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See detailInstabilities in Space and Laboratory Plasmas -- D. Melrose
Manfroid, Jean ULg

in Ciel et Terre (1987), 103

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See detailInstability analysis of a horizontal evaporating binary liquid layer with transient reference profiles
Machrafi, Hatim ULg; Alexey, Rednikov; Colinet, Pierre et al

(2011)

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See detailInstability and Overshoots of Solutions For A Class of Homogeneous Hybrid Systems By Lyapunov-like Analysis
Forni, Fulvio ULg; Teel, Andrew

in 49th IEEE Conference on Decision and Control (cdc 2010) (2010)

For a class of homogeneous hybrid systems we present a generalization to the hybrid systems framework of Chetaev's theorem and we propose a set of Lyapunov-like conditions for studying instability of the ... [more ▼]

For a class of homogeneous hybrid systems we present a generalization to the hybrid systems framework of Chetaev's theorem and we propose a set of Lyapunov-like conditions for studying instability of the point x e = 0 and overshoots of solutions (namely when the norm of the solution vector x at some time instant exceeds the norm of the initial condition of x). Based on these results, we design a sum of squares algorithm that constructs a suitable Lyapunov-like function to fulfill such conditions. [less ▲]

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See detailInstability regimes and self-excited vibrations in deep drilling systems
Depouhon, Alexandre ULg; Detournay, Emmanuel

in Journal of Sound and Vibration (2013)

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See detailInstability strip for pre-main-sequence stars
Grigahcene, A.; Dupret, Marc-Antoine ULg; Garrido, R. et al

in Communications in Asteroseismology (2006), 147

We apply the Time Dependent Convection (TDC) treatment presented in Grigahcene et al. (2005) to the study of Pre-main sequence pulsating stars. The stabilization of the p-modes at the red edge of the ... [more ▼]

We apply the Time Dependent Convection (TDC) treatment presented in Grigahcene et al. (2005) to the study of Pre-main sequence pulsating stars. The stabilization of the p-modes at the red edge of the Instability Strip (IS) is obtained by our models. The theoretical IS obtained with Mixing Length (ML) parameter alpha=1.8 is compared to observations and a good agreement is obtained. [less ▲]

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See detailThe instability strip of ZZ Ceti white dwarfs and its extension to the extremely low mass pulsators
Van Grootel, Valérie ULg; Fontaine, Gilles; Brassard, Pierre et al

in Astronomical Society of the Pacific Conference Series (2013, December), 479

The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection ... [more ▼]

The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection in these stars. We report here a detailed stability survey over the whole ZZ Ceti regime, including the very low masses where three pulsators have recently been found. We computed to this aim 29 evolutionary sequences of DA models with various masses and chemical layering. These models are characterized by the so-called ML2/α=1.0 convective efficiency and take into account the important feedback effect of convection on the atmospheric structure. We pulsated these models with the Liege nonadiabatic pulsation code MAD, which is the only one to conveniently incorporate a full time-dependent convection treatment and, thus, provides the best available description of the blue edge of the instability strip. On the other hand, given the failure of all nonadiabatic codes to account properly for the red edge of the strip, including MAD, we tested the idea that the red edge is due to energy leakage through the atmosphere. Using this approach, we found that our theoretical ZZ Ceti instability strip accounts remarkably well for the boundaries of the empirical strip. [less ▲]

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See detailThe instability strip of ZZ Ceti white dwarfs I. Introduction of time-dependent convection
Van Grootel, Valérie ULg; Dupret, Marc-Antoine ULg; Fontaine, Gilles et al

in Astronomy and Astrophysics (2012), 539

Aims. The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years due to the lack of a suitable treatment for ... [more ▼]

Aims. The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years due to the lack of a suitable treatment for convection in these stars. For the first time, a full nonadiabatic approach including time-dependent convection is applied to ZZ Ceti pulsators, and we provide the appropriate details related to the inner work- ings of the driving mechanism at work. Methods. We used the nonadiabatic pulsation code MAD with a representative evolutionary sequence of a 0.6 M⊙ DA white dwarf. This sequence is made of state-of-the-art models that include a detailed modeling of the feedback of convection on the atmospheric structure. The assumed convective efficiency in these models is the so-called ML2/α = 1.0 version. We also carried out, for comparison purposes, nonadiabatic computations within the frozen convection approximation, as well as calculations based on models with standard grey atmospheres. Results. We find that pulsational driving in ZZ Ceti stars is concentrated at the base of the superficial H convection zone, but at depths, near the blue edge of the instability strip, somewhat larger than those obtained with the frozen convection approach. Despite the fact that this approach is formally invalid in such stars, particularly near the blue edge of the instability strip, the predicted boundaries are not dramatically different in both cases. The revised blue edge for a 0.6 M⊙ model is found to be around Teff = 11,970 K, some 240 K hotter than the value predicted within the frozen convection approximation, in rather good agreement with the empirical value. On the other hand, our predicted red edge temperature for the same stellar mass is only about 5600 K (80 K hotter than with the frozen convection approach), much lower than the observed value. Conclusions. We correctly understand the development of pulsational instabilities of a white dwarf as it cools at the blue edge of the ZZ Ceti instability strip. Our current implementation of time-dependent convection however still lacks important ingredients to fully account for the observed red edge of the strip. We will explore a number of possibilities in the future papers of this series. [less ▲]

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See detailThe Instability Strip of ZZ Ceti White Dwarfs
Van Grootel, Valérie ULg; Fontaine, G.; Brassard, P. et al

in Astronomical Society of the Pacific Conference Series (in press)

The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection ... [more ▼]

The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection in these stars. We report here a detailed stability survey over the whole ZZ Ceti regime, including the low and extremely low masses. We computed to this aim 29 evolutionary sequences of DA models with various masses, chemical layering, and core compositions. These models are characterized by the so- called ML2/α=1.0 convective efficiency and take into account the important feedback effect of convection on the atmospheric structure. We computed pulsation spectra for these models with the Liège nonadiabatic pulsation code MAD, which is the only one to conveniently incorporate a full time-dependent convection treatment and, thus, provides the best available description of the blue edge of the instability strip. On the other hand, given the failure of all nonadiabatic codes to account properly for the red edge of the strip, including MAD, we tested the idea that the red edge is due to energy leakage through the atmosphere. Using this approach, we found that our theoretical ZZ Ceti instability strip accounts remarkably well for the boundaries of the empirical strip. [less ▲]

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See detailThe instability strip of ZZ Ceti white dwarfs
Van Grootel, Valérie ULg; Fontaine, G.; Brassard, P. et al

Conference (2014, August)

The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection ... [more ▼]

The determination of the location of the theoretical ZZ Ceti instability strip in the log g − Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection in these stars. We report here a detailed stability survey over the whole ZZ Ceti regime, including the low and extremely low masses. We computed to this aim 29 evolutionary sequences of DA models with various masses, chemical layering, and core compositions. These models are characterized by the so- called ML2/α=1.0 convective efficiency and take into account the important feedback effect of convection on the atmospheric structure. We computed pulsation spectra for these models with the Liège nonadiabatic pulsation code MAD, which is the only one to conveniently incorporate a full time-dependent convection treatment and, thus, provides the best available description of the blue edge of the instability strip. On the other hand, given the failure of all nonadiabatic codes to account properly for the red edge of the strip, including MAD, we tested the idea that the red edge is due to energy leakage through the atmosphere. Using this approach, we found that our theoretical ZZ Ceti instability strip accounts remarkably well for the boundaries of the empirical strip. [less ▲]

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See detailInstability strips of main sequence B stars: a parametric study of iron enhancement
Miglio, Andrea ULg; Bourge, P.-O.; Montalban Iglesias, Josefa ULg et al

in Communications in Asteroseismology (2007), 150

The discovery of beta Cephei stars in low metallicity environments, as well as the difficulty to theoretically explain the excitation of the pulsation modes observed in some beta Cephei and SPB stars ... [more ▼]

The discovery of beta Cephei stars in low metallicity environments, as well as the difficulty to theoretically explain the excitation of the pulsation modes observed in some beta Cephei and SPB stars, suggest that the iron opacity ``bump'' provided by standard models could be underestimated. We investigate, by means of a parametric study, the effect of a local iron enhancement on the location of the beta Cephei and SPB instability strips. [less ▲]

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See detailInstability strips of slowly pulsating B stars and beta Cephei stars: the effect of the updated OP opacities and of the metal mixture
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Dupret, Marc-Antoine ULg

in Monthly Notices of the Royal Astronomical Society (2007), 375

The discovery of beta Cephei stars in low-metallicity environments, as well as the difficulty in theoretically explaining the excitation of the pulsation modes observed in some beta Cephei and hybrid ... [more ▼]

The discovery of beta Cephei stars in low-metallicity environments, as well as the difficulty in theoretically explaining the excitation of the pulsation modes observed in some beta Cephei and hybrid slowly pulsating B-beta Cephei pulsators, suggest that the `iron opacity bump' provided by stellar models could be underestimated. We analyze the effect of uncertainties in the opacity computations and in the solar metal mixture on the excitation of pulsation modes in B-type stars. We carry out a pulsational stability analysis for four grids of main-sequence models with masses between 2.5 and 12M[SUB]solar[/SUB] computed with OPAL and OP opacity tables and two different metal mixtures. We find that in a typical beta Cephei model the OP opacity is 25 per cent larger than OPAL in the region where the driving of pulsation modes occurs. Furthermore, the difference in the Fe mass fraction between the two metal mixtures considered is of the order of 20 per cent. The implication on the excitation of pulsation modes is non-negligible: the blue border of the slowly pulsating B star (SPB) instability strip is displaced at higher effective temperatures, leading to a larger number of models being hybrid SPB-beta Cephei pulsators. Moreover, higher overtone p-modes are excited in beta Cephei models and unstable modes are found in a larger number of models for lower metallicities, in particular beta Cephei pulsations are also found in models with Z = 0.01. [less ▲]

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See detailInstallations fixes soumises à permis d'urbanisme en Région wallonne
Delnoy, Michel ULg

in Immobilier (2001), 1

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See detailL'instance arbitrale et le temps
Caprasse, Olivier ULg

in Saletti, A.; van Compernolle, J.; van Drooghenbroeck, J.-F. (Eds.) L'arbitre et le juge étatique - Etudes de droit comparté à la mémoire de Giuseppe Tarzia (2014)

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See detailL'instauration d'un seuil électoral de 5% en Belgique: analyse critique du raisonnement de la Cour constitutionnelle
Onclin, François ULg

in Revue de la Faculté de Droit de l'Université de Liège (2011), (3-4), 569-573

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See detailL'instauration et les effets du seuil électoral de 5%
Onclin, François ULg

in Courrier Hebdomadaire du CRISP (2009), (2041-2042),

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See detailInstituants et prix culturels, Québec, 1919-1939 : histoire culturelle et base de données
Dozo, Björn-Olav ULg; Lacroix, Michel; Lapointe, Olivier

E-print/Working paper (2012)

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See detailLa institución como metáfora del discurso. Análisis discursivo de la polémica en torno a 'Mundo Nuevo'
Vanden Berghe, Kristine ULg

in De Paepe, C.; Lie, N.; Rodríguez, L. (Eds.) et al Literatura y poder (1995)

Detailed reference viewed: 23 (1 ULg)