8,057 research outputs found
The Formation of the Double Pulsar PSR J0737-3039A/B
Recent timing observations of the double pulsar J0737-3039A/B have shown that
its transverse velocity is extremely low, only 10 km/s, and nearly in the Plane
of the Galaxy. With this new information, we rigorously re-examine the history
and formation of this system, determining estimates of the pre-supernova
companion mass, supernova kick and misalignment angle between the pre- and
post-supernova orbital planes. We find that the progenitor to the recently
formed `B' pulsar was probably less than 2 MSun, lending credence to
suggestions that this object may not have formed in a normal supernova
involving the collapse of an iron core. At the same time, the supernova kick
was likely non-zero. A comparison to the history of the double-neutron-star
binary B1534+12 suggests a range of possible parameters for the progenitors of
these systems, which should be taken into account in future binary population
syntheses and in predictions of the rate and spatial distribution of short
gamma-ray burst events.Comment: To appear in MNRAS Letters. Title typo fix only; no change to pape
Editors' introduction: the book, the conference, and fighting back
This book makes a strong case for the abiding relevance of Dewey's notion of learning through experience, with a community of others, and what this implies for democratic 21st century education
Ionization Structure and the Reverse Shock in E0102-72
The young oxygen-rich supernova remnant E0102-72 in the Small Magellanic
Cloud has been observed with the High Energy Transmission Grating Spectrometer
of Chandra. The high resolution X-ray spectrum reveals images of the remnant in
the light of individual emission lines of oxygen, neon, magnesium and silicon.
The peak emission region for hydrogen-like ions lies at larger radial distance
from the SNR center than the corresponding helium-like ions, suggesting passage
of the ejecta through the "reverse shock". We examine models which test this
interpretation, and we discuss the implications.Comment: 4 pages, 6 figures; To appear in "Young Supernova Remnants" (11th
Annual Astrophysics Conference in Maryland), S. S. Holt & U. Hwang (eds),
AIP, New York (2001
Scapegoat: John Dewey and the character education crisis
Many conservatives, including some conservative scholars, blame the ideas and influence of John Dewey for what has frequently been called a crisis of character, a catastrophic decline in moral behavior in the schools and society of North America. Dewey’s critics claim that he is responsible for the undermining of the kinds of instruction that could lead to the development of character and the strengthening of the will, and that his educational philosophy and example exert a ubiquitous and disastrous influence on students’ conceptions of moral behavior. This article sets forth the views of some of these critics and juxtaposes them with what Dewey actually believed and wrote regarding character education. The juxtaposition demonstrates that Dewey neither called for nor exemplified the kinds of character-eroding pedagogy his critics accuse him of championing; in addition, this paper highlights the ways in which Dewey argued consistently and convincingly that the pedagogical approaches advocated by his critics are the real culprits in the decline of character and moral education
High-Resolution X-ray Spectroscopy of SNR 1987A: Chandra LETG and HETG Observations in 2007
We present an extended analysis of the deep Chandra LETG and HETG
observations of the supernova remnant 1987A (SNR 1987A) carried out in 2007.
The global fits to the grating spectra show that the temperature of the X-ray
emitting plasma in the slower shocks in this system has remained stable for the
last three years, while that in the faster shocks has decreased. This
temperature evolution is confirmed by the first light curves of strong X-ray
emission lines and their ratios. On the other hand, bulk gas velocities
inferred from the X-ray line profiles are too low to account for the post-shock
plasma temperatures inferred from spectral fits. This suggests that the X-ray
emission comes from gas that has been shocked twice, first by the blast wave
and again by shocks reflected from the inner ring of SNR 1987A. A new model
that takes these considerations into account gives support to this physical
picture.Comment: 36 pages, 10 figures, Accepted for publication in Ap
Chandra observations of SN 1987A: the soft X-ray light curve revisited
We report on the present stage of SN 1987A as observed by the Chandra X-ray
Observatory. We reanalyze published Chandra observations and add three more
epochs of Chandra data to get a consistent picture of the evolution of the
X-ray fluxes in several energy bands. We discuss the implications of several
calibration issues for Chandra data. Using the most recent Chandra calibration
files, we find that the 0.5-2.0 keV band fluxes of SN 1987A have increased by
~6 x 10 ^-13 erg s^-1 cm^-2 per year since 2009. This is in contrast with our
previous result that the 0.5-2.0 keV light curve showed a sudden flattening in
2009. Based on our new analysis, we conclude that the forward shock is still in
full interaction with the equatorial ring.Comment: Accepted for publication by ApJ, 7 pages, 5 figure
Randomised controlled trial of fish oil supplement to treat cancer cachexia
This is the protocol for a review and there is no abstract. The objectives are as follows: Our overall aim is to provide an overview of interventions for preventing falls in older people by summarising the evidence from multiple Cochrane intervention reviews that evaluate the effects (primarily, rate of falls and number of fallers) of these interventions in different populations of older people, such as those defined by setting or by specific medical conditions. Fall prevention interventions will include those in the following categories: supervised or unsupervised exercises; medication; surgery; management of urinary incontinence; fluid or nutrition therapy; psychological; environment and assistive technologies; social environment; knowledge/education interventions and any other interventions that do not fall into one of these categories (Lamb 2007). Interventions tested may belong to one category ('single' intervention), or more than one category ('multiple' and 'multifactorial' interventions)
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