422 research outputs found
Susceptible periods during embryogenesis of the heart and endocrine glands.
One of the original principles of teratology states that, "Susceptibility to teratogenesis varies with the developmental stage at the time of exposure to an adverse influence" [Wilson JG. Environment and Birth Defects. New York:Academic Press, 1973]. The time of greatest sensitivity encompasses the period of organ formation during weeks 3-8 following fertilization in human gestation. At this time, stem cell populations for each organ's morphogenesis are established and inductive events for the initiation of differentiation occur. Structural defects of the heart and endocrine system are no exception to this axiom and have their origins during this time frame. Although the function and maturation of these organs may be affected at later stages, structural defects and loss of cell types usually occur during these early phases of development. Thus, to determine critical windows for studying mechanisms of teratogenesis, it is essential to understand the developmental processes that establish these organs
Isotropic Luminosity Indicators in a Complete AGN Sample
The [O IV] 25.89 micron line has been shown to be an accurate indicator of
active galactic nucleus (AGN) intrinsic luminosity in that it correlates well
with hard (10-200 keV) X-ray emission. We present measurements of [O IV] for 89
Seyfert galaxies from the unbiased Revised Shapley-Ames (RSA) sample. The [O
IV] luminosity distributions of obscured and unobscured Seyferts are
indistinguishable, indicating that their intrinsic AGN luminosities are quite
similar and that the RSA sample is well suited for tests of the unified model.
In addition, we analyze several commonly used proxies for AGN luminosity,
including [O III] 5007 A, 6 cm radio, and 2-10 keV X-ray emission. We find that
the radio luminosity distributions of obscured and unobscured AGNs show no
significant difference, indicating that radio luminosity is a useful isotropic
luminosity indicator. However, the observed [O III] and 2-10 keV luminosities
are systematically smaller for obscured Seyferts, indicating that they are not
emitted isotropically.Comment: Updated to match version published in ApJ. 9 pages, 4 figure
HST NIR Snapshot Survey of 3CR Radio Source Counterparts II: An Atlas and Inventory of the Host Galaxies, Mergers and Companions
We present the second part of an H-band (1.6 microns) atlas of z<0.3 3CR
radio galaxies, using the Hubble Space Telescope Near Infrared Camera and
Multi-Object Spectrometer (HST NICMOS2). We present new imaging for 21 recently
acquired sources, and host galaxy modeling for the full sample of 101
(including 11 archival) -- an 87% completion rate. Two different modeling
techniques are applied, following those adopted by the galaxy morphology and
the quasar host galaxy communities. Results are compared, and found to be in
excellent agreement, although the former breaks down in the case of strongly
nucleated sources. Companion sources are tabulated, and the presence of
mergers, tidal features, dust disks and jets are catalogued. The tables form a
catalogue for those interested in the structural and morphological dust-free
host galaxy properties of the 3CR sample, and for comparison with morphological
studies of quiescent galaxies and quasar host galaxies. Host galaxy masses are
estimated, and found to typically lie at around 2*10^11 solar masses. In
general, the population is found to be consistent with the local population of
quiescent elliptical galaxies, but with a longer tail to low Sersic index,
mainly consisting of low-redshift (z<0.1) and low-radio-power (FR I) sources. A
few unusually disky FR II host galaxies are picked out for further discussion.
Nearby external sources are identified in the majority of our images, many of
which we argue are likely to be companion galaxies or merger remnants. The
reduced NICMOS data are now publicly available from our website
(http://archive.stsci.edu/prepds/3cr/)Comment: ApJS, 177, 148: Final version; includes revised figures 1, 15b, and
section 7.5 (and other minor changes from editing process. 65 pages, inc. 17
figure
A celestial gamma-ray foreground due to the albedo of small solar system bodies and a remote probe of the interstellar cosmic ray spectrum
We calculate the gamma-ray albedo flux from cosmic-ray (CR) interactions with
the solid rock and ice in Main Belt asteroids (MBAs), Jovian and Neptunian
Trojan asteroids, and Kuiper Belt objects (KBOs) using the Moon as a template.
We show that the gamma-ray albedo for the Main Belt, Trojans, and Kuiper Belt
strongly depends on the small-body size distribution of each system. Based on
an analysis of the Energetic Gamma Ray Experiment Telescope (EGRET) data we
infer that the diffuse emission from the MBAs, Trojans, and KBOs has an
integrated flux of less than ~6x10^{-6} cm^{-2} s^{-1} (100-500 MeV), which
corresponds to ~12 times the Lunar albedo, and may be detectable by the
forthcoming Gamma Ray Large Area Space Telescope (GLAST). If detected by GLAST,
it can provide unique direct information about the number of small bodies in
each system that is difficult to assess by any other method. Additionally, the
KBO albedo flux can be used to probe the spectrum of CR nuclei at
close-to-interstellar conditions. The orbits of MBAs, Trojans, and KBOs are
distributed near the ecliptic, which passes through the Galactic center and
high Galactic latitudes. Therefore, the asteroid gamma-ray albedo has to be
taken into account when analyzing weak gamma-ray sources close to the ecliptic,
especially near the Galactic center and for signals at high Galactic latitudes,
such as the extragalactic gamma-ray emission. The asteroid albedo spectrum also
exhibits a 511 keV line due to secondary positrons annihilating in the rock.
This may be an important and previously unrecognized celestial foreground for
the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of
the Galactic 511 keV line emission including the direction of the Galactic
center.Comment: 10 pages, 5 figures, 1 table, emulateapj.cls; ApJ in press.
Calculations extended to include Jovian and Neptunian Trojan groups, and
Centaurs, in addition to Main Belt Asteroids and Kuiper Belt Objects. Many
other considerable change
Relapsing or refractory idiopathic thrombotic thrombocytopenic purpura-hemolytic uremic syndrome: the role of rituximab.
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