6,986 research outputs found
Flame resistant elastomeric polymer development
Elastomeric products were developed for use in the space shuttle program, and investigations were conducted to improve the properties of elastomers developed in previous programs, and to evaluate the possibility of using lower-cost general purpose polymers. Products were fabricated and processed on conventional processing equipment; these products include: foams based on fluorinated rubber flame-retarded compounds with a density of 20-30 pounds/cubic foot for use as padding and in helmets; foams based on urethane for use in instrument packaging in the space shuttle; flexible and semi-rigid films of fluorinated rubber and neoprene compounds that would not burn in a 70% nitrogen, 30% oxygen atmosphere, and in a 30% nitrogen, 70% oxygen atmosphere, respectively for use in packaging or in laminates; coated fabrics which used both nylon and Kelvar fabric substrates, coated with either fluorinated or neoprene polymer compositions to meet specific levels of flame retardancy; and other flame-resistant materials
Flame retardant spandex type polyurethanes
Flame retardant elastomeric compositions were developed, comprised of: (1) spandex type polyurethane having incorporated into the polymer chain, halogen containing polyols; (2) conventional spandex type polyurethanes in physical admixture flame retardant additives; and (3) fluoroelastomeric resins in physical admixture with flame retardant additives. Methods of preparing fibers of the flame retardant elastomeric materials are presented and articles of manufacture comprised of the elastomeric materials are mentioned
Flame resistant elastic elastomeric fiber
Compositions exhibit elastomeric properties and possess various degrees of flame resistance. First material polyurethane, incorporates halogen containing polyol and is flame resistant in air; second contains spandex elastomer with flame retardant additives; and third material is prepared from fluorelastomer composition of copolymer of vinylidene fluoride and hexafluoropropylene
Non-flammable elastomeric fiber from a fluorinated elastomer and containing an halogenated flame retardant
Flame retardant elastomeric compositions are described comprised of either spandex type polyurethane having incorporated into the polymer chain halogen containing polyols, conventional spandex type polyurethanes in physical admixture with flame retardant additives, or fluoroelastomeric resins in physical admixture with flame retardant additives. Methods are described for preparing fibers of the flame retardant elastomeric materials and articles of manufacture comprised of the flame retardant clastomeric materials and non elastic materials such as polybenzimidazoles, fiberglass, nylons, etc
Amplitude variability in satellite photometry of the non-radially pulsating O9.5V star zeta Oph
We report a time-series analysis of satellite photometry of the non-radially
pulsating Oe star zeta Oph, principally using data from SMEI obtained
2003--2008, but augmented with MOST and WIRE results. Amplitudes of the
strongest photometric signals, at 5.18, 2.96, and 2.67/d, each vary
independently over the 6-year monitoring period (from ca. 30 to <2 mmag at
5.18/d), on timescales of hundreds of days. Signals at 7.19/d and 5.18/d have
persisted (or recurred) for around two decades. Supplementary spectroscopic
observations show an H-alpha emission episode in 2006; this coincided with
small increases in amplitudes of the three strongest photometric signals.Comment: MNRAS, in pres
A detailed X-ray investigation of zeta Puppis IV. Further characterization of the variability
Previously, the X-ray emission of zeta Puppis was found to be variable with
light curves harbouring "trends" with a typical timescale longer than the
exposure length. The origin of these changes was proposed to be linked to
large-scale structures in the wind, but further characterization of the
variability at high energies was needed. Since then, a number of new X-ray
observations have become available. Furthermore, a cyclic behaviour with a
1.78d period was identified in long optical photometric runs, which is thought
to be associated with the launching mechanism of large-scale wind structures.
We analysed these new X-ray data, revisited the old data, and compared X-ray
with optical data, including when simultaneous. We found that the behaviour in
X-rays cannot be explained in terms of a perfect clock because the amplitude
and shape of its variations change with time. For example, zeta Puppis was much
more strongly variable between 2007 and 2011 than before and after this
interval. Comparing the X-ray spectra of the star at maximum and minimum
brightness yields no compelling difference beyond the overall flux change: the
temperatures, absorptions, and line shapes seem to remain constant, well within
errors. The only common feature between X-ray datasets is that the variation
amplitudes appear maximum in the medium (0.6-1.2keV) energy band. Finally, no
clear and coherent correlation can be found between simultaneous X-ray and
optical data. Only a subgroup of observations may be combined coherently with
the optical period of 1.78d, although the simultaneous optical behaviour is
unknown. The currently available data do not reveal any obvious, permanent, and
direct correlation between X-ray and optical variations. The origin of the
X-ray variability therefore still needs to be ascertained, highlighting the
need for long-term monitoring in multiwavelengths, i.e. X-ray, UV, and optical.Comment: accepted for publication by A&
Surface abundances of ON stars
Massive stars burn hydrogen through the CNO cycle during most of their
evolution. When mixing is efficient, or when mass transfer in binary systems
happens, chemically processed material is observed at the surface of O and B
stars. ON stars show stronger lines of nitrogen than morphologically normal
counterparts. Whether this corresponds to the presence of material processed
through the CNO cycle or not is not known. Our goal is to answer this question.
We perform a spectroscopic analysis of a sample of ON stars with atmosphere
models. We determine the fundamental parameters as well as the He, C, N, and O
surface abundances. We also measure the projected rotational velocities. We
compare the properties of the ON stars to those of normal O stars. We show that
ON stars are usually helium-rich. Their CNO surface abundances are fully
consistent with predictions of nucleosynthesis. ON stars are more chemically
evolved and rotate - on average - faster than normal O stars. Evolutionary
models including rotation cannot account for the extreme enrichment observed
among ON main sequence stars. Some ON stars are members of binary systems, but
others are single stars as indicated by stable radial velocities. Hence, mass
transfer is not a simple explanation for the observed chemical properties. We
conclude that ON stars show extreme chemical enrichment at their surface,
consistent with nucleosynthesis through the CNO cycle. Its origin is not clear
at present.Comment: 18 pages, 10 figures (+ appendix). A&A accepte
Recommended from our members
Development of an Integrated Governance Strategy for the Voluntary and Community Sector
This report on governance provides a framework for thinking about how policy makers, funders,regulators and advisers can all work with Board members and staff to enhance the effectiveness of nonprofit organisations. It was commissioned by the Active Community Unit (ACU) of the Home Office, in parallel with other reviews designed to improve the capacity of the voluntary and community sector, at a time when the sector plays an increasingly important role in the delivery of services using public funds. That role has recently been investigated in two Government reports, the Cross Cutting Review carried out by the Treasury, and the Strategy Unit review of charities and nonprofits. Our report proposes actions of three types: some that can be taken immediately, some that require further discussion with key interests, and some integration with the other ACU reviews. Taken together they provide the starting point for an evolving strategy to improve governance across the sector. We recommend ACU chairs a group charged with the responsibility for planning and implementing this. Our focus is on governance as 'the systems and processes concerned with ensuring the overall direction, supervision and accountability of an organisation'. This is often taken to mean the way that a Board, management committee or other governing body steers the overall development of an organisation, where day-to-day management is in the hands of staff or volunteers. Sometimes, of course, the committee and volunteers are the same. They – like all governing bodies – have to balance the interests of the organisation and those they are trying to serve, while being conscious of financial and legal responsibilities, and the requirements of funders and other supporters
Effects of Metallicity on the Rotation Rates of Massive Stars
Recent theoretical predictions for low metallicity massive stars predict that
these stars should have drastically reduced equatorial winds (mass loss) while
on the main sequence, and as such should retain most of their angular momentum.
Observations of both the Be/(B+Be) ratio and the blue-to-red supergiant ratio
appear to have a metallicity dependence that may be caused by high rotational
velocities. We have analyzed 39 archival Hubble Space Telescope Imaging
Spectrograph (STIS), high resolution, ultraviolet spectra of O-type stars in
the Magellanic Clouds to determine their projected rotational velocities V sin
i. Our methodology is based on a previous study of the projected rotational
velocities of Galactic O-type stars using International Ultraviolet Explorer
(IUE) Short Wavelength Prime (SWP) Camera high dispersion spectra, which
resulted in a catalog of V sin i values for 177 O stars. Here we present
complementary V sin i values for 21 Large Magellanic Cloud and 22 Small
Magellanic Cloud O-type stars based on STIS and IUE UV spectroscopy. The
distribution of V sin i values for O type stars in the Magellanic Clouds is
compared to that of Galactic O type stars. Despite the theoretical predictions
and indirect observational evidence for high rotation, the O type stars in the
Magellanic Clouds do not appear to rotate faster than their Galactic
counterparts.Comment: accepted by ApJ, to appear 20 December 2004 editio
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