Publications ORBi OA     Results 241-260 of 51059.   8 9 10 11 12 13 14 15 16 17 18   Characterization of the inner disk around HD 141569 A from Keck/NIRC2 L-band vortex coronagraphyMawet, Dimitri; Choquet, Élodie; Absil, Olivier et alin Astronomical Journal (The) (2017), 153(1), 44HD 141569 A is a pre-main sequence B9.5 Ve star surrounded by a prominent and complex circumstellar disk, likely still in a transition stage from protoplanetary to debris disk phase. Here, we present a ... [more ▼]HD 141569 A is a pre-main sequence B9.5 Ve star surrounded by a prominent and complex circumstellar disk, likely still in a transition stage from protoplanetary to debris disk phase. Here, we present a new image of the third inner disk component of HD 141569 A made in the L' band (3.8 micron) during the commissioning of the vector vortex coronagraph recently installed in the near-infrared imager and spectrograph NIRC2 behind the W.M. Keck Observatory Keck II adaptive optics system. We used reference point spread function subtraction, which reveals the innermost disk component from the inner working distance of $\simeq 23$ AU and up to $\simeq 70$ AU. The spatial scale of our detection roughly corresponds to the optical and near-infrared scattered light, thermal Q, N and 8.6 micron PAH emission reported earlier. We also see an outward progression in dust location from the L'-band to the H-band (VLT/SPHERE image) to the visible (HST/STIS image), likely indicative of dust blowout. The warm disk component is nested deep inside the two outer belts imaged by HST NICMOS in 1999 (respectively at 406 and 245 AU). We fit our new L'-band image and spectral energy distribution of HD 141569 A with the radiative transfer code MCFOST. Our best-fit models favor pure olivine grains, and are consistent with the composition of the outer belts. While our image shows a putative very-faint point-like clump or source embedded in the inner disk, we did not detect any true companion within the gap between the inner disk and the first outer ring, at a sensitivity of a few Jupiter masses. [less ▲]Detailed reference viewed: 14 (2 ULg) Ombres de réalitéChoffray, Jean-Marie Book published by Amazon, Kindle Edition - Seconde édition (2017)« Ombres de réalité » a pour objectif de partager avec vous nombre d’erreurs personnelles – factuelles et d’appréciation –, à la lumière de ce que d’autres ont eu l’élégance de nous transmettre. Le socle ... [more ▼]« Ombres de réalité » a pour objectif de partager avec vous nombre d’erreurs personnelles – factuelles et d’appréciation –, à la lumière de ce que d’autres ont eu l’élégance de nous transmettre. Le socle de la réalité, lieu de convergence de ses ombres, et que décrit à merveille la comédie humaine, ne peut jamais être approché qu’au travers d’une recherche sincère et permanente. Apprendre à désapprendre résolument, apprendre à reconstruire patiemment, et apprendre à transmettre modestement, constituent le but ultime de la vie. Personnellement, je n’en vois pas d’autre aujourd’hui. Après une brève introduction, ou « Sortie de l’ombre », de courts chapitres couvrent un thème particulier, généralement à la lumière d’observations, d’expériences personnelles, ou de lectures qui m’ont touché. La sélection et l’ordre des sujets ne traduit aucun souci particulier, même si je ne crois plus beaucoup au hasard. Tous deux pourraient évoluer au fil des révisions que connaîtra ce texte dans les années à venir. Le choix actuel va de « Chacun pour soi » au « Secret du silence », en passant par « L’aventure à deux », « La foire aux illusions », « La tyrannie des marchés », « L’intérêt général », « Non ! merci », et « Une chance d’être ». Chaque thème peut être exploré isolément. A vous, donc, de constituer votre menu en fonction de votre curiosité et de votre appétit. [less ▲]Detailed reference viewed: 129 (16 ULg) Aux armes, professeurs de sciences !du Jardin, Patrick Article for general public (2017)Detailed reference viewed: 18 (0 ULg) Discovery of a low-mass companion inside the debris ring surrounding the F5V star HD 206893Milli, J.; Hibon, P.; Christiaens, Valentin et alin Astronomy and Astrophysics (2017), 597
Conclusions: The detection of a low-mass companion inside a massive debris disc makes this system an analog of other young planetary systems such as β Pictoris, HR 8799 or HD 95086 and requires now further characterisation of both components to understand their interactions. [less ▲]Detailed reference viewed: 9 (3 ULg) The EACVI Echo Handbook.Nchimi Longang, Alain in European Heart Journal (2017)Detailed reference viewed: 10 (0 ULg) First limits on the occurrence rate of short-period planets orbiting brown dwarfsHe, Matthias Y.; Triaud, Amaury H. M. J.; Gillon, Michaël in Monthly Notices of the Royal Astronomical Society (2017), 464Planet formation theories predict a large but still undetected population of short-period terrestrial planets orbiting brown dwarfs. Should specimens of this population be discovered transiting relatively ... [more ▼]Planet formation theories predict a large but still undetected population of short-period terrestrial planets orbiting brown dwarfs. Should specimens of this population be discovered transiting relatively bright and nearby brown dwarfs, the Jupiter-size and the low luminosity of their hosts would make them exquisite targets for detailed atmospheric characterisation with JWST and future ground-based facilities. The eventual discovery and detailed study of a significant sample of transiting terrestrial planets orbiting nearby brown dwarfs could prove to be useful not only for comparative exoplanetology but also for astrobiology, by bringing us key information on the physical requirements and timescale for the emergence of life. In this context, we present a search for transit-signals in archival time-series photometry acquired by the Spitzer Space Telescope for a sample of 44 nearby brown dwarfs. While these 44 targets were not particularly selected for their brightness, the high precision of their Spitzer light curves allows us to reach sensitivities below Earth-sized planets for 75% of the sample and down to Europa-sized planets on the brighter targets. We could not identify any unambiguous planetary signal. Instead, we could compute the first limits on the presence of planets on close-in orbits. We find that within a 1.28 day orbit, the occurrence rate of planets with a radius between 0.75 and 3.25 R$_\oplus$ is {\eta} < 67 $\pm$ 1%. For planets with radii between 0.75 and 1.25 R$_\oplus$, we place a 95% confident upper limit of {\eta} < 87 $\pm$ 3%. If we assume an occurrence rate of {\eta} = 27% for these planets with radii between 0.75 and 1.25 R$_\oplus$, as the discoveries of the Kepler-42b and TRAPPIST-1b systems would suggest, we estimate that 175 brown dwarfs need to be monitored in order to guarantee (95%) at least one detection. [less ▲]Detailed reference viewed: 19 (1 ULg) Water loss from terrestrial planets orbiting ultracool dwarfs: implications for the planets of TRAPPIST-1Bolmont, E.; Selsis, F.; Owen, J. E. et alin Monthly Notices of the Royal Astronomical Society (2017), 464Ultracool dwarfs (UCD; $T_{\rm eff}<\sim3000~$K) cool to settle on the main sequence after $\sim$1 Gyr. For brown dwarfs, this cooling never stops. Their habitable zone (HZ) thus sweeps inward at least ... [more ▼]Ultracool dwarfs (UCD; $T_{\rm eff}<\sim3000~$K) cool to settle on the main sequence after $\sim$1 Gyr. For brown dwarfs, this cooling never stops. Their habitable zone (HZ) thus sweeps inward at least during the first Gyr of their lives. Assuming they possess water, planets found in the HZ of UCDs have experienced a runaway greenhouse phase too hot for liquid water prior to entering the HZ. It has been proposed that such planets are desiccated by this hot early phase and enter the HZ as dry worlds. Here we model the water loss during this pre-HZ hot phase taking into account recent upper limits on the XUV emission of UCDs and using 1D radiation-hydrodynamic simulations. We address the whole range of UCDs but also focus on the planets recently found around the $0.08~M_\odot$ dwarf TRAPPIST-1. Despite assumptions maximizing the FUV-photolysis of water and the XUV-driven escape of hydrogen, we find that planets can retain significant amounts of water in the HZ of UCDs, with a sweet spot in the $0.04$-$0.06~M_\odot$ range. We also studied the TRAPPIST-1 system using observed constraints on the XUV-flux. We find that TRAPPIST-1b and c may have lost as much as 15 Earth Oceans and planet d -- which might be inside the HZ -- may have lost less than 1 Earth Ocean. Depending on their initial water contents, they could have enough water to remain habitable. TRAPPIST-1 planets are key targets for atmospheric characterization and could provide strong constraints on the water erosion around UCDs. [less ▲]Detailed reference viewed: 10 (0 ULg) Rossiter-McLaughlin models and their effect on estimates of stellar rotation, illustrated using six WASP systemsBrown, D. J. A.; Triaud, A. H. M. J.; Doyle, A. P. et alin Monthly Notices of the Royal Astronomical Society (2017), 464We present new measurements of the projected spin--orbit angle $\lambda$ for six WASP hot Jupiters, four of which are new to the literature (WASP-61, -62, -76, and -78), and two of which are new analyses ... [more ▼]We present new measurements of the projected spin--orbit angle $\lambda$ for six WASP hot Jupiters, four of which are new to the literature (WASP-61, -62, -76, and -78), and two of which are new analyses of previously measured systems using new data (WASP-71, and -79). We use three different models based on two different techniques: radial velocity measurements of the Rossiter--McLaughlin effect, and Doppler tomography. Our comparison of the different models reveals that they produce projected stellar rotation velocities ($v \sin I_{\rm s}$) measurements often in disagreement with each other and with estimates obtained from spectral line broadening. The Bou\'e model for the Rossiter--McLaughlin effect consistently underestimates the value of $v\sin I_{\rm s}$ compared to the Hirano model. Although $v \sin I_s$ differed, the effect on $\lambda$ was small for our sample, with all three methods producing values in agreement with each other. Using Doppler tomography, we find that WASP-61\,b ($\lambda=4^\circ.0^{+17.1}_{-18.4}$), WASP-71\,b ($\lambda=-1^\circ.9^{+7.1}_{-7.5}$), and WASP-78\,b ($\lambda=-6^\circ.4\pm5.9$) are aligned. WASP-62\,b ($\lambda=19^\circ.4^{+5.1}_{-4.9}$) is found to be slightly misaligned, while WASP-79\,b ($\lambda=-95^\circ.2^{+0.9}_{-1.0}$) is confirmed to be strongly misaligned and has a retrograde orbit. We explore a range of possibilities for the orbit of WASP-76\,b, finding that the orbit is likely to be strongly misaligned in the positive $\lambda$ direction. [less ▲]Detailed reference viewed: 6 (0 ULg) Identification of complex nonlinearities using cubic splines with automatic discretizationDossogne, Tilàn ; Noël, Jean-Philippe ; Kerschen, Gaëtan in Proceedings of the International Modal Analysis Conference (IMAC) XXXV (2017, January)One of the major challenges in nonlinear system identification is the selection of appropriate mathematical functions to model the observed nonlinearities. In this context, piecewise polynomials, or ... [more ▼]One of the major challenges in nonlinear system identification is the selection of appropriate mathematical functions to model the observed nonlinearities. In this context, piecewise polynomials, or splines, offer a simple and flexible representation basis requiring limited prior knowledge. The generally-adopted discretization for splines consists in an even distribution of their control points, termed knots. While this may prove successful for simple nonlinearities, a more advanced strategy is needed for nonlinear restoring forces with strong local variations. The present paper specifically introduces a two-step methodology to select automatically the location of the knots. It proposes to derive an initial model, using nonlinear subspace identification, and incorporating cubic spline basis functions with fixed and equally-spaced abscissas. In a second step, the location of the knots is optimized iteratively by minimizing a least-squares cost function. A single-degree-of-freedom system with a discontinuous stiffness characteristic is considered as a case study. [less ▲]Detailed reference viewed: 24 (2 ULg) Experimental Assessment of the Influence of Interface Geometries on Structural Dynamic ResponseDossogne, Tilàn ; Jerome, Trevor; Lancereau, Damien et alin Proceedings of the International Modal Analysis Conference (IMAC) XXXV (2017, January)Jointed interfaces are sources of the greatest amount of uncertainty in the dynamics of a structural assembly. In practice, jointed connections introduce nonlinearity into a system, which is often ... [more ▼]Jointed interfaces are sources of the greatest amount of uncertainty in the dynamics of a structural assembly. In practice, jointed connections introduce nonlinearity into a system, which is often manifested as a softening response in frequency response, exhibiting amplitude dependent damping and stiffness. Additionally, standard joints are highly susceptible to unrepeatability and variability that make meaningful prediction of the performance of a system prohibitively difficult. This high degree of uncertainty in joint structure predictions is partly due to the physical design of the interface. This paper experimentally assesses the influence of the interface geometry on both the nonlinear and uncertain aspects of jointed connections. The considered structure is the Brake-Reuß beam, which possesses a lap joint with three bolted connections, and can exhibit several different interface configurations. Five configurations with different contact areas are tested, identified, and compared, namely joints with complete contact in the interface, contact only under the pressure cones, contact under an area twice that of the pressure cones, contact only away from the pressure cones and Hertzian contact. The contact only under the pressure cone and Hertzian contact are found to behave linearly in the range of excitation used in this work. The contact area twice that of the pressure cone behaves between the complete contact and contact only under the pressure cone cases. [less ▲]Detailed reference viewed: 14 (1 ULg) Impact of food type on respiration, fractionation and turnover of carbon and nitrogen stable isotopes in the marine amphipod Gammarus aequicauda (Martynov, 1931).Remy, François ; Darchambeau, François ; Melchior, Aurélie et alin Journal of Experimental Marine Biology & Ecology (2017), 486This study experimentally determined the impact of food source type on turnover rate and trophic enrichment factors (TEFs or ∆) of δ13C and δ15N, as well as on respiration rate, in captive populations of ... [more ▼]This study experimentally determined the impact of food source type on turnover rate and trophic enrichment factors (TEFs or ∆) of δ13C and δ15N, as well as on respiration rate, in captive populations of the marine amphipod Gammarus aequicauda. Gammarus aequicauda (318 individuals) were fed ad libitum with three food sources animal, algae, and dead Posidonia oceanica leaves (also called “litter”), varying in palatability, digestibility, nutritional qualities and isotopic compositions, for between four and six weeks in a controlled feeding experiment. The resulting death rate was lower for the amphipods fed with animal treatment (30.9%) than for individuals fed with algal (65.9%) or litter treatment (64.4%), indicating a better fitness of the individuals fed with the animal food source. Respiration rates also differed highly among the treatments. Animal treatment showed higher respiration rates than algal and litter treatments, potentially due to the toxicity of the algae and the very low nutritional quality of the litter. Amphipods fed with these treatments might have entered in a “low activity state” to cope with these unsuitable food sources, inducing low respiration rates. Due to the very low assimilation and toxicity of the algae source, turnover rate for δ13C was impossible to determine. Turnover rate for δ13C was much faster (half-life = 12.55 days) for amphipods fed with the animal food source than for amphipods fed with litter (half-life = 51.62 days), showing the faster assimilation of the most nutritionally optimal food sources by G. aequicauda. Turnover for δ15N was impossible to determine because the amphipods were already at isotopic equilibrium at the beginning of the experiment. Despite the detritus feeder status of Gammarus aequicauda, TEFs for the animal treatments were in accordance with values generally found for carnivorous organisms (∆13C = 0.9 ± 0.7‰; ∆15N = 2.9 ± 0.6‰). TEFs for the litter treatment were in accordance with values generally corresponding to detritivorous organisms (∆13C = 1.2‰; ∆15N = 1.0 ± 0.4‰). SIAR mixing model outputs obtained with these new TEF values were more constrained and coherent than outputs obtained with general literature TEFs. This study thus demonstrated the non-negligible impact of the food source on Gammarus aequicauda physiological status, fitness and turnover rates, but also on TEFs—highlighting the importance of TEF experimental calculations for every potential food source of a given organism to ensure more robust isotopic data interpretation. [less ▲]Detailed reference viewed: 41 (9 ULg) Investment in Flexible Resources with Demand Correlation: an application to cloud computingLam, Wing Man Wynne E-print/Working paper (2017)Detailed reference viewed: 22 (4 ULg) Quelques idées générales à propos de la compréhension en mathématiquesBair, Jacques E-print/Working paper (2017)Dans cet article, nous apportons des éléments de réponse à la question générale suivante : "Que signifie bien comprendre en mathématiques ?" Nous nous demandons pourquoi il est difficile d'y répondre et ... [more ▼]Dans cet article, nous apportons des éléments de réponse à la question générale suivante : "Que signifie bien comprendre en mathématiques ?" Nous nous demandons pourquoi il est difficile d'y répondre et apportons une piste de solution en distinguant les activités de production de celles de reproduction. De plus, nous abordons le problème étudié d'un point de vue aussi bien local que global. Enfin, nous nous interrogeons sur l'incompréhension en mathématiques en proposant une typologie, en repérant des causes possibles d'incompréhension et en donnant quelques conseils pratiques. [less ▲]Detailed reference viewed: 20 (4 ULg) Attention et simultanéité intellectuelle chez Descartes, Clauberg et SpinozaDubouclez, Olivier in Les études philosophiques (2017), 1Abstract. – is paper deals with a classical problem, can we think or apprehend many things at once ? as it was understood and solved by Descartes and its followers. e idea that we can apprehend di erent ... [more ▼]Abstract. – is paper deals with a classical problem, can we think or apprehend many things at once ? as it was understood and solved by Descartes and its followers. e idea that we can apprehend di erent ideas at once is central in Descartes’ theory of knowledge, especially in the Rules, and it relies on the claim that attention can be divided between two objects or ideas. Clauberg considers on the contrary that the imagination alone can graps things simultaneously and holds the living body as the true paradigm of simultaneous activity. Spinoza has a synthetic point of view : simultaneity within the body and the mind are expressions of the power of the individ- ual and of his develoment. Attention is no more a condition of intellectual simultaneity, as in Descartes, but is rather an obstacle which needs to be overcome to reach a richer and better understanding of reality. [less ▲]Detailed reference viewed: 26 (1 ULg) Linking pollutant exposure of humpback whales breeding in the Indian Ocean to their feeding habits and feeding areas off AntarcticaDas, Krishna ; Malarvannan, Govindan; Dirtu, Alin et alin Environmental Pollution (2017), 220Humpback whales, Megaptera novaeangliae, breeding off la Reunion Island (Indian Ocean) undergo large-scale seasonal migrations between summer feeding grounds near Antarctica and their reproductive winter ... [more ▼]Humpback whales, Megaptera novaeangliae, breeding off la Reunion Island (Indian Ocean) undergo large-scale seasonal migrations between summer feeding grounds near Antarctica and their reproductive winter grounds in the Indian Ocean. The main scope of the current study was to investigate chemical exposure of humpback whales breeding in the Indian Ocean by providing the first published data on this breeding stock concerning persistent organic pollutants (POPs), namely polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), hexachlorocyclohexanes (HCHs), DDT and its metabolites (DDTs), chlordane compounds (CHLs), polybrominated diphenyl ethers (PBDEs), and methoxylated PBDEs (MeO-PBDEs). Analyses of stable isotopes δ13C and δ15N in skin resulted in further insight in their feeding ecology, which was in agreement with a diet focused mainly on low trophic level prey species, such as krill from Antarctica. POPs were measured in all humpback whales in the order of HCB > DDTs > CHLs > HCHs > PCBs > PBDEs > MeO-BDEs. HCB (median: 24 ng.g-1 lw) and DDTs (median: 7.7 ng.g-1 lw) were the predominant compounds in all whale biopsies. Among DDT compounds, p,p’-DDE was the major organohalogenated pollutant, reflecting its long-term accumulation in humpback whales. Significantly lower concentrations of HCB and DDTs were found in females than in males (p<0.001). Other compounds were similar between the two genders (p>0.05). Differences in the HCB and DDTs suggested gender-specific transfer of some compounds to the offspring. POP concentrations were lower than previously reported results for humpback whales sampled near the Antarctic Peninsula, suggesting potential influence of their nutritional status and may indicate different exposures of the whales according to their feeding zones. Further investigations are required to assess exposure of southern humpback whales throughout their feeding zones. [less ▲]Detailed reference viewed: 59 (11 ULg) Spatial variation in the accumulation of POPs and mercury in bottlenose dolphins of the Lower Florida Keys and the coastal Everglades (South Florida)Damseaux, France ; Kiszka, J.; Heithaus, M.R. et alin Environmental Pollution (2017), 220The bottlenose dolphin (Tursiops truncatus) is an upper trophic level predator and the most common cetacean species found in nearshore waters of southern Florida, including the Lower Florida Keys (LFK ... [more ▼]The bottlenose dolphin (Tursiops truncatus) is an upper trophic level predator and the most common cetacean species found in nearshore waters of southern Florida, including the Lower Florida Keys (LFK) and the Florida Coastal Everglades (FCE). The objective of this study was to assess contamination levels of total mercury (T-Hg) in skin and persistent organic pollutants (PCBs, PBDEs, DDXs, HCHs, HCB, Σ PCDD/Fs and Σ DL-PCBs) in blubber samples of bottlenose dolphins from LFK (n = 27) and FCE (n = 24). PCBs were the major class of compounds found in bottlenose dolphin blubber and were higher in individuals from LFK (Σ 6 PCBs LFK males: 13421 ± 7730 ng.g-1 lipids, Σ 6 PCBs LFK females: 9683 ± 19007 ng.g-1 lipids) than from FCE (Σ 6 PCBs FCE males: 5638 ng.g-1 ± 3627 lipids, Σ 6 PCBs FCE females: 1427 ± 908 ng.g-1 lipids). These levels were lower than previously published data from the southeastern USA. The Σ DL-PCBs were the most prevalent pollutants of dioxin and dioxin like compounds (Σ DL-PCBs LFK: 739 ng.g-1 lipids, Σ DL-PCBs FCE: 183 ng.g-1 lipids) since PCDD/F concentrations were low for both locations (mean 0.1 ng.g-1 lipids for LFK and FCE dolphins). The toxicity equivalences of PCDD/Fs and DL-PCBs expressed as TEQ in LFK and FCE dolphins is mainly expressed by DL-PCBs (81% LFK - 65% FCE). T-Hg concentrations in skin were significantly higher in FCE (FCE median 9314 ng.g-1 dw) compared to LFK dolphins (LFK median 2941 ng.g-1 dw). These bottlenose dolphins concentrations are the highest recorded in the southeastern USA, and may be explained, at least partially, by the biogeochemistry of the Everglades and mangrove sedimentary habitats that create favourable conditions for the retention of mercury and make it available at high concentrations for aquatic predators. [less ▲]Detailed reference viewed: 70 (19 ULg) GREDOR. Outcomes and recommendationsCornélusse, Bertrand ; Ernst, Damien Report (2017)Detailed reference viewed: 201 (5 ULg) Bioclimatism in Architecture : an evolutionary perspectiveNguyen, Anh Tuan; Reiter, Sigrid in International Journal of Design and Nature and Ecodynamics (2017), 12(1), 16-29Fundamentals of vernacular architecture have been used in bioclimatic architecture which has gradually become the inspiration of various movements in contemporary architecture. The study points out that ... [more ▼]Fundamentals of vernacular architecture have been used in bioclimatic architecture which has gradually become the inspiration of various movements in contemporary architecture. The study points out that the development of bioclimatism in architecture has followed the pattern of a natural evolutionary process in which “natural selection” is likely motivated by several factors, including resources and environment problems, and driven by different mechanisms including novel building design concepts and methods, new standards and codes, discoveries in building science and construction costs. This study is an effort aimed to clarify the evolution process of the bioclimatic approach in architecture over time and its influences on contemporary movements in architecture. The paper shows also that the evolutionary theory generated new scientific tools able to improve building design thanks to simulation-based optimization methods applied to building performances. Finally, this study investigates new motivations in the era of climate change whose effects are expected to introduce more challenges as well as more trends towards a sustainable built environment through the new concept of Eco-adaptive architecture. [less ▲]Detailed reference viewed: 53 (8 ULg) How cognition affects perception: Brain activity modelling to unravel top-down dynamicsDesseilles, Martin ; Phillips, Christophe in Behavioral and Brain Sciences (2017), 39In this commentary on Firestone & Scholl's (F&S's) article, we argue that researchers should use brain-activity modelling to investigate top-down mechanisms. Using functional brain imaging and a specific ... [more ▼]In this commentary on Firestone & Scholl's (F&S's) article, we argue that researchers should use brain-activity modelling to investigate top-down mechanisms. Using functional brain imaging and a specific cognitive paradigm, modelling the BOLD signal provided new insight into the dynamic causalities involved in the influence of cognitions on perceptions. [less ▲]Detailed reference viewed: 12 (2 ULg) Invited CommentaryLancellotti, Patrizio ; Nchimi Longang, Alain in Annals of Thoracic Surgery (2017), 103(1), 81-82Detailed reference viewed: 13 (1 ULg)