297 research outputs found
Modelling the electric field applied to a tokamak
The vector potential for the Ohmic heating coil system of a tokamak is
obtained in semi-analytical form. Comparison is made to the potential of a
simple, finite solenoid. In the quasi-static limit, the time rate of change of
the potential determines the induced electromotive force through the
Maxwell-Lodge effect. Discussion of the gauge constraint is included.Comment: 13 pages, 7 figures, final versio
Accompagnement des personnes cérébrolésées en situation de handicap : le modèle organisationnel du Réseau TC-AVC 59-62
Compétences sociales et qualité de vie après traumatisme crânien léger ou modéré : influence des troubles cognitifs et de la communication
Validation d’une échelle d’évaluation analytique et fonctionnelle de l’équilibre et de la marche chez le patient hémiplégique vasculaire
Horizon effects with surface waves on moving water
Surface waves on a stationary flow of water are considered, in a linear model
that includes the surface tension of the fluid. The resulting gravity-capillary
waves experience a rich array of horizon effects when propagating against the
flow. In some cases three horizons (points where the group velocity of the wave
reverses) exist for waves with a single laboratory frequency. Some of these
effects are familiar in fluid mechanics under the name of wave blocking, but
other aspects, in particular waves with negative co-moving frequency and the
Hawking effect, were overlooked until surface waves were investigated as
examples of analogue gravity [Sch\"utzhold R and Unruh W G 2002 Phys. Rev. D 66
044019]. A comprehensive presentation of the various horizon effects for
gravity-capillary waves is given, with emphasis on the deep water/short
wavelength case kh>>1 where many analytical results can be derived. A
similarity of the state space of the waves to that of a thermodynamic system is
pointed out.Comment: 30 pages, 15 figures. Minor change
Dynamics of fluctuations in an optical analog of the Laval nozzle
Using the analogy between the description of coherent light propagation in a
medium with Kerr nonlinearity by means of nonlinear Schr\"odinger equation and
that of a dissipationless liquid we propose an optical analogue of the Laval
nozzle. The optical Laval nozzle will allow one to form a transonic flow in
which one can observe and study a very unusual dynamics of classical and
quantum fluctuations including analogue of the Hawking radiation of real black
holes. Theoretical analysis of this dynamics is supported by numerical
calculations and estimates for a possible experimental setup are presented.Comment: 7 pages, 4 figure
PIB potentiel et écart de PIB : quelques évaluations pour la France.
This Study and Research Paper is devoted to different estimates of the French economy's potential output and output gap. Several methods, which are presented in detail, are put forward to measure these indicators. The first two sections of the paper profile statistical univariate approaches: smoothing using the Hodrick-Prescott filter; and estimation of a trend, potentially including breaks. The next two sections extend the discussion on statistical techniques to multivariate cases. To be precise, they involve the analysis of structural VAR models and unobserved component models. The final section proposes a structural method for estimating potential output, where business sector output is described by a Cobb-Douglas function, while that of the non-business sector is assumed to be exogenous. For this structural method, the NAIRU has to be calculated before estimating the short to medium-term level of potential output.
On the electrodynamics of moving bodies at low velocities
We discuss the seminal article in which Le Bellac and Levy-Leblond have
identified two Galilean limits of electromagnetism, and its modern
implications. We use their results to point out some confusion in the
literature and in the teaching of special relativity and electromagnetism. For
instance, it is not widely recognized that there exist two well defined
non-relativistic limits, so that researchers and teachers are likely to utilize
an incoherent mixture of both. Recent works have shed a new light on the choice
of gauge conditions in classical electromagnetism. We retrieve Le
Bellac-Levy-Leblond's results by examining orders of magnitudes, and then with
a Lorentz-like manifestly covariant approach to Galilean covariance based on a
5-dimensional Minkowski manifold. We emphasize the Riemann-Lorenz approach
based on the vector and scalar potentials as opposed to the Heaviside-Hertz
formulation in terms of electromagnetic fields. We discuss various applications
and experiments, such as in magnetohydrodynamics and electrohydrodynamics,
quantum mechanics, superconductivity, continuous media, etc. Much of the
current technology where waves are not taken into account, is actually based on
Galilean electromagnetism
The Basics of Water Waves Theory for Analogue Gravity
This chapter gives an introduction to the connection between the physics of
water waves and analogue gravity. Only a basic knowledge of fluid mechanics is
assumed as a prerequisite.Comment: 36 pages. Lecture Notes for the IX SIGRAV School on "Analogue
Gravity", Como (Italy), May 201
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