14,303 research outputs found
Numerical simulations of current generation and dynamo excitation in a mechanically-forced, turbulent flow
The role of turbulence in current generation and self-excitation of magnetic
fields has been studied in the geometry of a mechanically driven, spherical
dynamo experiment, using a three dimensional numerical computation. A simple
impeller model drives a flow which can generate a growing magnetic field,
depending upon the magnetic Reynolds number, Rm, and the fluid Reynolds number.
When the flow is laminar, the dynamo transition is governed by a simple
threshold in Rm, above which a growing magnetic eigenmode is observed. The
eigenmode is primarily a dipole field tranverse to axis of symmetry of the
flow. In saturation the Lorentz force slows the flow such that the magnetic
eigenmode becomes marginally stable. For turbulent flow, the dynamo eigenmode
is suppressed. The mechanism of suppression is due to a combination of a time
varying large-scale field and the presence of fluctuation driven currents which
effectively enhance the magnetic diffusivity. For higher Rm a dynamo reappears,
however the structure of the magnetic field is often different from the laminar
dynamo; it is dominated by a dipolar magnetic field which is aligned with the
axis of symmetry of the mean-flow, apparently generated by fluctuation-driven
currents. The fluctuation-driven currents have been studied by applying a weak
magnetic field to laminar and turbulent flows. The magnetic fields generated by
the fluctuations are significant: a dipole moment aligned with the symmetry
axis of the mean-flow is generated similar to those observed in the experiment,
and both toroidal and poloidal flux expulsion are observed.Comment: 14 pages, 14 figure
Molecular imaging: novel tools in visualizing rheumatoid arthritis
Molecular imaging is a rapidly emerging field in biomedical research, aiming at the visualization, characterization and quantification of molecular and cellular processes non-invasively within intact living organisms. To sense biological processes such as gene expression, angiogenesis, apoptosis or cell trafficking in vivo, imaging reporter agents that interact specifically with molecular targets and appropriate imaging systems are currently under development. In rheumatoid arthritis, these novel tools will be used to evaluate physiological and pathophysiological processes, to facilitate diagnosis and monitor therapeutic regimens, to enable reliable prognosis and to support the development of new therapies. In this review, we summarize the basic principles of molecular imaging, such as the development of molecular imaging agents, the actual capabilities of different imaging modalities and the most recent advances in molecular imaging, demonstrating the potential of this technology. With regard to their applicability in rheumatic diseases, we discuss potential molecular targets, current experimental approaches and the future prospects for molecular imaging in rheumatoid arthriti
First Results from Pb+Pb collisions at the LHC
At the end of 2010, the CERN Large Hadron Collider started operation with
heavy ion beams, colliding lead nuclei at a centre-of-mass energy of 2.76
TeV/nucleon and opening a new era in ultra-relativistic heavy ion physics at
energies exceeding previous accelerators by more than an order of magnitude.
This review summarizes the results from the first year of heavy ion physics at
LHC obtained by the three experiments participating in the heavy ion program,
ALICE, ATLAS, and CMS.Comment: To appear in Annual Review of Nuclear and Particle Scienc
Interferometer-Type Structures for Guided Atoms
We experimentally demonstrate interferometer-type guiding structures for
neutral atoms based on dipole potentials created by micro-fabricated optical
systems. As a central element we use an array of atom waveguides being formed
by focusing a red-detuned laser beam with an array of cylindrical microlenses.
Combining two of these arrays, we realize X-shaped beam splitters and more
complex systems like the geometries for Mach-Zehnder and Michelson-type
interferometers for atoms.Comment: 4 pages, 6 figure
Fundamental scaling laws of on-off intermittency in a stochastically driven dissipative pattern forming system
Noise driven electroconvection in sandwich cells of nematic liquid crystals
exhibits on-off intermittent behaviour at the onset of the instability. We
study laser scattering of convection rolls to characterize the wavelengths and
the trajectories of the stochastic amplitudes of the intermittent structures.
The pattern wavelengths and the statistics of these trajectories are in
quantitative agreement with simulations of the linearized electrohydrodynamic
equations. The fundamental distribution law for the durations
of laminar phases as well as the power law of the amplitude distribution
of intermittent bursts are confirmed in the experiments. Power spectral
densities of the experimental and numerically simulated trajectories are
discussed.Comment: 20 pages and 17 figure
Far infrared study of the two dimensional dimer spin system SrCu_2(BO_3)_2
Using far-infrared spectroscopy in magnetic fields up to 12T we have studied
a two-dimensional dimer spin gap system SrCu_2(BO_3)_2. We found several
infrared active modes in the dimerized state (below 10K) in the frequency range
from 3 to 100cm^-1. The measured splitting from the ground state to the excited
triplet M_S=0 sublevel is Delta_1=24.2cm^-1 and the other two triplet state
sublevels in zero magnetic field are 1.4cm^-1 below and above the M_S=0
sublevel. Another multiplet is at Delta_2=37.6cm^-1 from the ground state. A
strong electric dipole active transition polarized in the (ab)-plane is
activated in the dimer spin system below 15K at 52cm^-1.Comment: 4 pages including 5 figures, submitted to PRB, instrumental arte
facts remove
Towards the Equation of State of Classical SU(2) Lattice Gauge Theory
We determine numerically the full complex Lyapunov spectrum of SU(2)
Yang-Mills fields on a 3-dimensional lattice from the classical chaotic
dynamics. The equation of state, S(E), is determined from the Kolmogorov-Sinai
entropy extrapolated to the large size limit.Comment: 12 pages, 8 PS figures, LaTe
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