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See detailOptimal design of multi-subject blocked fMRI experiments.
Maus, Bärbel ULg; van Breukelen, Gerard J P; Goebel, Rainer et al

in NeuroImage (2011), 56(3), 1338-1352

The design of a multi-subject fMRI experiment needs specification of the number of subjects and scanning time per subject. For example, for a blocked design with conditions A or B, fixed block length and ... [more ▼]

The design of a multi-subject fMRI experiment needs specification of the number of subjects and scanning time per subject. For example, for a blocked design with conditions A or B, fixed block length and block order ABN, where N denotes a null block, the optimal number of cycles of ABN and the optimal number of subjects have to be determined. This paper presents a method to determine the optimal number of subjects and optimal number of cycles for a blocked design based on the A-optimality criterion and a linear cost function by which the number of cycles and the number of subjects are restricted. Estimation of individual stimulus effects and estimation of contrasts between stimulus effects are both considered. The mixed-effects model is applied and analytical results for the A-optimal number of subjects and A-optimal number of cycles are obtained under the assumption of uncorrelated errors. For correlated errors with a first-order autoregressive (AR1) error structure, numerical results are presented. Our results show how the optimal number of cycles and subjects depend on the within- to between-subject variance ratio. Our method is a new approach to determine the optimal scanning time and optimal number of subjects for a multi-subject fMRI experiment. In contrast to previous results based on power analyses, the optimal number of cycles and subjects can be described analytically and costs are considered. [less ▲]

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See detailOptimal design of outdoor lighting systems by genetic algorithms - Discussion
Embrechts, Jean-Jacques ULg

in Lighting Research & Technology (2003), 35(3), 278-280

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See detailThe Optimal Design of the VSI T2 Control Chart
Faraz, Alireza ULg; Kazemzadeh, R. B.; Heuchenne, Cédric ULg et al

in Journal of Iranian Statistical Society (2010), 9(1), 1-19

Recent studies have shown that the variable sampling interval (VSI) scheme helps practitioners detect process shifts more quickly than the classical scheme (FRS). In this paper, the economically and ... [more ▼]

Recent studies have shown that the variable sampling interval (VSI) scheme helps practitioners detect process shifts more quickly than the classical scheme (FRS). In this paper, the economically and statistically optimal design of the VSI T2 control chart for monitoring the process mean vector is investigated. The cost model proposed by Lorenzen and Vance (1986) is minimized through a genetic algorithm (GA) approach. Then the effects of the costs and operating parameters on the optimal design (OD) of the chart parameters and resulting operating loss through a fractional factorial design is systematically studied and finally, based on the ANOVA results, a Meta model to facilitate implementation in industry is proposed to determine the OD of the VSI T2 control chart parameters from the process and cost parameters [less ▲]

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See detailOptimal dimensioning of pipe networks: the new situation when the distribution and the transportation functions are disconnected
Bakhouya, Bouchra; de Wolf, Daniel ULg

Conference (2008, January)

In [9], De Wolf and Smeers consider the problem of the optimal dimensioning of a gas transmission network when the topology of the network is known. The pipe diameters must been chosen to minimize the sum ... [more ▼]

In [9], De Wolf and Smeers consider the problem of the optimal dimensioning of a gas transmission network when the topology of the network is known. The pipe diameters must been chosen to minimize the sum of the investment and operating costs. This two stage prob- lem was solved by application of the bundle method for nonsmooth optimization. This model does not re ect any more the current situation on the gas industry. Today, the transportation function and gas buying func- tion are separated. This work considers the new situation for the trans- portation company. The objective for the transportation company is to determine the ows in the network that minimize the energy used for the gas transport. This corresponds to the minimization of the power used in the compressors. We introduce in the investment problem new decision variables, namely the maximal power of the compressor. We present here rst results obtained on the belgian gas network and on a realistic network corresponding to a part of the french network. [less ▲]

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See detailOptimal discovery with probabilistic expert advice
Bubeck, Sébastien; Ernst, Damien ULg; Garivier, Aurélien

in Proceedings of the 51st IEEE Conference on Decision and Control (CDC 2012) (2012, December)

Motivated by issues of security analysis for power systems, we analyze a new problem, called optimal discovery with probabilistic expert advice. We address it with an algorithm based on the optimistic ... [more ▼]

Motivated by issues of security analysis for power systems, we analyze a new problem, called optimal discovery with probabilistic expert advice. We address it with an algorithm based on the optimistic paradigm and the Good-Turingmissing mass estimator. We show that this strategy attains the optimal discovery rate in a macroscopic limit sense, under some assumptions on the probabilistic experts. We also provide numerical experiments suggesting that this optimal behavior may still hold under weaker assumptions. [less ▲]

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See detailOptimal discovery with probabilistic expert advice: finite time analysis and macroscopic optimality
Bubeck, Sébastien; Ernst, Damien ULg; Garivier, Aurélien

in Journal of Machine Learning Research (2013), 14

We consider an original problem that arises from the issue of security analysis of a power system and that we name optimal discovery with probabilistic expert advice. We address it with an algorithm based ... [more ▼]

We consider an original problem that arises from the issue of security analysis of a power system and that we name optimal discovery with probabilistic expert advice. We address it with an algorithm based on the optimistic paradigm and on the Good-Turing missing mass estimator. We prove two different regret bounds on the performance of this algorithm under weak assumptions on the probabilistic experts. Under more restrictive hypotheses, we also prove a macroscopic optimality result, comparing the algorithm both with an oracle strategy and with uniform sampling. Finally, we provide numerical experiments illustrating these theoretical findings. [less ▲]

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See detailThe optimal distance of TGV which operate on the classic railway
Marchal, Jean ULg; Han, B.

in Proceedings of the 1998 International Conference on Traffic and Transportation Studies (ICTTS’98 (1998)

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See detailOPTIMAL ELECTRODES SETTING FOR TRANSCUTANEOUS ELECTRICAL STIMULATION OF THE QUADRICEPS
Vanderthommen, Marc ULg; Troka, Sylvie; Demoulin, Christophe ULg

in Loland, S.; Fasting, K.; Ommundsen, Y. (Eds.) et al Book of Abstracts of 14th annual Congress of the European College of Sport Science (2009, June)

Introduction Treatment or training sessions with neuromuscular electrical stimulations (NMES) are generally performed in a transcutaneous manner with the aid of surface electrodes. Several investigators ... [more ▼]

Introduction Treatment or training sessions with neuromuscular electrical stimulations (NMES) are generally performed in a transcutaneous manner with the aid of surface electrodes. Several investigators have highlighted the benefits of quadriceps stimulation during rehabilitation following traumatic injury or surgery of the knee and during physical preparation of athletes (Kramer and Mendryyk, 1982). However, the practical modalities of quadriceps stimulation (number, size and localization of electrodes) remain controversial (Vanderthommen and Duchateau, 2007). The present work aimed to determine the optimal electrodes setting for NMES applied to the quadriceps. Methods Twenty physically active men (23 ± 2 years, 180 ± 8 cm, 75 ± 12 Kg) underwent first an evaluation of left quadriceps maximal isometric voluntary torque (QMIVT). The exact localization of the motor points of vastus medialis (MPVM) and vastus lateralis (MPVL) was also determined. Then, we tested unilaterally, isometrically and consecutively five electrodes settings (ES) including rectangular (10 x 5 cm) (RE) or square (5 x 5 cm) (SE) electrodes, with identical stimulation parameters (biphasic symmetric rectangular pulses, 80 Hz, pulse duration 0.35 ms, constant current intensity (42 ± 11 mA)): ES1= 1 channel, 2 RE transversally on the thigh (with the distal electrode placed on MPVM and MPVL); ES2= 1 channel, 2 RE longitudinally on MPVM and MPVL; ES3= 1 channel, 2 SE on MPVM and MPVL; ES4= 2 channels, 4 SE (with 2 SE placed on MPVM and MPVL); ES5= 2 channels, channel 1= 1 SE on MPVM and 1 RE transversally on the proximal part of the thigh, channel 2= 1 SE on MPVL and 1 RE transversally on the proximal part of the thigh. For each ES we measured the electrostimulated torque. Results The mean QMIVT reached 200 ± 51 Nm. The MPVM and MPVL were situated 10 ± 2 cm and 14 ± 3 from the patellar base, respectively. The stimulated contractions reached 9.2 ± 7.4 Nm (4.6% of QMIVT) for ES1, 8 ± 4.8 Nm (4% of QMIVT) for ES2, 15 ± 8.3 Nm (7.5% of QMIVT) for ES3, 16.3 ± 7.7 Nm (8.2% of QMIVT) for ES4 and 40.4 ± 11.3 Nm (20.2% of QMIVT) for ES5 (p<0.05). Discussion During NMES programs it appears crucial to use a proper electrode setting ensuring efficient muscle recruitment and therefore optimized training effects. However, physiotherapists and trainers often place electrodes empirically especially for NMES applied to the quadriceps. This study demonstrated the relevance of using two channels for quadriceps NMES and of setting, for each channel, one small “excitative” electrode exactly on the motor point of vastus medialis or lateralis and one bigger “dispersive” electrode transversally on the proximal part of the thigh (in order to close the circuit). References Kramer JF, Mendryyk SW. (1982). Phys Ther, 4, 1657-1667. Vanderthommen M, Duchateau J. (2007). Exerc Sport Sci Rev, 35, 180-185. [less ▲]

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See detailOptimal experimental designs for funtional magnetic resonance imaging
Maus, Bärbel ULg

Doctoral thesis (2011)

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See detailOptimal extraction of multiple overlapping spectra using a maximum entropy algorithm
Khmil, S. V.; Surdej, Jean ULg

in Astronomy and Astrophysics (2002), 387(1), 347-355

A general algorithm of slit spectra extraction for a system of point-like sources (e.g. multiple lensed images of a quasar) has been developed, assuming that the point-spread function (PSF) induced by the ... [more ▼]

A general algorithm of slit spectra extraction for a system of point-like sources (e.g. multiple lensed images of a quasar) has been developed, assuming that the point-spread function (PSF) induced by the measuring instrument and/or atmosphere and the positions of the spectra relative to the CCD frame are unknown. The main idea of the algorithm is to successively apply the maximum entropy method to each set of parameters, such as the spectra, the PSF, and the spectra positions, in order to iteratively improve their values. The algorithm uses all the a priori knowledge about the spectra (e.g. flux positivity, flux ratios between the components, astrometry, etc.) to compute the initial parameter sets. The main features of the algorithm, its implementation, as well as some important aspects of its practical use, are discussed in detail. Two sets of simulated spectroscopic data have been built in order to show the most characteristic properties of the algorithm and to justify its aplication to the spectra extraction of the gravitational lens system Q1009-0252 A [less ▲]

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See detailOptimal extraction of multiple overlapping spectra: a new algorithm based on the maximum entropy method
Khmil, S. V.; Surdej, Jean ULg

in Kinematika i Fizika Nebesnykh Tel Supplement (2000), 3

A general algorithm of slit spectra extraction for a system of point-like sources (e.g. multiple lensed images of the same quasar) has been developed, assuming that the point-spread function (PSF) of the ... [more ▼]

A general algorithm of slit spectra extraction for a system of point-like sources (e.g. multiple lensed images of the same quasar) has been developed, assuming that the point-spread function (PSF) of the measuring instrument and the positions of the spectra relative to the CCD frame are unknown. The main idea of the algorithm is to successively apply the maximum entropy method to each set of parameters, such as the spectra, the PSF, and the spectra positions, in order to iteratively improve their values. The algorithm uses all the a priori knowledge about the spectra (e.g. flux positivity, relative magnitudes between the components, astrometry, etc.) to compute the initial parameter sets. After careful testing, the algorithm was applied to extract the spectra of the gravitationally lensed system Q1009-0252 A & B (I[SUB]B[/SUB]/I[SUB]A[/SUB]=0.1, θ[SUB]AB[/SUB]=1.''55, 1{pxl}=0.''44, typical seeing FWHM=0.''8). [less ▲]

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See detailOptimal Fertility along the Lifecycle
Pestieau, Pierre ULg; Ponthiere, Grégory ULg

in Economic Theory (2013)

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See detailOptimal Foraging By Hoverflies (Diptera, Syrphidae) And Ladybirds (Coleoptera, Coccinellidae) - Mechanisms
Hemptinne, Jl.; Dixon, Afg.; Doucet, Jean-Louis ULg et al

in European Journal of Entomology (1993), 90(4), 451-455

Coccinellids and syrphids that feed on aphids and coccids face the same problem: an unstable food supply. Their eggs and larvae face cannibalism and/or starvation if the aphid colony they attack declines ... [more ▼]

Coccinellids and syrphids that feed on aphids and coccids face the same problem: an unstable food supply. Their eggs and larvae face cannibalism and/or starvation if the aphid colony they attack declines in abundance before they mature. Optimal foraging theory predicts that such predators should lay a few eggs early in the development of an aphid colony. Studies on two species of coccinellid and one species of syrphid revealed that they do respond to the quality as well as the abundance of their prey. By refraining from laying eggs in aphid colonies already exploited by predators and those that are shortly to decline in abundance when the aphids disperse, these predators are able to forage in a way that is consistent with the predictions of optimal foraging theory. [less ▲]

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See detailThe Optimal Gravitational Lens Telescope
Surdej, Jean ULg; Delacroix, Christian ULg; Coleman, P. et al

in Astronomical Journal (The) (2010), 139

Given an observed gravitational lens mirage produced by a foreground deflector (cf. galaxy, quasar, cluster, . . . ), it is possible via numerical lens inversion to retrieve the real source image, taking ... [more ▼]

Given an observed gravitational lens mirage produced by a foreground deflector (cf. galaxy, quasar, cluster, . . . ), it is possible via numerical lens inversion to retrieve the real source image, taking full advantage of the magnifying power of the cosmic lens. This has been achieved in the past for several remarkable gravitational lens systems. Instead, we propose here to invert an observed multiply imaged source directly at the telescope using an ad-hoc optical instrument which is described in the present paper. Compared to the previous method, this should allow one to detect fainter source features as well as to use such an optimal gravitational lens telescope to explore even fainter objects located behind and near the lens. Laboratory and numerical experiments illustrate this new approach. [less ▲]

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See detailOptimal heating control in a passive solar commercial building
Kummert, M.; Andre, Philippe ULg; Nicolas, Jacques ULg

in Proceedings EuroSun'2000 Congress (2000, June)

A smart heating controller has a twofold objective: to save as much energy as possible while maintaining an acceptable comfort level in the building. Due to very large time constants in the building ... [more ▼]

A smart heating controller has a twofold objective: to save as much energy as possible while maintaining an acceptable comfort level in the building. Due to very large time constants in the building response, it has to anticipate internal and external disturbances. In the case of a passive solar commercial building, the need for anticipation is reinforced by important solar and internal gains. Indeed, large solar gains increase the energy savings potential but also the overheating risk. Optimal control theory presents an ideal formalism to solve this problem : its principle is to anticipate the building behaviour using a model and a forecasting of the disturbances in order to compute the control sequence that minimises a given cost function over the optimisation horizon. This cost function can combine comfort level and energy consumption. This paper presents the application of optimal control to auxiliary heating of a passive solar commercial building. Simulation-based and experimental results show that it can lead to significant energy savings while maintaining or improving the comfort level in this type of building. [less ▲]

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See detailOptimal heating control in a passive solar commercial building.
Kummert, Michaël; Andre, Philippe ULg; Nicolas, Jacques ULg

in Solar Energy (2001), 69(6), 103-116

A smart heating controller has a twofold objective: to save as much energy as possible while maintaining an acceptable comfort level in the building. Due to very large time constants in the building ... [more ▼]

A smart heating controller has a twofold objective: to save as much energy as possible while maintaining an acceptable comfort level in the building. Due to very large time constants in the building response, it has to anticipate internal and external disturbances. In the case of a passive solar commercial building, the need for anticipation is reinforced by important solar and internal gains. Indeed, large solar gains increase the energy savings potential but also the overheating risk. Optimal control theory presents an ideal formalism to solve this problem: its principle is to anticipate the building behaviour using a model and a forecasting of the disturbances in order to compute the control sequence that minimises a given cost function over the optimisation horizon. This cost function can combine comfort level and energy consumption. This paper presents the application of optimal control to auxiliary heating of a passive solar commercial building. Simulation-based and experimental results show that it can lead to significant energy savings while maintaining or improving the comfort level in this type of building [less ▲]

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See detailOptimal income taxation and the ability distribution: Implications for migration equilibria
Hamilton, J.; Pestieau, Pierre ULg

in International Tax and Public Finance (2005), 12(1), 29-45

As recently argued by Diamond (1998), one of the key factors explaining the progressivity of an optimal non-linear income tax is the distribution of productivity among workers. Migration is one source of ... [more ▼]

As recently argued by Diamond (1998), one of the key factors explaining the progressivity of an optimal non-linear income tax is the distribution of productivity among workers. Migration is one source of changes in the productivity distribution. How changes in the population's ability distribution affect optimal income tax schedules has received little attention. Changing the distribution generally affects both the objective function and the government budget constraint. We first consider the comparative statics of the fraction of highly-skilled workers with maximin and maximax welfare functions (so that only the second effect is present) and a quasi-linear utility function. We also present some results for a utilitarian social welfare function. We then study the interaction between mobility and redistributive taxation. We consider mobility by either the skilled or unskilled population under majority voting where governments take the population as fixed. If individuals choose to relocate independently, having identical ability distributions is always a stable equilibrium when the unskilled are the mobile group. However, this is not always the case when the skilled are mobile. If groups of individuals can choose where to locate, having identical ability distributions across regions is only an equilibrium when the mobile type has an overall majority. [less ▲]

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See detailOPTIMAL LEVEL OF RAPESEED MEAL IN DIETS OF LAMBS.
Mandiki, S.; Bister, J.-L.; Deryke, G. et al

Poster (1999)

Two experiments were carried out in order to improve the strategy of rapeseed meal (RPM) incorporation in the diets of lambs. In a first experiment, the effects of RPM obtained from either a high ... [more ▼]

Two experiments were carried out in order to improve the strategy of rapeseed meal (RPM) incorporation in the diets of lambs. In a first experiment, the effects of RPM obtained from either a high-glucosinolate (HG) cultivar (Honk RPM) or a double-low strain (Samourai RPM) were studied. Two types of concentrates containing 25% of RPM were compared to a Control concentrate. In a second experiment, the effects of various proportions (0 – 40%) of an industrial low glucosinolate (LG)-RPM were studied in order to determine the disorder-threshold in diets for young ruminants. One hundred forty six Texel, Suffolk or crossbred lambs ranged in age from 1 to 2 months were used. Neither the Samourai nor the Honk RPM did affect negatively animal performance whatever the parameter considered (growth, food intake and conversion, slaughter performances). Low (P < 0.05) proportions of C10:0, C12:0 and C14:0 and high contents of C18:1trans, C22:2 were determined in the perirenal fat of lambs receiving the Honk RPM. The industrial LG-RPM had no negative effects on animalperformance, best results were obtained with 25 and 30% of RPM. The Samourai RPM had no effect on the thyroid weight, whereas, the Honk RPM modified (P < 0.05) the histology of this organ; the percentages of large thyroid follicles being higher (P < 0.05) in the Honk group than in the Control and Samourai groups. High levels of Canola industrial LG-RPM(from 20%) induced also an hyperthyroidism. The Samourai and Honk RPM decreased (P < 0.05) the secretions of thyroid hormones while the industrial LG-RPM did not affect these hormones in any way. RPM had no significative effects on other hormones. It was concluded that disturbance in thyroid histology and activity induced by the ingestion of RPM did not affect the physiology and performance of lambs and that the levels between 25 to 30% of a LG-RPM were optimal for growing and fattening lambs. [less ▲]

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See detailOptimal linear taxation under endogenous longevity
Pestieau, Pierre ULg; Leroux, ML; Ponthiere, Gregory

in Journal of Population Economics (2011), 24

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