L'orvet fragile Anguis fragilis (Linnaeus ,1758)

in Jacob, Jean-Paul; Percsy, Christiane; de Wavrin, Hellin (Eds.) et al Amphibiens et Reptiles de Wallonie (2007)

Oscillating blue stragglers, gamma Doradus stars and eclipsing binaries in the open cluster NGC 2506

in Astronomy and Astrophysics (2007), 465

Context: This is the first step in a project to combine studies of eclipsing binaries and oscillating stars to probe the interior of Blue Stragglers (BS). This may imply a way to discriminate ... [more ▼]

Context: This is the first step in a project to combine studies of eclipsing binaries and oscillating stars to probe the interior of Blue Stragglers (BS). This may imply a way to discriminate observationally between different birth mechanisms of BS stars. Aims: We study the open cluster NGC 2506 which contains oscillating BS stars and detached eclipsing binaries for which accurate parameters can be derived. This will tightly constrain the cluster isochrone and provide an absolute mass, radius and luminosity-scale for the cluster stars along with the cluster age, metallicity and distance. The present work focuses on obtaining the light curves of the binaries and determine their orbital periods, on obtaining power spectra of the oscillating BS stars to select targets for follow-up studies, and on searching for gamma Doradus type variables which are also expected to be present in the cluster. Methods: With a two-colour, dual-site photometric campaign we obtained 3120 CCD-images of NGC 2506 spread over four months. We analysed the BI time-series of the oscillating stars and used simulations to derive statistical uncertainties of the resulting frequencies, amplitudes and phases. A preliminary mode-identification was performed using frequency ratios for the oscillating BS stars, and amplitude ratios and phase differences for a population of newly detected gamma Doradus stars. Results: We quadrupled the number of known variables in NGC 2506 by discovering 3 new oscillating BS stars, 15 gamma Doradus stars and four new eclipsing binaries. The orbital periods of 2 known, detached eclipsing binaries were derived. We discovered a BS star with both p-mode and g-mode variability and we confronted our gamma Doradus observations with state-of-the-art seismic models, but found significant discrepancy between theory and observations. Conclusions: . NGC 2506 is an excellent target for asteroseismic tests of stellar models, as strong external constraints can be imposed on the models of a population of more than 20 oscillating stars of different types. Based on observations obtained at the Flemish Mercator telescope on La Palma, Spain, the Danish 1.5-m telescope at ESO, La Silla, Chile, and on observations collected at the European Southern Observatory, Paranal, Chile (ESO Programme 075.D-0206(B)). Catalog of individual photometry measurements for all variables is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/465/965 [less ▲]

Oscillation of Saturn's southern auroral oval

in Journal of Geophysical Research (2008), 113(A11),

Near-planetary-period oscillations in the Cassini plasma and magnetic field data have been observed throughout Saturn's magnetosphere despite the fact that Saturn's internal magnetic field is apparently ... [more ▼]

Near-planetary-period oscillations in the Cassini plasma and magnetic field data have been observed throughout Saturn's magnetosphere despite the fact that Saturn's internal magnetic field is apparently highly axisymmetric. In addition, the period of the Saturn kilometric radiation has been shown to vary over time. In this paper we present results from the recent Hubble Space Telescope observations of Saturn's southern ultraviolet auroral emission. We show that the center of the auroral oval oscillates with period 10.76 h +/- 0.15 h for both January 2007 and February 2008, i.e., close to the periods determined for oscillations in other magnetospheric phenomena. The motion of the oval center is described for 2007 by an ellipse with semimajor axis similar to 1.4 degrees +/- 0.3 degrees oriented toward similar to 09-21 h LT, eccentricity similar to 0.93, and center offset from the spin axis by similar to 1.8 degrees toward similar to 04 h LT. For 2008 the oscillation is consistent with an ellipse with semimajor axis similar to 2.2 degrees +/- 0.3 degrees oriented toward similar to 09-21 h LT, eccentricity similar to 0.99, and a center offset from the spin axis by similar to 2.2 degrees toward similar to 03 h LT. The motion of the auroral oval is thus highly elliptical in both cases, and the major oscillation axis is oriented toward prenoon/premidnight. This result places an independent constraint on the magnitude of the planet's dipole tilt and may also indicate the presence of an external current system that imposes an asymmetry in the ionospheric field modulated close to the planetary period. [less ▲]

Oscillations of bride stay cables induced by periodic motions of deck and/or towers

in Journal of Engineering Mechanics (1996), 122(7), 613-622

Cables in stayed bridges may oscillate due to periodic motions of the deck or tower induced by wind or traffic.

Oscillator Models and Collective Motion: spatial patterns in the dynamics of engineered and biological networks

in IEEE Control Systems Magazine (2007), 27(4), 89-105

Oscillatority of Nonlinear Systems with Static Feedback

in SIAM Journal on Control & Optimization (2009), 48(2), 618-640

New Lyapunov-like conditions for oscillatority of dynamical systems in the sense of Yakubovich are proposed. Unlike previous results these conditions are applicable to nonlinear systems and allow for ... [more ▼]

New Lyapunov-like conditions for oscillatority of dynamical systems in the sense of Yakubovich are proposed. Unlike previous results these conditions are applicable to nonlinear systems and allow for consideration of nonperiodic, e.g., chaotic modes. Upper and lower bounds for oscillations amplitude are obtained. The relation between the oscillatority bounds and excitability indices for the systems with the input are established. Control design procedure providing nonlinear systems with oscillatority property is proposed. Examples illustrating proposed results for Van der Pol system, Lorenz system, and Hindmarsh–Rose neuron model as well as computer simulation results are given. [less ▲]

Osculating circle with microscopes within microscopes

in Foundations of Science (2013), 18(2), 319-325

Classically, an osculating circle at a point of a planar curve is introduced technically, often with formula giving its radius and the coordinates of its center. In this note, we propose a new and ... [more ▼]

Classically, an osculating circle at a point of a planar curve is introduced technically, often with formula giving its radius and the coordinates of its center. In this note, we propose a new and intuitive definition of this concept: among all the circles which have, at the considered point, the same tangent as the studied curve and thus seem equal to the curve through a microscope, the osculating circle is this that seems equal to the curve through a microscope within microscope. [less ▲]

Oser la qualité : entre projet et réalité. Une démarche d'accompagnement à la qualité.

Conference (2010, January 16)

Oser le doctorat

Article for general public (2006)

According to the Bologna Process, the doctorate is now the (only) 3rd cycle of the university graduation in Belgium. The doctorate is made of 3 components : the doctoral education, the research works and ... [more ▼]

According to the Bologna Process, the doctorate is now the (only) 3rd cycle of the university graduation in Belgium. The doctorate is made of 3 components : the doctoral education, the research works and the public presentation of the thesis showing the graduate's capacity for creativity, research and dissemination. So that the graduation relies on the academic education as well as on the experience of research and on soft skills capacities. So : dare to do a PhD ? [less ▲]

OSI 95 Enhanced Transport Facilities and Functions

Report (1992)