1,910 research outputs found
ROSAT and ASCA observations of the Crab-Like Supernova Remnant N157B in the Large Magellanic Cloud
We report the results of ROSAT and ASCA X-ray observations of the supernova
remnant N157B (or 30 Dor B, SNR 0539-69.1) in the Large Magellanic Cloud. For
comparison, we also briefly describe the results on SNR 0540-69.3, the only
confirmed Crab-like remnant in the Cloud. The X-ray emission from N157B can be
decomposed into a bright comet-shaped feature, superimposed on a diffuse
emission region of a dimension pc. The flat and nearly featureless
spectrum of the remnant is distinctly different from those of young shell-like
remnants, suggesting a predominantly Crab-like nature of N157B. Characterized
by a power law with an energy slope , the spectrum of N157B above
keV is, however, considerably steeper than that of SNR 0540-69.3,
which has a slope of . At lower energies, the spectrum of N157B
presents marginal evidence for emission lines, which if real most likely arise
in hot gas of the diffuse emission region. The hot gas has a characteristic
thermal temperature of 0.4-0.7 keV. No significant periodic signal is detected
from N157B in the period range of s. The pulsed
fraction is (99% confidence) in the keV range. We discuss
the nature of the individual X-ray components. In particular, we suggest that
the synchrotron radiation of relativistic particles from a fast-moving () pulsar explains the size, morphology, spectrum, and energetics
of the comet-shaped X-ray feature. We infer the age of the remnant as yrs. The lack of radio polarization of the remnant may be due to
Faraday dispersion by foreground \ion{H}{2} gas.Comment: To be published in The Astrophysical Journal, 21 pages, plus 11
images in the PS, GIF, or jpeg format. Postscript files of images are
available at http://www.astro.nwu.edu/astro/wqd/paper/n157b
Supernova Remnants in the Magellanic Clouds. IV. X-Ray Emission from the Largest SNR in the LMC
We present the first X-ray detection of SNR 0450-70.9 the largest known
supernova remnant (SNR) in the Large Magellanic Cloud. To study the physical
conditions of this SNR, we have obtained XMM-Newton X-ray observations, optical
images and high-dispersion spectra, and radio continuum maps. Optical images of
SNR 0450-70.9 show a large, irregular elliptical shell with bright filaments
along the eastern and western rims and within the shell interior. The interior
filaments have higher [S II]/Halpha ratios and form an apparent inner shell
morphology. The X-ray emission region is smaller than the full extent of the
optical shell, with the brightest X-ray emission found within the small
interior shell and on the western rim of the large shell. The expansion
velocity of the small shell is ~220 km/s, while the large shell is ~120 km/s.
The radio image shows central brightening and a fairly flat radio spectral
index over the SNR. However, no point X-ray or radio source corresponding to a
pulsar is detected and the X-ray emission is predominantly thermal. Therefore,
these phenomena can be most reasonably explained in terms of the advanced age
of the large SNR. Using hydrodynamic models combined with a nonequilibrium
ionization model for thermal X-ray emission, we derived a lower limit on the
SNR age of about 45,000 yr, well into the later stages of SNR evolution.
Despite this, the temperature and density derived from spectral fits to the
X-ray emission indicate that the remnant is still overpressured, and thus that
the development is largely driven by hot gas in the SNR interior.Comment: Accepted for publication in The Astrophysical Journa
WR bubbles and HeII emission
We present the very first high quality images of the HeII 4686 emission in
three high excitation nebulae of the Magellanic Clouds. A fourth high
excitation nebula, situated around the WR star BAT99-2, was analysed in a
previous letter. Using VLT FORS data, we investigate the morphology of the ring
nebulae around the early-type WN stars BAT99-49 & AB7. We derive the total HeII
fluxes for each object and compare them with the most recent theoretical WR
models. Using Halpha, [OIII] and HeI 5876 images along with long-slit
spectroscopy, we investigate the physical properties of these ring nebulae and
find only moderate chemical enrichment. We also surveyed seven other LMC WR
stars but we failed to detect any HeII emission but note that the nebula around
BAT99-11 shows a N/O ratio and an oxygen abundance slightly lower than the LMC
values, while the nebula around BAT99-134 presents moderate chemical enrichment
similar to the one seen near BAT99-2, 49 and AB7. The third high excitation
nebula presented in this paper, N44C, does not harbor stars hotter than mid-O
main sequence stars. It was suggested to be a fossil X-ray nebula ionized but
our observations of N44C reveal no substantial changes in the excitation
compared to previous results reported in the literature.Comment: 13 pages, 8 figures (7 in jpg), accepted by A&A, also available from
http://vela.astro.ulg.ac.be/Preprints/P81/index.htm
Using strain to uncover the interplay between two- and three-dimensional charge density waves in high-temperature superconducting YBa<sub>2</sub>Cu<sub>3</sub>O<sub>y</sub>
Uniaxial pressure provides an efficient approach to control charge density waves in YBa2Cu3Oy. It can enhance the correlation volume of ubiquitous short-range two-dimensional charge-density-wave correlations, and induces a long-range three-dimensional charge density wave, otherwise only accessible at large magnetic fields. Here, we use x-ray diffraction to study the strain dependence of these charge density waves and uncover direct evidence for a form of competition between them. We show that this interplay is qualitatively described by including strain effects in a nonlinear sigma model of competing superconducting and charge-density-wave orders. Our analysis suggests that strain stabilizes the 3D charge density wave in the regions between disorder-pinned domains of 2D charge density waves, and that the two orders compete at the boundaries of these domains. No signatures of discommensurations nor of pair density waves are observed. From a broader perspective, our results underscore the potential of strain tuning as a powerful tool for probing competing orders in quantum materials
XMM-Newton observations of the giant HII region N11 in the LMC
Using the sensitive XMM-Newton observatory, we have observed the giant HII
region N11 in the LMC for \sim30 ks. We have detected several large areas of
soft diffuse X-ray emission along with 37 point sources. One of the most
interesting results is the possible association of a faint X-ray source with
BSDL 188, a small extended object of uncertain nature. The OB associations in
the field-of-view (LH9, LH10 and LH13) are all detected with XMM-Newton, but
they appear very different from one another. [...] (for complete abstract, see
paper) Finally, our XMM-Newton observation included simultaneous observations
with the OM camera that provide us with unique UV photometry of more than 6000
sources and enable the discovery of the UV emission from the SNR N11L.Comment: 13 pages, 16 figures (10 in gif or jpg), accepted by A&A, also
available from http://vela.astro.ulg.ac.be/Preprints/P88/index.htm
Perspectives of US women participating in a candidate PrEP study: adherence, acceptability and future use intentions
Introduction
Limited data exist on acceptability of candidate pre‐exposure prophylaxis (PrEP) regimens among US women. We evaluated PrEP experiences, attitudes and future use intentions among sexually active women who completed the US‐based HIV Prevention Trials Network 069/AIDS Clinical Trials Group 5305 study. Methods
Women participated in the study between March 2013 and November 2015. We analysed computer‐assisted self‐interview (CASI) surveys among 130 women and conducted in‐depth interviews among a subset of 26 women from three sites. Interviews were conducted in mid/late‐2015. Results
Most women (57%) reported very good/excellent PrEP adherence on CASI, although 21% acknowledged over‐reporting adherence at least some of the time. Commitment to preventing HIV infection, a sense of ownership of the study, and keeping pills stored in a visible location facilitated adherence. Adherence barriers included “simply forgetting” and being away from home. Most women interviewed did not intend to use PrEP in the future because of lack of perceived need due to their own (as opposed to their partners’) low‐risk behaviour and concerns about affordability – but not because of side effects or other characteristics of the regimens. Conclusions
Improving HIV prevention options for US women will require access to affordable PrEP as well as expanding women\u27s understanding of relationship‐ and community‐level factors that increase their risk of acquiring HIV
The (co-)occurrence of problematic video gaming, substance use, and psychosocial problems in adolescents
Aims. The current study explored the nature of problematic (addictive) video gaming and the association with game type, psychosocial health, and substance use. Methods. Data were collected using a paper and pencil survey in the classroom setting. Three samples were aggregated to achieve a total sample of 8478 unique adolescents. Scales included measures of game use, game type, the Video game Addiction Test (VAT), depressive mood, negative self-esteem, loneliness, social anxiety, education performance, and use of cannabis, alcohol and nicotine (smoking). Results. Findings confirmed problematic gaming is most common amongst adolescent gamers who play multiplayer online games. Boys (60%) were more likely to play online games than girls (14%) and problematic gamers were more likely to be boys (5%) than girls (1%). High problematic gamers showed higher scores on depressive mood, loneliness, social anxiety, negative self-esteem, and self-reported lower school performance. Nicotine, alcohol, and cannabis using boys were almost twice more likely to report high PVG than non-users. Conclusions. It appears that online gaming in general is not necessarily associated with problems. However, problematic gamers do seem to play online games more often, and a small subgroup of gamers – specifically boys – showed lower psychosocial functioning and lower grades. Moreover, associations with alcohol, nicotine, and cannabis use are found. It would appear that problematic gaming is an undesirable problem for a small subgroup of gamers. The findings encourage further exploration of the role of psychoactive substance use in problematic gaming
Branched Chain Fatty Acids Reduce the Incidence of Necrotizing Enterocolitis and Alter Gastrointestinal Microbial Ecology in a Neonatal Rat Model
Branched chain fatty acids (BCFA) are found in the normal term human newborn's gut, deposited as major components of vernix caseosa ingested during late fetal life. We tested the hypothesis that premature infants' lack of exposure to gastrointestinal (GI) BCFA is associated with their microbiota and risk for necrotizing enterocolitis (NEC) using a neonatal rat model.Pups were collected one day before scheduled birth. The pups were exposed to asphyxia and cold stress to induce NEC. Pups were assigned to one of three experimental treatments. DF (dam-fed); Control, hand-fed rat milk substitute; BCFA, hand-fed rat milk substitute with 20%w/w BCFA. Total fat was equivalent (11%wt) for both the Control and BCFA groups. Cecal microbiota were characterized by 16S rRNA gene pyrosequencing, and intestinal injury, ileal cytokine and mucin gene expression, interleukin-10 (IL-10) peptide immunohistochemistry, and BCFA uptake in ileum phospholipids, serum and liver were assessed.NEC incidence was reduced by over 50% in the BCFA group compared to the Control group as assessed in ileal tissue; microbiota differed among all groups. BCFA-fed pups harbored greater levels of BCFA-associated Bacillus subtilis and Pseudomonas aeruginosa compared to Controls. Bacillus subtilis levels were five-fold greater in healthy pups compared to pups with NEC. BCFA were selectively incorporated into ileal phospholipids, serum and liver tissue. IL-10 expression increased three-fold in the BCFA group versus Controls and no other inflammatory or mucosal mRNA markers changed.At constant dietary fat level, BCFA reduce NEC incidence and alter microbiota composition. BCFA are also incorporated into pup ileum where they are associated with enhanced IL-10 and may exert other specific effects
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