29,055 research outputs found
Bayesian model selection for electromagnetic kaon production on the nucleon
We present the results of a Bayesian analysis of a Regge model to describe
the background contribution for K+ Lambda and K+ Sigma0 photoproduction. The
model is based on the exchange of K+(494) and K*+(892) trajectories in the
t-channel. We utilise the Bayesian evidence Z to determine the best model
variant for each channel. The Bayesian evidence integrals were calculated using
the Nested Sampling algorithm. For different prior widths, we find decisive
Bayesian evidence (\Delta ln Z ~ 24) for a K+ Lambda photoproduction Regge
model with a positive vector coupling and a negative tensor coupling constant
for the K*+(892) trajectory, and a rotating phase factor for both trajectories.
Using the chi^2 minimisation method, one could not draw this conclusion from
the same dataset. For the K+ Sigma0 photoproduction Regge model, on the other
hand, the difference between the evidence integrals is insufficient to pinpoint
one model variant.Comment: 13 pages, 4 figure
Regge-model predictions for K+Sigma photoproduction from the nucleon
We present Regge-model predictions for the p(gamma,K+)Sigma0 and
n(gamma,K+)Sigma- differential cross sections and photon-beam asymmetries in
the resonance region. The reaction amplitude encompasses the exchange of
K+(494) and K*+(892) Regge-trajectories, introducing a mere three free
parameters. These are fitted to the available p(gamma,K+)Sigma0 data beyond the
resonance region. The n(gamma,K+)Sigma- amplitude is obtained from the
p(gamma,K+)Sigma0 one through SU(2) isospin symmetry considerations.Comment: 4 pages, 2 figures; Proceedings Tenth Conference on the Intersections
of Particle and Nuclear Physics, San Diego, 200
Prevalence and Antimicrobial Susceptibility of Methicillin-resistant Staphylococcus aureus in Pregnant Women and Their Newborns in Las Vegas, Nevada
Colonization and infection by resistant strains of Staphylococcus aureus are being reported in epidemic proportions. The goal of this study was to determine the local prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization in pregnant women in southern Nevada and how it correlates with colonization and infection of their neonates. Signed consent was obtained, and a brief questionnaire was administered by the medical staff to each pregnant woman to collect demographic data and pertinent medical, family and social history. Nasal and vaginal specimens were obtained from pregnant women at ≥35 weeks gestation, and nasal and umbilicus specimens were obtained from their newborns. Specimens were cultured onto two selective media for S. aureus and MRSA. Potential MRSA isolates were further evaluated for susceptibility to antibiotics. Specimens from 307 pregnant women and 174 neonates were collected, resulting in 172 mother-neonate paired specimens. A total of 278 questionnaires were received from study participants. MRSA prevalence in pregnant women was 1.0% and 0.3% for nasal and vaginal specimens, respectively. The MRSA prevalence in neonates was 0% and 0.6% for nasal and umbilical specimens, respectively. Four different antimicrobial susceptibility profiles were observed among the MRSA isolates. The results did not show transmission of MRSA from pregnant women to their newborns, or infections of newborns with MRSA. It is expected that the results of this study will inform future decisions on surveillance, treatment and prevention of MRSA infections in Nevada
Quantum Electrodynamics vacuum polarization solver
The self-consistent modeling of vacuum polarization due to virtual
electron-positron fluctuations is of relevance for many near term experiments
associated with high intensity radiation sources and represents a milestone in
describing scenarios of extreme energy density. We present a generalized
finite-difference time-domain solver that can incorporate the modifications to
Maxwell's equations due to vacuum polarization. Our multidimensional solver
reproduced in one dimensional configurations the results for which an analytic
treatment is possible, yielding vacuum harmonic generation and birefringence.
The solver has also been tested for two-dimensional scenarios where finite
laser beam spot sizes must be taken into account. We employ this solver to
explore different types of counter-propagating configurations that can be
relevant for future planned experiments aiming to detect quantum vacuum
dynamics at ultra-high electromagnetic field intensities
- …