Browsing
     by title


0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

or enter first few letters:   
OK
See detailOptimal Control Strategies for a Ducted RUAV
Hendrick, Patrick ULg; Depouhon, Alexandre ULg; Aernouts, Jean-François

in Proceedings of Platform Innovations and System Integration for Unmanned Air, Land and Sea Vehicles (AVT-SCI Joint Symposium) (2007)

Detailed reference viewed: 6 (1 ULg)
Full Text
See detailOptimal Data Fitting on Lie Groups: a Coset Approach
Lageman, Christian; Sepulchre, Rodolphe ULg

in Diehl, M. (Ed.) Recent Advances in Optimization and its Applications in Engineering (2010)

This work considers the problem of fitting data on a Lie group by a coset of a compact subgroup. This problem can be seen as an extension of the problem of fitting affine subspaces in Rn to data which can ... [more ▼]

This work considers the problem of fitting data on a Lie group by a coset of a compact subgroup. This problem can be seen as an extension of the problem of fitting affine subspaces in Rn to data which can be solved using principal component analysis. We show how the fitting problem can be reduced for biinvariant distances to a generalized mean calculation on an homogeneous space. For biinvariant Riemannian distances we provide an algorithm based on the Karcher mean gradient algorithm. We illustrate our approach by some examples on SO(n). [less ▲]

Detailed reference viewed: 17 (1 ULg)
Full Text
See detailOptimal Design and Dimensioning of Hydrogen Transmission Distribution Pipeline Networks
Andre, Jean; BRAC, Jean; de Wolf, Daniel ULg et al

Conference (2009, February 05)

This work considers the problem of the optimal design of an hydrogen transmission network. This design problem includes the topology determi- nation and the dimensioning problem. We define a solution ... [more ▼]

This work considers the problem of the optimal design of an hydrogen transmission network. This design problem includes the topology determi- nation and the dimensioning problem. We define a solution method that simultaneously looks for the least cost topology of the network and for the optimal diameter of each pipe. These two problems were generally solved separately these last years. The application to the case of development of future hydrogen pipeline networks in France has been conducted on several urban areas. [less ▲]

Detailed reference viewed: 82 (9 ULg)
Peer Reviewed
See detailOptimal design for functional magnetic resonance imaging (fMRI) experiments based on linear models
Maus, Bärbel ULg; van Breukelen, Gerard J P; Goebel, R et al

Conference (2010)

In the first part of this presentation it will be shown how the general linear model is used to describe experimental functional magnetic resonance imaging (fMRI) data from one subject. Functional ... [more ▼]

In the first part of this presentation it will be shown how the general linear model is used to describe experimental functional magnetic resonance imaging (fMRI) data from one subject. Functional magnetic resonance imaging is a neuroimaging method which is used to study the human brain and its functional areas. Based on the general linear model, optimal designs for one-subject fMRI experiments can be obtained by application of the D- and A-optimality criterion. Because of the huge design space for fMRI experiments, a genetic algorithm (GA) is employed to find optimal designs for fMRI experiments based on a multi-objective design criterion. The second part of the presentation will focus on the application of mixed effects models in analysis of fMRI experiments from multiple subjects. Optimal designs for multi-subject experiments are considered and the optimal combination of number of subjects and fMRI scanner time/imaging time per subject will be studied with respect to a linear cost function. [less ▲]

Detailed reference viewed: 20 (0 ULg)
Full Text
Peer Reviewed
See detailOptimal design for nonlinear estimation of the hemodynamic response function.
Maus, Bärbel ULg; van Breukelen, Gerard J P; Goebel, Rainer et al

in Human Brain Mapping (2012), 33(6), 1253-1267

Subject-specific hemodynamic response functions (HRFs) have been recommended to capture variation in the form of the hemodynamic response between subjects (Aguirre et al., [1998]: Neuroimage 8:360–369 ... [more ▼]

Subject-specific hemodynamic response functions (HRFs) have been recommended to capture variation in the form of the hemodynamic response between subjects (Aguirre et al., [1998]: Neuroimage 8:360–369). The purpose of this article is to find optimal designs for estimation of subject-specific parameters for the double gamma HRF. As the double gamma function is a nonlinear function of its parameters, optimal design theory for nonlinear models is employed in this article. The double gamma function is linearized by a Taylor approximation and the maximin criterion is used to handle dependency of the D-optimal design on the expansion point of the Taylor approximation. A realistic range of double gamma HRF parameters is used for the expansion point of the Taylor approximation. Furthermore, a genetic algorithm (GA) (Kao et al., [2009]: Neuroimage 44:849–856) is applied to find locally optimal designs for the different expansion points and the maximin design chosen from the locally optimal designs is compared to maximin designs obtained by m-sequences, blocked designs, designs with constant interstimulus interval (ISI) and random event-related designs. The maximin design obtained by the GA is most efficient. Random event-related designs chosen from several generated designs and m-sequences have a high efficiency, while blocked designs and designs with a constant ISI have a low efficiency compared to the maximin GA design. [less ▲]

Detailed reference viewed: 13 (7 ULg)
Full Text
See detailOptimal design of a CO2 absorption unit and assessment of solvent degradation
Léonard, Grégoire ULg

Conference (2010)

Presentation of the main research fields of my PhD thesis at the University of Liège

Detailed reference viewed: 20 (5 ULg)
Full Text
See detailOptimal design of a CO2 capture unit with assessment of solvent degradation
Léonard, Grégoire ULg

Doctoral thesis (2013)

CO2 capture in power plants by absorption in amine solvents is a technology aiming at the reduction of CO2 emissions while simultaneously addressing the growth of the global energy demand. However, the ... [more ▼]

CO2 capture in power plants by absorption in amine solvents is a technology aiming at the reduction of CO2 emissions while simultaneously addressing the growth of the global energy demand. However, the energy impact of this technology on the power plant efficiency is high and amine solvent degradation induces a non-negligible environmental impact. The main innovation of this thesis is to combine both aspects within a process model based on experimental data of solvent degradation. This model leads to the identification of optimal operating conditions for the CO2 capture process, from an energetic as well as environmental point of view. [less ▲]

Detailed reference viewed: 190 (35 ULg)
Full Text
See detailOptimal design of fixtures for vibration testing of structures on electro-dynamic shaker
Poncelet, Fabien ULg; Marin, Frédéric; Fleury, Claude ULg et al

Conference given outside the academic context (2005)

The structural design of fixtures for vibration testing of structures on electro-dynamic shakers correspond to a constrained optimization problem. The design methodology proposed in this paper is based on ... [more ▼]

The structural design of fixtures for vibration testing of structures on electro-dynamic shakers correspond to a constrained optimization problem. The design methodology proposed in this paper is based on topological optimization tools. It is illustrated on industrial application examples such as the vibration testing of a space mirror and a street lighting device. [less ▲]

Detailed reference viewed: 53 (7 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 48 (10 ULg)
Full Text
Peer Reviewed
See detailOptimal design of outdoor lighting systems by genetic algorithms - Discussion
Embrechts, Jean-Jacques ULg

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

Detailed reference viewed: 39 (0 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 38 (9 ULg)
Full Text
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 ▲]

Detailed reference viewed: 49 (4 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 8 (2 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 8 (5 ULg)
Peer Reviewed
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)

Detailed reference viewed: 10 (0 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 104 (4 ULg)
See detailOptimal experimental designs for funtional magnetic resonance imaging
Maus, Bärbel ULg

Doctoral thesis (2011)

Detailed reference viewed: 12 (1 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 25 (4 ULg)
Peer Reviewed
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 ▲]

Detailed reference viewed: 13 (1 ULg)
Full Text
Peer Reviewed
See detailOptimal Fertility along the Lifecycle
Pestieau, Pierre ULg; Ponthiere, Grégory ULg

in Economic Theory (2013)

Detailed reference viewed: 6 (0 ULg)