2,531 research outputs found
Young core collapse supernova remnants and their supernovae
Massive star supernovae can be divided into four categories depending on the
amount of mass loss from the progenitor star and the star's radius: red
supergiant stars with most of the H envelope intact (SN IIP), stars with some H
but most lost (IIL, IIb), stars with all H lost (Ib, Ic), and blue supergiant
stars with a massive H envelope (SN 1987A-like). Various aspects of the
immediate aftermath of the supernova are expected to develop in different ways
depending on the supernova category: mixing in the supernova, fallback on the
central compact object, expansion of any pulsar wind nebula, interaction with
circumstellar matter, and photoionization by shock breakout radiation. The
observed properties of young supernova remnants allow many of them to be placed
in one of the supernova categories; all the categories are represented except
for the SN 1987A-like type. Of the remnants with central pulsars, the pulsar
properties do not appear to be related to the supernova category. There is no
evidence that the supernova categories form a mass sequence, as would be
expected in a single star scenario for the evolution. Models for young pulsar
wind nebulae expanding into supernova ejecta indicate initial pulsar periods of
10-100 ms and approximate equipartition between particle and magnetic energies.
Ages are obtained for pulsar nebulae, including an age of 2400 pm 500 yr for
3C58, which is not consistent with an origin in SN 1181. There is no evidence
that mass fallback plays a role in neutron star properties.Comment: 43 pages, ApJ, revised, discussion of 3C58 changed, in press for Feb.
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Preparation of highly and generally enriched mammalian tissues for solid state NMR.
An appreciable level of isotope labelling is essential for future NMR structure elucidation of mammalian biomaterials, which are either poorly expressed, or unexpressable, using micro-organisms. We present a detailed protocol for high level (13)C enrichment even in slow turnover murine biomaterials (fur keratin), using a customized diet supplemented with commercial labelled algal hydrolysate and formulated as a gel to minimize wastage, which female mice consumed during pregnancy and lactation. This procedure produced approximately eightfold higher fur keratin labelling in pups, exposed in utero and throughout life to label, than in adults exposed for the same period, showing both the effectiveness, and necessity, of this approach.The authors would like to acknowledge funding from the Biotechnology and Biological Sciences Research Council for DGR and RR; Engineering and Physical Sciences Research Council for WYC and VWCW; National Institute of Health Research for RAB.This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s10858-015-9977-
Radio Frequency Spectra of 388 Bright 74 MHz Sources
As a service to the community, we have compiled radio frequency spectra from
the literature for all sources within the VLA Low Frequency Sky Survey (VLSS)
that are brighter than 15 Jy at 74 MHz. Over 160 references were used to
maximize the amount of spectral data used in the compilation of the spectra,
while also taking care to determine the corrections needed to put the flux
densities from all reference on the same absolute flux density scale. With the
new VLSS data, we are able to vastly improve upon previous efforts to compile
spectra of bright radio sources to frequencies below 100 MHz because (1) the
VLSS flux densities are more reliable than those from some previous low
frequency surveys and (2) the VLSS covers a much larger area of the sky
(declination >-30 deg.) than many other low frequency surveys (e.g., the 8C
survey). In this paper, we discuss how the spectra were constructed and how
parameters quantifying the shapes of the spectra were derived. Both the spectra
and the shape parameters are made available here to assist in the calibration
of observations made with current and future low frequency radio facilities.Comment: Accepted to ApJ
Study of the Composite Supernova Remnant MSH 11-62
We present the analysis of the X-ray data collected during an observation of
the supernova remnant (SNR) MSH 11-62 by the Advanced Satellite for Cosmology
and Astrophysics (ASCA). We show that MSH 11-62 is a composite remnant whose
X-ray emission comes from two distinct contributions. Nonthermal, synchrotron
emission, localized to a region of radius (~~)3' (consistent with a point
source) dominates the total flux above 2 keV. A second contribution comes from
a thermal component, extended up to a radius of (~~)6' and detected only at
energies below 2keV. The spatial and spectral analysis imply the presence of a
neutron star losing energy at a rate of about (10**36 - 10**37) ergs/s. No
pulsed emission is detected and we set a limit on the pulsed fraction of 10%.
This is consistent with the lack of a radio pulsar in the remnant, which may
indicate that the pulsed emission from the rapidly rotating compact object that
should be powering the synchrotron nebula is beamed and our viewing direction
is unfavorable. In either event, the central neutron star deposits much of its
spin-down energy into the surrounding synchrotron nebula where, through direct
imaging with broadband satellites such as ASCA, it is possible to study the
energetics and evolution of the compact remnant.Comment: 30 pages, including 5 figures, Latex. To appear in ApJ (May 20, 1998
issue, Vol. 499.
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NMR spectroscopy of native and in vitro tissues implicates polyADP ribose in biomineralization.
Nuclear magnetic resonance (NMR) spectroscopy is useful to determine molecular structure in tissues grown in vitro only if their fidelity, relative to native tissue, can be established. Here, we use multidimensional NMR spectra of animal and in vitro model tissues as fingerprints of their respective molecular structures, allowing us to compare the intact tissues at atomic length scales. To obtain spectra from animal tissues, we developed a heavy mouse enriched by about 20% in the NMR-active isotopes carbon-13 and nitrogen-15. The resulting spectra allowed us to refine an in vitro model of developing bone and to probe its detailed structure. The identification of an unexpected molecule, poly(adenosine diphosphate ribose), that may be implicated in calcification of the bone matrix, illustrates the analytical power of this approach
Novel Calicivirus Identified in Rabbits, Michigan, USA
This virus is distinct from rabbit hemorrhagic disease virus
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