1,415 research outputs found
XMM-Newton Observations of a Complete Sample of Optically Selected Type 2 Seyfert Galaxies
(abridged)The majority of Active Galactic Nuclei (AGN) suffer from
significant obscuration by surrounding dust and gas. X-ray surveys in the 2-10
keV band will miss the most heavily-obscured AGN in which the absorbing column
density exceeds cm (the Compton-thick AGN). It is therefore
vital to know the fraction of AGN that are missed in such X-rays surveys and to
determine if these AGN represent some distinct population in terms of the
fundamental properties of AGN and/or their host galaxies. In this paper we
present the analysis of \textit{XMM-Newton} X-ray data for a complete sample of
17 low-redshift Type 2 Seyfert galaxies chosen from the Sloan Digital Sky
Survey based solely on the high observed flux of the [OIII]5007
emission-line. This line is formed in the Narrow Line Region hundreds of
parsecs away from the central engine. Thus, unlike the X-ray emission, it is
not affected by obscuration due to the torus surrounding the black hole. It
therefore provides a useful isotropic indicator of the AGN luminosity. As
additional indicators of the intrinsic AGN luminosity, we use the Spitzer Space
Telescope to measure the luminosities of the mid-infrared continuum and the
[OIV]25.89m narrow emission-line. We then use the ratio of the 2-10 keV
X-ray luminosity to the [OIII], [OIV], and mid-infrared luminosities to assess
the amount of X-ray obscuration and to distinguish between Compton-thick and
Compton-thin objects. We find that the majority of the sources suffer
significant amounts of obscuration: the observed 2-10 keV emission is depressed
by more than an order-of-magnitude in 11 of the 17 cases (as expected for
Compton-thick sources).Comment: accepted for publication to ApJ; 48 pages, 15 figure
Penetration of the insect defensin A into phospholipid monolayers and formation of defensin A-lipid complexes
Defensin A is an inducible cationic protein secreted in the hemolymph of fleshfly Phormia terranovae larvae in response to bacterial or septic injuries. Defensin A is known to permeabilize the bacteria cell membranes by forming voltage-dependent channels. The penetration of this small protein into lipid monolayers was studied as a function of the polar head and acyl chain length of phospholipids. The extent of penetration by defensin A is higher in monolayers made of anionic phospholipids than in monolayers made of zwitterionic phospholipids (phosphatidylcholines), because of electrostatic interactions. From the analysis of the compression isotherm parameters of mixed defensin A/phospholipid monolayers, it appears that defensin A interacts with phospholipid by forming 1:4 complexes. These complexes are not miscible in the lipid phase and induce microheterogeneity in the lipid membrane. These clusters might be related to the ion-channel structures responsible for the biological activity of defensin A
A Chandra observation of the ultraluminous infrared galaxy IRAS 19254--7245 (the Superantennae): X-ray emission from the Compton-thick AGN and the diffuse starburst
We present a {\it Chandra} observation of IRAS 19254--7245, a nearby ULIRG
also known as {\it the Superantennae}. The high spatial resolution of {\it
Chandra} allows us to disentangle for the first time the diffuse starburst
emission from the embedded Compton-thick AGN. The 2-10 keV spectrum of the AGN
emission is fitted by a flat power-law ) and a He-like Fe K
line with EW1.5 keV, consistent with previous observations. The Fe
K line profile could be resolved as a blend of a neutral 6.4 keV line
and an ionized 6.7 keV (He-like) or 6.9 keV (H-like) line. Variability is
detected compared with the previous {\it XMM-Newton} and {\it suzaku}
observations, demonstrating the compact size of the iron line emission. We fit
the spectrum of the galaxy-scale extended emission excluding the AGN and other
bright point sources with a soft thermal component with kT~0.8 keV. The
luminosity of the extended emission is about one order of magnitude lower than
that of the AGN. The basic physical and structural properties of the extended
emission are fully consistent with a galactic wind being driven by the
starburst (no contribution to the feedback by the AGN is required). A candidate
ultra-luminous X-ray source is detected 8\arcsec\ south of the southern
nucleus. The 0.3-10 keV luminosity of this off-nuclear point source is
~ erg s if the emission is isotropic and the source is
associated with the Superantennae.Comment: 31 pages, 10 figures, submitted to Ap
A note on inverses of power series
AbstractWe show the recurrence formula for coefficients of an inverse of a power series of two variables. This problem arises from geodesy
The Relationship of Hard X-ray and Optical Line Emission in Low Redshift Active Galactic Nuclei
In this paper we assess the relationship of the population of Active Galactic
Nuclei (AGN) selected by hard X-rays to the traditional population of AGN with
strong optical emission lines. First, we study the emission-line properties of
a new hard X-ray selected sample of 47 local AGN (classified optically as both
Type 1 and Type 2 AGN). We find that the hard X- ray (3-20 keV) and
[OIII]5007 optical emission-line luminosities are well-correlated over
a range of about four orders-of-magnitude in luminosity (mean luminosity ratio
2.15 dex with a standard deviation of = 0.51 dex). Second, we study
the hard X-ray properties of a sample of 55 local AGN selected from the
literature on the basis of the flux in the [OIII] line. The correlation between
the hard X-ray (2-10 keV) and [OIII] luminosity for the Type 1 AGN is
consistent with what is seen in the hard X-ray selected sample. However, the
Type 2 AGN have a much larger range in the luminosity ratio, and many are very
weak in hard X-rays (as expected for heavily absorbed AGN). We then compare the
hard X-ray (3-20 keV) and [OIII] luminosity functions of AGN in the local
universe. These have similar faint-end slopes with a luminosity ratio of 1.60
dex (0.55 dex smaller than the mean value for individual hard X-ray selected
AGN). We conclude that at low redshift, selection by narrow optical emission-
lines will recover most AGN selected by hard X-rays (with the exception of BL
Lac objects). However, selection by hard X-rays misses a significant fraction
of the local AGN population with strong emission lines
Operator algebras from the discrete Heisenberg semigroup
We study reflexivity and structure properties of operator algebras generated
by representations of the discrete Heisenberg semi-group. We show that the left
regular representation of this semi-group gives rise to a semi-simple reflexive
algebra. We exhibit an example of a representation which gives rise to a
non-reflexive algebra. En route, we establish reflexivity results for subspaces
of H^{\infty}(\bb{T})\otimes\cl B(\cl H)
A food-based approach to reduce vitamin a deficiency in southern Ethiopia: a cross-sectional study of maternal nutrition and health indicators
One micronutrient essential for proper growth and development is Vitamin A. Children and pregnant women are most susceptible to vitamin A deficiency (VAD) because of the higher intake requirements needed during critical growth periods. Vitamin A deficiency is a serious but preventable public health problem in Ethiopia. In 2012, the International Potato Center (CIP) partnered with the University of Wisconsin-Madison (UW) and local stakeholders in the Southern Nations, Nationalities, and Peoples Region (SNNPR), Ethiopia, to address the issue of VAD among rural SNNPR households by increasing production and consumption of orange fleshed sweet potatoes (OFSP). This paper presents a cross-sectional analysis of vitamin A knowledge, consumption practices, and OFSP agronomic practices from surveys conducted among households who participated in a food-based intervention. The study population consisted of 150 mothers from rural households in five districts in the Sidama and Wolayta zones in the SNNPR. Data were collected during April and May 2013 by trained enumerators in the local language using structured questionnaires. Surveys were adapted from validated instruments, and included questions about household socioeconomic characteristics, agricultural practices, dietary diversity, food security, and general health for women between 20-60 years and children between 6-59 months. Among respondents, 63% of mothers reported knowledge about vitamin A, with responses varying by geographic location. Among those who reported knowledge about vitamin A, 8% identified OFSP as a source, 1% had consumed OFSP in the past 7 days, and 0% reported that they ever prepared OFSP with an animal- or vegetable-based fat. Vitamin A-related health issues reported by mothers include night-blindness (32%), measles (32%) and malaria (72%). Given that existing knowledge, behaviors and production levels of vitamin A rich foods (including OFSP) are limited within the SNNPR study population and vary by geographic location, an integrated, food-based approach to address VAD may be relevant in this context to sustainably support improved health and livelihoods.Key words: Nutrition, orange fleshed sweet potato, behavior change, Ethiopi
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