36 research outputs found
Antibiotic Resistance and Occurrence of Class 1 Integrons in Clinical Isolates of Salmonella enterica
A Bayesian analysis of pentaquark signals from CLAS data
We examine the results of two measurements by the CLAS collaboration, one of
which claimed evidence for a pentaquark, whilst the other found no
such evidence. The unique feature of these two experiments was that they were
performed with the same experimental setup. Using a Bayesian analysis we find
that the results of the two experiments are in fact compatible with each other,
but that the first measurement did not contain sufficient information to
determine unambiguously the existence of a . Further, we suggest a
means by which the existence of a new candidate particle can be tested in a
rigorous manner.Comment: 5 pages, 3 figure
Beamâtarget helicity asymmetry E in K+ÎŁâ photoproduction on the neutron
We report a measurement of a beamâtarget double-polarisation observable (E) for the Îłânâ(p)âK+ÎŁâ(p) reaction. The data were obtained impinging the circularly-polarised energy-tagged photon beam of Hall B at Jefferson Lab on a longitudinally-polarised frozen-spin hydrogen deuteride (HD) nuclear target. The E observable for an effective neutron target was determined for centre-of-mass energies 1.70â€Wâ€2.30 GeV, with reaction products detected over a wide angular acceptance by the CLAS spectrometer. These new double-polarisation data give unique constraints on the strange decays of excited neutron states. Inclusion of the new data within the Bonn-Gatchina theoretical model results in significant changes for the extracted photocouplings of a number of established nucleon resonances. Possible improvements in the PWA description of the experimental data with additional âmissingâ resonance states, including the N(2120)3/2â resonance, are also quantified
Lewis Base Mediated ÎČ-Elimination and Lewis Acid Mediated Insertion Reactions of Disilazido Zirconium Compounds
The reactivity of a series of disilazido zirconocene complexes is dominated by the migration of anionic groups (hydrogen, alkyl, halide, OTf) between the zirconium and silicon centers. The direction of these migrations is controlled by the addition of two-electron donors (Lewis bases) or two-electron acceptors (Lewis acids). The cationic nonclassical [Cp2ZrN(SiHMe2)2]+ ([2]+) is prepared from Cp2Zr{N(SiHMe2)2}H (1) and B(C6F5)3 or [Ph3C][B(C6F5)4], while reactions of B(C6F5)3 and Cp2Zr{N(SiHMe2)2}R (R = Me (3), Et (5), n-C3H7 (7), CHâCHSiMe3 (9)) provide a mixture of [2]+ and [Cp2ZrN(SiHMe2)(SiRMe2)]+. The latter products are formed through B(C6F5)3 abstraction of a ÎČ-H and R group migration from Zr to the ÎČ-Si center. Related ÎČ-hydrogen abstraction and X group migration reactions are observed for Cp2Zr{N(SiHMe2)2}X (X = OTf (11), Cl (13), OMe (15), O-i-C3H7 (16)). Alternatively, addition of DMAP (DMAP = 4-(dimethylamino)pyridine) to [2]+ results in coordination to a Si center and hydrogen migration to zirconium, giving the cationic complex [Cp2Zr{N(SiHMe2)(SiMe2DMAP)}H]+ ([19]+). Related hydrogen migration occurs from [Cp2ZrN(SiHMe2)(SiMe2OCHMe2)]+ ([18]+) to give [Cp2Zr{N(SiMe2DMAP)(SiMe2OCHMe2)}H]+ ([22]+), whereas X group migration is observed upon addition of DMAP to [Cp2ZrN(SiHMe2)(SiMe2X)]+ (X = OTf ([12]+), Cl ([14]+)) to give [Cp2Zr{N(SiHMe2)(SiMe2DMAP)}X]+ (X = OTf ([26]+), Cl ([20]+)). The species involved in these transformations are described by resonance structures that suggest ÎČ-elimination. Notably, such pathways are previously unknown in early metal amide chemistry. Finally, these migrations facilitate direct SiâH addition to carbonyls, which is proposed to occur through a pathway that previously had been reserved for later transition metal compounds
Search for the photo-excitation of exotic mesons in the pi+pi+pi- system
A search for exotic mesons in the system
photoproduced by the charge exchange reaction was carried out by the CLAS collaboration at
Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range,
produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on
a liquid-hydrogen target. A Partial Wave Analysis (PWA) was performed on a
sample of 83,000 events, the highest such statistics to date in this reaction
at these energies. The main objective of this study was to look for the
photoproduction of an exotic resonant state in the 1 to 2 GeV
mass range. Our PWA analysis, based on the isobar model, shows production of
the and the mesons, but no evidence for the
, nor the exotic state at the expected levels. An
upper limit of 13.5 nb is determined for the exotic cross
section, less than 2% of the production.Comment: 6 pages, 5 figures, to be submitted to Phys.Rev.Let
International Consensus Statement on Rhinology and Allergy: Rhinosinusitis
Background: The 5 years since the publication of the first International Consensus Statement on Allergy and Rhinology: Rhinosinusitis (ICARâRS) has witnessed foundational progress in our understanding and treatment of rhinologic disease. These advances are reflected within the more than 40 new topics covered within the ICARâRSâ2021 as well as updates to the original 140 topics. This executive summary consolidates the evidenceâbased findings of the document. Methods: ICARâRS presents over 180 topics in the forms of evidenceâbased reviews with recommendations (EBRRs), evidenceâbased reviews, and literature reviews. The highest grade structured recommendations of the EBRR sections are summarized in this executive summary. Results: ICARâRSâ2021 covers 22 topics regarding the medical management of RS, which are grade A/B and are presented in the executive summary. Additionally, 4 topics regarding the surgical management of RS are grade A/B and are presented in the executive summary. Finally, a comprehensive evidenceâbased management algorithm is provided. Conclusion: This ICARâRSâ2021 executive summary provides a compilation of the evidenceâbased recommendations for medical and surgical treatment of the most common forms of RS