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See detailUsing GAit Measuring System (GAIMS) to discriminate patients with multiple sclerosis from healthy person
Azrour, Samir ULg; Pierard, Sébastien ULg; Van Droogenbroeck, Marc ULg

Poster (2013, November 07)

Among voluntary movements, gait is the most affected by multiple sclerosis. Gait impairment is also a good indicator of the disease progression. However, measurement of gait character- istics made by ... [more ▼]

Among voluntary movements, gait is the most affected by multiple sclerosis. Gait impairment is also a good indicator of the disease progression. However, measurement of gait character- istics made by neurologists is usually limited to the use of a stopwatch. The GAit Measuring System (GAIMS), provides a wider range of measurements that allow the definition of several relevant gait descriptors. The work presented here shows the effectiveness of these gait descriptors and machine learning techniques to discriminate between healthy persons and patients with multiple sclerosis. [less ▲]

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See detailStudying Vulnerability: Participation and Incident Reports
Rossignol, Nicolas ULg

Conference (2013, November 07)

Scholars in many fields of research have developed models, theories and concepts attempting to grasp and manage dangers that are often difficult to concretely imagine. Their final objective is to maintain ... [more ▼]

Scholars in many fields of research have developed models, theories and concepts attempting to grasp and manage dangers that are often difficult to concretely imagine. Their final objective is to maintain the safety of the system considered. Dealing with potential hazards, some researchers distinguish between the vulnerability approach and the risk approach. The risk based approach is focused on acquiring accurate probabilistic information about the events themselves. Yet, Sarewitz (2003: 806) reminds that “there are numerous cases in which accurate assessment of risk is impossible” and that “lack of experience with many phenomena and outcomes means that understanding the uncertainty of the uncertainty estimates is impossible”. Thus, beyond the risk-based approach, another perspective emerged: vulnerability analysis (VA). Vulnerability can be described as “the degree to which a system, subsystem, or system component is likely to experience harm due to exposure to a hazard” (Turner et al. 2003: 8074). VA seems capable of overcoming the shortcomings of risk analysis in situations where knowledge about both probabilities and outcomes is incomplete or insufficient (Sarewitz 2003). The vulnerability approach and the classical risk analysis approach are thus based on different premises (Gilbert 2006): while risk analysis focuses on the hazard, VA focuses on the system under threat. From that starting point, we realized in order to analyse the state-of-the art in the field of vulnerability analysis, with particular emphasis on participatory approaches. The aims were: i) to study how the concept of vulnerability has been defined and used in different fields of application (e.g. natural and industrial hazards) and ii) to analyse whether the theoretical claim that participatory approaches to vulnerability analysis have the potential for great scientific and political outputs has been actually demonstrated in practice. Based on this study we formulate a threefold critique: first, VA has been treated separately in natural and technological hazards fields. This separation is unproductive for a fine-grained understanding of what vulnerability can provide as a concept, as it prevents vulnerability to unleash the full range of its potential. Second, VA focused on assessment tools that are mainly quantitative, whereas qualitative appraisal is a key to assess vulnerability in a comprehensive way and to inform policy-making. Third, a systematic literature review on participatory VA case studies allows us to argue that participation has been important to address the above, but it remains too closed down in its approach and would rather benefit from embracing a more opened, encompassing perspective. Therefore, we suggest re-thinking participatory VA as one part of a dynamic process between opening-up and closing-down strategies, in order to support a reflexive vulnerability governance framework. Doing so is not exempt of challenges, though. Since analytical reflection on vulnerability is to be transferred into practices of risk and vulnerability governance, taking into account the context in which governance agents need to take appropriate decisions is of primary importance. Thus, based on the conclusion of this presentation, the practical ways of realizing a reflexive vulnerability governance should now be explored. [less ▲]

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See detail"Climate change" and vulnerability analysis: poor will become poorer
Ozer, Pierre ULg

Conference (2013, November 07)

The recent Intergovernmental Panel on Climate Change’s Fifth Assessment Report (IPCC-AR5) considers new evidence of climate change based on many independent scientific analyses from observations of the ... [more ▼]

The recent Intergovernmental Panel on Climate Change’s Fifth Assessment Report (IPCC-AR5) considers new evidence of climate change based on many independent scientific analyses from observations of the climate system, paleoclimate archives, theoretical studies of climate processes and simulations using climate models. “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased”. “Changes in many extreme weather and climate events have been observed since about 1950. It is very likely that the number of cold days and nights has decreased and the number of warm days and nights has increased on the global scale”. “It is likely that the frequency of heat waves has increased”. “There are likely more land regions where the number of heavy precipitation events has increased than where it has decreased”. “The frequency or intensity of heavy precipitation events has likely increased”. In the meantime, it is now well known that climate change consequences (increasing magnitude and frequency of droughts, floods, storms and/or coastal erosion) will mainly impact the most vulnerable. Although there are multiple ways to define vulnerability, we here define vulnerability as the exposure of individuals or collective groups to livelihood stress as a result of the impacts of such climate change and consecutive socioeconomic and environmental changes. In the context of this paper, we will focus on natural disasters induced by “climate change”. We will travel across developing countries to illustrate the increasing vulnerability of the poor and the way they –sometimes– develop effective adaptation responses. We conclude that, for many reasons (mainly the protection of individual, financial and/or political interests), the poor will become poorer. [less ▲]

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See detailMeasuring the thermophysical properties of materials at high temperature - Application to the additive manufacturing of alloy Ti-6Al-4V and of stainless steel 316L
Mertens, Anne ULg; Paydas, Hakan ULg; Reginster, Sylvie ULg et al

Conference (2013, November 07)

In view of optimising the microstructures of metallic materials and obtaining the desired properties, the accurate characterisation of the thermophysical behaviour of these materials has long been ... [more ▼]

In view of optimising the microstructures of metallic materials and obtaining the desired properties, the accurate characterisation of the thermophysical behaviour of these materials has long been considered of paramount importance e.g. by allowing for the in-situ study of phase transformations, by providing data for numerical simulations and, essentially, by contributing to a better understanding of the fundamental mechanisms at play during processing. In the present work, the thermophysical behaviour of Ti-alloy Ti-6Al-4V and of stainless steel 316L has been characterised in details, in order to reach a better understanding of the phenomena controlling the microstructures and mechanical properties of parts made by additive manufacturing techniques that appear nowadays very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic materials. In particular, the thermal conductivity of Ti-alloy Ti-6Al-4V and of stainless steel 316L at high temperature has been determined by combining dilatometry, Differential Scanning Calorimetry (DSC) and laser flash diffusivimetry based on Laplace’s equation : k(T)=α(T)ρ(T)Cp(T) where k(T) is the thermal conductivity (W/m*K) α(T) is the thermal diffusivity (mm2/s) ρ(T) is the specific mass (g/cm3) Cp(T) is the specific heat capacity (J/g*K). Since Ti-alloy Ti-6Al-4V and stainless steel 316L exhibit quite different physical behaviours, their careful comparison is shown to shed more light into the role of phenomena such as epitaxial growth, out-of-equilibrium phase transformations and/or internal stresses in the additive manufacturing of metallic materials. [less ▲]

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See detailMeasuring feet trajectories: challenges and applications
Pierard, Sébastien ULg; Azrour, Samir ULg; Van Droogenbroeck, Marc ULg

Conference (2013, November 07)

Measuring reliable feet trajectories is needed in many applications. This paper provides the principles used in GAIMS, which is a non-intrusive system that measures feet trajectories based on multiple ... [more ▼]

Measuring reliable feet trajectories is needed in many applications. This paper provides the principles used in GAIMS, which is a non-intrusive system that measures feet trajectories based on multiple range laser scanners. We present the technical challenges that we had to address, as well as an overview of the implemented processing pipeline of GAIMS. [less ▲]

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See detailPotential paleoseismological records in the Western Gulf of Corinth sediments (Greece) for the last 500 years
Beckers, Arnaud ULg; Mortier, Clément; Beck, Christian et al

Conference (2013, November 06)

Related to the Gulf of Corinth rifting, five earthquakes of magnitude greater than 5.8 occurred in the last 35 years. Consequently, the question of earthquake (EQ) hazard is particularly relevant. Onland ... [more ▼]

Related to the Gulf of Corinth rifting, five earthquakes of magnitude greater than 5.8 occurred in the last 35 years. Consequently, the question of earthquake (EQ) hazard is particularly relevant. Onland paleoseismological data are scarce and offshore data were absent before the present study. We investigated recent sediments bounding three well-defined major seismogenic faults: Aegion, Trizonia and Psathopyrgos faults. We retrieved 12 gravity cores from 50 to 85 cm long in three distinct sites: the southern shelf (40 to 50 m deep), a 180 m deep sub-basin, and a transect from the southern coast to the center of the gulf. Chronology is based on 137Cs (Atmospheric Nuclear Experiments) and 210Pb decay for two sites (Aegion and Trizonia). Considering sedimentation rates estimates in these areas, the longer cores record about 500 years of sedimentary archives. We performed granulometry, magnetic susceptibility, loss on ignition and geochemical (X-Ray Fluorescence) measurements on cores from each site. Some samples were observed with a binocular to identify the nature of the grains. We sought to identify layers potentially attributed to EQ-related processes like liquefaction and tsunamis for the sites on the shelves or mass transport and turbidity currents for the basins. In Aegion, 3 coarser layers have been identified at identical depth in 3 cores across the scarp. 210Pb decay show erosion just under the first event, that we attributed to the 1995 tsunami (backwash deposit) (figure). In the Trizonia Sub-Basin, among 3 clear grain-size peaks, two have been attributed to the 1817 Aegion EQ and the 1660 Galaxidi EQ. In Psathopyrgos, 10 “events” (grain-size and Zr/Rb peaks) have been identified in the deepest part of the transect and at least 2 on the shelf. Their analysis is in progress. [less ▲]

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See detailLate Quaternay sedimentation and active faulting in the Western tip of the Gulf of Corinth, Greece
Hubert, Aurelia ULg; Beckers, Arnaud ULg; Beck, Christian et al

Poster (2013, November 06)

The Gulf of Corinth is one of the fastest-spreading intracontinental rifts on Earth. Present day kinematics (GPS data) indicates an opening direction oriented NNE-SSW and an opening rate increasing ... [more ▼]

The Gulf of Corinth is one of the fastest-spreading intracontinental rifts on Earth. Present day kinematics (GPS data) indicates an opening direction oriented NNE-SSW and an opening rate increasing westward from 11 mm y-1 in the central part to 16 mm y-1 in the westernmost part. A significant part of the deformation is localized offshore, where the fault geometry was not well known yet. The high extension rate would imply a high seismic hazard if faults are not creeping. We propose an accurate map of submarine faults in the western extremity of the Gulf of Corinth. The map is based on two high-resolution seismic reflection surveys (single channel sparker) performed aboard HCMR’s R/V ALKYON, within the frame of SISCOR ANR Project. About 600 km of seismic lines were acquired, with a 200 msTWTT maximum penetration down to what we infer to represent the MIS 5 discontinuity. Depocenters location is controlled by river deltas where up to 75m of post-LGM sediments are stored. Numerous, up to 15m thick, mass transport deposits fill the central and eastern parts. In the eastern part, the sedimentary infill is faulted by the known North Eratini, South Eratini and West Channel faults. At the longitude of the Trizonia Island, the seafloor in mainly horizontal and the only fault is the south dipping Trizonia fault. Between the Trizonia Island and the Mornos Delta, the shallower northern part of the gulf shows a diffuse pattern of deformation with faults striking mainly E-W and ESE-WNW. It shows south and north dipping normal faults, strike-slip faults, as well as an inherited basement relief. To the West, three young grabens have been identified, striking NE-SW and W-E. The northern, 6 km long, fault in this grabens system shows a clear strike-slip component (fig.1). [less ▲]

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See detailFaire un film avec Adorno. Alexander Kluge et le cinéma de l'indécision
Hamers, Jérémy ULg; Cormann, Grégory ULg

Scientific conference (2013, November 06)

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See detailTerres rares et métaux critiques. Pénurie ou incurie ?
Pirard, Eric ULg

Scientific conference (2013, November 06)

De l’Âge de la Pierre à l’Âge du Lithium, nous n’avons eu de cesse de perfectionner nos technologies. Progressant dans la découverte et la compréhension de notre environnement, nous nous sommes mis à ... [more ▼]

De l’Âge de la Pierre à l’Âge du Lithium, nous n’avons eu de cesse de perfectionner nos technologies. Progressant dans la découverte et la compréhension de notre environnement, nous nous sommes mis à exploiter toutes les ressources naturelles disponibles. Aujourd’hui, il n’y a pratiquement aucun élément du tableau de Mendeleïev qui ne trouve son champ d’application spécifique : du lithium dans les batteries à l’indium dans les écrans en passant par le tantale dans les capacités. Baignant quotidiennement dans un tel univers d’abondance, nous en oublions d’où proviennent ces ressources. Nous avons refoulé cette question au plus profond de nous-mêmes et avons poussé le syndrome NIMBY (not in my backyard) jusqu’à atteindre le NIMYCON (not in my continent). Depuis quelques années, l’Europe vit un réveil brutal. Elle réalise qu’elle ne produit que 3 % des métaux alors qu’elle en consomme plus de 20 %. Elle réalise que toute son industrie est dépendante de pays émergents qui ont l’ambition de développer un tissu industriel puissant sur base de leur accès aux ressources. L’Europe serait-elle un continent maudit ? Aurait-elle épuisé ses ressources ? Est-elle condamnée à dépendre de pays tiers pour poursuivre sa fuite en avant vers les « hautes technologies  » ? Nullement, mais il est évident qu’il n’y aura pas de ré-industrialisation sans une réflexion sur les matières premières. Le mot d’ordre aujourd’hui est Resource Efficiency. Certains traduisent cela par la nécessité de mettre au point des nouveaux matériaux moins gourmands en matières premières ou évitant l’utilisation d’éléments dits « critiques ». Mais en réalité, dans un monde avide de technologies qui voit le nombre de consommateurs croître sensiblement, il faudra nécessairement ouvrir de nouvelles mines et veiller à ne plus disperser dans l’environnement les métaux que nous en aurons laborieusement extraits. Pour l’Europe, cela signifie concrètement qu’il est temps de relancer la prospection du sous-sol et de développer une culture du recyclage intelligente et écologique. Il y a là un champ d’opportunités à saisir pour l’innovation et le développement de technologies qui sont restées trop longtemps dans l’ombre! Le Resource Efficiency c’est aussi extraire les métaux des minerais et des déchets électriques et électroniques en utilisant des procédés moins gourmands en énergie, en eau et en matière. Au travers de quelques exemples choisis, cet exposé présentera l’évolution des technologies et la nature des matières premières utilisées. Partant de la géochimie d’un simple jardin de banlieue, il introduira le concept de gisement qui est indispensable à une bonne compréhension des ressources et des réserves que recèle encore notre sous-sol. Suscitant la réflexion sur la nécessité de maintenir une industrie extractive, cette présentation analysera aussi les difficultés tant sociologiques que technologiques à mener à bien un recyclage efficace des ressources. [less ▲]

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See detailSimulations, Normes, Soufflerie en ingénierie du vent : Quel outil pour quelle application ?
Frère, Ariane; Andrianne, Thomas ULg; Parmentier, Benoit

Conference given outside the academic context (2013)

Cette présentation a pour objectif de présenter les 3 moyens principaux de mener une étude technique dans le domaine de l'ingénierie du vent : simulation numérique, essais en soufflerie et normes. Les ... [more ▼]

Cette présentation a pour objectif de présenter les 3 moyens principaux de mener une étude technique dans le domaine de l'ingénierie du vent : simulation numérique, essais en soufflerie et normes. Les avantages et inconvénients, ainsi que la complémentarité des 3 approches sont présentés et discutés. [less ▲]

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See detailAn optimum PML for scattering problems in the time domain
Modave, Axel ULg; Kameni, Abelin; Lambrechts, Jonathan et al

in European Physical Journal : Applied physics (2013), 64(2), 24502

In electromagnetic compatibility, scattering problems are defined in an infinite spatial domain, while numerical techniques such as finite element methods require a computational domain that is bounded ... [more ▼]

In electromagnetic compatibility, scattering problems are defined in an infinite spatial domain, while numerical techniques such as finite element methods require a computational domain that is bounded. The perfectly matched layer (PML) is widely used to simulate the truncation of the computational domain. However, its performance depends critically on an absorption function. This function is generally tuned by using case-dependent optimization procedures. In this paper, we will present some efficient functions that overcome any tuning. They will be compared using a realistic scattering benchmark solved with the Discontinuous Galerkin method. [less ▲]

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See detailSmart drug delivery systems based on specifically-designed macromolecules and inorganic colloids
Liu, Ji ULg

Doctoral thesis (2013)

In the past few decades, various hybrid nano-vehicles have been developed as new drug delivery systems (DDS), in which inorganic and organic components are integrated within a nano-object. An ideal DDS ... [more ▼]

In the past few decades, various hybrid nano-vehicles have been developed as new drug delivery systems (DDS), in which inorganic and organic components are integrated within a nano-object. An ideal DDS should satisfy the conflicting requirements for high stability in extracellular fluid, so that it maintains its integrity during the in vivo circulation; however, it becomes labile upon the activation of internal or external stimuli after targeting to the disease sites, allowing the triggered release of therapeutic agents. The aim of this thesis was to build different hybrid nano-vehicles, explore the possibility to manipulate the release behaviors and evaluate their potential biomedical application. The first part presents an original work on reversibly-crosslinked nanogels based on poly(vinyl alcohol)-b-poly (Nvinylcaprolactam) copolymers. The second part is devoted to stimuli-responsive hybrid nanovehicles, composed of inorganic cores, e.g. maghemite nanoparticles or gold nanorods, and a stimuli-responsive polymer corona, e.g. poly(vinyl alcohol)-b-poly(acrylic acid) or poly(ethyl glycol)-b-poly(N-vinylcaprolactam). The third part focuses on core-shell nanoparticles made of a maghemite core and a mesoporous silica shell, while phase-changed molecules, e.g. 1-tetradecanol with melting temperature of 39 °C, were introduced as gatekeepers to regulate the release behaviors. These different nanostructures were developed as DDS to accommodate cargo molecules, and the triggered cargo release upon variation in pH or temperature, activation of reductive agent or presence of glucose was explored. Moreover, remote stimuli, e.g. alternating magnetic field or near infrared light, were also applied to trigger the release. Studies on cytotoxicity, cellular uptake and in vitro triggered release with cell culture are also described. [less ▲]

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See detailLa coopération en RDC : une politique facultaire et institutionnelle
Lecocq, Pascale ULg

Conference given outside the academic context (2013)

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See detailDe la paléoécologie à l'écologie actuelle : 2000 ans d'interaction homme-milieu dans le nord du Bassin du Congo
Morin-Rivat, Julie ULg; Bentaleb, Ilham; Biwole, Achille ULg et al

Poster (2013, November 06)

La forêt tropicale africaine a longtemps été considérée comme vierge du passage de l’homme. Cependant, plusieurs études récentes en paléoécologie et archéologie ont démontré la présence d’activités ... [more ▼]

La forêt tropicale africaine a longtemps été considérée comme vierge du passage de l’homme. Cependant, plusieurs études récentes en paléoécologie et archéologie ont démontré la présence d’activités humaines anciennes à partir d’indices paléoenvironnementaux (i.e. pollens de plantes anthropophiles) et d’artefacts (i.e. tessons de céramique). Ces études sont toutefois trop rares en raison de difficultés de terrain pour repérer et accéder aux sites archéologiques (couvert végétale dense, absence de pistes). De grandes zones à l’intérieur des terres demeurent donc inexplorées. Par ailleurs, peu d’études se sont penchées sur la question de l’impact de ces activités anthropiques passées sur la structure et la composition de la végétation actuelle. Grâce à une approche multidisciplinaire à la frontière entre sciences humaines et sciences de l’environnement (archéologie, pédoanthracologie : charbons de bois des sols, écologie forestière), notre objectif est d’identifier des indices d’activités humaines anciennes, lesquels sont été mis en relation avec les patrons actuels de végétation. Nos trois zones d’étude sont localisées en forêt tropicale humide de type guinéo-congolais et sont réparties dans le sud-ouest et sud-est du Cameroun et le nord de la République du Congo. Le long d’une vingtaine de transects de plusieurs kilomètres, nous avons appliqué un protocole systématique de récolte de matériel archéologique et archéobotanique dans des fosses situées sur des parcelles d’inventaire botanique. Ceci nous a permis de récolter plus d’un millier d’échantillons contenant des macrorestes végétaux carbonisés ainsi que des artefacts inédits pour la région (pierre taillée et polie, tessons de céramique, scories de métallurgie) et d’inventorier la végétation dans l’environnement immédiat des découvertes. L’analyse spatiale et temporelle (chronologie relative et par datation radiocarbone) des macrorestes a permis d’identifier des villages entourés de probables champs agricoles (agriculture itinérante sur brûlis). Les 68 datations radiocarbones et les types céramiques obtenus suivent une chronologie archéologique en deux phases : un âge du Fer ancien entre 2300 et 1300 BP et un âge du Fer récent se poursuivant jusqu’à la période subactuelle, entre 670 et 20 BP. Entre ces deux phases d’occupation, les traces d’activités anthropiques sont rares. La première phase d’activités serait à mettre en relation avec une fragmentation de la forêt dense à la suite d’un épisode climatique aride autour de 2500 BP, permettant ainsi aux populations de pénétrer la forêt. Un épisode plus humide à partir de 800 BP, avec un retour d’un couvert plus dense, aurait fait reculer les populations humaines. Leur rétablissement dans les forêts se serait produit conjointement à des conditions plus sèches. Ces trois phases rejoignent la chronologie générale établie à l’échelle de l’Afrique centrale. Les premiers taxons identifiés parmi les macrorestes végétaux carbonisés, graines et charbons de bois, démontrent l’utilisation ancienne du palmier à huile et d’arbres fruitiers sauvages. Les espèces ligneuses identifiées sont présentes dans le cortège floristique actuel. L’identification taxonomique des charbons de bois devrait nous permettre de reconstituer l’environnement végétal au cours des deux derniers millénaires. Les différences observées dans les couverts forestiers passé et actuel en termes de composition floristique ainsi que la structure des peuplements actuels sont de bons indicateurs d’impacts récents de l’homme sur son milieu. [less ▲]

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See detailBLOOD GROUPS, HEMOGLOBIN PHENOTYPES AND CLINICAL DISORDERS OF CONSANGUINEOUS YANSI POPULATION
Munlemvo Mavanga, Nana ULg; BOEMER, François ULg; SEIDEL, Laurence ULg et al

in World Journal of Hematology (2013), 2(4), 109-114

AIM To study frequency of blood groups, prevalence of sickle-cell anemia trait and glucose-6-phosphate dehydrogenase deficiency, among consanguineous Yansi tribe. METHODS A total of 525 blood samples were ... [more ▼]

AIM To study frequency of blood groups, prevalence of sickle-cell anemia trait and glucose-6-phosphate dehydrogenase deficiency, among consanguineous Yansi tribe. METHODS A total of 525 blood samples were collected, of which 256 among the Yansi population, and 269 for the unrelated control group in the Bandundu province of Democratic Republic of Congo. Blood group antigens were determined in the following systems: ABO, Rh, Kell, Duffy, Kidd and MNS. Blood grouping and extended phenotype tests were performed according to standard immunohematological procedures. Spot tests and tandem mass spectrometry were used respectively for the assessment of glucose-6-phosphate dehydrogenase deficiency and sickle-cell anemia trait. RESULTS The frequency of ABO phenotypes conformed to the following order O>A>B>AB with notably 62.5, 23.8, 12.1 and 1.6% for the Yansi, and 54.6, 27.5, 14.1 and 3.7% for the unrelated control group, respectively (P=0.19). As for the Rh phenotypes, the most frequent were ccD.ee, ccD.Ee, CcD.ee, corresponding to 71.5, 12.1 and 12.1% for the Yansi, and 70.6, 15.6 and 8.2%, for the unrelated control group (P=0.27). The frequency of MN and Ss phenotypes were statistically different between groups (P=0.0021 and P=0.0006). G6PD deficiency was observed in 11.3% of subjects in the Yansi group, and in 12.4% of controls (P = 0.74). The sickle-cell anemia trait was present in 22.4% of Yansi subjects and 17.8% in the control group (P=0.24). Miscarriages and deaths in young age were more common among Yansi people. CONCLUSION This study shows a significant difference in MNS blood group distribution between the Yansi tribe and a control population. The distribution of other blood groups and the prevalence of hemoglobinopathies did not differ in the Yansi tribe. [less ▲]

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See detailImpacts of past Human disturbances on present-day tree species assembly in a tropical forest of South-East Cameroon
Vleminckx, Jason; Doucet, Jean-Louis ULg; Daïnou, Kasso ULg et al

Poster (2013, November 06)

Many evidence have been found for intensive past Human presence in the forests of Central Africa, notably widespread charcoal occurrence in the soil. Forest clearing for slash-and-burn agriculture may ... [more ▼]

Many evidence have been found for intensive past Human presence in the forests of Central Africa, notably widespread charcoal occurrence in the soil. Forest clearing for slash-and-burn agriculture may have favored the competitiveness of light-demanding species (LD) to the detriment of shade-bearer species (SB). Hypothesis: Positive correlation between abundance of charcoal in the soil (proxy for past Human clearing) and abundance of LD.Mostly “young” charcoals were thought to reflect past Human disturbances that would have shaped present-day species assembly. However, CAI 0-20cm and CAI 20-100cm were highly correlated with each other (r-Pearson = 0.55; P<0.001) and both displayed positive correlations with Non-Pioneer LD abundance (significant with a classic test) and negative correlations with SB abundance. Although this observation is coherent with our hypothesis, significance disappeared when correcting for spatial autocorrelation [4], even after removing small-diameter trees potentially too young to be linked with last Human disturbances (not shown). Correlation of CAI between the two soil layers => Humans found appropriate conditions for settlement in the same area at different periods? Absence of significant correlation in ❸ (i) Last Human disturbances are too old to detect any signal on present-day tree species assembly. (ii) Human impact is weak compared to other factors (soil properties, dispersal limitation,…) (iii) Local scale heterogeneity of LD abundance is weak compared to landscape scale. Parallel large scale gradients in the abundance of Non-Pioneer LD and charcoal abundance (proxy for past slash-and-burn activities) were observed, but a causal link cannot be established so far. [less ▲]

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See detailLe genre Guibourtia Benn: un modèle biologique idéal pour comprendre les mécanismes de spéciation
Tosso, Dji-ndé Félicien ULg; Daïnou, Kasso ULg; Hardy, Olivier et al

Poster (2013, November 06)

Les forêts denses tropicales humides se distinguent par leur grande diversité biologique qui leur confère un caractère complexe. Dans un tel contexte, comprendre le passé et l'histoire évolutive de la ... [more ▼]

Les forêts denses tropicales humides se distinguent par leur grande diversité biologique qui leur confère un caractère complexe. Dans un tel contexte, comprendre le passé et l'histoire évolutive de la dynamique de ces forêts, constitue un moyen efficace pour prédire leur dynamique future. De telles études qui traitent de la biologie évolutive (phylogénie et phylogéographie) sont rares en Afrique comparativement aux autres continents. Le présent travail ambitionne de contribuer, sur base d’un modèle biologique comportant plusieurs espèces sœurs, à la compréhension des mécanismes à l'origine de la diversité des écosystèmes forestiers tropicaux. Le modèle biologique choisi est le genre Guibourtia Benn daté de moins de 20.000 ans qui regroupe 13 espèces ligneuses africaines de grande importance socio-culturelle et économique. Ce modèle rassemble non seulement des espèces de formations végétales différentes (forêt et savane) mais aussi des espèces inféodées aux régions établies sur des sols variés (sableux, argilo-limoneux, calcaire, hydromorphe etc.). Spécifiquement, l’étude vise à (i) démêler les relations phylogénétiques au sein du genre Guibourtia sur la base de caractérisations physiologique et morphogénétique; (ii) inférer l'histoire évolutive au sein du genre Guibourtia grâce aux récents outils d'analyse phylogéographique et de datation moléculaire ; et (iii) examiner les possibilités de flux de gènes entre deux espèces morphologiquement semblables à savoir G. tessmannii (Harms) J. Léonard et G. pellegriniana J. Léonard à l’échelle du Gabon. Ce travail se distingue par son originalité du fait qu’il développe une approche qui combine la physiologie et la génétique. Les résultats contribueront à modéliser la distribution des différentes unités évolutives du genre Guibourtia avec un modèle dynamique de végétation (CARAIB) afin de conclure sur leur statut de conservation et déduire les stratégies de gestion durable appropriées. [less ▲]

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