15,377 research outputs found
Fermi matrix element with isospin breaking
Prompted by the level of accuracy now being achieved in tests of the
unitarity of the CKM matrix, we consider the possible modification of the Fermi
matrix element for the -decay of a neutron, including possible in-medium
and isospin violating corrections. While the nuclear modifications lead to very
small corrections once the Behrends-Sirlin-Ademollo-Gatto theorem is respected,
the effect of the mass difference on the conclusion concerning
is no longer insignificant. Indeed, we suggest that the correction to the value
of is at the level of
Effect of Nucleon Structure Variation in Super-allowed Fermi Beta-decay
There is a well known anomaly between the value of the Fermi decay constant
extracted from super-allowed Fermi beta-decay of nuclear isotriplets and that
required by unitarity of the Cabibbo-Kobayashi-Maskawa matrix. This discrepancy
remains at the level of a few tenths of a percent after the most rigorous
investigation of conventional nuclear and radiative corrections. Within the
framework of the quark-meson coupling model of nuclear matter, which has been
previously applied successfully to phenomena such as nuclear saturation and
nuclear charge symmetry violation, we show that it is possible to understand a
significant fraction of the observed anomaly.Comment: 11 pages with 1 figure and 1 tabl
The role of airway infection in chronic obstructive pulmonary disease
PhDThis. thesis examines the role of respiratory bacterial and viral infection in the natural
history of Chronic Obstructive Pulmonary Disease. The rationale for this study is
basedu pon previous data demonstratingt hat airway bacterial colonisationi s common
in stable COPD and that bacterial and viral pathogens are commonly detected at
exacerbations.
The methodsu sed have involved the careful characterisationa nd clinical follow up of
a cohort of patients with moderate to severe COPD in the stable state and at
exacerbation. Sampling of airway and systemic compartments enabled the detection
of respiratory pathogens and quantification of inflammation. Comparisons between
clinical indices and evidence of infection were performed to determine the
relationships between bacterial and viral infections and disease outcomes including
lung function decline and exacerbation severity.
The findings confirmed that lower airway bacterial colonisation is common in stable
COPD and is associated with airway inflammation. They demonstrated for the first
time a relationship between the degree of bacterial carriage and the rate of disease
progression. This study has also described novel evidence for persistence of
respiratorys yncytial virus in the lower airway and associationsw ith inflammation and
lung function decline and impaired anti-viral immune responsesT. he combined role
of human rhinoviral and bacterial infection at exacerbation has been studied and
factors influencing responsesto exacerbationt herapy determinedw ith the importance
of early initiation of treatment identified.
The findings in this thesis indicate that both viral and bacterial pathogens may play an
important role in the natural history of COPD and are therefore targets for potentially
novel interventions. This work suggests that viral and bacterial infections and their
interactions play an important role in modulating airway inflammation in stable
disease and at exacerbation thus impacting on both disease progression and
exacerbation severity. This work has provided a rationale for future investigation into
the mechanisms underlying susceptibility to infection in this important disease
Model-independent mixing and CP violation studies with and
Simulation studies are performed to assess the sensitivity of a
model-independent analysis of the flavour-tagged decays and to mixing and CP violation. The
analysis takes as input measurements of the decay strong-phase parameters
that are accessible in quantum-correlated pairs produced at the
resonance. It is shown that the model-independent approach is well
suited to the very large data sets expected at an upgraded LHCb experiment, or
future high luminosity facility, and that with 100M decays a statistical precision of around 0.01 and is
achievable on the CP violation parameters and , respectively.
Even with this very large sample the systematic uncertainties associated with
the strong-phase parameters will not be limiting, assuming that full use is
made of the available data sets of CLEO-c and BES-III.
Furthermore, it is demonstrated that large flavour-tagged samples can
themselves be exploited to provide information on the strong-phase parameters,
a feature that will be beneficial in the measurement of the CKM angle
with decays.Comment: 19 pages, 3 figures. New version fixes typos and incorrect references
after journal acceptanc
Conservation of structure and mechanism in primary and secondary transporters exemplified by SiaP, a sialic acid binding virulence factor from Haemophilus influenzae
Extracytoplasmic solute receptors (ESRs) are important components of solute uptake systems in bacteria, having been studied extensively as parts of ATP binding cassette transporters. Herein we report the first crystal structure of an ESR protein from a functionally characterized electrochemical ion gradient-dependent secondary transporter. This protein, SiaP, forms part of a tripartite ATP-independent periplasmic transporter specific for sialic acid in Haemophilus influenzae. Surprisingly, the structure reveals an overall topology similar to ATP binding cassette ESR proteins, which is not apparent from the sequence, demonstrating that primary and secondary transporters can share a common structural component. The structure of SiaP in the presence of the sialic acid analogue 2,3-didehydro-2-deoxyN-acetylneuraminic acid reveals the ligand bound in a deep cavity with its carboxylate group forming a salt bridge with a highly conserved Arg residue. Sialic acid binding, which obeys simple bimolecular association kinetics as determined by stopped-flow fluorescence spectroscopy, is accompanied by domain closure about a hinge region and the kinking of an alpha-helix hinge component. The structure provides insight into the evolution, mechanism, and substrate specificity of ESR-dependent secondary transporters that are widespread in prokaryotes
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