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See detailAn optimized DNA extraction and multiplex PCR for the detection of Fasciola sp. in lymnaeid snails.
Caron, Yannick ULg; Righi, Souad; Lempereur, Laetitia et al

Poster (2011, June 10)

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See detailOptimized extraction of daily bio-optical time series derived from MODIS/Aqua imagery for Lake Tanganyika, Africa
Horion, Stéphanie; Bergamino, Nadia; Stenuite, Stéphane et al

in Remote Sensing of Environment (2010)

Lake Tanganyika is one of the world's great freshwater ecosystems. In recent decades its hydrodynamic characteristics have undergone important changes that have had consequences on the lake's primary ... [more ▼]

Lake Tanganyika is one of the world's great freshwater ecosystems. In recent decades its hydrodynamic characteristics have undergone important changes that have had consequences on the lake's primary productivity. The establishment of a long-term Ocean Color dataset for Lake Tanganyika is a fundamental tool for understanding and monitoring these changes. We developed an approach to create a regionally calibrated dataset of chlorophyll-a concentrations (CHL) and attenuation coefficients at 490 nm (K490) for the period from July 2002 to December 2006 using daily calibrated radiances retrieved from the MODIS-Aqua sensor. Standard MODIS Aqua Ocean Color products were found to not provide a suitable calibration for high altitude lakes such as the Lake Tanganyika. An optimization of the extraction process and the validation of the dataset were performed with independent sets of in situ measurements. Our results show that for the geographical, atmospheric and optical conditions of Lake Tanganyika: (i) a coastal aerosol model set with high relative humidity (90%) provides a suitable atmospheric correction; (ii) a significant correlation between in situ data and CHL estimates using the MODIS specific OC3 algorithm is possible; and (iii) K490 estimates provide a good level of significance. The resulting validated time series of bio-optical properties provides a fundamental information base for the study of phytoplankton and primary production dynamics and interannual trends. A comparison between surface chlorophyll-a concentrations estimated from field monitoring and from the MODIS based dataset shows that remote sensing allows improved detection of surface blooms in Lake Tanganyika. [less ▲]

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See detailOptimized fringe sensors for the VLTI next generation instruments
Blind, N.; Absil, Olivier ULg; Le Bouquin, J.-B. et al

in Astronomy and Astrophysics (2011), 530

Context. With the arrival of the next generation of ground-based imaging interferometers combining from four to possibly six telescopes simultaneously, there is also a strong need for a new generation of ... [more ▼]

Context. With the arrival of the next generation of ground-based imaging interferometers combining from four to possibly six telescopes simultaneously, there is also a strong need for a new generation of fringe trackers able to cophase these arrays. These instruments have to be very sensitive and to provide robust operations in quickly varying observational conditions. <BR /> Aims: We aim at defining the optimal characteristics of fringe sensor concepts operating with four or six telescopes. The current detector limitations lead us to consider solutions based on co-axial pairwise combination schemes. <BR /> Methods: We independently study several aspects of the fringe sensing process: 1) how to measure the phase and the group delay, and 2) how to combine the telescopes to ensure a precise and robust fringe tracking in real conditions. Thanks to analytical developments and numerical simulations, we define the optimal fringe-sensor concepts and compute the expected performance of the four-telescope one with our dedicated end-to-end simulation tool sim2GFT. <BR /> Results: We first show that measuring the phase and the group delay by obtaining the data in several steps (i.e. by temporally modulating the optical path difference) is extremely sensitive to atmospheric turbulence and therefore conclude that it is better to obtain the fringe position with a set of data obtained simultaneously. Subsequently, we show that among all co-axial pairwise schemes, moderately redundant concepts increase the sensitivity as well as the robustness in various atmospheric or observing conditions. Merging all these results, end-to-end simulations show that our four-telescope fringe sensor concept is able to track fringes at least 90% of the time up to limiting magnitudes of 7.5 and 9.5 for the 1.8- and 8.2-meter VLTI telescopes respectively. [less ▲]

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See detailOptimized look-ahead tree policies
Maes, Francis ULg; Wehenkel, Louis ULg; Ernst, Damien ULg

in Proceedings of the 9th European Workshop on Reinforcement Learning (EWRL 2011) (2011)

We consider in this paper look-ahead tree techniques for the discrete-time control of a deterministic dynamical system so as to maximize a sum of discounted rewards over an in finite time horizon. Given ... [more ▼]

We consider in this paper look-ahead tree techniques for the discrete-time control of a deterministic dynamical system so as to maximize a sum of discounted rewards over an in finite time horizon. Given the current system state xt at time t, these techniques explore the look-ahead tree representing possible evolutions of the system states and rewards conditioned on subsequent actions ut, ut+1, ... . When the computing budget is exhausted, they output the action ut that led to the best found sequence of discounted rewards. In this context, we are interested in computing good strategies for exploring the look-ahead tree. We propose a generic approach that looks for such strategies by solving an optimization problem whose objective is to compute a (budget compliant) tree-exploration strategy yielding a control policy maximizing the average return over a postulated set of initial states. This generic approach is fully speci ed to the case where the space of candidate tree-exploration strategies are "best-first" strategies parameterized by a linear combination of look-ahead path features - some of them having been advocated in the literature before - and where the optimization problem is solved by using an EDA-algorithm based on Gaussian distributions. Numerical experiments carried out on a model of the treatment of the HIV infection show that the optimized tree-exploration strategy is orders of magnitudes better than the previously advocated ones. [less ▲]

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See detailOptimized look-ahead tree policies: a bridge between look-ahead tree policies and direct policy search
Jung, Tobias ULg; Wehenkel, Louis ULg; Ernst, Damien ULg et al

in International Journal of Adaptive Control and Signal Processing (2014), 28(3-5), 255-289

Direct policy search (DPS) and look-ahead tree (LT) policies are two popular techniques for solving difficult sequential decision-making problems. They both are simple to implement, widely applicable ... [more ▼]

Direct policy search (DPS) and look-ahead tree (LT) policies are two popular techniques for solving difficult sequential decision-making problems. They both are simple to implement, widely applicable without making strong assumptions on the structure of the problem, and capable of producing high performance control policies. However, computationally both of them are, each in their own way, very expensive. DPS can require huge offline resources (effort required to obtain the policy) to first select an appropriate space of parameterized policies that works well for the targeted problem, and then to determine the best values of the parameters via global optimization. LT policies do not require any offline resources; however, they typically require huge online resources (effort required to calculate the best decision at each step) in order to grow trees of sufficient depth. In this paper, we propose optimized look-ahead trees (OLT), a model-based policy learning scheme that lies at the intersection of DPS and LT. In OLT, the control policy is represented indirectly through an algorithm that at each decision step develops, as in LT using a model of the dynamics, a small look-ahead tree until a prespecified online budget is exhausted. Unlike LT, the development of the tree is not driven by a generic heuristic; rather, the heuristic is optimized for the target problem and implemented as a parameterized node scoring function learned offline via DPS. We experimentally compare OLT with pure DPS and pure LT variants on optimal control benchmark domains. The results show that the LT-based representation is a versatile way of compactly representing policies in a DPS scheme (which results in OLT being easier to tune and having lower offline complexity than pure DPS); while at the same time, DPS helps to significantly reduce the size of the look-ahead trees that are required to take high-quality decisions (which results in OLT having lower online complexity than pure LT). Moreover, OLT produces overall better performing policies than pure DPS and pure LT and also results in policies that are robust with respect to perturbations of the initial conditions. [less ▲]

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See detailOptimized Look-Ahead Trees: Extensions to Large and Continuous Action Spaces
Jung, Tobias ULg; Ernst, Damien ULg; Maes, Francis

in Proc. of IEEE Symposium on Adaptive Dynamic Programming and Reinforcement Learning (ADPRL'13) (2013)

This paper studies look-ahead tree based control policies from the viewpoint of online decision making with constraints on the computational budget allowed per decision (expressed as number of calls to ... [more ▼]

This paper studies look-ahead tree based control policies from the viewpoint of online decision making with constraints on the computational budget allowed per decision (expressed as number of calls to the generative model). We consider optimized look-ahead tree (OLT) policies, a recently introduced family of hybrid techniques, which combine the advantages of look-ahead trees (high precision) with the advantages of direct policy search (low online cost) and which are specifically designed for limited online budgets. We present two extensions of the basic OLT algorithm that on the one side allow tackling deterministic optimal control problems with large and continuous action spaces and that on the other side can also help to further reduce the online complexity. [less ▲]

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See detailOptimized Remeshing for Incremental Forming Simulation
Rabahallah, François ULg; Bouffioux, Chantal ULg; Duchene, Laurent ULg et al

in Proceedings of the Advances in Materials and Processing Technologies Conference (2010)

This work presents an advanced numerical methodology which aims to improve the simulations of incremental forming processes [3]. A specific numerical treatment is required to optimize the remeshing ... [more ▼]

This work presents an advanced numerical methodology which aims to improve the simulations of incremental forming processes [3]. A specific numerical treatment is required to optimize the remeshing procedure, in order to decrease the simulation CPU time and deals with the strong process nonlinearities. The algorithm remeshing procedure is implemented in the Lagamine FE code [2] developed at the University of Liège. An elastoplastic law is combined with an isotropic kinematic hardening model. The identification procedure for the material parameters determination takes into account a set of mechanical tests (inverse approach). Numerical simulations of the forming of a pyramid part with two wall angles are performed in order to address the robustness of the implementation and the ability of this numerical methodology to predict the force values. Comparisons between measured and predicted force values are performed. [less ▲]

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See detailOptimized Schwarz Algorithm with Double Sweep Preconditioner for the Helmholtz Equation
Vion, Alexandre ULg; Geuzaine, Christophe ULg

in Proceedings of the 9th International Symposium on Electric and Magnetic Fields, EMF 2013 (2013, April)

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See detailOptimized thermal zone controller for integration within a building energy management system.
Kummert, M.; Andre, Philippe ULg; Nicolas, Jacques ULg

in Proceedings Clima 2000 (1997)

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See detailOptimized Waveform Relaxation Methods for Modeling Electromagnetic Field-Circuit Problems
Nshimiyimana, Jean de Dieu ULg; Plumier, Frédéric ULg; Dular, Patrick ULg et al

in Proceedings of Sixteenth Biennal IEEE Conference on Electromagnetic Field Computation (2014, April)

The convergence of classical and optimized waveform relaxation methods is compared for the simulation of field-circuit problems, where a finite element solver is used for the solution of the field problem ... [more ▼]

The convergence of classical and optimized waveform relaxation methods is compared for the simulation of field-circuit problems, where a finite element solver is used for the solution of the field problem and a circuit simulator is used for the electronic circuit. [less ▲]

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See detailOptimizing active avoidance conditioning for high-throughput behavioral and cognitive screening in fish. Proceedings of Measuring behaviour
Ylieff, Marc ULg; Ferrara, André ULg; Fagniart, C. et al

in A.J. Spink et al. (Ed.) Proceedings of Measuring Behaviour (2008)

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See detailOptimizing early nutritional support based on recent recommendations in VLBW infants and postnatal growth restriction
SENTERRE, Thibault ULg; Rigo, Jacques ULg

in Journal of Pediatric Gastroenterology and Nutrition (2011), 53(5), 536-542

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See detailOptimizing Early Nutritional Support Based on Recent Recommendations in VLBW Infants.
SENTERRE, Thibault ULg

in 4th Congress of the European Academy of Paediatric Societies (2012, October)

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See detailOptimizing nutrition after birth with a unique standardized parenteral nutrition solution may reduce electrolytes anomalies in <1250g infants
SENTERRE, Thibault ULg; rigo, jacques

in Archives of Disease in Childhood (2012), 97(S2), 394

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See detailOptimizing Nutritional Supply Reduces Postnatal Growth Restriction in VLBW Infants
SENTERRE, Thibault ULg; Habibi, Fakher; Rigo, J

in Pediatric Academic Societies and Asian Society for Pediatric Research Joint Meeting (2011)

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See detailOptimizing patient adherence and persistence in strontium ranelate phase 3 program using a short term run-in study
Reginster, Jean-Yves ULg; Spector, Tim; Badurski, J. et al

in Osteoporosis International (2002, November), 13(Suppl.3), 35-36

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See detailOptimizing Perfectly Matched Layers in Discrete Contexts
Modave, Axel ULg; Delhez, Eric ULg; Geuzaine, Christophe ULg

in International Journal for Numerical Methods in Engineering (2014), 99(6), 410437

Perfectly Matched Layers (PMLs) are widely used for the numerical simulation of wave-like problems defined on large or infinite spatial domains. However, for both the time-dependent and the time-harmonic ... [more ▼]

Perfectly Matched Layers (PMLs) are widely used for the numerical simulation of wave-like problems defined on large or infinite spatial domains. However, for both the time-dependent and the time-harmonic cases, their performance critically depends on the so-called absorption function. This paper deals with the choice of this function when classical numerical methods are used (based on finite differences, finite volumes, continuous finite elements and discontinuous finite elements). After reviewing the properties of the PMLs at the continuous level, we analyse how they are altered by the different spatial discretizations. In the light of these results, different shapes of absorption function are optimized and compared by means of both one- and two-dimensional representative time-dependent cases. This study highlights the advantages of the so-called shifted hyperbolic function, which is efficient in all cases and does not require the tuning of a free parameter, by contrast with the widely used polynomial functions. [less ▲]

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