99 research outputs found
A multistate outbreak of Escherichia coli O157:H7 infections linked to alfalfa sprouts grown from contaminated seeds.
A multistate outbreak of Escherichia coli O157:H7 infections occurred in the United States in June and July 1997. Two concurrent outbreaks were investigated through independent case-control studies in Michigan and Virginia and by subtyping isolates with pulsed-field gel electrophoresis (PFGE). Isolates from 85 persons were indistinguishable by PFGE. Alfalfa sprouts were the only exposure associated with E. coli O157:H7 infection in both Michigan and Virginia. Seeds used for sprouting were traced back to one common lot harvested in Idaho. New subtyping tools such as PFGE used in this investigation are essential to link isolated infections to a single outbreak
Black hole hair formation in shift-symmetric generalised scalar-tensor gravity
A linear coupling between a scalar field and the GaussâBonnet invariant is the only known interaction term between a scalar and the metric that: respects shift symmetry; does not lead to higher order equations; inevitably introduces black hole hair in asymptotically flat, 4-dimensional spacetimes. Here we focus on the simplest theory that includes such a term and we explore the dynamical formation of scalar hair. In particular, we work in the decoupling limit that neglects the backreaction of the scalar onto the metric and evolve the scalar configuration numerically in the background of a Schwarzschild black hole and a collapsing dust star described by the OppenheimerâSnyder solution. For all types of initial data that we consider, the scalar relaxes at late times to the known, static, analytic configuration that is associated with a hairy, spherically symmetric black hole. This suggests that the corresponding black hole solutions are indeed endpoints of collapse
Beam-Recoil Transferred Polarization in K+Y Electroproduction in the Nucleon Resonance Region with CLAS12
Beam-recoil transferred polarizations for the exclusive electroproduction of K + Î and K + ÎŁ0 final states from an unpolarized proton target have been measured using the CLAS12 spectrometer at Jefferson Laboratory. The measurements at beam energies of 6.535 and 7.546 GeV span the range of four-momentum transfer Q2 from 0.3 to 4.5 GeV2 and invariant energy W from 1.6 to 2.4 GeV, while covering the full center-of-mass angular range of the K+. These new data extend the existing hyperon polarization data from CLAS in a similar kinematic range but from a significantly larger dataset. They represent an important addition to the world data, allowing for better exploration of the reaction mechanism in strangeness production processes, for further understanding of the spectrum and structure of excited nucleon states, and for improved insight into the strong interaction in the regime of nonperturbative dynamics
First CLAS12 Measurement of Deeply Virtual Compton Scattering Beam-Spin Asymmetries in the Extended Valence Region
Deeply virtual Compton scattering (DVCS) allows one to probe generalized parton distributions describing the 3D structure of the nucleon. We report the first measurement of the DVCS beam-spin asymmetry using the CLAS12 spectrometer with a 10.2 and 10.6 GeV electron beam scattering from unpolarized protons. The results greatly extend the Q2 and Bjorken-x phase space beyond the existing data in the valence region and provide 1600 new data points measured with unprecedented statistical uncertainty, setting new, tight constraints for future phenomenological studies
A new look at the LTR retrotransposon content of the chicken genome
BACKGROUND: LTR retrotransposons contribute approximately 10 % of the mammalian genome, but it has been previously reported that there is a deficit of these elements in the chicken relative to both mammals and other birds. A novel LTR retrotransposon classification pipeline, LocaTR, was developed and subsequently utilised to re-examine the chicken LTR retrotransposon annotation, and determine if the proposed chicken deficit is biologically accurate or simply a technical artefact. RESULTS: Using LocaTR 3.01 % of the chicken galGal4 genome assembly was annotated as LTR retrotransposon-derived elements (nearly double the previous annotation), including 1,073 that were structurally intact. Element distribution is significantly correlated with chromosome size and is non-random within each chromosome. Elements are significantly depleted within coding regions and enriched in gene sparse areas of the genome. Over 40 % of intact elements are found in clusters, unrelated by age or genera, generally in poorly recombining regions. The transcription of most LTR retrotransposons were suppressed or incomplete, but individual domain and full length retroviral transcripts were produced in some cases, although mostly with regularly interspersed stop codons in all reading frames. Furthermore, RNAseq data from 23 diverse tissues enabled greater characterisation of the co-opted endogenous retrovirus Ovex1. This gene was shown to be expressed ubiquitously but at variable levels across different tissues. LTR retrotransposon content was found to be very variable across the avian lineage and did not correlate with either genome size or phylogenetic position. However, the extent of previous, species-specific LTR retrotransposon annotation appears to be a confounding factor. CONCLUSIONS: Use of the novel LocaTR pipeline has nearly doubled the annotated LTR retrotransposon content of the chicken genome compared to previous estimates. Further analysis has described element distribution, clustering patterns and degree of expression in a variety of adult tissues, as well as in three embryonic stages. This study also enabled better characterisation of the co-opted gamma retroviral envelope gene Ovex1. Additionally, this work suggests that there is no deficit of LTR retrotransposons within the Galliformes relative to other birds, or to mammalian genomes when scaled for the three-fold difference in genome size
Diversity of endogenous Avian Leukosis Virus subgroup E (ALVE) insertions in indigenous chickens
Observation of azimuth-dependent suppression of hadron pairs in electron scattering off nuclei
We present the first measurement of di-hadron angular correlations in
electron-nucleus scattering. The data were taken with the CLAS detector and a
5.0 GeV electron beam incident on deuterium, carbon, iron, and lead targets.
Relative to deuterium, the nuclear yields of charged-pion pairs show a strong
suppression for azimuthally opposite pairs, no suppression for azimuthally
nearby pairs, and an enhancement of pairs with large invariant mass. These
effects grow with increased nuclear size. The data are qualitatively described
by the GiBUU model, which suggests that hadrons form near the nuclear surface
and undergo multiple-scattering in nuclei. These results show that angular
correlation studies can open a new way to elucidate how hadrons form and
interact inside nucleiComment: 6 pages, 4 figure
Observation of Azimuth-Dependent Suppression of Hadron Pairs in Electron Scattering Off Nuclei
We present the first measurement of dihadron angular correlations in electron-nucleus scattering. The data were taken with the CLAS detector and a 5.0 GeV electron beam incident on deuterium, carbon, iron, and lead targets. Relative to deuterium, the nuclear yields of charged-pion pairs show a strong suppression for azimuthally opposite pairs, no suppression for azimuthally nearby pairs, and an enhancement of pairs with large invariant mass. These effects grow with increased nuclear size. The data are qualitatively described by the gibuu model, which suggests that hadrons form near the nuclear surface and undergo multiple scattering in nuclei. These results show that angular correlation studies can open a new way to elucidate how hadrons form and interact inside nuclei
Measurement of the helicity asymmetry E for the Îłâ pâ â pÏ reaction in the resonance region: The CLAS Collaboration
The double-spin-polarization observable E for Îłâ pâ â pÏ has been measured with the CEBAF Large Acceptance Spectrometer (CLAS) at photon beam energies EÎł from 0.367 to 2.173GeV (corresponding to center-of-mass energies from 1.240 to 2.200GeV) for pion center-of-mass angles, cosΞÏ0c.m. , between - 0.86 and 0.82. These new CLAS measurements cover a broader energy range and have smaller uncertainties compared to previous CBELSA data and provide an important independent check on systematics. These measurements are compared to predictions as well as new global fits from The George Washington University, Mainz, and Bonn-Gatchina groups. Their inclusion in multipole analyses will allow us to refine our understanding of the single-pion production contribution to the Gerasimov-Drell-Hearn sum rule and improve the determination of resonance properties, which will be presented in a future publication
First Measurement of Electroproduction off Nuclei in the Current and Target Fragmentation Regions
We report results of hyperon production in semi-inclusive
deep-inelastic scattering off deuterium, carbon, iron, and lead targets
obtained with the CLAS detector and the Continuous Electron Beam Accelerator
Facility 5.014~GeV electron beam. These results represent the first
measurements of the multiplicity ratio and transverse momentum
broadening as a function of the energy fraction~() in the current and target
fragmentation regions. The multiplicity ratio exhibits a strong suppression at
high~~and~an enhancement at~low~. The measured transverse momentum
broadening is an order of magnitude greater than that seen for light mesons.
This indicates that the propagating entity interacts very strongly with the
nuclear medium, which suggests that propagation of diquark configurations in
the nuclear medium takes place at least part of the time, even at high~. The
trends of these results are qualitatively described by the Giessen
Boltzmann-Uehling-Uhlenbeck transport model, particularly for the multiplicity
ratios. These observations will potentially open a new era of studies of the
structure of the nucleon as well as of strange baryons.Comment: 14 pages, 6 figure
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