3,249 research outputs found
Monitoring the spread of meticillin-resistant Staphylococcus aureus in The Netherlands from a reference laboratory perspective
SummaryBackgroundIn The Netherlands, efforts to control meticillin-resistant Staphylococcus aureus (MRSA) in hospitals have been largely successful due to stringent screening of patients on admission and isolation of those that fall into defined risk categories. However, Dutch hospitals are not free of MRSA, and a considerable number of cases are found that do not belong to any of the risk categories. Some of these may be due to undetected nosocomial transmission, whereas others may be introduced from unknown reservoirs.AimIdentifying multi-institutional clusters of MRSA isolates to estimate the contribution of potential unobserved reservoirs in The Netherlands.MethodsWe applied a clustering algorithm that combines time, place, and genetics to routine data available for all MRSA isolates submitted to the Dutch Staphylococcal Reference Laboratory between 2008 and 2011 in order to map the geo-temporal distribution of MRSA clonal lineages in The Netherlands.FindingsOf the 2966 isolates lacking obvious risk factors, 579 were part of geo-temporal clusters, whereas 2387 were classified as MRSA of unknown origin (MUOs). We also observed marked differences in the proportion of isolates that belonged to geo-temporal clusters between specific multi-locus variable number of tandem repeat analysis (MLVA) clonal complexes, indicating lineage-specific transmissibility. The majority of clustered isolates (74%) were present in multi-institutional clusters.ConclusionThe frequency of MRSA of unknown origin among patients lacking obvious risk factors is an indication of a largely undefined extra-institutional but genetically highly diverse reservoir. Efforts to understand the emergence and spread of high-risk clones require the pooling of routine epidemiological information and typing data into central databases
Experimental evidence for the sensitivity of the air-shower radio signal to the longitudinal shower development
We observe a correlation between the slope of radio lateral distributions,
and the mean muon pseudorapidity of 59 individual cosmic-ray-air-shower events.
The radio lateral distributions are measured with LOPES, a digital radio
interferometer co-located with the multi-detector-air-shower array
KASCADE-Grande, which includes a muon-tracking detector. The result proves
experimentally that radio measurements are sensitive to the longitudinal
development of cosmic-ray air-showers. This is one of the main prerequisites
for using radio arrays for ultra-high-energy particle physics and astrophysics.Comment: 6 pages, 5 figures, accepted for publication by Physical Review
Frege on the Generality of Logical Laws
Frege claims that the laws of logic are characterized by their “generality,” but it is hard to see how this could identify a special feature of those laws. I argue that we must understand this talk of generality in normative terms, but that what Frege says provides a normative demarcation of the logical laws only once we connect it with his thinking about truth and science. He means to be identifying the laws of logic as those that appear in every one of the scientific systems whose construction is the ultimate aim of science, and in which all truths have a place. Though an account of logic in terms of scientific systems might seem hopelessly antiquated, I argue that it is not: a basically Fregean account of the nature of logic still looks quite promising
A comparison of the cosmic-ray energy scales of Tunka-133 and KASCADE-Grande via their radio extensions Tunka-Rex and LOPES
The radio technique is a promising method for detection of cosmic-ray air
showers of energies around PeV and higher with an array of radio
antennas. Since the amplitude of the radio signal can be measured absolutely
and increases with the shower energy, radio measurements can be used to
determine the air-shower energy on an absolute scale. We show that calibrated
measurements of radio detectors operated in coincidence with host experiments
measuring air showers based on other techniques can be used for comparing the
energy scales of these host experiments. Using two approaches, first via direct
amplitude measurements, and second via comparison of measurements with air
shower simulations, we compare the energy scales of the air-shower experiments
Tunka-133 and KASCADE-Grande, using their radio extensions, Tunka-Rex and
LOPES, respectively. Due to the consistent amplitude calibration for Tunka-Rex
and LOPES achieved by using the same reference source, this comparison reaches
an accuracy of approximately - limited by some shortcomings of LOPES,
which was a prototype experiment for the digital radio technique for air
showers. In particular we show that the energy scales of cosmic-ray
measurements by the independently calibrated experiments KASCADE-Grande and
Tunka-133 are consistent with each other on this level
The wavefront of the radio signal emitted by cosmic ray air showers
Analyzing measurements of the LOPES antenna array together with corresponding
CoREAS simulations for more than 300 measured events with energy above
eV and zenith angles smaller than , we find that the radio
wavefront of cosmic-ray air showers is of approximately hyperbolic shape. The
simulations predict a slightly steeper wavefront towards East than towards
West, but this asymmetry is negligible against the measurement uncertainties of
LOPES. At axis distances m, the wavefront can be approximated by
a simple cone. According to the simulations, the cone angle is clearly
correlated with the shower maximum. Thus, we confirm earlier predictions that
arrival time measurements can be used to study the longitudinal shower
development, but now using a realistic wavefront. Moreover, we show that the
hyperbolic wavefront is compatible with our measurement, and we present several
experimental indications that the cone angle is indeed sensitive to the shower
development. Consequently, the wavefront can be used to statistically study the
primary composition of ultra-high energy cosmic rays. At LOPES, the
experimentally achieved precision for the shower maximum is limited by
measurement uncertainties to approximately g/cm. But the simulations
indicate that under better conditions this method might yield an accuracy for
the atmospheric depth of the shower maximum, , better than
g/cm. This would be competitive with the established air-fluorescence
and air-Cherenkov techniques, where the radio technique offers the advantage of
a significantly higher duty-cycle. Finally, the hyperbolic wavefront can be
used to reconstruct the shower geometry more accurately, which potentially
allows a better reconstruction of all other shower parameters, too.Comment: accepted by JCA
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