468 research outputs found
Optical spectroscopy of faint gigahertz peaked spectrum sources
We present spectroscopic observations of a sample of faint Gigahertz Peaked
Spectrum (GPS) radio sources drawn from the Westerbork Northern Sky Survey
(WENSS). Redshifts have been determined for 19 (40%) of the objects. The
optical spectra of the GPS sources identified with low redshift galaxies show
deep stellar absorption features. This confirms previous suggestions that their
optical light is not significantly contaminated by AGN-related emission, but is
dominated by a population of old (>9 Gyr) and metal-rich (>0.2 [Fe/H]) stars,
justifying the use of these (probably) young radio sources as probes of galaxy
evolution. The optical spectra of GPS sources identified with quasars are
indistinguishable from those of flat spectrum quasars, and clearly different
from the spectra of Compact Steep Spectrum (CSS) quasars. The redshift
distribution of the GPS quasars in our radio-faint sample is comparable to that
of the bright samples presented in the literature, peaking at z ~ 2-3. It is
unlikely that a significant population of low redshift GPS quasars is missed
due to selection effects in our sample. We therefore claim that there is a
genuine difference between the redshift distributions of GPS galaxies and
quasars, which, because it is present in both the radio-faint and bright
samples, can not be due to a redshift-luminosity degeneracy. It is therefore
unlikely that the GPS quasars and galaxies are unified by orientation, unless
the quasar opening angle is a strong function of redshift. We suggest that the
GPS quasars and galaxies are unrelated populations and just happen to have
identical observed radio-spectral properties, and hypothesise that GPS quasars
are a sub-class of flat spectrum quasars.Comment: LaTeX, 13 pages. Accepted by MNRAS. For related papers see
http://www.ast.cam.ac.uk/~snelle
Spreading dynamics on spatially constrained complex brain networks
The study of dynamical systems defined on complex networks provides a natural framework with which to investigate myriad features of neural dynamics and has been widely undertaken. Typically, however, networks employed in theoretical studies bear little relation to the spatial embedding or connectivity of the neural networks that they attempt to replicate. Here, we employ detailed neuroimaging data to define a network whose spatial embedding represents accurately the folded structure of the cortical surface of a rat brain and investigate the propagation of activity over this network under simple spreading and connectivity rules. By comparison with standard network models with the same coarse statistics, we show that the cortical geometry influences profoundly the speed of propagation of activation through the network. Our conclusions are of high relevance to the theoretical modelling of epileptic seizure events and indicate that such studies which omit physiological network structure risk simplifying the dynamics in a potentially significant way
Melatonin treatment for newborns with hypoxic ischaemic encephalopathy
OBJECTIVES: This is a protocol for a Cochrane Review (intervention). The objectives are as follows:. To assess the effects and safety of melatonin compared to standard care, including therapeutic hypothermia, for improving survival and reducing neurological sequelae in newborns with neonatal encephalopathy
New prediction of extragalactic GeV gamma-ray emission from radio lobes of young AGN jets
We present a new prediction of GeV -ray emission from radio lobes of
young AGN jets. In the previous work of Kino et al. (2007), MeV -ray
bremsstrahlung emission was predicted from young cocoons/radio-lobes in the
regime of no coolings. In this study, we include cooling effects of
bremsstrahlung emission and adiabatic loss. With the initial conditions
determined by observed young radio lobes, we solve a set of equations
describing the expanding lobe evolution. Then we find that the lobes initially
have electron temperature of GeV, and they cool down to MeV by the
adiabatic loss. Correspondingly, the lobes initially yield bright
bremsstrahlung luminosity in GeV range and they fade out. We estimate
these -ray emissions and show that nearby young radio lobes could be
detected with Fermi Gamma-ray Space Telescope.Comment: 5 pages, 3 figures, MNRAS Letters, accepte
HST/STIS low dispersion spectroscopy of three Compact Steep Spectrum sources Evidence for jet-cloud interaction
We present Hubble Space Telescope Imaging Spectrograph long-slit spectroscopy
of the emission line nebulae in the compact steep spectrum radio sources 3C 67,
3C 277.1, and 3C 303.1. We derive BPT (Baldwin- Philips-Terlevich; Baldwin et
al. 1981) diagnostic emission line ratios for the nebulae which are consistent
with a mix of shock excitation and photoionization in the extended gas. In
addition, line ratios indicative of lower ionization gas are found to be
associated with higher gas velocities. The results are consistent with a
picture in which these galaxy scale radio sources interact with dense clouds in
the interstellar medium of the host galaxies, shocking the clouds thereby
ionizing and accelerating them.Comment: Accepted for publication in A&A. 6 pages, 8 figure
Star Formation, Radio Sources, Cooling X-ray Gas, and Galaxy Interactions in the Brightest Cluster Galaxy in 2A0335+096
We present deep emission-line imaging taken with the SOAR Optical Imaging
Camera of the brightest cluster galaxy (BCG) in the nearby (z=0.035) X-ray
cluster 2A0335+096. We analyze long-slit optical spectroscopy, archival VLA,
Chandra X-ray, and XMM UV data. 2A0335+096 is a bright, cool-core X-ray
cluster, once known as a cooling flow. Within the highly disturbed core
revealed by Chandra X-ray observations, 2A0335+096 hosts a highly structured
optical emission-line system. The redshift of the companion is within 100 km/s
of the BCG and has certainly interacted with the BCG, and is likely bound to
it. The comparison of optical and radio images shows curved filaments in
H-alpha emission surrounding the resolved radio source. The velocity structure
of the emission-line bar between the BCG nucleus and the companion galaxy
provides strong evidence for an interaction between the two in the last ~50
Myrs. The age of the radio source is similar to the interaction time, so this
interaction may have provoked an episode of radio activity. We estimate a star
formation rate of >7 solar mass/yr based on the Halpha and archival UV data, a
rate similar to, but somewhat lower than, the revised X-ray cooling rate of
10-30 solar masses/year estimated from XMM spectra by Peterson & workers. The
Halpha nebula is limited to a region of high X-ray surface brightness and cool
X-ray temperature. The detailed structures of H-alpha and X-ray gas differ. The
peak of the X-ray emission is not the peak of H-alpha emission, nor does it lie
in the BCG. The estimated age of the radio lobes and their interaction with the
optical emission-line gas, the estimated timescale for depletion and
accumulation of cold gas, and the dynamical time in the system are all similar,
suggesting a common trigger mechanism.Comment: Accepted AJ, July 2007 publication. Vol 134, p. 14-2
Observations of HI Absorbing Gas in Compact Radio Sources at Cosmological Redshifts
We present an overview of the occurrence and properties of atomic gas
associated with compact radio sources at redshifts up to z=0.85. Searches for
HI 21cm absorption were made with the Westerbork Synthesis Radio Telescope at
UHF-high frequencies (725-1200 MHz). Detections were obtained for 19 of the 57
sources with usable spectra (33%). We have found a large range in line depths,
from tau=0.16 to tau<=0.001. There is a substantial variety of line profiles,
including Gaussians of less than 10km/s, to more typically 150km/s, as well as
irregular and multi-peaked absorption profiles, sometimes spanning several
hundred km/s. Assuming uniform coverage of the entire radio source, we obtain
column depths of atomic gas between 1e19 and 3.3e21(Tsp/100K)(1/f)cm^(-2).
There is evidence for significant gas motions, but in contrast to earlier
results at low redshift, there are many sources in which the HI velocity is
substantially negative (up to v=-1420km/s) with respect to the optical
redshift, suggesting that in these sources the atomic gas, rather than falling
into the centre, may be be flowing out, interacting with the jets, or rotating
around the nucleus.Comment: 10 pages, accepted for publication in A&
Consideration of nutritional value and food labels are associated with food intake in adults with depression
Background/Aims: Individuals with depression are more likely to consume poor diets and as a result are at increased risk of poor cardiometabolic health. Healthy diet may reduce depressive symptoms, however better understanding is needed of factors that support healthy eating in this population. There is limited evidence about how much consideration of the nutritional value of foods may be associated with food choices. The aim of this study was to investigate associations between food intake and consideration of nutritional value of foods in adults with depression. Methods: Adults (n = 161) with depression completed a semi-quantitative food frequency questionnaire and shopping and budgeting questionnaire. Associations between consideration of nutritional value and nutrition label use with vegetable, wholegrain, legume, snack food and soft drink intake were evaluated using linear regression, adjusting for age, gender and education. Results: In adjusted models, more consideration of the nutrition value of foods was positively associated with vegetable intake (β = 0.188; p = 0.025), wholegrain intake (β = 0.213; p = 0.015) and negatively associated with snack food intake (β = -0.236, p = 0.006). More frequent reading of nutrition labels was positively associated with legume intake (β = 0.185; p = 0.036). Better understanding of nutrition labels was positively associated with vegetable intake (β = 0.780; p = 0.035), wholegrain intake (β = 0.233; p = 0.008), and legume intake (β = 0.254; p = 0.004). There were no associations between soft drink intake and nutrition value consideration or nutrition label use. Conclusions: These findings suggest that increasing consideration of the nutrition value of foods and nutrition label use may support healthy eating in adults with depression
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