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See detailMapping key pollutants in the English Channel region: the Channel Catchments Cluster (3C) cross-border project
Richir, Jonathan ULg; Pini, Jennifer; Watson, Gordon

Conference (2014, August 16)

The EU Water Framework Directive was a response to concerns about the previous disparate ways in which water quality was managed under Member State law and early European Directives. Within this context ... [more ▼]

The EU Water Framework Directive was a response to concerns about the previous disparate ways in which water quality was managed under Member State law and early European Directives. Within this context, the Interreg IVA France (Channel) England Region established the ‘sustainable environmental development of this common space’ as one of its priorities to integrate areas that face common problems. The wide variety of cooperative cross-border projects have brought together UK and French scientists and environmental managers to develop practical environmental management tools for the region (3Cs cluster). Using the Solent in the UK as a case study, maps of key pollutants (e.g. metals such as Zn and Cu) will be produced to assess their spatial diversity within the sediment. The incorporation of historical datasets will also provide a temporal component. The inclusion of bioavailable fractions (using sequential extraction methods) will enable the pollutants to be linked to the tissue concentrations of key benthic species such as the polychaete Nereis virens and possible impacts. Not only will this information provide a detailed account of the water quality of key areas of the English Channel, but it will also highlight the gaps in the data and sampling regimes that are necessary to achieve good environmental status for the future, thus ensuring more effective European environmental policy regarding the long-term protection and conservation of aquatic ecosystems. [less ▲]

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See detailContribution à l'exploration de la structure des sols par microtomographie aux rayons X : vers une amélioration de la modélisation hydropédologique
Beckers, Eléonore ULg

Doctoral thesis (2014)

The aim of this thesis is to tend towards a better representation of soil water horizontal fluxes in hydropedological modelling. Tillage practices result in soil structural modifications which impact soil ... [more ▼]

The aim of this thesis is to tend towards a better representation of soil water horizontal fluxes in hydropedological modelling. Tillage practices result in soil structural modifications which impact soil hydrodynamic behaviour. This study takes place in this context, aiming to understand these modifications using X-ray microtomography (µCT), which allows a more fundamental analysis of soil. Indeed, this tool becomes a key in the field of soil science, giving a direct insight of the internal structure of soil. Besides, anisotropy studies are still rare as tiresome, and this work shows that the current hydrological models are anyway unable to represent it correctly: when it is taken into account, it rests on the hypothesis of a simple ratio between vertical and horizontal conductivity functions. First, microtomography is used supplementary to usual methods for the establishment of hydrodynamic functions near saturation. We showed that the retention curve designed with µCT information is more realistic since it leads to a better estimation of unsaturated hydraulic conductivity. However, these results could be doubtful depending on the different µCT acquisition or processing choices and hypothesis. Particularly, the thresholding step is crucial. Consequently, we propose a new global thresholding method based on the visible part of soil sample porosity. This method has been tested and validated in the context of the present study. This step allows us to use microtomography results to increase our knowledge of soil structure. A principal component analysis on soil pores structural parameters confirms that connectivity, specific surface, volume and radius are key factors for the differentiation of soil horizons texturally similar but structurally different. Our results show that structural parameters have to be taken into account to improve hydropedological modelling, especially if pores orientation is considered. We described thus the relevant parameters that can be obtained with µCT and which could help to better model water fluxes in soil while discussing the remaining limits and uncertainties, about upscaling issues notably. [less ▲]

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See detailAnalysis of spray retention on a 3D black-grass plant model as a function of spray nozzle and formulation using a process-driven approach
Massinon, Mathieu ULg; Ouled Taleb Salah, Sofiene ULg; Dumont, Benjamin ULg et al

Poster (2014, August 13)

The efficiency of spray application of foliar plant protection products can be variable because of the different amount of spray solution intercepted and retained by leaves. On one hand, the spray ... [more ▼]

The efficiency of spray application of foliar plant protection products can be variable because of the different amount of spray solution intercepted and retained by leaves. On one hand, the spray interception by plants is affected by nozzle kind, size and operating pressure as well as by the plant architecture. On the other hand, the spray retention is affected by application parameters resulting from droplet size and velocity as well as spray mixture physicochemical properties. In this paper, spray retention is tackled with a physical approach at the droplet scale. The methodology deals with high-speed imaging to characterize droplet impacts; adhesion, rebound or shatter on small excised leaf areas and the spray granulometry. The 3D reconstruction of a black-grass plant involves a structured light technique. The overall spray retention was determined by using an interception algorithm combined with a process-driven retention approach as a function of the spray nozzle and formulation used. The interception model allowed determining the spray retention by a single plant and discriminating application parameters by explaining the variability resulting from various droplet size distributions intercepted by single plant. Such a model can be used to increase the understanding of interactions between spray techniques and plant architectures. [less ▲]

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See detailExperimental study of the magnetic shielding performances of a Bi2223 tube closed by a Bi2223 cap.
Wera, Laurent ULg; Fagnard, Jean-François ULg; Hogan, Kevin ULg et al

Poster (2014, August 12)

A superconducting tube can be used as an efficient magnetic shield. However, the shielding factor (defined as the ratio between the applied magnetic induction and the magnetic induction measured inside ... [more ▼]

A superconducting tube can be used as an efficient magnetic shield. However, the shielding factor (defined as the ratio between the applied magnetic induction and the magnetic induction measured inside the tube) decreases towards tube extremities because of the field penetration through the open ends of the tube. To improve the performances at tube extremities, the tube should be closed. This can be achieved by using a superconducting vessel or by closing both extremities with a cap. The purpose of the present work is to study experimentally the shielding performances of a Bi2223 tube closed by a superconducting Bi2223 cap. The cap is a circular plate with a diameter equal to the outer diameter of the tube and there is no superconducting joint between the cap and the tube. Our interest is to characterize the effect of the cap on the shielding factor distribution along the tube axis when only one extremity of the tube is closed. We also study the effect of the gap size between the cap and the tube in axial configuration. Finally, a tube closed at its both ends is also characterized. All experiments are carried out at 77K. The tube is subjected to a quasi-static (“DC”) uniform magnetic field. A Hall probe measures the three components of the local magnetic induction along the axis of the tube as a function of the applied magnetic induction. Results show that the shielding performances in the axial configuration are highly improved at the closed extremity as the cap reduces the penetration through the open end. The shielding factor distribution along the tube axis is affected by the presence of the cap. For an open tube, the shielding factor is maximum near the center and decreases towards both extremities. For the tube closed at one extremity, the shielding factor is maximum at the closed extremity and decreases towards the center. Moreover, the shielding factor distribution between the tube center and the open extremity is not affected by the presence of the cap. The experimental results show that, a small gap between the tube and the cap, which can be necessary for applications, does not strongly affect the magnetic shielding performances of the assembly. [less ▲]

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See detailRobustness and efficiency of multivariate coefficients of variation
Aerts, Stéphanie ULg; Haesbroeck, Gentiane ULg; Ruwet, Christel ULg

Conference (2014, August 12)

The coefficient of variation is a well-known measure used in many fields to compare the variability of a variable in several populations. However, when the dimension is greater than one, comparing the ... [more ▼]

The coefficient of variation is a well-known measure used in many fields to compare the variability of a variable in several populations. However, when the dimension is greater than one, comparing the variability only marginally may lead to controversial results. Several multivariate extensions of the univariate coefficient of variation have been introduced in the literature. In practice, these coefficients can be estimated by using any pair of location and covariance estimators. However, as soon as the classical mean and covariance matrix are under consideration, the influence functions are unbounded, while the use of any robust estimators yields bounded influence functions. While useful in their own right, the influence functions of the multivariate coefficients of variation are further exploited in this talk to derive a general expression for the corresponding asymptotic variances under elliptical symmetry. Then, focusing on two of the considered multivariate coefficients, a diagnostic tool based on their influence functions is derived and compared, on a real-life dataset, with the usual distance-plot. [less ▲]

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See detailARTICLE: Reflexions ULG. Geerkens Mélanie. Paroles d'ados.
Boulard, Aurore ULg

Diverse speeche and writing (2014)

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See detailGlobal power grids for harnessing world renewable energy
Chatzivasileiadis, Spyros; Ernst, Damien ULg; Andersson, Göran

in Jones, Lawrence (Ed.) Renewable Energy Integration: Practical Management of Variability, Uncertainty and Flexibility in Power Grids (2014)

The Global Grid advocates the connection of all regional power systems into one electricity transmission system spanning the whole globe. Power systems are currently forming larger and larger ... [more ▼]

The Global Grid advocates the connection of all regional power systems into one electricity transmission system spanning the whole globe. Power systems are currently forming larger and larger interconnections. Environmental awareness and increased electricity consumption leads more investments towards renewable energy sources, abundant in remote locations (off-shore or in deserts). The Global Grid will facilitate the transmission of this “green” electricity to load centers, serving as backbone. This chapter elaborates on the concept presenting four stages that could gradually lead to the development of a globally interconnected power network. Quantitative analyses are carried out for all stages, demonstrating that a Global Grid is both technically feasible and economically competitive. Real price data from Europe and the USA are used to identify the potential of intercontinental electricity trade, showing that substantial profits can be generated through such interconnections. [less ▲]

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See detailRecueil de réglementation interne des principaux partis allemands, belges et britanniques
Bouhon, Frédéric ULg

E-print/Working paper (2014)

Le présent recueil compile des extraits de la réglementation interne des principaux partis allemands, belges et britanniques. Cette documentation vient principalement appuyer le chapitre 1er de la ... [more ▼]

Le présent recueil compile des extraits de la réglementation interne des principaux partis allemands, belges et britanniques. Cette documentation vient principalement appuyer le chapitre 1er de la deuxième partie de notre étude sur le droit électoral et le principe d’égalité (à paraître en septembre 2014 aux éditions Bruylant) dans laquelle nous avons notamment étudié une partie du droit interne de certaines formations politiques. [less ▲]

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See detailIntraspecific variation of copper tolerance of four endemic plant species from the katangan Copperbelt (D. R. Congo)
Boisson, Sylvain ULg; garin, olivier; Seleck, Maxime ULg et al

Conference (2014, August 04)

Harsh ecosystems are at the origin of speciation processes in plant communities. In metalliferous areas, plants develop physiological adaptations to tolerate metal excesses which lead to high species and ... [more ▼]

Harsh ecosystems are at the origin of speciation processes in plant communities. In metalliferous areas, plants develop physiological adaptations to tolerate metal excesses which lead to high species and population diversity. South of the Katanga province (D.R. Congo), plant communities occur on soils with one of the world’s largest concentrations of copper and cobalt. More than 600 species including 54 endemics are distributed along a copper gradient (up to 10 000 mg kg-1 available Cu) and the populations are isolated on more than 100 copper hills scattered in miombo forest. In order to improve restoration strategies of threatened species, we aimed to identify intraspecific copper tolerance of 4 endemic plant species from katangan copper outcrops: Crotalaria cobalticola, Diplolophium marthozianum, Gladiolus ledoctei and Triumfetta welwitschii. Seeds were collected in 3 different populations in the katangan Copperbelt and sown according three soil contamination modalities: control (no addition of Cu), 100 mg kg-1 and 1000 mg kg-1 of Cu concentration using hydrated copper (II) sulfate. For each combination (species x populations x soils), we had 10 repetitions. For each population, sample of 5 seeds was weighed before seedling in pot in November 2013. One individual by pot was kept for measures. Height (cm), number of leaves, number of flowers and number of fruits were measured once a week during one rainy season. For all species, no significant difference of copper tolerance appeared between populations. In contrast, populations had distinct germination rate and growth rate, especially for T. welwitshii and D. marthozianum. C. cobalticola grew significantly better in highly contaminated soil than other soils. G. ledoctei did not show any significant difference between populations and soil treatments. [less ▲]

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See detailFeeding ecology of harpacticoid copepod species: Insights from stable isotopes analysis and fatty acid profiling
Mascart, Thibaud ULg; De Troch, Marleen; Remy, François ULg et al

Conference (2014, August 04)

Understanding how biodiversity influence ecosystem functioning is a major research question in current ecology research. Trophic diversity within communities strongly affects ecosystem functioning through ... [more ▼]

Understanding how biodiversity influence ecosystem functioning is a major research question in current ecology research. Trophic diversity within communities strongly affects ecosystem functioning through trophic interactions between species. Various studies tackled ecosystem functioning via interactions between trophic guilds such as bottom-up and top-down control. However, few studies focussed on interspecific variability in the feeding ecology of organisms with overlapping trophic niche. Here, we in a North-Western Corsican Posidonia oceanica seagrass meadow and its variability over one year. The extensive P. oceanica meadows are occasionally interrupted by bare sand patches which serve as deposition and accumulation area for detritus, mainly derived from senescent macrophytes. These macrophytodetritus accumulation harbour a diverse community of Harpacticoida (Crustacea, Copepoda). The most abundant harpacticoids and their potential food sources (i.e. macrophytodetritus, epiphytic biofilm, macroalgae and particulate matter) were analysed for stable isotope ratios (δ13C, δ15N). Bayesian mixing model (SIAR) showed a minor contribution of macrophytodetritus while the epiphytic biofilm, present on the macrophytodetritus, appeared to be the major food source of harpacticoid copepods. In order to distinguish the several components of the epiphytic biofilm and their contribution, fatty acid profiling was used. The outcome revealed a general harpacticoid diet preference towards diatoms and bacteria, however specialisation for certain components seemed to reduce competition between harpacticoid species. In conclusion, our results underline the importance of multiple biomarker species-specific analysis, especially in complex and dynamic environments where a wide variety of potential trophic niches are present. [less ▲]

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See detailDroit constitutionnel belge - Notes provisoires (année 2014-2015) - Partie introductive
Behrendt, Christian ULg

Learning material (2014)

Notes officielles de cours (partim) pour l'enseignement de Droit constitutionnel dispensé en 2e année de baccalauréat en droit et en 2e année de baccalauréat en sciences politiques.

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See detailDroit constitutionnel belge - Plan général du cours (année 2014-2015)
Behrendt, Christian ULg

Learning material (2014)

Le document constitue le Plan général de l'enseignement de Droit constitutionnel dispensé à l'Université de Liège en 2e année de bachelier en droit et en 2e année de bachelier en science politique.

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See detailEn attendant Toussaint
Demoulin, Laurent ULg

E-print/Working paper (2014)

Présentation et analyse de deux courtes pièces, Rideau et Ni l'un ni l'autre, écrites par Jean-Philippe Toussaint en 1981, quand il était un jeune auteur inconnu influencé par Samuel Beckett.

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See detailA Deep Chandra Observation of the Giant H II Region N11. I. X-Ray Sources in the Field
Nazé, Yaël ULg; Wang, Q. Daniel; Chu, You-Hua et al

in The Astrophysical Journal Supplement Series (2014), 213

A very sensitive X-ray investigation of the giant H II region N11 in the Large Megallanic Cloud was performed using the Chandra X-ray Observatory. The 300 ks observation reveals X-ray sources with ... [more ▼]

A very sensitive X-ray investigation of the giant H II region N11 in the Large Megallanic Cloud was performed using the Chandra X-ray Observatory. The 300 ks observation reveals X-ray sources with luminosities down to 10[SUP]32[/SUP] erg s[SUP]–1[/SUP], increasing the number of known point sources in the field by more than a factor of five. Among these detections are 13 massive stars (3 compact groups of massive stars, 9 O stars, and one early B star) with log (L [SUB]X[/SUB]/L [SUB]BOL[/SUB]) ~–6.5 to –7, which may suggest that they are highly magnetic or colliding-wind systems. On the other hand, the stacked signal for regions corresponding to undetected O stars yields log (L [SUB]X[/SUB]/L [SUB]BOL[/SUB]) ~–7.3, i.e., an emission level comparable to similar Galactic stars despite the lower metallicity. Other point sources coincide with 11 foreground stars, 6 late-B/A stars in N11, and many background objects. This observation also uncovers the extent and detailed spatial properties of the soft, diffuse emission regions, but the presence of some hotter plasma in their spectra suggests contamination by the unresolved stellar population. [less ▲]

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See detailImprovement of defect detection in shearography by using Principal Component Analysis
Vandenrijt, Jean-François ULg; Lièvre, Nicolas; Georges, Marc ULg

in Proceedings of Conference on Interferometry XVII: Techniques and Analysis (2014, August)

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See detailCrop association to improve aphid biological control
Chevalier Mendes Lopes, Thomas ULg; Bodson, Bernard ULg; Francis, Frédéric ULg

Poster (2014, August)

This research focused on the development of sustainable alternative methods to control aphids, giving special emphasis on cultural practices and plant management systems. Increasing the diversity within ... [more ▼]

This research focused on the development of sustainable alternative methods to control aphids, giving special emphasis on cultural practices and plant management systems. Increasing the diversity within crops may have several beneficial effects on pest control, creating attractive habitats for indigenous beneficial fauna and simultaneously deterring pests (“push-pull” approach). In this field study, two wheat/pea associations (mixed cropping and strip cropping) where compared to monocultures of pea and wheat. The abundance and diversity of adult aphidophagous beneficials (predators and parasitoids) were accessed weekly, using yellow traps, while aphids were observed directly on plants. All individuals were identified down to the level of species. In both crops, the percentage of aphid infestation and density of colonies were significantly higher in monocultures during the abundance periods. The mixing was particularly beneficial for the pea, while strip cropping was more efficient for the wheat. Concerning beneficials, their abundance was also significantly higher in monocultures, comparing with the other treatments. This study shows that increasing diversity within crops can prevent them from aphid infestations. However, additional methods are needed to attract more efficiently the aphidophagous beneficials, in order to promote the natural control of aphids. [less ▲]

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See detailScalar triplet flavored leptogenesis: a systematic approach
Aristizabal Sierra, Diego ULg; Dhen, Mikael; Hambye, Thomas

in Journal of Cosmology and Astroparticle Physics [= JCAP] (2014), 2014

Type-II seesaw is a simple scenario in which Majorana neutrino masses are generated by the exchange of a heavy scalar electroweak triplet. When endowed with additional heavy fields, such as right-handed ... [more ▼]

Type-II seesaw is a simple scenario in which Majorana neutrino masses are generated by the exchange of a heavy scalar electroweak triplet. When endowed with additional heavy fields, such as right-handed neutrinos or extra triplets, it also provides a compelling framework for baryogenesis via leptogenesis. We derive in this context the full network of Boltzmann equations for studying leptogenesis in the flavored regime. To this end we determine the relations which hold among the chemical potentials of the various particle species in the thermal bath. This takes into account the standard model Yukawa interactions of both leptons and quarks as well as sphaleron processes which, depending on the temperature, may be classified as faster or slower than the Universe Hubble expansion. We find that when leptogenesis is enabled by the presence of an extra triplet, lepton flavor effects allow the production of the B-L asymmetry through lepton number conserving CP asymmetries. This scenario becomes dominant as soon as the triplets couple more to leptons than to standard model scalar doublets. In this case, the way the B-L asymmetry is created through flavor effects is novel: instead of invoking the effect of L-violating inverse decays faster than the Hubble rate, it involves the effect of L-violating inverse decays slower than the Hubble rate. We also analyze the more general situation where lepton number violating CP asymmetries are present and actively participate in the generation of the B-L asymmetry, pointing out that as long as L-violating triplet decays are still in thermal equilibrium when the triplet gauge scattering processes decouple, flavor effects can be striking, allowing to avoid all washout suppression effects from seesaw interactions. In this case the amount of B-L asymmetry produced is limited only by a universal gauge suppression effect, which nevertheless goes away for large triplet decay rates. [less ▲]

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See detailRelaxations for multi-period optimal power flow problems with discrete decision variables
Gemine, Quentin ULg; Ernst, Damien ULg; Louveaux, Quentin ULg et al

in Proceedings of the 18th Power Systems Computation Conference (PSCC'14) (2014, August)

We consider a class of optimal power flow (OPF) applications where some loads offer a modulation service in exchange for an activation fee. These applications can be modeled as multi-period formulations ... [more ▼]

We consider a class of optimal power flow (OPF) applications where some loads offer a modulation service in exchange for an activation fee. These applications can be modeled as multi-period formulations of the OPF with discrete variables that define mixed-integer non-convex mathematical programs. We propose two types of relaxations to tackle these problems. One is based on a Lagrangian relaxation and the other is based on a network flow relaxation. Both relaxations are tested on several benchmarks and, although they provide a comparable dual bound, it appears that the constraints in the solutions derived from the network flow relaxation are significantly less violated. [less ▲]

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