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See detailGlobal analysis of a continuum model for monotone pulse-coupled oscillators
Mauroy, Alexandre ULg; Sepulchre, Rodolphe ULg

in IEEE Transactions on Automatic Control (2013), 58(5), 1154-1166

We consider a continuum of phase oscillators on the circle interacting through an impulsive instantaneous coupling. In contrast with previous studies on related pulse-coupledmodels, the stability results ... [more ▼]

We consider a continuum of phase oscillators on the circle interacting through an impulsive instantaneous coupling. In contrast with previous studies on related pulse-coupledmodels, the stability results obtained in the continuum limit are global. For the nonlinear transport equation governing the evolution of the oscillators, we propose (under technical assumptions) a global Lyapunov function which is induced by a total variation distance between quantile densities. The monotone time evolution of the Lyapunov function completely characterizes the dichotomic behavior of the oscillators: either the oscillators converge in finite time to a synchronous state or they asymptotically converge to an asynchronous state uniformly spread on the circle. The results of the present paper apply to popular phase oscillators models (e.g., the well-known leaky integrate-and-fire model) and show a strong parallel between the analysis of finite and infinite populations. In addition, they provide a novel approach for the (global) analysis of pulse-coupled oscillators. © 2012 IEEE. [less ▲]

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See detailGlobal Analysis of Firing Maps
Mauroy, Alexandre ULg; Hendrickx, Julien; Megretski, Alexandre et al

in Proceedings of the 19th International Symposium on Mathematical Theory of Networks and Systems (2010, July)

In this paper, we study the behavior of pulse-coupled integrate-and-fire oscillators. Each oscillator is characterized by a state evolving between two threshold values. As the state reaches the upper ... [more ▼]

In this paper, we study the behavior of pulse-coupled integrate-and-fire oscillators. Each oscillator is characterized by a state evolving between two threshold values. As the state reaches the upper threshold, it is reset to the lower threshold and emits a pulse which increments by a constant value the state of every other oscillator. The behavior of the system is described by the so-called firing map: depending on the stability of the firing map, an important dichotomy characterizes the behavior of the oscillators (synchronization or clustering). The firing map is the composition of a linear map with a scalar nonlinearity. After briefly discussing the case of the scalar firing map (corresponding to two oscillators), the stability analysis is extended to the general n-dimensional firing map (for n +1 oscillators). Different models are considered (leaky oscillators, quadratic oscillators,...), with a particular emphasis on the persistence of the dichotomy in higher dimensions. [less ▲]

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See detailGlobal analysis of gene expression in the skin of mice after a 92 days journey in microgravity.
Neutelings, Thibaut ULg; Liu, Y.; Cancedda, R et al

Conference (2012)

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See detailGlobal analysis of gene expression in the skin of mice after a 92 days journey in microgravity.
Neutelings, Thibaut ULg; Liu, Y.; Cancedda, R. et al

Poster (2012, May 04)

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See detailA global analysis of Spitzer and new HARPS data confirms the loneliness and metal-richness of GJ 436 b
Lanotte, Audrey ULg; Gillon, Michaël ULg; Demory, B.-O. et al

in Astronomy and Astrophysics (in press)

Context. GJ 436b is one of the few transiting warm Neptunes for which a detailed characterisation of the atmosphere is possible, whereas its non-negligible orbital eccentricity calls for further ... [more ▼]

Context. GJ 436b is one of the few transiting warm Neptunes for which a detailed characterisation of the atmosphere is possible, whereas its non-negligible orbital eccentricity calls for further investigation. Independent analyses of several individual datasets obtained with Spitzer have led to contradicting results attributed to the different techniques used to treat the instrumental effects. Aims. We aim at investigating these previous controversial results and developing our knowledge of the system based on the full Spitzer photometry dataset combined with new Doppler measurements obtained with the HARPS spectrograph. We also want to search for additional planets. Methods. We optimise aperture photometry techniques and the photometric deconvolution algorithm DECPHOT to improve the data reduction of the Spitzer photometry spanning wavelengths from 3-24 {\mu}m. Adding the high precision HARPS radial velocity data, we undertake a Bayesian global analysis of the system considering both instrumental and stellar effects on the flux variation. Results. We present a refined radius estimate of RP=4.10 +/- 0.16 R_Earth, mass MP=25.4 +/- 2.1 M_Earth and eccentricity e= 0.162 +/- 0.004 for GJ 436b. Our measured transit depths remain constant in time and wavelength, in disagreement with the results of previous studies. In addition, we find that the post-occultation flare-like structure at 3.6 {\mu}m that led to divergent results on the occultation depth measurement is spurious. We obtain occultation depths at 3.6, 5.8, and 8.0 {\mu}m that are shallower than in previous works, in particular at 3.6 {\mu}m. However, these depths still appear consistent with a metal-rich atmosphere depleted in methane and enhanced in CO/CO2, although perhaps less than previously thought. We find no evidence for a potential planetary companion, stellar activity, nor for a stellar spin-orbit misalignment. [ABRIDGED] [less ▲]

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See detailGlobal and regional parameters of dyssynchrony in ischemic and nonischemic cardiomyopathy
Van de Veire, N.; De Sutter, J.; Van Camp, G. et al

in American Journal of Cardiology (2005), 95(3), 421-423

In this study, color tissue Doppler imaging was used to assess global and regional mechanical dyssynchrony in patients with ischemic cardiomyopathy and those with idiopathic dilated cardiomyopathy ... [more ▼]

In this study, color tissue Doppler imaging was used to assess global and regional mechanical dyssynchrony in patients with ischemic cardiomyopathy and those with idiopathic dilated cardiomyopathy. Potential differences in the area of latest mechanical activation could have practical implications regarding lead positioning and the success rate of biventricular pacemaker implantation.. (C) 2005 by Excerpta Medica Inc. [less ▲]

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See detailA global approach of the unsteady surface flows computations including shocks, by finite elements
Pirotton, Michel ULg

in Cerrolaza; Gajardo; Brebbia (Eds.) Numerical Methods in Engineering Simulation (1996, March 25)

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See detailA Global Approach to Mutual Funds Market Timing Ability
Bodson, Laurent ULg; Sougné, Danielle ULg; Cavenaile, Laurent

in Journal of Empirical Finance (2013)

• We propose a generalized specification to study market timing. Instead of considering an average market exposure for mutual funds, we allow mutual fund market betas to follow a random walk in the ... [more ▼]

• We propose a generalized specification to study market timing. Instead of considering an average market exposure for mutual funds, we allow mutual fund market betas to follow a random walk in the absence of market timing ability. As a consequence, we capture market exposure dynamics which is effectively due to manager market timing skills while allowing exposure dynamics to come from other sources than market timing. • We find that on average 6% of mutual funds display return market timing abilities while this percentage amounts to respectively 13% and 14% for volatility and liquidity market timing. We also analyse market timing by investment strategies and for surviving and dead funds. Dead fund exhibit lower volatility and liquidity timing skills than live funds. [less ▲]

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See detailA Global Approach to Mutual Funds Market Timing Ability
Sougné, Danielle ULg; Bodson, Laurent ULg; Cavenaile, Laurent

E-print/Working paper (2012)

In this paper, we globally investigate market timing abilities of mutual fund managers from the three perspectives: market return, market-wide volatility and aggregate liquidity. We propose a new ... [more ▼]

In this paper, we globally investigate market timing abilities of mutual fund managers from the three perspectives: market return, market-wide volatility and aggregate liquidity. We propose a new specification to study market timing. Instead of considering an average market exposure for mutual funds, we allow mutual fund market betas to follow a random walk in the absence of market timing ability. As a consequence, we capture market exposure dynamics which is really due to manager market timing skills while allowing dynamics to come from other sources than market timing. We find that on average 6% of mutual funds display return market timing abilities while this percentage amounts to respectively 13% and 14% for volatility and liquidity market timing. We also analyze market timing by investment strategies and for surviving and dead funds. Dead fund exhibit lower volatility and liquidity timing skills than live funds. [less ▲]

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See detailGlobal auroral conductance distribution due to electron and proton precipitation from IMAGE-FUV observations
Coumans, Valérie ULg; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in Annales Geophysicae [= ANGEO] (2004), 22(5), 1595-1611

The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a global view of the north auroral region in three spectral channels, including the SI 12 camera sensitive to Doppler shifted ... [more ▼]

The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a global view of the north auroral region in three spectral channels, including the SI 12 camera sensitive to Doppler shifted Lyman-alpha emission. FUV images are used to produce instantaneous maps of electron mean energy and energy fluxes for precipitated protons and electrons. We describe a method to calculate ionospheric Hall and Pedersen conductivities induced by auroral proton and electron ionization based on a model of interaction of auroral particles with the atmosphere. Different assumptions on the energy spectral distribution for electrons and protons are compared. Global maps of ionospheric conductances due to instantaneous observation of precipitating protons are calculated. The contribution of auroral protons in the total conductance induced by both types of auroral particles is also evaluated and the importance of proton precipitation is evaluated. This method is well adapted to analyze the time evolution of ionospheric conductances due to precipitating particles over the auroral region or in particular sectors. Results are illustrated with conductance maps of the north polar region obtained during four periods with different activity levels. It is found that the proton contribution to conductance is relatively higher during quiet periods than during substorms. The proton contribution is higher in the period before the onset and strongly decreases during the expansion phase of substorms. During a substorm which occurred on 28 April 2001, a region of strong proton precipitation is observed with SI 12 around 14:00MLT at similar to75degrees MLAT. Calculation of conductances in this sector shows that neglecting the protons contribution would produce a large error. We discuss possible effects of the proton precipitation on electron precipitation in aurora] arcs. The increase in the ionospheric conductivity, induced by a former proton precipitation can reduce the potential drop along field lines in the upward field-aligned currents by creating an opposite polarization electric field. This feedback mechanism possibly reduces the electron acceleration. [less ▲]

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See detailGlobal auroral proton precipitation observed by IMAGE-FUV: Noon and midnight brightness dependence on solar wind characteristics and IMF orientation
Coumans, Valérie ULg; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in Journal of Geophysical Research. Space Physics (2006), 111(A5),

The brightness of proton aurora observed near solar maximum at summer and winter solstices with the FUV-SI12 global imager on board the IMAGE satellite has been correlated with the solar wind and the ... [more ▼]

The brightness of proton aurora observed near solar maximum at summer and winter solstices with the FUV-SI12 global imager on board the IMAGE satellite has been correlated with the solar wind and the interplanetary magnetic field characteristics measured by ACE satellite instruments. By contrast to the electron aurora, we find a strong correlation both on nightside and dayside between the proton precipitated power and the solar wind dynamic pressure calculated with 1-hour averaged solar wind data. For both southward and northward IMF, the proton power increases with \B-z\, but much more rapidly on the nightside for southward IMF orientation. Correlations for the nightside aurora were also calculated with a series of solar wind-magnetosphere coupling functions. We find highest correlation coefficients for expressions containing the dynamic pressure or involving the solar wind electric field in the Y-Z plane. The influence of the solar wind dynamic pressure on the proton aurora is tentatively explained by the effect of the pressure on the shape of the magnetosphere, generating stretching of the magnetotail and proton precipitation but also by other coupling processes between the solar wind and the magnetosphere. Adding FUV-WIC and SI13 electron aurora images in the study, we determine how proton and electron precipitations simultaneously react to solar wind and IMF characteristics and Kp. Results shows that protons are more reactive to dynamic pressure variations than electrons when B-z is positive, while the influence on of both types of particles is similar for negative B-z. The precipitating proton flux is found proportionally larger compared with the electron flux when the total auroral flux increases for low activity level. Instead, for high activity level, the proportion of the proton and the electron powers are similar when auroral power increases. Consequently, it is suggested that similar mechanisms cause proton and electron auroral precipitation for high activity levels, while they appear somewhat decoupled for lower activity conditions. [less ▲]

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See detailThe global biogeography of semi-arid periodic vegetation patterns.
Deblauwe, V; Barbier, N; Couteron, P et al

in Global Ecology & Biogeography (2008), 17(6), 715-723

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See detailThe global carbon cycle and its changes over glacial-interglacial cycles - Preface
François, Louis ULg; Faure, H.; Probst, J. L.

in Global and Planetary Change (2002), 33(1-2), -

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See detailGlobal Character of the Venus UV Night Airglow.
Stewart, A. I.; Gérard, Jean-Claude ULg; Bougher, S.

in Bulletin of the American Astronomical Society (1979, March 01)

Not Available

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See detailGlobal climate warming and decline of the Black Grouse in western Europe: Are predictions reliable?
Loneux, Michèle ULg

in Journal of Ornithology (2006, August), 147(5, Suppl. 1), 203

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See detailGlobal comparison of light use efficiency models for simulating terrestrial vegetation gross primary production based on the LaThuile database
Yuan, W.; Cai, W.; Xia, J. et al

in Agricultural and Forest Meteorology (2014), 192-193

Simulating gross primary productivity (GPP) of terrestrial ecosystems has been a major challenge in quantifying the global carbon cycle. Many different light use efficiency (LUE) models have been ... [more ▼]

Simulating gross primary productivity (GPP) of terrestrial ecosystems has been a major challenge in quantifying the global carbon cycle. Many different light use efficiency (LUE) models have been developed recently, but our understanding of the relative merits of different models remains limited. Using CO2 flux measurements from multiple eddy covariance sites, we here compared and assessed major algorithms and performance of seven LUE models (CASA, CFix, CFlux, EC-LUE, MODIS, VPM and VPRM). Comparison between simulated GPP and estimated GPP from flux measurements showed that model performance differed substantially among ecosystem types. In general, most models performed better in capturing the temporal changes and magnitude of GPP in deciduous broadleaf forests and mixed forests than in evergreen broadleaf forests and shrublands. Six of the seven LUE models significantly underestimated GPP during cloudy days because the impacts of diffuse radiation on light use efficiency were ignored in the models. CFlux and EC-LUE exhibited the lowest root mean square error among all models at 80% and 75% of the sites, respectively. Moreover, these two models showed better performance than others in simulating interannual variability of GPP. Two pairwise comparisons revealed that the seven models differed substantially in algorithms describing the environmental regulations, particularly water stress, on GPP. This analysis highlights the need to improve representation of the impacts of diffuse radiation and water stress in the LUE models. © 2014 Elsevier B.V. [less ▲]

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See detailGlobal comparison of magnetospheric ion fluxes and auroral precipitation during a substorm
Mende, S. B.; Frey, H. U.; Immel, T. J. et al

in Geophysical Research Letters (2002), 29

Integrated fluxes from global images taken by the High Energy Neutral Atom (HENA) and the far ultraviolet (FUV) imagers on the IMAGE spacecraft were compared for a six-hour period, during which a ... [more ▼]

Integrated fluxes from global images taken by the High Energy Neutral Atom (HENA) and the far ultraviolet (FUV) imagers on the IMAGE spacecraft were compared for a six-hour period, during which a reasonably intense substorm occurred. HENA and the FUV proton auroral imager (SI-12) monitor emissions which are representative of trapped and precipitating magnetospheric proton fluxes, respectively. For several hours prior to substorm onset, measurements of the fluxes of lower energy (10-16 and 16-27 keV) magnetospheric Energetic Neutral Atoms (ENA-s) by HENA and precipitating auroral protons by FUV SI-12 show strong similarities, with the implication that, in general, proton precipitation is controlled by a steady pitch angle diffusion process. Less similarity is seen between ENA-s and the auroral electron precipitation, which is monitored with the FUV Wideband Imaging Camera. Prior to substorm onset, ENA intensity at large radial distance (L > 8) is reduced while the overall integrated ENA flux increases signifying earthward motion and accumulation of the plasma. About 20 minutes before onset, the auroral fluxes decrease while the ENA intensity continues to grow. The observations are consistent with a pre-onset increase in plasma pressure in the inner magnetosphere without an increase in precipitation showing more efficient trapping perhaps by the distorted nightside magnetosphere. At substorm onset the increase in precipitation intensity is very sudden while the more gradual intensification of the energetic ENA-s continues. At onset the electron aurora shows an increase in intensity of one order of magnitude, while the increase in precipitating proton flux is only 50%. The intensification of the precipitation is relatively short lived (~10 minutes) while the ENA substorm enhancements last about an hour. [less ▲]

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See detailGlobal compartmental analysis of the fluorescence decay surface of the halato telechelic polymer (N,N-dimethyl-N-[3-(1-pyrenyl)propyl]ammonio)-trifluoro-methanesulfonate-end-capped poly(tetrahydrofuran
Hermans, Bart; De Schryver, Frans C; Van Stam, Jan et al

in Macromolecules (1995), 28(9), 3380-3386

The kinetic behavior of the halato telechelic polymer (N,N-dimethyl-N-[3-(1-pyrenyl)propyl]-ammonio)trifluoromethanesulfonate-end-capped poly(tetrahydrofuran) (POLYPROBE) in tetrahydrofuran is ... [more ▼]

The kinetic behavior of the halato telechelic polymer (N,N-dimethyl-N-[3-(1-pyrenyl)propyl]-ammonio)trifluoromethanesulfonate-end-capped poly(tetrahydrofuran) (POLYPROBE) in tetrahydrofuran is investigated by global compartmental analysis of the fluorescence decay surface. At low POLYPROBE concentrations the emission decays monoexponentially. When an analogous end-capped halato telechelic polymer without the pyrene chromophore ((N,N,N-triethylammonio)trifluoromethanesulfonate-end-capped poly(tetrahydrofuran), POLYSALT) is added to solutions containing a low POLYPROBE concentration, the emission can be fitted by a biexponential decay function. From these observations it is concluded that the second excited-state species in the POLYPROBE-POLYSALT system is POLYPROBE involved in ion aggregation due to dipole-dipole or ion-dipole interaction. At higher POLYPROBE concentrations, without added POLYSALT, a triexponential decay function is needed to describe the emission. The third excited-state species is POLYPROBE excimer, which can be formed via two pathways: either intermolecularly when a locally excited POLYPROBE encounters a ground-state POLYPROBE or intramolecularly when an aggregate of two POLYPROBE molecules rearranges. From the global compartmental analysis in which the value of one of the rate constants is scanned, it is found that the bimolecular processes are slowed down by the presence of the polymer chain, while intramolecular rearrangements are not affected. [less ▲]

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