207 research outputs found
Reconstructing the projected gravitational potential of Abell 1689 from X-ray measurements
Context. Galaxy clusters can be used as cosmological probes, but to this end,
they need to be thoroughly understood. Combining all cluster observables in a
consistent way will help us to understand their global properties and their
internal structure. Aims. We provide proof of the concept that the projected
gravitational potential of galaxy clusters can directly be reconstructed from
X-ray observations. We also show that this joint analysis can be used to
locally test the validity of the equilibrium assumptions in galaxy clusters.
Methods. We used a newly developed reconstruction method, based on
Richardson-Lucy deprojection, that allows reconstructing projected
gravitational potentials of galaxy clusters directly from X-ray observations.
We applied this algorithm to the well-studied cluster Abell 1689 and compared
the gravitational potential reconstructed from X-ray observables to the
potential obtained from gravitational lensing measurements. [...] Results.
Assuming spherical symmetry and hydrostatic equilibrium, the potentials
recovered from gravitational lensing and from X-ray emission agree very well
beyond 500 kpc. Owing to the fact that the Richardson-Lucy deprojection
algorithm allows deprojecting each line of sight independently, this result may
indicate that non-gravitational effects and/or asphericity are strong in the
central regions of the clusters. Conclusions. We demonstrate the robustness of
the potential reconstruction method based on the Richardson-Lucy deprojection
algorithm and show that gravitational lensing and X-ray emission lead to
consistent gravitational potentials. Our results illustrate the power of
combining galaxy-cluster observables in a single, non-parametric, joint
reconstruction of consistent cluster potentials that can be used to locally
constrain the physical state of the gas.Comment: 8 pages, 4 figures. Accepted in A&
International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM), Rossendorf, 11.-13.10.99, Proceedings: International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM), Rossendorf, 11.-13.10.99, Proceedings
The International Workshop on "Measuring Techniques in Liquid Metal Flows" (MTLM Workshop) was organised in frame of the Dresden "Innovationskolleg Magnetofluiddynamik". The subject of the MTLM Workshop was limited to methods to determine physical flow quantities such as velocity, pressure, void fraction, inclusion properties, crystallisation fronts etc. The present proceedings contain abstracts and viewgraphs of the oral presentations. During the last decades numerical simulations have become an important tool in industry and research to study the structure of flows and the properties of heat and mass transfer. However, in case of liquid metal flows there exists a significant problem to validate the codes with experimental data due to the lack of available measuring techniques. Due to the material properties (opaque, hot, chemical aggressive) the measurement of flow quantities is much more delicate in liquid metals compared to ordinary water flows. The generalisation of results obtained by means of water models to real liquid metal flows has often to be considered as difficult due to the problems to meet the actual values of non-dimensional flow parameters (Re, Pr, Gr, Ha, etc.). Moreover, a strong need has to be noted to make measuring techniques available to monitor and to control flow processes in real industrial facilities
Collapse of Coherent Large Scale Flow in Strongly Turbulent Liquid Metal Convection
The large-scale flow structure and the turbulent transfer of heat and
momentum are directly measured in highly turbulent liquid metal convection
experiments for Rayleigh numbers varied between and and Prandtl numbers of . Our
measurements are performed in two cylindrical samples of aspect ratios diameter/height and 1 filled with the eutectic alloy GaInSn. The
reconstruction of the three-dimensional flow pattern by 17 ultrasound Doppler
velocimetry sensors detecting the velocity profiles along their beamlines in
different planes reveals a clear breakdown of coherence of the large-scale
circulation for . As a consequence, the scaling laws for heat and
momentum transfer inherit a dependence on the aspect ratio. We show that this
breakdown of coherence is accompanied with a reduction of the Reynolds number
. The scaling exponent of the power law
crosses \FIN{eventually} over from to 0.124 when the liquid metal
flow at reaches and the coherent
large-scale flow is completely collapsed.Comment: 4 pages, 5 figures, 1 supplementary with 1 figure and 4 tables, 1
movi
Synchronizing the helicity of Rayleigh-B\'enard convection by a tide-like electromagnetic forcing
We present results on the synchronization of the helicity in a liquid-metal
Rayleigh-B\'enard (RB) experiment under the influence of a tide-like
electromagnetic forcing with azimuthal wavenumber m=2. We show that for a
critical forcing strength the typical Large Scale Circulation (LSC) in the
cylindrical vessel of aspect ratio unity is entrained by the period of the
tide-like forcing, leading to synchronized helicity oscillations with opposite
signs in two half-spaces. The obtained experimental results are consistent with
and supported by numerical simulations. A similar entrainment mechanism for the
helicity in the solar tachocline may be responsible for the astonishing
synchronization of the solar dynamo by the 11.07-year triple synodic alignment
cycle of the tidally dominant planets Venus, Earth and Jupiter
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