12 research outputs found
An Asymptotic Preserving Scheme for the Euler equations in a strong magnetic field
This paper is concerned with the numerical approximation of the isothermal
Euler equations for charged particles subject to the Lorentz force. When the
magnetic field is large, the so-called drift-fluid approximation is obtained.
In this limit, the parallel motion relative to the magnetic field direction
splits from perpendicular motion and is given implicitly by the constraint of
zero total force along the magnetic field lines. In this paper, we provide a
well-posed elliptic equation for the parallel velocity which in turn allows us
to construct an Asymptotic-Preserving (AP) scheme for the Euler-Lorentz system.
This scheme gives rise to both a consistent approximation of the Euler-Lorentz
model when epsilon is finite and a consistent approximation of the drift limit
when epsilon tends to 0. Above all, it does not require any constraint on the
space and time steps related to the small value of epsilon. Numerical results
are presented, which confirm the AP character of the scheme and its Asymptotic
Stability
Numerical approximation of the Euler-Poisson-Boltzmann model in the quasineutral limit
This paper analyzes various schemes for the Euler-Poisson-Boltzmann (EPB)
model of plasma physics. This model consists of the pressureless gas dynamics
equations coupled with the Poisson equation and where the Boltzmann relation
relates the potential to the electron density. If the quasi-neutral assumption
is made, the Poisson equation is replaced by the constraint of zero local
charge and the model reduces to the Isothermal Compressible Euler (ICE) model.
We compare a numerical strategy based on the EPB model to a strategy using a
reformulation (called REPB formulation). The REPB scheme captures the
quasi-neutral limit more accurately
Numerical approximation of the Euler-Maxwell model in the quasineutral limit
International audienceWe derive and analyze an Asymptotic-Preserving scheme for the Euler-Maxwell system in the quasi-neutral limit. We prove that the linear stability condition on the time-step is independent of the scaled Debye length when . Numerical validation performed on Riemann initial data and for a model Plasma Opening Switch device show that the AP-scheme is convergent to the Euler-Maxwell solution when where is the spatial discretization. But, when , the AP-scheme is consistent with the quasi-neutral Euler-Maxwell system. The scheme is also perfectly consistent with the Gauss equation. The possibility of using large time and space steps leads to several orders of magnitude reductions in computer time and storage
All-sky photogrammetry techniques to georeference a cloud field
In this study, we present a novel method of identifying and
geolocalizing cloud field elements from a portable all-sky camera stereo
network based on the ground and oriented towards zenith. The methodology is
mainly based on stereophotogrammetry which is a 3-D reconstruction technique
based on triangulation from corresponding stereo pixels in rectified images.
In cases where clouds are horizontally separated, identifying individual
positions is performed with segmentation techniques based on hue filtering
and contour detection algorithms. Macroscopic cloud field characteristics
such as cloud layer base heights and velocity fields are also deduced. In
addition, the methodology is fitted to the context of measurement campaigns
which impose simplicity of implementation, auto-calibration, and portability.
Camera internal geometry models are achieved a priori in the laboratory and
validated to ensure a certain accuracy in the peripheral parts of the all-sky
image. Then, stereophotogrammetry with dense 3-D reconstruction is applied
with cameras spaced 150âŻm apart for two validation cases. The first
validation case is carried out with cumulus clouds having a cloud base height
at 1500âŻmâŻa.g.l. The second validation case is carried out with two cloud
layers: a cumulus fractus layer with a base height at 1000âŻmâŻa.g.l. and
an altocumulus stratiformis layer with a base height of 2300âŻmâŻa.g.l.
Velocity fields at cloud base are computed by tracking image rectangular
patterns through successive shots. The height uncertainty is estimated by
comparison with a Vaisala CL31 ceilometer located on the site. The
uncertainty on the horizontal coordinates and on the velocity field are
theoretically quantified by using the experimental uncertainties of the cloud
base height and camera orientation. In the first cumulus case, segmentation
of the image is performed to identify individuals clouds in the cloud field
and determine the horizontal positions of the cloud centers
Cryogenic System Design for SPIRAL2 LINAC Project at GANIL (France)
The future superconducting Linear accelerator of the SPIRAL2 project at GANIL (France) will require a complete heliumcryogenic system. Air Liquide DTA has been selected to provide around 1300W equivalent refrigeration power at 4.5K with mainly refrigeration load but also helium liquefaction rate and 60K thermal shields feed. The Helium cold box designed and manufactured by Air Liquide DTA will be derived from the standard HELIAL LF product to match the need for the SPIRAL2 project. The cryogenic system also includes a liquid Dewar, cryogenic lines and recovery system for liquefaction rate. Cryogenic distribution line and valves boxes for LINAC Cryomodules are designed and installed by GANIL
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A pre-registered, multi-lab non-replication of the action-sentence compatibility effect (ACE)
The Action-sentence Compatibility Effect (ACE) is a well-known demonstration of the role of motor activity in the comprehension of language. Participants are asked to make sensibility judgments on sentences by producing movements toward the body or away from the body. The ACE is the finding that movements are faster when the direction of the movement (e.g., toward) matches the direction of the action in the to-be-judged sentence (e.g., Art gave you the pen describes action toward you). We report on a pre-registered, multi-lab replication of one version of the ACE. The results show that none of the 18 labs involved in the study observed a reliable ACE, and that the meta-analytic estimate of the size of the ACE was essentially zero