23,618 research outputs found
Constraints on hot metals in the Vicinity of the Galaxy
We have searched for evidence of soft X-ray absorption by hot metals in the
vicinity of the Galaxy in the spectra of a small sample of fifteen Type I AGN
observed with the high resolution X-ray gratings on board Chandra. This is an
extension of our previous survey of hot OVII and OVIII absorbing gas in the
vicinity of the Galaxy. The strongest absorption signatures within a few
hundred km/s of their rest-frame energies are most likely due to warm absorbing
outflows from the nearest AGN, which are back-lighting the local hot gas. We
emphasize that absorption signatures in the spectra of some distant AGN that
are kinematically consistent with the recessional velocity of the AGN are most
likely to be due to hot local gas. Along the sightline towards PG 1211+143, PDS
456 and MCG-6-30-15 there is a very large absorbing Fe column density which is
kinematically consistent with absorption by hot, local Fe. The sightlines to
these three AGN pass through the limb of the Northern Polar Spur (NPS), a local
bubble formed from several supernovae which, if rich in Fe, may account for a
large local Fe column.
We obtain limits on the column density of local, highly ionized N, Ne, Mg, Si
along all of the sightlines in our sample. We correlate the column density
limits with those of highly ionized O along the same sightlines. Assuming the
hot local gas is in collisionally ionized equilibrium, we obtain limits on the
temperature and relative abundances of the metals in the hot local gas. Our
limits on the ionic column densities in the local hot gas seem to be consistent
with those observed in the hot halo gas of edge-on normal spiral galaxies.Comment: 9 pages,2 figures, MNRAS (accepted
Compressor and fan wake characteristics
A triaxial probe and a rotating conventional probe, mounted on a traverse gear operated by two step motors were used to measure the mean velocities and turbulence quantities across a rotor wake at various radial locations and downstream stations. The data obtained was used in an analytical model developed to study how rotor flow and blade parameters and turbulence properties such as energy, velocity correlations, and length scale affect the rotor wake characteristics and its diffusion properties. The model, includes three dimensional attributes, can be used in predicting the discrete as well as broadband noise generated in a fan rotor, as well as in evaluating the aerodynamic losses, efficiency and optimum spacing between a rotor and stator in turbomachinery
Energetic Impact of Jet Inflated Cocoons in Relaxed Galaxy Clusters
Jets from active galactic nuclei (AGN) in the cores of galaxy clusters have
the potential to be a major contributor to the energy budget of the
intracluster medium (ICM). To study the dependence of the interaction between
the AGN jets and the ICM on the parameters of the jets themselves, we present a
parameter survey of two-dimensional (axisymmetric) ideal hydrodynamic models of
back-to-back jets injected into a cluster atmosphere (with varying Mach numbers
and kinetic luminosities). We follow the passive evolution of the resulting
structures for several times longer than the active lifetime of the jet. The
simulations fall into roughly two classes, cocoon-bounded and non-cocoon
bounded sources. We suggest a correspondence between these two classes and the
Faranoff-Riley types. We find that the cocoon-bounded sources inject
significantly more entropy into the core regions of the ICM atmosphere, even
though the efficiency with which energy is thermalized is independent of the
morphological class. In all cases, a large fraction (50--80%) of the energy
injected by the jet ends up as gravitational potential energy due to the
expansion of the atmosphere.Comment: 12 pages, Accepted for publication in Ap
A three-dimensional simulation of transition and early turbulence in a time-developing mixing layer
The physics of the transition and early turbulence regimes in the time developing mixing layer was investigated. The sensitivity of the mixing layer to the disturbance field of the initial condition is considered. The growth of the momentum thickness, the mean velocity profile, the turbulence kinetic energy, the Reynolds stresses, the anisotropy tensor, and particle track pictures of computations are all examined in an effort to better understand the physics of these regimes. The amplitude, spectrum shape, and random phases of the initial disturbance field were varied. A scheme of generating discrete orthogonal function expansions on some nonuniform grids was developed. All cases address the early or near field of the mixing layer. The most significant result shows that the secondary instability of the mixing layer is produced by spanwise variations in the straining field of the primary vortex structures
Stabilized lanthanum sulphur compounds
Lanthanum sulfide is maintained in the stable cubic phase form over a temperature range of from 500 C to 1500 C by adding to it small amounts of calcium, barium, or strontium. This compound is an excellent thermoelectric material
A computer operated mass spectrometer system
Digital computer system for processing mass spectrometer output dat
Recommended from our members
Dr Reynolds and Dr Armstrong response to the EFRA committee enquiry COVID-19 and food supply
We provide this response to highlight data collected through online survey research. Our most important finding is that UK citizens typically perceive individual items of food to be higher risk following the UK lockdown. By risk we mean increased likelihood that eating the food would damage their health due to risks of contamination, food poisoning, improper handling, food fraud and mislabeling. However, this increased perception of food risk varies by food type. Post lockdown UK citizens perceive foods from China and the USA to be higher risk than that from the UK or the EU (this data is currently under peer review). This has implications for post lockdown (and post Brexit) trade policy and public trust. To rebuild the UK food system post COVID19, communication of food safety and food supply decisions must be coordinated, transparent and wide reaching. Our research confirms three key findings of other surveys carried out since the COVID19 lockdown that: 1) cooking and shopping practices have changed since lockdown with larger less frequent shops; 2) household food waste behaviour has changed since lockdown, with different population segments (age/income) self reporting wasting more or less than usual; 3) household food insecurity has increased by at least 10% since lockdown and the COVID crisis. We recommend that the Government and food industry should highlight to the public that the risk of contracting COVID19 through food or food packaging is highly unlikely. As perceptions of food risk influence citizen food choice it is key to understand whether specific foods or food groups show a greater increase in perceived food risk (e.g. fruit and vegetables vs. high fat sugar and salt foods), as this could have a negative impact on the uptake and consumption of sustainable healthy diets within the UK population post lockdown. We highlight that citizen science is uniquely placed as a research method to 1) investigate food issues, and 2) communicate information to the UK public. Providing further funding for citizen science research would be advantageous as the UK rebuilds the food system post lockdown
Computer control of mass analyzers
Digital computer control of mass spectrometer
School violence, school differences and school discourses
This article highlights one strand of a study which investigated the concept of the violenceresilient school. In six inner-city secondary schools, data on violent incidents in school and violent crime in the neighbourhood were gathered, and compared with school practices to minimise violence, accessed through interviews. Some degree of association between the patterns of behaviour and school practices was found: schools with a wider range of wellconnected practices seemed to have less difficult behaviour. Interviews also showed that the different schools had different organisational discourses for construing school violence, its possible causes and the possible solutions. Differences in practices are best understood in connection with differences in these discourses. Some of the features of school discourses are outlined, including their range, their core metaphor and their silences. We suggest that organisational discourse is an important concept in explaining school effects and school differences, and that improvement attempts could have clearer regard to this concept
Parsec-scale radio morphology and variability of a changing-look AGN: the case of Mrk 590
We investigate the origin of the parsec-scale radio emission from the
changing-look active galactic nucleus (AGN) of Mrk 590, and examine whether the
radio power has faded concurrently with the dramatic decrease in accretion
rates observed between the 1990s and the present. We detect a compact core at
1.6 GHz and 8.4 GHz using new Very Long Baseline Array observations, finding no
significant extended, jet-like features down to 1 pc scales. The flat
spectral index () and high brightness temperature
() indicate self-absorbed synchrotron emission
from the AGN. The radio to X-ray luminosity ratio of , similar to that in coronally active stars, suggests
emission from magnetized coronal winds, although unresolved radio jets are also
consistent with the data. Comparing new Karl G. Jansky Very Large Array
measurements with archival and published radio flux densities, we find ,
, and (insignificantly) flux density decreases between the 1990s
and the year 2015 at 1.4 GHz, 5 GHz and 8.4 GHz respectively. This trend,
possibly due to the expansion and fading of internal shocks within the
radio-emitting outflow after a recent outburst, is consistent with the decline
of the optical-UV and X-ray luminosities over the same period. Such correlated
variability demonstrates the AGN accretion-outflow connection, confirming that
the changing-look behaviour in Mrk 590 originates from variable accretion rates
rather than dust obscuration. The present radio and X-ray luminosity
correlation, consistent with low/hard state accretion, suggests that the black
hole may now be accreting in a radiatively inefficient mode.Comment: 14 pages, 5 tables, 5 figures, accepted for publication in MNRA
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