5,767 research outputs found
Central galaxy growth and feedback in the most massive nearby cool core cluster
We present multi-wavelength observations of the centre of RXCJ1504.1-0248 -
the galaxy cluster with the most luminous and relatively nearby cool core at
z~0.2. Although there are several galaxies within 100 kpc of the cluster core,
only the brightest cluster galaxy (BCG), which lies at the peak of the X-ray
emission, has blue colours and strong line-emission. Approximately 80 Msun/yr
of intracluster gas is cooling below X-ray emitting temperatures, similar to
the observed UV star formation rate of ~140 Msun/yr. Most star formation occurs
in the core of the BCG and in a 42 kpc long filament of blue continuum, line
emission, and X-ray emission, that extends southwest of the galaxy. The
surrounding filamentary nebula is the most luminous around any observed BCG.
The number of ionizing stars in the BCG is barely sufficient to ionize and heat
the nebula, and the line ratios indicate an additional heat source is needed.
This heat source can contribute to the H\alpha-deduced star formation rates
(SFRs) in BCGs and therefore the derived SFRs should only be considered upper
limits. AGN feedback can slow down the cooling flow to the observed mass
deposition rate if the black hole accretion rate is of the order of 0.5 Msun/yr
at 10% energy output efficiency. The average turbulent velocity of the nebula
is vturb ~325 km/s which, if shared by the hot gas, limits the ratio of
turbulent to thermal energy of the intracluster medium to less than 6%.Comment: 15 pages, 11 figures, MNRAS in press. Corrected typo in abstract
New Approach to Nonlinear Dynamics of Fullerenes and Fullerites
New type of nonlinear (anharmonic) excitations -- bushes of vibrational modes
-- in physical systems with point or space symmetry are discussed. All infrared
active and Raman active bushes for C60 fulerene are found by means of special
group-theoretical methods.Comment: LaTeX, 8 pages, to be published in Fizika Tverdogo Tela, 200
Hydrogen Two-Photon Continuum Emission from the Horseshoe Filament in NGC 1275
Far ultraviolet emission has been detected from a knot of Halpha emission in
the Horseshoe filament, far out in the NGC 1275 nebula. The flux detected
relative to the brightness of the Halpha line in the same spatial region is
very close to that expected from Hydrogen two-photon continuum emission in the
particle heating model of Ferland et al. (2009) if reddening internal to the
filaments is taken into account. We find no need to invoke other sources of far
ultraviolet emission such as hot stars or emission lines from CIV in
intermediate temperature gas to explain these data.Comment: 9 pages, 8 figures. Accepted for publication in MNRA
Electron Power-Law Spectra in Solar and Space Plasmas
Particles are accelerated to very high, non-thermal energies in solar and
space plasma environments. While energy spectra of accelerated electrons often
exhibit a power law, it remains unclear how electrons are accelerated to high
energies and what processes determine the power-law index . Here, we
review previous observations of the power-law index in a variety of
different plasma environments with a particular focus on sub-relativistic
electrons. It appears that in regions more closely related to magnetic
reconnection (such as the `above-the-looptop' solar hard X-ray source and the
plasma sheet in Earth's magnetotail), the spectra are typically soft ( 4). This is in contrast to the typically hard spectra ( 4) that are observed in coincidence with shocks. The difference
implies that shocks are more efficient in producing a larger non-thermal
fraction of electron energies when compared to magnetic reconnection. A caveat
is that during active times in Earth's magnetotail, values seem
spatially uniform in the plasma sheet, while power-law distributions still
exist even in quiet times. The role of magnetotail reconnection in the electron
power-law formation could therefore be confounded with these background
conditions. Because different regions have been studied with different
instrumentations and methodologies, we point out a need for more systematic and
coordinated studies of power-law distributions for a better understanding of
possible scaling laws in particle acceleration as well as their universality.Comment: 67 pages, 15 figures; submitted to Space Science Reviews; comments
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Multi-Scale Interactions of Microtearing Turbulence in the Tokamak Pedestal
Microtearing turbulence in an idealized pedestal scenario is found to saturate via zonal fields, while also exciting strong zonal flows; a concurrent upshift of the non-linear critical gradient is observed. The zonal flows cause electron-temperature-gradient-driven turbulence to be ameliorated. When applying resonant magnetic perturbations, the prompt charge loss off the flux surface erodes the zonal flow, leading to higher electron-scale fluxes, while leaving microtearing saturation physics unaffected.</p
Influence of Geometry and Flow Variation on Jet Mixing and NO Formation in a Model Staged Combustor Mixer with Eight Orifices
A series of non-reacting parametric experiments was conducted to investigate the effect of geometric and flow variations on mixing of cold jets in an axis-symmetric, heated cross flow. The confined, cylindrical geometries tested represent the quick mix region of a Rich-Burn/Quick-Mix/Lean-Burn (RQL) combustor. The experiments show that orifice geometry and jet to mainstream momentum-flux ratio significantly impact the mixing characteristic of jets in a cylindrical cross stream. A computational code was used to extrapolate the results of the non-reacting experiments to reacting conditions in order to examine the nitric oxide (NO) formation potential of the configurations examined. The results show that the rate of NO formation is highest immediately downstream of the injection plane. For a given momentum-flux ratio, the orifice geometry that mixes effectively in both the immediate vicinity of the injection plane, and in the wall regions at downstream locations, has the potential to produce the lowest NO emissions. The results suggest that further study may not necessarily lead to a universal guideline for designing a low NO mixer. Instead, an assessment of each application may be required to determine the optimum combination of momentum-flux ratio and orifice geometry to minimize NO formation. Experiments at reacting conditions are needed to verify the present results
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