1,343 research outputs found
In search of dying radio sources in the local universe
Up till now very few dying sources were known, presumably because the dying
phase is short at centimeter wavelengths. We therefore have tried to improve
the statistics on sources that have ceased to be active, or are intermittently
active. The latter sources would partly consist of a fossil radio plasma left
over from an earlier phase of activity, plus a recently restarted core and
radio jets. Improving the statistics of dying sources will give us a better
handle on the evolution of radio sources, in particular the frequency and time
scales of radio activity. We have used the WENSS and NVSS surveys, in order to
find sources with steep spectral indices, associated with nearby elliptical
galaxies. In the cross correlation we presently used only unresolved sources,
with flux densities at 1.4 GHz larger than 10 mJy. The eleven candidates thus
obtained were observed with the VLA in various configurations, in order to
confirm the steepness of the spectra, and to check whether active structures
like flat-spectrum cores and jets are present, perhaps at low levels. We
estimated the duration of the active and relic phases by modelling the
integrated radio spectra using the standard models of spectral evolution. We
have found six dying sources and three restarted sources, while the remaining
two candidates remain unresolved also with the new VLA data and may be Compact
Steep Spectrum sources, with an unusually steep spectrum. The typical age of
the active phase, as derived by spectral fits, is in the range 10^7 - 10^8
years. For our sample of dying sources, the age of the relic phase is on
average shorter by an order of magnitude than the active phase.Comment: 21 pages, 17 figures, accepted by A&A. For a version with high
quality figures, see http://erg.ca.astro.it/preprints/dying2007
The nature of close companions of the BL Lac Objects 1ES 0502+675 and 1ES 1440+122
We report on deep radio images and optical spectroscopy of two BL Lac objects
that have very close compact companions. The two targets, 1ES 0502+675 and 1ES
1440+122, were selected from the HST imaging survey of 110 BL Lacs as
candidates for possible gravitational lensing. The new observations clearly
demonstrate that the companion objects are not secondary images of the active
nuclei but, in spite of the relatively low chance projection probability,
foreground Galactic stars. Gravitational lensing appears to be unimportant to
the BL Lac phenomenon. We discuss the radio properties of the BL Lac objects in
the context of standard beaming models, and show they are as expected for
beamed FRI radio galaxies.Comment: 13 pages, 5 figures, ApJ in pres
Chandra Observations of Dying Radio Sources in Galaxy Clusters
Context. The dying radio sources represent a very interesting and largely unexplored stage of the active galactic nucleus (AGN) evolution. They are considered to be very rare, and almost all of the few known ones were found in galaxy clusters. However, considering the small number detected so far, it has not been possible to draw any firm conclusions about their X-ray environment. Aims. We present X-ray observations performed with the Chandra satellite of the three galaxy clusters Abell 2276, ZwCl 1829.3+6912, and RX J1852.1+5711, which harbor at their center a dying radio source with an ultra-steep spectrum that we recently discovered. Methods. We analyzed the physical properties of the X-ray emitting gas surrounding these elusive radio sources. We determined the global X-ray properties of the clusters, derived the azimuthally averaged profiles of metal abundance, gas temperature, density, and pressure. Furthermore, we estimated the total mass profiles. Results. The large-scale X-ray emission is regular and spherical, suggesting a relaxed state for these systems. Indeed, we found that the three clusters are also characterized by significant enhancements in the metal abundance and declining temperature profiles toward the central region. For all these reasons, we classified RX J1852.1+5711, Abell 2276, and ZwCl 1829.3+6912 as cool-core galaxy clusters. Conclusions. We calculated the non-thermal pressure of the radio lobes assuming that the radio sources are in the minimum energy condition. For all dying sources we found that this is on average about one to two orders of magnitude lower than that of the external gas, as found for many other radio sources at the center of galaxy groups and clusters. We found marginal evidence for the presence of X-ray surface brightness depressions coincident with the fossil radio lobes of the dying sources in A2276 and ZwCl 1829.3+691. We estimated the outburst age and energy output for these two dying sources. The energy power from the AGN outburst is significantly higher than the X-ray luminosity in both clusters. Indeed, it is sufficient that a small fraction of this power is dissipated in the intra-cluster medium to reheat the cool cores
X-ray-emitting Atmospheres of B2 Radio Galaxies
We report ROSAT PSPC spatial and spectral analysis of the eight B2 radio
galaxies NGC 315, NGC 326, 4C 35.03, B2 0326+39, NGC 2484, B2 1040+31, B2
1855+37, and 3C 449, expected to be representative of the class of low-power
radio galaxies. Multiple X-ray components are present in each, and the gas
components have a wide range of linear sizes and follow an extrapolation of the
cluster X-ray luminosity/temperature correlation, implying that there is no
relationship between the presence of a radio galaxy and the gas fraction of the
environment. No large-scale cooling flows are found. There is no correlation of
radio-galaxy size with the scale or density of the X-ray atmosphere. This
suggests that it is processes on scales less than those of the overall gaseous
environments which are the major influence on radio-source dynamics. The
intergalactic medium is usually sufficient to confine the outer parts of the
radio structures, in some cases even to within 5 kpc of the core. In the case
of NGC 315, an extrapolation suggests that the pressure of the atmosphere may
match the minimum pressure in the radio source over a factor of about 40 in
linear size (a factor of about 1600 in pressure).Comment: 34 pages, including 10 figures, using aasms4.sty To appear in the Ap
Annual survey air quality 2001
The air quality for 2001 is found to strongly resemble that for 2000. The decreasing trend in concentrations seen in the nineties, is still valid on the whole. Concerning the meteorological influences, 2001 can be considered as a normal year. Widespread exceedances occurred for ozone and PM10, and in the deposition of potential acid and total nitrogen. In the urban environment, exceedances of the annual mean limit value for NO2 occurred along road length of about 2000 km. Calculations for benzene and benzo[a]pyrene showed that exceedances were incidental. This annual air quality survey provides an overview of the air quality and the load placed on soils and surface water by atmospheric deposition in the Netherlands, on the basis of measurements and model calculations. The report describes global, photochemical, acidifying, particulate and local air pollution. Special attention has been paid to the Dutch air quality in relation to the new European legislation on air quality.Als we de luchtkwaliteit over 2001 vergelijken met die van 2000 blijken deze in grote lijnen met elkaar overeen te komen. De trendmatige daling van concentraties heeft zich in grote lijnen doorgezet. 2001 was wat meteorologische invloed betreft een normaal jaar. Normoverschrijdingen op landelijke schaal hebben zich voorgedaan van ozon, zwevende deeltjes (PM10), depositie van potentieel zuur en stikstof. In de stedelijke omgeving is de jaargemiddelde norm NO2 overschreden langs een weglengte van circa 2000 km. Voor benzeen en benzo[a]pyreen geven berekeningen aan dat incidenteel overschrijdingen van grenswaarden kunnen zijn voorgekomen. In het jaaroverzicht luchtkwaliteit 2001 wordt op basis van metingen en modelberekeningen een samenvattend beeld gegeven van de luchtkwaliteit en de belasting van bodem en oppervlaktewater door atmosferische depositie in Nederland over 2001. Het rapport beschrijft de onderwerpen: mondiale, fotochemische, verzurende, deeltjesvormige en lokale luchtverontreiniging. Als extra onderwerp is een hoofdstuk opgenomen over de Nederlandse luchtkwaliteit in relatie tot de nieuwe Europese wetgeving voor luchtkwaliteit
Transceiver ASIC in HVCMOS Technology for 3D Ultrasound Computer Tomography
Abstract3D Ultrasound Computer Tomography (3D USCT) is an imaging method for the early de-tection of breast cancer. It provides three-dimensional multimodal images of the breast. Thenew 3D USCT device developed currently at Karlsruhe Institute of Technology containsmore than two thousand ultrasound transducers placed in a water-filled aperture where thepatient submerges one breast. The ultrasound transducers are grouped as transducer arraysystems (TAS) of 18 receiver (RX) and transmitter (TX) elements. The transducer front-end electronics contain high-voltage (HV) and low-voltage (LV) amplifiers and switcheswhich are implemented as an application-specific integrated circuit (ASIC). This contribu-tion presents a patented mixed signal, multichannel, transceiver ASIC developed in a com-mercial 350 nm high-voltage CMOS (HV-CMOS) process. The HV-CMOS process provideslow-voltage and high-voltage transistors that can be combined on the same substrate. TheHV transistors can sustain voltages up to 120 V
Antenatal atazanavir: a retrospective analysis of pregnancies exposed to atazanavir.
INTRODUCTION: There are few data regarding the tolerability, safety, or efficacy of antenatal atazanavir. We report our clinical experience of atazanavir use in pregnancy.
METHODS: A retrospective medical records review of atazanavir-exposed pregnancies in 12 London centres between 2004 and 2010.
RESULTS: There were 145 pregnancies in 135 women: 89 conceived whilst taking atazanavir-based combination antiretroviral therapy (cART), "preconception" atazanavir exposure; 27 started atazanavir-based cART as "first-line" during the pregnancy; and 29 "switched" to an atazanavir-based regimen from another cART regimen during pregnancy. Gastrointestinal intolerance requiring atazanavir cessation occurred in five pregnancies. Self-limiting, new-onset transaminitis was most common in first-line use, occurring in 11.0%. Atazanavir was commenced in five switch pregnancies in the presence of transaminitis, two of which discontinued atazanavir with persistent transaminitis. HIV-VL < 50 copies/mL was achieved in 89.3% preconception, 56.5% first-line, and 72.0% switch exposures. Singleton preterm delivery (<37 weeks) occurred in 11.7% preconception, 9.1% first-line, and 7.7% switch exposures. Four infants required phototherapy. There was one mother-to-child transmission in a poorly adherent woman.
CONCLUSIONS: These data suggest that atazanavir is well tolerated and can be safely prescribed as a component of combination antiretroviral therapy in pregnancy
Optical Morphologies of Millijansky Radio Galaxies Observed by HST and in the VLA FIRST Survey
We report on a statistical study of the 51 radio galaxies at the millijansky
flux level from the Faint Images of the Radio Sky at Twenty centimeters,
including their optical morphologies and structure obtained with the Hubble
Space Telescope. Our optical imaging is significantly deeper (~2 mag) than
previous studies with the superior angular resolution of space-based imaging.
We that find 8/51 (16%) of the radio sources have no optically identifiable
counterpart to AB~24 mag. For the remaining 43 sources, only 25 are
sufficiently resolved in the HST images to reliably assign a visual
classification: 15 (60%) are elliptical galaxies, 2 (8%) are late-type spiral
galaxies, 1 (4%) is an S0, 3 (12%) are point-like objects (quasars), and 4
(16%) are merger systems. We find a similar distribution of optical types with
measurements of the Sersic index. The optical magnitude distribution of these
galaxies peaks at I~20.7+-0.5 AB mag, which is ~3 mag brighter than the depth
of our typical HST field and is thus not due to the WFPC2 detection limit. This
supports the luminosity-dependent density evolutionary model, where the
majority of faint radio galaxies typically have L*-optical luminosities and a
median redshift of z~0.8 with a relatively abrupt redshift cut-off at z>~2. We
discuss our results in the context of the evolution of elliptical galaxies and
active galactic nuclei.Comment: 20 pages, 8 figures, 51 galaxy images, and 5 tables. Uses
emulateapj.cls and natbib.sty. Accepted to ApJS. High resolution images are
available upon reques
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