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See detailLimit Cycle Oscillation Control and Suppression
Dimitriadis, Grigorios ULg; Cooper, Jonathan E

in Aeronautical Journal (1999), 103(1023), 257-263

The prediction and characterization of the Limit Cycle Oscillation (LCO) behaviour of nonlinear aeroelastic systems has become of great interest recently. However, much of this work has concentrated on ... [more ▼]

The prediction and characterization of the Limit Cycle Oscillation (LCO) behaviour of nonlinear aeroelastic systems has become of great interest recently. However, much of this work has concentrated on determining the existence of LCOs. This paper concentrates on LCO stability. By considering the energy present in di®erent limit cycles, and also using the Harmonic Balance Method, it is shown how the stability of limit cycles can be determined. The analysis is then extended to show that limit cycles can be controlled, or even suppressed, by the use of suitable excitation signals. A basic control scheme is developed to achieve this, and is demonstrated on a simple simulated nonlinear aeroelastic system. [less ▲]

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See detailLimit Cycle Oscillations of a Delta Wing in a Low Speed Wind Tunnel
Korbahti, Banu; Kagambage, Emile ULg; Andrianne, Thomas ULg et al

in Proceedings of ISMA2010 (2010, September 22)

Limit cycle oscillations involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of structural or aerodynamic nonlinearity. In this paper, a ... [more ▼]

Limit cycle oscillations involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of structural or aerodynamic nonlinearity. In this paper, a flexible half-Delta wing is tested in a low speed wind tunnel in order to investigate its dynamic response. Specifically, an investigation to determine the effects of a steady angle of attack on nonlinear Limit Cycle Oscillations (LCO) of a delta wing-plate model in low subsonic flow has been undertaken. It was found that, at several combinations of airspeed and angle of attack, the wing undergoes limit cycle oscillations. Two types of such oscillations are observed. One of them is low amplitude, low complexity limit cycle oscillations that occur at lower airspeeds; the other is high amplitude, high complexity limit cycle oscillations that occur a higher airspeeds and can appear abruptly. Some of the LCOs are the result of a subcritical Hopf bifurcation occurring at low steady angles of attack. At higher angles, a nontypical bifurcation was observed, whereby LCOs appear, grow with airspeed but then diminish and finally disappear as the airspeed is increased further. [less ▲]

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See detailLimit Cycle Prediction For Subsonic Aeroelastic Systems Using Nonlinear System Identification
Dimitriadis, Grigorios ULg; Vio, Gareth Arthur; Cooper, Jonathan Edward

in Ferman, M. A.; Petersson, B. A. T.; Rizzi, S. A. (Eds.) et al Proceedings of the VIII International Conference on Recent Advances in Structural Dynamics (2003, July)

The prediction of aeroelastic instabilities caused by nonlinear unsteady aerodynamic forces acting on aircraft has recently become an important area of research. Emphasis is placed on the capability to ... [more ▼]

The prediction of aeroelastic instabilities caused by nonlinear unsteady aerodynamic forces acting on aircraft has recently become an important area of research. Emphasis is placed on the capability to predict the occurrence of Limit Cycle Oscillations (LCOs) at both the design and prototype testing stages. In this paper, the prediction of LCOs is attempted for a simulated aeroelastic system subjected to nonlinear subsonic unsteady aerodynamic forces, using system identification. Response data from the simulated system are curve-fitted by means of a series of polynomial basis functions. This approach yields very accurate identified models of the actual system at individual flight conditions. These identified models are extrapolated to a global aeroelastic identified model. Using this model, the flight conditions at which LCOs occur is accurately predicted but the amplitude of the oscillations is underestimated. [less ▲]

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See detailLimit cycling behavior of a hybrid system: Application to percussive drilling
Depouhon, Alexandre ULg; Detournay, Emmanuel; Denoël, Vincent ULg

in Proceedings of the 2nd International Colloquium on Non-Linear Dynamics and Control of Deep Drilling Systems, Eindhoven, May 2012 (2012, May)

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See detailLimitation des reliquats azotes apres cereales d'hiver par un raisonnement approprie de la fumure azotee.
Bodson, Bernard ULg; Falisse, André ULg; Guiot, Joseph

in Calvet, R. (Ed.) Nitrates-agriculture-eau: Symposium international (1990, November 07)

L'azote minéral présent dans le sol et son utilisation par le froment d'hiver ont été régulièrement suivis dans trente-cinq essais installés au cours de six années. Il en ressort que la fumure azotée ... [more ▼]

L'azote minéral présent dans le sol et son utilisation par le froment d'hiver ont été régulièrement suivis dans trente-cinq essais installés au cours de six années. Il en ressort que la fumure azotée optimale (dose totale et fractionnement) est propre à être calculé en fonction des facteurs pédoclimatiques, du passé cultural de la parcelle et de l'état de la culture. La fumure ainsi déterminée permet d'atteindre un rendement proche de l'optimum économique tout en limitant au maximum les reliquats en azote minéral après culture. [less ▲]

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See detailLimitation du patrimoine commun
Leleu, Yves-Henri ULg

in Bourgeois, Marc; Leleu, Yves-Henri; Verbeke, A. (Eds.) et al Manuel de planification patrimoniale. Le couple, vie commune (2009)

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See detailThe limitation of the plausible values
Monseur, Christian ULg; Adams, Ray

in Garner, M. L.; Engelhard, G.; Wilson, M. (Eds.) Advances in Rasch Measurement (2010)

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See detailLimitation of the Pupil Replication Technique in the Presence of Instrumental Defects
Riaud, Pierre ULg; Mawet, Dimitri; Absil, Olivier ULg

in Astrophysical Journal Letters (2005), 628

Pupil replication has been proposed by Greenaway et al. as a new optical technique to improve the suppression of starlight in high dynamic imaging. This Letter extends numerical simulations in the two ... [more ▼]

Pupil replication has been proposed by Greenaway et al. as a new optical technique to improve the suppression of starlight in high dynamic imaging. This Letter extends numerical simulations in the two-dimensional case with various realistic imperfections (surface error, chromatic smearing, and pupil shift). These results demonstrate some strong limitations compared to single-pupil apodization techniques for exoplanet detection. [less ▲]

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See detailLimitations in transplantation of astroglia-biomatrix bridges to stimulate corticospinal axon regrowth across large spinal lesion gaps
Deumens, Ronald; Koopmans, Guido C; Honig, Wiel MM et al

in Neuroscience Letters (2006), 400(3), 208-212

Regrowth of injured axons across rather small spinal cord lesion gaps and subsequent functional recovery has been obtained after many interventions. Long-distance regeneration of injured axons across ... [more ▼]

Regrowth of injured axons across rather small spinal cord lesion gaps and subsequent functional recovery has been obtained after many interventions. Long-distance regeneration of injured axons across clinically relevant large spinal lesion gaps is relatively unexplored. Here, we aimed at stimulating long-distance regrowth of the injured corticospinal (CS) tract. During development, an oriented framework of immature astrocytes is important for correct CS axon outgrowth. Furthermore, a continuous growth promoting substrate may be needed to maintain a CS axon regrowth response across relatively large spinal lesion gaps. Hence, we acutely transplanted poly(D,L)-lactide matrices, which after seeded with immature astrocytes render aligned astrocyte-biomatrix complexes (R. Deumens, et al. Alignment of glial cells stimulates directional neurite growth of CNS neurons in vitro. Neuroscience 125 (3) (2004) 591-604), into 2-mm long dorsal hemisection lesion gaps. In order to create a growth promoting continuum, astrocyte suspensions were also injected rostral and caudal to the lesion gap. During 2 months, locomotion was continuously monitored. Histological analysis showed that astrocytes injected into host spinal tissue survived, but did not migrate. None of the astrocytes on the biomatrices survived within the lesion gap. BDA-labeled CS axons did not penetrate the graft. However, directly rostral to the lesion gap, 120.9 +/- 38.5% of the BDA-labeled CS axons were present in contrast to 12.8 +/- 3.9% in untreated control animals. The observed anatomical changes were not accompanied by locomotor improvements as analyzed with the BBB and CatWalk. We conclude that although multifactorial strategies may be needed to stimulate long-distance CS axon regrowth, future studies should focus on enhancing the viability of cell/biomatrix complexes within large spinal lesion gaps. [less ▲]

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See detailLimitations of the current practice in neonatal PN across Europe
SENTERRE, Thibault ULg

in 3rd International Congress of Union of European Neonatal and Perinatal Societies (2012, November)

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See detailLimitations of the use of GFP transgenic mice in bone marrow transplantation studies.
Van Overstraeten-Schlogel, Nancy; Delgaudine, Marie ULg; Beguin, Yves ULg et al

in Leukemia & Lymphoma (2006), 47(7), 1392-3

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See detailLa limite Paléocène-Eocène dans le Bassin de Douala Biostratigraphie et essai de reconstitution des paléoenvironnements
Mbesse, Cecile Olive ULg

Doctoral thesis (2013)

ABSTRACT This work consists of the analysis of the palynoflora (dinoflagellates and sporomorphs) identified from four petroleum exploration wells drilled through the Nkapa Formation (Douala Basin ... [more ▼]

ABSTRACT This work consists of the analysis of the palynoflora (dinoflagellates and sporomorphs) identified from four petroleum exploration wells drilled through the Nkapa Formation (Douala Basin, Cameroon). The vertical distribution of index taxa in the Moulongo, Ngata, Mamiwater and North Matanda wells allowed establishing a biostratigraphic frame of the first half of the Paleogene of the Douala Basin and identifying the Paleocene/Eocene boundary in each well through a comparison with surrounding sedimentary basins. Seventy dinoflagellate species have been identified, among which 30 are stratigraphically informative. Four biozones have been established, three for the Paleocene and one for the Early Eocene. The biozone 1 is characterized by Cretaceous species such as Cerodinium diebelii, Lejeunecysta hyalina, Andalusiella gabonensis, Palaeocystodinium australinum and Palaeocystodinium golzowense. The biozone 2 is defined by the acme of Areoligera coronata, Adnatosphaeridium multispinosum and Glaphyrocysta ordinata. The biozone 3 is defined by the acme of several Apectodinium species (A. hyperacanthum, A. homomorphum, A. paniculatum, A. parvum, A. quinquelatum). The biozone 4 is defined by the occurrence of Eocene taxa such as Deflandrea cf. oebisfeldensis, Hystrichosphaeridium tubiferum and Wetzeliella sp. Based on the position of the Paleocene/Eocene boundary in the Moulongo well, correlations have been established with the others sedimentary sequences analysed. Our study shows that, as previously demonstrated for Nigeria in an other study, the acme of Apectodinium in the Douala Basin can be attributed a Late Paleocene age and hence occurred before the carbon isotope excursion (CIE) of the Paleocene-Eocene boundary and the coeval Paleocene-Eocene thermal maximum (PETM). The acme of Apectodinium in the Douala Basin is thus markedly diachronous with the Apectodinium acme identified in various Nordic Basins, where it is contemporaneous with the PETM (earliest Eocene). Ninety-four sporomorph species have been recognized, among which fifty are stratigraphically informative. Three biozones have been established. The biozone 1 is predominantly characterized by Palmae- and Proteaceae-type pollens, the latter with Cretaceous characteristics. The biozone 2, Late Paleocene in age, is characterized by a transition from original floras towards more « modern » floras. The biozone 3 is earliest Eocene in age and shows the early steps of the extant « Leguminosae flora » of West Africa. Together with the biostratigraphic analysis, a palaeoenvironmental reconstruction is proposed, based on dinoflagellate ecology, on the evolution of the dinoflagellate /sporomorph ratio, as well as on the reconstruction of the plant environments in the studied sedimentary sequences. The evolution of the Douala Basin during the timespan studied occurred according to two geographical axes: a WE (Moulongo-Ngata) axis and a SSW-NNE (Moulongo-Mamiwater-North Matanda) axis. During the Early and Middle Paleocene, the Douala Basin was open towards the sea and showed a coastal-estuarine environment, with marginal mangroves and lowland swamp forests. During the Late Paleocene, the marine character of the sedimentation was less prominent as brackish fluvio-lagoonal intertidal environments developped. They were accompanied by gallery forests and surrounded by dense, periodically flooded, forests northwards and by forests on wet soils eastwards. During the earliest Eocene, a marine regression occurred. The palaeoenvironments included confined coastal lagoon systems with a peripheral impoverished local flora northwards, and moist, dense, evergreen forests eastwards. [less ▲]

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See detailLa limite Paléocène-Eocène dans le Bassin de Douala Biostratigraphie et essai de reconstitution des paléoenvironnements
Mbesse, Cécile ULg

Doctoral thesis (2013)

RESUME Ce travail présente une analyse du phytoplancton et des sporomorphes recensés dans divers puits de prospection pétrolière ayant traversé la Formation de Nkapa dans le Bassin de Douala au Cameroun ... [more ▼]

RESUME Ce travail présente une analyse du phytoplancton et des sporomorphes recensés dans divers puits de prospection pétrolière ayant traversé la Formation de Nkapa dans le Bassin de Douala au Cameroun. La distribution verticale de taxons marqueurs dans les sondages de Moulongo, Ngata, Mamiwater et Nord Matanda a permis d’établir une biostratigraphie du Tertiaire inférieur du Bassin et d’y préciser la position de la limite Paléocène-Eocène sur base d’une comparaison avec les bassins sédimentaires avoisinants. En considérant trente espèces de dinoflagellés à caractère stratigraphique sur les quelque septante inventoriées, quatre biozones ont pu être établies, trois pour le Paléocène, une pour l’Eocène basal. La biozone 1 se caractérise par des espèces héritées du Crétacé, Cerodinium diebelii, Lejeunecysta hyalina, Andalusiella gabonensis, Palaeocystodinium australinum et Palaeocystodinium golzowense; les biozones 2 et 3 par les acmés de certaines espèces, pour la 2, de Areoligera coronata, Adnatosphaeridium multispinosum et Glaphyrocysta ordinata, pour la 3, de diverses espèces du genre Apectodinium (A. hyperacanthum, A. homomorphum, A. paniculatum, A. parvum, A. quinquelatum). La biozone 4 voit apparaître des espèces caractéristiques de l’Eocène: Deflandrea cf. oebisfeldensis, Hystrichosphaeridium tubiferum et Wetzeliella sp. En tenant compte de la limite Paléocène/Eocène établie par les stratigraphes pétroliers à Moulongo, les corrélations ont été précisées avec les autres séquences analysées. L’étude a mis en évidence l’existence d’un diachronisme entre deux acmés d’Apectodinium, celui pré-CIE (Carbon Isotope Excursion) observé au Paléocène supérieur dans le Bassin de Douala comme dans celui du Nigeria voisin et celui contemporain du PETM (Paleocene-Eocene Thermal Maximum) dans l’Eocène basal de divers bassins nordiques passés en revue dans le travail. Sur les nonante-quatre espèces de sporomorphes identifiées, une cinquantaine de taxons a été retenue dans un objectif biostratigraphique. Trois biozones à caractère évolutif se sont dégagées: une biozone inférieure à caractère paléocène soulignée par une dominance de formes de types « Palmae » et « Proteaceae », ces dernières d’aspect archaïque crétacé; une biozone intermédiaire du Paléocène supérieur avec évolution de la flore originelle vers un ensemble qui peut être qualifié de plus « moderne » et enfin, à l’Eocène basal, de l’installation d’associations annonçant les prémices de la mise en place de la flore actuelle à « Légumineuses » d’Afrique de l’Ouest. En parallèle de l’analyse biostratigraphique est proposée une reconstitution paléoenvironnementale basée sur l’écologie des dinoflagellés, sur l’évolution du ratio dinoflagellés/pollen et spores et sur la reconstitution des milieux végétaux dans les différentes séquences étudiées. L’évolution du Bassin selon deux axes géographiques a été mise en évidence: un axe WE (Moulongo-Ngata) et un axe SSW-NNE (Moulongo-Mamiwater-Nord Matanda). Au Paléocène inférieur et moyen, le Bassin, largement ouvert sur la mer, présente un milieu côtier-estuarien frangé de mangroves et de forêts de basse plaine marécageuse. Au Paléocène supérieur, l’influence marine se faisant moins importante, des milieux saumâtres fluvio-lagunaires soumis aux marées se développent, ils sont bordés de galeries forestières et entourés de forêts denses périodiquement inondées vers le Nord et de forêts sur sols humides vers l’Est. Avec la régression marine amorcée à la base de l’Eocène, les paléoenvironnements s’individualisent: vers le Nord s’installent des milieux lagunaires confinés entourés d’une flore locale appauvrie et vers l’Est, autour de milieux d’eau douce d’arrière-delta, une forêt dense sempervirente humide de terre ferme occupe le terrain. [less ▲]

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See detailLimited clinical utility of a self-evaluating risk assessment scale for postmenopausal osteoporosis: lack of predictive value of lifestyle-related factors
Goemaere, S; Zegels, Brigitte ULg; Toye, K et al

in Calcified Tissue International (1999), 65(5), 354-358

The aim of this study was to assess the efficiency of a self-administered questionnaire to identify subjects with postmenopausal osteoporosis in the setting of first line medical care. A sample of 300 ... [more ▼]

The aim of this study was to assess the efficiency of a self-administered questionnaire to identify subjects with postmenopausal osteoporosis in the setting of first line medical care. A sample of 300 postmenopausal women completed the questionnaire based on 18 items. Bone mineral density at the lumbar spine (BMD-L), total hip (BMD-H), and femoral neck (BMD-N) was used as objective criterion for evaluation. The mean risk score was 8.2 +/- 3.21. BMD was correlated with total risk score: r = -0.32 for BMD-L, -0.36 for BMD-N, and -0.43 for BMD-H. Cutoff points for the risk score (equal likelihood points) according to a T-score threshold of -2.5 were 8.6 for BMD-L and BMD-N and 9.3 for BMD-H; specificity and sensitivity was 62% and 62%, respectively, for BMD-L, 65% and 62% for BMD-N, and 75% and 63% for BMD-H. Stepwise multiple regression analysis of the questionnaire items in relation to BMD showed higher correlation coefficients for models including individual items rather than the overall risk score. Items concerning low weight, older age, and wrist fracture after 50 years of age were always selected as significant determinants of BMD (R = 0.43-0.55). Hormonal replacement therapy was also an important determinant. Lifestyle-related items did not contribute significantly. In conclusion, the diagnostic performance of the 18-item self-administered questionnaire was poorer than a shortened questionnaire omitting lifestyle factors. The clinical utility of a questionnaire should ultimately be evaluated in the specific optic of a chosen global strategy for prevention of osteoporotic fractures. [less ▲]

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See detailLimited effects of placental and pituitary growth hormone on cytokine expression in vitro
Thellin, Olivier ULg; Coumans, Bernard ULg; Devos, Sébastien ULg et al

in European Cytokine Network (2000), 11(3), 452-455

The hypothesis that growth hormone (GH) can affect immune responses in man has been evaluated by monitoring cytokine expression in cultures from peripheral blood mononuclear cells, by enzyme-linked ... [more ▼]

The hypothesis that growth hormone (GH) can affect immune responses in man has been evaluated by monitoring cytokine expression in cultures from peripheral blood mononuclear cells, by enzyme-linked immunosorbent assay (ELISA) and ribonuclease protection assay, and in tonsillar cells by ELISA. In addition to pituitary GH (GH-N), the placental form (GH-V), differing from pituitary GH by 13 amino acids has also been tested. Only few effects reached statistical significance and were in no case greater than 15%. Pituitary GH slightly reduced IL-5 production and stimulated IFN-gamma production. The latter effect was also observed with prolactin and could thus be induced through the prolactin receptor. It is proposed that GH has no strong effects on the parameters investigated, possibly as a result of redundancy in the cytokine network. Alternatively, effects on leukocytes are mediated by other tissues such as the liver or are clear only in response to stronger challenges. [less ▲]

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See detailLimited impact of abiotic stress on surfactin production in planta and on disease resistance induced by Bacillus amyloliquefaciens S499 in tomato and bean
Pertot, I.; Puopolo, G.; Hosni, T. et al

in FEMS Microbiology Ecology (2013), 86(3), 505-519

Understanding how temperature and water stress affect protocooperation between plants and beneficial rhizobacteria may enhance the efficacy of biocontrol agents in reducing plant diseases. However, little ... [more ▼]

Understanding how temperature and water stress affect protocooperation between plants and beneficial rhizobacteria may enhance the efficacy of biocontrol agents in reducing plant diseases. However, little is known about the impact of these factors on biocontrol mechanisms and effectiveness, especially when provided by beneficial Bacillus spp. This work aimed to evaluate the influence of low/high temperature combined with a normal and reduced water regime on the interaction between Bacillus amyloliquefaciens strain S499 and plants, resulting in the induction of systemic resistance (ISR). A reduction in ISR level was observed when plants were subjected to stress before bacterization; however, root treatment with S499 prior to stress exposure attenuated this negative effect. Colonization of S499 during exposure to temperature/water stress allowed the three crops to conserve their overall ability to mount defense lines to a similar degree at all the temperatures tested. Further investigation revealed that relative production of surfactin by S499 was clearly enhanced at low temperature, making it possible to counter-balance the negative effect on traits associated with rhizosphere fitness (colonization, motility, and biofilm formation) observed in vitro in cold conditions. This work thus represents a first step in deciphering the effect of high/low temperatures and/or drought on key plant-microorganism interactions culminating in ISR. © 2013 Federation of European Microbiological Societies. [less ▲]

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