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
Full Text
Peer Reviewed
See detailEstimating survival rates in ecological studies with small unbalanced sample sizes: an alternative Bayesian point estimator
Damgaard, Christian; Fayolle, Adeline ULg

in Computational Ecology and Software (2011), 1(4), 243-248

Increasingly, the survival rates in experimental ecology are presented using odds ratios or log response ratios, but the use of ratio metrics has a problem when all the individuals have either died or ... [more ▼]

Increasingly, the survival rates in experimental ecology are presented using odds ratios or log response ratios, but the use of ratio metrics has a problem when all the individuals have either died or survived in only one replicate. In the empirical ecological literature, the problem often has been ignored or circumvented by different, more or less ad hoc approaches. Here, it is argued that the best summary statistic for communicating ecological results of frequency data in studies with small unbalanced samples may be the mean of the posterior distribution of the survival rate. The developed approach may be particularly useful when effect size indexes, such as odds ratios, are needed to compare frequency data between treatments, sites or studies. [less ▲]

Detailed reference viewed: 18 (4 ULg)
Full Text
See detailEstimating Systematic Risk in the Presence of Thin Trading and Conditional Heteroscedasticity
Corhay, Albert ULg; Tourani Rad, Alireza; Urbain, Jean-Pierre

in In The Money (1997), 2

Detailed reference viewed: 7 (4 ULg)
Full Text
Peer Reviewed
See detailEstimating The Cost of Improving Quality in Electricity Distribution: A Parametric Distance Function Approach
Coelli, Tim; Gautier, Axel ULg; Perelman, Sergio ULg et al

in Energy Policy (2013), 53

The quality of electricity distribution is being more and more scrutinized by regulatory authorities, with explicit reward and penalty schemes based on quality targets having been introduced in many ... [more ▼]

The quality of electricity distribution is being more and more scrutinized by regulatory authorities, with explicit reward and penalty schemes based on quality targets having been introduced in many countries (France, Germany, Italy, UK,...). It is then of prime importance to know the cost of improving the quality for a distribution system operator. In this paper, we focus on one dimension of quality, the continuity of supply, and we estimated the cost of preventing power outages. For that, we make use of the parametric distance function approach, assuming that outages enter in the firm production set as an input, an imperfect substitute for maintenance activities and capital investment. This allows us to identify the sources of technical inefficiency and the underlying trade-­‐off faced by operators between quality and other inputs and costs. For this purpose, we use panel data on 92 electricity distribution units operated by ERDF (Electricité de France - Réseau Distribution) in the 2003–2005 financial years. Assuming a multi-output multi-input translog technology, we estimate that the cost of preventing one interruption varies substantily among the distribution units from 2.7 € to 15.7 €. Furthermore, as one would expect, marginal quality improvements tend to be more expensive as quality itself improves. [less ▲]

Detailed reference viewed: 133 (22 ULg)
Full Text
See detailEstimating the costs of collective treatment of wastewater : the case of Walloon Region (Belgium)
Dogot, Thomas ULg; Xanthoulis, Y.; Fonder, N. et al

Conference (2009)

Detailed reference viewed: 14 (1 ULg)
Full Text
Peer Reviewed
See detailEstimating the costs of collective treatment of wastewater: the case of Walloon Region (Belgium)
Dogot, Thomas ULg; Xanthoulis, Yanni; Fonder, Nathalie et al

in Water Science & Technology (2010), 62(3), 640-648

This paper contributes to a better understanding of costs for collective wastewater treatment in the Walloon Region (Belgium). Based on a large set of data, unit costs to population equivalents are ... [more ▼]

This paper contributes to a better understanding of costs for collective wastewater treatment in the Walloon Region (Belgium). Based on a large set of data, unit costs to population equivalents are modelled. Considering investment as well as exploitation costs, the model includes not only wastewater treatment plants but also collector and sewage networks in an integrated approach at the technical basin level. Beyond this modelling, each type of process is analyzed independently in order to explore the structure of investment costs and their variation factors. Then, the model was used to forecast the upcoming expenses for 36 areas which are not yet equipped with collective wastewater treatment facilities. In light of these results, strategic choices for decision makers are discussed. [less ▲]

Detailed reference viewed: 52 (25 ULg)
Full Text
Peer Reviewed
See detailEstimating the driver function of a cardiovascular system model
Stevenson, D; Hann, CE; Chase, JG et al

in Proceedings of CONTROL 2010 (2010)

Detailed reference viewed: 3 (0 ULg)
Full Text
Peer Reviewed
See detailEstimating the Greenland ice sheet surface mass balance contribution to future sea level rise using the regional atmospheric climate model MAR
Fettweis, Xavier ULg; Franco, Bruno ULg; Tedesco, M. et al

in Cryosphere (The) (2013), 7

To estimate the sea level rise (SLR) originating from changes in surface mass balance (SMB) of the Greenland ice sheet (GrIS), we present 21st century climate projections obtained with the regional ... [more ▼]

To estimate the sea level rise (SLR) originating from changes in surface mass balance (SMB) of the Greenland ice sheet (GrIS), we present 21st century climate projections obtained with the regional climate model MAR (Modèle Atmosphérique Régional), forced by output of three CMIP5 (Coupled Model Intercomparison Project Phase 5) general circulation models (GCMs). Our results indicate that in a warmer climate, mass gain from increased winter snowfall over the GrIS does not compensate mass loss through increased meltwater run-off in summer. Despite the large spread in the projected near-surface warming, all the MAR projections show similar non-linear increase of GrIS surface melt volume because no change is projected in the general atmospheric circulation over Greenland. By coarsely estimating the GrIS SMB changes from GCM output, we show that the uncertainty from the GCM-based forcing represents about half of the projected SMB changes. In 2100, the CMIP5 ensemble mean projects a GrIS SMB decrease equivalent to a mean SLR of +4 ± 2 cm and +9 ± 4 cm for the RCP (Representative Concentration Pathways) 4.5 and RCP 8.5 scenarios respectively. These estimates do not consider the positive melt–elevation feedback, although sensitivity experiments using perturbed ice sheet topographies consistent with the projected SMB changes demonstrate that this is a significant feedback, and highlight the importance of coupling regional climate models to an ice sheet model. Such a coupling will allow the assessment of future response of both surface processes and ice-dynamic changes to rising temperatures, as well as their mutual feedbacks. [less ▲]

Detailed reference viewed: 1581 (375 ULg)
Full Text
Peer Reviewed
See detailEstimating the p-mode frequencies of the solar twin 18 Scorpii
Bazot, M.; Campante, T.L.; Chaplin, W.J. et al

in Astronomy and Astrophysics (2012), 544

Solar twins have been a focus of attention for more than a decade, because their structure is extremely close to that of the Sun. Today, thanks to high-precision spectrometers, it is possible to use ... [more ▼]

Solar twins have been a focus of attention for more than a decade, because their structure is extremely close to that of the Sun. Today, thanks to high-precision spectrometers, it is possible to use asteroseismology to probe their interiors. Our goal is to use time series obtained from the HARPS spectrometer to extract the oscillation frequencies of 18 Sco, the brightest solar twin. We used the tools of spectral analysis to estimate these quantities. We estimate 52 frequencies using an MCMC algorithm. After examination of their probability densities and comparison with results from direct MAP optimization, we obtain a minimal set of 21 reliable modes. The identification of each pulsation mode is straightforwardly accomplished by comparing to the well-established solar pulsation modes. We also derived some basic seismic indicators using these values. These results offer a good basis to start a detailed seismic analysis of 18 Sco using stellar models. [less ▲]

Detailed reference viewed: 9 (0 ULg)
Full Text
Peer Reviewed
See detailEstimating the parameters of a 3-D root distribution function from root observations with the trench profile method: case study with simulated and field-observed root data
Vansteenkiste, Joachim; Van Loon, Jelle; Garré, Sarah ULg et al

in Plant and Soil (2013)

Background and Aims Root length density (RLD) is a parameter that is difficult to measure, but crucial to estimate water and nutrient uptake by plants. In this study a novel approach is presented to ... [more ▼]

Background and Aims Root length density (RLD) is a parameter that is difficult to measure, but crucial to estimate water and nutrient uptake by plants. In this study a novel approach is presented to characterize the 3-D root length distribution by supplementing data of the 3-D distribution of root intersections with data of root length density from a limited number of soil cores. Methods The method was evaluated in a virtual experiment using the RootTyp model and a field experiment with cauliflower (Brassica oleracea L. botrytis) and leek (Allium porrum, L.). Results The virtual experiment shows that total root length and root length distribution can be accurately estimated using the novel approach. Implementation of the method in a field experiment was successful for characterizing the growth of the root distribution with time both for cauliflower and leek. In contrast with the virtual experiment, total root length could not be estimated based upon root intersection measurements in the field. Conclusions The novel method of combining root intersection data with root length density data from core samples is a powerful tool to supply root water uptake models with root system information. [less ▲]

Detailed reference viewed: 25 (6 ULg)
Full Text
Peer Reviewed
See detailEstimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry
Kains, N.; Bramich, D. M.; Arellano Ferro, A. et al

in Astronomy and Astrophysics (2013), 555

<BR /> Aims: We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this ... [more ▼]

<BR /> Aims: We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this cluster and refine the periods of known variables; we then used our variable star light curves to derive values for the cluster's parameters. <BR /> Methods: We used difference image analysis to reduce our data to obtain high-precision light curves of variable stars. We then estimated the cluster parameters by performing a Fourier decomposition of the light curves of RR Lyrae stars for which a good period estimate was possible. We also derived an estimate for the age of the cluster by fitting theoretical isochrones to our colour-magnitude diagram (CMD). <BR /> Results: Out of 13 stars previously catalogued as variables, we find that only 4 are bona fide variables. We detect two new RR Lyrae variables, and confirm two additional RR Lyrae candidates from the literature. We also detect four other new variables, including an eclipsing blue straggler system, and an SX Phoenicis star. This amounts to a total number of confirmed variable stars in M 30 of 12. We perform Fourier decomposition of the light curves of the RR Lyrae stars to derive cluster parameters using empirical relations. We find a cluster metallicity [Fe/H][SUB]ZW[/SUB] = -2.01 ± 0.04, or [Fe/H][SUB]UVES[/SUB] = -2.11 ± 0.06, and a distance of 8.32 ± 0.20 kpc (using RR0 variables), 8.10 kpc (using one RR1 variable), and 8.35 ± 0.42 kpc (using our SX Phoenicis star detection in M 30). Fitting isochrones to the CMD, we estimate an age of 13.0 ± 1.0 Gyr for M 30. This work is based on data collected by MiNDSTEp with the Danish 1.54 m telescope at the ESO La Silla Observatory.The full light curves, an extract of which is shown in Table 2 are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A36">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A36</A>Tables 8-10, and Figs. 6 and 9 are available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 18 (10 ULg)
Full Text
See detailEstimating the residual distribution in a semiparametric transformation model.
Heuchenne, Cédric ULg; Samb, Rawane; Van Keilegom, Ingrid

E-print/Working paper (2011)

Detailed reference viewed: 16 (3 ULg)
Full Text
Peer Reviewed
See detailEstimating the revenues of a hydrogen-based high-capacity storage device: methodology and results
François-Lavet, Vincent ULg; Fonteneau, Raphaël ULg; Ernst, Damien ULg

in Proceedings des 9èmes Journée Francophones de Planification, Décision et Apprentissage (2014, May)

This paper proposes a methodology to estimate the maximum revenue that can be generated by a company that operates a high-capacity storage device to buy or sell electricity on the day-ahead electricity ... [more ▼]

This paper proposes a methodology to estimate the maximum revenue that can be generated by a company that operates a high-capacity storage device to buy or sell electricity on the day-ahead electricity market. The methodology exploits the Dynamic Programming (DP) principle and is specified for hydrogen-based storage devices that use electrolysis to produce hydrogen and fuel cells to generate electricity from hydrogen. Experimental results are generated using historical data of energy prices on the Belgian market. They show how the storage capacity and other parameters of the storage device influence the optimal revenue. The main conclusion drawn from the experiments is that it may be interesting to invest in large storage tanks to exploit the inter-seasonal price fluctuations of electricity. [less ▲]

Detailed reference viewed: 35 (17 ULg)
Full Text
See detailEstimation and approximation in multidimensional dynamics
Frasso, Gianluca ULg; Jaeger, Jonathan ULg; Lambert, Philippe ULg

E-print/Working paper (2013)

Differential equations (DEs) are commonly used to describe dynamic systems evolving in one (ordinary differential equations or ODEs) or in more than one dimensions (partial differential equations or PDEs ... [more ▼]

Differential equations (DEs) are commonly used to describe dynamic systems evolving in one (ordinary differential equations or ODEs) or in more than one dimensions (partial differential equations or PDEs). In real data applications the parameters involved in the DE models are usually unknown and need to be estimated from the available measurements together with the state function. In this paper, we present frequentist and Bayesian approaches for the joint estimation of the parameters and of the state functions involved in PDEs. We also propose two strategies to include differential (initial and/or boundary) conditions in the estimation procedure. We evaluate the performances of the proposed strategy on simulated and real data applications. [less ▲]

Detailed reference viewed: 45 (13 ULg)
Full Text
See detailEstimation and approximation in nonlinear dynamic systems using quasilinearization
Frasso, Gianluca ULg; Jaeger, Jonathan ULg; Lambert, Philippe ULg

E-print/Working paper (2014)

Nonlinear (systems of) ordinary differential equations (ODEs) are common tools in the analysis of complex one-dimensional dynamic systems. In this paper we propose a smoothing approach regularized by a ... [more ▼]

Nonlinear (systems of) ordinary differential equations (ODEs) are common tools in the analysis of complex one-dimensional dynamic systems. In this paper we propose a smoothing approach regularized by a quasilinearized ODE-based penalty in order to approximate the state functions and estimate the parameters defining nonlinear differential systems from noisy data. Within the quasilinearized spline based framework, the estimation process reduces to a conditionally linear problem for the optimization of the spline coefficients. Furthermore, standard ODE compliance parameter(s) selection criteria are easily applicable and conditions on the state function(s) can be eventually imposed using soft or hard constraints. The approach is illustrated on real and simulated data. [less ▲]

Detailed reference viewed: 10 (6 ULg)
Full Text
Peer Reviewed
See detailEstimation by simulation of the efficiency of the French marker-assisted selection program in dairy cattle.
Guillaume, François; Fritz, Sébastien; Boichard, Didier et al

in Genetics, Selection, Evolution (2008), 40(1), 91-102

The efficiency of the French marker-assisted selection (MAS) was estimated by a simulation study. The data files of two different time periods were used: April 2004 and 2006. The simulation method used ... [more ▼]

The efficiency of the French marker-assisted selection (MAS) was estimated by a simulation study. The data files of two different time periods were used: April 2004 and 2006. The simulation method used the structure of the existing French MAS: same pedigree, same marker genotypes and same animals with records.The program simulated breeding values and new records based on this existing structure and knowledge on the QTL used in MAS (variance and frequency). Reliabilities of genetic values of young animals (less than one year old) obtained with and without marker information were compared to assess the efficiency of MAS for evaluation of milk, fat and protein yields and fat and protein contents. Mean gains of reliability ranged from 0.015 to 0.094 and from 0.038 to 0.114 in 2004 and 2006, respectively. The larger number of animals genotyped and the use of a new set of genetic markers can explain the improvement of MAS reliability from 2004 to 2006. This improvement was also observed by analysis of information content for young candidates. The gain of MAS reliability with respect to classical selection was larger for sons of sires with genotyped progeny daughters with records. Finally, it was shown that when superiority of MAS over classical selection was estimated with daughter yield deviations obtained after progeny test instead of true breeding values, the gain was underestimated. [less ▲]

Detailed reference viewed: 21 (7 ULg)
Full Text
See detailEstimation d'un indice de la valeur récréative des forêts
Lejeune, Philippe ULg; Rondeux, Jacques ULg; Verstraete, Philippe

in Mitteilungen der Abteilung für Forstliche Biometrie (1997), 97(2), 20-30

Detailed reference viewed: 9 (4 ULg)
Full Text
Peer Reviewed
See detailEstimation de densité par ensemble aléatoire de poly-arbres
Ammar, Sourour; Leray, Philippe; Wehenkel, Louis ULg

(2008)

La notion de mélange de modèles simples aléatoires est de plus en plus utilisée et avec succès dans la littérature de l’apprentissage supervisé ces dernières années. Parmi les avantages de ces méthodes ... [more ▼]

La notion de mélange de modèles simples aléatoires est de plus en plus utilisée et avec succès dans la littérature de l’apprentissage supervisé ces dernières années. Parmi les avantages de ces méthodes, citons l’amélioration du passage à l’échelle des algorithmes d’apprentissage grâce à leur aspect aléatoire et l’amélioration de l’exactitude de la prédiction des modèles induits grâce à une flexibilité plus élevée en ce qui concerne le compromis biais/variance. Dans le présent travail, nous proposons d’explorer cette idée dans le contexte de l’estimation de la densité. Nous proposons une nouvelle famille de méthodes d’apprentissage non-supervisé à base de mélange de grands ensembles aléatoires de poly-arbres. La caractéristique spécifique de ces méthodes est leur passage à l’échelle, aussi bien en terme de nombre de variables que de données à traiter. Cette étude, exploratoire, compare empiriquement ces méthodes sur un ensemble de problèmes de test discrets de taille et de complexité croissantes et ouvre de nombreuses perspectives auxquelles nous prévoyons de nous intéresser. [less ▲]

Detailed reference viewed: 4 (0 ULg)
Full Text
Peer Reviewed
See detailEstimation de l'accroissement et de la production forestiere à l'aide de placettes permanentes concentriques.
Hebert, Jacques ULg; Bourland, Nils ULg; Rondeux, Jacques ULg

in Annals of Forest Science : a Multidisciplinary and International Journal (2005), 62(3), 229-236

In many permanent national forest inventories the sampling units consist of 3–4 concentric circular plots in which only trees belonging to conventionally prefixed classes of diameter are measured ... [more ▼]

In many permanent national forest inventories the sampling units consist of 3–4 concentric circular plots in which only trees belonging to conventionally prefixed classes of diameter are measured. Assessing increment is rather complex because of the modification in plot composition (“shifting” trees) during the growth’s period between successive inventories. The recommended method has been validated in an unevenaged stand of beech and an evenaged stand of spruce. It takes into account different pools of trees. The estimations of two increment types have been calculated using single plots of constant area and concentric plots. No significant difference has been observed in this validation step using computer simulation. [less ▲]

Detailed reference viewed: 65 (13 ULg)
Full Text
Peer Reviewed
See detailEstimation de l’impact de différents modes d’exploitation forestière sur les stocks de carbone en Afrique centrale
Durrieu de Madron, Luc; Bauwens, Sébastien ULg; Giraud, Adeline et al

in Bois et Forêts des Tropiques (2011), 308(2), 75-86

There has been little in-depth research to date on logging impacts in Central Africa in terms of carbon emissions. The REDD mechanism (Reducing Emissions from Deforestation and forest Degradation), has ... [more ▼]

There has been little in-depth research to date on logging impacts in Central Africa in terms of carbon emissions. The REDD mechanism (Reducing Emissions from Deforestation and forest Degradation), has brought this topic to the forefront, with the increase in managed logging concessions and the spread of low-impact logging methods. The aim of this study was to make a meta-analysis covering different experiences reported in the literature. The data collected were applied to a hypothetical logging operation in order to produce a theoretical assessment of its impact on carbon stocks. Our results show that, based on the assumptions used, managed forestry in a conventional logging concession with no forward planning would reduce carbon losses by one tenth, with 10 to 20 m3 of timber extracted per hectare. Most of the carbon savings would result from an increase in the minimum logging diameter. The other gains from low-impact logging would result from improving the design of logging roads, i.e., 5 to 8% of carbon losses due to conventional logging practice. These gains are higher than the error found for the nearest reality measurements made for clear-felled biomass in French Guiana. However, they are much lower than the errors calculated for biomass estimations in several studies available in the literature. In any case, introducing development planning and low-impact logging techniques in timber concessions are able to induce a favourable difference to carbon stocks in Africa’s dense forests. [less ▲]

Detailed reference viewed: 96 (23 ULg)