473 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
Loss of treatment benefit due to low compliance with bisphosphonate therapy
Among 8,822 new female bisphosphonate users, non-compliant bisphosphonate use was associated with a 45% increased risk of osteoporotic fracture compared to compliant use (MPR â„80%). Classifying compliance into five categories, fracture risk gradually increased with poorer compliance. These results emphasize the importance of treatment compliance in obtaining maximal treatment benefit. Introduction: Bisphosphonates are widely used to treat osteoporosis and reduce fracture risk. Low compliance is frequent and will limit treatment benefit. Methods: New female users of alendronate or risedronate between 1999-2004, aged â„45 years were identified from PHARMO-RLS, including drug-dispensing and hospitalization data of â„2 million residents of the Netherlands. Patients were followed until first hospitalisation for an osteoporotic fracture, death, or end of study period. Compliance with bisphosphonates during follow-up was measured over 90-day intervals using Medication Possession Ratio (MPR). The association between compliance and fracture risk was analyzed using time-dependent Cox-regression. Results: The study cohort included 8,822 new female bisphosphonate users, contributing in total 22,484 person-years of follow-up. During follow-up, 176 osteoporotic fractures occurred (excluding the first six months). Non-compliant bisphosphonate use was associated with a 45% increased fracture risk compared to compliant use (MPR â„80%). Classifying compliance into five categories, fracture risk gradually increased with poorer compliance (p-value <0.05 for trend). A MPR <20% was associated with an 80% increased fracture risk compared to a MPR â„90%. Conclusions: These results show a statistically significant association between level of compliance with bisphosphonates and level of fracture risk, emphasizing the importance of treatment compliance in obtaining maximal treatment benefit
Analytic frameworks for assessing dialogic argumentation in online learning environments
Over the last decade, researchers have developed sophisticated online learning environments to support students engaging in argumentation. This review first considers the range of functionalities incorporated within these online environments. The review then presents five categories of analytic frameworks focusing on (1) formal argumentation structure, (2) normative quality, (3) nature and function of contributions within the dialog, (4) epistemic nature of reasoning, and (5) patterns and trajectories of participant interaction. Example analytic frameworks from each category are presented in detail rich enough to illustrate their nature and structure. This rich detail is intended to facilitate researchersâ identification of possible frameworks to draw upon in developing or adopting analytic methods for their own work. Each framework is applied to a shared segment of student dialog to facilitate this illustration and comparison process. Synthetic discussions of each category consider the frameworks in light of the underlying theoretical perspectives on argumentation, pedagogical goals, and online environmental structures. Ultimately the review underscores the diversity of perspectives represented in this research, the importance of clearly specifying theoretical and environmental commitments throughout the process of developing or adopting an analytic framework, and the role of analytic frameworks in the future development of online learning environments for argumentation
XMM-Newton observations of the Narrow-Line Seyfert 1 galaxy Mrk 335 in an historical low X-ray flux state
We report the discovery of strong soft X-ray emission lines and a hard
continuum above 2 keV in the Narrow-Line Seyfert 1 galaxy Mrk 335 during an
extremely low X-ray flux state. Mrk 335 was observed for 22 ks by XMM-Newton in
July 2007 as a Target of Opportunity to examine it in its X-ray low-flux state,
which was discovered with Swift. Long-term light curves suggest that this is
the lowest flux state this AGN has ever been seen in. However, Mrk 335 is still
sufficiently bright that its X-ray properties can be studied in detail. The
X-ray continuum spectrum is very complex and requires several components to
model. Statistically, partial covering and blurred reflection models work well.
We confirm the presence of a strong narrow Fe line at 6.4 keV. High-resolution
spectroscopy with the XMM-RGS reveals strong, soft X-ray emission lines not
detected in previous, higher signal-to-noise, XMM-Newton observations, such as:
highly ionized Fe lines, O VII, Ne IX and Mg XI lines. The optical/UV fluxes
are similar to those previously measured with Swift. Optical spectroscopy taken
in 2007 September do not show any changes to optical spectra obtained 8 years
earlier.Comment: Accepted for publication in ApJ; 26 pages, 10 figues, in press, ApJ
681 (July 01, 2008); Updated version with corrections made by the edito
A novel approach to study the morphology and chemistry of pollen in a phylogenetic context, applied to the halophytic taxon <em>Nitraria</em> L. (Nitrariaceae)
A novel approach to study the morphology and chemistry of pollen in a phylogenetic context, applied to the halophytic taxon <em>Nitraria</em> L. (Nitrariaceae)
Probing the Ionizing Continuum of Narrow-Line Seyfert 1 Galaxies. I.Observational Results
We present optical spectra and emission-line ratios of 12 Narrow-Line Seyfert
1 (NLS1) galaxies that we observed to study the ionizing EUV continuum. A
common feature in the EUV continuum of active galactic nuclei is the big blue
bump (BBB), generally associated with thermal accretion disk emission. While
Galactic absorption prevents direct access to the EUV range, it can be mapped
by measuring the strength of a variety of forbidden optical emission lines that
respond to different EUV continuum regions. We find that narrow emission-line
ratios involving [OII]3727, Hbeta, [OIII]5007, [OI]6300, Halpha,[NII]6583, and
[SII]6716,6731 indicate no significant difference between NLS1s and Broad-Line
Seyfert 1 (BLS1) galaxies, which suggests that the spectral energy
distributions of their ionizing EUV - soft X-ray continua are similar. The
relative strength of important forbidden high ionization lines like [NeV]3426
compared to HeII4686 and the relative strength of [FeX]6374 appear to show the
same range as in BLS1 galaxies. However, a trend of weaker
F([OI]6300)/F(Halpha) emission-line ratios is indicated for NLS1s compared to
BLS1s. To recover the broad emission-line profiles we used Gaussian components.
This approach indicates that the broad Hbeta profile can be well described with
a broad component (FWHM = 3275 +- 800 km/s) and an intermediate broad component
(FWHM = 1200 +- 300 km/s). The width of the broad component is in the typical
range of normal BLS1s. The emission-line flux that is associated with the broad
component in these NLS1s amounts to at least 60% of the total flux. Thus it
dominates the total line flux, similar to BLS1 galaxies.Comment: 34 pages, 9 figures. accepted for publication in the
Astrophys.Journa
Scientists' warning to humanity on tree extinctions
Societal Impact Statement
Trees play vital roles in many of the world's ecosystems while providing many
benefits to people. New evidence indicates that a third of tree species are threatened
with extinction, representing a tree extinction crisis. Here we demonstrate how tree
species extinction will lead to the loss of many other plants and animals and significantly alter the world's ecosystems. We also show how tree extinction will negatively
affect billions of people through loss of livelihoods and benefits. We highlight a series
of urgent actions needed to avert an ecological, cultural and socio-economic catastrophe caused by widespread extinction of tree species.
Summary
Trees are of exceptional ecological importance, playing a major functional role in the
world's ecosystems, while also supporting many other plants, animals and fungi.
Many tree species are also of direct value to people, providing a wide range of socioeconomic benefits. Loss of tree diversity could lead to abrupt declines in biodiversity,
ecosystem functions and services and ultimately ecosystem collapse. Here we provide an overview of the current knowledge regarding the number of tree species that
are threatened with extinction, and the threats that affect them, based on results of
the Global Tree Assessment. This evidence suggests that a third of the world's tree
species are currently threatened with extinction, which represents a major ecological
crisis. We then examine the potential implications of tree extinctions, in terms of the
functioning of the biosphere and impacts on human well-being. Large-scale extinction of tree species will lead to major biodiversity losses in other species groups and
substantially alter the cycling of carbon, water and nutrients in the world's
ecosystems. Tree extinction will also undermine the livelihoods of the billions of
people who currently depend on trees and the benefits they provide. This warning to
humanity aims to raise awareness of the tree extinction crisis, which is a major environmental issue that requires urgent global attention. We also identify some priority
actions that need to be taken to reduce the extinction risk of tree species and to
avert the ecological and socio-economic catastrophe that will result from large-scale
extinction of tree specie
Chromosomeâlevel reference genome of the soursop (Annona muricata) : a new resource for Magnoliid research and tropical pomology
The flowering plant family Annonaceae includes important commercially grown tropical crops, but development of promising species is hindered by a lack of genomic resources to build breeding programs. Annonaceae are part of the magnoliids, an ancient lineage of angiosperms for which evolutionary relationships with other major clades remain unclear. To provide resources to breeders and evolutionary researchers, we report a chromosome-level genome assembly of the soursop (Annona muricata). We assembled the genome using 444.32 Gb of DNA sequences (676x sequencing depth) from PacBio and Illumina short-reads, in combination with 10x Genomics and Bionano data (v1). A total of 949 scaffolds were assembled to a final size of 656.77 Mb, with a scaffold N50 of 3.43 Mb (v1), and then further improved to seven pseudo-chromosomes using Hi-C sequencing data (v2; scaffold N50: 93.2 Mb, total size in chromosomes: 639.6 Mb). Heterozygosity was very low (0.06%), while repeat sequences accounted for 54.87% of the genome, and 23,375 protein-coding genes with an average of 4.79 exons per gene were annotated using de novo, RNA-seq and homology-based approaches. Reconstruction of the historical population size showed a slow continuous contraction, probably related to Cenozoic climate changes. The soursop is the first genome assembled in Annonaceae, supporting further studies of floral evolution in magnoliids, providing an essential resource for delineating relationships of ancient angiosperm lineages. Both genome-assisted improvement and conservation efforts will be strengthened by the availability of the soursop genome. As a community resource, this assembly will further strengthen the role of Annonaceae as model species for research on the ecology, evolution and domestication potential of tropical species in pomology and agroforestry
Toward a Self Consistent Model of the Ionized Absorber in NGC 3783
We present a detailed model for the ionized absorbing gas evident in the 900
ksec Chandra HETGS spectrum of NGC 3783. The analysis was carried out with
PHASE a new tool designed to model X-ray and UV absorption features in ionized
plasmas. The 0.5-10 keV intrinsic continuum of the source is well represented
by a single power law (Gamma=1.53) and a soft black-body component (kT=10 keV).
The spectrum contains over 100 features, which are well fit by PHASE with just
six free parameters. The model consists of a simple two phase absorber with
difference of 35 in the ionization parameter and difference of 4 in the column
density of the phases. The two absorption components turned out to be in
pressure equilibrium, and are consistent with a single outflow (750 kms-1) an a
single turbulent velocity (300 km s-1), and with solar elemental abundances.
The main features of the low ionization phase are an Fe M-shell unresolved
transition array (UTA) and the OVII lines. The OVII features, usualy identified
with the OVIII and a warm absorber, are instead produced in a cooler medium
also producing OVI lines. The UTA sets tight constraints on the ionization
degree of the absorbers, making the model more reliable. The high ionization
phase is required by the OVII and the Fe L-shell lines, and there is evidence
for an even more ionized component in the spectrum. A continuous range of
ionization parameters is disfavored by the fits, particularly to the UTA. The
low ionizaton phase can be decomposed into three subcomponents based on the
outflow velocity, FWHM, and H column densities found for three out of the four
UV absorbers detected in NGC 3783. However, the ionization parametes are
systematically smaller in our model than derived from UV data, indicating a
lower degree of ionization.Comment: 42 pages, 7 tables and 17 figures. Replaced with version accepted for
publication in Ap
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