3,206 research outputs found
X-ray properties of the Parkes sample of flat-spectrum radio sources: dust in radio-loud quasars?
We investigate the X-ray properties of the Parkes sample of flat-spectrum
radio sources using data from the ROSAT All-Sky Survey and archival pointed
PSPC observations. In total, 163 of the 323 sources are detected. For the
remaining 160 sources 2 sigma upper limits to the X-ray flux are derived. We
present power-law photon indices for 115 sources, which were either determined
with a hardness ratio technique or from direct fits to pointed PSPC data. For
quasars, the soft X-ray photon index is correlated with redshift and with radio
spectral index. Webster et al. (1995) discovered many sources with unusually
red optical continua among the quasars of this sample and interpreted this
result in terms of extinction by dust. Although the X-ray spectra in general do
not show excess absorption, we find that low-redshift optically red quasars
have significantly lower soft X-ray luminosities on average than objects with
blue optical continua. The difference disappears for higher redshifts, as is
expected for intrinsic absorption by cold gas associated with the dust.
Alternative explanations are briefly discussed. We conclude, however, that dust
does play an important role in some of the radio-loud quasars with red optical
continua.Comment: 21 pages, 13 figures, to appear in MNRA
Glasgow's Stereo Image Database of Garments
To provide insight into cloth perception and manipulation with an active
binocular robotic vision system, we compiled a database of 80 stereo-pair
colour images with corresponding horizontal and vertical disparity maps and
mask annotations, for 3D garment point cloud rendering has been created and
released. The stereo-image garment database is part of research conducted under
the EU-FP7 Clothes Perception and Manipulation (CloPeMa) project and belongs to
a wider database collection released through CloPeMa (www.clopema.eu). This
database is based on 16 different off-the-shelve garments. Each garment has
been imaged in five different pose configurations on the project's binocular
robot head. A full copy of the database is made available for scientific
research only at https://sites.google.com/site/ugstereodatabase/.Comment: 7 pages, 6 figure, image databas
Blob ejection from advection-dominated accretion flow: observational consequences
There is increasing evidence for the presence of an optically thin
advection-dominated accretion flow (ADAF) in low luminosity active galactic
nuclei and radio-loud quasars. The present paper is devoted to explore the fate
of a blob ejected from an ADAF, and to discuss its observational consequences.
It is inevitable for the ejected blob to drastically expand into its
surroundings. Consequently, it is expected that a group of relativistic
electrons should be accelerated, which may lead to nonthermal flares, since a
strong shock will be formed by the interaction between the blob and its
surroundings. Then the blob cools down efficiently, leading to the appearance
of recombination lines about s after its ejection from an ADAF. We apply
this model to NGC 4258 for some observational prediction, and to PKS 2149--306
for the explanation of observational evidence. Future simultaneous observations
of recombination X-ray lines and continuum emission are highly desired to test
the present model.Comment: 4 pages in emulateapj.sty, no figure. Accepted by ApJ Letter
HAEMODYNAMIC RESPONSE DURING EXERCISE TESTING IN PATIENTS WITH CORONARY ARTERY DISEASE UNDERGOING A CARDIAC REHABILITATION PROGRAMME
Haemodynamic monitoring during exercise testing is seldom used during cardiac rehabilitation. The aim was to evaluate haemodynamic changes using the cardiac impedance method during exercise testing in patients after percutaneous coronary interventions and coronary artery bypass grafting during cardiac rehabilitation. Thirty (25 M; 5 F) patients were included in the programme. The group was divided according to ejection fraction (EF): low – below 50% normal – equal to or above 50%. The exercise test was performed simultaneously with a four-electrode impedance cardiogram before and after rehabilitation. ECG, blood pressure, thoracic impedance, first derivative dz/dt, stroke volume (SV) and cardiac output were recorded. Contractility index (Heather index – HI) and vascular peripheral resistance were calculated. The pattern of haemodynamic changes was normal in 24 patients. The deflection points for HI and SV trend patterns were observed among patients with low EF. The contractility index decreased 90 s before maximal exercise and after the next 30-60 s a deflection point was observed in SV curve trends. In 24 patients with normal EF the contractility index trends did not decrease and SV trends increased until the end of exercise or a deflection point was not noted. The deflection points of the contractility index and SV curves were observed before the clinical indications for exercise test termination appeared in patients with a low ejection fraction. Impedance cardiography may indicate the threshold of the workload during real-time exercise testing
The 3-53 keV Spectrum of the Quasar 1508+5714: X-rays from z = 4.3
We present a high-quality X-ray spectrum in the 3--53 keV rest-frame band of
the radio-loud quasar 1508+5714, by far the brightest known X-ray source at z >
4. A simple power-law model with an absorption column density equal to the
Galactic value in the direction of the source provides an excellent and fully
adequate fit to the data; the measured power-law photon index Gamma = 1.42
(+0.13,-0.10). Upper limits to Fe K alpha line emission and Compton-reflection
components are derived. We offer evidence for both X-ray and radio variability
in this object and provide the first contemporaneous radio spectrum (alpha =
-0.25). The data are all consistent with a picture in which the emission from
this source is dominated by a relativistically beamed component in both the
X-ray and radio bands.Comment: 8 pages, TeX, 2 postscript figures; to appear in ApJ Letter
The Radio Quiescence of Active Galaxies with High Accretion Rates
We present 6 cm Very Large Array observations of the Greene & Ho (2004)
sample of 19 low-mass active galaxies with high accretion rates. This is one of
the only studies of a uniform sample of narrow-line Seyfert 1 (NLS1) galaxies
with such high sensitivity and resolution. Although we detect only one source,
the entire sample is very radio-quiet down to strong limits. GH10 was found to
have a radio power of 8.5 x 10^21 W/Hz, and a ratio R = f(6 cm)/f(4400 A) of
2.8. The 3 sigma upper limits for the remaining nondetections correspond to
radio powers from 3 x 10^20 to 8 x 10^21 W/Hz and 0.47 < R <9.9. Stacking all
nondetections yields an even stronger upper limit of R < 0.27. An assessment of
existing observations in the literature confirms our finding that NLS1s are
consistently radio-quiet, with a radio-loud fraction of 0%-6%, which is
significantly lower than the 10%-20% observed in the general quasar population.
By analogy with stellar-mass black holes, we argue that AGNs undergo a state
transition at L_bol/L_Edd~0.01. Below this value a radiatively inefficient
accretion flow effectively drives an outflow, which disappears when the flow
turns into an optically thick, geometrically thin disk, or a radiation
pressure-dominated slim disk at still higher L_bol/L_Edd.Comment: To appear in ApJ; 8 pages, 3 figures; uses emulateapj5.st
Radio Loud AGN in the Context of the Eigenvector 1 Parameter Space
We consider the properties of radio-loud (RL) AGN in the context of the
Eigenvector 1 (E1) parameter space. RL sources show a restricted E1 parameter
space occupation relative to the radio-quiet (RQ) majority. The Fanaroff-Riley
II ``parent population'' of relatively un-boosted RL sources (median
radio/optical flux ratio ~490) shows the most restricted occupation. RL sources
have different broad line properties (and inferred black hole masses and
Eddington ratios). FWHM H_beta for the broad line component in RL sources are
at least twice as large as the RQ majority. The average broad FeII emission
line strength is also about half that for RQ sources. Our sample suggests that
the RL cutoff occurs near R_k=70 or logP(6cm)=32.0 ergs/s/Hz. Sources below
this cutoff are RQ although we cannot rule out the existence of a distinct
intermediate population. We show that the Doppler boosted core-dominated RL
sources (median flux ratio ~1000) lie towards smaller FWHM(H_beta_bc) and
stronger FeII in E1 as expected if the lines arise in an accretion disk. Our
subsample of superluminal sources, with orientation inferred from the
synchrotron self Compton model, reinforce this general E1 trend and allow us to
estimate the role of source orientation in driving E1 domain occupation.Comment: 9 pages, 3 figures, accepted for publication in ApJ
The asymmetric drift, the local standard of rest, and implications from RAVE data
Context. The determination of the local standard of rest (LSR), which corresponds to the measurement of the peculiar motion of the Sun based on the derivation of the asymmetric drift of stellar populations, is still a matter of debate. The classical value of the tangential peculiar motion of the Sun with respect to the LSR was challenged in recent years, claiming a significantly larger value.
Aims. We present an improved Jeans analysis, which allows a better interpretation of the measured kinematics of stellar populations in the Milky Way disc. We show that the Radial Velocity Experiment (RAVE) sample of dwarf stars is an excellent data set to derive tighter boundary conditions to chemodynamical evolution models of the extended solar neighbourhood.
Methods. We propose an improved version of the Stromberg relation with the radial scalelengths as the only unknown. We redetermine the asymmetric drift and the LSR for dwarf stars based on RAVE data. Additionally, we discuss the impact of adopting a different LSR value on the individual scalelengths of the subpopulations.
Results. Binning RAVE stars in metallicity reveals a bigger asymmetric drift (corresponding to a smaller radial scalelength) for more metal-rich populations. With the standard assumption of velocity-dispersion independent radial scalelengths in each metallicity bin, we redetermine the LSR. The new Stromberg equation yields a joint LSR value of V-circle dot = 3.06 +/- 0.68 km s(-1), which is even smaller than the classical value based on Hipparcos data. The corresponding radial scalelength increases from 1.6 kpc for the metal-rich bin to 2.9 kpc for the metal-poor bin, with a trend of an even larger scalelength for young metal-poor stars. When adopting the recent Schonrich value of V-circle dot = 12.24 km s(-1) for the LSR, the new Stromberg equation yields much larger individual radial scalelengths of the RAVE subpopulations, which seem unphysical in part.
Conclusions. The new Stromberg equation allows a cleaner interpretation of the kinematic data of disc stars in terms of radial scalelengths. Lifting the LSR value by a few km s(-1) compared to the classical value results in strongly increased radial scalelengths with a trend of smaller values for larger velocity dispersions
Communications Biophysics
Contains research objectives and reports on four research projects.National Science Foundation (Grant G-16526)National Science Foundation (Grant G-7364)National Institutes of Health (Grant MP-4737)U.S. Air Force (Electronic Systems Division) under Contract AF19(604)-411
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