240 research outputs found
Profesjonaliseringen av dykkergruppa/ingeniørbataljonen : i hvilken grad har profesjonaliseringen av dykkergruppa vært vellykket med tanke på å utvikle, øke og beholde kompetanse?
Bachelor i militære studier; ledelse og landmak
Organizing the Carotid Revascularization Endarterectomy versus Stenting Trial (CREST): National Institutes of Health, Health Care Financing Administration, and industry funding
The Carotid Revascularization Endarterectomy versus Stenting Trial (CREST) is a prospective, randomized, multicenter clinical trial of carotid endarterectomy (CEA) versus carotid artery stenting (CAS) as prevention for stroke in patients with symptomatic stenosis greater than or equal to 50%. CREST is sponsored by the US National Institute of Neurological Disorders and Stroke (NINDS) of the US National Institutes of Health (NIH), with additional support by a device manufacturer, and will provide data to the US Food and Drug Administration (FDA) for evaluation of a stent device. Because of budget constraints for CREST, Health Care Financing Administration (HCFA) reimbursement for hospital costs incurred by CREST patients will be essential. The involvement of academic scientists, industry, and three separate government agencies (NIH, FDA, HCFA) has presented many challenges in conducting the trial. A review of the pathways followed to meet these challenges may be helpful to others seeking to facilitate sharing of the costs and burdens of conducting innovative clinical research
Critical fields and growth rates of the Tayler instability as probed by a columnar gallium experiment
Many astrophysical phenomena (such as the slow rotation of neutron stars or
the rigid rotation of the solar core) can be explained by the action of the
Tayler instability of toroidal magnetic fields in the radiative zones of stars.
In order to place the theory of this instability on a safe fundament it has
been realized in a laboratory experiment measuring the critical field strength,
the growth rates as well as the shape of the supercritical modes. A strong
electrical current flows through a liquid-metal confined in a resting columnar
container with an insulating outer cylinder. As the very small magnetic Prandtl
number of the gallium-indium-tin alloy does not influence the critical Hartmann
number of the field amplitudes, the electric currents for marginal instability
can also be computed with direct numerical simulations. The results of this
theoretical concept are confirmed by the experiment. Also the predicted growth
rates of the order of minutes for the nonaxisymmetric perturbations are
certified by the measurements. That they do not directly depend on the size of
the experiment is shown as a consequence of the weakness of the applied fields
and the absence of rotation.Comment: 8 pages, 5 figures, accepted by Ap
Disk Evolution in OB Associations - Deep Spitzer/IRAC Observations of IC 1795
We present a deep Spitzer/IRAC survey of the OB association IC 1795 carried
out to investigate the evolution of protoplanetary disks in regions of massive
star formation. Combining Spitzer/IRAC data with Chandra/ACIS observations, we
find 289 cluster members. An additional 340 sources with an infrared excess,
but without X-ray counterpart, are classified as cluster member candidates.
Both surveys are complete down to stellar masses of about 1 Msun. We present
pre-main sequence isochrones computed for the first time in the Spitzer/IRAC
colors. The age of the cluster, determined via the location of the Class III
sources in the [3.6]-[4.5]/[3.6] color-magnitude diagram, is in the range of 3
- 5 Myr. As theoretically expected, we do not find any systematic variation in
the spatial distribution of disks within 0.6 pc of either O-type star in the
association. However, the disk fraction in IC 1795 does depend on the stellar
mass: sources with masses >2 Msun have a disk fraction of ~20%, while lower
mass objects (2-0.8 Msun) have a disk fraction of ~50%. This implies that disks
around massive stars have a shorter dissipation timescale.Comment: Accepted for publication in Ap
The Extended Environment of M17: A Star Formation History
M17 is one of the youngest and most massive nearby star-formation regions in
the Galaxy. It features a bright H II region erupting as a blister from the
side of a giant molecular cloud (GMC). Combining photometry from the Spitzer
GLIMPSE survey with complementary infrared (IR) surveys, we identify candidate
young stellar objects (YSOs) throughout a 1.5 deg x 1 deg field that includes
the M17 complex. The long sightline through the Galaxy behind M17 creates
significant contamination in our YSO sample from unassociated sources with
similar IR colors. Removing contaminants, we produce a highly-reliable catalog
of 96 candidate YSOs with a high probability of association with the M17
complex. We fit model spectral energy distributions to these sources and
constrain their physical properties. Extrapolating the mass function of 62
intermediate-mass YSOs (M >3 Msun), we estimate that >1000 stars are in the
process of forming in the extended outer regions of M17.
From IR survey images from IRAS and GLIMPSE, we find that M17 lies on the rim
of a large shell structure ~0.5 deg in diameter (~20 pc at 2.1 kpc). We present
new maps of CO and 13CO (J=2-1) emission, which show that the shell is a
coherent, kinematic structure associated with M17 at v = 19 km/s. The shell is
an extended bubble outlining the photodissociation region of a faint, diffuse H
II region several Myr old. We provide evidence that massive star formation has
been triggered by the expansion of the bubble. The formation of the massive
cluster ionizing the M17 H II region itself may have been similarly triggered.
We conclude that the star formation history in the extended environment of M17
has been punctuated by successive waves of massive star formation propagating
through a GMC complex.Comment: 31 pages, 15 figures, accepted for publication in ApJ. For a version
with higher-quality figures, see
http://www.astro.wisc.edu/glimpse/Povich2009_M17.pd
Rotation and Internal Structure of Population III Protostars
We analyze the cosmological simulations performed in the recent work of Greif
et al. (2012), which followed the early growth and merger history of Pop III
stars while resolving scales as small as 0.05 R_sol. This is the first set of
cosmological simulations to self-consistently resolve the rotation and internal
structure of Pop III protostars. We find that Pop III stars form under
significant rotational support which is maintained for the duration of the
simulations. The protostellar surfaces spin from ~50% to nearly 100% of
Keplerian rotational velocity. These rotation rates persist after experiencing
multiple stellar merger events. In the brief time period simulated (~ 10 yr),
the protostars show little indication of convective instability, and their
properties furthermore show little correlation with the properties of their
host minihaloes. If Pop III protostars within this range of environments
generally form with high degrees of rotational support, and if this rotational
support is maintained for a sufficient amount of time, this has a number of
crucial implications for Pop III evolution and nucleosynthesis, as well as the
possibility for Pop III pair-instability supernovae, and the question of
whether the first stars produced gamma-ray bursts.Comment: 19 pages, 12 figures, to appear in MNRA
Early Endarterectomy Carries a Lower Procedural Risk Than Early Stenting in Patients With Symptomatic Stenosis of the Internal Carotid Artery: Results From 4 Randomized Controlled Trials.
BACKGROUND AND PURPOSE: Patients undergoing carotid endarterectomy (CEA) for symptomatic stenosis of the internal carotid artery benefit from early intervention. Heterogeneous data are available on the influence of timing of carotid artery stenting (CAS) on procedural risk. METHODS: We investigated the association between timing of treatment (0-7 days and >7 days after the qualifying neurological event) and the 30-day risk of stroke or death after CAS or CEA in a pooled analysis of individual patient data from 4 randomized trials by the Carotid Stenosis Trialists' Collaboration. Analyses were done per protocol. To obtain combined estimates, logistic mixed models were applied. RESULTS: Among a total of 4138 patients, a minority received their allocated treatment within 7 days after symptom onset (14% CAS versus 11% CEA). Among patients treated within 1 week of symptoms, those treated by CAS had a higher risk of stroke or death compared with those treated with CEA: 8.3% versus 1.3%, risk ratio, 6.7; 95% confidence interval, 2.1 to 21.9 (adjusted for age at treatment, sex, and type of qualifying event). For interventions after 1 week, CAS was also more hazardous than CEA: 7.1% versus 3.6%, adjusted risk ratio, 2.0; 95% confidence interval, 1.5 to 2.7 (P value for interaction with time interval 0.06). CONCLUSIONS: In randomized trials comparing stenting with CEA for symptomatic carotid artery stenosis, CAS was associated with a substantially higher periprocedural risk during the first 7 days after the onset of symptoms. Early surgery is safer than stenting for preventing future stroke. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00190398; URL: http://www.controlled-trials.com. Unique identifier: ISRCTN57874028; Unique identifier: ISRCTN25337470; URL: http://www.clinicaltrials.gov. Unique identifier: NCT00004732
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