Le portrait du roi : entre art, histoire, anthropologie et sémiologie

Dans la théorie des arts à l’époque moderne, le portrait du roi a un statut singulier : en tant que portrait, il dépend du dictat de la ressemblance au modèle naturel, qui l’éloigne de la noble quête de l’idéal, mais en tant que représentation du souverain, donc d’un personnage hors norme à la perfection incomparable, il a vocation d’être un chef-d’œuvre. De ce fait, le portrait du roi échappe, du moins dans la littérature encomiastique, au discrédit qui frappe progressivement le genre du por..

Current channel evolution in ideal Z pinch for general velocity profiles

Recent diagnostic advances in gas-puff Z pinches at the Weizmann Institute for the first time allow the reconstruction of the current flow as a function of time and radius. These experiments show an unexpected radially-outward motion of the current channel, as the plasma moves radially-inward [C. Stollberg, Ph.D thesis, Weizmann Institute, 2019]. In this paper, a mechanism that could explain this current evolution is described. We examine the impact of advection on the distribution of current in a cylindrically symmetric plasma. In the case of metric compression, with |v_r| proportional to r, the current enclosed between each plasma fluid element and the axis is conserved, and so the current profile maintains its shape. We show that for more general velocity profiles, this simple behavior quickly breaks down, allowing for non-conservation of current in a compressing conductor, rapid redistribution of the current density, and even for the formation of reverse currents. In particular, a specific inward radial velocity profile is shown to result in radially-outward motion of the current channel, recovering the surprising current evolution discovered at the Weizmann Institute.Comment: 12 pages, 6 figure

Revisiting the Stark Width and Shift of He II Pα

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Helicon volume production of H−^− and D−^− using a resonant birdcage antenna on RAID

International audienceNegative ion production by volumetric processes is investigated in the RAID linear device using experiments and modeling. Measurements by optical emission spectroscopy, cavity ring-down spectroscopy, and Langmuir probe assisted laser photodetachment are combined and reveal that H$^−$ and D$^−$ ions are distributed in a halo around the plasma column with densities of 2 × 10$^{16}$ m$^{-3}$ for only a few kilowatts of RF power in a Cs-free plasma. A hydrogen transport fluid code shows that RAID plasmas have a hot electron core favorable to ro-vibrational excitation and dissociation of H$_2$ molecules. Dissociative attachment to ro-vibrationally excited H$_2$ molecules is the only significant source of H$^−$ anywhere in the RAID volum

Physics of helicon waves and negative ions in the Resonant Antenna Ion Device (RAID)

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Physics of helicon waves and negative ions in the Resonant Antenna Ion Device (RAID)

International audienc

Art et pouvoir

« Des images de l’histoire de l’art à celles des médias visuels de masse, des arts visuels à la culture visuelle, l’image poursuit sa marche triomphale. » – Peter Weibel Alliances, résistances, compromissions, les rapports entre l’art et le pouvoir s’imposent dans le monde visuel, du portrait au muralisme, de l’empire au musée, de la propagande à l’iconoclasme. Investissant des objets, des méthodes, des géographies et des temps multiples, l’histoire de l’art réinterroge les pouvoirs de l’image

The AWAKE Run 2 Programme and Beyond

Plasma wakefield acceleration is a promising technology to reduce the size of particle accelerators. The use of high energy protons to drive wakefields in plasma has been demonstrated during Run 1 of the AWAKE programme at CERN. Protons of energy 400 GeV drove wakefields that accelerated electrons to 2 GeV in under 10 m of plasma. The AWAKE collaboration is now embarking on Run 2 with the main aims to demonstrate stable accelerating gradients of 0.5-1 GV/m, preserve emittance of the electron bunches during acceleration and develop plasma sources scalable to 100s of metres and beyond. By the end of Run 2, the AWAKE scheme should be able to provide electron beams for particle physics experiments and several possible experiments have already been evaluated. This article summarises the programme of AWAKE Run 2 and how it will be achieved as well as the possible application of the AWAKE scheme to novel particle physics experiments.De fyra första författarna delar förstaförfattarskapet.</p