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See detailOn the Impact of Layer-2 on Node Degree Distribution
Mérindol, Pascal; Donnet, Benoît ULg; Bonaventure, Olivier et al

in 10th annual conference on Internet measurement (2010, November)

The Internet topology data collected through traceroute exploration has been extensively studied in the past. In particular, a remarkable property of the Internet, the power-law shape of node degree ... [more ▼]

The Internet topology data collected through traceroute exploration has been extensively studied in the past. In particular, a remarkable property of the Internet, the power-law shape of node degree distribution, drew the attention of the research community. Several studies have since questioned this property. In this paper, based on a large dataset collected using mrinfo, we show that the node degree distribution is strongly impacted by the presence of layer-2 (L2) networks, such as switches. L2 devices interconnect a large number of routers, themselves being also involved in multiple L2 interconnec- tions. Such a situation induces nodes with very high degree when analyzing the layer-3 (L3) graph with traceroute probing. Considering the physical design of a network, our analysis provides a lower bound on the bias generated by using only an L3 view. We also provide a model that can be a first step towards L2 aware topology generation. [less ▲]

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See detailOn the implementation of a sensitivity analysis in a flexible multibody dynamics environment
Bruls, Olivier ULg; Duysinx, Pierre ULg; Eberhard, Peter

Conference (2006, June)

The dynamic performance of complex mechanisms, such as machine tools, manipulators, vehicles, engines or foldable structures, can be strongly affected by flexible phenomena. Therefore, the deformation ... [more ▼]

The dynamic performance of complex mechanisms, such as machine tools, manipulators, vehicles, engines or foldable structures, can be strongly affected by flexible phenomena. Therefore, the deformation effects should be considered as soon as possible in the design procedure, which motivates the development of automatic optimization techniques for flexible multibody systems. Advanced software tools are able to simulate the dynamic behaviour of such systems, but they typically involve extensive numerical treatments. Hence, gradient-based optimization methods are of special interest since they require a quite low number of simulations, but an important problem is to obtain the sensitivities of the objective function with respect to the design parameters. Since finite difference approaches lack robustness and computational efficiency, we propose to investigate analytical or semi-analytical sensitivity analysis. Several difficulties are inherent to the simulation of flexible mechanisms. A consistent geometric formulation is necessary to describe large amplitude motion as well as possible large deformations. Here, according to the nonlinear finite element formulation, the motion is parameterized using absolute nodal coordinates, and an updated Lagrangian point of view is adopted for the rotation parameters. The joints and the rigid-body conditions are represented by algebraic constraints between the nodal coordinates, leading to differential algebraic equations of motion (DAEs). Finally, the computation of the trajectories requires a reliable simulation algorithm for nonlinear DAEs. A strong advantage of the finite element method comes from its very systematic implementation, which facilitates the development of a semi-analytical sensitivity analysis. In this work, sensitivity analysis is performed for beam elements, rigid bodies and ideal joints. The global sensitivity is then obtained by numerical assembly of the elementary contributions and by integration in the time domain. Thus, a single but extended simulation is sufficient to compute the sensitivities with respect to all parameters. In order to illustrate the method and to demonstrate its efficiency, we consider the optimal design of a car engine, where the flexibility of the connecting rods between the crankshaft and the pistons is taken into account. The objective is to find a feasible mechanical design which minimizes the level of vibrations. [less ▲]

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See detailOn the implementation of morphological operations
Van Droogenbroeck, Marc ULg

in Serra, Jean; Soille, Pierre (Eds.) Mathematical morphology and its applications to image processing (1994)

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See detailOn the importance of an M2 depopulating channel for a KrII metastable state
Biémont, Emile ULg; Derkatch, A.; Lundin, P. et al

in Physical Review Letters (2004), 93(6),

An experimental investigation of the radiative lifetime of the metastable 4s(2)4p(4)(P-3)4d D-4(7/2) level in Kr II shows an unusual situation regarding the importance of an M2 depopulation channel. While ... [more ▼]

An experimental investigation of the radiative lifetime of the metastable 4s(2)4p(4)(P-3)4d D-4(7/2) level in Kr II shows an unusual situation regarding the importance of an M2 depopulation channel. While the first order M1 and E2 channels are expected to contribute in a dominant way to the decay, the experimental result, obtained using a laser probing technique on a stored ion beam, tau=0.57+/-0.03 s, is far too short to be due to these channels according to our relativistic multiconfiguration Dirac-Fock calculation. Only if second order contributions to the decay branches (including essentially the M2 contribution) are taken into account in the calculations could the unexpected short lifetime be explained. [less ▲]

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See detailOn the Importance of Being (More) Attentive. Another Look at Descartes' Practice of Meditation.
Dubouclez, Olivier ULg

Conference (2014, October 11)

At the beginning of Meditation IV the meditator triumphantly announces that he has “now no difficulty in turning away (convertam) from imaginable things and toward things which are objects of the ... [more ▼]

At the beginning of Meditation IV the meditator triumphantly announces that he has “now no difficulty in turning away (convertam) from imaginable things and toward things which are objects of the intellect alone” (AT, VII, 53). Meditation VI thereafter confirms that pure intellection, as opposed to imagination, consists only in turning towards oneself (convertat) and demands no “peculiar effort of the mind” (73). However efforts of attention are required throughout the Meditations and Meditations IV, V and VI are no exceptions in this respect. Descartes’ Second Set of Replies (156-159) confirms that attention is needed as a mental support for metaphysical analysis in order to embrace different ideas and connect different parts of a demonstration. A thorough examination of the Meditations shows something even more interesting: attention is conceived by Descartes as a varying force that can be diminished or relaxed but also, and most importantly, increased as comparative forms like “attentius” (19; 55; 66; 71) or “diligentius” (32; 35; 45) suggest. For sure, it is an original aspect of Cartesian meditative exercise: we are not only invited to maintain our attention but also to make it more intense at a certain point. Such an increase is crucial for the development of the dream argument (55) and also for the achievement of both proofs of the existence of God (45; 66). But is it not a kind of deus ex machina that the meditator puts forward in order to overcome otherwise unsolvable difficulties? A posterior work, The Passions of the Soul, can help us understand such a strategy. In article 72, Descartes distinguishes between two kinds of attention; the first one stems from wonder and is “at its full strength from the start” (XI, 382); it is contrasted with a second type “which, being weak at first and growing only gradually, can be easily diverted” (Ibid.) Further on Descartes says that passion is useful in “strengthening thoughts… and causing them to endure into the soul” (383) but that “the application of our understanding” has the same effect when “our will fixes [it] in a particular attention or reflection” (384). This last case applies to the Meditations: the meditator who is constantly exposed to misleading influences would be easily “diverted” and even stopped if he was not pushed by his own will to go further in his metaphysical inquiry. “Peaks” of attention occurring in the Meditations are caused by volitions originating in the meditator’s resolution to attain truth and certainty and, as we shall see, they are used against three types of harmful influence: sensitive in Meditation I, imaginative in Meditation II and III, and intellectual in Meditation IV and V where old philosophical habits stand in the way of Cartesian theology. [less ▲]

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See detailOn the Importance of Octupole Transitions in Atomic Spectra
Biémont, Emile ULg

in Physica Scripta (1997), T73

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See detailOn the importance of the 1-loop finite corrections to seesaw neutrino masses.
Aristizabal Sierra, Diego ULg; Yaguna, Carlos

in Journal of High Energy Physics [=JHEP] (2011)

In the standard seesaw mechanism, finite corrections to the neutrino mass matrix arise from 1-loop self-energy diagrams mediated by a heavy neutrino. We study in detail these corrections and demonstrate ... [more ▼]

In the standard seesaw mechanism, finite corrections to the neutrino mass matrix arise from 1-loop self-energy diagrams mediated by a heavy neutrino. We study in detail these corrections and demonstrate that they can be very significant, exceeding in several cases the tree-level result. We consider the normal and inverted hierarchy spectra for light neutrinos and compute the finite corrections to the different elements of the neutrino mass matrix. Special attention is paid to their dependence with the parameters of the seesaw model. Among the cases in which the corrections can be large, we identify the fine-tuned models considered previously in the literature, where a strong cancellation between the different parameters is required to achieve compatibility with the experimental data. As a particular example, we also analyze how these corrections modify the tribimaximal mixing pattern and find that the deviations may be sizable, in particular for θ13. Finally, we emphasize that due to their large size, the finite corrections to neutrino masses have to be taken into account if one wants to properly scan the parameter space of seesaw models. [less ▲]

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See detailOn the increasing relevance of time in later Late Egyptian: jw sDm=f and jw jw=f r sDm, and other things
Winand, Jean ULg

in Lingua Aegyptia [= LingAeg] (2015), 22

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See detailON THE INFLUENCE OF A NON-LOCAL ELECTRODYNAMICS IN THE IRREVERSIBLE MAGNETIZATION OF NON-MAGNETIC BOROCARBIDES
Silhanek, Alejandro ULg; Civale, L.; Thompson, J.R. et al

in Annett, James F.; Kruchinin, Sergei (Eds.) New Trends in Superconductivity (2002)

We present an overview of the temperature, field and angular dependence of the irreversible magnetization of non-magnetic borocarbides (Y;Lu)Ni2B2C.We show that nonlocal electrodynamics influences pinning ... [more ▼]

We present an overview of the temperature, field and angular dependence of the irreversible magnetization of non-magnetic borocarbides (Y;Lu)Ni2B2C.We show that nonlocal electrodynamics influences pinning via the unusual behavior of the shear modulus in non-hexagonal lattices. On top of that, we observe that the pinning force density Fp exhibits a rich anisotropic behavior that sharply contrasts with its small mass anisotropy. When H⊥c, Fp is much larger and has a quite different H dependence, indicating that other pinning mechanisms are present. [less ▲]

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See detailOn the influence of aluminium and silicon contents on the kinetics of bainite transformation of intercritical austenite
Mertens, Anne ULg; Jacques, Pascal J.; Zhao, Lie et al

Conference (2002, June)

TRIP-assisted steels show enhanced mechanical properties thanks to the strain-induced transformation of retained austenite to martensite (TRIP effect). Stabilization of austenite is made possible by the ... [more ▼]

TRIP-assisted steels show enhanced mechanical properties thanks to the strain-induced transformation of retained austenite to martensite (TRIP effect). Stabilization of austenite is made possible by the combination of appropriate chemical composition (containing classically high levels of silicon, or, as developed more recently, aluminium) and of a two-steps heat treatment comprising an intercritical annealing followed by an isothermal holding in the bainite formation range. A detailed understanding of the effects of both elements on the bainite transformation kinetics is thus of primary importance for the optimization of austenite retention. The present study aims at a better knowledge of the influence of aluminium levels on the kinetics of the bainite transformation of intercritical austenite, as compared to the effect of silicon. The bainite transformation kinetics was followed by dilatometry in a set of 6 steel grades with varying aluminium and silicon contents. These dilatometry experiments were coupled with a characterization of the microstructures by X-ray diffraction, SEM and image analysis in order to assess the occurrence of an incomplete reaction phenomenon. It was shown that aluminium has a less pronounced effect than silicon in retarding the bainite transformation. A model was proposed to account for this retarding effect as a function of aluminium or silicon contents. [less ▲]

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See detailOn the influence of aluminium and silicon contents on the kinetics of bainite transformation of intercritical austenite
Mertens, Anne ULg; Jacques, Pascal J.; Zhao, Lie et al

in Journal de Physique IV (2003), 112

TRIP-assisted steels show enhanced mechanical properties thanks to the strain-induced transformation of retained austenite to martensite (TRIP effect). Stabilisation of austenite is made possible by the ... [more ▼]

TRIP-assisted steels show enhanced mechanical properties thanks to the strain-induced transformation of retained austenite to martensite (TRIP effect). Stabilisation of austenite is made possible by the combination of appropriate chemical composition (containing classically high levels of silicon, or, as developed more recently, aluminium) and of a two-steps heat treatment comprising an intercritical annealing followed by an isothermal holding in the bainite formation range. A detailed understanding of the effects of both elements on the bainite transformation kinetics is thus of primary importance for the optimisation of austenite retention. The present study aims at a better knowledge of the influence of aluminium levels on the kinetics of the bainite transformation of intercritical austenite, as compared to the effect of silicon. The bainite transformation kinetics was followed by dilatometry in a set of 6 steel grades with varying aluminium and silicon contents. These dilatometry experiments were coupled with a characterisation of the microstructures by X-ray diffraction, SEM and image analysis. It was shown that aluminium has a less pronounced effect than silicon in retarding the bainite transformation [less ▲]

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See detailOn the influence of aluminium content on the stability of retained austenite in multiphase TRIP-assisted steels
Mertens, Anne ULg; Jacques, Pascal J.; Lazarova, Roumiana et al

in Journal de Physique IV (2001), 11

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See detailOn the influence of aluminium content on the stability of retained austenite in multiphase TRIP-assisted steels
Mertens, Anne ULg; Jacques, Pascal J.; Lazarova, Roumiana et al

Poster (2000, September)

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See detailOn the influence of background component in resonance of cables
Canor, Thomas ULg; Denoël, Vincent ULg

in 9th International Symposium on Cable Dynamics: ISCD 2011, Proceedings (2011)

This work deals with nonlinear dynamical behaviour of cables in the context of random excitations of one of its anchors. Different studies have already been realized, that highlight different cable ... [more ▼]

This work deals with nonlinear dynamical behaviour of cables in the context of random excitations of one of its anchors. Different studies have already been realized, that highlight different cable responses under random excitations such as white noise or narrow band processes. This work can be seen as an extension of these former works. It aims at modeling a more realistic random excitation by associating a background component to a resonant excitation. The background component models the effects of turbulence on the structure and the resonant component results from structural vibrations of the primary system. Any direct excitation on the cable is disregarded in this work. The first part of this paper describes the model and the random excitation generators. The second part deals with the influence of the background component on the possible resonance of a cable. Results are presented for a given level of energy in the excitation, and as a function of its dispatching between the background and resonant components. This work shows that the background component reduces the vibration in the out-of-plane mode and can avoid resonance from taking place. The on-off intermittency phenomenon is also observed for the out-of-plane mode and it depends also on the background component. [less ▲]

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See detailOn the Influence of Blends on the Potential of Ground-based Transit Surveys
Gillon, Michaël ULg; Magain, Pierre ULg

in Afonso, C.; Weldrake, D.; Henning, T. (Eds.) Transiting Extrapolar Planets Workshop (2007, July 01)

Transit surveys have to observe many stars all at once in order to compensate for the rarity of the searched events. Such surveys, especially the ones observing a deep field of view and/or broadening ... [more ▼]

Transit surveys have to observe many stars all at once in order to compensate for the rarity of the searched events. Such surveys, especially the ones observing a deep field of view and/or broadening their stellar images, have to deal with a relatively high level of crowding. This crowding could lead to a reduction of the number of detectable transits, and the estimation of the potential of such surveys without taking into account the influence of blends could give overoptimistic results. We have developed a code which allows to estimate the extent by which such a survey is affected by the crowding of the field of view. Our results show that the influence of blends is important only for severe levels of crowding and is in general much less crucial than the influence of red noise. [less ▲]

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