82,504 research outputs found
Embedded function methods for compressible high speed turbulent flow
Fundamental issues relating to compressible turbulent flow are addressed. The focus has been on developing methods and testing concepts for attached flows rather than trying to force a conventional law of the wall into a zone of backflow. Although the dynamics of the near-wall flow in an attached turbulent boundary layer are relatively well documented, the dynamical features of a zone of reversed turbulent flow are not, nor are they well understood. Incompressibility introduces effects and issues that have been dealt with only marginally in the literature, therefore, the present work has been focussed on attached high-speed flows. The wall function method has been extended up through the supersonic to hypersonic speeds. Algorithms have been successfully introduced into the code that calculates the flow all the way to the wall, and testing is being carried out for progressively more complex flow situations
Wall-layer eruptions in turbulent flows
The near-wall region of a turbulent flow is investigated in the limit of large Reynolds numbers. When low-speed streaks are present, the governing equations are shown to be of the boundary-layer type. Physical processes leading to local breakdown and a strong interaction with the outer region are considered. It is argued that convected vortices, predominantly of the hairpin type, will provoke eruptions and regenerative interactions with the outer region
Working Together to Build Beacon Centers in San Francisco: Evaluation Findings from 1998-2000
Since 1996, private and public funders in San Francisco have supported a city-wide Beacons Initiative. Eight Beacon Centers, located in public schools, serve 7500 youth and adults each year, providing a rich array of developmental activities in the non-school hours. This report looks at how the centers were created; it describes the centers' operation; and investigates the role of the initiative's "theory of change" in organizing and guiding the effort
What fraction of the density fluctuations in the Perseus cluster core is due to gas sloshing rather than AGN feedback?
Deep Chandra observations of the core of the Perseus cluster show a plethora
of complex structure. It has been found that when the observed density
fluctuations in the intracluster medium are converted into constraints on AGN
induced turbulence, the resulting turbulent heating rates are sufficient to
balance cooling locally throughout the central 220kpc. However while the
signatures of AGN feedback (inflated bubbles) dominate the central 60kpc in
X-ray images, beyond this radius the intracluster medium is increasingly shaped
by the effects of gas sloshing, which can also produce subtle variations in
X-ray surface brightness. We use mock Chandra observations of gas sloshing
simulations to investigate what fraction of the observed density fluctuations
in the core of the Perseus galaxy cluster may originate from sloshing rather
than AGN induced feedback. Outside 60kpc, we find that the observed level of
the density fluctuations is broadly consistent with being produced by sloshing
alone. If this is the case, AGN-generated turbulence is likely to be
insufficient in combating cooling outside 60kpc.Comment: 9 pages, 5 figures, accepted for publication in MNRA
Control of common scab without the use of water
The most effective way to control common scab is by irrigating a potato crop at tuber initiation. With the introduction of legislation such as the Water Framework Directive this will become increasingly difficult. In this field experiment, we assessed the potential of a number of non-water measures for controlling this disease. Common scab on daughter tubers at harvest was reduced by applying rapeseed meal at 1 t ha-1 to the beds and then incorporating it into the soil, and adding a mixture of Trichoderma viride isolates into the furrow at planting. None of these treatments was as effective as using water
Large scale gas sloshing out to half the virial radius in the strongest cool core REXCESS galaxy cluster, RXJ2014.8-2430
We search the cool core galaxy clusters in the REXCESS sample for evidence of
large scale gas sloshing, and find clear evidence for sloshing in
RXJ2014.8-2430, the strongest cool core cluster in the REXCESS cluster sample.
The residuals of the surface brightness distribution from the azimuthal average
for RXJ2014 show a prominent swirling excess feature extending out to an abrupt
surface brightness discontinuity at 800 kpc from the cluster core (half the
virial radius) to the south, which the XMM-Newton observations confirm to be
cold, low entropy gas. The gas temperature is significantly higher outside this
southern surface brightness discontinuity, indicating that this is a cold front
800 kpc from the cluster core. Chandra observations of the central 200 kpc show
two clear younger cold fronts on opposite sides of the cluster. The scenario
appears qualitatively consistent with simulations of gas sloshing due to minor
mergers which raise cold, low entropy gas from the core to higher radius,
resulting in a swirling distribution of opposing cold fronts at increasing
radii. However the scale of the observed sloshing is much larger than that
which has been simulated at present, and is similar to the large scale sloshing
recently observed in the Perseus cluster and Abell 2142.Comment: 5 pages, 5 figures. Accepted for publication in MNRA
An XMM-Newton view of the merging activity in the Centaurus cluster
We report the results of XMM-Newton observations of the regions around the
core of the Centaurus cluster where evidence for merging activity between the
subgroup Cen 45 and the main Centaurus cluster has previously been observed
using ASCA and ROSAT data. We confirm the ASCA findings of a temperature excess
surrounding Cen 45. We find that this temperature excess can be explained using
simple shock heating given the large line of sight velocity difference between
Cen 45 and the surrounding main Centaurus cluster. We find that there is a
statistically significant excess in metallicity around Cen 45, showing that Cen
45 has managed to retain its gas as it has interacted with the main Centaurus
cluster. There is a pressure excess to the east in the direction of the merger,
and there is also an entropy excess around the central galaxy of Cen 45. The
metallicity between 50-100 kpc to the north of NGC 4696 is higher than to the
south, which may be the result of the asymmetric distribution of metals due to
previous sloshing of the core, or which may be associated with the filamentary
structure we detect between NGC 4696 and NGC 4696B.Comment: 11 pages, 12 figures. Accepted for publication in MNRA
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