934 research outputs found
Contributions of chaperone and glycosyltransferase activities of O-fucosyltransferase 1 to Notch signaling
<p>Abstract</p> <p>Background</p> <p><it>O</it>-fucosyltransferase1 (OFUT1) is a conserved ER protein essential for Notch signaling. OFUT1 glycosylates EGF domains, which can then be further modified by the <it>N</it>-acetylglucosaminyltransferase Fringe. OFUT1 also possesses a chaperone activity that promotes the folding and secretion of Notch. Here, we investigate the respective contributions of these activities to Notch signaling in <it>Drosophila</it>.</p> <p>Results</p> <p>We show that expression of an isoform lacking fucosyltransferase activity, <it>Ofut1</it><sup><it>R</it>245<it>A</it></sup>, rescues the requirement for <it>Ofut1 </it>in embryonic neurogenesis. Lack of requirement for <it>O</it>-fucosylation is further supported by the absence of embryonic phenotypes in <it>Gmd </it>mutants, which lack all forms of fucosylation. Requirements for <it>O</it>-fucose during imaginal development were evaluated by characterizing clones of cells expressing only <it>Ofut1</it><sup><it>R</it>245<it>A</it></sup>. These clones phenocopy <it>fringe </it>mutant clones, indicating that the absence of <it>O</it>-fucose is functionally equivalent to the absence of elongated <it>O</it>-fucose.</p> <p>Conclusion</p> <p>Our results establish that Notch does not need to be <it>O</it>-fucosylated for <it>fringe</it>-independent Notch signaling in <it>Drosophila</it>; the chaperone activity of OFUT1 is sufficient for the generation of functional Notch.</p
Goddard Robotic Telescope - Optical Follow-up of GRBs and Coordinated Observations of AGNs -
Since it is not possible to predict when a Gamma-Ray Burst (GRB) will occur
or when Active Galactic Nucleus (AGN) flaring activity starts,
follow-up/monitoring ground telescopes must be located as uniformly as possible
all over the world in order to collect data simultaneously with Fermi and Swift
detections. However, there is a distinct gap in follow-up coverage of
telescopes in the eastern U.S. region based on the operations of Swift.
Motivated by this fact, we have constructed a 14" fully automated optical
robotic telescope, Goddard Robotic Telescope (GRT), at the Goddard Geophysical
and Astronomical Observatory. The aims of our robotic telescope are 1) to
follow-up Swift/Fermi GRBs and 2) to perform the coordinated optical
observations of Fermi Large Area Telescope (LAT) AGN. Our telescope system
consists of off-the-shelf hardware. With the focal reducer, we are able to
match the field of view of Swift narrow instruments (20' x 20'). We started
scientific observations in mid-November 2008 and GRT has been fully remotely
operated since August 2009. The 3 sigma upper limit in a 30-second exposure in
the R filter is ~15.4 mag; however, we can reach to ~18 mag in a 600-second
exposures. Due to the weather condition at the telescope site, our observing
efficiency is 30-40% on average.Comment: 14 pages, 14 figures, accepted for publication in ASR special issue
on Neutron Stars and Gamma Ray Burst
Precision Fe Kalpha and Fe Kbeta Line Spectroscopy of the Seyfert 1.9 Galaxy NGC 2992 with Suzaku
We present detailed time-averaged X-ray spectroscopy in the 0.5--10 keV band
of the Seyfert~1.9 galaxy NGC 2992 with the Suzaku X-ray Imaging Spectrometers
(XIS). We model the complex continuum in detail. There is an Fe K line emission
complex that we model with broad and narrow lines and we show that the
intensities of the two components are decoupled at a confidence level >3sigma.
The broad Fe K line has an EW of 118 (+32,-61) eV and could originate in an
accretion disk (with inclination angle greater than ~30 degrees). The narrow Fe
Kalpha line has an EW of 163 (+47,-26) eV and is unresolved FWHM <4090 km/s)
and likely originates in distant matter. The absolute flux in the narrow line
implies that the column density out of the line-of-sight could be much higher
than measured in the line-of-sight, and that the mean (historically-averaged)
continuum luminosity responsible for forming the line could be a factor of
several higher than that measured from the data. We also detect the narrow Fe
Kbeta line with a high signal-to-noise ratio and describe a new robust method
to constrain the ionization state of Fe responsible for the Fe Kalpha and Fe
Kbeta lines that does not require any knowledge of possible gravitational and
Doppler energy shifts affecting the line energies. For the distant
line-emitting matter (e.g. the putative obscuring torus) we deduce that the
predominant ionization state is lower than Fe VIII (at 99% confidence),
conservatively taking into account residual calibration uncertainties in the
XIS energy scale and theoretical and experimental uncertainties in the Fe K
fluorescent line energies. From the limits on a possible Compton-reflection
continuum it is likely that the narrow Fe Kalpha and Fe Kbeta lines originate
in a Compton-thin structure.Comment: Abstract is abridged. Accepted for publication in the Suzaku special
issue of PASJ (November 2006). 18 pages, 6 figure
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Measurement of the equivalent fundamental-mode source strength
The steady-state multiplication, M, of a subcritical system that is in equilibrium with an external/intrinsic source is defined as the total neutron-production rate divided by the external/ intrinsic neutron source rate, S. The total neutron-production rate, in this context, is the sum of the fission-production rate plus the source rate. Because the system is in equilibrium, the total neutron-production rate is identically equal to the loss rate from the system due to absorption plus leakage. If the source S is distributed identically to the fission source distribution (i.e., angle, energy, and space), then M will be related to the effective multiplication factor of the system, k{sub eff}, as M = 1/1-k{sub eff}
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The equivalent fundamental-mode source
In 1960, Hansen analyzed the problem of assembling fissionable material in the presence of a weak neutron source. Using point kinetics, he defined the weak source condition and analyzed the consequences of delayed initiation during ramp reactivity additions. Although not clearly stated in Hansen`s work, the neutron source strength that appears in the weak source condition corresponds to the equivalent fundamental-mode source. In this work, we describe the concept of an equivalent fundamental-mode source and we derive a deterministic expression for a factor, g*, that converts any arbitrary source distribution to an equivalent fundamental-mode source. We also demonstrate a simplified method for calculating g* in subcritical systems. And finally, we present a new experimental method that can be employed to measure the equivalent fundamental-mode source strength in a multiplying assembly. We demonstrate the method on the zero-power, XIX-1 assembly at the Fast Critical Assembly (FCA) Facility, Japan Atomic Energy Research Institute (JAERI)
MOA 2003-BLG-37: A Bulge Jerk-Parallax Microlens Degeneracy
We analyze the Galactic bulge microlensing event MOA-2003-BLG-37. Although
the Einstein timescale is relatively short, t_e=43 days, the lightcurve
displays deviations consistent with parallax effects due to the Earth's
accelerated motion. We show that the chi^2 surface has four distinct local
minima that are induced by the ``jerk-parallax'' degeneracy, with pairs of
solutions having projected Einstein radii, \tilde r_e = 1.76 AU and 1.28 AU,
respectively. This is the second event displaying such a degeneracy and the
first toward the Galactic bulge. For both events, the jerk-parallax formalism
accurately describes the offsets between the different solutions, giving hope
that when extra solutions exist in future events, they can easily be found.
However, the morphologies of the chi^2 surfaces for the two events are quite
different, implying that much remains to be understood about this degeneracy.Comment: 19 pages, 3 figures, 1 table, ApJ, in press, 1 July 200
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Gas Production Due to Alpha Particle Degradation of Polyethylene and Polyvinylchloride
Alpha particle degradation experiments were performed on polyethylene (PE) and polyvinylchloride (PVC) plastic samples typical of Westinghouse Savannah River Company (WSRC) transuranic (TRU) waste. This was done to evaluate the effects of sealing TRU waste during shipment. Experiments were conducted at three temperatures using low dose rates. Predominant products from both plastics were hydrogen, carbon dioxide, and various organic species, with the addition of hydrochloric acid from PVC. In all experiments, the total pressure decreased. Irradiation at 30 and 60 C and at various dose rates caused small changes for both plastics, but at 100 C coupled thermal-radiolytic effects included discoloration of the material as well as large differences in the gas phase composition
Probing the atmosphere of a solar-like star by galactic microlensing at high magnification
We report a measurement of limb darkening of a solar-like star in the very
high magnification microlensing event MOA 2002-BLG-33. A 15 hour deviation from
the light curve profile expected for a single lens was monitored intensively in
V and I passbands by five telescopes spanning the globe. Our modelling of the
light curve showed the lens to be a close binary system whose centre-of-mass
passed almost directly in front of the source star. The source star was
identified as an F8-G2 main sequence turn-off star. The measured stellar
profiles agree with current stellar atmosphere theory to within ~4% in two
passbands. The effective angular resolution of the measurements is <1
micro-arcsec. These are the first limb darkening measurements obtained by
microlensing for a Solar-like star.Comment: Accepted for publication in A&A Letters. 5 pages, 2 embedded colour
ps figures plus 1 jpg figure. Version with all figures embedded available
from: http://www.roe.ac.uk/~iab/moa33paper
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