4,923 research outputs found
Chemical functionalization of emulsion-templated porous polymers by thiol–ene “click” chemistry
Highly porous polymers (polyHIPEs) have been prepared by the photopolymerization of high internal phase emulsions (HIPEs) with varying ratios of thiol and acrylate monomers. The resulting polymers have a nominal porosity of 80%, and are seen to have a well-defined, interconnected pore morphology, with average pore diameters ranging from 30 to 60 μm. The polyHIPE polymers have been shown using a colourimetric (Ellman's) assay to contain residual thiols which are reactive towards a range of (meth)acrylates (hexafluoroisopropyl acrylate, fluorescein O-acrylate and poly(ethylene glycol) methyl ether methacrylate). Functionalization was explored using thermally- and UV-initiated radical-mediated “click” reactions and an amine-catalysed Michael addition reaction. The extent of functionalization was investigated qualitatively and quantitatively using a range of techniques (solid state NMR spectroscopy; FTIR spectroscopy; X-ray photoelectron spectroscopy (XPS); observation of fluorescence); high levels of conversion (up to 90–95%) were observed for the thermally-initiated radical reaction and the Michael reaction
Operation and performance of the OSSE instrument
The Oriented Scintillation Spectrometer Experiment (OSSE) on the Arthur Holly Compton Gamma Ray Observatory is described. An overview of the operation and control of the instrument is given, together with a discussion of typical observing strategies used with OSSE and basic data types produced by the instrument. Some performance measures for the instrument are presented that were obtained from pre-launch and in-flight data. These include observing statistics, continuum and line sensitivity, and detector effective area and gain stability
Multi-object spectroscopy of stars in the CoRoT fields I: Early-type stars in the CoRoT-fields IRa01, LRa01, LRa02
Observations of giant stars indicate that the frequency of giant planets is
much higher for intermediate-mass stars than for solar-like stars. Up to now
all known planets of giant stars orbit at relatively far distances from their
host stars. It is not known whether intermediate-mass stars also had many
close-in planets when they were on the main sequence, which were then engulfed
when the star became a giant star. To understand the formation and evolution of
planets it is therefore important to find out whether main-sequence stars of
intermediate-mass have close-in planets or not. A survey for transiting planets
of intermediate-mass stars would be ideal to solve this question, because the
detection of transiting planets is not affected by the rapid rotation of these
stars. As a first step for an efficient survey we need to identify
intermediate-mass stars in the CoRoT-fields, which can then be used as an input
list. To compile the input list we derived the spectral types of essentially
all O, B and A stars down to 14.5 mag in the CoRoT fields IRa01, LRa01, LRa02
taken with the multi-object spectrograph AAOmega. We determined the spectral
types by comparing the spectra with template spectra from a library. In total
we identify 1856 A and B stars that have been observed with CoRoT. Given the
number of planets that have been detected in these fields amongst late-type
stars, we estimate that there are one to four transiting planets of
intermediate-mass stars waiting to be discovered. Our survey not only allows us
to carry out a dedicated planet search programme but is also essential for any
types of studies of the light curves of early-type stars in the CoRoT database.
We also show that it would be possible to extend the survey to all fields that
CoRoT has observed using photometrically determined spectral types.Comment: 57 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
Small-for-gestational age & Large-for-gestational age thresholds to predict infants at risk of adverse delivery and neonatal outcomes: are current charts adequate? An observational study from the Born in Bradford cohort
Objectives: Construct an ethnic specific chart and compare the prediction of adverse outcomes using this chart with the clinically recommended UK-WHO (United Kingdom-World Health Organization) and customised birth weight charts using cut offs for small-for-gestational age (SGA: birth weight 90th centile). Design: Prospective cohort study. Setting: Born in Bradford (BiB) study, UK. Participants: 3980 White British and 4448 Pakistani infants with complete data for gestational age, birth weight, ethnicity, maternal height, weight and parity. Main outcome measures: Prevalence of SGA and LGA, using the three charts and indicators of diagnostic utility (sensitivity, specificity and area-under-the curve (AUROC)) of these chart-specific cut-offs to predict delivery and neonatal outcomes and a composite outcome. Results: In White British and Pakistani infants, the prevalence of SGA and LGA differed depending on the chart used. Increased risk of SGA was observed when using the UK-WHO and customised charts as opposed to the ethnic-specific, whilst the opposite was apparent when classifying LGA infants. However, the predictive utility all three charts to identify adverse clinical outcomes was poor, with only the prediction of shoulder dystocia achieving an AUROC>0.62 on all three charts. Conclusion: Despite being recommended in national clinical guidelines, the UK-WHO and the customised birth weight charts perform poorly at identifying infants at risk of adverse neonatal outcomes. Being small or large may increase the risk of an adverse outcome, however size alone is not sensitive or specific enough with current detection to be useful. However, a significant amount of missing data for some of the outcomes may have limited the power needed to determine true associations
Near-monochromatic tuneable cryogenic niobium electron field emitter
Creating, manipulating, and detecting coherent electrons is at the heart of
future quantum microscopy and spectroscopy technologies. Leveraging and
specifically altering the quantum features of an electron beam source at low
temperatures can enhance its emission properties. Here, we describe electron
field emission from a monocrystalline, superconducting niobium nanotip at a
temperature of 5.9 K. The emitted electron energy spectrum reveals an
ultra-narrow distribution down to 16 meV due to tunable resonant tunneling
field emission via localized band states at a nano-protrusion's apex and a
cut-off at the sharp low-temperature Fermi-edge. This is an order of magnitude
lower than for conventional field emission electron sources. The self-focusing
geometry of the tip leads to emission in an angle of 3.7 deg, a reduced
brightness of 3.8 x 10exp8 A/(m2 sr V), and a stability of hours at 4.1 nA beam
current and 69 meV energy width. This source will decrease the impact of lens
aberration and enable new modes in low-energy electron microscopy, electron
energy loss spectroscopy, and high-resolution vibrational spectroscopy.Comment: to be published in Phys. Rev. Lett. (2022
Line-profile tomography of exoplanet transits -- II. A gas-giant planet transiting a rapidly-rotating A5 star
Most of our knowledge of extrasolar planets rests on precise radial-velocity
measurements, either for direct detection or for confirmation of the planetary
origin of photometric transit signals. This has limited our exploration of the
parameter space of exoplanet hosts to solar- and later-type, sharp-lined stars.
Here we extend the realm of stars with known planetary companions to include
hot, fast-rotating stars. Planet-like transits have previously been reported in
the lightcurve obtained by the SuperWASP survey of the A5 star HD15082
(WASP-33; V=8.3, v sin i = 86 km/sec). Here we report further photometry and
time-series spectroscopy through three separate transits, which we use to
confirm the existence of a gas giant planet with an orbital period of 1.22d in
orbit around HD15082. From the photometry and the properties of the planet
signal travelling through the spectral line profiles during the transit we
directly derive the size of the planet, the inclination and obliquity of its
orbital plane, and its retrograde orbital motion relative to the spin of the
star. This kind of analysis opens the way to studying the formation of planets
around a whole new class of young, early-type stars, hence under different
physical conditions and generally in an earlier stage of formation than in
sharp-lined late-type stars. The reflex orbital motion of the star caused by
the transiting planet is small, yielding an upper mass limit of 4.1 Jupiter
masses on the planet. We also find evidence of a third body of sub-stellar mass
in the system, which may explain the unusual orbit of the transiting planet. In
HD 15082, the stellar line profiles also show evidence of non-radial
pulsations, clearly distinct from the planetary transit signal. This raises the
intriguing possibility that tides raised by the close-in planet may excite or
amplify the pulsations in such stars.Comment: 9 pages, 6 figures, accepted for publication in MNRA
Field measurements of trace gases emitted by prescribed fires in southeastern US pine forests using an open-path FTIR system
We report trace-gas emission factors from three pine-understory prescribed
fires in South Carolina, US measured during the fall of 2011. The fires
were more intense than many prescribed burns because the fuels included
mature pine stands not subjected to prescribed fire in decades that were lit
following an extended drought. Emission factors were measured with a fixed
open-path Fourier transform infrared (OP-FTIR) system that was deployed on
the fire control lines. We compare these emission factors to those measured
with a roving, point sampling, land-based FTIR and an airborne FTIR deployed
on the same fires. We also compare to emission factors measured by a similar
OP-FTIR system deployed on savanna fires in Africa. The data suggest that
the method used to sample smoke can strongly influence the relative
abundance of the emissions that are observed. The majority of fire emissions
were lofted in the convection column and were sampled by the airborne FTIR.
The roving, ground-based, point sampling FTIR measured the contribution of
individual residual smoldering combustion fuel elements scattered throughout
the burn site. The OP-FTIR provided a ~ 30 m path-integrated
sample of emissions transported to the fixed path via complex ground-level
circulation. The OP-FTIR typically probed two distinct combustion regimes,
"flaming-like" (immediately after adjacent ignition and before the
adjacent plume achieved significant vertical development) and
"smoldering-like." These two regimes are denoted "early" and "late",
respectively. The path-integrated
sample of the ground-level smoke layer adjacent to the fire from the OP-FTIR
provided our best estimate of fire-line exposure to smoke for wildland fire
personnel. We provide a table of estimated fire-line exposures for numerous
known air toxics based on synthesizing results from several studies. Our
data suggest that peak exposures are more likely to challenge permissible
exposure limits for wildland fire personnel than shift-average (8 h)
exposures
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