22,347 research outputs found
Matched-filter study and energy budget suggest no detectable gravitational-wave 'extended emission' from GW170817
Get PDFVan Putten & Della Valle (2018) have reported a possible detection of
gravitational-wave 'extended emission' from a neutron star remnant of GW170817.
Starting from the time-frequency evolution and total emitted energy of their
reported candidate, we show that such an emission is not compatible with the
current understanding of neutron stars. We explore the additional required
physical assumptions to make a full waveform model, for example, taking the
optimistic emission from a spining-down neutron star with fixed quadrupolar
deformation, and study whether even an ideal single-template matched-filter
analysis could detect an ideal, fully phase-coherent signal. We find that even
in the most optimistic case an increase in energy and extreme parameters would
be required for a confident detection with LIGO sensitivity as of 2018-08-17.
The argument also holds for other waveform models following a similar
time-frequency track and overall energy budget. Single-template matched
filtering on the LIGO data around GW170817, and on data with added simulated
signals, verifies the expected sensitivity scaling and the overall statistical
expectation.Comment: 9 pages, 6 figures, updated version as accepted by MNRA
A very deep Chandra observation of Abell 1795: The Cold Front and Cooling Wake
Get PDFWe present a new analysis of very deep Chandra observations of the galaxy
cluster Abell 1795. Utilizing nearly 750 ks of net ACIS imaging, we are able to
resolve the thermodynamic structure of the Intracluster Medium (ICM) on length
scales of ~ 1 kpc near the cool core. We find several previously unresolved
structures, including a high pressure feature to the north of the BCG that
appears to arise from the bulk motion of Abell 1795's cool core. To the south
of the cool core, we find low temperature (~ 3 keV), diffuse ICM gas extending
for distances of ~ 50 kpc spatially coincident with previously identified
filaments of H-alpha emission. Gas at similar temperatures is also detected in
adjacent regions without any H-alpha emission. The X-ray gas coincident with
the H-alpha filament has been measured to be cooling spectroscopically at a
rate of ~ 1 Solar Masses/ yr, consistent with measurements of the star
formation rate in this region as inferred from UV observations, suggesting that
the star formation in this filament as inferred by its H and UV
emission can trace its origin to the rapid cooling of dense, X-ray emitting
gas. The H-alpha filament is not a unique site of cooler ICM, however, as ICM
at similar temperatures and even higher metallicities not cospatial with
H emission is observed just to the west of the H-alpha filament,
suggesting that it may have been uplifted by Abell 1795's central active
galaxy. Further simulations of cool core sloshing and AGN feedback operating in
concert with one another will be necessary to understand how such a dynamic
cool core region may have originated and why the H-alpha emission is so
localized with respect to the cool X-ray gas despite the evidence for a
catastrophic cooling flow.Comment: 14 Pages, 10 Figures, Resubmitted to ApJ after first referee report,
Higher Resolution Figures available upon reques
New Challenges For Wind Shock Models: The Chandra Spectrum Of The Hot Star Delta Orionis
Get PDFThe Chandra spectrum of delta Ori A shows emission lines from hydrogen- and helium-like states of Si, Mg, Ne, and O, along with N VII Lyalpha and lines from ions in the range Fe XVII-Fe XXI In contrast to the broad lines seen in zeta Pup and zeta Ori (850 +/- 40 and 1000 +/- 240 km s(-1) half-width at half-maximum [HWHM], respectively), these lines are broadened to only 430 +/- 60 km s(-1) HWHM. This is much lower than the measured wind terminal velocity of 2000 km s(-1). The forbidden, intercombination, and resonance (fir) lines from He-like ions indicate that the majority of the X-ray line emission does not originate at the base of the wind, in agreement with the standard wind shock models for these objects. However, in that model the X-ray emission is distributed throughout an expanding, X-ray-absorbing wind, and it is therefore surprising that the emission lines appear relatively narrow, unshifted, and symmetric. We compare the observed line profiles to recent detailed models for X-ray line pro le generation in hot stars, but none of them offers a fully satisfactory explanation for the observed line profiles
Lipoprotein lipase regulates hematopoietic stem progenitor cell maintenance through DHA supply.
Get PDFLipoprotein lipase (LPL) mediates hydrolysis of triglycerides (TGs) to supply free fatty acids (FFAs) to tissues. Here, we show that LPL activity is also required for hematopoietic stem progenitor cell (HSPC) maintenance. Knockout of Lpl or its obligatory cofactor Apoc2 results in significantly reduced HSPC expansion during definitive hematopoiesis in zebrafish. A human APOC2 mimetic peptide or the human very low-density lipoprotein, which carries APOC2, rescues the phenotype in apoc2 but not in lpl mutant zebrafish. Creating parabiotic apoc2 and lpl mutant zebrafish rescues the hematopoietic defect in both. Docosahexaenoic acid (DHA) is identified as an important factor in HSPC expansion. FFA-DHA, but not TG-DHA, rescues the HSPC defects in apoc2 and lpl mutant zebrafish. Reduced blood cell counts are also observed in Apoc2 mutant mice at the time of weaning. These results indicate that LPL-mediated release of the essential fatty acid DHA regulates HSPC expansion and definitive hematopoiesis
What Are Agriculture Industry Professionals Trying to Tell Us? Implications for University-Level Agricultural Communications Curricula
Get PDFTwo recent activities have solicited the input of professionals on the future of agricultural communications within the agriculture industry. This paper reexamines these industry-based information and research activities for potential themes that could impact the current and future direction of communications-related activities within the agriculture profession. A reexamination of the outcomes of these two activities may provide insight and guidance for curricular and degree changes being considered by university-level agricultural communications educators. The four themes identified and discussed in this article are as follows: (a) the rapidly changing communication needs, wants, and expectations of the agriculture industry; (b) the new stakeholders of agricultural communications activities and products, and their diverse communication needs, wants, and preferences; (c) the shortened response time for communication-related activities; and (d) the increasing importance of the image of the agriculture industry and agricultural communications professionals. The themes that have emerged from industry through this study underscore the importance of researching the employee needs of the 21st century agriculturalist and agricultural communicator. These results may also positively influence university-level curricula and degree programs both within and outside of agricultural communications
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