1,281 research outputs found
Multiresistant Salmonella enterica serovar 4,[5],12:i:- in Europe: a new pandemic strain?
A marked increase in the prevalence of S. enterica serovar 4,[5],12:i:- with resistance to ampicillin, streptomycin, sulphonamides and tetracyclines (R-type ASSuT) has been noted in food-borne infections and in pigs/pig meat in several European countries in the last ten years. One hundred and sixteen strains of S. enterica serovar 4,[5],12:i:- from humans, pigs and pig meat isolated in England and Wales, France, Germany, Italy, Poland, Spain and the Netherlands were further subtyped by phage typing, pulsed-field gel electrophoresis and multilocus variable number tandem repeat analysis to investigate the genetic relationship among strains. PCR was performed to identify the fljB flagellar gene and the genes encoding resistance to ampicillin, streptomycin, sulphonamides and tetracyclines. Class 1 and 2 integrase genes were also sought. Results indicate that genetically related serovar 4,[5],12:i:- strains of definitive phage types DT193 and DT120 with ampicillin, streptomycin, sulphonamide and tetracycline resistance encoded by blaTEM, strA-strB, sul2 and tet(B) have emerged in several European countries, with pigs the likely reservoir of infection. Control measures are urgently needed to reduce spread of infection to humans via the food chain and thereby prevent the possible pandemic spread of serovar 4,[5],12:i:- of R-type ASSuT as occurred with S. Typhimurium DT104 during the 1990s
A new limit on the Ultra-High-Energy Cosmic-Ray flux with the Westerbork Synthesis Radio Telescope
A particle cascade (shower) in a dielectric, for example as initiated by an
ultra-high energy cosmic ray, will have an excess of electrons which will emit
coherent \v{C}erenkov radiation, known as the Askaryan effect. In this work we
study the case in which such a particle shower occurs in a medium just below
its surface. We show, for the first time, that the radiation transmitted
through the surface is independent of the depth of the shower below the surface
when observed from far away, apart from trivial absorption effects. As a direct
application we use the recent results of the NuMoon project, where a limit on
the neutrino flux for energies above \,eV was set using the Westerbork
Synthesis Radio Telescope by measuring pulsed radio emission from the Moon, to
set a limit on the flux of ultra-high-energy cosmic rays.Comment: Accepted for publication in Phys. Rev.
The effect of the ionosphere on ultra-low-frequency radio-interferometric observations
Context. The ionosphere is the main driver of a series of systematic effects that limit our ability to explore the low-frequency (<1 GHz) sky with radio interferometers. Its effects become increasingly important towards lower frequencies and are particularly hard to calibrate in the low signal-to-noise ratio (S/N) regime in which low-frequency telescopes operate. Aims. In this paper we characterise and quantify the effect of ionospheric-induced systematic errors on astronomical interferometric radio observations at ultra-low frequencies (<100 MHz). We also provide guidelines for observations and data reduction at these frequencies with the LOw Frequency ARray (LOFAR) and future instruments such as the Square Kilometre Array (SKA). Methods. We derive the expected systematic error induced by the ionosphere. We compare our predictions with data from the Low Band Antenna (LBA) system of LOFAR. Results. We show that we can isolate the ionospheric effect in LOFAR LBA data and that our results are compatible with satellite measurements, providing an independent way to measure the ionospheric total electron content (TEC). We show how the ionosphere also corrupts the correlated amplitudes through scintillations. We report values of the ionospheric structure function in line with the literature. Conclusions. The systematic errors on the phases of LOFAR LBA data can be accurately modelled as a sum of four effects (clock, ionosphere first, second, and third order). This greatly reduces the number of required calibration parameters, and therefore enables new efficient calibration strategies
Wide-field LOFAR-LBA power-spectra analyses: Impact of calibration, polarization leakage and ionosphere
Contamination due to foregrounds (Galactic and Extra-galactic), calibration
errors and ionospheric effects pose major challenges in detection of the cosmic
21 cm signal in various Epoch of Reionization (EoR) experiments. We present the
results of a pilot study of a field centered on 3C196 using LOFAR Low Band
(56-70 MHz) observations, where we quantify various wide field and calibration
effects such as gain errors, polarized foregrounds, and ionospheric effects. We
observe a `pitchfork' structure in the 2D power spectrum of the polarized
intensity in delay-baseline space, which leaks into the modes beyond the
instrumental horizon (EoR/CD window). We show that this structure largely
arises due to strong instrumental polarization leakage () towards
{Cas\,A} ( kJy at 81 MHz, brightest source in northern sky), which is
far away from primary field of view. We measure an extremely small ionospheric
diffractive scale ( m at 60 MHz) towards {Cas\,A}
resembling pure Kolmogorov turbulence compared to
km towards zenith at 150 MHz for typical ionospheric conditions. This is one of
the smallest diffractive scales ever measured at these frequencies. Our work
provides insights in understanding the nature of aforementioned effects and
mitigating them in future Cosmic Dawn observations (e.g. with SKA-low and HERA)
in the same frequency window.Comment: 20 pages, 11 figures, accepted for publication in MNRA
An air shower array for LOFAR: LORA
LOFAR is a new form of radio telescope which can detect radio emission from
air showers induced by very high-energy cosmic rays. It can also look for radio
emission from particle cascades on the Moon induced by ultra high-energy cosmic
rays or neutrinos. To complement the radio detection, we are setting up a small
particle detector array LORA (LOfar Radboud Air shower array) within an area of
m diameter in the LOFAR core. It will help in triggering and
confirming the radio detection of air showers with the LOFAR antennas. In this
paper, we present a short overview about LORA and discuss its current status.Comment: 10 pages (using article.cls), 6 figures, accepted for the proceedings
of 22nd European Cosmic Ray Symposium, 3-6 August 2010, Finlan
The Management of Pediatric Polytrauma: Review
Polytrauma is a major cause of mortality and morbidity in both developed and developing countries. The primary goal of this review is to provide a comprehensive overview on current knowledge in the management of pediatric polytrauma patients (PPPs). A database review was con- ducted based on a search in the Embase, Medline OVID-SP, Web of Science, Cochrane central, and Pubmed databases. Only studies with “paediatric population” and “polytrauma” as criteria were included. A total of 3310 citations were retrieved. Of these, 3271 were excluded after screening, based on title and abstract. The full texts of 39 articles were assessed; further selection left 25 articles to be included in this review. The most crucial point in the management of PPPs is preparedness of the staff and an emergency room furnished with age-appropriate drugs and equipment combined with a systemic approach
Complete Sequence of pSAM7, an IncX4 Plasmid Carrying a Novel bla[sub]CTX-M-14b Transposition Unit Isolated from ' Escherichia coli ' and ' Enterobacter cloacae ' from cattle
The same plasmid carrying blaCTX-M-14b was identified from an Escherichia coli isolate and an Enterobacter cloacae isolate collected from cattle in the United Kingdom by complete plasmid sequencing. This 35,341-bp plasmid, pSAM7, had an IncX4 backbone that is 99% identical to that of pJIE143 from a human isolate in Australia. PCR screening identified pSAM7-like plasmids in three other E. coli isolates of different multilocus sequence types isolated from cattle on different farms in the United Kingdom
The Scintillating Tail of Comet C/2020 F3 (Neowise)
Context. The occultation of a radio source by the plasma tail of a comet can
be used to probe structure and dynamics in the tail. Such occultations are
rare, and the occurrence of scintillation, due to small-scale density
variations in the tail, remains somewhat controversial. Aims. A detailed
observation taken with the Low-Frequency Array (LOFAR) of a serendipitous
occultation of the compact radio source 3C196 by the plasma tail of comet
C/2020 F3 (Neowise) is presented. 3C196 tracked almost perpendicularly behind
the tail, providing a unique profile cut only a short distance downstream from
the cometary nucleus itself. Methods. Interplanetary scintillation (IPS) is
observed as the rapid variation of the intensity received of a compact radio
source due to density variations in the solar wind. IPS in the signal received
from 3C196 was observed for five hours, covering the full transit behind the
plasma tail of comet C/2020 F3 (Neowise) on 16 July 2020, and allowing an
assessment of the solar wind in which the comet and its tail are embedded.
Results. The results reveal a sudden and strong enhancement in scintillation
which is unequivocally attributable to the plasma tail. The strongest
scintillation is associated with the tail boundaries, weaker scintillation is
seen within the tail, and previously-unreported periodic variations in
scintillation are noted, possibly associated with individual filaments of
plasma. Furthermore, contributions from the solar wind and comet tail are
separated to measure a sharp decrease in the velocity of material within the
tail, suggesting a steep velocity shear resulting in strong turbulence along
the tail boundaryComment: Accepted for publication in Astronomy and Astrophysics, 8 pages, 9
figure
Precision requirements for interferometric gridding in the analysis of a 21 cm power spectrum
Context. Experiments that try to observe the 21 cm redshifted signals from the epoch of reionisation (EoR) using interferometric low-frequency instruments have stringent requirements on the processing accuracy.
Aims. We analyse the accuracy of radio interferometric gridding of visibilities with the aim to quantify the power spectrum bias caused by gridding. We do this ultimately to determine the suitability of different imaging algorithms and gridding settings for an analysis of a 21 cm power spectrum.
Methods. We simulated realistic Low-Frequency Array (LOFAR) data and constructed power spectra with convolutional gridding and w stacking, w projection, image-domain gridding, and without w correction. These were compared against data that were directly Fourier transformed. The influence of oversampling, kernel size, w-quantization, kernel windowing function, and image padding were quantified. The gridding excess power was measured with a foreground subtraction strategy, for which foregrounds were subtracted using Gaussian progress regression, as well as with a foreground avoidance strategy.
Results. Constructing a power spectrum with a significantly lower bias than the expected EoR signals is possible with the methods we tested, but requires a kernel oversampling factor of at least 4000, and when w-correction is used, at least 500 w-quantization levels. These values are higher than typically used values for imaging, but they are computationally feasible. The kernel size and padding factor parameters are less crucial. Of the tested methods, image-domain gridding shows the highest accuracy with the lowest imaging time.
Conclusions. LOFAR 21 cm power spectrum results are not affected by gridding. Image-domain gridding is overall the most suitable algorithm for 21 cm EoR power spectrum experiments, including for future analyses of data from the Square Kilometre Array (SKA) EoR. Nevertheless, convolutional gridding with tuned parameters results in sufficient accuracy for interferometric 21 cm EoR experiments. This also holds for w stacking for wide-field imaging. The w-projection algorithm is less suitable because of the requirements for kernel oversampling, and a faceting approach is unsuitable because it causes spatial discontinuities
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