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See detailQuartiles d'une série statistique univariée : quelles définitions ?
Henry, Valérie ULg

in Losanges (2010), 7

Sur base d'une étude comparative de la littérature sur le sujet, nous proposons une définition du premier quartile qui permette de rester en cohérence avec la définition de celui-ci pour une variable ... [more ▼]

Sur base d'une étude comparative de la littérature sur le sujet, nous proposons une définition du premier quartile qui permette de rester en cohérence avec la définition de celui-ci pour une variable quantitative dont les données ont été réparties en classes. [less ▲]

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See detailIl quarto musicista
Emmanuel, François; Ricciardi, Stefania ULg

Book published by San Paolo (2003)

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See detailQuasar Candidates in a Large Field Centered around NGC450 and the Discovery of a New Very Interesting Pair of Quasars
Swings, Jean-Pierre ULg; Surdej, Jean ULg; Henry, A. et al

in Revista Mexicana de Astronomia y Astrofisica, vol. 10 (1985), 10

Abstract image available at: http://esoads.eso.org/abs/1985RMxAA..10...91S

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See detailQuasar Host Orientation and Polarization: Insights into the Type 1/Type 2 Dichotomy
Borguet, Benoît ULg; Hutsemekers, Damien ULg; Letawe, Géraldine ULg et al

in Revista Mexicana de Astronomía y Astrofísica (2008), 32

We investigate correlations between the optical linear polarization position angle and the orientation of the host galaxy/extended emission of Type 1 and Type 2 Radio-Loud (RL) and Radio-Quiet (RQ ... [more ▼]

We investigate correlations between the optical linear polarization position angle and the orientation of the host galaxy/extended emission of Type 1 and Type 2 Radio-Loud (RL) and Radio-Quiet (RQ) quasars. We have used high resolution Hubble Space Telescope (HST) data and deconvolution process to obtain a good determination of the host galaxy orientation. With these new measurements and a compilation of data from the literature, we find a significant correlation between the polarization position angle and the position angle of the major axis of the host galaxy/extended emission. The correlation appears different for Type 1 and Type 2 objects and depends on the redshift of the source. Interpretations in the framework of the unification model are discussed. [less ▲]

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See detailQuasar induced galaxy formation: a new paradigm?
Elbaz, David; Jahnke, Knud; Pantin, eric et al

in Astronomy and Astrophysics (2009), 507

Aims: We discuss observational evidence that quasars play a key role in the formation of galaxies, starting from the detailed study of the quasar HE0450-2958 and extending the discussion to a series of ... [more ▼]

Aims: We discuss observational evidence that quasars play a key role in the formation of galaxies, starting from the detailed study of the quasar HE0450-2958 and extending the discussion to a series of converging evidence that radio jets may trigger galaxy formation. Methods: We use mid infrared imaging with VISIR at the ESO-VLT to model the mid to far infrared energy distribution of the system and the stellar population of the companion galaxy using optical VLT-FORS spectroscopy. The results are combined with optical, CO, radio continuum imaging from ancillary data. Results: The direct detection with VISIR of the 7 kpc distant companion galaxy of HE0450-2958 allows us to spatially separate the sites of quasar and star formation activity in this composite system made of two ultra-luminous infrared galaxies (ULIRGs), where the quasar generates the bulk of the mid infrared light and the companion galaxy powered by star formation dominates in the far infrared. No host galaxy has yet been detected for this quasar, but the companion galaxy stellar mass would bring HE0450-2958 in the local MBH - Mstar-bulge relation if it were to merge with the QSO. This is bound to happen because of their close distance (7 kpc) and low relative velocity ( 60-200 km s-1). We conclude that we may be witnessing the building of the MBH - Mstar-bulge relation, or at least of a major event in that process. The star formation rate ( 340 Mȯ yr-1), age (40-200 Myr) and stellar mass ( [5-6]×10^10 Mȯ) are consistent with jet-induced formation of the companion galaxy. We suggest that HE0450-2958 may be fueled by fresh material from cold gas accretion from intergalactic filaments. We map the projected galaxy density surrounding the QSO as a potential tracer of intergalactic filaments and discuss a putative detection. Comparison to other systems suggest that an inside-out formation of quasar host galaxies and jet-induced galaxy formation may be a common process. Two tests are proposed for this new paradigm: (1) the detection of offset molecular gas or dust emission with respect to the position of distant QSOs; (2) the delayed formation of host galaxies as a result of QSO activity, hence the two step building of the M_BH/Mstar-bulge ratio. [less ▲]

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See detailQuasar pairs with arcminute angular separations
Zhdanov, V. I.; Surdej, Jean ULg

in Astronomy and Astrophysics (2001), 372

We use the Véron-Cetty & Véron (\cite {veron}) catalog (VV) of 13 213 quasars to investigate their possible physical grouping over angular scales 10arcsec <=Delta theta <= 1000arcsec . We first estimate ... [more ▼]

We use the Véron-Cetty & Véron (\cite {veron}) catalog (VV) of 13 213 quasars to investigate their possible physical grouping over angular scales 10arcsec <=Delta theta <= 1000arcsec . We first estimate the number of quasar pairs that would be expected in VV assuming a random distribution for the quasar positions and taking into account observational selection effects affecting heterogeneous catalogs. We find in VV a statistically significant (>3sigma ) excess of pairs of quasars with similar redshifts (Delta z<= 0.01) and angular separations in the 50arcsec -100arcsec range, corresponding to projected linear separations (0.2-0.5) Mpc/h[SUB]75[/SUB] (Omega[SUB]M[/SUB] =1, Omega[SUB]Lambda[/SUB] =0) or (0.4-0.7) Mpc/h[SUB]75[/SUB] (Omega[SUB]M[/SUB] =0.3, Omega[SUB]Lambda[/SUB] = 0.7). There is also some excess in the 100arcsec -600arcsec range corresponding to (1-5) Mpc in projected linear separations. If most of these quasar pairs do indeed belong to large physical entities, these separations must represent the inner scales of huge mass concentrations (cf. galaxy clusters or superclusters) at high redshifts; but it is not excluded that some of the pairs may actually consist of multiple quasar images produced by gravitational lensing. Of course, a fraction of these pairs could also arise due to random projections of quasars on the sky. The list of 11 pairs of quasars with redshift differences Delta z<= 0.02 and angular separations 50arcsec <= Delta theta <= 100arcsec is presented in order to stimulate further observational studies and to better understand the astrophysical and cosmological significance of these interesting objects. [less ▲]

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See detailQuasar polarization (Hutsemekers 1998)
Hutsemekers, Damien ULg

Textual, factual or bibliographical database (1997)

The table contains optical polarization data for a sample of 170 moderate to high-redshift quasars (1 data file).

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See detailQuasar polarization (Hutsemekers+ 1998)
Hutsemekers, Damien ULg; Lamy, H.; Remy, Marc

Textual, factual or bibliographical database (1998)

Table 2 contains optical (V) polarimetric measurements for 42 optically selected QSOs including 29 broad absorption line QSOs. Table 3 contains a series of spectral indices characterizing the broad ... [more ▼]

Table 2 contains optical (V) polarimetric measurements for 42 optically selected QSOs including 29 broad absorption line QSOs. Table 3 contains a series of spectral indices characterizing the broad absorption line QSOs. (2 data files). [less ▲]

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See detailQuasars et lentilles gravitationnelles
Surdej, Jean ULg

Article for general public (1984)

Not Available

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See detailQuasars in a control field far from bright galaxies
Arp, H.; Surdej, Jean ULg

in Astronomy and Astrophysics (1982), 109

The density of quasars in a control field of the sky selected to be free of bright galaxies is investigated in order to derive a value for the average background density of quasars and to analyze quasar ... [more ▼]

The density of quasars in a control field of the sky selected to be free of bright galaxies is investigated in order to derive a value for the average background density of quasars and to analyze quasar distribution within the field. Schmidt plates were obtained in the ultraviolet and blue for a control field surrounding SAO 45758 at R.A. 15 h 49 min, declination plus 48 deg 38 arcmin. Examination of the spectra of 25 of the 137 objects found to exhibit an ultraviolet excess reveals 12 of them to be quasars, indicating a quasar density of 6.7 plus or minus 0.9/sq deg down to a limiting magnitiude of 20 over the 19 sq deg area of the field. This value is noted to be in agreement with previous values of quasar background density deduced for other regions of the sky. Large fluctuations of quasar density are found, however, within the field which may be correlated with groups of intermediate brightness galaxies. [less ▲]

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See detailQuasars with Gaia: Identification and Astrophysical Parameters
Claeskens, Jean-François ULg; Smette, A.; Surdej, Jean ULg

in Turon, C.; O'Flaherty, K. S.; Perryman, M. A. C. (Eds.) Proceedings of the Gaia Symposium "The Three-Dimensional Universe with Gaia" (ESA SP-576) (2005, January 01)

Gaia will provide astrometric and photometric observations for about 500 000 quasars distributed over the whole sky. The latter would constitute an isotropic grid of fixed sources perfectly suited to ... [more ▼]

Gaia will provide astrometric and photometric observations for about 500 000 quasars distributed over the whole sky. The latter would constitute an isotropic grid of fixed sources perfectly suited to determine the referential frame. However, they must first be properly identified among stars, whose population is about 2000 times larger. Using broad and medium band photometry, we first compare the efficiency of two analysis methods (Ï 2 fitting and Artificial Neural Networks, ANNs) to produce the QSO catalogue with the lowest amount of contamination by stars. We then investigate whether the Gaia photometry could also provide precise values of the QSO astrophysical parameters (APs, like the redshift, the continuum slope, the emission line strength and possibly the extinction). To reach that purpose, we also compare the performances of the Spectral Principal Component Analysis (SPCA) with those of the Ï 2 fitting and ANN analysis. [less ▲]

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See detailLes quasars.
Henry, A.; Swings, Jean-Pierre ULg; Gosset, Eric ULg

in Ciel (Le) (1984), 46

Not Available

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See detailQuasi 2D-numerical model of aerated flow over stepped chutes
Dewals, Benjamin ULg; André, Stéphanie

Conference (2003, August 29)

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See detailQuasi 2D-numerical model of aerated flow over stepped chutes
André, Stéphanie; Dewals, Benjamin ULg; Pirotton, Michel ULg et al

in Proc. 30th IAHR Congress (2003)

Aerated flow over stepped chutes is principally studied on laboratory models. Consequently, the obtained design relations have a limited field of application. In order to propose a more general ... [more ▼]

Aerated flow over stepped chutes is principally studied on laboratory models. Consequently, the obtained design relations have a limited field of application. In order to propose a more general description of the flow, a quasi-2D numerical model is developed. The fluid is considered as an air-water mixture governed by the shallow-water equations. Moreover, a transport equation for air concentration represents the self-aeration of the flow and a coefficient of uneven vertical velocity distribution integrates indirectly the turbulent structures. The paper includes a brief description of the flow behaviour, the quasi-2D model equations, and a comparison of the numerical results with the measured flow characteristics in a 30° stepped flume. [less ▲]

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See detailQuasi steady-state models for long-term voltage and frequency dynamics simulation
Grenier, Marie-Eve; Lefebvre, Daniel; Van Cutsem, Thierry ULg

(2005, June)

The Quasi Steady-State (QSS) approximation of long-term dynamics relies on time-scale decomposition and consists of replacing faster phenomena by their equilibrium conditions, in order to reduce the ... [more ▼]

The Quasi Steady-State (QSS) approximation of long-term dynamics relies on time-scale decomposition and consists of replacing faster phenomena by their equilibrium conditions, in order to reduce the complexity of the whole model and increase the computation efficiency of time simulations. This paper describes the extension of a QSS model extensively used in long-term voltage stability studies, to readily incorporate the frequency dynamics that takes place over the same time scale. This extended QSS model relies on a common-frequency assumption. Its advantages, limitations and possible improvements are discussed through simulation results on the Hydro-Québec system, where it has been compared to full time scale simulations. Disturbances with an impact on either frequency or voltages are considered and the coupling between these two aspects of long-term dynamics is briefly discussed. [less ▲]

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See detailQuasi steady-state simulation diagnosis using Newton method with optimal multiplier
Rousseaux, Patricia ULg; Van Cutsem, Thierry ULg

in IEEE PES General Meeting (Montreal) (2006)

This paper deals with the quasi steady-state approximation of the long-term dynamics. This fast time simulation method assumes that the short-term dynamics are stable and can be replaced by their ... [more ▼]

This paper deals with the quasi steady-state approximation of the long-term dynamics. This fast time simulation method assumes that the short-term dynamics are stable and can be replaced by their equilibrium equations. When the latter stop having a solution, the simulation undergoes a singularity. This paper proposes a method to identify which component(s) are responsible for the loss of equilibrium. The corresponding equations are identified using the Newton method with optimal multiplier. The method has been validated with respect to full time simulation. Very good results are shown on the Nordic-32 system, in cases where long-term voltage instability triggers loss of synchronism. The proposed method enhances time simulation at very low computational cost and can also help correcting model and/or operating point errors. [less ▲]

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See detailQuasi umbræ entium. Suárez e Brentano sull’ens rationis
Boccaccini, Federico ULg

in Sgarbi, Marco (Ed.) Francisco Suárez and His Legacy. The Impact of Suarezian Metaphysics and Epistemology on Modern Philosophy (2010)

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See detailQuasi-asymptotic development of conditioned hyperactivity induced by intermittent injections of cocaine in C57BL/6J mice
Brabant, Christian ULg; Tambour, Sophie ULg; Tirelli, Ezio ULg

in Pharmacology, Biochemistry & Behavior (2003), 75(2), 273-280

The emergence of a conditioned cocaine-induced hyperlocomotion was examined in C57BL/6J mice using a procedure that has not been used previously. Two days after a session of preexposure to the test ... [more ▼]

The emergence of a conditioned cocaine-induced hyperlocomotion was examined in C57BL/6J mice using a procedure that has not been used previously. Two days after a session of preexposure to the test chambers under saline, a first group of mice (cocaine-cued) received five once-daily injections of 10-mg/kg sc cocaine every other day (on the odd days of the chronic treatment period) and a saline injection on the 5 days following each cocaine injection day (on the even days of the treatment period), in all cases before being placed in the test chamber. Another group of mice (saline-cued) received 10 injections of saline on both the even and the odd days in the same context, and a third group of mice (cocaine-uncued) received five injections of saline on the even days in the test context and five injections of cocaine on the odd days in an alternative context. On the odd days sessions, the cocaine-cued group showed significant repeated increases in locomotion without behavioural sensitisation being induced, whereas the saline-cued levels of locomotion remained on baseline levels. On the first even session, the three groups did not differ from each other and showed lower levels of locomotion than on the preexposure session. During the two following even sessions, the cocaine-cued group showed an increase in locomotion that levelled off on the two remaining sessions, whereas the saline-cued and the cocame-uncued groups (which presented comparable values) exhibited significantly lower levels of locomotion. That pattern of successive placebo responses resembles the typical S-shaped development of a Pavlovian conditioned response, albeit the increase described here was quite rapid. The protocol used here may provide an additional method for the experimental analysis of stimulant-induced conditioned placebo activity. (C) 2003 Elsevier Science Inc. All rights reserved. [less ▲]

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