Philippe Arnault

Bio: Philippe Arnault is an academic researcher from Institut d'Astrophysique de Paris. The author has contributed to research in topics: Warm dense matter & Diffusion (business). The author has an hindex of 14, co-authored 34 publications receiving 496 citations.

Transport properties of an asymmetric mixture in the dense plasma regime.

Abstract: We study how concentration changes ionic transport properties along isobars-isotherms for a mixture of hydrogen and silver, representative of turbulent layers relevant to inertial confinement fusion and astrophysics. Hydrogen will typically be fully ionized while silver will be only partially ionized but can have a large effective charge. This will lead to very different physical conditions for the H and Ag. Large first principles orbital free molecular dynamics simulations are performed and the resulting transport properties are analyzed. Comparisons are made with transport theory in the kinetic regime and in the coupled regime. The addition of a small amount of heavy element in a light material has a dramatic effect on viscosity and diffusion of the mixture. This effect is explained through kinetic theory as a manifestation of a crossover between classical diffusion and Lorentz diffusion.

Opacity measurements of tamped NaBr samples heated by z-pinch X-rays

Abstract: Laboratory measurements provide benchmark data for wavelength-dependent plasma opacities to assist inertial confinement fusion, astrophysics, and atomic physics research. There are several potential benefits to using z-pinch radiation for opacity measurements, including relatively large cm-scale lateral sample sizes and relatively-long 3– 5 ns experiment durations. These features enhance sample uniformity. The spectrally resolved transmission through a CH-tamped NaBr foil was measured. The z-pinch produced the X-rays for both the heating source and backlight source. The (50±4) eV foil electron temperature and (3±1)×10 21 cm −3 foil electron density were determined by analysis of the Na absorption features. LTE and NLTE opacity model calculations of the n=2 to 3, 4 transitions in bromine ionized into the M-shell are in reasonably good agreement with the data.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

Abstract: to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.

Dust Absorption and the Ultraviolet Luminosity Density at z ≈ 3 as Calibrated by Local Starburst Galaxies*

Abstract: We refine a technique to measure the absorption-corrected ultraviolet (UV) luminosity of starburst galaxies using rest-frame UV quantities alone and apply it to Lyman-limit U dropouts at z ? 3 found in the Hubble Deep Field (HDF). The method is based on an observed correlation between the ratio of far-infrared (FIR) to UV fluxes with spectral slope ? (a UV color). A simple fit to this relation allows the UV flux absorbed by dust and reprocessed to the FIR to be calculated, and hence the dust-free UV luminosity to be determined. International Ultraviolet Explorer spectra and Infrared Astronomical Satellite fluxes of local starbursts are used to calibrate the FFIR/F1600 versus ? relation in terms of A1600 (the dust absorption at 1600 ?) and the transformation from broadband photometric color to ?. Both calibrations are almost completely independent of theoretical stellar-population models. We show that the recent marginal and nondetections of HDF U dropouts at radio and submillimeter wavelengths are consistent with their assumed starburst nature and our calculated A1600. This is also true of recent observations of the ratio of optical emission-line flux to UV flux density in the brightest U dropouts. This latter ratio turns out not to be a good indicator of dust extinction. In U dropouts, absolute magnitude M1600,0 correlates with ?: brighter galaxies are redder, as is observed to be the case for local starburst galaxies. This suggests that a mass-metallicity relationship is already in place at z ? 3. The absorption-corrected UV luminosity function of U dropouts extends up to M1600,0 ? -24 AB mag, corresponding to a star formation rate ~200 ? yr-1 (H0 = 50 km s-1 Mpc-3 and q0 = 0.5 are assumed throughout). The absorption-corrected UV luminosity density at z ? 3 is ?1600,0 ? 1.4 ? 1027 ergs-1 Hz-1 Mpc-1. It is still a lower limit since completeness corrections have not been done and because only galaxies with A1600 3.6 mag are blue enough in the UV to be selected as U dropouts. The luminosity-weighted mean dust-absorption factor of our sample is 5.4 ? 0.9 at 1600 ?.

The Dust Opacity of Star‐forming Galaxies

Abstract: The presence of dust in galaxies removes one‐half or more of the stellar energy from the UV‐optical budget of the universe and has a profound impact on our understanding of how galaxies evolve. Measures of opacity in local galaxies are reviewed together with widely used theoretical and empirical methods for quantifying its effects. Existing evidence shows that the dust content of nearby galaxies depends not only on their morphology but also on their luminosity and activity level. A digression is devoted to starbursts in view of their potential relevance for measures of opacity in distant galaxies. Scarcity of coherent multiwavelength data sets hampers our ability to derive reliable obscuration estimates in intermediate‐ and high‐redshift galaxies. This, in turn, limits the reliability of inferred physical quantities, such as star formation rates, stellar population ages, galaxy luminosity functions, and others.

Theory Of Simple Liquids

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