1,141 research outputs found
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.
Observations of High Definition Symmetric QuasiâPeriodic Scintillations in the MidâLatitude Ionosphere With LOFAR
We present broadband ionospheric scintillation observations of highly defined symmetric quasiâperiodic scintillations (QPS: Maruyama, 1991, https://doi.org/10.1029/91rs00357) caused by plasma structures in the midâlatitude ionosphere using the LOw Frequency ARray (LOFAR: van Haarlem et al., 2013, https://doi.org/10.1051/0004â6361/201220873). Two case studies are shown, one from 15 December 2016, and one from 30 January 2018, in which wellâdefined main signal fades are observed to be bounded by secondary diffraction fringing. The ionospheric plasma structures effectively behave as a Fresnel obstacle, in which steep plasma gradients at the periphery result in a series of decreasing intensity interference fringes, while the center of the structures largely block the incoming radio signal altogether. In particular, the broadband observing capabilities of LOFAR permit us to see considerable frequency dependent behavior in the QPSs which, to our knowledge, is a new result. We extract some of the clearest examples of scintillation arcs reported in an ionospheric context, from delayâDoppler spectral analysis of these two events. These arcs permit the extraction of propagation velocities for the plasma structures causing the QPSs ranging from 50 to 00 m sâ1, depending on the assumed altitude. The spacing between the individual plasma structures ranges between 5 and 20 km. The periodicities of the main signal fades in each event and, in the case of the 2018 data, coâtemporal ionosonde data, suggest the propagation of the plasma structures causing the QPSs are in the Eâregion. Each of the two events is accurately reproduced using a thin screen phase model. Individual signal fades and enhancements were modeled using small variations in total electron content (TEC) amplitudes of order 1 mTECu, demonstrating the sensitivity of LOFAR to very small fluctuations in ionospheric plasma density. To our knowledge these results are among the most detailed observations and modeling of QPSs in the literature
Observations of High Definition Symmetric QuasiâPeriodic Scintillations in the MidâLatitude Ionosphere With LOFAR
We present broadband ionospheric scintillation observations of highly defined symmetric quasiâperiodic scintillations (QPS: Maruyama, 1991, https://doi.org/10.1029/91rs00357) caused by plasma structures in the midâlatitude ionosphere using the LOw Frequency ARray (LOFAR: van Haarlem et al., 2013, https://doi.org/10.1051/0004â6361/201220873). Two case studies are shown, one from 15 December 2016, and one from 30 January 2018, in which wellâdefined main signal fades are observed to be bounded by secondary diffraction fringing. The ionospheric plasma structures effectively behave as a Fresnel obstacle, in which steep plasma gradients at the periphery result in a series of decreasing intensity interference fringes, while the center of the structures largely block the incoming radio signal altogether. In particular, the broadband observing capabilities of LOFAR permit us to see considerable frequency dependent behavior in the QPSs which, to our knowledge, is a new result. We extract some of the clearest examples of scintillation arcs reported in an ionospheric context, from delayâDoppler spectral analysis of these two events. These arcs permit the extraction of propagation velocities for the plasma structures causing the QPSs ranging from 50 to 00 m sâ1, depending on the assumed altitude. The spacing between the individual plasma structures ranges between 5 and 20 km. The periodicities of the main signal fades in each event and, in the case of the 2018 data, coâtemporal ionosonde data, suggest the propagation of the plasma structures causing the QPSs are in the Eâregion. Each of the two events is accurately reproduced using a thin screen phase model. Individual signal fades and enhancements were modeled using small variations in total electron content (TEC) amplitudes of order 1 mTECu, demonstrating the sensitivity of LOFAR to very small fluctuations in ionospheric plasma density. To our knowledge these results are among the most detailed observations and modeling of QPSs in the literature
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 âpaediatric populationâ and âpolytraumaâ 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
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
Quantifying antimicrobial resistance at veal calf farms
This study was performed to determine a sampling strategy to quantify the prevalence of antimicrobial resistance on veal calf farms, based on the variation in antimicrobial resistance within and between calves on five farms. Faecal samples from 50 healthy calves (10 calves/farm) were collected. From each individual sample and one pooled faecal sample per farm, 90 selected Escherichia coli isolates were tested for their resistance against 25 mg/L amoxicillin, 25 mg/L tetracycline, 0.5 mg/L cefotaxime, 0.125 mg/L ciprofloxacin and 8/152 mg/L trimethoprim/sulfamethoxazole (tmp/s) by replica plating. From each faecal sample another 10 selected E. coli isolates were tested for their resistance by broth microdilution as a reference. Logistic regression analysis was performed to compare the odds of testing an isolate resistant between both test methods (replica plating vs. broth microdilution) and to evaluate the effect of pooling faecal samples. Bootstrap analysis was used to investigate the precision of the estimated prevalence of resistance to each antimicrobial obtained by several simulated sampling strategies. Replica plating showed similar odds of E. coli isolates tested resistant compared to broth microdilution, except for ciprofloxacin (OR 0.29, p=0.05). Pooled samples showed in general lower odds of an isolate being resistant compared to individual samples, although these differences were not significant. Bootstrap analysis showed that within each antimicrobial the various compositions of a pooled sample provided consistent estimates for the mean proportion of resistant isolates. Sampling strategies should be based on the variation in resistance among isolates within faecal samples and between faecal samples, which may vary by antimicrobial. In our study, the optimal sampling strategy from the perspective of precision of the estimated levels of resistance and practicality consists of a pooled faecal sample from 20 individual animals, of which 90 isolates are tested for their susceptibility by replica plating
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
Constraining the epoch of reionization with the variance statistic: simulations of the LOFAR case
Several experiments are underway to detect the cosmic redshifted 21-cm signal
from neutral hydrogen from the Epoch of Reionization (EoR). Due to their very
low signal-to-noise ratio, these observations aim for a statistical detection
of the signal by measuring its power spectrum. We investigate the extraction of
the variance of the signal as a first step towards detecting and constraining
the global history of the EoR. Signal variance is the integral of the signal's
power spectrum, and it is expected to be measured with a high significance. We
demonstrate this through results from a simulation and parameter estimation
pipeline developed for the Low Frequency Array (LOFAR)-EoR experiment. We show
that LOFAR should be able to detect the EoR in 600 hours of integration using
the variance statistic. Additionally, the redshift () and duration
() of reionization can be constrained assuming a parametrization. We
use an EoR simulation of and to test the
pipeline. We are able to detect the simulated signal with a significance of 4
standard deviations and extract the EoR parameters as and in 600 hours,
assuming that systematic errors can be adequately controlled. We further show
that the significance of detection and constraints on EoR parameters can be
improved by measuring the cross-variance of the signal by cross-correlating
consecutive redshift bins.Comment: 13 pages, 14 figures, Accepted for publication in MNRA
Optimized Trigger for Ultra-High-Energy Cosmic-Ray and Neutrino Observations with the Low Frequency Radio Array
When an ultra-high energy neutrino or cosmic ray strikes the Lunar surface a
radio-frequency pulse is emitted. We plan to use the LOFAR radio telescope to
detect these pulses. In this work we propose an efficient trigger
implementation for LOFAR optimized for the observation of short radio pulses.Comment: Submitted to Nuclear Instruments and Methods in Physics Research
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