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Peer Reviewed
See detailOptimal multi-subject fMRI experiments
Maus, Bärbel ULg; van Breukelen, Gerard J P; Goebel, R et al

Conference (2011)

Functional magnetic resonance imaging is a neuroimaging method which is used to study the human brain and its functional areas. In multi-subject fMRI experiments, data from several subjects is collected ... [more ▼]

Functional magnetic resonance imaging is a neuroimaging method which is used to study the human brain and its functional areas. In multi-subject fMRI experiments, data from several subjects is collected while these subjects perform each the same task of interest, e.g., passive viewing of houses presented on a screen, in the scanner. In my talk optimal designs for multi-subject fMRI experiments with fixed experimental budget are considered. The optimal combination of number of subjects and fMRI scanner time/imaging time per subject will be studied. Analytical and numerical results based on a linear mixed effects model with uncorrelated and correlated errors will be presented for common parameters of fMRI experiments. It will be shown how the optimal number of subjects and optimal scanner [less ▲]

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Peer Reviewed
See detailOptimal nutrition of the very low birth weight infant
SENTERRE, Thibault ULg

Conference (2014)

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See detailOptimal parametrizations for surface remeshing
Marchandise, Emilie; Remacle, Jean-François; Geuzaine, Christophe ULg

in Engineering with Computers (2014), 30(3), 383-402

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See detailOptimal power flow computations with a limited number of controls allowed to move
Capitanescu, Florin ULg; Wehenkel, Louis ULg

in IEEE Transactions on Power Systems (2010), 25(1), 586-587

This letter focuses on optimal power flow (OPF) computations in which no more than a pre-specified number of controls are allowed to move. To determine an efficient subset of controls satisfying this ... [more ▼]

This letter focuses on optimal power flow (OPF) computations in which no more than a pre-specified number of controls are allowed to move. To determine an efficient subset of controls satisfying this constraint we rely on the solution of a mixed integer linear programming (MILP) problem fed with sensitivity information of controls' impact on the objective and constraints. We illustrate this approach on a 60-bus system and for the OPF problem of minimum load curtailment cost to remove thermal congestion. [less ▲]

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See detailOptimal power flow computations with constraints limiting the number of control actions
Capitanescu, Florin ULg; Rosehart, William; Wehenkel, Louis ULg

in IEEE Power Tech conference (2009, July)

This paper focuses on optimal power flow (OPF) computations in which no more than a pre-specified number of controls are allowed to move. The benchmark formulation of this OPF problem constitutes a mixed ... [more ▼]

This paper focuses on optimal power flow (OPF) computations in which no more than a pre-specified number of controls are allowed to move. The benchmark formulation of this OPF problem constitutes a mixed integer nonlinear programming (MINLP) problem. To avoid the prohibitive computational time required by classical MINLP approaches to provide a (potentially sub-optimal) solution, we propose instead two alternative approaches. The first one consists in reformulating the MINLP problem as a mathematical program with equilibrium constraints (MPEC). The second approach includes in the classical OPF problem a nonlinear constraint which approximates the integral constraint limiting the number of control variables movement. Both approaches are solved by an interior point algorithm (IPA), slightly adapted to the particular characteristics of each approach. We provide numerical results with the proposed approaches on two test systems and for two practical problems: minimum cost to remove thermal congestion, and minimum cost of load curtailment to restore a feasible equilibrium point. [less ▲]

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See detailOptimal processing of wind tunnel measurements in view of stochastic structural design of large flexible structures
Blaise, Nicolas ULg; Denoël, Vincent ULg

in Lerner, J. C.; Boldes, U. (Eds.) Wind Tunnels and Experimental Fluid Dynamics Research (2011)

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See detailOptimal procurement decisions in the presence of total quantity discounts and alternative product recipes
Crama, Yves ULg; Pascual, R.; Torres, A.

in European Journal of Operational Research (2004), 159(2), 364-378

We describe the purchasing decisions faced by a multi-plant company. The suppliers of this company offer complex discount schedules based on the total quantity (rather than cost) of ingredients purchased ... [more ▼]

We describe the purchasing decisions faced by a multi-plant company. The suppliers of this company offer complex discount schedules based on the total quantity (rather than cost) of ingredients purchased. The schedules simultaneously account both for corporate purchases and for purchases at the individual plant level. The complexity of the purchasing decisions is further increased due to the existence of alternative production recipes for each final product. We formulate the corresponding cost-minimization problem as a nonlinear mixed 0-1 programming problem. We propose various ways to linearize this formulation, and we evaluate the quality of the resulting models on real-world data. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

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See detailOptimal propellantless rendez-vous using differential drag
Dell'Elce, Lamberto ULg; Kerschen, Gaëtan ULg

in Acta Astronautica (2015), 109

Optimization of fuel consumption is a key driver in the design of spacecraft maneuvers. For this reason, growing interest in propellant-free maneuvers is observed in the literature. Because it allows us ... [more ▼]

Optimization of fuel consumption is a key driver in the design of spacecraft maneuvers. For this reason, growing interest in propellant-free maneuvers is observed in the literature. Because it allows us to turn the often-undesired drag perturbation into a control force for relative motion, differential drag is among the most promising propellantless techniques for low-Earth orbiting satellites. An optimal control approach to the problem of orbital rendez-vous using differential drag is proposed in this paper. Thanks to the scheduling of a reference maneuver by means of a direct transcription, the method is flexible in terms of cost function and can easily account for constraints of various nature. Considerations on the practical realization of differential-drag-based maneuvers are also provided. The developments are illustrated by means of high-fidelity simulations including coupled 6-degree-of-freedom simulations and an advanced aerodynamic model. [less ▲]

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See detailOptimal Pump Scheduling for Water Supply Using Genetic Algorithms
Kelner, Vincent ULg; Léonard, Olivier ULg

in Proceedings od Eurogen'03 (2003, March)

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See detailOptimal rail-road container terminal locations on the European network
Limbourg, Sabine ULg; Jourquin, Bart

in Transportation Research. Part E: Logistics and Transportation Review (2009), 45(4), 551-563

The European transport policy has focused on sustainable transport solutions, among which intermodal transport is a key player. However, its efficiency is strongly dependent on the location of the ... [more ▼]

The European transport policy has focused on sustainable transport solutions, among which intermodal transport is a key player. However, its efficiency is strongly dependent on the location of the container terminals. In this paper, a set of estimated potential locations is used as input for an iterative procedure based on the p-hub median problem that takes the variation in trans-shipment costs according to the number of trans-shipped containers into account. The final results are the optimal locations for European transfer terminals embedded in a hub-and-spoke network. [less ▲]

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See detailOptimal rail-road container terminal locations on the European network
Limbourg, Sabine ULg

Scientific conference (2009)

Detailed reference viewed: 21 (3 ULg)
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See detailOptimal redistribution with unobservable disability:Welfarist versus non-welfarist social objectives
Racionero, María; Pestieau, Pierre ULg

in European Economic Review (2009), (53), 636-644

This paper examines the optimal non-linear income and commodity tax when the same labor disutility can receive two alternative interpretations, taste for leisure or disability, but the disability is not ... [more ▼]

This paper examines the optimal non-linear income and commodity tax when the same labor disutility can receive two alternative interpretations, taste for leisure or disability, but the disability is not readily observable. We compare the optimal policy under alternative social objectives, welfarist and non-welfarist, and conclude that the nonwelfarist objective, in which the planner gives a higher weight to the disutility of labor of the disabled individuals, is the only reasonable specification. It has some foundation in the theory of responsibility; further, unlike the other specifications it yields an optimal solution that may involve a lower labor supply requirement from disabled individuals [less ▲]

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See detailOptimal sample selection for batch-mode reinforcement learning
Rachelson, Emmanuel ULg; Schnitzler, François ULg; Wehenkel, Louis ULg et al

in Proceedings of the 3rd International Conference on Agents and Artificial Intelligence (ICAART 2011) (2011)

We introduce the Optimal Sample Selection (OSS) meta-algorithm for solving discrete-time Optimal Control problems. This meta-algorithm maps the problem of finding a near-optimal closed-loop policy to the ... [more ▼]

We introduce the Optimal Sample Selection (OSS) meta-algorithm for solving discrete-time Optimal Control problems. This meta-algorithm maps the problem of finding a near-optimal closed-loop policy to the identification of a small set of one-step system transitions, leading to high-quality policies when used as input of a batch-mode Reinforcement Learning (RL) algorithm. We detail a particular instance of this OSS metaalgorithm that uses tree-based Fitted Q-Iteration as a batch-mode RL algorithm and Cross Entropy search as a method for navigating efficiently in the space of sample sets. The results show that this particular instance of OSS algorithms is able to identify rapidly small sample sets leading to high-quality policies [less ▲]

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See detailOptimal selection of a portfolio of options under Value-at-Risk constraints: a scenario approach
Schyns, Michael ULg; Crama, Yves ULg; Hübner, Georges ULg

in Annals of Operations Research (2010), 181

This paper introduces a multiperiod model for the optimal selection of a financial portfolio of options linked to a single index. The objective of the model is to maximize the expected return of the ... [more ▼]

This paper introduces a multiperiod model for the optimal selection of a financial portfolio of options linked to a single index. The objective of the model is to maximize the expected return of the portfolio under constraints limiting its Value-at-Risk. We rely on scenarios to represent future security prices. The model contains several interesting features, like the consideration of transaction costs, bid-ask spreads, arbitrage-free option pricing, and the possibility to rebalance the portfolio with options introduced at the start of each period. The resulting mixed integer programming model is applied to realistic test instances involving options on the S&P500 index. In spite of the large size and of the numerical difficulty of this model, near-optimal solutions can be computed by a standard branch-and-cut solver or by a specialized heuristic. The structure and the financial features of the selected portfolios are also investigated. [less ▲]

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See detailOptimal synthesis of mechanisms using time-varying dimensions and natural coordinates
Collard, Jean-François; Fisette, Paul; Duysinx, Pierre ULg

in Herskowitz, José (Ed.) Proceedings of the 6th World Congress of Structural and Multidisciplinary Optimization (WCSMO6) (2005, June)

This paper presents a simple approach to optimize the dimensions and the positions of 2D mechanisms for path or function-generator synthesis. The proposed method is particularly adapted to assembled ... [more ▼]

This paper presents a simple approach to optimize the dimensions and the positions of 2D mechanisms for path or function-generator synthesis. The proposed method is particularly adapted to assembled mechanisms since time-varying dimensions always satisfy the assembly conditions which may represent a real difficulty when dealing with closed-loop mechanisms. The objective is to minimize the strain energy of the bars - considered as flexible - of the mechanism when this one follows perfectly the desired path. Two optimization strategies are developed and criticized. The first one is based on separated optimizations of design parameters and point coordinates. The second one is more global and is performed in two stages : multiple local synthesis are needed first to find the initial point coordinates, and then a global synthesis stage is undertaken to find both the best dimensions and coordinates. The use of natural coordinates is also particularly interesting since the only non linear functions to optimize are distance functions, and the objective function is rather well-conditioned for a gradient-based optimizer. The question of finding the global optimum is addressed and discussed. Since a standard genetic algorithm may fail to find it, a different approach is proposed: exploring the design space to find several local optima among which the designer will choose the most relevant one taking other design constraints into account. A simple technique is applied which consists in running multiple optimization processes starting from uniformly-distributed initial dimensions (full-factorial design of experiments) across the parameter space. Three applications are presented: a simple four-bar path synthesis to illustrate the optimization strategies, a four-bar steering linkage synthesis for function generation – Ackermann relation to highlight the limits of both strategies, and eventually a six-bar steering mechanism to explore the design space and find different local optima. [less ▲]

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See detailOptimal synthesis of planar mechanisms via an extensible-link approach
Collard, Jean-François; Duysinx, Pierre ULg; Fisette, Paul

(2006, September)

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See detailOptimal T2 control chart with double sampling scheme - an alternative to the MEWMA chart
Faraz, Alireza ULg; Heuchenne, Cédric ULg; Saniga, Erwin

in Quality and Reliability Engineering International (2012), 28(7), 751-760

Recent studies have shown that the double sampling (DS) scheme yields rapid detection of out of control situations, but the economic consequences of applying the proposed method are not discussed in the ... [more ▼]

Recent studies have shown that the double sampling (DS) scheme yields rapid detection of out of control situations, but the economic consequences of applying the proposed method are not discussed in the literature yet. In this paper, the economic statistical design of the DS T2 control chart is designed to address this issue. In this regard, upon the Lorenzen and Vance (1986)’s economic model, the problem is formulized and then the cost function is minimized using the genetic algorithm search method to obtain the optimal design parameters. Besides, we assumed that the length of the time that process remains in control is exponentially distributed. Through an illustrative example we show that by applying the proposed method relatively large benefits can be achieved in a comparison with the classical T2 and the statistical DS T2 charts. Furthermore the performance of the ESD DS T2 charts is compared to the MEWMA and other variable ratio sampling (VRS) T2 control charts in the literature. [less ▲]

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See detailOptimal timing of elective caesarean section in Belgian White and Blue breed of cattle: The calf's point of view
Uystepruyst, Christophe; Coghe, Joost; Dorts, Thierry et al

in Veterinary Journal (2002), 163(3), 267-282

The purpose of this study was to evaluate whether the timing of elective caesarean section (ECS) during parturition affects pulmonary and metabolic adaptation to extra-uterine life in healthy Belgian ... [more ▼]

The purpose of this study was to evaluate whether the timing of elective caesarean section (ECS) during parturition affects pulmonary and metabolic adaptation to extra-uterine life in healthy Belgian White and Blue (BWB) calves delivered at term. Vaginal palpation was performed and deliveries divided into six categories of timing for ECS: cervix closed (TECS 1) passive and active cervical dilatation (TECS 2 and TECS 3); full cervical dilatation (TECS 4); spontaneous rupture of allantoic (TECS 5) and amniotic (TECS 6) membranes. One hundred and eighteen BWB calves were examined at birth, 5, 15, 30, 45 and 60 min and 2, 3, 6, 12 and 24 h after birth using the following measurements: physical examination (time between birth and sternal recumbency [T-SR]) heart rate (mHR); arterial blood gas analyses (arterial partial pressure in oxygen [PaO2], in carbon dioxide [PaCO2], arterial haemoglobin oxygen saturation [SaO(2)], alveolo-arterial difference in oxygen [AaDO(2)]); pulmonary function tests using the oesophageal balloon catheter technique (respiratory rate [RR], total pulmonary resistance [R-I], dynamic lung compliance [C-Ldyn], tidal volume [V-T] and minute Volume [V-E]; arterial and venous blood acid-base balance analyses (arterial and venous pH [pHa and pHv], bicarbonate concentration [HCO(3)a and HCO(3)v], base excess [BEa and BEv]); rectal temperature (RT); jugular venous blood sampling for, determination of metabolic variables (blood glucose [G], plasma lactate [L], serum cortisol [C], plasma noradrenaline [NA] and adrenaline [A] concentrations); haematological variables (red blood cell count [RBC], total haemoglobin concentration [Hb], Packed Cell Volume [PCV]) and passive immune transfer variables (total serum protein [TP] and beta(2)gammaglobulin [beta(2)gamma] concentrations). TECS significantly (Pless than or equal to0.05) influenced PaO2, SaO(2), AaDO(2), RR, V-T, V-E, C-Ldyn, RT, G, NA, A, RBC, Hb and TP: compared to TECSgreater than or equal to4 calves, TECSless than or equal to3 calves showed lower PaO2, SaO(2), V-T, C-Ldyn, RT, G, NA, A, RBC, Hb and TP and higher AaDO(2), RR, V-E. TECS differences progressively decreased and disappeared between 6 and 12 h after birth in TECS 2 and 3 calves but remained tip to 24 h in TECS 1 calves. Improved postnatal respiratory and metabolic adaptation in TECSgreater than or equal to4 calves were mainly related to differences in exposure to labour and subsequent hormonal surge: catecholamines, particularly A, enabled more effective removal of lung liquid and/or release of surfactant which contribute to better gas exchanges and induced greater energy mobilization to maintain adequate body temperature. It was concluded waiting for full cervical dilatation before performing CS should be encouraged because it promotes postnatal respiratory and metabolic adaptation in full-term BWB calves. [less ▲]

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See detailOptimal use of proton pump inhibitors for treating acid peptic diseases in primary care.
Tack, Jacques ULg; Louis, Edouard ULg; Persy, V. et al

in Acta gastro-enterologica Belgica (2013), 76(4), 393-402

Heartburn, reflux and epigastric pain are frequently encountered symptoms in primary care medicine. Acid peptic diseases such as peptic ulcer and gastrointestinal reflux disease have a high prevalence ... [more ▼]

Heartburn, reflux and epigastric pain are frequently encountered symptoms in primary care medicine. Acid peptic diseases such as peptic ulcer and gastrointestinal reflux disease have a high prevalence, can have important impact on patient quality of life and represent a considerable health care cost. Proton pump inhibitors (PPIs) are the most potent pharmacological inhibitors of gastric acid secretion currently available and are the mainstay medical therapy for acid peptic diseases. This review summarizes current evidence on treatment of acid-peptic diseases with proton pump inhibitors and provides primary care clinicians with best practice guidelines for optimal use of these drugs. [less ▲]

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