928 research outputs found
Differential Regulation of Mouse B Cell Development by Transforming Growth Factor β1
Transforming growth factor β (TGFβ) can inhibit the in vitro proliferation, survival and differentiation of B cell progenitors, mature B lymphocytes and plasma cells. Here we demonstrate unexpected, age-dependent reductions in the bone marrow (BM) B cell progenitors and immature B cells in TGFβ1-/- mice. To evaluate TGFβ responsiveness during normal B lineage development, cells were cultured in interleukin 7 (IL7)±TGFβ. Picomolar doses of TGFβ1 reduced pro-B cell recoveries at every timepoint. By contrast, the pre-B cells were initially reduced in number, but subsequently increased compared to IL7 alone, resulting in a 4-fold increase in the growth rate for the pre-B cell population. Analysis of purified BM sub-populations indicated that pro-B cells and the earliest BP1- pre-B cells were sensitive to the inhibitory effects of TGFβ1. However, the large BP1+ pre-B cells, although initially reduced, were increased in number at days 5 and 7 of culture. These results indicate that TGFβ1 is important for normal B cell development in vivo, and that B cell progenitors are differentially affected by the cytokine according to their stage of differentiation
Jet Breaks in Short Gamma-Ray Bursts. I: The Uncollimated Afterglow of GRB 050724
We report the results of the \chandra observations of the \swift-discovered
short Gamma-Ray Burst GRB 050724. \chandra observed this burst twice, about two
days after the burst and a second time three weeks later. The first \chandra
pointing occurred at the end of a strong late-time flare. About 150 photons
were detected during this 49.3 ks observation in the 0.4-10.0 keV range. The
spectral fit is in good agreement with spectral analysis of earlier \swift XRT
data. In the second \chandra pointing the afterglow was clearly detected with 8
background-subtracted photons in 44.6 ks. From the combined \swift XRT and
\chandra-ACIS-S light curve we find significant flaring superposed on an
underlying power-law decay slope of =0.98. There is
no evidence for a break between about 1 ks after the burst and the last
\chandra pointing about three weeks after the burst. The non-detection of a jet
break places a lower limit of 25 on the jet opening angle, indicating
that the outflow is less strongly collimated than most previously-reported long
GRBs. This implies that the beaming corrected energy of GRB 050724 is at least
ergs.Comment: 7 pages, ApJ acceped, scheduled for December 20, 2006, ApJ, 65
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PIV measurements of flow-field downstream of a cylinder with and without fairing and comparison with CFD
textThis work examines the ability of two dimensional CFD models to predict the unsteady flow downstream of a cylinder, with and without fairing, in uniform flow. PIV measurements of the flow-field downstream of the cylinder and fairing in uniform flow are first presented. “Slices” of the flow at several locations along the cylinder are compared to show the variation of the flow in the cross-stream direction. Then the PIV flow is compared with RANS and LES simulations of the flow. Velocity time histories are compared and hydrodynamic coefficients are discussed. In a general sense, two dimensional CFD can give a functional approximation of the unsteady flow field downstream of the cylinder or fairing.Civil, Architectural, and Environmental Engineerin
Mapping High-velocity H-alpha and Lyman-alpha Emission from Supernova 1987A
We present new {\it Hubble Space Telescope} images of high-velocity
H- and Lyman- emission in the outer debris of SN~1987A. The
H- images are dominated by emission from hydrogen atoms crossing the
reverse shock. For the first time we observe emission from the reverse shock
surface well above and below the equatorial ring, suggesting a bipolar or
conical structure perpendicular to the ring plane. Using the H imaging,
we measure the mass flux of hydrogen atoms crossing the reverse shock front, in
the velocity intervals (7,500~~~~2,800 km s) and
(1,000~~~~7,500 km s), =
1.2~~10 M yr. We also present the first
Lyman- imaging of the whole remnant and new X-ray
observations. Comparing the spatial distribution of the Lyman- and
X-ray emission, we observe that the majority of the high-velocity
Lyman- emission originates interior to the equatorial ring. The
observed Lyman-/H- photon ratio, ~17, is significantly higher than the theoretically
predicted ratio of 5 for neutral atoms crossing the reverse shock
front. We attribute this excess to Lyman- emission produced by X-ray
heating of the outer debris. The spatial orientation of the Lyman- and
X-ray emission suggests that X-ray heating of the outer debris is the dominant
Lyman- production mechanism in SN 1987A at this phase in its evolution.Comment: 6 pages, 5 figures. ApJL - accepte
Developing an online knowledge sharing platform and community of practice for health professionals: Experiences from C-WorKS developed in North East England and Yorkshire during COVID-19
AbstractBackgroundAlthough knowledge sharing online has been recognised as an important strategy for health professionals to apply research findings to their practice, limited research exists on how to develop and implement these platforms to help facilitate collaboration and knowledge sharing.ObjectivesThis study evaluated an online knowledge sharing platform and community of practice developed in the North East of England and Yorkshire during COVID-19 to support UK health and care professionals to reduce the impact of the wider consequences of COVID-19.MethodsSemi-structured interviews with stakeholders (n = 8) and users of C-WorKS (n = 13), followed by an online survey (n = 19) among a wider group of users to analyse knowledge use.ResultsInterview and survey findings highlighted several strengths, weaknesses, opportunities and threats to support future development of online knowledge sharing platforms.DiscussionOnline knowledge sharing supports six ‘pillars’ of successful research and innovation partnerships. This requires distributed forms of leadership and linking of different knowledge sharing strategies, and careful combination of platforms with communities of practice.ConclusionOnline knowledge sharing provides pragmatic and timely strategies for health professionals in the UK to apply research evidence to their practice. Our study provides generalisable, practical insights in how to develop and implement a knowledge sharing platform
Dynamical Bar-Mode Instability in Differentially Rotating Magnetized Neutron Stars
This paper presents a numerical study over a wide parameter space of the
likelihood of the dynamical bar-mode instability in differentially rotating
magnetized neutron stars. The innovative aspect of this study is the
incorporation of magnetic fields in such a context, which have thus far been
neglected in the purely hydrodynamical simulations available in the literature.
The investigation uses the Cosmos++ code which allows us to perform three
dimensional simulations on a cylindrical grid at high resolution. A sample of
Newtonian magneto-hydrodynamical simulations starting from a set of models
previously analyzed by other authors without magnetic fields has been
performed, providing estimates of the effects of magnetic fields on the
dynamical bar-mode deformation of rotating neutron stars. Overall, our results
suggest that the effect of magnetic fields are not likely to be very
significant in realistic configurations. Only in the most extreme cases are the
magnetic fields able to suppress growth of the bar mode.Comment: 12 pages, 16 figures. References added and minor edits made to match
published versio
Swift Observations of GRB 050603: An afterglow with a steep late time decay slope
We report the results of Swift observations of the Gamma Ray Burst GRB
050603. With a V magnitude V=18.2 about 10 hours after the burst the optical
afterglow was the brightest so far detected by Swift and one of the brightest
optical afterglows ever seen. The Burst Alert Telescope (BAT) light curves show
three fast-rise-exponential-decay spikes with =12s and a fluence of
7.6 ergs cm in the 15-150 keV band. With an ergs it was also one of the most energetic
bursts of all times. The Swift spacecraft began observing of the afterglow with
the narrow-field instruments about 10 hours after the detection of the burst.
The burst was bright enough to be detected by the Swift UV/Optical telescope
(UVOT) for almost 3 days and by the X-ray Telescope (XRT) for a week after the
burst. The X-ray light curve shows a rapidly fading afterglow with a decay
index =1.76. The X-ray energy spectral index was
=0.71\plm0.10 with the column density in agreement with the
Galactic value. The spectral analysis does not show an obvious change in the
X-ray spectral slope over time. The optical UVOT light curve decays with a
slope of =1.8\plm0.2.
The steepness and the similarity of the optical and X-ray decay rates suggest
that the afterglow was observed after the jet break. We estimate a jet opening
angle of about 1-2Comment: 14 pages, accepted for publication in Ap
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