Suppression of Rayleigh-Benard Convection with Proportional-Derivative Controller

We study theoretically (linear stability) and experimentally the use of proportional and derivative controllers to postpone the transition from the no-motion state to the convective state in a circular cylinder heated from below and cooled from above. The heating is provided with an array of individually controlled actuators whose power is adjusted in proportion to temperatures measured in the cylinder\u27s interior. As the proportional controller\u27s gain increases, so does the critical Rayleigh number for the onset of convection. Relatively large proportional controller gains lead to oscillatory convection. The oscillatory convection can be suppressed with the application of a derivative controller, allowing further increases in the critical Rayleigh number. The experimental observations are compared with theoretical predictions

Canalisation de particules chargées dans un cristal

École thématiqu

ELT HARMONI: Image Slicer Preliminary Design

Harmoni is the ELT's first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 x 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers from R 3500 to R 20000 and instantaneous wavelength coverage spanning the 0.47 - 2.45 {\mu}m wavelength range of the instrument. The consortium consists of several institutes in Europe under leadership of Oxford University. Harmoni is starting its Final Design Phase after a Preliminary Design Phase in November, 2017. The CRAL has the responsibility of the Integral Field Unit design linking the Preoptics to the 4 Spectrographs. It is composed of a field splitter associated with a relay system and an image slicer that create from a rectangular Field of View a very long (540mm) output slit for each spectrograph. In this paper, the preliminary design and performances of Harmoni Image Slicer will be presented including image quality, pupil distortion and slit geometry. It has been designed by CRAL for Harmoni PDR in November, 2017. Special emphases will be put on straylight analysis and slice diffraction. The optimisation of the manufacturing and slit geometry will also be reported.Comment: 13 pages, 19 figures, 4 tables, Submitted to SPIE Astronomical Telescopes and Instrumentatio

Knowledge sharing in change management : a case study in the French railways company

International audienceThis paper describes a project to represent and share tacit change management knowledge. Based on an ontology, this project enables French Railways Company (SNCF)'s project managers to share their know-how through an IT device called "knowledge server". This paper contains two kinds of contributions. The first contribution is the ontology itself. The second contribution is methodological. By describing the ontology's design process, based on a study of project managers' practices, the paper indicates how to build an ontology that refers to tacit knowledge, to human professional know-how

Design of a low-noise aeroacoustic wind tunnel facility at Brunel University

This paper represents the design principle of a quiet, low turbulence and moderately high speed aeroacoustic wind tunnel which was recently commissioned at Brunel University. A new hemi-anechoic chamber was purposely built to facilitate aeroacoustic measurements. The wind tunnel can achieve a maximum speed of about 80 ms-1. The turbulence intensity of the free jet in the potential core is between 0.1–0.2%. The noise characteristic of the aeroacoustic wind tunnel was validated by three case studies. All of which can demonstrate a very low background noise produced by the bare jet in comparison to the noise radiated from the cylinder rod/flat plate/airfoil in the air stream.The constructions of the aeroacoustic wind tunnel and the hemi-anechoic chamber are financially supported by the School of Engineering and Design at Brunel University

Les enjeux de l’hadronthérapie par ions carbone

National audienceL’ambition de doter la France d’un centre de traitement des tumeurs par faisceaux d’ions carbone est née, à la fin des années 1990, de la rencontre à l’Université Claude Bernard Lyon 1 de quelques médecins et physiciens, convaincus que la France avait toutes les capacités médicales et scientifiques pour initier un tel programme. Ce projet de « carbonethérapie » prit le nom de projet ETOILE (Espace de Traitement Oncologique par Ions Légers en Europe) au début des années 2000. Pour comprendre pourquoi il n’a pas été réalisé et évaluer les chances pour qu’il le soit un jour, il faut analyser les enjeux, les difficultés et les avantages de la carbonethérapie, comparée à la protonthérapie et aux formes les plus avancées de la radiothérapie

INTERACTION OF FAST HYDROGEN IONIC CLUSTERS WITH MATTER

Fast ionic clusters Hn+ interact with matter in a specific way which is observed to deviate strongly from the interaction of atomic ions at the same velocity. We present some results obtained at Lyon about foil and gas interactions of hydrogen clusters (5 ≤ n ≤ 23) at projectile velocities close to the Bohr velocity, i.e. dynamics of the cluster fragmentation, charge state of atomic fragments and absolute dissociation cross sections in gas. We also discuss future experiments specially at higher velocities

Probing material nonlinearity at various depths by time reversal mirrors

International audienceIn this letter, the time reversal mirror is used to focus elastic energy at a prescribed location and to analyze the amplitude dependence of the focus signal, thus providing the nonlinearity of the medium. By varying the frequency content of the focused waveforms, the technique can be used to probe the surface, by penetrating to a depth defined by the wavelength of the focused waves. The validity of this concept is shown in the presence of gradual and distributed damage in concrete by comparing actual results with a reference nonlinear measurement and X ray tomography images

I.B.S. coatings on large substrates: Towards an improvement of the mechanical and optical performances

présenté par A. RemillieuxLarge mirrors (350 mm), having extremely low optical loss (absorption, scattering, wavefront) were coated for the VIRGO interferometer. The new mirror generation needs better wavefront and lower mechanical loss. The first results are discussed