21 research outputs found
Chandra Observation of 3C 212: a New Look at the X-ray and UV Absorbers
The red quasar 3C 212 (z=1.049) is one of the most distant and most luminous
AGN which has shown evidence of an X-ray warm absorber. In order to further
investigate this unusual quasar, we used Chandra/ACIS-S to observe 3C 212 for
19.5 ksec, resulting in a net detection of ~4000 counts. The Chandra data
confirm the presence of an excess absorbing column N_H ~ 4 x 10^21 cm^-2 at the
quasar redshift, but we find no compelling evidence for a warm absorber. Using
both the Chandra and archival ROSAT PSPC data, we obtain very good fits for
both a partially covered neutral absorber and a low-ionization (U = 0.03)
photo-ionized absorber. In the ultraviolet, 3C 212 shows a strong associated
MgII absorber. Based on a moderate resolution (80 km/s) MMT spectrum we show
that the absorber is highly saturated and has a covering fraction less than
60%, implying that the absorber is truly intrinsic to the quasar.
Photo-ionization modeling of the MgII absorber yields a constraint on the
ionization parameter of U < 0.03, inconsistent with a warm UV/X-ray absorber.
In addition to our spectral analysis, we find evidence in the ACIS image data
for weak extended emission surrounding the quasar as well as emission
corresponding to the radio lobes at a distance of 5 arcsec from 3C 212. The
statistical significance of these features is low, but we briefly explore the
implications if the detections are valid.Comment: 8 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
Resonant Absorption in the AGN spectra emerging from photoionized gas: differences between steep and flat ionizing continua
We present photoionization models accounting for both photoelectric and
resonant absorption. Resonance absorption lines from C, O, Ne, Mg, Si S and Fe
between 0.1 and 10 keV are treated. In particular we consider the complex of
almost 60 strong Fe L absorption lines around 1 keV. We calculate profiles,
intensities and equivalent widths of each line, considering both Doppler and
natural broadening mechanisms. Doppler broadening includes a term accounting
for turbulence of the gas along the line of sight. We computed spectra
transmitted by gas illuminated by drastically different ionizing continua and
compared them to spectra observed in flat X-ray spectrum, broad optical
emission line type 1 AGN, and steep X-ray spectrum, narrow optical emission
line type 1 AGN. We show that the keV absorption feature observed in
moderate resolution X-ray spectra of several Narrow Line Seyfert 1 galaxies can
be explained by photoionization models, taking into account for resonance
absorption, without requiring relativistic outflowing velocities of the gas, if
the physical properties of these absorbers are close to those found in flat
X-ray spectrum Seyfert 1 galaxies.Comment: 22 pages, 10 figures. Accepted for publication on Ap
Why Don't We Ask? A Complementary Method for Assessing the Status of Great Apes
Species conservation is difficult. Threats to species are typically high and immediate. Effective solutions for counteracting these threats, however, require synthesis of high quality evidence, appropriately targeted activities, typically costly implementation, and rapid re-evaluation and adaptation. Conservation management can be ineffective if there is insufficient understanding of the complex ecological, political, socio-cultural, and economic factors that underlie conservation threats. When information about these factors is incomplete, conservation managers may be unaware of the most urgent threats or unable to envision all consequences of potential management strategies. Conservation research aims to address the gap between what is known and what knowledge is needed for effective conservation. Such research, however, generally addresses a subset of the factors that underlie conservation threats, producing a limited, simplistic, and often biased view of complex, real world situations. A combination of approaches is required to provide the complete picture necessary to engage in effective conservation. Orangutan conservation (Pongo spp.) offers an example: standard conservation assessments employ survey methods that focus on ecological variables, but do not usually address the socio-cultural factors that underlie threats. Here, we evaluate a complementary survey method based on interviews of nearly 7,000 people in 687 villages in Kalimantan, Indonesia. We address areas of potential methodological weakness in such surveys, including sampling and questionnaire design, respondent biases, statistical analyses, and sensitivity of resultant inferences. We show that interview-based surveys can provide cost-effective and statistically robust methods to better understand poorly known populations of species that are relatively easily identified by local people. Such surveys provide reasonably reliable estimates of relative presence and relative encounter rates of such species, as well as quantifying the main factors that threaten them. We recommend more extensive use of carefully designed and implemented interview surveys, in conjunction with more traditional field methods
The eck fistula in animals and humans
In all species so far studied, including man, portacaval shunt causes the same changes in liver morphology, including hepatocyte atrophy, fatty infiltration, deglycogenation, depletion and disorganization of the rough endoplasmic reticulum (RER) and its lining polyribosomes and variable but less specific damage to other organelles. Many, perhaps all, biosynthetic processes are quickly depressed, largely secondary to the selective damage to the RER, which is the "factory" of the cell. These structural and metabolic changes in the liver after portal diversion are caused by the diversion around the liver of the hepatotrophic substances in portal venous blood, of which endogenous insulin is the most important. In experimental animals, the injury of Eck's fistula can be prevented by infusing insulin into the tied-off hilar portal vein. The subtle but far-reaching changes in hepatic function after portal diversion have made it possible to use this procedure in palliating three inborn errors of metabolism: glycogen storage disease, familial hypercholesterolemia, and α1-antitrypsin deficiency In these three diseases, the abnormalities caused by portal diversion have counteracted abnormalities in the patients that were caused by the inborn errors. In these diseases, amelioration of the inborn errors depends on the completeness of the portal diversion. In contrast, total portal diversion to treat complications of portal hypertension is undesirable and always will degrade hepatic function if a significant amount of hepatopetal portal venous blood is taken from the liver. When total portal diversion is achieved (and this is to be expected after all conventional shunts), the incidence of hepatic failure and hepatic encephalopathy is increased. If portal diversion must be done for the control of variceal hemorrhage, a selective procedure such as the Warren procedure is theoretically superior to the completely diverting shunt. In practice, better patient survival has not been achieved after selective shunts than after conventional shunts, but the incidence of hepatic encephalopathy has been less. © 1983 Year Book Medical Publishers, Inc