, peer users, perceptual enhancement and craving effect expectancies. Others factors significantly protect from initiation: negative behavioral effect expectancies and social anxiety. Gender, age, relaxation/social facilitation and cognitive impairment effect expectancies, trait-anxiety and depression do not significantly influence cannabis use initiation. In moderated mediation model, after controlling for relevant variables, social anxiety protected from initiation trough the mediating role of perceptual enhancement and craving effect expectancies. The number of peer users and alcohol use do not moderate this mediation. Negative behavioral effect expectancies do not significantly mediate the relation between social anxiety and cannabis initiation. Interpretation of findings: Through low positive expectancies, adolescents with social anxiety symptoms are less likely to initiate cannabis use than the others, whatever the number of peer users and the alcohol use. Findings are discussed in terms of risk and protective characteristics of relevant factors, in an overall and evolutionary approach including internalizing factors. Results support the identification of internalizing profile of adolescents concerned by prevention or treatment and the importance of social anxiety and expectancies in intervention. [less ▲]

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See detailIs Geometallurgy Teachable? A challenge for the new Erasmus Mundus EMerald
Pirard, Eric ULg

Conference (2014, September 05)

designate any kind of advanced ore characterisation prior to mineral processing operations while in fact it should clearly refer to a multidisciplinary integration of geological, mining, metallurgical ... [more ▼]

designate any kind of advanced ore characterisation prior to mineral processing operations while in fact it should clearly refer to a multidisciplinary integration of geological, mining, metallurgical, environmental and economic information into a single orebody model. In order to instil the best available geometallurgical practices in the professional world, it seems essential to break the traditional cleavages among disciplines and educate a new generation of engineers. The Erasmus Mundus EMerald “Master in Georesources Engineering” program initiated by four European universities under the coordination of University of Liege, has been designed to exactly tackle this challenge. It is not surprising that this program has been set up by universities having a long tradition in mixing a double perspective of geology and engineering (Nancy; Lulea; Liege and Freiberg). Geometallurgy requires both an excellent understanding of the natural variability and complexity of an ore and a comprehensive overview of the techniques available to extract and concentrate any valuable material. The course program has been designed to achieve a right balance between knowledge of mineral resources (geology, resource characterisation, reserve estimation, modelling) and processing (comminution, preconcentration, leaching, waste disposal,...). It also includes a broader view on life cycle analysis and urban mining. A series of professional seminars, suggested by an industrial advisory board, shed light on strategic issues, economic and environmental challenges, corporate social responsibilities, etc. Mobility and multicultural experience is an added-value of the Erasmus Mundus experience which definitely contributes to breeding engineers for tomorrow. [less ▲]

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See detailMulti-period Stochastic Optimization Problems in Transportation Management
Pironet, Thierry ULg

Doctoral thesis (2014)

The topic of this thesis in management science is to propose a methodology to tackle multi-period decision problems including stochastic forecasts and to apply it to the field of transportation management ... [more ▼]

The topic of this thesis in management science is to propose a methodology to tackle multi-period decision problems including stochastic forecasts and to apply it to the field of transportation management. This methodology relies mostly on a sequence of numerical experimentations based on a set of algorithms to assess the value of the multi-period setting and the interest to use the stochastic information contained in the forecasts. Moreover, a statistical validation method to compare the performances of algorithms enables us to rank them meaningfully. From theory to practice, the thesis is structured into four parts. Firstly, we define the thesis subject and content. Then, based on a literature review, we present the past and present issues within the research field: "Optimization in Transportation". Mainly, we define the differences between multi-period stochastic models and classical deterministic mono-period ones. We explain how dynamism and stochasticity are taken into account within transportation problems. Secondly, our methodology, which is our main contribution, is exposed from a generic point of view in the theoretical research field: "Multi-period Stochastic Optimization Problems". On the one hand, temporal parameters and computational issues in multi-period optimization are detailed; on the other hand a summary of optimization techniques and algorithms for stochastic optimization problems is provided. Afterwards, the statistical validation of algorithmic performance is discussed. Then, part three contains two applications that lead us to set up the methodology, following an inductive method. The first problem, based on an industrial application at the start of the research, investigates a "multi-period vehicle loading problem with stochastic release dates". The second application, based on a more generic approach for the deployment of the methodology, deals with a "multi-period vehicle assignment problem with stochastic load availability". Finally, in the fourth part, we conclude on the thesis contributions and propose some perspectives. [less ▲]

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See detailThe PLATO 2.0 Mission
Rauer, H.; Catala, C.; Aerts, C. et al

in Experimental Astronomy (2014)

PLATO 2.0 has recently been selected for ESA’s M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental ... [more ▼]

PLATO 2.0 has recently been selected for ESA’s M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, including potentially habitable planets? The PLATO 2.0 instrument consists of 34 small aperture telescopes (32 with 25 s readout cadence and 2 with 2.5 s candence) providing a wide field-of-view (2232 deg 2) and a large photometric magnitude range (4–16 mag). It focusses on bright (4–11 mag) stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for these bright stars to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2 %, 4–10 % and 10 % for planet radii, masses and ages, respectively. The planned baseline observing strategy includes two long pointings (2–3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50 % of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include terrestrial planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0. The PLATO 2.0 catalogue allows us to e.g.: - complete our knowledge of planet diversity for low-mass objects, - correlate the planet mean density-orbital distance distribution with predictions from planet formation theories,- constrain the influence of planet migration and scattering on the architecture of multiple systems, and - specify how planet and system parameters change with host star characteristics, such as type, metallicity and age. The catalogue will allow us to study planets and planetary systems at different evolutionary phases. It will further provide a census for small, low-mass planets. This will serve to identify objects which retained their primordial hydrogen atmosphere and in general the typical characteristics of planets in such low-mass, low-density range. Planets detected by PLATO 2.0 will orbit bright stars and many of them will be targets for future atmosphere spectroscopy exploring their atmosphere. Furthermore, the mission has the potential to detect exomoons, planetary rings, binary and Trojan planets. The planetary science possible with PLATO 2.0 is complemented by its impact on stellar and galactic science via asteroseismology as well as light curves of all kinds of variable stars, together with observations of stellar clusters of different ages. This will allow us to improve stellar models and study stellar activity. A large number of well-known ages from red giant stars will probe the structure and evolution of our Galaxy. Asteroseismic ages of bright stars for different phases of stellar evolution allow calibrating stellar age-rotation relationships. Together with the results of ESA’s Gaia mission, the results of PLATO 2.0 will provide a huge legacy to planetary, stellar and galactic science. [less ▲]

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See detailRegionalism Does Matter but Nationalism Prevails. A Comparative Analysis of Career Patterns in Western Multi-Level Democracies
Dodeigne, Jérémy ULg

Conference (2014, September 04)

The processes of regionalization and federalization are unquestionable trends in Europe considering the flow of powers from states to subnational levels. In multi-level systems, the patterns of regional ... [more ▼]

The processes of regionalization and federalization are unquestionable trends in Europe considering the flow of powers from states to subnational levels. In multi-level systems, the patterns of regional and national careers have responded to this structural evolution. In the literature, two positions oppose each other about the effects of regionalism. Some authors argue that it does affect career patterns while other scholars found little evidence of the regionalism hypothesis. Unclear results in the literature are partly due to the limited number of comparative research across country and across time, choice in case selection, and bias of the unit of analysis. This paper seeks to address these three issues based on an original dataset of 4.991 regional and national careers in Belgium (Flanders, Wallonia, and Brussels), Canada (Ontario and Quebec), Spain (Catalonia and Castilla-La-Mancha), and the UK (Wales and Scotland). The intranational and international comparison proves that regionalism does matter – regional politics attract more professionalized MPs where regionalism is stronger – but the national parliament remains ultimately the most attractive political arena across regions. [less ▲]

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See detailEtude de l'implication de cellulases dans la voie de biosynthèse de cellulose chez les bactéries
Delsaute, Maud ULg

Doctoral thesis (2014)

By definition, cellulases are enzymes that catalyze the degradation of cellulose. However, their involvement in cellulose biosynthesis by bacteria and plants has been reported, although their exact ... [more ▼]

By definition, cellulases are enzymes that catalyze the degradation of cellulose. However, their involvement in cellulose biosynthesis by bacteria and plants has been reported, although their exact contribution remains unclear. In the present study, we have investigated the involvement of cellulases from glycoside hydrolase family 5 (GH5) in cellulose synthesis. In particular, we have functionally and structurally characterized the Ps_Cel5A cellulase from Pseudomonas stutzeri and its metagenome-derived homolog RBcel1, which both belong to the GH5 family and are suspected to be involved in cellulose biosynthesis. In addition, we have also compared these enzymes with the well-characterized Ta_Cel5A cellulase from the cellulolytic fungus Thermoascus aurantiacus. The first part of the work was devoted to the description of the tridimensional structure of RBcel1, in comparison with other glycoside hydrolases from GH5. In the second part of the study, we focused on the functional and structural comparison between RBcel1, Ps_CelA and Ta_Cel5A. Biochemical analysis has highlighted that, besides their hydrolytic activity, RBcel1 and Ps_Cel5A were able to catalyze transglycosylation in vitro. This synthesis reaction was not detected for Ta_Cel5A, which seemed to remain hydrolytic only. Determination of the structure of RBcel1 in complex with cellobiose has revealed distinct features in the aglycone substrate binding sites compared to Ta_Cel5A which could potentially explain the observed differences in their activities in vitro. Finally, the involvement of Ps_Cel5A in cellulose production by P. stutzeri was confirmed, by analysis the ability of P. stutzeri-ΔPs_Cel5A to produce the polymer. Complementation of this mutant strain by the three cellulases was also performed and discussed. [less ▲]

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See detail"'What is an incident?': Conceptual Boundaries under the Microscope"
Rossignol, Nicolas ULg

Scientific conference (2014, September 04)

Within the context of a nuclear facility, how can an event be qualified as an incident or not, depending on different definitions, either formal or corresponding to actors' own representations? In this ... [more ▼]

Within the context of a nuclear facility, how can an event be qualified as an incident or not, depending on different definitions, either formal or corresponding to actors' own representations? In this presentation, we show how different those definitions are, and we elaborate on the reasons why such a focus on conceptual boundaries is interesting in the context of "incident reporting". [less ▲]

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See detailLes effets délétères métaboliques et oxydants induits lors d'un sepsis sur la fonction rénale
Quoilin, Caroline ULg

Doctoral thesis (2014)

Acute kidney injury (AKI) is a frequent complication of sepsis that can increase mortality as high as 70%. The pathophysiology of this kidney failure was previously believed to be secondary to decreased ... [more ▼]

Acute kidney injury (AKI) is a frequent complication of sepsis that can increase mortality as high as 70%. The pathophysiology of this kidney failure was previously believed to be secondary to decreased global renal perfusion causing hypoxia-induced injury. However, new research suggests this paradigm is overly simplistic, and injury is now considered multifactorial in origin. Mechanisms that contribute to kidney injury mainly include inflammation, alterations in microvascular renal blood flow and changes in bioenergetics. To study the mechanism of oxygen regulation in acute kidney injury during sepsis, we developed a sepsis-induced in vitro model using proximal tubular epithelial cells (HK-2) exposed to a bacterial endotoxin (lipopolysaccharide, LPS). Our first investigation, by using both high-resolution respirometry and electron spin resonance spectroscopy, showed that HK-2 cells exhibit a decreased oxygen consumption rate when treated with LPS. Surprisingly, this cellular respiration alteration persists even after the stress factor is removed. We suggested that this irreversible decrease in renal oxygen consumption after LPS challenge is related to a pathologic metabolic down-regulation such as a lack of oxygen utilization by cells for ATP production. In the long term, this metabolic disturbance leads cells to a predominantly apoptotic death. To confirm this hypothesis of cytopathic hypoxia, we demonstrated that this alteration in the renal respiratory function is mainly due to an impairment in the metabolic activity of HK-2 cell mitochondria. Following LPS treatment, the oxidative phosphorylation is interrupted because of the inhibition of cytochrome c oxidase activity. As a consequence, disruptions in the electron transport and the proton pumping across the system occur, leading to a decrease of the mitochondrial membrane potential, the release of apoptotic-inducing factors and a decrease in ATP production. To clarify the mechanism by which the LPS induces mitochondrial alterations, we studied the oxidative stress generation in HK-2 cells. Interestingly, we revealed that the induction of a cytosolic oxidative stress is an event that appears before mitochondrial dysfunction in the LPS-treated HK-2 cells. This primary redox state is notably due to the activation of the two enzymes NADPH oxidase 4 and inducible NO synthase. The simultaneous production of anion superoxide and nitric oxide strongly suggests the formation of peroxynitrite, a relative stable powerful oxidant that can diffuse through mitochondrial compartments and undergo cytotoxic reactions. To our knowledge, our model reveals for the first time the role of NADPH oxidase-derived cytosolic ROS in triggering tubular cell damage. Moreover, after being first target of the oxidative stress, mitochondria become in turn producer of reactive oxygen species that carry on mitochondrial dysfunction. It seems thus that a mechanism of oxidative stress-induced redox cycling is a main cause of the mitochondrial dysfunction of LPS-treated HK-2 cells. The role of oxidants in mitochondrial dysfunction was further confirmed by the use of iNOS inhibitors or antioxidants that preserve cytochrome c oxidase activity and block mitochondrial membrane potential dissipation. Overall, these results suggest that sepsis-induced AKI should not only be regarded as failure of energy status but also as an integrated response, including transcriptional events, ROS signaling, mitochondrial activity and metabolic orientation such as apoptosis. [less ▲]

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See detailUn référentiel de compétences pour la formation des architectes et après?
Scheffers, Patricia ULg

Scientific conference (2014, September 03)

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See detailNarration et jeu vidéo. Pour une exploration des univers fictionnels
Barnabé, Fanny ULg

Book published by Bebooks (2014)

Un jeu vidéo peut-il raconter une histoire ? De quels moyens spécifiques dispose-t-il pour y parvenir ? Classique en game studies, la question de la narration dans le jeu vidéo continue d’interpeller ... [more ▼]

Un jeu vidéo peut-il raconter une histoire ? De quels moyens spécifiques dispose-t-il pour y parvenir ? Classique en game studies, la question de la narration dans le jeu vidéo continue d’interpeller chercheurs, consommateurs et professionnels de l’industrie, après avoir participé à la structuration du champ de recherche ces quinze dernières années. Partant de ces questions, l’ouvrage Narration et jeu vidéo. Pour une exploration des univers fictionnels propose un modèle explicatif fondé sur la notion riche d’univers fictionnel. Sur cette base, il propose de penser la narration vidéoludique hors des cadres traditionnels et de la concevoir comme un dispositif non figé, ouvert à l’infinité d’actualisations possibles que représente chaque partie jouée. Alternant réflexion théorique et analyses de cas, ce livre se destine tant au chercheur qu’au game designer ou au joueur désireux de réfléchir sur sa pratique. Ce livre a été lauréat du prix BiLA en 2012 (Bibliothèque des Littératures d'Aventures). [less ▲]

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See detailCompeting as a Luxury SME
Riguelle, France ULg; Van Caillie, Didier ULg

in Reinecke, Sven; Berghaus, Benjamin; Müller-Stewens, Günter (Eds.) The Management of Luxury (2014)

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See detailMineralogy of fine particles in slurry from multispectral imaging
Leroy, Sophie ULg; Dislaire, Godefroid ULg; Barnabé, Pierre ULg et al

Conference (2014, September 02)

Quantitative mineralogy of fine particles in slurry from multispectral imaging Sophie Leroy, Godefroid Dislaire, Pierre Barnabé and Eric Pirard Mineral processing especially in its final stages relies ... [more ▼]

Quantitative mineralogy of fine particles in slurry from multispectral imaging Sophie Leroy, Godefroid Dislaire, Pierre Barnabé and Eric Pirard Mineral processing especially in its final stages relies heavily on the differential behavior of particles in pulps. In order to monitor hydrocyclones and flotation cells in almost real time, it is important to develop at line particle characterization providing information on particle distribution but also mineralogy. A sampling device has been elaborated based on a flow cell with variable wall spacing linked to a high pressure peristaltic pump. This setup allows for dispersion and dilution of the mineral slurry into the cell. Depending on the ore or gangue minerals to be controlled, particles can be imaged either in diffuse reflectance or in transmittance mode. A simple multispectral imaging module has been designed to acquire images at eight different wavelengths. The design is based on a series of dichroic filters thereby avoiding any moving part and enabling a very fast acquisition of multispectral images. Imaging artifacts due, among others, to specular reflectance from the glass window are minimized. Multispectral classification is used to outline particles appearing in the field of view and to qualify their main mineral component. In particular, areas reflecting a meaningful and discriminative spectrum are identified and compared to a multispectral database. The database is continuously enriched through testing of pure mineral particles under similar pulp conditions (dilution, grain size,…). Results of final classification are compared to the modal analysis obtained from polished blocks and conventional reflected light microscopy. The technology developed in this work sets the basis for at line monitoring of ore slurries with reasonably simple mineralogy. Extension of the spectral range is being considered for future developments. [less ▲]

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See detailFrom geometallurgy to ecometallurgy:Building mines for the future
Pirard, Eric ULg

Conference (2014, September 02)

geometallurgy will become the central pivot of a successful mining operation. Recently, Europe has awakened from a long period of lethargy in the raw materials sector. A series of important initiatives ... [more ▼]

geometallurgy will become the central pivot of a successful mining operation. Recently, Europe has awakened from a long period of lethargy in the raw materials sector. A series of important initiatives inspired by the European Innovation Partnership (EIP) have paved the way for more intense cooperation between industry, research centres and universities. Among these, the establishment of a Knowledge Innovation Community (KIC) in 2015 will definitely boost innovation and education in the sector. Interestingly, EIP addresses the whole value chain and considers mining, recycling and substitution as essential pillars of the raw materials policy. This vision strengthens the role of geometallurgy but also brings up the need for a close dialogue between mineralogists, metallurgists and product designers. Microelectronics and nanotechnologies are ubiquitous in our technologies and have greatly improved their functionality, but they have also made recycling and efficient recovery of metals a tough technical challenge. Our urban mines formed by the accumulation of end-of-life products should be scrutinized from now on using an ecometallurgical approach whereby important questions should be addressed such as: 1. Metal concentrations: Is the metal grade high enough to pay for recycling? Does the manufacturer help to maintain grades above a technological cut-off? 2. Metal speciation: Under which form (alloy, salt, organic compound,…) is the metal present? Is there a processing technology available to separate these species? 3. Metal paragenesis: What are the metal assemblages found in the product? Will it be feasible to separate those metals and at what costs? Are there penalty or contaminating elements associated? 4. Textural assemblage: How will the product behave during dismantling? Is it realistic to liberate a given component? What comminution strategy will be needed to achieve phase liberation? 5. Reserve estimation: What are the tonnages expected for this kind of product? Can selective collection be organised? 6. Homogeneity: What will the next generation of products look like? Should one expect strong differences in concentration, speciation, paragenesis, etc.? Will this kind of product be blended with others during collection? How will this impact on downstream recycling? Ecometallurgy, as introduced here, is essentially about establishing a dialogue with product designers and material scientists to make sure that, once unearthed, metals will remain easily and sustainably available for the future generations. Geologists and mineralogists, even though generally kept away from the synthetic materials, could greatly contribute to this progress by bringing their expertise in dealing with complex and variable orebodies of the future. [less ▲]

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See detailCost monitoring to promote the value added for clam raising farmers in the Northern area of Vietnam
Bui Thi, Nga; Tran Thu, Hoai; Tran Huu, Cuong et al

Conference (2014, September 02)

Clam farming in coastal provinces of Vietnam has notably developed since the last decade. It generated high income, improve socio-economic development for many local communities. However, many clam ... [more ▼]

Clam farming in coastal provinces of Vietnam has notably developed since the last decade. It generated high income, improve socio-economic development for many local communities. However, many clam raising farms are facing difficulties of farm management, disease control, markets and systems of quality control. This research aims to study about the real situation of cost monitoring in the clam raising farms in the Northern area of Vietnam and suggest some recommendation for apply a suitable model for cost monitoring to promote the value added for farmers. The paper based on the semi-structure, standard questionnaires and PRA method to collect data from 89 clam raising farms in two coastal provinces (Nam Dinh and Thai Binh) in the Northern area of Vietnam in 2014. The findings show that clam raising provides farmers a chance of getting high income parallel with high risk. There were 32.15% surveyed farms got profit, 32.14% of them met the breakeven and 35.71% was lost. The study finds out four key factors affecting farms’ economic performance and efficiency. The first is capacity of farm cost control as the cost for clam raising was very high at 8,142 to 9,190 USD per ha. The second is the farmers’ experience, skill, technique and ability of risk control. The third is low, unstable market price and unsuitable market channel with the dominant of the traders. Final factors is the area and location of clam raising. Despite of these difficulties, 55.14% surveyed farms still want to expand their production, 25% of them will continue, and only 17.86% will stop or change to other activities. In order to promote the value added for clam raising farmers, cost control should be paid more attention, improvement of the farmers’ capacity is necessary, and market should be regarded. [less ▲]

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See detailI know what you did last summer - High resolution mapping of wild boar damages with drones
Michez, Adrien ULg; Morelle, Kevin ULg; Lehaire, François ULg et al

Poster (2014, September 01)

Wild boar ability to cause important damages to agricultural lands is not anymore to be demonstrated. These damages often raise conflicts between farmers and hunters due to the associated economic losses ... [more ▼]

Wild boar ability to cause important damages to agricultural lands is not anymore to be demonstrated. These damages often raise conflicts between farmers and hunters due to the associated economic losses. Objective and accurate method for real impact assessment of losses suffered by farmers is thus needed. Currently,in Wallonia damage assessment is performed from the ground by experts, asked to evaluate precisely the area impacted. This task is time and man power consuming. Moreover, damaged areas are often large and consequently, sampling is mandatory and can induce accuracy issues. Recent development of unmanned aerial vehicle (UAV / drone) toghether with lower cost and better accessibility for civil society and scientific community, makes now possible the use of this technology for wildlife researches. Through photogrammetric 3D reconstruction of the field crop, UAV can allow to objectively and precisely measure the area impacted by wild boar damages. In a context of increasing issues caused by wild boar to agriculture, and the need for stakeholders for accurate impact assessment, we tested an innovative approach to estimate more effectively the area impacted by wild boar. [less ▲]

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See detailElastic damage to crack transition in a coupled non-local implicit discontinuous Galerkin/extrinsic cohesive law framework
Wu, Ling ULg; Becker, Gauthier ULg; Noels, Ludovic ULg

in Computer Methods in Applied Mechanics & Engineering (2014), 279

One current challenge related to computational fracture mechanics is the modeling of ductile fracture and in particular the damage to crack transition. On the one hand, continuum damage models, especially ... [more ▼]

One current challenge related to computational fracture mechanics is the modeling of ductile fracture and in particular the damage to crack transition. On the one hand, continuum damage models, especially in their non-local formulation which avoids the loss of solution uniqueness, can capture the material degradation process up to the localization of the damage, but are unable to represent a discontinuity in the structure. On the other hand cohesive zone methods can represent the process zone at the crack tip governing the crack propagation, but cannot account for the diffuse material damaging process. In this paper we propose to combine, in a small deformations setting, a non-local elastic damage model with a cohesive zone model. This combination is formulated within a discontinuous Galerkin nite element discretization. Indeed this DG weak formulation can easily be developed in a non-local implicit form and naturally embeds interface elements that can be used to integrate the traction separation law of the cohesive zone model. The method remains thus consistent and computationally e cient as compared to other cohesive element approaches. The effects of the damage to crack transition and of the mesh discretization are respectively studied on the compact tension specimen and on the double-notched specimen, demonstrating the efficiency and accuracy of the method. [less ▲]

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See detailTechnical variability in the Gravettian with tanged tools: new results from Belgium
Touzé, Olivier; Flas, Damien ULg; Pesesse, Damien

Conference (2014, September 01)

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See detailPredictive microbiology combined with metagenomic analysis targeted on the 16S rDNA : A new approach for food quality
Delhalle, Laurent ULg; Ellouze, Mariem; Taminiau, Bernard ULg et al

Poster (2014, September 01)

The food spoilage process is mainly caused by alteration micro-organisms and classical culture-based methods may not be relevant to understand the modifications of the microbial ecology in food products ... [more ▼]

The food spoilage process is mainly caused by alteration micro-organisms and classical culture-based methods may not be relevant to understand the modifications of the microbial ecology in food products. Metagenomic analysis targeted on 16S ribosomal DNA can elucidate microbial community structures at a muche higher resolution than was previously possible. Combined with predictive microbiological models, a new approach was investigated to take into account bacterial populations dynamics in perishable foods under different environmental conditions. White pudding samples, a typical Belgian pork meat product, were packed under food wrap (atmospheric air condition). Durability studies were conducted at 4°C, 12°C and a dynamic temperature profile according to the NF V01-003 standards (4°C (1/3 of the shelf life) - 8°C (2/3 of the shelf life)) during 15 days. The effect of organic acids was also investigated using a lactic acid (1.8% w/w) treatment. At each day of the trials, classical microbiological (total flora) and 16S rDNA metagenomic analysis were carried out on all these samples. For the metagenomic analysis, a sequencing library was generated, targeting the V1-V3 region of the 16S rDNA. The two major bacterial populations were thus identified (Psychrobacter sp and Brochotrix thermosphacta) and predictive microbiology models used to assess the growth parameters. Cardinal parameters for temperature were collected on the two main bacterial species. The model was validated using the data obtained at a dynamic temperature profile. The results of the simulations for Psychrobacter sp and Brochotrix thermosphacta show a good compliance between predicted and observed data. Compared to culture based methods on selective media and previous independent culture techniques, metagenomic analysis combined with predictive microbiology gives more valuable information, and could be considered as a technological breakthrough to control the quality or for accurately determining shelf life. [less ▲]

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