Publications ORBi OA     Results 221-240 of 39345.   7 8 9 10 11 12 13 14 15 16 17   Revisiting the SN1987A gamma-ray limit on ultralight axion-like particlesPayez, Alexandre ; Evoli, Carmelo; Fischer, Tobias et alin Journal of Cosmology and Astroparticle Physics [= JCAP] (2015), 2015(02), 006We revise the bound from the supernova SN1987A on the coupling of ultralight axion-like particles (ALPs) to photons. In a core-collapse supernova, ALPs would be emitted via the Primakoff process, and ... [more ▼]We revise the bound from the supernova SN1987A on the coupling of ultralight axion-like particles (ALPs) to photons. In a core-collapse supernova, ALPs would be emitted via the Primakoff process, and eventually convert into gamma rays in the magnetic field of the Milky Way. The lack of a gamma-ray signal in the GRS instrument of the SMM satellite in coincidence with the observation of the neutrinos emitted from SN1987A therefore provides a strong bound on their coupling to photons. Due to the large uncertainty associated with the current bound, we revise this argument, based on state-of-the-art physical inputs both for the supernova models and for the Milky-Way magnetic field. Furthermore, we provide major amendments, such as the consistent treatment of nucleon-degeneracy effects and of the reduction of the nuclear masses in the hot and dense nuclear medium of the supernova. With these improvements, we obtain a new upper limit on the photon-ALP coupling: g_{a\gamma} < 5.3 x 10^{-12} GeV^{-1}, for m_a < 4.4 x 10^{-10} eV, and we also give its dependence at larger ALP masses. Moreover, we discuss how much the Fermi-LAT satellite experiment could improve this bound, should a close-enough supernova explode in the near future. [less ▲]Detailed reference viewed: 17 (13 ULg) Single Wavelength Coarse Phasing In Segmented TelescopesSimar, Juan Felipe in Applied Optics (2015), 54Space observations of fainter and more distant astronomical objects constantly require telescope primary mirrors with a larger size. The diameter of monolithic primary mirrors is limited to 10 m because ... [more ▼]Space observations of fainter and more distant astronomical objects constantly require telescope primary mirrors with a larger size. The diameter of monolithic primary mirrors is limited to 10 m because of manufacturing limitations. For space telescopes, the primary mirrors are limited to less than 5 m due to fairing capacity. Segmented primary mirrors thus constitute an alternative solution to deal with the steadily increase of the primary mirror size. The optical path di erence between the individual segments must be close to zero (few nm) in order to be di raction limited. We propose in this paper a new inter-segment piston sensor based on coherence measurement of a star image. This sensor is intended to be used in the co-phasing system of future segmented mirrors. [less ▲]Detailed reference viewed: 42 (31 ULg) Comment les disciplines se reconstruisent dans des environnements hybrides et dynamiquesFallon, Catherine ; Thoreau, François Scientific conference (2015, February 06)Les chercheurs en sciences politiques et sociales, voire les philosophes politiques, sont de plus en plus souvent « embarqués » dans des projets résolument transdisciplinaires, portés par les groupes de ... [more ▼]Les chercheurs en sciences politiques et sociales, voire les philosophes politiques, sont de plus en plus souvent « embarqués » dans des projets résolument transdisciplinaires, portés par les groupes de recherche de différentes disciplines, engagés dans les développement scientifico-technologiques les plus pointus, que ce soit dans le secteur des nanotechnologies ou des biotechnologies médicales (pour citer deux exemples récents,Thoreau 2013) . Cet article prend comme point de départ un projet pluriannuel qui a obtenu des subsides pour plonger pendant une longue période trois chercheurs (philosophe, anthropologue, politologue) dans un centre de recherche en génomique humaine appliquée, installé dans une aile du Centre-Hospitalo-Universitaire. En tant que coordinateurs de ce projet, nous voulons aborder ab initio (1) la question des conditions d’exercice de notre démarche de terrain et (2) les conditions de notre service en tant que politologues au fil de cette trajectoire. [less ▲]Detailed reference viewed: 10 (0 ULg) Ecole et citoyenneté : à quand un grand débat sur l'enseignement des sciences humaines ?Jadoulle, Jean-Louis Article for general public (2015)Detailed reference viewed: 20 (2 ULg) A mixed integer nonlinear programming bi-objective model for intermodal network designMostert, Martine ; Caris, An; Limbourg, Sabine Conference (2015, February 05)Detailed reference viewed: 37 (0 ULg) Quaternary prevention, an answer of family doctors to overmedicalizationJamoulle, Marc in International Journal of Health Policy and Management (2015), 4((X)), 1-4In response to the questioning of Health Policy and Management (HPAM) by colleagues on the role of rank and file family physicians in the same journal, the author, a family physician in Belgium, is trying ... [more ▼]In response to the questioning of Health Policy and Management (HPAM) by colleagues on the role of rank and file family physicians in the same journal, the author, a family physician in Belgium, is trying to highlight the complexity and depth of the work of his colleagues and their contribution to the understanding of the organization and economy of healthcare. It addresses, in particular, the management of health elements throughout the ongoing relationship of the family doctor with his/her patients. It shows how the three dimensions of prevention, clearly included in the daily work, are complemented with the fourth dimension, quaternary prevention or prevention of medicine itself, whose understanding could help to control the economic and human costs of healthcare [less ▲]Detailed reference viewed: 345 (6 ULg) Suppression of Limit Cycle Oscillations using the Nonlinear Tuned Vibration AbsorberHabib, Giuseppe ; Kerschen, Gaëtan in Proceeding IMAC XXXIII A Conference and Exposition on Structural Dynamics, Orlando 2-5 February 2015 (2015, February 03)The objective of the present study is to mitigate, or even completely eliminate, the limit cycle oscillations in mechanical systems using a passive nonlinear absorber, termed the nonlinear tuned vibration ... [more ▼]The objective of the present study is to mitigate, or even completely eliminate, the limit cycle oscillations in mechanical systems using a passive nonlinear absorber, termed the nonlinear tuned vibration absorber (NLTVA). An unconventional aspect of the NLTVA is that the mathematical form of its restoring force is not imposed a priori, as it is the case for most existing nonlinear absorbers. The NLTVA parameters are determined analytically using stability and bifurcation analyses, and the resulting design is validated numerically using the MATCONT software. The proposed developments are illustrated using a Van der Pol-Du ng primary system. [less ▲]Detailed reference viewed: 63 (13 ULg) Contribution to the Macrophytic Typology of Belgian Reference WatercoursesGaloux, Daniel; Cherot, Frédéric; Rosillon, Francis et alin Advances in Botany (2015), Volume 2015, Article ID 651369The objective of the study is to create a typology of macrophytes for the reference watercourses of the Meuse River catchment ... [more ▼]The objective of the study is to create a typology of macrophytes for the reference watercourses of the Meuse River catchment basininWalloniaasasteptowardstheimplementationoftheEuropeanWaterFrameworkDirective.The50sitesstudiedarethe objectofaphysicochemicalandenvironmentalcharacterizationfollowedbyafloristicsurvey(phanerogams,mosses,liverworts, andmacroalgae).Sixclustersofwatercourseswiththeircharacteristicspeciesarehighlightedbytwo-wayclusteringandindicator species. The abundance of phanerogams in some watercourses of the Arden region is not only linked to light intensity but also dependsonthedegreeofslopeandthenatureofthegeologicalsubstrate [less ▲]Detailed reference viewed: 11 (2 ULg) Economics of a decision-support system for managing the main fungal diseases of winter wheat in the Grand-Duchy of LuxembourgEl Jarroudi, Moussa ; Kouadio, Louis; Beyer, Marco et alin Field Crops Research (2015), 172(2), 32-41We evaluated the cost effectiveness of a decision-support system (DSS) developed for assessing in real time the risk of progression of the main fungal diseases (i.e., Septoria leaf blotch, powdery mildew ... [more ▼]We evaluated the cost effectiveness of a decision-support system (DSS) developed for assessing in real time the risk of progression of the main fungal diseases (i.e., Septoria leaf blotch, powdery mildew, leaf rusts and Fusarium head blight) of winter wheat in the Grand-Duchy of Luxembourg (GDL). The study was conducted in replicated field experiments located in four agricultural locations (representative of the main agro-ecological regions of the country) over a 10-year period (2003-2012). Three fungicide spray strategies were compared: a single DSS-based system and two commonly used spray practices in the GDL, a double- (2T)- and a triple- spray (3T) spray treatment; there was also a non-treated control. In years with a high disease pressure, the DSS-based recommendation resulted in protection of the three upper leaves comparable to that achieved with the 2T and 3T treatments, with significant grain yield increases (P > 0.05) compared to the control (a 4 to 42% increase, depending on the site and year). Overall, the financial gain in treated plots compared with the control ranged from 3 to 16% at the study sites. Furthermore, in seasons when dry weather conditions precluded epidemic development, no the DSS-basedDSS recommended no fungicide spray was recommended, reducing use of fungicide, and thus saving the cost of the product. The gain in yield for the 2T and 3T plots (compared with control) did not necessarily result in a financial gain during the duration of the experiment. This study demonstrates the potential advantages and profitability of using a DSS -based approach for disease management. [less ▲]Detailed reference viewed: 11 (1 ULg) Les PPP comme nouveau mode de régulation du marché de l'accompagnement des demandeurs d'emploi. A chaque modèle de partenariat son type de stratégieRemy, Céline in Cahiers Loyola (2015, February), 1Cette communication vise à montrer en quoi les partenariats publics-privés (PPP) constituent désormais un nouveau mode de régulation du marché de l’accompagnement des demandeurs d’emploi. Les services ... [more ▼]Cette communication vise à montrer en quoi les partenariats publics-privés (PPP) constituent désormais un nouveau mode de régulation du marché de l’accompagnement des demandeurs d’emploi. Les services publics de l’emploi (SPE) doivent établir des PPP avec des prestataires de service pour la mise en place de formation à destination des demandeurs d’emploi. La réalisation de trois études de cas au sein des SPE, dont deux en Belgique et une en Suisse, nous permet de mettre en évidence une forte influence du modèle de gestion du PPP sur la collaboration entre les parties-prenantes mais aussi sur les stratégies développées par les prestataires pour surmonter les problèmes liés à la collaboration avec l’Office de l’Emploi et à la mise en place de la prestation de service. [less ▲]Detailed reference viewed: 22 (4 ULg) Effects of low dose endosulfan exposure on brain neurotransmitter levels in the African clawed frog Xenopus laevisPreud'Homme, Valérie; Milla, Sylvain; Gillardin, Virginie et alin Chemosphere (2015), 120(2), 357-364Understanding the impact of pesticides in amphibians is of growing concern to assess the causes of their decline. Among pesticides, endosulfan belongs to one of the potential sources of danger because of ... [more ▼]Understanding the impact of pesticides in amphibians is of growing concern to assess the causes of their decline. Among pesticides, endosulfan belongs to one of the potential sources of danger because of its wide use and known effects, particularly neurotoxic, on a variety of organisms. However, the effect of endosulfan was not yet evaluated on amphibians at levels encompassing simultaneously brain neurotransmitters and behavioural endpoints. In this context, tadpoles of the African clawed frog Xenopus laevis were submitted to four treatments during 27 d: one control, one ethanol control, and two low environmental concentrations of endosulfan (0.1 and 1 μg L−1). Endosulfan induced a significant increase of brain serotonin level at both concentrations and a significant increase of brain dopamine and GABA levels at the lower exposure but acetylcholinesterase activity was not modified by the treatment. The gene coding for the GABA transporter 1 was up-regulated in endosulfan contaminated tadpoles while the expression of other genes coding for the neurotransmitter receptors or for the enzymes involved in their metabolic pathways was not significantly modified by endosulfan exposure. Endosulfan also affected foraging, and locomotion in links with the results of the physiological assays, but no effects were seen on growth. These results show that low environmental concentrations of endosulfan can induce adverse responses in X. laevis tadpoles. At a broader perspective, this suggests that more research using and linking multiple markers should be used to understand the complex mode of action of pollutants. [less ▲]Detailed reference viewed: 72 (27 ULg) Experimental modal analysis of nonlinear structures using broadband dataNoël, Jean-Philippe ; Renson, Ludovic ; Grappasonni, Chiara et alin Proceedings of the International Modal Analysis Conference (IMAC) XXXIII (2015, February)The objective of the present paper is to develop a rigorous identification methodology of nonlinear normal modes (NNMs) of engineering structures. This is achieved by processing experimental measurements ... [more ▼]The objective of the present paper is to develop a rigorous identification methodology of nonlinear normal modes (NNMs) of engineering structures. This is achieved by processing experimental measurements collected under broadband forcing. The use of such a type of forcing signal allows to excite multiple NNMs simultaneously and, in turn, to save testing time. A two-step methodology integrating nonlinear system identification and numerical continuation of periodic solutions is proposed for the extraction of the individual NNMs from broadband input and output data. It is demonstrated using a numerical cantilever beam possessing a cubic nonlinearity at its free end. The proposed methodology can be viewed as a nonlinear generalization of the phase separation techniques routinely utilized for experimental modal analysis of linear structures. The paper ends with a comparison between this new nonlinear phase separation technique and a previously-developed nonlinear phase resonance method. [less ▲]Detailed reference viewed: 38 (7 ULg) Experimental nonlinear identification of an aircraft with bolted connectionsDe Filippis, Giovanni; Noël, Jean-Philippe ; Kerschen, Gaëtan et alin Proceedings of the International Modal Analysis Conference (IMAC) XXXIII (2015, February)Aircraft structures are known to be prone to nonlinear phenomena, especially as they constantly become lighter and hence more flexible. One specific challenge that is regularly encountered is the modeling ... [more ▼]Aircraft structures are known to be prone to nonlinear phenomena, especially as they constantly become lighter and hence more flexible. One specific challenge that is regularly encountered is the modeling of the mounting interfaces between aircraft subcomponents. Indeed, for large amplitudes of vibration, such interfaces may loosen and, in turn, trigger complex mechanisms such as friction and clearances. In this context, the present work intends to investigate the nonlinear dynamics of the Morane–Saulnier Paris aircraft, accessible at ONERA. This aircraft possesses multiple bolted connections between two external fuel tanks and wing tips. The objective of the paper is specifically to carry out an adequate identification of the numerous nonlinearities affecting the dynamics of this full-scale structure. Nonlinearity detection and the subsequent subspace-based parameter estimation have been performed on experimental data, collected during an on-ground test campaign. Nonlinearity detection is first achieved by the comparison of frequency response functions estimated at low excitation level, with those obtained at high amplitude level, yielding insight towards accurately characterizing the behavior of the bolted connections. Then, a nonlinear subspace identification method is applied to measured data to estimate the linear and nonlinear parameters of the structure and novel strategies and tools that overcome specific arisen problems are developed. [less ▲]Detailed reference viewed: 86 (2 ULg) On modular decompositions of system signaturesMarichal, Jean-Luc; Mathonet, Pierre in Journal of Multivariate Analysis (2015), 134Considering a semicoherent system made up of $n$ components having i.i.d. continuous lifetimes, Samaniego defined its structural signature as the $n$-tuple whose $k$-th coordinate is the probability that ... [more ▼]Considering a semicoherent system made up of $n$ components having i.i.d. continuous lifetimes, Samaniego defined its structural signature as the $n$-tuple whose $k$-th coordinate is the probability that the $k$-th component failure causes the system to fail. This $n$-tuple, which depends only on the structure of the system and not on the distribution of the component lifetimes, is a very useful tool in the theoretical analysis of coherent systems. It was shown in two independent recent papers how the structural signature of a system partitioned into two disjoint modules can be computed from the signatures of these modules. In this work we consider the general case of a system partitioned into an arbitrary number of disjoint modules organized in an arbitrary way and we provide a general formula for the signature of the system in terms of the signatures of the modules. The concept of signature was recently extended to the general case of semicoherent systems whose components may have dependent lifetimes. The same definition for the $n$-tuple gives rise to the probability signature, which may depend on both the structure of the system and the probability distribution of the component lifetimes. In this general setting, we show how under a natural condition on the distribution of the lifetimes, the probability signature of the system can be expressed in terms of the probability signatures of the modules. We finally discuss a few situations where this condition holds in the non-i.i.d. and nonexchangeable cases and provide some applications of the main results. [less ▲]Detailed reference viewed: 14 (0 ULg) Experimental demonstration of a 3D-printed nonlinear tuned vibration absorberGrappasonni, Chiara ; Habib, Giuseppe ; Detroux, Thibaut et alin Proceedings of the International Modal Analysis Conference (IMAC) XXXIII (2015, February)Engineering structures are designed to be lighter and more flexible, hence reducing the extent of application of linear dynamic models. Concurrently, vibration mitigation is required for enhancing the ... [more ▼]Engineering structures are designed to be lighter and more flexible, hence reducing the extent of application of linear dynamic models. Concurrently, vibration mitigation is required for enhancing the performance, comfort or safety in real-life applications. Passive linear vibration absorbers are purpose-built, often designed using Den Hartog's equal-peak strategy. However, nonlinear systems are known to exhibit frequency-energy-dependent oscillations which linear absorbers cannot effectively damp out. In this context, the paper introduces a new nonlinear tuned vibration absorber (NLTVA) whose nonlinear functional form is tailored according to the frequency-energy dependence of the nonlinear primary structure. The NLTVA design aims at ensuring equal peaks in the nonlinear receptance function for an as large as possible range of forcing amplitudes, hence generalizing Den Hartog's method to nonlinear systems. Our focus in this study is on experimental demonstration of the NLTVA performance using a primary structure consisting of a cantilever beam with a geometrically nonlinear component at its free end. The absorber is implemented using a doubly-clamped beam fabricated thanks to 3D printing. The NLTVA performance is also compared with that of the classical linear tuned vibration absorber. [less ▲]Detailed reference viewed: 52 (5 ULg) Geräusch, Gerücht, Gerede. Formen und Funktionen der Fama in Erzähltexten Theodor Storms und Arthur SchnitzlersLeyh, Valérie Doctoral thesis (2015)Dans sa représentation allégorique de Fama, le poète latin Ovide évoque trois phénomènes précis : son aspect acoustique (le bruit), sa forme discursive (les racontars) et son lien au récit (la rumeur ... [more ▼]Dans sa représentation allégorique de Fama, le poète latin Ovide évoque trois phénomènes précis : son aspect acoustique (le bruit), sa forme discursive (les racontars) et son lien au récit (la rumeur). Alors que ces phénomènes ont très souvent fait l'objet d’études sociologiques et anthropologiques, il s’agit ici de les étudier en tant qu’objets d’un processus d’esthétisation. La thèse vise ainsi à décrire une « poétique de Fama » par l’analyse d’un choix de textes narratifs des auteurs germanophones Theodor Storm (1817 – 1888) et Arthur Schnitzler (1862 – 1931). En effet, les recherches récentes sur l’anticipation de la psychologie et sur les questions de perception chez Storm soulignent l’importance de stratégies narratives au caractère indirect, voilé et mettant à mal la plausibilité ; elles révèlent la nécessité d’étudier la rumeur comme élément thématique mais aussi structurel et formel. Les nombreux aspects de Fama intimement liés aux processus narratifs (polyphonie, psychologisation, contournement de la censure) permettent ensuite de confronter les textes de Storm à ceux de Schnitzler et d'y préciser les interactions subtiles entre bruit, racontars et rumeur. Dans ce traitement littéraire de Fama, il s’avère en outre primordial de mettre en lumière ses multiples fonctions selon les différents niveaux textuels (personnages, narrateur, auteur) et d’accorder une place au lecteur qui, dans une approche interactionnelle du récit, prend souvent part à la communication rumorale. Ces distinctions permettent de mettre en exergue la dimension poétologique de Fama dans ses différentes formes : si celle-ci participe à la création d’effets paradoxaux et de structures équivoques au sein des textes, c’est parce que la rumeur, en tant que forme de narration à caractère ambivalent et protéiforme, est fortement autoréflexive. L’instabilité et la contingence, l’indétermination de seuils et de frontières sont autant de traits qui caractérisent non seulement la rumeur et les racontars mais aussi les textes d’une époque marquée par de grandes mutations et par la mise en doute de valeurs et données acquises jusque-là. [less ▲]Detailed reference viewed: 27 (7 ULg) B fields in OB stars (BOB): on the detection of weak magnetic fields in the two early B-type stars beta CMa and epsilon CMaFossati, L.; Castro, N.; Morel, Thierry et alin Astronomy and Astrophysics (2015), 574Within the context of the "B fields in OB stars (BOB)" collaboration, we used the HARPSpol spectropolarimeter to observe the early B-type stars beta CMa (HD44743; B1 II/III) and epsilon CMa (HD52089; B1.5 ... [more ▼]Within the context of the "B fields in OB stars (BOB)" collaboration, we used the HARPSpol spectropolarimeter to observe the early B-type stars beta CMa (HD44743; B1 II/III) and epsilon CMa (HD52089; B1.5 II). For both stars, we consistently detected the signature of a weak (<30 G in absolute value) longitudinal magnetic field. We determined the physical parameters of both stars and characterise their X-ray spectrum. For beta CMa, our mode identification analysis led to determining a rotation period of 13.6+/-1.2 days and of an inclination angle of the rotation axis of 57.6+/-1.7 degrees, with respect to the line of sight. On the basis of these measurements and assuming a dipolar field geometry, we derived a best fitting obliquity of ~22 degrees and a dipolar magnetic field strength (Bd) of ~100 G (60