16 research outputs found
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The Mars Climate Database
The Mars Climate Database (MCD) [1] is a database of statistics describing the climate and environment of the Martian atmosphere. It was constructed directly on the basis of output from mulitannual integrations of two general circulation models (GCMs)developed by Laboratoire de Météorologie Dynamique du CNRS, France, the University of Oxford, UK, and Instituto de Astrofisica de Andalucia, Spain, with support from the European Space Agency (ESA) and Centre National d–Etudes Spatiales (CNES). A description of the MCD is given along with a comparison between spacecraft observations of Mars and results predicted at similar locations and times in the MCD.
The MCD can be used as a tool for mission planning and has been applied to prepare for several missions in Europe and the USA. It also provides information for mission design specialists on the mean state and variability of the Martian environment from the surface to above 120km. The GCMs on which the database is founded, include a set of physical parameterizations (radiative transfer in the visible and thermal infrared ranges, turbulent mixing, condensation-sublimation of CO2, thermal conduction in
the soil and representation of gravity waves) and two
different codes for the representation of large scale
dynamics: a spectral code for the AOPP version and
a grid-point code for the LMD version. The GCMs correctly reproduce the main meteorological features of Mars, as observed by the Mariner 9 and Viking orbiters, the Viking landers, and Mars Global Surveyor (MGS). As well as the standard statistical measures for mission design studies, the MCD includes a novel representation of large-scale variability, using empirical eigenfunctions derived from an
analysis of the full simulations, and small-scale variability based on parameterizations of processes such
as gravity wave propagation. The database allows the user to choose from 5 dust storm scenarios including a best guess, default scenario, deduced from recent MGS observations, an upper boundary for an atmosphere without dust storms, as observed by Viking the landers, and a clear, cold, lower boundary scenario, as observed by Phobos 2 and from Earth. The full version of the MCD is available on CDROM (for UNIX systems and PCs) and is also
accessible through an interactive WWW interface at
http://www-mars.lmd.jussieu.fr/
Improved Holographic QCD
We provide a review to holographic models based on Einstein-dilaton gravity
with a potential in 5 dimensions. Such theories, for a judicious choice of
potential are very close to the physics of large-N YM theory both at zero and
finite temperature. The zero temperature glueball spectra as well as their
finite temperature thermodynamic functions compare well with lattice data. The
model can be used to calculate transport coefficients, like bulk viscosity, the
drag force and jet quenching parameters, relevant for the physics of the
Quark-Gluon Plasma.Comment: LatEX, 65 pages, 28 figures, 9 Tables. Based on lectures given at
several Schools. To appear in the proceedinds of the 5th Aegean School
(Milos, Greece
Jet evolution in the N=4 SYM plasma at strong coupling
Within the framework of the AdS/CFT correspondence, we study the time
evolution of an energetic R-current propagating through a finite temperature,
strongly coupled, N=4 SYM plasma and propose a physical picture for our
results. In this picture, the current splits into a pair of massless partons,
which then evolve via successive branchings, in such a way that energy is
quasi-democratically divided among the products of a branching. We point out a
duality between the transverse size of the partonic system produced through
branching and the radial distance traveled by the dual Maxwell wave in the AdS
geometry. For a time-like current, the branching occurs already in the vacuum,
where it gives rise to a system of low-momentum partons isotropically
distributed in the transverse plane. But at finite temperature, the branching
mechanism is modified by the medium, in that the rate for parton splitting is
enhanced by the transfer of transverse momentum from the partons to the plasma.
This mechanism, which controls the parton energy loss, is sensitive to the
energy density in the plasma, but not to the details of the thermal state. We
compute the lifetime of the current for various kinematical regimes and provide
physical interpretations for other, related, quantities, so like the meson
screening length, the drag force, or the trailing string, that were previously
computed via AdS/CFT techniques.Comment: 37 pages, 4 figure
Measurement of the proton structure function F2 (x, Q2) in the low-x region at HERA
A measurement of the proton structure function F2 (x, Q2) is presented with about 1000 neutral current deep inelastic scattering events for Bjorken x in the range x {reversed tilde equals} 10-2 - 10-4 and Q2 > 5 GeV2. The measurement is based on an integrated luminosity of 22.5 nb-1 recorded by the H1 detector in the first year of HERA operation. The structure function F2 (x, Q2) shows a significant rise with decreasing x. © 1993.0320 auteursSCOPUS: ar.jinfo:eu-repo/semantics/publishe