1,562 research outputs found
Evaluation of present thermal barrier coatings for potential service in electric utility gas turbines
The resistance of present-day thermal barrier coatings to combustion gases found in electric utility turbines was assessed. The plasma sprayed coatings, both duplex and graded types, were primarily zirconia-based, although a calcium silicate was also evaluated. Both atmospheric burner rig tests and high pressure tests (135 psig) showed that several present-day thermal barrier coatings have a high potential for service in gas turbines burning the relatively clean GT No. 2 fuel. However, coating improvements are needed for use in turbines burning lower grade fuel such as residual oil. The duplex ZrO2.8Y2O3/NiCrA1Y coating was ranked highest and selected for near-term field testing, with Ca2SiO4/NiCrA1Y ranked second. Graded coatings show potential for corrosive turbine operating conditions and warrant further development. The coating degradation mechanisms for each coating system subjected to the various environmental conditions are also described
Advanced ceramic coating development for industrial/utility gas turbine applications
The effects of ceramic coatings on the lifetimes of metal turbine components and on the performance of a utility turbine, as well as of the turbine operational cycle on the ceramic coatings were determined. When operating the turbine under conditions of constant cooling flow, the first row blades run 55K cooler, and as a result, have 10 times the creep rupture life, 10 times the low cycle fatigue life and twice the corrosion life with only slight decreases in both specific power and efficiency. When operating the turbine at constant metal temperature and reduced cooling flow, both specific power and efficiency increases, with no change in component lifetime. The most severe thermal transient of the turbine causes the coating bond stresses to approach 60% of the bond strengths. Ceramic coating failures was studied. Analytic models based on fracture mechanics theories, combined with measured properties quantitatively assessed both single and multiple thermal cycle failures which allowed the prediction of coating lifetime. Qualitative models for corrosion failures are also presented
A study of atmospheric neutrinos with the IMB detector
A sample of 401 contained neutrino interactions collected in the 3300 metric ton fiducial mass IMB detector was used to study neutrino oscillations, geomagnetic modulation of the flux and to search for point sources. The majority of these events are attributed to neutrino interactions. For the most part, these neutrinos are believed to originate as tertiary products of cosmic ray interactions in the atmosphere. The neutrinos are a mixture of v sub e and v sub micron
Gravitational Radiation from Triple Star Systems
We have studied the main features of the gravitational radiation generated by
an astrophysical system constituted of three compact objects attracting one
another (only via gravitational interaction) in such a manner that stable
orbits do exist. We have limited our analysis to systems that can be treated
with perturbative methods. We show the profile of the gravitational waves
emitted by such systems. These results can be useful within the framework of
the new gravitational astronomy which will be made feasible by means of the new
generation of gravitational detectors such as LISA in a no longer far future.Comment: 10 pages plus 9 postscript figures; revtex; accepted for publication
in Int. J. Mod. Phys.
Ultra-Transparent Antarctic Ice as a Supernova Detector
We have simulated the response of a high energy neutrino telescope in deep
Antarctic ice to the stream of low energy neutrinos produced by a supernova.
The passage of a large flux of MeV-energy neutrinos during a period of seconds
will be detected as an excess of single counting rates in all individual
optical modules. We update here a previous estimate of the performance of such
an instrument taking into account the recent discovery of absorption lengths of
several hundred meters for near-UV photons in natural deep ice. The existing
AMANDA detector can, even by the most conservative estimates, act as a galactic
supernova watch.Comment: 9 pages, Revtex file, no figures. Postscript file also available from
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-888.ps.Z or from
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-888.ps.
Guidelines for the Management of Severe Traumatic Brain Injury: 2020 Update of the Decompressive Craniectomy Recommendations
© Congress of Neurological Surgeons 2020. When the fourth edition of the Brain Trauma Foundation\u27s Guidelines for the Management of Severe Traumatic Brain Injury were finalized in late 2016, it was known that the results of the RESCUEicp (Trial of Decompressive Craniectomy for Traumatic Intracranial Hypertension) randomized controlled trial of decompressive craniectomy would be public after the guidelines were released. The guideline authors decided to proceed with publication but to update the decompressive craniectomy recommendations later in the spirit of living guidelines, whereby topics are updated more frequently, and between new editions, when important new evidence is published. The update to the decompressive craniectomy chapter presented here integrates the findings of the RESCUEicp study as well as the recently published 12-mo outcome data from the DECRA (Decompressive Craniectomy in Patients With Severe Traumatic Brain Injury) trial. Incorporation of these publications into the body of evidence led to the generation of 3 new level-IIA recommendations; a fourth previously presented level-IIA recommendation remains valid and has been restated. To increase the utility of the recommendations, we added a new section entitled Incorporating the Evidence into Practice. This summary of expert opinion provides important context and addresses key issues for practitioners, which are intended to help the clinician utilize the available evidence and these recommendations. The full guideline can be found at: https://braintrauma.org/guidelines/guidelines-for-the-management-of-severe-tbi-4th-ed#/
Resonant Spin-Flavor Conversion of Supernova Neutrinos and Deformation of the Electron Antineutrino Spectrum
The neutrino spin-flavor conversion of \bar\nu_e and \nu_\mu which is induced
by the interaction of the Majorana neutrino magnetic moment and magnetic fields
in the collapse-driven supernova is investigated in detail. We calculate the
conversion probability by using the latest precollapse models of Woosley and
Weaver (1995), and also those of Nomono and Hashimoto (1988), changing the
stellar mass and metallicity in order to estimate the effect of the
astrophysical uncertainties. Contour maps of the conversion probability are
given for all the models as a function of neutrino mass squared difference and
the neutrino magnetic moment times magnetic fields. It is shown that in the
solar metallicity models some observational effects are expected with \Delta
m^2 = 10^{-5}--10^{-1} [eV^2] and \mu_\nu >~ 10^{-12} (10^9 G / B_0) [\mu_B],
where B_0 is the strength of the magnetic fields at the surface of the iron
core. We also find that although the dependence on the stellar models or
stellar mass is not so large, the metallicity of precollapse stars has
considerable effects on this conversion. Such effects may be seen in a
supernova in the Large or Small Magellanic Clouds, and should be taken into
account when one considers an upper bound on \mu_\nu from the SN1987A data.Comment: 19 pages, LaTeX, using revtex. To appear in Phys. Rev. D. 16 figures
attatche
Gravity Wave and Neutrino Bursts from Stellar Collapse: A Sensitive Test of Neutrino Masses
New methods are proposed with the goal to determine absolute neutrino masses
from the simultaneous observation of the bursts of neutrinos and gravitational
waves emitted during a stellar collapse. It is shown that the neutronization
electron neutrino flash and the maximum amplitude of the gravitational wave
signal are tightly synchronized with the bounce occuring at the end of the core
collapse on a timescale better than 1 ms. The existing underground neutrino
detectors (SuperKamiokande, SNO, ...) and the gravity wave antennas soon to
operate (LIGO, Virgo, ...) are well matched in their performance for detecting
galactic supernovae and for making use of the proposed approach. Several
methods are described, which apply to the different scenarios depending on
neutrino mixing. Given the present knowledge on neutrino oscillations, the
methods proposed are sensitive to a mass range where neutrinos would
essentially be mass-degenerate. The 95 % C.L. upper limit which can be achieved
varies from 0.75 eV/c2 for large electron neutrino survival probabilities to
1.1 eV/c2 when in practice all electron neutrinos convert into muon or tau
neutrinos. The sensitivity is nearly independent of the supernova distance.Comment: 17 pages, 4 figure
Neutrino Oscillations and the Supernova 1987A Signal
We study the impact of neutrino oscillations on the interpretation of the
supernova (SN) 1987A neutrino signal by means of a maximum-likelihood analysis.
We focus on oscillations between with or
with those mixing parameters that would solve the solar
neutrino problem. For the small-angle MSW solution (, ), there are no
significant oscillation effects on the Kelvin-Helmholtz cooling signal; we
confirm previous best-fit values for the neutron-star binding energy and
average spectral temperature. There is only marginal overlap
between the upper end of the 95.4\% CL inferred range of and the lower end of the range of theoretical
predictions. Any admixture of the stiffer spectrum by
oscillations aggravates the conflict between experimentally inferred and
theoretically predicted spectral properties. For mixing parameters in the
neighborhood of the large-angle MSW solution (, ) the oscillations in the SN are adiabatic,
but one needs to include the regeneration effect in the Earth which causes the
Kamiokande and IMB detectors to observe different spectra. For
the solar vacuum solution (,
) the oscillations in the SN are nonadiabatic; vacuum
oscillations take place between the SN and the detector. If either of the
large-angle solutions were borne out by the upcoming round of solar neutrino
experiments, one would have to conclude that the SN~1987A
and/or spectra had been much softer than predicted by currentComment: Final version with very minor wording changes, to be published in
Phys. Rev.
Screening of Long-Range Leptonic Forces by Cosmic Background Neutrinos
The absence of dispersion effects of the SN~1987A neutrino pulse has been
used to constrain novel long-range forces between neutrinos and galactic
baryonic or non-baryonic matter. If these forces are mediated by vector bosons,
screening effects by the cosmic neutrino background invalidate the SN~1987A
limits and other related arguments.Comment: REVTeX 3.0 document, 6 pages, no figures
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