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See detailBiostratigraphy of the JLMD-EW8 borehole and palaeogeographic interpretation
Steemans, Philippe ULg; Breuer, P.; Al-Hajri, S. et al

Conference (2016, December 21)

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See detailMiscelanea Palaeontologica 2016
Steemans, Philippe ULg; Gerrienne, Philippe ULg

Book published by Université de Liège (2016)

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See detailUn grand juriste liégeois, Charles de Méan
Lagasse, Benoît ULg

Conference given outside the academic context (2016)

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See detailHigh resolution (1 km) positive degree-day modelling of Greenland ice sheet surface mass balance, 1870–2012 using reanalysis data
Wilton, D.; Jowett, A.; Hanna, E. et al

in Journal of Glaciology (2016), online

We show results from a positive degree-day (PDD) model of Greenland ice sheet (GrIS) surface mass balance (SMB), 1870–2012, forced with reanalysis data. The model includes an improved daily temperature ... [more ▼]

We show results from a positive degree-day (PDD) model of Greenland ice sheet (GrIS) surface mass balance (SMB), 1870–2012, forced with reanalysis data. The model includes an improved daily temperature parameterization as compared with a previous version and is run at 1 km rather than 5 km resolution. The improvements lead overall to higher SMB with the same forcing data. We also compare our model with results from two regional climate models (RCMs). While there is good qualitative agreement between our PDD model and the RCMs, it usually results in lower precipitation and lower runoff but approximately equivalent SMB: mean 1979–2012 SMB (± standard deviation), in Gt a−1, is 382 ± 78 in the PDD model, compared with 379 ± 101 and 425 ± 90 for the RCMs. Comparison with in situ SMB observations suggests that the RCMs may be more accurate than PDD at local level, in some areas, although the latter generally compares well. Dividing the GrIS into seven drainage basins we show that SMB has decreased sharply in all regions since 2000. Finally we show correlation between runoff close to two calving glaciers and either calving front retreat or calving flux, this being most noticeable from the mid-1990s. [less ▲]

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See detailTrophic ecology of Southern Ocean sea stars inferred from stable isotopes ratios of C and N
Le Bourg, Baptiste ULg; Blanchard, Alice; Danis, Bruno et al

Conference (2016, December 17)

The Southern Ocean undergoes strong and contrasted impacts of climate change. Increasing seawater temperature and sea ice cover reduction in Western Antarctic Peninsula and associated regions will likely ... [more ▼]

The Southern Ocean undergoes strong and contrasted impacts of climate change. Increasing seawater temperature and sea ice cover reduction in Western Antarctic Peninsula and associated regions will likely impact food web structure and function. Sea stars (Echinoderms: Asteroidea) are an important group of the Southern Ocean benthos. They typically have highly variable feeding habits and are potentially more resistant than other organisms to temperature changes. Consequently, they will likely be impacted by modifications of the food web rather than by direct warming. Investigating their trophic ecology is therefore necessary to infer how climate change will impact them. In this context, the aim of this study was to use stable isotopes ratios of C, N and S to infer sea stars trophic ecology. During austral summers 2006 and 2009, sea stars were sampled in Subantarctic and Antarctic locations, with most of the samples coming from South Shetland Islands and South Georgia. The isotopic niche (proxy of the trophic niche) associated to each sea star population was explored through SIBER (Stable Isotope Bayesian Ellipses in R) metrics. Stable isotope ratios of sea stars were clearly different between South Shetland Islands and South Georgia. Sea stars of South Shetland Islands had smaller isotopic niches than sea stars of South Georgia. The overlap between the isotopic niches of sea star species was also important in South Shetland Islands, while isotopic niches of South Georgia were well separated. Difference of niche width and overlap between the two regions may be the result of different environmental conditions. In South Shetland Islands, sea star species may exploit a common benthic community relying on organic matter released during sea ice summer melting. In contrast, South Georgia is an oligotrophic environment with no sea ice. As resources are more limited, a higher trophic segregation between sea stars may appear to limit competition. Ultimately, this project highlighted the importance of sea ice in the trophic ecology of Antarctic sea stars. Our results suggest that future reduction of sea ice extent in Western Antarctica may have deleterious effect on sea star populations. [less ▲]

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See detailMulti-GNSS relative positioning with Galileo, BeiDou and GPS
Deprez, Cécile ULg; Warnant, René ULg

Conference (2016, December 16)

For several years, the number of Global Navigation Satellite Systems (GNSS) has been increasing, opening new perspectives in the field of precise positioning. Particularly, the European system, Galileo ... [more ▼]

For several years, the number of Global Navigation Satellite Systems (GNSS) has been increasing, opening new perspectives in the field of precise positioning. Particularly, the European system, Galileo, is experiencing a prompt expansion with the launch, in 2015 and 2016, of 8 satellites belonging to the new Full Operational Capability (FOC) generation. Broadcasting new signals, with new modulations, the first studies addressing this system reveal promising level of precisions on both code and carrier phase observables. Yet, Galileo is far from being the only GNSS undergoing a noteworthy revolution. Alternatively, the Chinese program BeiDou, still in a developing phase, as well as the American GPS, currently undergoing a modernization of its signals, also knew major progress these last two years. Indeed, 7 new satellites have reached the initial BeiDou constellation, bringing to 20 the number of active satellites. Among them, 5 spacecraft inaugurated the Phase III generation, broadcasting the new B1, B2 and B3 signals. Regarding GPS, the block IIF, made of L5 signal broadcasting satellites, kept expanding but at a less steep rate than BeiDou or Galileo. In this study, we first estimated the individual precisions of each signals broadcast by the aforementioned GNSS. For this purpose, we created two short baselines of approximatively 5 meters between similar type receivers. We combined their measurements to form double differences, leaving in the position equations only multipath and receiver noise. The great expectations regarding Galileo’s quality turned into affirmations as long as we studied this system. As a matter of a fact, the code pseudoranges values of the 4 signals of Galileo we have considered (E1, E5a, E5b, E5a+b) presented outstanding precisions (from 5 to 17 centimetres on code pseudoranges with an elevation mask of 10 degrees) when compared to GPS (from 12 to 20 centimetres on codes pseudoranges) and BeiDou (from 26 to 40 centimetres for codes and for phases) in identical conditions. Even though the precision of Galileo observables is noticeable, the influence of the poor geometry of the satellite constellation degrades in a significant way the resulting precision of the position estimated, no matter the recent increase in the number of satellites. Indeed, in this incomplete constellation, the addition of new satellites results in longer visibility period but not in larger number of satellites observed at a single epoch. Combining Galileo with GPS or BeiDou is a way to solve this issue, as the three systems have been designed to be compatible. Therefore, multi-GNSS relative positioning based on overlapping frequencies should entail better accuracy and reliability in position estimations. However, the differences between satellite systems induce inter-system biases (ISBs) inside the multi-GNSS equations of observation. The overlapping frequencies of these GNSS are the L1 and L5 frequencies of GPS with the E1 and E5a signals of Galileo, respectively. As far as BeiDou is concerned, the B2 signal of emitted by the Phase II BeiDou satellites corresponds to the E5b frequency of Galileo. Regarding the new Phase III satellites, the B2 frequencies will correspond to the Galileo E5a+b signal and B1 of BeiDou will be compatible with E1 of Galileo and GPS. The combined use of these overlapping frequencies in zero baseline double differences (ZB DD) based on a unique pivot satellite is employed to resolve ISBs. This model removes all the satellite- and receiver-dependent error sources by differentiating and the zero baseline configuration allows atmospheric and multipath effects elimination. We conducted this study on the L1/E1, L5/E5a, B1(phase II)/E5b overlapping frequencies. Our receivers were not able to receive the phase III signals of BeiDou satellites. An analysis of the long-term stability of ISBs (GPS- Galileo and Galileo - BeiDou) was conducted on various pairs of receivers over large time spans. The possible influence of temperature variations inside the receivers over ISB values was also investigated. Our study is based on the 6 multi-GNSS receivers (2 Septentrio PolaRx4, 1 Septentrio PolaRxS, 1 Septentrio PolaRx5 and 2 Trimble NetR9) installed on the roof of our building in Liege. The estimated ISBs are then used as corrections in the multi- GNSS observation model and the resulting accuracy of multi-GNSS positioning is compared to GPS, Galileo and BeiDou standalone solutions. [less ▲]

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See detailChapter VIII "Equations and languages" in J.-É. Pin, Mathematical Foundations of Automata Theory
Stipulanti, Manon ULg

Conference (2016, December 16)

We present the chapter VIII titled "Equations and Langages" in Jean-Éric Pin, Mathematical Foundations of Automata Theory.

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See detail"'Unreadable' Texts: From the Metaphysical Detective Story to the Metacognitive Mystery Tale"
Dechene, Antoine ULg

Doctoral thesis (2016)

This dissertation aims at establishing the genealogy of a literary genre called the metacognitive mystery tale. Its main goal is to delineate a corpus of texts presenting "unreadable" mysteries which ... [more ▼]

This dissertation aims at establishing the genealogy of a literary genre called the metacognitive mystery tale. Its main goal is to delineate a corpus of texts presenting "unreadable" mysteries which, under the deceptively monolithic appearance of subverting "traditional" detective story conventions, offer a multiplicity of motifs – the overwhelming presence of chance, the unfulfilled quest for knowledge, the urban stroller lost in a labyrinthine text – that generate a vast array of epistemological and ontological uncertainties explored by the genre. The selected corpus, composed of some of the genre's most emblematic avatars as well as of less usual suspects, accounts for the specificity and heterogeneity of authors who, in different but related ways, have addressed a certain number of issues underlying the acquisition of knowledge. Following three major intertextual matrices based on the concepts of the "unreadable" city, the "dark" grotesque and the sublime, respectively, this project brings together texts by writers as diverse as Percy Bysshe Shelley, Edgar Allan Poe, Nathaniel Hawthorne, Herman Melville, Henry James, Horacio Quiroga, Jorge Luis Borges, Franz Kafka, Samuel Beckett, Paul Auster, Iain Sinclair and Roberto Bolaño under the banner of the metacognitive mystery tale. This approach represents an opportunity to gather canonical and barely academically studied works and provide new perspectives on stories dealing with the darker, more anxious aspects of investigations led by defective sleuths. [less ▲]

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See detailWho would want to live in there? A history of Posidonia oceanica detritus accumulations, the associated invertebrate community, and its food web…
Remy, François ULg; Michel, Loïc ULg; Darchambeau, François ULg et al

Conference (2016, December 16)

Most seagrasses are rarely consumed directly by herbivore organisms. The "detrital pathway" thus represents a potentially important way of transfer of the seagrasses production to the coastal food webs ... [more ▼]

Most seagrasses are rarely consumed directly by herbivore organisms. The "detrital pathway" thus represents a potentially important way of transfer of the seagrasses production to the coastal food webs. The case of Posidonia oceanica is particularly interesting since up to 90% of its foliar primary production may constitute extensive and highly dynamic exported litter accumulations. Preliminary studies concerning these detritus accumulations suggest that an abundant community of vagile macro invertebrates (size > 500μm) lives inside them. We characterized for the first time this community in an exhaustive way (multi-site, seasonal and multi-year study), we linked the observed density and diversity variations to environmental parameters, but also described the trophic web these invertebrates compose. We sampled an abundant (up to 5000 organisms/m²) community composed of 115 species. We showed that crustaceans were massively dominant, followed by annelids and mollusks, and that one single amphipod species Gammarella fucicola represented from 20 to 85% of the whole sampled community. Observed variations appeared to be mostly linked to litter oxygen water concentration in a very species specific way. Most species were linked to no measured environmental parameter at all, but several dominant species were demonstrated (observation and in situ experimentation) to be linked positively or negatively to litter oxygen concentration. The described food web was composed of more than 3 trophic levels, indicating the presence of a trophic web composed of primary consumers/detritivore species, of omnivore species, but also of first and second order predators, each level occupying a distinct isotopic niche. From a specific point of view, we highlighted several different feeding preferences, with SIAR mixing model runs indicating that some species feed mostly on detrital material, other species feed on a mixture of detrital and algal material, other species feed on both animal and vegetal material and finally predator species feed exclusively on animal material. The fact that P. oceanica detritus constituted a non-negligible food source for some dominant species confirmed the importance of this macrofauna community as a key transfer link of seagrass organic matter from P. oceanica to the coastal food webs. [less ▲]

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See detailInsects complex associated with the tropical basil, Ocimum gratissimum L. (Lamiaceae) in southern Benin.
Yarou, Boni Barthélémy ULg; Bokonon-Ganta, H. Aimé; Assogba Komlan, Françoise et al

Poster (2016, December 16)

Tropical basil is an aromatic leafy vegetable used for its medicinal and therapeutic properties in numerous countries in West Africa (Benin, Nigeria, Togo, etc.). In Benin, it is produced on almost all ... [more ▼]

Tropical basil is an aromatic leafy vegetable used for its medicinal and therapeutic properties in numerous countries in West Africa (Benin, Nigeria, Togo, etc.). In Benin, it is produced on almost all urban and periurban garden throughout the year for fresh market. Until now there are few or nearly no publications about the arthropod community of this specie, even less in the context of Benin. Thus, to assess this community, basil plots were mowed using a sweep net in three localities (Ouidah, Togba and Sèmè) of southern Benin. Preliminary results focus on the different insect families that colonized tropical basil in southern Benin environmental conditions. These include: Aphididae (Homoptera), Cercopidae (Homoptera), Chrysomelidae (Coleoptera), Coccinelledidea (Coleoptera), Meloidae (Coleoptera), Braconidae (Hymenoptera), Ichneumonidae (Hymenoptera), Formicidae (Hymenoptera), Vespidae (Hymenoptera), Apoidae (Hymenoptera), Reduviidae (Heteroptera), Pentatomidae (Heteroptera), Pyrgomorphidae (Orthoptera), Acrididae (Orthoptera), Syrphidae (Diptera), Diopsidae (Diptera). Among these families, there are pests: Aphis gossypii G. (Homoptera: Aphididae), Zonocerus variegatus L. (Orthoptera: Pyrgomorphidae), etc.; predators: Ischiodon aegyptius W. (Diptera: Syrphidae), Cheilomenes spp. (Coleoptera: Coccinelledidea), Rhynocoris spp. (Heteroptera: Reduviidae), etc.; parasitoids and pollinators. From this study, it appeared that there is a large diversity of families and functional groups (pests, predators, parasitoids and pollinators) associated with tropical basil . Moreover, the presence of natural enemies could be an advantage for farmers in intercropping systems. This would help reduce the use of synthetic insecticides. This result, which is a first knowledge of the insect fauna associated with tropical basil under the environmental conditions of Southern Benin, will be supplemented by a spatio temporal study to assess the variability and the dynamics of this insect fauna. [less ▲]

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See detailExploring a Mediterranean mesozooplankton 13 year time-series.
Fullgrabe, Lovina; Richir, Jonathan ULg; Batigny, Antoine et al

Poster (2016, December 16)

Zooplankton plays diverse crucial roles within the marine ecosystem and can also be used as bio- indicator of climate changes since it is very sensitive to environmental changes. Therefore it is essential ... [more ▼]

Zooplankton plays diverse crucial roles within the marine ecosystem and can also be used as bio- indicator of climate changes since it is very sensitive to environmental changes. Therefore it is essential to consider long-term plankton series. Given the analysis of plankton samples is time- consuming, it requires an effective and rapid analytical method. We have used in this work a supervised learning approach adapted for the semi-automatic classification of digital images of the mesozooplankton of the Bay of Calvi (Corsica, France) by using the Zoo/PhytoImage software. Together with a 11-years long zooplankton time-series, a set of nine environmental variables were monitored in order to identify controlling factors and determine whether the communities were sensitive to global environmental changes. The main components of the mesozooplankton community were characterized by both seasonal and inter-annual variability. Additionally, variation of holoplankton and meroplankton differentiated one from each other. The holoplanktonic community could be split into two subgroups according to its variation in function of the environment: cladocerans and appendicularians, and to a lesser extent, copepods on one hand, and cnidarians, chaetognathes and thaliaceans, on the other hand. Regarding inter-annual variation, one year (2007) showed particularly low production of total zooplankton which was also the case for all the different holoplanktonic taxa. Accounting for that phenomenon were identified some potentially underlying environmental factors. Finally, although water temperature increased significantly over the last years along with the frequency of marine heat wave events, no evident change in the global zooplankton composition was observed yet. [less ▲]

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See detailInstillation de surfactant chez le prématuré en respiration spontanée : méta-analyse
RIGO, Vincent ULg; LEFEBVRE, Caroline ULg; BROUX, Isabelle ULg

in Baud, Olivier; Saliba, Elie (Eds.) Congrès SFN-JFRN 2016, livre des communications (2016, December 15)

Justification: Lors du traitement par surfactant dit moins invasif (Less invasive surfactant therapy- LIST), le produit est instillé dans la trachée par un cathéter fin alors que l’enfant respire ... [more ▼]

Justification: Lors du traitement par surfactant dit moins invasif (Less invasive surfactant therapy- LIST), le produit est instillé dans la trachée par un cathéter fin alors que l’enfant respire spontanément sous CPAP. Différentes études ont donné des résultats variables mais encourageants. L’objectif de cette méta-analyse est de comparer le devenir respiratoire des prématurés traités par LIST avec celui de ceux traités par administration de surfactant par un tube endotrachéal. Méthodes : les études randomisées contrôlées (ERC) sont recherchées dans les bases de données et dans les références d’articles pertinents. Les devenirs respiratoires (dysplasie broncho-pulmonaire (DBP), décès ou DBP, échec précoce de CPAP, nécessité de ventilation invasive) et les morbidités classiques sont reprises de ces études. Pour chaque morbidité, le risque relatif (RR) des données mutualisées est calculé avec une analyse de Mantel-Haenszel à modèle d’effet aléatoire. Le RR est également calculé pour des sous-groupes établis selon l’intervention contrôle. Résultats : six ERC évaluent le LIST : 4 le comparent à l’INSURE (Intubation-Surfactant-Extubation), et les 2 autres à l’intubation (immédiate ou après maintient en CPAP) avec surfactant. Les méthodes LIST diminuent les risques de DBP (RR= 0,71 (0,52-0,99) ; nombre nécessaire à traiter NNT= 21), et de décès ou DBP (RR= 0,7 (0,58- 0,94) ; NNT= 15). L’échec précoce de CPAP et le recours à la ventilation invasive sont également réduits (RR= 0,67 (0,53-0,84) ; NNT= 8 et RR= 0,69 (0,53- 0,88) ; NNT= 6). Comparé à l’INSURE, le LIST diminue le risque combiné de décès ou DBP (RR= 0,63 (0,44-0,92) ; NNT= 11), et d’échec précoce de CPAP (RR=0,71 (0,53-0,96) ; NNT= 11). Les autres morbidités néonatales classiques sont similaires pour les différents groupes. Conclusions : une stratégie d’administration dite moins invasive de surfactant diminue les risques de morbidité respiratoire à moyen terme (DBP, décès ou DBP) et le recours à la ventilation invasive. Cette approche semble sure mais les données de suivi à long terme sont insuffisantes. [less ▲]

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See detailCathéters pour instillation moins invasive de SURFACTANT : une étude de simulation
RIGO, Vincent ULg; Debauche, Christian; Maton, Pierre et al

in Baud, Olivier; Saliba, Elie (Eds.) Congrès JFN-JFRN 2016, livre des communications (2016, December 15)

Introduction et objectifs : l’instillation trachéale de surfactant par un cathéter fin (Less invasive surfactant therapy- LIST) chez le prématuré sous CPAP permet de diminuer la morbidité respiratoire ... [more ▼]

Introduction et objectifs : l’instillation trachéale de surfactant par un cathéter fin (Less invasive surfactant therapy- LIST) chez le prématuré sous CPAP permet de diminuer la morbidité respiratoire. Plusieurs cathéters sont décrits à cette fin : une sonde oro-gastrique insérée avec (LISA-Köln, K) ou sans pince de Maggil (Take Care- Ankara, A), un cathéter veineux de 13 cm (MIST- Hobart, H), un cathéter d’angiographie de 30 cm (Stockholm, S) ou un cathéter ombilical fixé à un stylet d’intubation utilisé localement (Liège, L). L’objectif de l’étude est d’évaluer l’efficacité de ces techniques en prenant l’INSURE (Intubation-Surfactant-Extubation) comme référence. Intervention : 20 néonatologues travaillant dans 4 services ayant des stratégies d’administration du surfactant différentes ont participé. Ils ont simulé ces 6 techniques sur deux têtes d’intubation de difficulté croissante. L’efficacité de l’intervention est évaluée par le taux d’échec et la durée de procédure mesurée sur vidéo. Chaque intervenant apprécie la facilité d’utilisation sur une échelle de 1 à 9 (Difficile> facile). Résultats : Pour le premier modèle, les durées médianes de procédure pour Köln et Ankara sont allongées [K: 21s (IQR 17-24); A: 23s (15-42); H: 10s (8-16); S: 12s (10-22); L (10-20); INSURE: 14s (11-21); p<.0001]. Pour le second modèle, seul Liège permet une durée de procédure similaire à l’INSURE [K: 32s (25-44); A: 39s (27-95); H: 34s (27-46); S: 37s (29-42); L: 24s (15-35); INSURE: 24s (17-32); p<.002]. Les taux d’échec des méthodes LIST sont similaires entre eux (de 3 à 8/ 40 essais), mais supérieurs à celui de l’INSURE (0/40). Köln et Ankara sont considérés comme plus difficiles [scores de facilité : K: 5 (4-6); A: 3 (2-4); H: 6,5 (6-7); S: 7 (4-8); L: 8 (6,5-8); INSURE: 7 (6-8); p<.001]. Conclusions : les cathéters plus rigides sont plus efficaces et perçus comme plus simples d’utilisation. L’insertion d’un cathéter guidé et incurvé pourrait être plus rapide dans les cas difficiles. [less ▲]

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See detailAjustement des marqueurs d’insertion des tubes endotrachéaux selon l’âge gestationnel.
RIGO, Vincent ULg; Fayoux, Pierre

in Baud, Olivier; Saliba, Elie (Eds.) Congrès SFN-JFRN 2016, livre des communications (2016, December 15)

Introduction et objectifs: le positionnement adéquat d’un tube endotrachéal (TET) peut être difficile en raison de la marge de manœuvre limitée associée aux faibles distances laryngo-trachéales du ... [more ▼]

Introduction et objectifs: le positionnement adéquat d’un tube endotrachéal (TET) peut être difficile en raison de la marge de manœuvre limitée associée aux faibles distances laryngo-trachéales du prématuré. Les marqueurs distaux censés faciliter l’évaluation de ce positionnement ne sont pas standardisés entre les fabriquants, et le marquage généralement unique par taille de tube ne tient pas compte de la croissance associée à l’âge gestationnel. L’objectif de l’étude est de décrire les distances entre les cordes vocales (CV) et la moitié de la trachée en fonction de l’âge gestationnel et proposer des nouveaux marquages adaptés. Méthodes : la moitié de la longueur de la trachée ajoutée à la hauteur de la lame postérieure du cricoïde permet d’estimer la distance entre les CV et la moitié de la trachée (CV-MiTr). Ces longueurs sont issues à postériori d’une base de données prospective reprenant les distances détaillées du larynx et de la trachée mesurées lors d’autopsies de fœtus et nouveau-nés exempts de malformation des voies respiratoires (Fayoux et coll., Journal of anatomy 2008). Une corrélation est établie avec l’âge gestationnel. Résultats : les données proviennent de 121 patients. Il existe une corrélation linéaire entre la distance CV-MiTr et l’AG (r=0,91; y=2,6043+0,6275x; p<.0001). Des marqueurs d’insertion positionnés à 17,7; 18,9; 20,8; 22,7; 24,6 et 26,4 mm correspondraient à des AG de 24, 26, 29, 32, 35 et 38 semaines respectivement. Ils pourraient être indiqués par des lignes de couleurs contrastées. Conclusion : la relation linéaire entre la distance CV-mi-trachée et l’AG donne l’opportunité de revoir les marqueurs d’insertion des tubes endotrachéaux pour les patients les plus petits. Ces nouveaux marqueurs devraient être comparés cliniquement à ceux actuellement en usage avant d’être généralisés. [less ▲]

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See detailApplication des techniques de photogrammétrie par drone à la caractérisation des ressources forestières
Lisein, Jonathan ULg

Doctoral thesis (2016)

Une gestion raisonnée et multifonctionnelle des forêts n’est possible qu’avec une description à jour de l’état de la ressource naturelle. Les inventaires forestiers traditionnels, réalisés sur le terrain ... [more ▼]

Une gestion raisonnée et multifonctionnelle des forêts n’est possible qu’avec une description à jour de l’état de la ressource naturelle. Les inventaires forestiers traditionnels, réalisés sur le terrain, sont couteux et ne couvrent qu’un échantillonnage de la surface boisée. L’essor des drones civils pour la cartographie a initié une révolution dans le domaine de la télédétection environnementale. La polyvalence et la diversité des systèmes drones sont une aubaine pour la foresterie de précision. Ceux-ci sont utilisés pour la réalisation de cartographie très fine des habitats naturels avec une résolution temporelle et spatiale sans précédent. Nous explorons les possibilités d’utilisation de mini-drones pour la caractérisation quantitative et qualitative de la ressource forestière. Nous nous intéressons en particulier à l’estimation de la hauteur des arbres et à la caractérisation de la composition spécifique au sein de peuplements forestiers. La hauteur de la canopée est une variable dendrométrique de première importance : elle est un bon indicateur du stade de développement des peuplements et intervient notamment dans les estimations de biomasse ou de niveau de productivité. La composition spécifique est une information essentielle en regard des principales fonctions que remplit la forêt (conservation, production, récréation, etc). Nous avons comparé l’estimation de la hauteur des peuplements à partir de mesures LiDAR et celle obtenue par photogrammétrie. Bien que permettant une mesure de hauteur individuelle avec une incertitude de l’ordre de 1.04 m (RMSE) en feuillus, la photogrammétrie par drone sur des zones forestières est systématiquement moins précise que les mesures par LiDAR (RMSE de 0.83 m). Ces résultats sont cependant prometteurs, étant donné que la mesure sur terrain de la hauteur totale des arbres est également sujette à une importante imprécision. De plus, la grande flexibilité que confère les petits drones permet d’acquérir, au moment propice du stade de végétation, et l’information de relief de la canopée, et l’information spectrale. La période de fin de feuillaison, au début du mois de juin, s’est avérée le moment le plus propice à une discrimination automatique de cinq groupes d’essences feuillues (le chênes pédonculé, les bouleaux, l’érable sycomore, le frêne commun et les peupliers). Une erreur globale de classification des houppiers de 16% est obtenue avec des acquisitions monotemporelles, alors que l’utilisation d’images acquises à différentes dates permet encore d’améliorer cette classification (erreur globale de classification de 9% pour la meilleure combinaison de 3 dates). Les contraintes de la législation régissant l’utilisation des aéronefs sans pilote à bord restreignent le champs d’action des drones civils. Ainsi, afin d’assurer une sécurité pour tous les usagers de l’espace aérien, les opérations avec un drone sont limitées sous un seuil d’altitude et à une distance maximale du télépilote, ce qui ne permet pas une utilisation optimale de cette technologie pour la couverture de grands domaines forestiers (plusieurs milliers d’hectares). De plus, d’autres outils de télédétection utilisés en foresterie, tels que le LiDAR et l’imagerie satellite et aéroportée, sont plus compétitifs que les drones dès qu’il s’agit de couvrir de grandes surfaces (plusieurs milliers d’hectacre). C’est pourquoi nous pensons que les drones resterons un outils d’analyse de petites surfaces (dizaines voire centaines d’hectares), plus utiles à des fins de recherches scientifiques qu’à une utilisation en gestion forestière. [less ▲]

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See detailVibrio spp chez l’Homme - Vibrio spp bij de mens
MELIN, Pierrette ULg; SACHELI, Rosalie ULg

in POLET, Marie (Ed.) Vibrio spp dans l’alimentation et chez l’Homme - Formation (2016, December 15)

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See detailIntegrating Non-Collocated Well and Geophysical Data to Capture Lithological Heterogeneity at a Managed Aquifer Recharge and Recovery Site
Gottschalk, Ian; Hermans, Thomas ULg; Caers, Jef et al

Poster (2016, December 15)

Aquifer recharge and recovery (ARR) is the process of enhancing natural groundwater resources and recovering water for later use by constructing engineered conveyances. Insufficient understanding of ... [more ▼]

Aquifer recharge and recovery (ARR) is the process of enhancing natural groundwater resources and recovering water for later use by constructing engineered conveyances. Insufficient understanding of lithological heterogeneity at ARR sites often hinders attempts to predict where and how quickly infiltrating water will flow in the subsurface, which can adversely affect the quality and quantity of available water in the ARR site. In this study, we explored the use of electrical resistivity tomography (ERT) to assist in characterizing lithological heterogeneity at an ARR site, so as to incorporate it into a flow and contaminant transport model. In this case, we had non-collocated well core log data and ERT data from a full-scale ARR basin. We compared three independent methods for producing conditional lithology-resistivity probability distributions: 1) a search template to relate the nearest logged well lithologies with ERT resistivity panels, given search criteria; 2) a maximum likelihood estimation (MLE) to match bimodal normal distributions to the histogram of each ERT line; and 3) variogram-based lithology indicator simulations constrained to well data. Each approach leverages Bayes’ Rule to estimate lithology probability given electrical resistivity. The simplest approach (method 1) yields an erroneous conditional probability function where sand dominates the conditional probability at nearly all resistivities, due in part to the strong presence of sand in the wells nearest the ERT lines. The approaches using MLE and lithology simulations (methods 2 and 3) produce similar, more realistic lithofacies probability functions. The range of resistivities where clay and sand overlap differs between methods 2 and 3: ranging between 100 and 200 ohm-m for method 2, and between 30 and 50 ohm-m for the method 3. These differences affect the posterior lithology distributions in multiple point geostatistical (MPS) simulations, and in turn, predictions of flow from models which integrate these results. To test the models, we can compare measured breakthrough times of recharged water at the site to groundwater flow simulation results using the lithofacies models created by each method. The methods described here can inform the integration of non-collocated geophysical data into a variety of applications. [less ▲]

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