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See detailOptical study of a solar concentrator for space applications based on a diffractive/refractive optical combination
Michel, Céline ULg; Loicq, Jerôme ULg; Languy, Fabian ULg et al

in Solar Energy Materials & Solar Cells (2014), 120PA

This paper presents a new design of a planar solar concentrator for space applications. The concentrator focuses light onto two spatially separated photovoltaic cells, allowing for independent control of ... [more ▼]

This paper presents a new design of a planar solar concentrator for space applications. The concentrator focuses light onto two spatially separated photovoltaic cells, allowing for independent control of the output power of each cell. Thanks to a blazed diffraction grating superimposed on a Fresnel lens, advantages of both spectral splitting and light focusing can be combined. The theoretical model of the optical design is presented, with the optimization of either element. Moreover, configuration improvement is proposed: a symmetrical configuration composed of two lenses. First numerical results are presented, highlighting the possibility to design a concentrator at about 10× for each cell, with an optical efficiency of about 75% and less than 10% of losses for tracking errors lower than ±0.9°. [less ▲]

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See detailAn Optical Time Delay Estimate for the Double Gravitational Lens System B1600+434
Burud, I.; Hjorth, J.; Jaunsen, A. O. et al

in Astrophysical Journal (2000), 544

We present optical I-band light curves of the gravitationally lensed double QSO B1600+434 from observations obtained at the Nordic Optical Telescope (NOT) between 1998 April and 1999 November. The ... [more ▼]

We present optical I-band light curves of the gravitationally lensed double QSO B1600+434 from observations obtained at the Nordic Optical Telescope (NOT) between 1998 April and 1999 November. The photometry has been performed by simultaneous deconvolution of all the data frames, involving a numerical lens galaxy model. Four methods have been applied to determine the time delay between the two QSO components, giving a mean estimate of Deltat=51+/-4 days (95% confidence level). This is the fourth optical time delay ever measured. Adopting a Omega=0.3, Lambda=0 universe and using the mass model of Maller et al., this time delay estimate yields a Hubble parameter of H[SUB]0[/SUB]=52[SUP]+14[/SUP][SUB]-8[/SUB] km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP] (95% confidence level), where the errors include time delay as well as model uncertainties. There are time-dependent offsets between the two (appropriately shifted) light curves that indicate the presence of external variations due to microlensing. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. [less ▲]

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See detailAn optical time delay for the double gravitational lens system FBQ 0951+2635
Jakobsson, P.; Hjorth, J.; Burud, I. et al

in Astronomy and Astrophysics (2005), 431(1), 103-109

We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay ... [more ▼]

We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay of Deltatau = 16 +/- 2 days (1sigma) is determined from the light curves. New constraints on the lensing geometry are provided by the position and ellipticity of the lensing galaxy. For a (Omega(m), Omega(Lambda)) = (0.3, 0.7) cosmology, the time delay yields a Hubble parameter of H-0 = 60(-7)(+9) (random, 1sigma) +/-2 (systematic) km s(-1) Mpc(-1) for a singular isothermal ellipsoid model and H-0 = 63(-7)(+9) (random, 1sigma) +/-1 (systematic) km s(-1) Mpc(-1) for a constant mass-to-light ratio model. In both models, the errors are mainly due to the time-delay uncertainties. Non-parametric models yield H-0 = 64(-7)(+9) (random, 1sigma) +/- 14 (systematic) km s(-1) Mpc(-1). [less ▲]

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See detailAn optical time-delay for the lensed BAL quasar HE 2149-2745
Burud, I.; Courbin, F.; Magain, Pierre ULg et al

in Astronomy and Astrophysics (2002), 383(1), 71-81

We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149-2745. The data, obtained with the 1.5 m Danish Telescope (ESO-La Silla) between October 1998 and December 2000 ... [more ▼]

We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149-2745. The data, obtained with the 1.5 m Danish Telescope (ESO-La Silla) between October 1998 and December 2000, are the first from a long-term project aimed at monitoring selected lensed quasars in the Southern Hemisphere. A time delay of 103+/-12 days is determined from the light curves. In addition, VLT/FORS1 spectra of HE 2149 2745 are deconvolved in order to obtain the spectrum of the faint lensing galaxy, free of any contamination by the bright nearby two quasar images. By cross-correlating the spectrum with galaxy-templates we obtain a tentative redshift estimate of z = 0.495+/-0:01. Adopting this redshift, a Omega = 0.3, Lambda = 0.7 cosmology, and a chosen analytical lens model, our time-delay measurement yields a Hubble constant of H-0 = 66+/-8 km s(-1) Mpc(-1) (1sigma error) with an estimated systematic error of +/-3 km s(-1) Mpc(-1). Using non-parametric models yields H-0 = 65+/-8 km s(-1) Mpc(-1) (1sigma error) and confirms that the lens exhibits a very dense/concentrated mass profile. Finally, we note, as in other cases, that the flux ratio between the two quasar components is wavelength dependent. While the flux ratio in the broad emission lines-equal to 3.7-remains constant with wavelength, the continuum of the brighter component is bluer. Although the data do not rule out extinction of one quasar image relative to the other as a possible explanation, the effect could also be produced by differential microlensing by stars in the lensing galaxy. [less ▲]

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See detailOptical variability of the B-type star HD 105382: Pulsation or rotation?
Briquet, Maryline ULg; Aerts, C.; De Cat, P.

in Astronomy and Astrophysics (2001)

We present ground-based multi-colour Geneva photometry and high-resolution high S/N spectra of the variable B-type star HD 105382. We provide evidence that this star is not a Be star, as indicated in the ... [more ▼]

We present ground-based multi-colour Geneva photometry and high-resolution high S/N spectra of the variable B-type star HD 105382. We provide evidence that this star is not a Be star, as indicated in the literature. The monoperiodic variability found in the Hipparcos data is confirmed in our ground-based follow-up observations. All existing data give rise to the detection of the period of 1.295 days. We try to interpret the variability of the star in terms of a non-radial g-mode pulsation model and of a rotational modulation model. None of these two is able to explain the observed line-profile variations in full detail. Based on observations obtained with the Swiss photometric telescope and ESO's CAT/CES telescope, both situated at La Silla, Chile. [less ▲]

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See detailOptical Variability of the Lambda Eri Star HD 105382: Pulsation or Rotation?
Briquet, Maryline ULg; Aerts, C.; De Cat, P.

in The Impact of Large-Scale Surveys on Pulsating Star Research, ASP Conference Series, Vol. 203; also IAU Colloquium #176. (2000)

HD 105382 is clearly a monoperiodic, very active λ Eri star with the frequency 0.7721 d[SUP]-1[/SUP]. Its photometric behaviour and the moment variations are not typical for a standard pulsational model.

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See detailOptical Vectorial Vortex Coronagraphs using Liquid Crystal Polymers: theory, manufacturing and laboratory demonstration
Mawet, D.; Serabyn, E.; Liewer, K. et al

in Optics Express (2009), 17

Not Available

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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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