558 research outputs found
Chaotic motion of charged particles in toroidal magnetic configurations
We study the motion of a charged particle in a tokamak magnetic field and
discuss its chaotic nature. Contrary to most of recent studies, we do not make
any assumption on any constant of the motion and solve numerically the
cyclotron gyration using Hamiltonian formalism. We take advantage of a
symplectic integrator allowing us to make long-time simulations. First
considering an idealized magnetic configuration, we add a non generic
perturbation corresponding to a magnetic ripple, breaking one of the invariant
of the motion. Chaotic motion is then observed and opens questions about the
link between chaos of magnetic field lines and chaos of particle trajectories.
Second, we return to a axi-symmetric configuration and tune the safety factor
(magnetic configuration) in order to recover chaotic motion. In this last
setting with two constants of the motion, the presence of chaos implies that no
third global constant exists, we highlight this fact by looking at variations
of the first order of the magnetic moment in this chaotic setting. We are
facing a mixed phase space with both regular and chaotic regions and point out
the difficulties in performing a global reduction such as gyrokinetics
The decay of Batchelor and Saffman rotating turbulence
The decay rate of isotropic and homogeneous turbulence is known to be
affected by the large-scale spectrum of the initial perturbations, associated
with at least two cannonical self-preserving solutions of the von
K\'arm\'an-Howarth equation: the so-called Batchelor and Saffman spectra. The
effect of long-range correlations in the decay of anisotropic flows is less
clear, and recently it has been proposed that the decay rate of rotating
turbulence may be independent of the large-scale spectrum of the initial
perturbations. We analyze numerical simulations of freely decaying rotating
turbulence with initial energy spectra (Batchelor turbulence) and
(Saffman turbulence) and show that, while a self-similar decay
cannot be identified for the total energy, the decay is indeed affected by
long-range correlations. The decay of two-dimensional and three-dimensional
modes follows distinct power laws in each case, which are consistent with
predictions derived from the anisotropic von K\'arm\'an-Howarth equation, and
with conservation of anisotropic integral quantities by the flow evolution
The CERN Cryogenic Test Facility for the Atlas Barrel Toroid Magnets
The superconducting magnet system of the ATLAS detector will consist of a central solenoid, two end-cap toroidal magnets (ECT) and the barrel toroid magnet (BT) made of eight coils symmetrically placed around the central axis of the detector. The magnets will be tested individually in a 5000 m2 experimental area prior to their final installation at an underground cavern of the LHC Collider. For the BT magnets, a dedicated cryogenic test facility has been designed which is currently under the construction and commissioning phase. A liquid nitrogen pre-cooling unit and a 1200 [email protected] refrigerator will allow flexible operating conditions via a rather complex distribution and transfer line system. Flow of two-phase helium for cooling the coils is provided by centrifugal pumps immersed in a saturated liquid helium bath. The integration of the pumps in an existing cryostat required the adoption of novel mechanical solutions. Tests conducted permitted the validation of the technical design of the cryostat and its instrumentation. The characteristics of one pump were measured and pressure rise of 300 mbar at nominal flow of 80 g/s confirmed the specifications
Note prĂ©liminaire sur lâemploi dâun vaccin inactivĂ© contre la peste Ă©quine
Bourdin P., Monnier-Cambon J. Note prĂ©liminaire sur lâemploi du vaccin inactivĂ© contre la peste Ă©quine(avec la collaboration technique de A. Vautier et de Diallo Mamadou Saliou) . In: Bulletin de l'AcadĂ©mie VĂ©tĂ©rinaire de France tome 120 n°4, 1967. pp. 187-191
Scaling and energy transfer in rotating turbulence
The inertial-range properties of quasi-stationary hydrodynamic turbulence
under solid-body rotation are studied via high-resolution direct numerical
simulations. For strong rotation the nonlinear energy cascade exhibits
depletion and a pronounced anisotropy with the energy flux proceeding mainly
perpendicularly to the rotation axis. This corresponds to a transition towards
a quasi-two-dimensional flow similar to a linear Taylor-Proudman state. In
contrast to the energy spectrum along the rotation axis which does not scale
self-similarly, the perpendicular spectrum displays an inertial range with
-behavior. A new phenomenology gives a rationale for the
observations. The scaling exponents of structure functions up to
order measured perpendicular to the rotation axis indicate reduced
intermittency with increasing rotation rate. The proposed phenomenology is
consistent with the inferred asymptotic non-intermittent behavior
.Comment: to be published in Europhysics Letters (www.epletters.net), minor
changes to match version in prin
New insights on <i>Rimicaris exoculata</i> bacterial ectosymbiosis: a moult cycle related perspective
Normalized Affymetrix expression data are biased by G-quadruplex formation
Probes with runs of four or more guanines (G-stacks) in their sequences can exhibit a level of hybridization that is unrelated to the expression levels of the mRNA that they are intended to measure. This is most likely caused by the formation of G-quadruplexes, where inter-probe guanines form Hoogsteen hydrogen bonds, which probes with G-stacks are capable of forming. We demonstrate that for a specific microarray data set using the Human HG-U133A Affymetrix GeneChip and RMA normalization there is significant bias in the expression levels, the fold change and the correlations between expression levels. These effects grow more pronounced as the number of G-stack probes in a probe set increases. Approximately 14 of the probe sets are directly affected. The analysis was repeated for a number of other normalization pipelines and two, FARMS and PLIER, minimized the bias to some extent. We estimate that âŒ15 of the data sets deposited in the GEO database are susceptible to the effect. The inclusion of G-stack probes in the affected data sets can bias key parameters used in the selection and clustering of genes. The elimination of these probes from any analysis in such affected data sets outweighs the increase of noise in the signal. © 2011 The Author(s)
oxidative stress by monoamine oxidase mediates receptor-independent cardiomyocyte apoptosis by serotonin and post-ischemic myocardial injury
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