1,346 research outputs found
Economics of zoonoses surveillance in a ‘One Health’ context: an assessment of Campylobacter surveillance in Switzerland
A Simple, Quick, and Precise Procedure for the Determination of Water in Organic Solvents
A procedure for the UV/VIS-spectroscopic determination of water by the use of a solvatochromic pyridiniumphenolate betaine is given. The water content of organic solvents is calculated by a two parameter equation from λmax of the dye. A typical, detection limit is of the order of 1 mg in 1 ml solvent for routine spectrometers. The parameters for the determination of water are given for a number of commonly used solvents
Resolution of Corneal Fibrosis After Descemet's Stripping Automated Endothelial Keratoplasty: A Case Report.
To report the resolution of anterior corneal fibrosis after Descemet's stripping automated endothelial keratoplasty (DSAEK), in a patient with chronic corneal edema and anterior stromal scarring.
A 63-year-old woman, with a history of Fuchs endothelial dystrophy, presented with increasing discomfort and gradual visual loss in her right eye. Clinical examination revealed long-standing bullous keratopathy accompanied by marked subepithelial fibrosis (SEF). Based on the low postoperative visual potential due to glaucomatous optic neuropathy, we decided to proceed with DSAEK.
During the follow-up period, SEF was found to gradually resolve. Corneal clarity was restored and an improvement in visual acuity was observed up to 12 months after surgery.
DSAEK alone may represent an effective therapeutic option for the restoration of impaired corneal clarity in patients with long-standing corneal edema and concomitant anterior subepithelial scarring
The Neon Abundance of Galactic Wolf-Rayet Stars
The fast, dense winds which characterize Wolf-Rayet (WR) stars obscure
their underlying cores, and complicate the verification of evolving
core and nucleosynthesis models. Core evolution can be probed by
measuring abundances of wind-borne nuclear processed elements,
partially overcoming this limitation. Using ground-based mid-infrared
spectroscopy and the 12.81um [NeII] emission line measured in
four Galactic WR stars, we estimate neon abundances and compare to
long-standing predictions from evolved-core models. For the WC star
WR121, this abundance is found to be >~11x the cosmic
value, in good agreement with predictions. For the three less-evolved
WN stars, little neon enhancement above cosmic values is measured, as
expected. We discuss the impact of clumping in WR winds on this
measurement, and the promise of using metal abundance ratios to
eliminate sensitivity to wind density and ionization structure.Comment: Accepted for publication in ApJ; 9 pages, 2 color figures, 4 table
Fundamental stellar parameters of zeta Pup and gamma^2 Vel from HIPPARCOS data
We report parallax measurements by the HIPPARCOS satellite of zeta Puppis and
gamma^2 Velorum. The distance of zeta Pup is d=429 (+120/ -77) pc, in agreement
with the commonly adopted value to Vela OB2. However, a significantly smaller
distance is found for the gamma^2 Vel system: d=258 (+41/-31) pc. The total
mass of gamma^2 Vel derived from its parallax, the angular size of the
semi-major axis as measured with intensity interferometry, and the period is
M(WR+O)=29.5 (+/-15.9) Msun. This result favors the orbital solution of Pike et
al. (1983) over that of Moffat et al. (1986). The stellar parameters for the O
star companion derived from line blanketed non-LTE atmosphere models are:
Teff=34000 (+/-1500) K, log L/Lsun=5.3 (+/-0.15) from which an evolutionary
mass of M=29 (+/-4) Msun and an age of 4.0 (+0.8/-0.5) Myr is obtained from
single star evolutionary models. With non-LTE model calculations including He
and C we derive a luminosity log L/Lsun~4.7 (+/-0.2) for the WR star. The
mass-luminosity relation of hydrogen-free WR stars implies a mass of M(WR)~5
(+/-1.5) Msun. From our data we favor an age of ~10 Myr for the bulk of the
Vela OB2 stars. Evolutionary scenarios for zeta Pup and gamma^2 Vel are
discussed in the light of our results.Comment: Submitted to ApJ Letters (misprints corrected
XMM-Newton Detection of Hard X-ray Emission in the Nitrogen-Type Wolf-Rayet Star WR110
We have used the excellent sensitivity of XMM-Newton to obtain the first
high-quality X-ray spectrum of a Wolf-Rayet (WR) star which is not known to be
a member of a binary system. Our target, the nitrogen-type star WR 110 (= HD
165688) was also observed and detected with the VLA at four different
frequencies. The radio data are in excellent agreement with that expected for
free-free wind emission. and the ionized mass-loss rate is derived. The X-ray
emission measure distribution shows a dominant contribution from cool plasma at
kT = 0.5 keV (6 MK) which is only weakly absorbed. We argue that this
cool emission originates at hundreds of radii if the wind is spherical and
homogeneous and derive shock velocities and the X-ray filling factor using
radiative shock models. A surprising result is the unambiguous detection of a
hard X-ray component clearly seen in the hard-band images and the spectra. This
hard component accounts for about half of the observed flux and can be
acceptably fitted by a hot optically thin thermal plasma or a power-law model.
If the emission is thermal, then a temperature kT 3 keV is
derived. Such high temperatures are not predicted by current instability-driven
wind shock models. We examine several alternatives and show that the hard
emission could be accounted for by the WR wind shocking onto a close stellar
companion which has so far escaped detection. However, until persuasive
evidence for binarity is found we are left with the intriguing possibility that
the hard X-ray emission is produced entirely by the Wolf-Rayet star.Comment: 2 tables, 7 figure
EU-Rotate_N – a decision support system – to predict environmental and economic consequences of the management of nitrogen fertiliser in crop rotations
A model has been developed which assesses the economic and environmental performance of crop rotations, in both conventional and organic cropping, for over 70 arable and horticultural crops, and a wide range of growing conditions in Europe. The model, though originally based on the N_ABLE model, has been completely rewritten and contains new routines to simulate root development, the mineralisation and release of nitrogen (N) from soil organic matter and crop residues, and water dynamics in soil. New routines have been added to estimate the effects of sub-optimal rates of N and spacing on the marketable outputs and gross margins. The model provides a mechanism for generating scenarios to represent a range of differing crop and fertiliser management strategies which can be used to evaluate their effects on yield, gross margin and losses of nitrogen through leaching. Such testing has revealed that nitrogen management can be improved and that there is potential to increase gross margins whilst reducing nitrogen losses
Neon Abundances from a Spitzer/IRS Survey of Wolf-Rayet Stars
We report on neon abundances derived from {\it Spitzer} high resolution
spectral data of eight Wolf-Rayet (WR) stars using the forbidden line of
[\ion{Ne}{3}] 15.56 microns. Our targets include four WN stars of subtypes
4--7, and four WC stars of subtypes 4--7. We derive ion fraction abundances
of Ne^{2+} for the winds of each star. The ion fraction abundance is a
product of the ionization fraction in stage i and the abundance by
number of element E relative to all nuclei. Values generally
consistent with solar are obtained for the WN stars, and values in excess of
solar are obtained for the WC stars.Comment: to appear in Astrophysical Journa
Wind clumping and the wind-wind collision zone in the Wolf-Rayet binary gamma Velorum
We present XMM-Newton observations of gamma^2 Velorum (WR 11, WC8+O7.5III, P
= 78.53 d), a nearby Wolf-Ray binary system, at its X-ray high and low states.
At high state, emission from a hot collisional plasma dominates from about 1 to
8 keV. At low state, photons between 1 and 4 keV are absorbed. The hot plasma
is identified with the shock zone between the winds of the primary Wolf-Rayet
star and the secondary O giant. The absorption at low state is interpreted as
photoelectric absorption in the Wolf-Rayet wind. This absorption allows us to
measure the absorbing column density and to derive a mass loss rate 8x10^{-6}
M_sun/yr for the WC8 star. This mass loss rate, in conjunction with a previous
Wolf-Rayet wind model, provides evidence for a clumped WR wind. A clumping
factor of 16 is required. The X-ray spectra below 1 keV (12 Ang) show no
absorption and are essentially similar in both states. There is a rather clear
separation in that emission from a plasma hotter than 5 MK is heavily absorbed
in low state while the cooler plasma is not. This cool plasma must come from a
much more extended region than the hot material. The Neon abundance in the
X-ray emitting material is 2.5 times the solar value. The unexpected detection
of CV (25.3 Ang) and CVI (31.6 Ang) radiative recombination continua at both
phases indicates the presence of a cool (~40,000 K) recombination region
located far out in the binary system.Comment: 16 page
A One-sided, Highly Relativistic Jet from Cygnus X-3
Very Long Baseline Array images of the X-ray binary, Cygnus X-3, were
obtained 2, 4 and 7 days after the peak of a 10 Jy flare on 4 February 1997.
The first two images show a curved one-sided jet, the third a scatter-broadened
disc, presumably at the position of the core. The jet curvature changes from
the first to the second epoch, which strongly suggests a precessing jet. The
ratio of the flux density in the approaching to that in the (undetected)
receding jet is > 330; if this asymmetry is due to Doppler boosting, the
implied jet speed is > 0.81c. Precessing jet model fits, together with the
assumptions that the jet is intrinsically symmetric and was ejected during or
after the major flare, yield the following constraints: the jet inclination to
the line of sight must be < 14 degrees; the cone opening angle must be < 12
degrees; and the precession period must be > 60 days.Comment: 12 pages 7 figures, accepted by Ap
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