12,639 research outputs found
Graphite/polyimide laminates with near-zero thermal expansion
Composite structures can be laminated to have very low coefficients of thermal expansion. Such structures are light and strong and have many uses where expansion or contraction with temperature change is undesirable. One application is with instruments that measure thermal expansion
Remote Monitoring of Implantable Cardioverter Defibrillator
The rate of implantable cardioverter defibrillator (ICD) implantation has gone up as primary and secondary prevention trials have relatively consistently shown significant improvement in mortality and morbidity. Most patients with ICDs are followed routinely at intervals ranging from 3 to 6 months. Many patients require additional non-scheduled visits to investigate symptoms that may or may not relate to their cardiac disease or device. Appropriate and inappropriate therapies of implantable cardioverter defibrillators have a major impact on morbidity and quality of life in ICD recipients. Remote monitoring systems can substitute for routine follow-up visits and/ or deliver continuous diagnostic and device status information. Remote monitoring of ICDs can decrease the need for many patient visits and, thereby, probably reduce expense
A powerful and highly variable off-nuclear X-ray source in the composite starburst/Seyfert 2 galaxy NGC 4945
We report on a powerful and variable off-nuclear X-ray source in the nearby
spiral galaxy NGC 4945. Two ROSAT PSPC observations show the source to brighten
in 0.5--2.0 keV flux by a factor of about 9 on a time-scale of 11 months or
less. It is seen by ASCA about one month after the second PSPC pointing, and is
seen to have dimmed by a factor of > 7 in a ROSAT HRI pointing about one year
after the second PSPC pointing. Its maximum observed 0.8--2.5 keV luminosity is
about 8E38 erg/s, making it brighter than any known persistent X-ray binary in
the Milky Way. Its total X-ray luminosity is probably larger than 1.2E39 erg/s.
The observed variability argues against a superbubble interpretation, and the
off-nuclear position argues against a low-luminosity active galactic nucleus.
The source is therefore probably either an ultra-powerful X-ray binary or an
ultra-powerful supernova remnant. Optical monitoring has not identified any
supernovae in NGC 4945 during the time of the X-ray observations, and any
supernova would have had to have been either very highly absorbed or
intrinsically optically faint.Comment: 5 pages, uuencoded compressed tar file, MNRAS in pres
Microfocus Radiography
I should emphasize that what I am going to talk about is really the result of a very brief program which was funded at Harwell by David Godfrey of AMTE, who is probably well-known to ceramic practitioners here. We were very glad to have this contact because it gave us access to the TTCP specimens which were prepared in this country; specimens, in particular, of silicon nitride tiles containing seeded defects, which many of you have studied by various techniques
Scalar entrainment in the mixing layer
New definitions of entrainment and mixing based on the passive scalar field in the plane mixing layer are proposed. The definitions distinguish clearly between three fluid states: (1) unmixed fluid, (2) fluid engulfed in the mixing layer, trapped between two scalar contours, and (3) mixed fluid. The difference betwen (2) and (3) is the amount of fluid which has been engulfed during the pairing process, but has not yet mixed. Trends are identified from direct numerical simulations and extensions to high Reynolds number mixing layers are made in terms of the Broadwell-Breidenthal mixing model. In the limit of high Peclet number (Pe = ReSc) it is speculated that engulfed fluid rises in steps associated with pairings, introducing unmixed fluid into the large scale structures, where it is eventually mixed at the Kolmogorov scale. From this viewpoint, pairing is a prerequisite for mixing in the turbulent plane mixing layer
An RXTE Observation of the Seyfert 1 Galaxy MCG-6-30-15 : X-ray Reflection and the Iron Abundance
We report on a 50 ks observation of the bright Seyfert 1 galaxy MCG--6-30-15
with the Rossi X-ray Timing Explorer. The data clearly show the broad
fluorescent iron line (equivalent width ~ 250 eV), and the Compton reflection
continuum at higher energies. A comparison of the iron line and the reflection
continuum has enabled us to constrain reflective fraction and the elemental
abundances in the accretion disk. Temporal studies provide evidence that
spectral variability is due to changes in both the amount of reflection seen
and the properties of the primary X-ray source itself.Comment: 6 pages, Late
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