37 research outputs found
Recommended from our members
Short lived radionuclide modeling from nuclear weapons test sites and nuclear power plant accidents
textNuclear accidents and weapons tests are monitored by a worldwide network of air sensors, seismic detectors and several other techniques. At the site of the incident, contaminants are distributed and can provide insight into the time of the incident and type of incident. That information can then be used to affect policy decisions or better understand health risks. In order to evaluate a post nuclear test scenario, we must better understand the background readings at potential test sites where false positive or false negative allegations are more likely (e.g. the Nevada Test Site, the Chernobyl Nuclear Power Plate, etc.) Data from these sites have been compiled and compared to high purity germanium detector background readings and activities from a hypothetical nuclear weapon test. The results indicate that the following nuclides would be the best indicator of a recent nuclear test: â¸âšSr, âšÂšY, âšâľZr, šâ°ÂłRu, š²âśSb, š²âš[superscript m]Te, šâ´âˇNd, šâľâśEu. Nuclides such as âšÂšSr or âšâˇZr have a steady state concentration due to plutonium spontaneous fission thus would not be a good indication of a recent nuclear test.Mechanical Engineerin
High energy from space
The following subject areas are covered: (1) important scientific problems for high energy astrophysics (stellar activity, the interstellar medium in galaxies, supernovae and endpoints of stellar evolution, nucleosynthesis, relativistic plasmas and matter under extreme conditions, nature of gamma-bursts, identification of black holes, active nuclei, accretion physics, large-scale structures, intracluster medium, nature of dark matter, and the X- and gamma-ray background); (2) the existing experimental programs (Advanced X-Ray Astrophysics Facility (AXAF), Gamma Ray Observatory (GRO), X-Ray Timing Explorer (XTE), High Energy Transient Experiment (HETE), U.S. participation in foreign missions, and attached Shuttle and Space Station Freedom payloads); (3) major missions for the 1990's; (4) a new program of moderate missions; (5) new opportunities for small missions; (6) technology development issues; and (7) policy issues
Two Massive, Low-Luminosity Cores Toward Infrared Dark Clouds
This article presents high-resolution interferometric mosaics in the 850
micron waveband of two massive, quiescent infrared dark clouds. The two clouds
were chosen based on their likelihood to represent environments preceding the
formation of massive stars. The brightest compact sources detected in each
cloud have masses of approximately 110 and 60 solar masses with radii < 0.1 pc,
implying mean volume densities of approximately 1 million particles per cubic
centimeter and mean column densities of about 1 gram per square centimeter.
Supplementary data show these cores to be cold and inactive. Low upper limits
to their bolometric luminosities and temperatures place them at a very early
stage of evolution while current models of massive star formation suggest they
have the potential to form massive stars.Comment: 6 pages, 5 figures. Accepted for publication by the Astrophysical
Journa
A Bow Shock Nebula Around a Compact X-Ray Source in the Supernova Remnant IC443
We present spectra and high resolution images of the hard X-ray feature along
the southern edge of the supernova remnant IC443. Data from the Chandra X-ray
Observatory reveal a comet-shaped nebula of hard emission, which contains a
softer point source at its apex. We also present 20cm, 6cm, and 3.5cm images
from the Very Large Array that clearly show the cometary nebula. Based on the
radio and X-ray morphology and spectrum, and the radio polarization properties,
we argue that this object is a synchrotron nebula powered by the compact source
that is physically associated with IC443. The spectrum of the soft point source
is adequately but not uniquely fit by a black body model (kT=0.71 +/- 0.08 keV,
L=(6.5 +/- 0.9) * 10^31 erg/s). The cometary morphology of the nebula is the
result of the supersonic motion of the neutron star (V_NS=250 +/- 50 km/s),
which causes the relativistic wind of the pulsar to terminate in a bow shock
and trail behind as a synchrotron tail. This velocity is consistent with an age
of 30,000 years for the SNR and its associated neutron star.Comment: 9 pages, 5 figures, accepted for publication in the ApJ Letter
Anti-Semitism and apostasy in Nineteenth-Century France: A response to Jonathan Helfand
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43005/1/10835_2005_Article_BF01668931.pd
Chandra ACIS Survey of M33 (ChASeM33): A First Look
We present an overview of the Chandra ACIS Survey of M33 (ChASeM33): A Deep
Survey of the Nearest Face-on Spiral Galaxy. The 1.4 Ms survey covers the
galaxy out to R \approx 18\arcmin (\approx 4 kpc). These data provide the
most intensive, high spatial resolution assessment of the X-ray source
populations available for the confused inner regions of M33. Mosaic images of
the ChASeM33 observations show several hundred individual X-ray sources as well
as soft diffuse emission from the hot interstellar medium. Bright, extended
emission surrounds the nucleus and is also seen from the giant \hii regions NGC
604 and IC 131. Fainter extended emission and numerous individual sources
appear to trace the inner spiral structure. The initial source catalog, arising
from ~2/3 of the expected survey data, includes 394 sources significant
at the confidence level or greater, down to a limiting luminosity
(absorbed) of 1.6\ergs{35} (0.35 -- 8.0 keV). The hardness ratios of the
sources separate those with soft, thermal spectra such as supernova remnants
from those with hard, non-thermal spectra such as X-ray binaries and background
active galactic nuclei. Emission extended beyond the Chandra point spread
function is evident in 23 of the 394 sources. Cross-correlation of the ChASeM33
sources against previous catalogs of X-ray sources in M33 results in matches
for the vast majority of the brighter sources and shows 28 ChASeM33 sources
within 10\arcsec of supernova remnants identified by prior optical and radio
searches. This brings the total number of such associations to 31 out of 100
known supernova remnants in M33.Comment: accepted for publication ApJS, full resolution images and complete
tables available at http://hea-www.harvard.edu/vlp_m33_public
The frankaus of London: A study in radical assimilation, 1837â1967
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43006/1/10835_2005_Article_BF01915911.pd
Common carotid intima media thickness and ankle-brachial pressure index correlate with local but not global atheroma burden:a cross sectional study using whole body magnetic resonance angiography
Common carotid intima media thickness (CIMT) and ankle brachial pressure index (ABPI) are used as surrogate marker of atherosclerosis, and have been shown to correlate with arterial stiffness, however their correlation with global atherosclerotic burden has not been previously assessed. We compare CIMT and ABPI with atheroma burden as measured by whole body magnetic resonance angiography (WB-MRA).50 patients with symptomatic peripheral arterial disease were recruited. CIMT was measured using ultrasound while rest and exercise ABPI were performed. WB-MRA was performed in a 1.5T MRI scanner using 4 volume acquisitions with a divided dose of intravenous gadolinium gadoterate meglumine (Dotarem, Guerbet, FR). The WB-MRA data was divided into 31 anatomical arterial segments with each scored according to degree of luminal narrowing: 0â=ânormal, 1â=â<50%, 2â=â50-70%, 3â=â70-99%, 4â=âvessel occlusion. The segment scores were summed and from this a standardized atheroma score was calculated.The atherosclerotic burden was high with a standardised atheroma score of 39.5Âą11. Common CIMT showed a positive correlation with the whole body atheroma score (β 0.32, pâ=â0.045), however this was due to its strong correlation with the neck and thoracic segments (β 0.42 pâ=â0.01) with no correlation with the rest of the body. ABPI correlated with the whole body atheroma score (β -0.39, pâ=â0.012), which was due to a strong correlation with the ilio-femoral vessels with no correlation with the thoracic or neck vessels. On multiple linear regression, no correlation between CIMT and global atheroma burden was present (β 0.13 pâ=â0.45), while the correlation between ABPI and atheroma burden persisted (β -0.45 pâ=â0.005).ABPI but not CIMT correlates with global atheroma burden as measured by whole body contrast enhanced magnetic resonance angiography in a population with symptomatic peripheral arterial disease. However this is primarily due to a strong correlation with ilio-femoral atheroma burden
Uphold the nuclear weapons test moratorium
The Trump administration is considering renewing nuclear weapons testing (1), a move that could increase the risk of another nuclear arms race as well as an inadvertent or intentional nuclear war. Following in the long tradition of scientists opposing nuclear weapons due to their harmful effects on both humanity and the planet (2), we ask the U.S. government to desist from plans to conduct nuclear tests.
During the Cold War, the United States conducted 1030 nuclear weapons tests, more than all other nuclear-armed nations combined (3). In 1996, the United States signed the Comprehensive Nuclear Test Ban Treaty (CTBT), agreeing not to conduct a nuclear weapons test of any yield (4). The United States has not yet ratified the CTBT but did spearhead the 2016 adoption of UN Security Council Resolution 2310, which calls upon all countries to uphold the object and purpose of the CTBT by not conducting nuclear tests (5).
Eight of the nine nuclear-armed states, including the five permanent members of the UN Security Council, have observed a moratorium on nuclear testing since 1998 (3, 4). The ninth, North Korea, responding to international pressure, stopped testing warhead detonations (as opposed to missile flights) in 2017 (6). If the United States ratified the CTBT, joining the 168 countries who have already done so (4), there is a good chance that the other holdout countries would ratify the treaty as well (7)
Uphold the nuclear weapons test moratorium
The Trump administration is considering renewing nuclear weapons testing (1), a move that could increase the risk of another nuclear arms race as well as an inadvertent or intentional nuclear war. Following in the long tradition of scientists opposing nuclear weapons due to their harmful effects on both humanity and the planet (2), we ask the U.S. government to desist from plans to conduct nuclear tests.
During the Cold War, the United States conducted 1030 nuclear weapons tests, more than all other nuclear-armed nations combined (3). In 1996, the United States signed the Comprehensive Nuclear Test Ban Treaty (CTBT), agreeing not to conduct a nuclear weapons test of any yield (4). The United States has not yet ratified the CTBT but did spearhead the 2016 adoption of UN Security Council Resolution 2310, which calls upon all countries to uphold the object and purpose of the CTBT by not conducting nuclear tests (5).
Eight of the nine nuclear-armed states, including the five permanent members of the UN Security Council, have observed a moratorium on nuclear testing since 1998 (3, 4). The ninth, North Korea, responding to international pressure, stopped testing warhead detonations (as opposed to missile flights) in 2017 (6). If the United States ratified the CTBT, joining the 168 countries who have already done so (4), there is a good chance that the other holdout countries would ratify the treaty as well (7)