343 research outputs found
Pairs of Noncrossing Free Dyck Paths and Noncrossing Partitions
Using the bijection between partitions and vacillating tableaux, we establish
a correspondence between pairs of noncrossing free Dyck paths of length
and noncrossing partitions of with blocks. In terms of the
number of up steps at odd positions, we find a characterization of Dyck paths
constructed from pairs of noncrossing free Dyck paths by using the Labelle
merging algorithm.Comment: 9 pages, 5 figures, revised version, to appear in Discrete
Mathematic
Method for Generating Long-Range Correlations for Large Systems
We propose a new method to generate a sequence of random numbers with
long-range power-law correlations that overcomes known difficulties associated
with large systems. The new method presents an improvement on the commonly-used
methods. We apply the algorithm to generate enhanced diffusion, isotropic and
anisotropic self-affine surfaces, and isotropic and anisotropic correlated
percolation.Comment: 4 pages, REVTEX, figures available upon request from
[email protected]
Reversible vancomycin susceptibility within emerging ST1421 Enterococcus faecium strains is associated with rearranged vanA-gene clusters and increased vanA plasmid copy number
Vancomycin variable enterococci (VVE) are van-positive enterococci with a vancomycin-susceptible phenotype (VVE-S) that can convert to a resistant phenotype (VVE-R) and be selected for during vancomycin
exposure. VVE-R outbreaks have been reported in Canada and Scandinavian countries. The aim of this
study was to examine the presence of VVE in whole genome sequenced (WGS) Australian bacteremia
Enterococcus faecium (Efm) isolates collected through the Australian Group on Antimicrobial resistance
(AGAR) network. Eight potential VVEAus isolates, all identified as Efm ST1421, were selected based on the
presence of vanA and a vancomycin-susceptible phenotype. During vancomycin selection, two potential
VVE-S harboring intact vanHAX genes, but lacking the prototypic vanRS and vanZ genes, reverted to a
resistant phenotype (VVEAus-R). Spontaneous VVEAus-R reversion occurred at a frequency of 4-6 × 10−8
resistant colonies per parent cell in vitro after 48 h and led to high-level vancomycin and teicoplanin
resistance. The S to R reversion was associated with a 44-bp deletion in the vanHAX promoter region
and an increased vanA plasmid copy number. The deletion in the vanHAX promoter region enables an
alternative constitutive promoter for the expression of vanHAX. Acquisition of vancomycin resistance was
associated with a low fitness cost compared with the corresponding VVEAus-S isolate. The relative proportion of VVEAus-R vs. VVEAus-S decreased over time in serial passages without vancomycin selection.
Efm ST1421 is one of the predominant VanA-Efm multilocus sequence types found across most regions of
Australia, and has also been associated with a major prolonged VVE outbreak in Danish hospitals
Genomic diversity and adaptation of Salmonella enterica serovar Typhimurium from analysis of six genomes of different phage types
Hopf algebras and Markov chains: Two examples and a theory
The operation of squaring (coproduct followed by product) in a combinatorial
Hopf algebra is shown to induce a Markov chain in natural bases. Chains
constructed in this way include widely studied methods of card shuffling, a
natural "rock-breaking" process, and Markov chains on simplicial complexes.
Many of these chains can be explictly diagonalized using the primitive elements
of the algebra and the combinatorics of the free Lie algebra. For card
shuffling, this gives an explicit description of the eigenvectors. For
rock-breaking, an explicit description of the quasi-stationary distribution and
sharp rates to absorption follow.Comment: 51 pages, 17 figures. (Typographical errors corrected. Further fixes
will only appear on the version on Amy Pang's website, the arXiv version will
not be updated.
Clonal expansion of new penicillin-resistant clade of neisseria meningitidis serogroup w clonal complex 11, Australia
In Western Australia, Neisseria meningitidis serogroup W clonal complex 11 became the predominant cause of invasive meningococcal disease in 2016. We used core-genome analysis to show emergence of a penicillin-resistant clade that had the penA_253 allele. This new penicillin-resistant clade might affect treatment regimens for this disease
Optimal Renormalization Scale and Scheme for Exclusive Processes
We use the BLM method to fix the renormalization scale of the QCD coupling in
exclusive hadronic amplitudes such as the pion form factor and the
photon-to-pion transition form factor at large momentum transfer.
Renormalization-scheme-independent commensurate scale relations are established
which connect the hard scattering subprocess amplitudes that control exclusive
processes to other QCD observables such as the heavy quark potential and the
electron-positron annihilation cross section. The commensurate scale relation
connecting the heavy quark potential, as determined from lattice gauge theory,
to the photon-to-pion transition form factor is in excellent agreement with
data assuming that the pion distribution amplitude is
close to its asymptotic form . We also reproduce the
scaling and normalization of the data at large
momentum transfer. Because the renormalization scale is small, we argue that
the effective coupling is nearly constant, thus accounting for the nominal
scaling behavior of the data. However, the normalization of the space-like pion
form factor obtained from electroproduction experiments is
somewhat higher than that predicted by the corresponding commensurate scale
relation. This discrepancy may be due to systematic errors introduced by the
extrapolation of the electroproduction data to the
pion pole.Comment: 22 pages, Latex, 7 Latex figures. Several references added,
discussion of scale fixing revised for clarity. Final version to appear in
Phys. Rev.
British Society of Gastroenterology (BSG)-led multisociety consensus care bundle for the early clinical management of acute upper gastrointestinal bleeding
Medical care bundles improve standards of care and patient outcomes. Acute upper gastrointestinal bleeding (AUGIB) is a common medical emergency which has been consistently associated with suboptimal care. We aimed to develop a multisociety care bundle centred on the early management of AUGIB. Commissioned by the British Society of Gastroenterology (BSG), a UK multisociety task force was assembled to produce an evidence-based and consensus-based care bundle detailing key interventions to be performed within 24 hours of presentation with AUGIB. A modified Delphi process was conducted with stakeholder representation from BSG, Association of Upper Gastrointestinal Surgeons, Society for Acute Medicine and the National Blood Transfusion Service of the UK. A formal literature search was conducted and international AUGIB guidelines reviewed. Evidence was appraised using the Grading of Recommendations, Assessment, Development and Evaluation tool and statements were formulated and subjected to anonymous electronic voting to achieve consensus. Accepted statements were eligible for incorporation into the final bundle after a separate round of voting. The final version of the care bundle was reviewed by the BSG Clinical Services and Standards Committee and approved by all stakeholder groups. Consensus was reached on 19 statements; these culminated in 14 corresponding care bundle items, contained within 6 management domains: Recognition, Resuscitation, Risk assessment, Rx (Treatment), Refer and Review. A multisociety care bundle for AUGIB has been developed to facilitate timely delivery of evidence-based interventions and drive quality improvement and patient outcomes in AUGIB
Dissemination and persistence of extended-spectrum cephalosporin- resistance encoding IncI1-blaCTXM-1 plasmid among Escherichia coli in pigs
This study investigated the ecology, epidemiology and plasmid characteristics of extended-spectrum cephalosporin (ESC)-resistant E. coli in healthy pigs over a period of 4 years (2013–2016) following the withdrawal of ESCs. High carriage rates of ESC-resistant E. coli were demonstrated in 2013 (86.6%) and 2014 (83.3%), compared to 2015 (22%) and 2016 (8.5%). ESC resistance identified among E. coli isolates was attributed to the carriage of an IncI1 ST-3 plasmid (pCTXM1-MU2) encoding blaCTXM-1. Genomic characterisation of selected E. coli isolates (n = 61) identified plasmid movement into multiple commensal E. coli (n = 22 STs). Major STs included ST10, ST5440, ST453, ST2514 and ST23. A subset of the isolates belong to the atypical enteropathogenic E. coli (aEPEC) pathotype that harboured multiple LEE pathogenic islands. pCTXM1-MU2 was similar (99% nt identity) to IncI1-ST3 plasmids reported from Europe, encoded resistance to aminoglycosides, sulphonamides and trimethoprim, and carried colicin Ib. pCTXM1-MU2 appears to be highly stable and readily transferable. This study demonstrates that ESC resistance may persist for a protracted period following removal of direct selection pressure, resulting in the emergence of ESC-resistance in both commensal E. coli and aEPEC isolates of potential significance to human and animal health.This study was funded by the DVM clinical research programme,
University of Adelaide and Small Grant Scheme of School of Veterinary Life Sciences, Murdoch University
Validity of modified early warning, Glasgow Blatchford, and pre-endoscopic Rockall scores in predicting prognosis of patients presenting to emergency department with upper gastrointestinal bleeding
- …