8,456 research outputs found
Electronic structure and chemical bonding of nc-TiC/a-C nanocomposites
The electronic structure of nanocrystalline (nc-) TiC/amorphous C
nanocomposites has been investigated by soft x-ray absorption and emission
spectroscopy. The measured spectra at the Ti 2p and C 1s thresholds of the
nanocomposites are compared to those of Ti metal and amorphous C. The
corresponding intensities of the electronic states for the valence and
conduction bands in the nanocomposites are shown to strongly depend on the TiC
carbide grain size. An increased charge-transfer between the Ti 3d-eg states
and the C 2p states has been identified as the grain size decreases, causing an
increased ionicity of the TiC nanocrystallites. It is suggested that the
charge-transfer occurs at the interface between the nanocrystalline TiC and the
amorphous C matrix and represents an interface bonding which may be essential
for the understanding of the properties of nc-TiC/amorphous C and similar
nanocomposites.Comment: 13 pages, 6 figures, 1 table;
http://link.aps.org/doi/10.1103/PhysRevB.80.23510
Latitudinal Shear Instabilities during Type I X-ray Bursts
Coherent oscillations have been observed during Type I X-ray bursts from 14
accreting neutron stars in low mass X-ray binaries, providing important
information about their spin frequencies. However, the origin of the brightness
asymmetry on the neutron star surface producing these oscillations is still not
understood. We study the stability of a zonal shearing flow on the neutron star
surface using a shallow water model. We show that differential rotation of >2%
between pole and equator, with the equator spinning faster than the poles, is
unstable to hydrodynamic shear instabilities. The unstable eigenmodes have
properties well-matched to burst oscillations: low azimuthal wavenumber m, wave
speeds 1 or 2% below the equatorial spin rate, and e-folding times close to a
second. Instability is related to low frequency buoyantly driven r-modes that
have a mode frequency within the range of rotation frequencies in the
differentially rotating shell. We discuss the implications for burst
oscillations. Growth of shear instabilities may explain the brightness
asymmetry in the tail of X-ray bursts, although some fine tuning of the level
of differential rotation and a spin frequency near 300 Hz are required in order
for the fastest growing mode to have m=1. If shear instabilities are to operate
during a burst, temperature contrasts of 30% across the star must be created
during ignition and spreading of the flash.Comment: To appear in ApJ (12 pages, 11 figures
Relativistic Iron Lines in Galactic Black Holes: Recent Results and Lines in the ASCA Archive
Recent observations with Chandra and XMM-Newton, aided by broad-band spectral
coverage from RXTE, have revealed skewed relativistic iron emission lines in
stellar-mass Galactic black hole systems. Such systems are excellent
laboratories for testing General Relativity, and relativistic iron lines
provide an important tool for making such tests. In this contribution to the
Proceedings of the 10th Annual Marcel Grossmann Meeting on General Relativity,
we briefly review recent developments and present initial results from fits to
archival ASCA observations of Galactic black holes. It stands to reason that
relativistic effects, if real, should be revealed in many systems (rather than
just one or two); the results of our archival work have borne-out this
expectation. The ASCA spectra reveal skewed, relativistic lines in XTE
J1550-564, GRO J1655-40, GRS 1915+105, and Cygnus X-1.Comment: to appear in the proc. of the 10th Annual Marcel Grossmann Meeting on
General Relativity, 5 pages, 1 figure, uses specific .cls and .sty file
Snakebite: An Exploratory Cost-Effectiveness Analysis of Adjunct Treatment Strategies.
The cost-effectiveness of the standard of care for snakebite treatment, antivenom, and supportive care has been established in various settings. In this study, based on data from South Indian private health-care providers, we address an additional question: "For what cost and effectiveness values would adding adjunct-based treatment strategies to the standard of care for venomous snakebites be cost-effective?" We modeled the cost and performance of potential interventions (e.g., pharmacologic or preventive) used adjunctively with antivenom and supportive care for the treatment of snakebite. Because these potential interventions are theoretical, we used a threshold cost-effectiveness approach to explore this forward-looking concept. We examined economic parameters at which these interventions could be cost-effective or even cost saving. A threshold analysis was used to examine the addition of new interventions to the standard of care. Incremental cost-effectiveness ratios were used to compare treatment strategies. One-way, scenario, and probabilistic sensitivity analyses were conducted to analyze parameter uncertainty and define cost and effectiveness thresholds. Our results suggest that even a 3% reduction in severe cases due to an adjunct strategy is likely to reduce the cost of overall treatment and have the greatest impact on cost-effectiveness. In this model, for example, an investment of 75 per individual. These findings illustrate the striking degree to which an adjunct intervention could improve patient outcomes and be cost-effective or even cost saving
Transformer Oil Passivation and Impact of Corrosive Sulphur
In recent years a significant volume of research has been undertaken in order to understand the recent failures in oil insulated power apparatus due to deposition of copper sulphide on the conductors and in the insulation paper. Dibenzyl Disulfide (DBDS) has been found to be the leading corrosive sulphur compound in the insulation oil [1]. The process of copper sulphide formation and the deposition in the paper is still being investigated, but a recently proposed method seems to be gaining some confidence [1]. This method suggests a two-step process; initially the DBDS and some oil soluble copper complexes are formed. Secondly the copper complexes are absorbed in the paper insulation, where they then decompose into copper sulphide [2]. The most commonly used mitigating technique for corrosive sulphur contaminated oil is passivation, normally using Irgamet 39 or 1, 2, 3-benzotriazole (BTA). The passivator is diluted into the oil to a concentration of around 100ppm, where it then reacts with the copper conductors to form a complex layer around the copper, preventing it from interacting with DBDS compounds and forming copper sulphide. This research project will investigate the electrical properties of HV transformers which have tested positive for corrosive sulphur, and the evolution of those properties as the asset degrades due to sulphur corrosion. Parallel to this the long term properties of transformers with passivated insulation oil will be analysed in order to understand the passivator stability and whether it is necessary to keep adding the passivator to sustain its performance. Condition monitoring techniques under investigation will include dielectric spectroscopy, frequency response analysis, recovery voltage method (aka interfacial polarisation) amongst others. Partial discharge techniques will not be investigated, as the voltage between the coil plates is low and therefore it will not contribute significantly to the overall insulation breakdown, in corrosive oil related faults [3]. The goal of this research is to establish key electrical properties in both passivated and non-passivated power transformers that demonstrate detectable changes as the equipment degrades due to the insulation oil being corrosive
The development of a new measure of quality of life for children with congenital cardiac disease
The purpose of the study was to develop a questionnaire measuring health-related R1 quality of life for children and adolescents with congenital heart disease, the ConQol, that would have both clinical and research applications. We describe here the process of construction of a questionnaire, the piloting and the development of a weighted scoring system, and data on the psychometric performance of the measure in a sample of 640 children and young people recruited via 6 regional centres for paediatric cardiology from across the United Kingdom. The ConQol has two versions, one designed for children aged from 8 to 11 years, and the other for young people aged from 12 to 16 years. Initial findings suggest that it is a valid and reliable instrument, is acceptable to respondents, and is simple to administer in both a research and clinical context
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