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See detailIncertitudes liées à la modélisation agro-environnementale en vue de développer des outils d'aide à la décision
Dumont, Benjamin ULg

Doctoral thesis (2014)

The European Nitrates Directive 91/6/76/EEC aims to ensure water quality by preventing pollution of surface and groundwater induced by nitrates originating from agricultural sources and by promoting ... [more ▼]

The European Nitrates Directive 91/6/76/EEC aims to ensure water quality by preventing pollution of surface and groundwater induced by nitrates originating from agricultural sources and by promoting agronomical good practices. While the implementation of this Directive seems effective, it appears however that the use of nitrogen has still increased by 6% over the last four years in 27 European countries. Furthermore, agricultural sources would be still at the origin of 50% of the total amount of nitrogen discharged into surface waters (http://ec.europa.eu/environment/water/water-nitrates/index_en.html). In Wallonia (Belgium), the Nitrates Directive has been transposed under the Sustainable Nitrogen Management in Agriculture Program (PGDA). Launched in 2002, it involves different sets of actions, like rules definitions concerning fertilizers application, specific and appropriate crop management in vulnerable areas, the control of potentially leachable nitrogen (APL) levels in soils, etc. This is the global context in which lies the present thesis. The main aim is to optimise the nitrogen fertiliser practices to ensure that the needs of a winter wheat culture (Triticum aestivum L.) could be met while reducing the environmental pressure. It relies on the use of crop models, which describe the growth and the development of a culture interacting with its environment, namely the soil and the atmosphere. The major difficulty while working with crop models and model-based decision support tools lies in the fact that different sources of uncertainties have an impact on the modelled phenomena. Indeed, crop models are constituted by a consequent number of differential non-linear equations, involving a lot of parameters which need to be determined as accurately as possible in order to match as close as possible observed sequences of measurements. The first source of uncertainty is thus constituted by the parameters definition. Once the model has been correctly and robustly calibrated it can be used to perform predictions. However, in an agronomical context, the time-delay between sowing and harvest is consequent. As the end-season yield is often the expected output, the uncertainty linked to the non-knowledge of the future implies for the modeller to refer to different hypothesis concerning upcoming climatic scenarios. Finally, moving from models to decision systems dealing with N management involves a last source of uncertainty. Indeed the main problem is that the impact of a given practice is delayed in time from its realisation. In addition to the uncertainty linked to climatic projections themselves, it is highly important to consider the interactions between the practices and the climate. Furthermore, in a decision-making process, it could be highly relevant to know the uncertainty's estimation that could be tolerated on the decision.. Therefore, the present thesis aims to study these different sources of uncertainty in order to design an efficient decision support system. It is divided into five parts. In the first part, a Bayesian sampling algorithm, known as DREAM (DiffeRential Evolution Adaptative Metropolis) will be presented. It was successfully coupled with the STICS soil-crop model used in this study. The a posteriori probability density function of many parameters was sampled in order to improve the simulations of the growth of a winter wheat culture (Triticum aestivum L.). The DREAM algorithm offers different advantages in comparison to usual methods. Among these, it is possible to study i) the most probable a posteriori parameters distributions, ii) the parameters correlations, and iii) the uncertainties impacted on model outputs. Furthermore, a new version of the likelihood function was proposed, making an explicit use of the coefficient of variation. Results showed that it allowed the noise existing on measurements to be considered, but also the heteroscedasticity phenomenon usually encountered in biological growth processes. In parallel, assimilation data is another way to improve models simulations. These techniques allow considering measurements performed in real-time (e.g. remote measures of LAI or soil water content) in order to correct and adjust the possible drift of model simulations. In particular, a recently developed algorithm, known as variational filter, was evaluated. Its superiority, both in term of state variables simulations improvement and parameter resampling, was demonstrated. The third part of the research focuses on the real-time end season yield prediction. It involves building climate matrix ensembles, combining different time ranges of projected mean data and real measured weather originating from the historical records. As the crop growing season progresses, the effects of real monitored data plays a greater role and the prediction reliability increases. Our results demonstrated that a reliable predictive delay of 3-4 weeks before harvest could be obtained. Finally, using real-time data acquired with a micrometeorological station enabled to (i) predict, daily, potential yield at the local level, (ii) detect stress occurrence, and (iii) quantify yield losses (or gains). Being based on projected seasonal norms, this methodology is in opposition to another technique that consists to offer a panel of solution for what concerns the future. Such probabilistic technique relies on the use of stochastic weather generator (LARS-WG in this case). However, in the fourth part of this thesis, on the basis of the convergence in law theorem, it was demonstrated that in 90% of the climatic situations, both approaches were equivalent, exhibiting RRMSE and normalised deviation criteria inferior to 10%. Furthermore the two approaches offered similar predictive delay-time. The main difference between techniques lies in the finality. The first allows to quickly simulate the remaining yield potential, while the second aims to quantify the uncertainty level associated to the predictions. In the fifth and last part of this thesis, in order to quantify the uncertainty level associated to different modalities of N applications, the STICS model answers were studied under stochastic climatic realisations. It was demonstrated that, if no N was applied, under our temperate climatic conditions, the yield distribution could be considered as normal. However, with increasing N practices, the asymmetry level was found itself increasing. As soon as N was applied, not only were the yields higher, but also was the probability to achieve yields that were at least superior to the mean of the distribution. This undoubtedly reduced the risk for the farmer to achieve low yields levels. To summary all the researches conducted in this thesis, a N strategic decision support system was developed. In a general way, for what concerns the Hesbaye Region, the superiority of three fractions N protocols was demonstrated. In addition, the three rates fertilisation management based on the systematic applications of 60 kgN.ha-1 at tillering and stem extension stages and offering the possibility to adapt the flag-leaf fraction in real-time appeared as an optimal strategy. Within this tool, the uncertainty associated to climatic variability could be finely characterised, and the risk encountered by the farmer was quantified for different investigated practices. But far more important, it was demonstrated that N management could be optimised in real-time. In a general way, the research should be pursued by studying more fundamentally and systematically a wide range of different agro-environmental situations. In particular, it would be interesting to study of the Genotype × Environment × Cultural practices interactions to ensure food security in a climatic changing world. [less ▲]

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See detailPreparation of polyaniline-modified local clay and study of its sorption capacity
Benhebal, Hadj; Chaid, Messaoud; Léonard, Angélique ULg et al

in Journal of Nanostructure in Chemistry (2014), 4(98), 6

Clay minerals are frequently used in adsorption processes with aqueous solution; it was found that the adsorption properties of clays change when the samples are modified. In this context, polyaniline ... [more ▼]

Clay minerals are frequently used in adsorption processes with aqueous solution; it was found that the adsorption properties of clays change when the samples are modified. In this context, polyaniline-modified clay nanocomposite (at 10 %) was prepared by in situ polymerization processes. The structural and morphological characteristics of the synthesized material are systematically examined by X-ray diffraction, scanning electron microscopy, thermo-gravimetry, differential scanning calorimetry and infrared spectroscopy techniques. The adsorption property of the modified clay was evaluated for the removal of a reactive dye (methylene blue) from aqueous solution at room temperature (25 C) via batch adsorption. [less ▲]

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See detailRéaction immédiate à l'alcool
LIBON, Florence ULg; DEZFOULIAN, Bita ULg; NIKKELS, Arjen ULg

Poster (2014, April 17)

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See detailAtrial Natriuretic Peptide in cardiac horses
Leroux, Aurélia ULg; Al-Haidar, Ali; Remy, Benoît ULg et al

in Voorjaarsdagen Proceedings (2014, April 17)

Background: Natriuretic peptides are cardiac biomarkers that have been shown to have high potential for diagnosis, prognosis, and guidance of treatment in human and small animal cardiology. However, their ... [more ▼]

Background: Natriuretic peptides are cardiac biomarkers that have been shown to have high potential for diagnosis, prognosis, and guidance of treatment in human and small animal cardiology. However, their diagnostic and prognosis value in the equine species has only been studied in a limited number of cases. Objective: To investigate the plasma atrial natriuretic peptide concentration (ANPPl) in a large group of horses with various degrees of valvular regurgitation (VR) and heart failure (HF). Animals: Ninety-one horses, admitted at the equine teaching hospital of the University of Liege, and with no, mild, moderate or severe VR and presenting various stages of HF, according to human and canine grading system (A: no VR, B1: asymptomatic VR without cardiac remodelling, B2: asymptomatic VR with cardiac remodelling, C: symptomatic VR). Methods: All horses underwent clinical and Doppler echocardiographic examination, which allowed determining the presence, nature, and severity of VR, and the HF stage. The ANPPl was measured using a commercially available human RIA test. The mean values of body weight, age, ANPPl and each echocardiographic parameter were compared between horses in stage A, B1, B2 or C of HF and between horses with no, mild, moderate or severe VR, using a one-way ANOVA test. Then, correlations between ANPPl and each echocardiographic parameter were assessed using a Pearson’s product-moment analysis. Results: Horses with severe and moderate VR had significantly higher ANPPl than horses with mild or no VR. ANPPl was significantly higher in horses at stage B2 and C of HF than horses at stage A and B1. Moreover, ANPPl was significantly correlated with most of the measured echocardiographic variables. This correlation was especially strong with the left atrial diameter and its percentage of dilation. Conclusions and Clinical Importance: Those results suggest that ANPPl in horses suffering from VR could have a high diagnostic value of HF, especially in horses with tricuspid or mitral insufficiency and with enlargement or dysfunction of the atria. [less ▲]

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See detail"Belgique, quo vadis ?" (conférence donnée dans le cadre des 'Grandes conférences liégeoises')
Behrendt, Christian ULg; Sinardet, Dave; Quatremer, Jean

Conference given outside the academic context (2014)

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See detailApplication of isotopic tracers as a tool for understanding hydrodynamic behavior of the highly exploited Diass aquifer system (Senegal)
Madioune, Diakher Hélène; Faye, Serigne; Orban, Philippe ULg et al

in Journal of Hydrology (2014), 511

The Diass horst aquifer system located 50 km east of Dakar (Senegal) is exploited in two main aquifers covered by a sandy superficial aquifer: the confined/unconfined Palaeocene karstic limestone and the ... [more ▼]

The Diass horst aquifer system located 50 km east of Dakar (Senegal) is exploited in two main aquifers covered by a sandy superficial aquifer: the confined/unconfined Palaeocene karstic limestone and the confined Maastrichtian sandstone aquifer underneath. This system has experienced intensive groundwater abstraction during the last 50 years to supply increasing water demand, agricultural and industrial needs. The high abstraction rate from 1989 to 2009 (about 109,000 m3/d) has caused a continuous groundwater level decline (up to 30 m), a modification of the groundwater flow and salinization in parts of the aquifers. The objective of the study is to improve our understanding of the system functioning with regards to high pumping, identify the geochemical reactions that take place in the system, infer origin and timing of recharge by using mainly stable (δ18O, δ2H, 13C) and radioactive (3H and 14C) isotopes. Water types defined in the Piper diagram vary in order of abundance from Ca–HCO3 (65%), Ca/Na–Cl (20%), Na–HCO3 (3%) and Na–Cl (12%). Values of δ18O and δ2H for the superficial aquifer range between −5.8 and −4.2‰ and between −42 and −31‰, respectively. For the Palaeocene aquifer they range from −5.8 to −5.0‰ and from −38 to −31‰, respectively; values in the Maastrichtian aquifer are between −5.9 and −4.3‰ for δ18O and −38 to −26‰ for δ2H. Plotted against the conventional δ18O vs δ2H diagram, data from the upper aquifer exhibit a dispersed distribution with respect to isotopic fractionation while those of the Palaeocene and Maastrichtian aquifers are aligned parallel and slightly below/or on the Global Meteoric Water Line (GMWL) evidencing ancient waters which had evaporated during infiltration. The low tritium (generally <0.7 TU) and 14C (0.7–57.2 pmc) contents indicate predominance of older water being recharged during the Pleistocene and Holocene periods. However, few boreholes which exhibit high tritium (1.2–4.3 TU) and 14C (65.7–70.8 pmc) values indicate some mixture with recent water likely through faulting and vertical drainage from the upper to deeper aquifers as well as lateral flow along flow paths to the piezometric depressions created by pumping. [less ▲]

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See detailStudy of a solar concentrator for space based on a diffractive/refractive optical combination
Michel, Céline ULg; Loicq, Jerôme ULg; Thibert, Tanguy ULg et al

Conference (2014, April 16)

The present work proposes a theoretical optical study of a new planar solar concentrator for space applications. The concentrator focuses light onto three spatially separated photovoltaic cells (three ... [more ▼]

The present work proposes a theoretical optical study of a new planar solar concentrator for space applications. The concentrator focuses light onto three spatially separated photovoltaic cells (three single-junctions, dedicated to two different light spectra), allowing for independent control of the output power of each cell. The design, based on a blazed diffraction grating superimposed on a Fresnel lens, combines advantages of both spectral splitting and light focusing. Theoretical model and optimization of the optical design are presented, including the variation of the grating period along the lens. Numerical results are detailed, highlighting the possibility to design a concentrator at more than 10× for each cell, with an optical efficiency of ~71% and less than 10% of losses for tracking errors < ±0.85°. A thermal study completes the work, as well as a first theoretical comparison with a planar Fresnel based solar concentrator focusing on a GaAs cell. [less ▲]

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See detailAprès le Communisme
Florence, Eric ULg

in Vie des Idées (La) (2014)

Souvent traités séparément, les cas chinois et européens de l’Est sont abordés conjointement dans un ouvrage interdisciplinaire consacré aux institutions politiques et sociales, aux transformations socio ... [more ▼]

Souvent traités séparément, les cas chinois et européens de l’Est sont abordés conjointement dans un ouvrage interdisciplinaire consacré aux institutions politiques et sociales, aux transformations socio-économiques et aux relations entre État et société. L’angle d’approche tend à présenter l’action de l’État-Parti en Chine sous un jour favorable. [less ▲]

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See detailKlemtoon in het Nederlands van Franstalige immersie- en niet-immersieleerlingen
Hiligsmann, Philippe; Bui-Anh, Vu ULg; Jouniaux, Anthony et al

Scientific conference (2014, April 16)

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See detailThe paravesical and para rectal space, parameter and paracervix
Bonnet, Pierre ULg

Conference (2014, April 15)

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See detailThe anatomy of the internal iliac artery
Bonnet, Pierre ULg

Conference (2014, April 15)

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See detailPelvic neuroanatomy
Bonnet, Pierre ULg

Conference (2014, April 15)

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See detailThe vascular anatomy of the para-aortic spaces
Bonnet, Pierre ULg

Conference (2014, April 15)

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