3,262 research outputs found
GMRT 610-MHz observations of the faint radio source population – and what these tell us about the higher radio-frequency sky
We present 610-MHz Giant Metrewave Radio Telescope observations of 0.84 deg of the AMI001 field (centred on 002310, +31°53′) with an rms noise of 18 μJy beam in the centre of the field. A total of 955 sources are detected, and 814 are included in the source count analysis. The source counts from these observations are consistent with previous work. We have used these data to study the spectral index distribution of a sample of sources selected at 15.7 GHz from the recent deep extension to the Tenth Cambridge (10C) survey. The median spectral index, α, (where S ∝ ν) between 0.08</mJy<0.2 is 0.32 ± 0.14, showing that star-forming galaxies, which have much steeper spectra, are not contributing significantly to this population. This is in contrast to several models, but in agreement with the results from the 10C ultradeep source counts; the high-frequency sky therefore continues to be dominated by radio galaxies down to S = 0.1 mJy.The GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. IHW thanks the Science and Technologies Facilities Council for a studentship. IHW and MJJ acknowledge support from the Square Kilometre Array South Africa. IHW thanks the South African Astronomical Observatory, where some of this work was carried out
The faint radio source population at 15.7 GHz-IV. The dominance of core emission in faint radio galaxies
We present 15-GHz Karl G. Jansky Very Large Array observations of a complete
sample of radio galaxies selected at 15.7 GHz from the Tenth Cambridge (10C)
survey. 67 out of the 95 sources (71 per cent) are unresolved in the new
observations and lower-frequency radio observations, placing an upper limit on
their angular size of ~2 arcsec. Thus compact radio galaxies, or radio galaxies
with very faint jets, are the dominant population in the 10C survey. This
provides support for the suggestion in our previous work that low-luminosity
() radio galaxies are core-dominated, although
higher-resolution observations are required to confirm this directly. The 10C
sample of compact, high-frequency selected radio galaxies is a mixture of
high-excitation and low-excitation radio galaxies and displays a range of radio
spectral shapes, demonstrating that they are a mixed population of objects
The faint radio source population at 15.7 GHz - II. Multi-wavelength properties
A complete, flux density limited sample of 96 faint ( mJy) radio
sources is selected from the 10C survey at 15.7 GHz in the Lockman Hole. We
have matched this sample to a range of multi-wavelength catalogues, including
SERVS, SWIRE, UKIDSS and optical data; multi-wavelength counterparts are found
for 80 of the 96 sources and spectroscopic redshifts are available for 24
sources. Photometric reshifts are estimated for the sources with
multi-wavelength data available; the median redshift of the sample is 0.91 with
an interquartile range of 0.84. Radio-to-optical ratios show that at least 94
per cent of the sample are radio loud, indicating that the 10C sample is
dominated by radio galaxies. This is in contrast to samples selected at lower
frequencies, where radio-quiet AGN and starforming galaxies are present in
significant numbers at these flux density levels. All six radio-quiet sources
have rising radio spectra, suggesting that they are dominated by AGN emission.
These results confirm the conclusions of Paper I that the faint, flat-spectrum
sources which are found to dominate the 10C sample below mJy are the
cores of radio galaxies. The properties of the 10C sample are compared to the
SKADS Simulated Skies; a population of low-redshift starforming galaxies
predicted by the simulation is not found in the observed sample.IHW acknowledges a Science and Technology Facilities Council studentship. IHW, MJ, MV acknowledge support from the Square Kilometre Array South Africa project and the South African National Research Foundation. MV is supported by the European Commission Research Executive Agency FP7-SPACE- 2013-1 Scheme (Grant Agreement 607254 - Herschel Extragalactic Legacy Project - HELP). This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Opinions expressed and conclusions arrived at are those of the authors and not necessarily attributed to the SKA SA. We thank the anonymous referee for their helpful comments.This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stv190
Upcycling of low value end-of-life cathode material into next generation cathode materials
The increase in the use of electric vehicles (EVs) will ultimately lead to an increase in the number of end-of-life lithium-ion batteries (LIBs) that need to be recycled. A particular challenge concerns how to deal with low value cathodes, such as LiMn2O4 (LMO). To this end, this paper investigates recycling cathode material from an end-of-life Gen 1 Nissan Leaf (2011 model, 40 000 miles) which contains a mixture of spinel (LMO) and a Ni-rich layered oxide (LO). Citric acid was employed to selectively leach LMO into solution while leaving the remaining LO as a solid. The citric acid also acts as a delamination agent to remove the remaining LO from the Al current collector. The LMO was then recovered from solution and upcycled to form new cathode materials. Ni-doping of the solution allowed the synthesis of the high voltage cathode LiMn1.5Ni0.5O4 (LMNO) which is attracting commercial interest. Disordered rocksalt compounds Li4Mn2O5 and Li2MnO2.25F were also synthesised and gave high specific discharge capacities of 293 and 279 mA h g−1 respectively. This proof of concept work demonstrates a method to upcycle end-of-life cathode material into next generation cathode materials
Interaction between occupational exposures and antioxidant genes on chronic obstructive pulmonary disease in UK Biobank
The Dark Energy Survey Data Management System
The Dark Energy Survey collaboration will study cosmic acceleration with a
5000 deg2 griZY survey in the southern sky over 525 nights from 2011-2016. The
DES data management (DESDM) system will be used to process and archive these
data and the resulting science ready data products. The DESDM system consists
of an integrated archive, a processing framework, an ensemble of astronomy
codes and a data access framework. We are developing the DESDM system for
operation in the high performance computing (HPC) environments at NCSA and
Fermilab. Operating the DESDM system in an HPC environment offers both speed
and flexibility. We will employ it for our regular nightly processing needs,
and for more compute-intensive tasks such as large scale image coaddition
campaigns, extraction of weak lensing shear from the full survey dataset, and
massive seasonal reprocessing of the DES data. Data products will be available
to the Collaboration and later to the public through a virtual-observatory
compatible web portal. Our approach leverages investments in publicly available
HPC systems, greatly reducing hardware and maintenance costs to the project,
which must deploy and maintain only the storage, database platforms and
orchestration and web portal nodes that are specific to DESDM. In Fall 2007, we
tested the current DESDM system on both simulated and real survey data. We used
Teragrid to process 10 simulated DES nights (3TB of raw data), ingesting and
calibrating approximately 250 million objects into the DES Archive database. We
also used DESDM to process and calibrate over 50 nights of survey data acquired
with the Mosaic2 camera. Comparison to truth tables in the case of the
simulated data and internal crosschecks in the case of the real data indicate
that astrometric and photometric data quality is excellent.Comment: To be published in the proceedings of the SPIE conference on
Astronomical Instrumentation (held in Marseille in June 2008). This preprint
is made available with the permission of SPIE. Further information together
with preprint containing full quality images is available at
http://desweb.cosmology.uiuc.edu/wik
Galaxy luminosity evolution: how much is due to a model choice?
The cluster and field luminosity functions (LFs) determined on large
homogeneous samples (N>2200 galaxies each) are almost indistinguishable, down
to M^*+4 in the r and i filters, hence suggesting that the effect of the
cluster environment on the galaxy properties does not affect the galaxy
luminosity function in red bands. The similarity of the red band LFs in
different environments suggests that the galaxy mass function is preserved
during the galaxy infall in the cluster. By analyzing a large sample of
galaxies in clusters, ideal from many points of view (multicolor data, large
size, many clusters, metric magnitudes) we found that luminosity evolution is
required by the data but the latter do not unambiguously derive its flavour if
a differential luminosity evolution between bright and faint galaxies is
allowed. We show that the LF parameters (slope, characteristic magnitude and
their evolution) and errors depend on assumptions in a way seldom recognized in
literature. We also point out logical inconsistencies between hypothesis
assumed in deriving literature LF and presented results, suggesting caution in
interpreting similar published results.Comment: A&A, in pres
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