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See detailThe global modal parameterization for non-linear model-order reduction in flexible multibody dynamics
Bruls, Olivier ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

in International Journal for Numerical Methods in Engineering (2007), 69(5), 948-977

In flexible multibody dynamics, advanced modelling methods lead to high-order non-linear differential-algebraic equations (DAEs). The development of model reduction techniques is motivated by control ... [more ▼]

In flexible multibody dynamics, advanced modelling methods lead to high-order non-linear differential-algebraic equations (DAEs). The development of model reduction techniques is motivated by control design problems, for which compact ordinary differential equations (ODEs) in closed-form are desirable. In a linear framework, reduction techniques classically rely on a projection of the dynamics onto a linear subspace. In flexible multibody dynamics, we propose to project the dynamics onto a submanifold of the configuration space, which allows to eliminate the non-linear holonomic constraints and to preserve the Lagrangian structure. The construction of this submanifold follows from the definition of a global modal parameterization (GMP): the motion of the assembled mechanism is described in terms of rigid and flexible modes, which are configuration-dependent. The numerical reduction procedure is presented, and an approximation strategy is also implemented in order to build a closed-form expression of the reduced model in the configuration space. Numerical and experimental results illustrate the relevance of this approach. Copyright (c) 2006 John Wiley [less ▲]

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See detailA global model of the biosphere : validation and applications to present and past climatic conditions
François, Louis ULg; Gérard, Jean-Claude ULg; Nemry, Bernard et al

in Sciences Géologiques. Bulletin (1997), 50(1-4), 89-107

Detailed reference viewed: 21 (7 ULg)
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See detailGlobal Modeling of X-Ray Spectra Produced in O-type Star Winds
Hervé, Anthony ULg; Rauw, Grégor ULg; Nazé, Yaël ULg et al

in Astrophysical Journal (2012), 748

High-resolution X-ray spectra of O-type stars revealed less wind absorption than expected from smooth winds with conventional mass-loss rates. Various solutions have been proposed, including porous winds ... [more ▼]

High-resolution X-ray spectra of O-type stars revealed less wind absorption than expected from smooth winds with conventional mass-loss rates. Various solutions have been proposed, including porous winds, optically thick clumps, or an overall reduction of the mass-loss rates. The latter has a strong impact on the evolution of the star. Our final goal is to analyze high-resolution X-ray spectra of O-type stars with a multi-temperature plasma model in order to determine crucial stellar and wind parameters such as the mass-loss rate, the CNO abundances, and the X-ray temperature plasma distribution in the wind. In this context we are developing a modeling tool to calculate synthetic X-ray spectra. We present here the main ingredients and physics necessary for such a work. Our code uses the most recent version of the AtomDB emissivities to compute the intrinsic emissivity of the hot plasma as well as the CMFGEN model atmosphere code to evaluate the opacity of the cool wind. Following the comparison between two formalisms of stellar wind fragmentation, we introduce, for the first time in X-rays, the effects of a tenuous inter-clump medium. We then explore the quantitative impact of different model parameters on the X-ray spectra such as the position in the wind of the X-ray emitting plasma. For the first time, we also show that the two formalisms of stellar wind fragmentation yield different results, although the differences for individual lines are small and can probably not be tested with the current generation of X-ray telescopes. As an illustration of our method, we compare various synthetic line profiles to the observed O VIII λ18.97 line in the spectrum of ζ Puppis. We illustrate how different combinations of parameters can actually lead to the same morphology of a single line, underlining the need to analyze the whole spectrum in a consistent way when attempting to constrain the parameters of the wind. [less ▲]

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See detailGlobal modelling of structures in fire
Gillie, M.; Burgess, I.; Franssen, Jean-Marc ULg et al

in Mazzolani, Federico (Ed.) Proceedings of Urban Habitat Constructions under Catastrophic Events (COST Action C26) (2008)

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See detailGlobal modelling of structures in fire
Gillie, Martin; Burgess, Ian; Franssen, Jean-Marc ULg et al

in Urban Habitat Constructions under catastrophic events - Technical sheets – Fire Resistance (2009)

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See detailGlobal morphology of substorm growth phases observed by the IMAGE-SI12 imager
Blockx, Caroline ULg; Gérard, Jean-Claude ULg; Coumans, Valérie ULg et al

Poster (2007)

Growth phases are observed to start from less than 30 minutes to over an hour before the substorm onset. The sector of maximum proton precipitation during the growth phase is generally located around 2200 ... [more ▼]

Growth phases are observed to start from less than 30 minutes to over an hour before the substorm onset. The sector of maximum proton precipitation during the growth phase is generally located around 2200 MLT. It rapidly moves in local time by about 1.2 hour toward midnight at the time of the onset. The open magnetic flux increases by as much as a 33% during the growth phase. The mean value of the open flux at the end of the growth phase, immediately preceding the substorm, onset is about 0.74. GWb for substorms triggered by external (solar wind) factors and 0.67 GWb for non-triggered substorms. The open magnetic flux generally drops following the onset of triggered substorms but continues to increase for non-triggered events. We interpret this behavior as an indication that the rate of opening of closed field lines on the dayside can exceed that of the nightside reconnection after the onset in non-triggered substorms. By contrast, flux closure is more efficient while the flux opening rate drops in the case of externally triggered onset, so that the closure rate exceeds that of field line opening on the dayside. The rate of equatorward displacement is typically ~ 3 deg/hour. It is statistically correlated with the magnitude of the southward Bz component of the IMF measured by the ACE satellite. It is also correlated with transfer functions describing the efficiency of solar wind energy transfer which involve the transverse electric field carried by the solar wind. The equatorward motion may be global, restricted to local time sectors or a combination of both. No nightside local time sector appears favored where the motion of the equatorial boundary would be more pronounced. The maximum displacement of the polar boundary is statistically located around midnight MLT. [less ▲]

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See detailGlobal morphology of substorm growth phases observed by the IMAGE-SI12 imager
Coumans, Valérie ULg; Blockx, Caroline ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research (2007), 112(A11),

We present case studies and a statistical summary of optical observations of proton precipitation made during substorm growth phases. Our analysis is based on observations of the Doppler-shifted Lyman ... [more ▼]

We present case studies and a statistical summary of optical observations of proton precipitation made during substorm growth phases. Our analysis is based on observations of the Doppler-shifted Lyman-alpha auroral emission obtained with the SI12 Spectrographic Imager on board the IMAGE satellite. These images are used to determine the morphology and dynamics of the auroral oval and of the polar cap boundary on a global scale, as well as the total open magnetic flux and its time evolution. We also investigate the relationship with the solar wind and the interplanetary magnetic field ( IMF) characteristics measured by the ACE satellite and with the magnetic elevation angle measured by GOES-8. The statistical study shows that the sector of maximum proton precipitation during the growth phase is on average centered around 2200 MLT and rapidly shifts in local time by about 1.2 h toward midnight at the time of the onset. The open magnetic flux increases by 33% on average during the growth phase. The mean value of the open flux immediately before the substorm onset is about 0.66 GWb for substorms triggered by a northward turning of B-z and 0.74 GWb for nontriggered substorms. The averaged open flux at the substorm onset is smallest when the substorm is triggered by a sudden reversal of B-z, suggesting that the accumulation of energy by the magnetosphere is perturbed by changes in B-z. The open magnetic flux continues to increase during the 20 min following the onset, for a large number of events. The rate of equatorward displacement of the auroral oval boundaries during growth phase is typically similar to 3 deg/h. It is statistically correlated (r=0.40) with the magnitude of the Bz component of the IMF measured by the ACE satellite. It is also correlated, with higher coefficient (r=0.54), with functions describing the efficiency of solar wind energy transfer involving the transverse electric field carried by the solar wind. The equatorward motion may be global, restricted to local time sectors or a combination of both. At no nightside local time sector does the motion of the equatorial boundary appear more pronounced than at others, but the maximum displacement of the polar boundary is statistically located around midnight MLT. [less ▲]

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See detailGlobal Navigation Satellite Systems : A new tool in atmosphere sciences
Warnant, René ULg; Jodogne, Jean-Claude; Delobbe, Laurent et al

in Arijs, E.; Ducarme, B. (Eds.) Proceedings of the Earth Science Day : “Geodesy and Geophysics for the third Millenium in Belgium” (2005)

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See detailGlobal observations of proton and electron auroras in a substorm
Mende, S. B.; Frey, H. U.; Lampton, M. et al

in Geophysical Research Letters (2001), 28

This is the first report of a substorm observed by the IMAGE FUV instruments permitting global observations of electron and proton produced auroras. On the 28th of June 2000 at 1956 UT in the pre-substorm ... [more ▼]

This is the first report of a substorm observed by the IMAGE FUV instruments permitting global observations of electron and proton produced auroras. On the 28th of June 2000 at 1956 UT in the pre-substorm phase at early evening local time the proton aurora was equatorward of the electron precipitation and near midnight they were collocated. There was bright electron and proton aurora in the post midday afternoon side. The sudden brightening of the aurora at substorm onset near midnight is seen in the electrons only although there are protons present at this location. During the expansive phase both the electrons and protons expand poleward. The electron aurora forms a bright surge at the poleward boundary while the protons just show diffuse spreading. The peak intensity of the protons did not change substantially during the entire event. The proton aurora is brighter on the dusk while the electron aurora on the dawn side. As the electron surge expands poleward it leaves the protons behind. The electrons form a discrete auroral feature near the aurora-polar cap boundary, which is devoid of substantial energetic (>1 keV) proton precipitation. The presence of precipitating protons at the point where the initial brightening is seen shows that substorms are initiated on closed field lines. [less ▲]

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See detailA global overview of performance evaluation
Mouchamps, Hugues ULg

Conference (2011, March 04)

Performance evaluation presents two specific difficulties for social enterprises. At the one hand, it is complex to define what performance is, to measure the factors impacting performance through ... [more ▼]

Performance evaluation presents two specific difficulties for social enterprises. At the one hand, it is complex to define what performance is, to measure the factors impacting performance through indicators, and to sum up the scores of all the indicators. At the other hand, performance evaluation should vary with the purpose of the evaluation and the type of organization. Thus the characteristics of an ideal performance evaluation tool for social enterprises should both reflect this complexity and be contingent. [less ▲]

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See detailGlobal overview of the educational system in the French speaking Community of Belgium
Schillings, Patricia ULg; Gabelica, C.

E-print/Working paper (2007)

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See detailGlobal Power after the post-Cold War: the case of Chinese Power
Wintgens, Sophie ULg

in Revista Brasileira de Politica Internacional (in press)

The pre-eminence of the realistic conception has long locked the field of study of the power in International Relations, which is nowadays highly questioned. The analysis of some “new powers” emergence is ... [more ▼]

The pre-eminence of the realistic conception has long locked the field of study of the power in International Relations, which is nowadays highly questioned. The analysis of some “new powers” emergence is as such a tremendous learning experience. In order to go beyond the classical antagonism between the institutional perspectives (cooperation) and the realistic ones (rivalry), this paper deals with the power in an alternative way, from a heterodox approach of hegemony, which allows us to make out the phenomena of insidious and not felt so domination. Following the example of China, committed to building a status of world power, sustained by a self-legitimizing discourse abounding with Third-World overtones (anti-hegemonism, multipolarization of the world, South-South cooperation, etc.), the increase in its global influence does not only depend on the availability of its – tangible and intangible – resources, nor on its ability to mobilize them adequately (smart power). China also values the image that it has of itself (self-perception), the image that it tends to convey on the international stage (representation), as well as the perception of its status by the other actors of the international system (external recognition). The power of China is measured through its capacity to “assert itself as a reference” for its emerging peers, or even for Western powers. [less ▲]

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See detailGlobal power grids for harnessing world renewable energy
Chatzivasileiadis, Spyros; Ernst, Damien ULg; Andersson, Göran

in Jones, Lawrence (Ed.) Renewable Energy Integration: Practical Management of Variability, Uncertainty and Flexibility in Power Grids (2014)

The Global Grid advocates the connection of all regional power systems into one electricity transmission system spanning the whole globe. Power systems are currently forming larger and larger ... [more ▼]

The Global Grid advocates the connection of all regional power systems into one electricity transmission system spanning the whole globe. Power systems are currently forming larger and larger interconnections. Environmental awareness and increased electricity consumption leads more investments towards renewable energy sources, abundant in remote locations (off-shore or in deserts). The Global Grid will facilitate the transmission of this “green” electricity to load centers, serving as backbone. This chapter elaborates on the concept presenting four stages that could gradually lead to the development of a globally interconnected power network. Quantitative analyses are carried out for all stages, demonstrating that a Global Grid is both technically feasible and economically competitive. Real price data from Europe and the USA are used to identify the potential of intercontinental electricity trade, showing that substantial profits can be generated through such interconnections. [less ▲]

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See detailGlobal prevalence and skeletal implications of vitamin D inadequacy
Reginster, Jean-Yves ULg; Richy, Florent; Rabenda, Véronique ULg et al

in Annals of the Rheumatic Diseases (2005, June), 64(Suppl.III), 362

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See detailA Global Procedure for the Measurement of Selected POPs in Food
PIRARD, Catherine ULg; Focant, Jean-François ULg

Scientific conference (2007, June)

Detailed reference viewed: 3 (0 ULg)
See detailA Global Procedure for the Measurement of Selected POPs in Food
Focant, Jean-François ULg; PIRARD, Catherine ULg

Scientific conference (2007, June)

Detailed reference viewed: 4 (0 ULg)
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See detailGlobal Sensitivity Analysis applied to Total Energy Use in Buildings
Ruiz Flores, Roberto ULg; Bertagnolio, Stéphane ULg; Lemort, Vincent ULg

in Proceedings of the 2nd International High Performance Buildings Conference (2012, July 16)

The work presented in this paper has been carried out in the frame of the IEA-ECBCS Annex 53 project: “Total Energy Use in Buildings: Analysis and evaluation methods”. The aim of this work is to present a ... [more ▼]

The work presented in this paper has been carried out in the frame of the IEA-ECBCS Annex 53 project: “Total Energy Use in Buildings: Analysis and evaluation methods”. The aim of this work is to present a methodology to identify the most influential parameters affecting the final energy consumption in office buildings. In order to represent buildings and HVAC systems, a representative typology was defined, modeled and simulated and subsequently a global sensitivity analysis (variance-based method) was performed. This paper provides useful information to future works related to design building decisions, building calibration, energy management strategy, etc. helping to detect and rank those factors which need to be better measured and/or estimated, in order to improve building energy efficiency. [less ▲]

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See detailGlobal Social Economy: Historical Context and Current Progress
Defourny, Jacques ULg; Develtere, Patrick; Zhao, Li

in Journal of Comparative Economic and Social Systems = Jingji Shehui Tizhi Bijiao (2011), 153(1), 146-157

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See detailGlobal stabilization of feedforward systems with exponentially unstable Jacobian linearization
Grognard, F.; Sepulchre, Rodolphe ULg; Bastin, G.

in Systems & Control Letters (1999), 37(2), 107-115

The global stabilization of a class of feedforward systems having an exponentially unstable Jacobian linearization is achieved by a high gain feedback saturated at a low level. The control law forces the ... [more ▼]

The global stabilization of a class of feedforward systems having an exponentially unstable Jacobian linearization is achieved by a high gain feedback saturated at a low level. The control law forces the derivatives of the state variables to small values along the closed loop trajectories. This “slow control” design is illustrated with a benchmark example and its limitations are emphasized. [less ▲]

Detailed reference viewed: 18 (1 ULg)