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See detailQuasi-Elastic Production at Hadronic Colliders
Dechambre, Alice ULg

Book published by Les Editions de l'Université de Liège (2010)

Quasi-elastic production is usually viewed as a golden signal for the detection of objects such as the Higgs boson(s) or exotic particles and this is due to the very clean final state and the lack of ... [more ▼]

Quasi-elastic production is usually viewed as a golden signal for the detection of objects such as the Higgs boson(s) or exotic particles and this is due to the very clean final state and the lack of hadronic remnants after the interaction. In view of the recent data from CDF Run II, we critically re-evaluated the standard approach to the calculation of quasi-elastic cross sections in the high-energy limit and evaluated the uncertainties that affect this kind of process. The main idea of this work was to understand the various ingredients that enter the calculation and the uncertainties coming from each of them. We studied and narrowed down these uncertainties using available data on dijets quasi-elastic event at the TeVatron. All the arguments developed apply to high-mass central systems and lead to a prediction of the Higgs quasi-elastic cross section at the LHC energies. [less ▲]

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See detailQuasi-loss of nationality - a new concept or a non-issue?
Wautelet, Patrick ULg; de Groot, Gerard-René

Conference (2014, April)

Quasi-loss of nationality : “is this a loss I see before me?” Prof. Gerard-René de Groot (University Maastricht, Aruba and Hasselt) Prof. Patrick Wautelet (University Liège) This paper focuses on ... [more ▼]

Quasi-loss of nationality : “is this a loss I see before me?” Prof. Gerard-René de Groot (University Maastricht, Aruba and Hasselt) Prof. Patrick Wautelet (University Liège) This paper focuses on situations in which a person is said never to have had the nationality of a country, even though (s)he assumed (and in many cases the authorities of the country concerned shared that assumption) that (s)he possessed that nationality. Contrary to situations of loss of nationality, where something is taken away which existed, those situations involve a decision that a nationality was never acquired. This subtle distinction between loss and non-acquisition will in most cases be lost on the persons concerned who will experience the decision as a loss of nationality. The central question of this paper is, whether these situations of quasi-loss differ so much from loss cases, that they have to be treated differently. If and insofar as this would be the case, a next question is, whether a person should under certain circumstances be protected against quasi-loss of her or his nationality. In order to answer these questions, the paper will first attempt to map out situations of quasi-loss in EU member states. Typical cases will be described in which a person did never acquire the nationality of the country, although (s)he was considered as a national before certain facts happened. Drawing on this taxonomy, the paper will offer a first attempt at uncovering whether national, European and international law offer some protection, and if yes, to which extent, for situations of quasi-loss. This paper will conclude with outlining best practices which Member States should comply with in handling quasi-loss situations. [less ▲]

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See detailLe "quasi-marché" de l'accompagnement des demandeurs d'emploi
Remy, Céline ULg

Conference given outside the academic context (2013)

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See detailA quasi-Newton algorithm for first-odrer saddle-point location
Culot, Patrick; Dive, Georges ULg; Nguyen, Van Hen et al

in Theoretica Chimica Acta (1992), 82

A new algorithm for the location of a transition-state structure on an energy hypersurface is proposed. The method is compared to three other quasi-Newton step calculations available in literature ... [more ▼]

A new algorithm for the location of a transition-state structure on an energy hypersurface is proposed. The method is compared to three other quasi-Newton step calculations available in literature. Numerical results derived from several examples are compared to those obtained by the two algorithms implemented in the Gaussian package. [less ▲]

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See detailA Quasi-One Dimensiona Model for Axial Turbines
Adam, Olivier; Léonard, Olivier ULg

in Proceedings of the 18th ISABE Conference (2007, September)

An axial turbine model is presented that is intended to predict its aerodynamic performance based only on the turbine geometry and thermodynamic environment. The model is an extension of an existing quasi ... [more ▼]

An axial turbine model is presented that is intended to predict its aerodynamic performance based only on the turbine geometry and thermodynamic environment. The model is an extension of an existing quasi-1D compressor representation. The simulation tool is able to compute the flow through a whole multistage turbine, with detail at the blade row level. It relies upon a quasi-one dimensional Euler system of equations, expressed here in curvilinear coordinates, and resulting from the application of mass, momentum and energy conservation principles in finite-volume formalism. The source terms expressing the interactions between the flow, the blades and the flowpath are determined using the velocity triangles for each blade row, at mid-span. The solver performs an elaborate implicit time-marching resolution of the equations. The enthalpy loss coefficients as well as the blade outlet flow angles are evaluated through open literature correlations. An efficient representation of the Craig-Cox loss coefficients and the Ainley-Mathieson outlet flow angle correlation brings the necessary empirical information for the velocity triangle computations. The computer code was validated against a high pressure turbine test case featuring multiple cooling flows. The results show the good capabilities of the turbine model using only standard correlations. The computed efficiency also shows the need to model the cooling losses. The low speed, low expansion rate results may finally indicate that the code accuracy would benefit from a correlation parametric identification such as the one led in the compressor case. [less ▲]

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See detailA Quasi-One Dimensional Model for Axial Compressors
Adam, Olivier; Léonard, Olivier ULg

in Proceedings od the 17th ISABE Conference (2005, September)

The object of the present paper is to present a fast and reliable CFD tool that is able to simulate stationary and transient operations of multistage axial compressors. The computational domain is the ... [more ▼]

The object of the present paper is to present a fast and reliable CFD tool that is able to simulate stationary and transient operations of multistage axial compressors. The computational domain is the compressor flow path, using a row-by-row, quasi-one-dimensional representation of the machine at mid-span. This analysis tool is based on an adapted version of the Euler equations solved by a time-marching, finite-volume method. The basic Euler equations have been extended by including source terms expressing the blade-flow interactions. The source terms are determined using the velocity triangles for each blade row, at mid-span. The losses and deviations undergone by the fluid in each blade row are supplied by correlations. The resulting flow solver is a performance prediction tool based only on compressor geometry. It offers the possibility of exploring the entire characteristic map of a compressor before its construction. Its efficiency in terms of CPU time makes it possible to use it as a fast design tool by coupling it to an optimization algorithm. In this paper, this CFD tool (called Quads hereafter) has been applied to two test-cases. Calculated characteristic curves are presented and compared to experimental ones. A correlation tuning process is described for an undocumented family of blade profiles. [less ▲]

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See detailA quasi-one-dimensional CFD model for multistage turbomachines
Léonard, Olivier ULg; Adam, Olivier

in Journal Of Thermal Science (2008), 17(1), 7-20

The objective of this paper is to present a fast and reliable CFD model that is able to simulate stationary and transient operations of multistage compressors and turbines. This analysis tool is based on ... [more ▼]

The objective of this paper is to present a fast and reliable CFD model that is able to simulate stationary and transient operations of multistage compressors and turbines. This analysis tool is based on an adapted version of the Euler equations solved by a time-marching, finite-volume method. The Euler equations have been extended by including source terms expressing the blade-flow interactions. These source terms are determined using the velocity triangles and a row-by-row representation of the blading at mid-span. The losses and deviations undergone by the fluid across each blade row are supplied by correlations. The resulting flow solver is a performance prediction tool based only on the machine geometry, offering the possibility of exploring the entire characteristic map of a multistage compressor or turbine. Its efficiency in terms of CPU time makes it possible to couple it to an optimization algorithm or to a gas turbine performance tool. Different test-cases are presented for which the calculated characteristic maps are compared to experimental ones. [less ▲]

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See detailQuasi-One-Dimensional Numerical Simulations of Post-Stall Compression Systems
Du, Wenhai ULg

Doctoral thesis (2013)

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See detailQuasi-Optimal Convergence of Non Overlapping Domain Decomposition Method: the Helmholtz Equation
Boubendir, Y.; Antoine, X.; Geuzaine, Christophe ULg

in Proceedings of the AMS 2010 Fall Central Section Meeting (2010, November)

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See detailA Quasi-Optimal Non-Overlapping Domain Decomposition Algorithm for the Helmholtz Equation
Boubendir, Y.; Antoine, X.; Geuzaine, Christophe ULg

in Journal of Computational Physics (2012), 231(2), 262-280

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See detailQuasi-periodic flares in Jupiter's aurora : new results
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, Sarah et al

Conference (2014, April 29)

Two recent Hubble Space Telescope observation campaigns have been dedicated to the Jovian Far-UV aurora (GO 12883 – PI: D. Grodent and GO 13035 – PI: S. Badman). Both of them made use of the Time-Tag mode ... [more ▼]

Two recent Hubble Space Telescope observation campaigns have been dedicated to the Jovian Far-UV aurora (GO 12883 – PI: D. Grodent and GO 13035 – PI: S. Badman). Both of them made use of the Time-Tag mode of the Space Telescope Imaging Spectrograph (STIS), a high time resolution mode which allows to observe temporal variations on timescales of tens of seconds. In the present study, we focus on sudden and spectacular bursts of auroral emissions taking place in the active region located poleward of the main emissions and called “flares”. A previous study, based on only two image sequences acquired with rather unfavorable viewing angles, showed that these flares could reappear quasi-periodically on time scales of 2-3 minutes. Phenomena with similar timescales have been identified by in-situ spacecraft in relativistic electron and radio data as well as in reconnection signatures, for example. But the physical mechanism behind these ubiquitous signatures remains to be unveiled. Here we make use of the most recent and much larger data set to study in further details the occurrence rate, the period, the location, the extent and the motion of these quasi-periodic flares and to compare their behavior in both hemispheres. Quantifying these parameters allows us to narrow down the possibilities among likely explanations and provide a tentative scenario for these short timescale quasi-periodic features. [less ▲]

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See detailQuasi-periodic polar flares at Jupiter: A signature of pulsed dayside reconnections?
Bonfond, Bertrand ULg; Vogt, M. F.; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2011), 38

The most dynamic part of the Jovian UV aurora is located inside the main auroral oval. This region is known to regularly show localized but dramatic enhancements on timescales of several tens of seconds ... [more ▼]

The most dynamic part of the Jovian UV aurora is located inside the main auroral oval. This region is known to regularly show localized but dramatic enhancements on timescales of several tens of seconds, called polar flares. They have often been associated with the polar cusp, based on their location in the polar cap. The present study is based on the longest high-time resolution image sequences ever acquired by the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. We report the first observations of a regularity in the occurrence of these flares, with a timescale of 2-3 minutes. We use a magnetic flux mapping model to identify the region corresponding to these emissions in the equatorial plane: the radial distance ranges from 55 to 120 Jovian radii and the local times are between 10: 00 and 18: 00. The analogy with similar phenomena observed at Earth suggests that these quasi-periodic auroral flares could be related to pulsed reconnections at the dayside magnetopause. Indeed, the flares' projected location in the equatorial plane and their rate of re-occurrence show some similarities with the properties of the flux transfer events observed by the Pioneer and Voyager probes. [less ▲]

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See detailQuasi-simultaneous XMM-Newton and VLA observation of the non-thermal radio emitter HD 168112 (O5.5III(f+))
De Becker, Michaël ULg; Rauw, Grégor ULg; Blomme, Ronny et al

in Astronomy and Astrophysics (2004), 420

We report the results of a multiwavelength study of the non-thermal radio emitter HD 168112 (O5.5III(f+)). The detailed analysis of two quasi-simultaneous XMM-Newton and VLA observations reveals strong ... [more ▼]

We report the results of a multiwavelength study of the non-thermal radio emitter HD 168112 (O5.5III(f+)). The detailed analysis of two quasi-simultaneous XMM-Newton and VLA observations reveals strong variability of this star both in the X-ray and radio ranges. The X-ray observations separated by five months reveal a decrease of the X-ray flux of ˜30%. The radio emission on the other hand increases by a factor 5-7 between the two observations obtained roughly simultaneously with the XMM-Newton pointings. The X-ray data reveal a hard emission that is most likely produced by a thermal plasma at kT ˜ 2-3 keV while the VLA data confirm the non-thermal status of this star in the radio waveband. Comparison with archive X-ray and radio data confirms the variability of this source in both wavelength ranges over a yet ill defined time scale. The properties of HD 168112 in the X-ray and radio domain point towards a binary system with a significant eccentricity and an orbital period of a few years. However, our optical spectra reveal no significant changes of the star's radial velocity suggesting that if HD 168112 is indeed a binary, it must be seen under a fairly low inclination. [less ▲]

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See detailQUASI-STATIC MECHANICAL BEHAVIOUR OF TI-6AL-4V ALLOY AT ROOM TEMPERATURE
Tuninetti Vásquez, Victor ULg; Gilles, Gaëtan ULg; Milis, Olivier ULg et al

in Complas XII (2013), XII

In order to determine the mechanical behavior of a bulk TA6V alloy, a set of mechanical tests such as shear, compression, tensile monotonic tests, and tensile tests on notched samples are performed. The ... [more ▼]

In order to determine the mechanical behavior of a bulk TA6V alloy, a set of mechanical tests such as shear, compression, tensile monotonic tests, and tensile tests on notched samples are performed. The material is tested at constant strain rate. Full-field optical technique for displacement measurements and strain computation are used for all the experiments. Plastic anisotropy and tension–compression asymmetry are observed. The CPB06 [1] yield criterion adapted for hexagonal close packed (hcp) material is identified. The sensitivity of the material parameters on the identification method as well as the efficiency of the model to predict forces and displacement field are discussed. Validation is done by using Finite Element method (FEM) simulations and 3D Digital Image Correlation (3D-DIC) measurements on specimens with multi-axial stress and strain fields subjected to large deformation. [less ▲]

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See detailQuasi-Static Response
Rigo, Philippe ULg; Sumi, et al.; Comité II.1

in 13th Int. Ship and Offshore Structures Congress (1997)

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See detail"Quasi-Static Response" (Discussion on the Report of Committee II.1); Reply to E. Rizzuto)
Rigo, Philippe ULg

in 13th Int. Ship and Offshore Structures Congress (1999)

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See detailQuasicontinuum study of the shear behavior of defective tilt grain boundaries in Cu
Péron-Lührs, Vincent ULg; Sansoz, Frédéric; Noels, Ludovic ULg

in Acta Materialia (2014), 64

Atomistic simulations using the quasicontinuum method are used to study the role of vacancy defects and angström-scale voids on the mechanical behavior of five tilt bicrystals containing grain boundaries ... [more ▼]

Atomistic simulations using the quasicontinuum method are used to study the role of vacancy defects and angström-scale voids on the mechanical behavior of five tilt bicrystals containing grain boundaries (GBs) that have been predicted to exhibit characteristic deformation processes of nanocrystalline and nanotwinned metals: GB-mediated dislocation emission, interface sliding, and shear-coupled GB migration. We demonstrate that such nanoscale defects have a profound impact on interfacial shear strength and underlying deformation mechanisms in copper GBs due to void-induced local stresses. In asymmetric high and low angle GBs, we find that voids become preferential sites for dislocation nucleation when the void size exceeds 4 Å. In symmetric 9(221) GBs prone to sliding, voids are shown to shield the local shear stress, which considerably reduces the extent of atom shuffling at the interface. In symmetric Sigma5(210) and Sigma27(115) GBs, we find that the effect of voids on shear-coupled GB migration depends on the GB tilt direction considered, as well as on the size and number of voids. Remarkably, large voids can completely abate the GB migration process in Sigma 27(115) GBs. For all GB types, the interfacial shear strength is shown to decrease linearly as the volume fraction of voids at the interface increases; however, this study also suggests that this decrease is much more pronounced in GBs deforming by sliding than by dislocation nucleation or migration, owing to larger void-induced stresses. [less ▲]

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