235 research outputs found
Lower seroreactivity to European than to North American H3N2 swine influenza viruses in humans, Luxembourg, 2010
Seroreactivity to H3N2 swine influenza viruses (SIVs) was evaluated in serum samples collected from 843 people aged 0 to 100 years in 2010 in Luxembourg. Sera were analysed by haemagglutination inhibition (HI) and virus neutralisation (VN) assays targeting a European H3N2 SIV, a North American H3N2 variant of swine origin (H3N2v) and human seasonal H3N2 viruses isolated in 1975, 1995 and 2005. HI antibodies (titre ≥ 10) against European H3N2 SIV were almost exclusively detected in those born before 1990, of whom 70% were seropositive. HI antibodies against H3N2v were predominantly found in those born before 2000, with 86% seropositive. Titres against the North American H3N2v were higher than against the European H3N2 SIV. VN patterns were similar, but with higher rates and titres. We also demonstrated lower seroreactivity to European H3N2 SIV than to North American H3N2v virus. Finally, we found a strong correlation between HI titres against the European H3N2 SIV and H3N2v and their respective human ancestors, A/Victoria/3/75 and A/Nanchang/933/95. This finding and the minimal contacts between humans and pigs in Luxembourg suggest that anti-SIV antibodies in human serum samples reflect serological cross-reactivity with historical human H3N2 viruses. Our findings help assess the pandemic risk of H3N2 SIV
Absolute differential positronium-formation cross sections
The first absolute experimental determinations of the differential cross-sections for the formation of ground-state positronium are presented for He, Ar, H2 and CO2 near 0â—‹. Results are compared with available theories. The ratio of the differential and integrated cross-sections for the targets exposes the higher propensity for forward-emission of positronium formed from He and H2
The HERMES Solar Atlas and the spectroscopic analysis of the seismic solar analogue KIC3241581
Solar-analog stars provide an excellent opportunity to study the Sun's
evolution, i.e. the changes with time in stellar structure, activity, or
rotation for solar-like stars. The unparalleled photometric data from the NASA
space telescope Kepler allows us to study and characterise solar-like stars
through asteroseismology. We aim to spectroscopically investigate the
fundamental parameter and chromospheric activity of solar analogues and twins,
based on observations obtained with the HERMES spectrograph and combine them
with asteroseismology. Therefore, we need to build a solar atlas for the
spectrograph, to provide accurate calibrations of the spectroscopically
determined abundances of solar and late type stars observed with this
instrument and thus perform differential spectral comparisons. We acquire
high-resolution and high signal-to-noise spectroscopy to construct three solar
reference spectra by observing the reflected light of Vesta and Victoria
asteroids and Europa (100<S/N<450) with the \Hermes spectrograph. We then
observe the Kepler solar analog KIC3241581 (S/N~170). We constructed three
solar spectrum atlases from 385 to 900 nm obtained with the Hermes spectrograph
from observations of two bright asteroids and Europa. A comparison between our
solar spectra atlas to the Kurucz and HARPS solar spectrum shows an excellent
agreement. KIC3241581 was found to be a long-periodic binary system. The
fundamental parameter for the stellar primary component are Teff=5689+/-11K,
logg=4.385+/-0.005, [Fe/H]=+0.22+/-0.01, being in agreement with the published
global seismic values confirming its status of solar analogue. KIC 3241581 is a
metal rich solar analogue with a solar-like activity level in a binary system
of unknown period. The chromospheric activity level is compatible to the solar
magnetic activity.Comment: 12 pages, 8 figures, accepted for publication in A&
Recommended from our members
Deep Minima and Vortices for Positronium Formation in Low-Energy Positron-Hydrogen Collisions
Article using the two-channel Kohn inverse and Kohn variational methods to investigate ground-state positronium (Ps) formation in positron-hydrogen collisions in the Ore gap. This is the Accepted Manuscript Version of the article
Gravity-mode period spacings as seismic diagnostic for a sample of gamma Doradus stars from Kepler space photometry and high-resolution ground-based spectroscopy
Gamma Doradus stars (hereafter gamma Dor stars) are gravity-mode pulsators of
spectral type A or F. Such modes probe the deep stellar interior, offering a
detailed fingerprint of their structure. Four-year high-precision space-based
Kepler photometry of gamma Dor stars has become available, allowing us to study
these stars with unprecedented detail. We selected, analysed, and characterized
a sample of 67 gamma Dor stars for which we have Kepler observations available.
For all the targets in the sample we assembled high-resolution spectroscopy to
confirm their F-type nature. We found fourteen binaries, among which four
single-lined binaries, five double-lined binaries, two triple systems and three
binaries with no detected radial velocity variations. We estimated the orbital
parameters whenever possible. For the single stars and the single-lined
binaries, fundamental parameter values were determined from spectroscopy. We
searched for period spacing patterns in the photometric data and identified
this diagnostic for 50 of the stars in the sample, 46 of which are single stars
or single-lined binaries. We found a strong correlation between the
spectroscopic vsini and the period spacing values, confirming the influence of
rotation on gamma Dor-type pulsations as predicted by theory. We also found
relations between the dominant g-mode frequency, the longest pulsation period
detected in series of prograde modes, vsini, and log Teff.Comment: 61 pages, 61 figures, 6 tables, accepted for publication in ApJ
Detecting non-uniform period spacings in the Kepler photometry of gamma Doradus stars: methodology and case studies
Context. The analysis of stellar oscillations is one of the most reliable
ways to probe stellar interiors. Recent space missions such as Kepler have
provided us with an opportunity to study these oscillations with unprecedented
detail. For many multi-periodic pulsators such as {\gamma} Doradus stars, this
led to the detection of dozens to hundreds of oscillation frequencies that
could not be found from ground-based observations. Aims. We aim to detect
non-uniform period spacings in the Fourier spectra of a sample of {\gamma}
Doradus stars observed by Kepler. Such detection is complicated by both the
large number of significant frequencies in the space photometry and by
overlapping non-equidistant rotationally split multiplets. Methods. Guided by
theoretical properties of gravity-mode oscillation of {\gamma} Doradus stars,
we developed a period-spacing detection method and applied it to Kepler
observations of a few stars, after having tested the performance from
simulations. Results. The application of the technique resulted in the clear
detection of non-uniform period spacing series for three out of the five
treated Kepler targets. Disadvantages of the technique are also discussed, and
include the disability to distinguish between different values of the spherical
degree and azimuthal order of the oscillation modes without additional
theoretical modelling. Conclusions. Despite the shortcomings, the method is
shown to allow solid detections of period spacings for {\gamma} Doradus stars,
which will allow future asteroseismic analyses of these stars.Comment: 10 pages, 13 figures, 2 tables. Accepted for publication in Astronomy
& Astrophysic
Swine Influenza Virus Antibodies in Humans, Western Europe, 2009
Serologic studies for swine influenza viruses (SIVs) in humans with occupational exposure to swine have been reported from the Americas but not from Europe. We compared levels of neutralizing antibodies against 3 influenza viruses—pandemic (H1N1) 2009, an avian-like enzootic subtype H1N1 SIV, and a 2007–08 seasonal subtype H1N1—in 211 persons with swine contact and 224 matched controls in Luxembourg. Persons whose profession involved contact with swine had more neutralizing antibodies against SIV and pandemic (H1N1) 2009 virus than did the controls. Controls also had antibodies against these viruses although exposure to them was unlikely. Antibodies against SIV and pandemic (H1N1) 2009 virus correlated with each other but not with seasonal subtype H1N1 virus. Sequential exposure to variants of seasonal influenza (H1N1) viruses may have increased chances for serologic cross-reactivity with antigenically distinct viruses. Further studies are needed to determine the extent to which serologic responses correlate with infection
The CubeSpec space mission: Asteroseismology of massive stars from time-series optical spectroscopy
The ESA/KU Leuven CubeSpec mission is specifically designed to provide
low-cost space-based high-resolution optical spectroscopy. Here we highlight
the science requirements and capabilities of CubeSpec. The primary science goal
is to perform pulsation mode identification from spectroscopic line profile
variability and empower asteroseismology of massive stars.Comment: Authors' submitted version of poster proceedings paper for IAU
Symposium 361: Massive Stars Near and Far, held in Ballyconnell, Ireland,
9-13 May 202
Many-body theory of gamma spectra from positron-atom annihilation
A many-body theory approach to the calculation of gamma spectra of positron
annihilation on many-electron atoms is developed. We evaluate the first-order
correlation correction to the annihilation vertex and perform numerical
calculations for the noble gas atoms. Extrapolation with respect to the maximal
orbital momentum of the intermediate electron and positron states is used to
achieve convergence. The inclusion of correlation corrections improves
agreement with experimental gamma spectra.Comment: 25 pages, 9 figures, submitted to J. Phys.
- …