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See detailOptical-model potential in a relativistic quantum field model
Jaminon, Martine ULg; Mahaux, Claude ULg; Rochus, Pierre ULg

in Physical Review. C : Nuclear Physics (1980), 22

The average nucleon-nucleus potential at low and medium energy is investigated in the framework of a relativistic quantum field model. Using the same input parameters as Brockmann in his recent study of ... [more ▼]

The average nucleon-nucleus potential at low and medium energy is investigated in the framework of a relativistic quantum field model. Using the same input parameters as Brockmann in his recent study of nuclear ground states, we calculate the self-consistent relativistic Hartree potential at positive energy in the case of infinite nuclear matter and of [SUP]16[/SUP]O and [SUP]40[/SUP]Ca. This potential is the sum of a scalar operator and of the fourth component of a vector operator. We construct its Schrödinger-equivalent potential by eliminating the small component of the Dirac spinor. The central part of this Schrödinger-equivalent potential is in fair agreement with empirical values at low and intermediate energy. Particular attention is paid to the intermediate energy domain, in which the calculated potential is repulsive in the nuclear interior and attractive at the nuclear surface. This is in keeping with some empirical evidence and is similar to results found in the framework of the nonrelativistic Brueckner-Hartree-Fock approximation. The spin-orbit potential of the relativistic Hartree model is also in good agreement with empirical values. NUCLEAR REACTIONS Calculated average nuclear field of nuclear matter, [SUP]16[/SUP]O and [SUP]40[/SUP]Ca at positive energy from relativistic Hartree approximation. [less ▲]

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See detailOptimal accumulation in an endogenous growth setting with human capital
Docquier, Frédéric; Paddison, Olivier; Pestieau, Pierre ULg

in Journal of Economic theory (2006), 134(1), 361-378

This paper considers a three-overlapping-generations model of endogenous growth wherein human capital is the engine of growth. It first contrasts the laissez-faire and the optimal solutions Three possible ... [more ▼]

This paper considers a three-overlapping-generations model of endogenous growth wherein human capital is the engine of growth. It first contrasts the laissez-faire and the optimal solutions Three possible accumulation regimes are distinguished. Then it discusses a standard set of tax-transfer instruments that allow for decentralization of the social optimum. Within the limits of our model, the rationale for the standard pattern of intergenerational transfers (the working-aged financing the education of the young and the pension of the old) is seriously questioned. On pure efficiency grounds, the case for generous public pensions is rather weak. (c) 2006 Elsevier Inc. All rights reserved. [less ▲]

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See detailOptimal acquisition of video images in reflected light microscopy
Pirard, Eric ULg; Lebrun, Vincent; Nivart, Jean-François

in European Microscopy and Analysis (1999), 60(9-11),

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See detailOptimal age at first calving for improved milk yield and lengh of productive life in Tunisian Holstein cows
Ben Gara, Abderrahmen; Bouraoui, Rachid; Rekik, Boulbaba et al

in American-Eurasian Journal of Agronomy (2009), 2(3), 162-167

The effects of age at first calving on milk production and true herd life were studied in Tunisian Holstein cows. There were 33,407 first lactation records of cows born between 1987 and 2001 from 166 ... [more ▼]

The effects of age at first calving on milk production and true herd life were studied in Tunisian Holstein cows. There were 33,407 first lactation records of cows born between 1987 and 2001 from 166 herds. Firstly, age at first calving was analyzed using an animal model that included herd, calving year, herd-calving year interaction, calving month, and age of dam as fixed effects and the random additive genetic effect. Secondly, differences in first lactation and productive life milk yields and in true herd life were explained by age at first calving in addition to herd, year at first calving, herd-year at first calving interaction and month at first calving. A cow produced on the average 5669.8 kg milk (SD=1812 kg) during a 305-d first lactation period. The lifetime production of a cow was was 19,496.3 kg (SD=12,192 kg) during 3.3 lactations (SD=1.8 lactations). Coefficients of determination ranged from 14% for true herd life to 64% for first lactation milk yield. The mean of true herd life was 38.6 months (SD=24 months) and the mean age at first calving was 28.7 months (SD=3.4 months). Posterior mean of heritability of the age at first calving derived by a Markov Chain Monte Carlo Bayesien method via a Gibbs sampling algorithm was 0.08. The reduction of age at first calving to around 24 months may result in improved 305-d and lifetime yields and a longer herd life in Tunisian Holsteins. [less ▲]

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See detailOptimal and robust event-related designs for fMRI
Maus, Bärbel ULg; van Breukelen, Gerard J P; Goebel, R et al

Conference (2011)

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See detailOptimal Blood Pressure Level and Best Measurement Procedure in Hemodialysis Patients
Saint-Remy, Annie ULg; Krzesinski, Jean-Marie ULg

in Vascular Health and Risk Management (2005), 1(3), 235-244

Hypertension occurs frequently among hemodialysis (HD) patients and can be due to many factors, such as salt intake, elevated sympathetic tone, and uremic toxins. It is responsible for the high ... [more ▼]

Hypertension occurs frequently among hemodialysis (HD) patients and can be due to many factors, such as salt intake, elevated sympathetic tone, and uremic toxins. It is responsible for the high cardiovascular risk associated with renal disease. Generally, in HD patients, while there is an elevation of systolic blood pressure (BP), diastolic BP seems to decrease, and the resultant effect is high pulse pressure, which can have a deleterious effect on the cardiovascular system. Although controversial, in the HD population the relationship between BP and risk of death seems to be U shaped, probably because of pre-existing cardiac disease in patients with the lowest BP. In chronic kidney disease, BP lower than 130/80 mmHg is recommended, but an appropriate target for BP in the HD population remains to be established. Moreover, there is no consensus regarding which routine peridialysis BP (pre- or post-dialysis BP, or both) can ensure the diagnosis of hypertension in this population. Ambulatory BP monitoring remains the gold standard to quantify the integrated BP load applied to the cardiovascular system. As well, home BP assessment could contribute to improve the definition of an optimal BP in the HD population. An ideal goal for post-dialysis systolic BP seems to be a value higher than 110 mmHg and lower than 150 mmHg. However, HD patients are generally old and often have cardiac complications, so a reasonable pre-dialysis target systolic BP could be 150 mmHg. It is prudent to suggest that an improvement in BP control is necessary in the HD population, first by slow and smooth removal of extracellular volume (dry weight) and thereafter by the use of appropriate antihypertensive medication. [less ▲]

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See detailOptimal concentrations in nectar feeding
Kim, Wonjung; Gilet, Tristan ULg; Bush, John W.M.

in Proceedings of the National Academy of Sciences of the United States of America (2011), 108(40), 16618

Nectar drinkers must feed quickly and efficiently due to the threat of predation. While the sweetest nectar offers the greatest ener- getic rewards, the sharp increase of viscosity with sugar concentra ... [more ▼]

Nectar drinkers must feed quickly and efficiently due to the threat of predation. While the sweetest nectar offers the greatest ener- getic rewards, the sharp increase of viscosity with sugar concentra- tion makes it the most difficult to transport. We here demonstrate that the sugar concentration that optimizes energy transport depends exclusively on the drinking technique employed. We iden- tify three nectar drinking techniques: active suction, capillary suction, and viscous dipping. For each, we deduce the dependence of the volume intake rate on the nectar viscosity and thus infer an optimal sugar concentration consistent with laboratory mea- surements. Our results provide the first rationale for why suction feeders typically pollinate flowers with lower sugar concentration nectar than their counterparts that use viscous dipping. [less ▲]

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See detailOptimal conception of a post-combustion CO2 capture unit with assessment of solvent degradation
Léonard, Grégoire ULg; Toye, Dominique ULg; Heyen, Georges ULg

Poster (2013, September)

Solvent degradation may be a major drawback for the large-scale implementation of post-combustion CO2 capture due to amine consumption and emission of degradation products. A kinetics model describing ... [more ▼]

Solvent degradation may be a major drawback for the large-scale implementation of post-combustion CO2 capture due to amine consumption and emission of degradation products. A kinetics model describing solvent oxidative and thermal degradation has been developed based on experimental results. This model has been included into a global Aspen Plus model of the CO2 capture process, so that optimal operating conditions can be identified to minimize both energy and environmental impacts of the process. [less ▲]

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See detailOptimal control simulation of the Deutsch-Josza algorithm in a two-dimensional double well coupled to an environment
Ndong, Mamadou; Lauvergnat, David; Chapuisat, Xavier et al

in Journal of Chemical Physics (2007), 126

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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)

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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

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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 ▲]

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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 ▲]

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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 ▲]

Detailed reference viewed: 38 (9 ULg)