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See detailAnalyzing transient instability phenomena beyond the classical stability boundary
Ali, Mahmoud; Glavic, Mevludin; Buisson, Jean et al

in Proceedings of the 40th North American Power Symposium (NAPS 2008) (2008)

We consider power systems for which the amount of power produced by their individual power plants is small with respect to the total generation of the system, and analyze how the transient instability ... [more ▼]

We consider power systems for which the amount of power produced by their individual power plants is small with respect to the total generation of the system, and analyze how the transient instability mechanisms of these systems change qualitatively when their size or the dispersion of their generators increases. Simulation results show that loss of synchronism will propagate more slowly and even stop propagating. Given the evolution of power systems towards more dispersed generation and geographically larger interconnections, we conclude that research in transient stability should focus more on the propagation of the loss of synchronism over longer time periods, so as to assess what happens to the overall system subsequently to the loss of synchronism of the first generators. We also argue that such studies might be very useful in order to provide guidelines for setting up power system control schemes to contain the propagation of instabilities, and we discuss some ideas for designing islanding based emergency control schemes for this. [less ▲]

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See detailCross-entropy based rare-event simulation for the identification of dangerous events in power systems
Belmudes, Florence ULg; Ernst, Damien ULg; Wehenkel, Louis ULg

in Proceedings of the 10th International Conference on Probabilistic Methods Applied to Power Systems (PMAPS-08) (2008)

We propose in this paper a novel approach for identifying rare events that may endanger power system integrity. This approach is inspired by the rare-event simulation literature and, in particular, by the ... [more ▼]

We propose in this paper a novel approach for identifying rare events that may endanger power system integrity. This approach is inspired by the rare-event simulation literature and, in particular, by the cross-entropy (CE) method for rare event simulation. We propose a general framework for exploiting the CE method in the context of power system reliability evaluation, when a severity function defined on the set of possible events is available. The approach is illustrated on the IEEE 30 bus test system when instability mechanisms related to static voltage security are considered. [less ▲]

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See detailHow compatible is perfect competition with transmission loss allocation methods?
Jing, Dai; Phulpin, Yannick; Rious, Vincent et al

in Proceedings of the 5th International Conference on the European Electricity Market (EEM-08) (2008)

This paper addresses the problem of transmission loss allocation in a power system where the generators, the demands and the system operator are independent. We suppose that the transmission losses are ... [more ▼]

This paper addresses the problem of transmission loss allocation in a power system where the generators, the demands and the system operator are independent. We suppose that the transmission losses are exclusively charged to the generators, which are willing to adopt a perfectly competitive behavior. In this context, their offers must reflect their production costs and their transmission loss costs, the latter being unknown beforehand and having to be predicted. We assume in this paper that the generators predict their loss costs from the past observations by using a weighted average of their past allocated costs. Under those assumptions, we simulate the market dynamics for different types of transmission loss allocation methods. The results show that the transmission loss allocation scheme can lead to a poorly efficient market in terms of social welfare. [less ▲]

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See detailConsistency of fuzzy model-based reinforcement learning
Busoniu, Lucian; Ernst, Damien ULg; Babuska, Robert et al

in Proceedings of the 2008 IEEE International Conference on Fuzzy Systems (FUZZ-IEEE-08) (2008)

Reinforcement learning (RL) is a widely used paradigm for learning control. Computing exact RL solutions is generally only possible when process states and control actions take values in a small discrete ... [more ▼]

Reinforcement learning (RL) is a widely used paradigm for learning control. Computing exact RL solutions is generally only possible when process states and control actions take values in a small discrete set. In practice, approximate algorithms are necessary. In this paper, we propose an approximate, model-based Q-iteration algorithm that relies on a fuzzy partition of the state space, and a discretization of the action space. Using assumptions on the continuity of the dynamics and of the reward function, we show that the resulting algorithm is consistent, i.e., that the optimal solution is obtained asymptotically as the approximation accuracy increases. An experimental study indicates that a continuous reward function is also important for a predictable improvement in performance as the approximation accuracy increases. [less ▲]

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See detailFuzzy partition optimization for approximate fuzzy Q-iteration
Busoniu, Lucian; Ernst, Damien ULg; Babuska, Robert et al

in Proceedings of the 17th IFAC World Congress (IFAC-08) (2008)

Reinforcement learning (RL) is a widely used learning paradigm for adaptive agents. Because exact RL can only be applied to very simple problems, approximate algorithms are usually necessary in practice ... [more ▼]

Reinforcement learning (RL) is a widely used learning paradigm for adaptive agents. Because exact RL can only be applied to very simple problems, approximate algorithms are usually necessary in practice. Many algorithms for approximate RL rely on basis-function representations of the value function (or of the Q-function). Designing a good set of basis functions without any prior knowledge of the value function (or of the Q-function) can be a difficult task. In this paper, we propose instead a technique to optimize the shape of a constant number of basis functions for the approximate, fuzzy Q-iteration algorithm. In contrast to other approaches to adapt basis functions for RL, our optimization criterion measures the actual performance of the computed policies in the task, using simulation from a representative set of initial states. A complete algorithm, using cross-entropy optimization of triangular fuzzy membership functions, is given and applied to the car-on-the-hill example. [less ▲]

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See detailVariable selection for dynamic treatment regimes: a reinforcement learning approach
Fonteneau, Raphaël ULg; Wehenkel, Louis ULg; Ernst, Damien ULg

Conference (2008)

Dynamic treatment regimes (DTRs) can be inferred from data collected through some randomized clinical trials by using reinforcement learning algorithms. During these clinical trials, a large set of ... [more ▼]

Dynamic treatment regimes (DTRs) can be inferred from data collected through some randomized clinical trials by using reinforcement learning algorithms. During these clinical trials, a large set of clinical indicators are usually monitored. However, it is often more convenient for clinicians to have DTRs which are only defined on a small set of indicators rather than on the original full set. To address this problem, we analyse the approximation architecture of the state-action value functions computed by the fitted Q iteration algorithm - a RL algorithm - using tree-based regressors in order to identify a small subset of relevant ones. The RL algorithm is then rerun by considering only as state variables these most relevant indicators to have DTRs defined on a small set of indicators. The approach is validated on benchmark problems inspired from the classical ‘car on the hill’ problem and the results obtained are positive. [less ▲]

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See detailVivre à quarante kilomètres de Rome : Juxtaposition des modes d’habiter dans les campagnes romaines
Schmitz, Serge ULg; Banini, Tiziana

in Bulletin de la Société Géographique de Liège (2008), 50

By a study of the rural ways of living, the paper analyses the dynamics of the countryside around Rome from a residential point of view. It describes the people and their expectations of the countryside ... [more ▼]

By a study of the rural ways of living, the paper analyses the dynamics of the countryside around Rome from a residential point of view. It describes the people and their expectations of the countryside. It suggests five types of ways of living the countryside. It stresses that the lack of land and planning policy leads to a dismantling of rural communities. Finally, the analysed communes are classified according to a typology of countryside (agricultural countryside, fragile countryside, suburban countryside, and living countryside). The analysis demonstrates the high spatial variability of the suburban countryside, especially when they are analysed at the village level. [less ▲]

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See detailAccuracy of prediction of gene content in large animal populations and its use for candidate gene detection and genetic evaluation
Gengler, Nicolas ULg; Abras, S.; Verkenne, C. et al

in Journal of Dairy Science (2008), 91(4), 1652-1659

To estimate and to use the effects of single genes on quantitative traits, genotypes need to be known. However, in large animal populations, the majority of animals are not genotyped. These missing ... [more ▼]

To estimate and to use the effects of single genes on quantitative traits, genotypes need to be known. However, in large animal populations, the majority of animals are not genotyped. These missing genotypes have to be estimated. However, currently used methods are impractical for large pedigrees. An alternative method to estimate missing gene content, defined as the number of copies of a particular allele, was recently developed. In this study, the proposed method was tested by assessing its accuracy in estimation and use of gene content in large animal populations. This was done for the bovine transmembrane growth hormone receptor and its effects on first-lactation milk, fat, and protein test-day yields and somatic cell score in Holstein cows. Estimated gene substitution effects of replacing a copy of the phenylalanine-coding allele with a copy of the tyrosine-coding allele were 295 g/d for milk, -8.14 g/d for fat, -1.83 g/d for protein, and -0.022/d for somatic cell score. However, only the gene substitution effect for milk was found to be significant. The accuracy of the estimated effects was evaluated by simulations and permutations. To validate the use of predicted gene content in a mixed inheritance model, a cross-validation study was done. The model with an additional regression of milk, fat, and protein yields and SCS on predicted gene content showed a better capacity to predict breeding values for milk, fat, and protein. Given these results, the estimation and use of allelic effects using this method proved functional and accurate. [less ▲]

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See detailRecherche-intervention en développement durable
Stassart, Pierre ULg; Mormont, Marc ULg; Pichault, François ULg et al

in Pichault, François (Ed.) La recherche-intervention peut-elle être socialement responsable ? (2008)

Les questions de développement durable sont non seulemenr complexes, mais le caractère crucial de leurs enjeux suppose en outre, de la part des chercheurs en sciences sociales, une approche renouvelée de ... [more ▼]

Les questions de développement durable sont non seulemenr complexes, mais le caractère crucial de leurs enjeux suppose en outre, de la part des chercheurs en sciences sociales, une approche renouvelée de leurs analyses et de leurs interventions. Cette approche engage des processus « multistakeholders » dont la caractéristique est d'impliquer simultanément des acteurs aux caractéristiques hétérogènes qui sont dans notre cas les acteurs de la filière bovine bio. La proposition de recherche-intervention force les chercheurs à clarifier leur relation à l'objet qu'ils étudient et la qualité de leur travail dépend de la qualité et de la légitimité des traductions successives qu'ils opkrent. Ce travail suppose de prendre au sérieux la construction de nouveaux rapports entre science de la nature, recherche technique et action collective. La question de la responsabilité sociale des chercheurs est ancrée dans cette démarche, elle renvoie à une triple dimension éthique. [less ▲]

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See detailCocaïne dans nos rivières : une approche méthodologique originale dans le domaine de la toxicologie environnementale
Theunis, Laetitia ULg; van Nuijs, Alexander; Pecceu, Bert et al

in Revue Médicale de Liège (2008), 63(S1), 39-43

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See detailRespect des environnements
Mormont, Marc ULg; Zaccaï-Renders, N.

in Reyners-Zaccaï, Nathalie (Ed.) Questions de respect. Enquête sur les figures contemporaines du respect (2008)

Le respect de la nature engage une réflexion éthique sur la valeur de l'autre en particulier sur la valeur de ceux qui composent nécessairement les formes d'organisation écologique que nous appoelons ... [more ▼]

Le respect de la nature engage une réflexion éthique sur la valeur de l'autre en particulier sur la valeur de ceux qui composent nécessairement les formes d'organisation écologique que nous appoelons nature. [less ▲]

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See detailA self-critical analysis of a running research project to improve the sustainability of public place management
Schmitz, Serge ULg; De Graef, Sarai

in Girardot, Jean Jacques; Miedes, Blanca (Eds.) International Conference of territorial intelligence, Papers on Territorial Intelligence and Governance, Participatory Action-Research and Territorial Development (2008)

The paper presents the way a framework for (self-)assessment to improve the sustainability of practices in public places and spaces was created during the first months of the Topozym action research. It ... [more ▼]

The paper presents the way a framework for (self-)assessment to improve the sustainability of practices in public places and spaces was created during the first months of the Topozym action research. It underlines obstacles encountered and solutions found by a multidisciplinary team in creating this tool. Based on this critical self-analysis, the difficulties of putting the theoretical ideas on action research in practice are discussed. [less ▲]

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See detailRoman road pollution assessed by elemental and lead isotope geochemistry in East Belgium
Renson, Virginie; Fagel, Nathalie ULg; Mattielli, Nadine et al

in Applied Geochemistry (2008), 23(12), 3253-3266

The ability of inorganic geochemistry to record environmental change and especially human impact has been evidenced by several studies across Europe, especially in peat, where it is possible to record the ... [more ▼]

The ability of inorganic geochemistry to record environmental change and especially human impact has been evidenced by several studies across Europe, especially in peat, where it is possible to record the impact of agriculture, mining and other industries. However, despite the numerous investigations on the impact of ancient human activities such as ore mining and smelting, little attention has been paid to geochemistry as a tool to solve problems of palaeopollution in the surroundings of archaeological sites. This paper presents geochemical evidence of the impact of a possible early Roman road built in SE Belgian peatland. Increased Zn and Pb concentrations suggest that Pb-Zn ores were transported on the road, Lead isotope analyses suggest that these ores are locally derived, being compatible with those found in the nearby Pb-Zn ore deposits from East Belgium. Present results provide direct evidence that East Belgian Pb-Zn ores were already being mined during Roman times, i.e. earlier than previously suspected (i.e. 14th century) and that Zn appears to be relatively immobile here. On a broader scale, it also demonstrates that such an early road already had an impact on the environment in terms of metal pollution. This paper enlarges on the range of possibilities offered by geochemistry in the field of geoarchaeology. (C) 2008 Elsevier Ltd. All rights reserved. [less ▲]

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See detailLong term mobilisation of chemical elements in tephra-rich peat (NE Iceland)
De Vleeschouwer, François ULg; Lanoe, Brigitte Van Vliet; Fagel, Nathalie ULg

in Applied Geochemistry (2008), 23(12), 3819-3839

This paper presents geochemical profiles of a tephra-bearing minerotrophic peat column from NE-Iceland obtained using various elemental analyses of the solid phase and the pore water. The influence of ... [more ▼]

This paper presents geochemical profiles of a tephra-bearing minerotrophic peat column from NE-Iceland obtained using various elemental analyses of the solid phase and the pore water. The influence of tephra grain size, thickness and composition of each tephra on the peat geochemistry was investigated. Interpretations are supported by a statistical approach, in particular by autocorrelation, and by microscopy observations. Minerotrophic peat geochemistry may be strongly dependent upon post-depositional mobilization and possible leaching of elements as demonstrated by Fe and trace metal concentration profiles. Chemical elements, and more specifically potentially harmful metals, can be slowly leached out of volcanic falls during their weathering and re-accumulate downwards. It is emphasised that a tephra deposit can act as an active geochemical barrier, blocking downward elemental movements and leading to the formation of enriched layers. In this study, the formation of poorly amorphous Fe phases above the Hekla 3 tephra is shown. These poorly crystalline Fe phases scavenged Ni. (c) 2008 Elsevier Ltd. All rights reserved. [less ▲]

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See detailCompte rendu de Carlos Steel (éd.), Procli in Platonis Parmenidem Commentaria. Tomus I, Libros I-III continens
Gavray, Marc-Antoine ULg

in Antiquité Classique : Revue Interuniversitaire d'Etudes Classiques (2008), 77

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See detailRisk-aware decision making and dynamic programming
Defourny, Boris ULg; Ernst, Damien ULg; Wehenkel, Louis ULg

Conference (2008)

This paper considers sequential decision making problems under uncertainty, the tradeoff between the expected return and the risk of high loss, and methods that use dynamic programming to find optimal ... [more ▼]

This paper considers sequential decision making problems under uncertainty, the tradeoff between the expected return and the risk of high loss, and methods that use dynamic programming to find optimal policies. It is argued that using Bellman's Principle determines how risk considerations on the return can be incorporated. The discussion centers around returns generated by Markov Decision Processes and conclusions concern a large class of methods in Reinforcement Learning. [less ▲]

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See detailRéalité et représentations dans l’art romain. L’exemple des trophées aux captifs
Huby, Caroline ULg

in MethIS : Méthodes et Interdisciplinarité en Sciences Humaines (2008), 1

Le trophée accompagné de captifs, motif iconographique récurrent dans l’art romain, a fait l’objet de maints commentaires et tentatives d’interprétation. Certaines de ces approches, illustrées ici par ... [more ▼]

Le trophée accompagné de captifs, motif iconographique récurrent dans l’art romain, a fait l’objet de maints commentaires et tentatives d’interprétation. Certaines de ces approches, illustrées ici par l’exemple des trophées dits de Marius, se sont particulièrement attachées à identifier les prisonniers figurés et la victoire que le trophée a pu célébrer ou commémorer. Or, pour appréhender ces représentations dans toute leur complexité, il s’agit de renouveler la problématique en intégrant les compositions dans le contexte global qui les a suscitées et produites. C’est la signification de l’image comme élément faisant partie d’un système de représentations et participant à la diffusion d’un discours cohérent sur le succès, la défaite et l’ennemi qu’il nous incombe de mettre en évidence. Les trophées aux captifs sont des représentations orientées de la réalité, contribuant à définir l’identité de la société qui les a émises. [less ▲]

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See detailLa démarche scientifique expérimentale en formation initiale d'enseignants du fondamental : analyse d'un module de formation
Hindryckx, Marie-Noëlle ULg

in Cahiers des Sciences de l'Education (Les) (2008), 27/28

Dans le cadre d'une recherche AGERS intitulée: "Pour une formation des futurs instituteurs à une autre didactique des sciences à l'école primaire. Recherche-action pluridisciplinaire visant à la maîtrise ... [more ▼]

Dans le cadre d'une recherche AGERS intitulée: "Pour une formation des futurs instituteurs à une autre didactique des sciences à l'école primaire. Recherche-action pluridisciplinaire visant à la maîtrise de l'enseignement de la démarche scientifique" des modules d'activités ont été construits. Le présent article raconte la mise en oeuvre de ce type d'activités et ses enjeux, en formation initiale des enseignants de première année en maternelle, lors d'ateliers de formation professionnelle (AFP). [less ▲]

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See detailRetrievals of C2H2 from high-resolution FTIR solar spectra recorded at the Jungfraujoch station (46.5ºN) and comparison with ACE-FTS observations
Mahieu, Emmanuel ULg; Duchatelet, Pierre ULg; Bernath, P. F. et al

in Geophysical Research Abstracts (2008), 10

Acetylene (C2H2) is among the nonmethane hydrocarbons (NMHCs) accessible to infrared remote sensing technique. As a product of combustion and biomass burning, it is emitted at the Earth’s surface and ... [more ▼]

Acetylene (C2H2) is among the nonmethane hydrocarbons (NMHCs) accessible to infrared remote sensing technique. As a product of combustion and biomass burning, it is emitted at the Earth’s surface and further transported and mixed into the troposphere. Destruction by OH is the main removal process. The average tropospheric lifetime of C2H2 is estimated at about 1 month on the global scale; at mid-latitudes, it varies between 20 days in summer to 160 days in winter. This compound is appropriate to study tropospheric pollution and transport, and is often used in conjunction with other tracers of fires. C2H2 presents exploitable infrared absorption features near 3 and 15 μm, where weak isolated lines of the nu5 and the nu2 + nu4 + nu5 bands are found, respectively. Several of these lines can be used to retrieve abundances of C2H2 from high-resolution groundbased infrared solar spectra. Typical observations recorded at the Jungfraujoch station (46.5ºN, 8.0ºE, 3580m asl, Swiss Alps) by the NDACC (Network for the Detection of Atmospheric Composition Change)-affiliated Bruker instrument have been fitted with the OEM-SFIT-2 (v3.91) algorithm. Various approaches and combination of lines have been tested, seeking for the optimum inversion strategy. The HITRAN-2004 spectroscopic line parameters including the August 2006 updates for water vapor have been adopted in the retrievals. These approaches will be presented and critically compared, with the help of error budget and information content analyses, taking into account the impact of major interferences such as water vapor. The time series of C2H2 tropospheric column abundances above Jungfraujoch will also be presented, including determination of its long-term trend and strong seasonal cycle. The ground-based results will further be compared with zonal mean observations performed by the ACE-FTS space-based instrument since early 2004. [less ▲]

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