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See detailStructure et dynamique temporelle des communautés de crustacés amphipodes associés aux herbiers à Posidonia oceanica de la baie de Calvi
Michel, Loïc ULg

Master of advanced studies dissertation (2007)

L’objectif principal de ce travail était l’étude de la structure de la communauté d’amphipodes associés à la canopée des herbiers à Posidonia oceanica de la baie de Calvi, et de la dynamique saisonnière ... [more ▼]

L’objectif principal de ce travail était l’étude de la structure de la communauté d’amphipodes associés à la canopée des herbiers à Posidonia oceanica de la baie de Calvi, et de la dynamique saisonnière et nycthémérale de cette communauté. Il apparaît que la communauté étudiée est assez complexe. Elle est très riche en individus comme en espèces, et montre dans l’ensemble une diversité importante. De plus, les assemblages sont toujours dominés par quelques espèces très abondantes. Nous ne sommes pas parvenus à dégager de tendances claires quant à la variation saisonnière de la communauté étudiée. Néanmoins, seuls les prélèvements de deux saisons (novembre et mars) ont été traités dans le cadre de ce mémoire. Il est vraisemblable que la situation soit plus claire lors de l’examen des prélèvements d’une année entière. La variation nycthémérale, par contre, est très marquée. Les assemblages faunistiques sont beaucoup plus riches en individus et en espèces durant la nuit. De plus, nos résultats semblent indiquer que les amphipodes séjournent majoritairement dans la couche de litière à l’"interface" entre la matte et la strate foliaire durant la journée, alors qu’ils se déplaceraient activement au sein de la strate foliaire la nuit. Cette migration nycthémérale pourrait être une réponse à la prédation diurne par les poissons et/ou un moyen de maximiser l’exploitation des ressources trophiques offertes par l’herbier. Le second objectif de ce travail était de standardiser une méthode de prélèvement simple à mettre en œuvre, mais efficace et si possible quantitative. A cet effet, nous avons comparé trois méthodes, à savoir le filet fauchoir, le ramassage manuel de la litière et les pièges à lumière. Chaque méthode présente des avantages et des inconvénients. De plus, Les résultats obtenus via les trois méthodes ne convergent pas totalement. La communauté étudiée étant complexe, il est possible que ces divergences proviennent du fait que chacune d’entre elles ne permet de voir qu’une facette partielle d’un assemblage plus grand. Dans le but d’échantillonner aussi efficacement que possible l’ensemble de la communauté étudiée, il apparaît donc opportun de continuer à appliquer de front ces 3 méthodes. Par ailleurs, une série de pistes pour améliorer ces techniques sont proposées. Le troisième objectif était la mise en évidence des espèces les plus caractéristiques de la communauté, afin de désigner des espèces-cibles pour une étude trophique ultérieure. Nos résultats montrent que Apherusa chiereghinii, Aora spinicornis, Dexamine spiniventris, Caprella acanthifera acanthifera et Gammarella fucicola sont des espèces intéressantes pour le type d’étude envisagé. Quelques autres candidats potentiels peuvent être désignés, mais leur situation est moins évidente. Il est vraisemblable que, pour ce point comme pour la plupart des précédents, l’analyse des résultats d’un cycle annuel complet permettra de tirer des conclusions plus franches. [less ▲]

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See detailVariétés: escourgeon et orge d'hiver fourragers
Monfort, Bruno; Herman, Jean-Luc; Couvreur, Luc et al

in Livre Blanc: Céréales - Gembloux - Informations avant les semis (2007, September 13)

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See detailImplantation des cultures
Bodson, Bernard ULg; Vancutsem, Françoise ULg; Monfort, Bruno

in Livre Blanc: Céréales - Gembloux - Informations avant les semis (2007, September 13)

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See detailModelling the Mid-latitude Ionosphere: Assessment of the NeQuick Model using GPS TEC and Ionosonde Data
Bidaine, Benoît ULg

Master of advanced studies dissertation (2007)

The ionosphere plays a crucial role in Global Navigation Satellite Systems (GNSS) accuracy. In extreme cases, this electrically charged part of the atmosphere can lead to errors in positioning exceeding ... [more ▼]

The ionosphere plays a crucial role in Global Navigation Satellite Systems (GNSS) accuracy. In extreme cases, this electrically charged part of the atmosphere can lead to errors in positioning exceeding 100 m. At first approximation, ionospheric effects depend mainly on the total content in free electrons of the ionosphere ("total electron content", TEC) defined as the integral of the electron density on the path between the satellite and the receiver. The modelling of the latter parameter reveals thus itself critical in particular for single frequency receivers, the most common ones constituting the mass market. In the framework of GALILEO, the European system in development, the NeQuick model has been chosen to this extent. Computing monthly median electron densities as a basis, it will be integrated into a global algorithm providing the users with daily updated information and allowing them to calculate TEC and thus to mitigate the ionospheric effects. In order to reach the specified correction level, the model itself and its latest evolutions as well as its use for GALILEO are investigated. Different situations have to be considered e.g. different latitude regions and the results can be compared to various data sets. As a first step in a thorough analysis, we take benefit of ionosonde and GPS TEC data from the Dourbes Geophysical Observatory (Belgium) to study the mid-latitudes. Constraining the model with ionosonde measurements, we first investigate the difference between GPS-derived vertical TEC (vTEC) for Dourbes station and corresponding values from NeQuick for the latest years (for solar maximum in 2002 and minimum in 2006). With this approach, we reach residual errors of about 20% RMS for 2002 and 30% for 2006 keeping in mind that TEC values are far lower in this low solar activity year. Through a focusing process, we identify then gradually best and worst months and days for which we observe the evolution between two versions of NeQuick. We highlight among others improvements from the latest modification in the topside formulation which appears clearly in the electron density profiles examined at the end of the assessment. [less ▲]

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See detailÉtude climatologique des irrégularités ionosphériques détectées à l'aide des GNSS
Wautelet, Gilles ULg

Master of advanced studies dissertation (2007)

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See detailSimulation et aide au dimensionnement des chaudières de récupération
Dumont, Marie-Noëlle ULg

Doctoral thesis (2007)

Heat recovery steam generators (HRSG) play a very important role in combined cycle (CC) power plants, where steam is generated from a gas turbine exhaust and supplied at the appropriate pressure and ... [more ▼]

Heat recovery steam generators (HRSG) play a very important role in combined cycle (CC) power plants, where steam is generated from a gas turbine exhaust and supplied at the appropriate pressure and temperature to steam turbines for further power generation. The power plants achieve an overall efficiency above 55% and are ideally suited for combined heat and power generation in utility systems. The performance of energy conversion is improved by reducing exergy losses which implies reducing the temperature difference between the combustion gas and the steam cycle. Thus recent HRSG designs include up to three pressure levels with reheat in the steam cycle for maximum energy recovery and the use of high pressure, high temperature superheater and reheater in CC plants. Super critical boilers are also conceivable. Since HRSG performance has a large impact on the overall efficiency of the CC power plant, an accurate simulation of the performance of the HRSG is necessary. We present a steady state HRSG model to support design and rating simulations of vertical units. The simulation model, called FELVAL, divides the boiler in its rows. The row model can also be divided several times following the tube length, to better estimate the fumes temperature distribution across the hot gas path. Another model, called SUFVAL, carries out the design as well as the automatic generation of the FELVAL units and all the needed connections. The log mean temperature difference (LMTD) method and the effectiveness-NTU (ε -NTU) method are alternatively used to compute the overall heat transferred in each part of the HRSG. The problem of convergence of boiler models with more than one row in parallel is discussed. Good initialisation of the different variables is crucial to obtain convergence. The models are tested on 2 references HRSG. The first one is an assisted circulation boiler that operates at 3 subcritical pressure levels. The second is a once through boiler able to operate above the critical pressure of water. These new models were introduced into a commercial software of data reconciliation (VALI of Belsim sa) already used by the engineering and design departments of a HRSG manufacturer. They thus have a general-purpose package enabling them to make design, data reconciliation and simulation with the same software. Moreover, the use of FELVAL model will enable them to simulate any type of boiler and to obtain informations on the change of the temperatures inside the heat exchangers. This information is crucial for well monitoring closely the operation of a boiler, and better understanding its behaviour. This knowledge improvement allows to limit the overdesign and the safety margins and to reduce the investment costs. [less ▲]

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See detailVariétés: froment d'hiver
Vancutsem, Françoise ULg; Couvreur, Luc; Bodson, Bernard ULg et al

in Livre Blanc: Céréales - Gembloux (2007, September 13)

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See detailQualité: récolte 2007: encore une récolte difficile à gérer!
Sinnaeve, Geoges; Paridaens, A.-M.; Chandelier, Anne et al

in Livre Blanc: Céréales - Gembloux (2007, September 13)

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See detailPotential of space-based infrared Bracewell interferometers for planet detection
Defrere, Denis ULg; Absil, Olivier ULg; Hanot, Charles ULg et al

in Coulter, D. (Ed.) Techniques and Instrumentation for Detection of Exoplanets III (2007, September 12)

The Darwin and TPF-I space missions will be able to study the atmosphere of distant worlds similar to the Earth. Flying these space-based interferometers will however be an extraordinary technological ... [more ▼]

The Darwin and TPF-I space missions will be able to study the atmosphere of distant worlds similar to the Earth. Flying these space-based interferometers will however be an extraordinary technological challenge and a first step could be taken by a smaller mission. Several proposals have already been made in this context, using the simplest nulling scheme composed of two collectors, i.e., the original Bracewell interferometer. Two of these projects, viz. Pegase and the Fourier-Kelvin Space Interferometer, show very good perspectives for the characterisation of hot extra-solar giant planets (i.e., Jupiter-size planets orbiting close to their parent star). In this paper, we build on these concepts and try to optimise a Bracewell interferometer for the detection of Earth-like planets. The major challenge is to efficiently subtract the emission of the exo-zodiacal cloud which cannot be suppressed by classical phase chopping techniques as in the case of multi-telescopes nulling interferometers. We investigate the potential performance of split-pupil configurations with phase chopping and of OPD modulation techniques, which are good candidates for such a mitigation. Finally, we give a general overview of the performance to be expected from space-based Bracewell interferometers for the detection of extra-solar planets. In particular, the prospects for known extra-solar planets are presented. [less ▲]

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See detailEtude des principales maladies du système locomoteur chez le veau de race Blanc-Bleu Belge
Sartelet, Arnaud ULg

Master of advanced studies dissertation (2007)

The mortality rate due to musculoskeletal diseases in calves is 9 % of the overall mortality rate. It may then have major consequences on the future of the animal and on breeder’s economics. The most ... [more ▼]

The mortality rate due to musculoskeletal diseases in calves is 9 % of the overall mortality rate. It may then have major consequences on the future of the animal and on breeder’s economics. The most common musculoskeletal diseases are septic arthritis, congenital articular rigidity, fractures and spastic paresis. Two clinical studies were performed on 295 and 40 Belgian Blue calves. The first one reported a 72.3 % success rate in surgical treatments of septic arthritis. The 83.9 % rate of posterior presentation and the 90 % rate of males confirmed the hypothesis of hypomobility of calves affected by congenital articular rigidity. The success rate after appropriate treatment was 82.8 %. This study also confirmed the predisposition of Belgian Blue calves to tibial fractures (52 %). The success rate of fractures in calves was 74.1 %. An alternative to treatment in case of quadriceps or combined spastic paresis is fattening. Seventy height percent of affected calves have indeed been fattened with an almost normal growth rate. This alternative remains economically advantageous. The second study developed a classification of gastrocnemius spastic paresis based on general examination, special examination and postoperative results. This classification demonstrates the progressive nature of this disease and its consequences on body condition, allowing a more accurate diagnosis and prognosis. The success rate after partial tibial nevrectomy for grade II, III and IV was respectively 100 %, 72.7 % and 42.9 %. Those 2 studies demonstrate the effectiveness of accurate diagnosis and prognosis associated with an appropriate treatment to offer a better output to breeders despite the presence of these diseases. [less ▲]

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See detailLes images anachroniques de l'histoire de l'univers
Dondero, Maria Giulia ULg

in Espressione/Contenuto : Rivista dell’Associazione Italiana di Studi Semiotici (2007)

Cet article étudie les techniques de détection utilisées par l’astrophysique permettant la formulation d’hypothèses sur la vie et les parcours des astres (extinction, explosion, etc.). Le corpus se ... [more ▼]

Cet article étudie les techniques de détection utilisées par l’astrophysique permettant la formulation d’hypothèses sur la vie et les parcours des astres (extinction, explosion, etc.). Le corpus se constitue d’images tirées du dernier livre du célèbre astrophysicien Jean-Pierre Luminet "Le destin de l’Univers. Trous noirs et énergie sombre". Cet ouvrage de vulgarisation savante montre que ce sont les rapports entre images prises selon différentes longueurs d’onde (radio, infrarouge, spectre visible, ultraviolet, rayons X, gamma) et à différents moments qui permettent de visualiser des données, de les manipuler, de dater les phénomènes, de confirmer des hypothèses et de relancer l’investigation. Ce travail montre que les images en astrophysique sont des mosaïques construites à partir de mesures effectuées à travers une longue série de réglages des paramètres (température, composition chimique, vitesse de rotation, etc.) dont les couleurs surtout rendent compte. On y distingue les différentes fonctions des images à partir des processus qu’elles entendent détecter, mesurer, visualiser, imaginer à partir de la « densité » des agencements entre elles. On s’y enquête aussi sur des images à statut « artistique » qui sont contenue dans l’ouvrage de Luminet et on fait des hypothèses sur le rôle qu’elles jouent dans l’état d’acquisitions théoriques et de recherches en cours sur les trous noirs et d’autres phénomènes encore méconnus par la discipline. [less ▲]

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See detailEtude du rôle des bactéries symbiotiques de pucerons dans l'adaptation aux plantes hôtes
Yattara, Almouner Ag Alhamis ULg

Master of advanced studies dissertation (2007)

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See detailMacromolecular engineering of cyclic aliphatic polyesters by ring-opening polymerization and "click" chemistry
Lecomte, Philippe ULg; Li, Haiying; Riva, Raphaël ULg et al

Conference (2007, September 04)

The last decades have witnessed a steadily increasing progress in the macromolecular engineering of the main families of synthetic polymers. Ring-shaped copolymers show a unique topology due to the ... [more ▼]

The last decades have witnessed a steadily increasing progress in the macromolecular engineering of the main families of synthetic polymers. Ring-shaped copolymers show a unique topology due to the absence of any chain-end and exhibit distinct properties from their linear counterparts, such as glass transition temperature, order-disorder transition, reduced viscosity, lower hydrodynamic volumes. This communication aims at reporting on a novel route to biodegradable cyclic polyesters. Our strategy is based on the work of Prof. Kricheldorf who initiated the ring-opening polymerization of ε-caprolactone by cyclic tin dialkoxides, e.g., 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP) in order to obtain “living” macrocyclic PCL, still containing two endocyclic tin-oxygen bonds. In this work, the resumption of polymerization by a few units of ε-caprolactone substituted by an acrylic unit, e.g., 1-(2-oxooxepan-3-yl)ethyl prop- 2-enoate, followed by intramolecular photo-crosslinking of pendant unsaturations and finally by hydrolysis gave rise to macrocyclic PCL. As a rule, this strategy is very well-suited for the synthesis of high molecular weight PCL. Moreover, tin alkoxides were kept untouched after the cross-linking step and remained thus available for further macromolecular engineering. The process was extended to the synthesis of other architectures such as sun-shaped, two-tail tadpoleshaped, and eight-shaped copolyesters. The second part of the lecture, it will be shown that the copper(I)-catalyzed Huisgen’s [3+2] cycloaddition, which is the most popular “Click" reaction, is very efficient to graft alkynes, duly substituted by functional groups or chains, onto aliphatic copolyesters bearing pendant azides. Interestingly enough, mild conditions were found and no degradation was observed during the “click” derivatization of copolyesters of PCL. The “click” reactions of alkynes onto pendant azides of copolyesters of PLA, by far more sensitive than PCL, was also successfully carried out without any detectable degradation. ”Click” chemistry is very versatile because this reaction was successfully implemented to graft functional groups or chains directly onto ω-azido-ε-caprolactone, without any ring-opening of the lactone, in order to make available a new range of functional caprolactones. Finally, the “click” grafting of PEO onto the tails of tadpole-shaped copolymers will be shown to be a route to amphiphilic copolymers with an original architecture. [less ▲]

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See detailA Patient with Hiv Infection, Cough, Asthenia, and Fever
Mayasi, N.; Chandrikakumari, Kavitha; Mukeba, D. et al

in Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America (2007), 45(5), 662-3559-600

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See detailThe annular groove phase mask coronagraph: an achromatic optical vortex
Mawet, D.; Riaud, Pierre ULg; Hanot, Charles ULg et al

in Coulter, Daniel R (Ed.) "Techniques and Instrumentation for Detection of Exoplanets III" Proceedings of the SPIE, Volume 6693, Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (2007, September 01)

The Annular Groove Phase Mask coronagraph (AGPM) is an intrinsically achromatic vectorial vortex. It consists of integrated subwavelength optical elements whose space-variant polarization properties can ... [more ▼]

The Annular Groove Phase Mask coronagraph (AGPM) is an intrinsically achromatic vectorial vortex. It consists of integrated subwavelength optical elements whose space-variant polarization properties can be engineered and optimized to synthesize one of the theoretically most efficient coronagraphs. This paper briefly recalls the principles of the AGPM, presents the benefit of its implementation inside a polarimetric differential imager, realistic numerical simulations assessing its performances, as well as the current status of the near-infrared and visible prototype manufacturing operations. [less ▲]

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See detailFresnel rhombs as achromatic phase shifters for infrared nulling interferometry: first experimental results
Hanot, Charles ULg; Mawet, D.; Loicq, Jerôme ULg et al

in Coulter, Daniel R (Ed.) "Techniques and Instrumentation for Detection of Exoplanets III" Proceedings of the SPIE, Volume 6693, Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (2007, September 01)

One of the most critical units of nulling interferometers is the Achromatic Phase Shifter. The concept we propose here is based on optimized Fresnel rhombs, using the total internal reflection phenomenon ... [more ▼]

One of the most critical units of nulling interferometers is the Achromatic Phase Shifter. The concept we propose here is based on optimized Fresnel rhombs, using the total internal reflection phenomenon, modulated or not. The total internal reflection induces a phase shift between the polarization components of the incident light. We present the principles, the current status of the prototype manufacturing and testing operations, as well as preliminary experiments on a ZnSe Fresnel rhomb in the visible that have led to a first error source assessment study. Thanks to these first experimental results using a simple polarimeter arrangement, we have identified the bulk scattering as being the main error source. Fortunately, we have experimentally verified that the scattering can be mitigated using spatial filters and does not decrease the phase shifting capabilities of the ZnSe Fresnel rhomb. [less ▲]

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See detailSWAP: a novel EUV telescope for space weather
Defise, Jean-Marc ULg; Halain, Jean-Philippe ULg; Berghmans, David et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (2007, September 01)

The SWAP telescope (Sun Watcher using Active Pixel System detector and Image Processing) is being developed to be part of the PROBA2 payload, an ESA technological mission to be launched in early 2008 ... [more ▼]

The SWAP telescope (Sun Watcher using Active Pixel System detector and Image Processing) is being developed to be part of the PROBA2 payload, an ESA technological mission to be launched in early 2008. SWAP is directly derived from the concept of the EIT telescope that we developed in the '90s for the SOHO mission. Several major innovations have been introduced in the design of the instrument in order to be compliant with the requirements of the PROBA2 mini-satellite: compactness with a new of-axis optical design, radiation resistance with a new CMOS-APS detector, a very low power electronics, an athermal opto-mechanical system, optimized onboard compression schemes combined with prioritization of collected data, autonomy with automatic triggering of observation and off-pointing procedures in case of Solar event occurrence, ... All these new features result from the low resource requirements (power, mass, telemetry) of the mini-satellite, but also take advantage of the specificities of a modern technological platform, such as quick pointing agility, new powerful on-board processor, Packetwire interface and autonomous operations. These new enhancements will greatly improve the operations of SWAP as a space weather sentinel from a low Earth orbit while the downlink capabilities are limited. This paper summarizes the conceptual design, the development and the qualification of the instrument, the autonomous operations and the expected performances for science exploitation. [less ▲]

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See detailSTEREO: Heliospheric Imager design, pre-flight, and in-flight response comparison
Halain, Jean-Philippe ULg; Mazy, Emmanuel ULg; Defise, Jean-Marc ULg et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (2007, September 01)

The Heliospheric Imager (HI) is part of the SECCHI suite of instruments on-board the two STEREO observatories launched in October 2006. The two HI instruments provide stereographic image pairs of solar ... [more ▼]

The Heliospheric Imager (HI) is part of the SECCHI suite of instruments on-board the two STEREO observatories launched in October 2006. The two HI instruments provide stereographic image pairs of solar coronal plasma and coronal mass ejections (CME) over a field of view ranging from 13 to 330 R[SUB]0[/SUB]. The HI instrument is a combination of two refractive optical systems with a two stage multi-vane baffle system. The key challenge of the instrument design is the rejection of the solar disk light by the front baffle, with total straylight attenuation at the detector level of the order of 10[SUP]-13[/SUP] to 10[SUP]-15[/SUP]. Optical systems and baffles were designed and tested to reach the required rejection. This paper presents the pre-flight optical tests performed under vacuum on the two HI flight models in flight temperature conditions. These tests included an end-to-end straylight verification of the front baffle efficiency, a co-alignment and an optical calibration of the optical systems. A comparison of the theoretical predictions of the instrument response and performance with the calibration results is presented. The instrument in-flight photometric and stray light performance are also presented and compared with the expected results. [less ▲]

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