1,236 research outputs found
C3b/iC3b Deposition on Streptococcus pneumoniae Is Not Affected by HIV Infection
Streptococcus pneumoniae is a common cause of infection in both HIV positive patients and those with complement deficiencies. We hypothesised that HIV positive individuals might exhibit reduced opsonisation of pneumococcus with complement due to reduced levels of S. pneumoniae specific IgG. We discovered no difference in C3 deposition on S. pneumoniae between HIV positive or negative individuals, and furthermore C3 deposition remained unchanged as HIV progressed towards AIDS. We found no correlation between C3 deposition on S. pneumoniae and CD4 cell count in HIV infected individuals. Hence we have demonstrated no failure of complement immunity in HIV positive patients
On the precision of chiral-dispersive calculations of scattering
We calculate the combination (the Olsson sum rule)
and the scattering lengths and effective ranges , and ,
dispersively (with the Froissart--Gribov representation) using, at
low energy, the phase shifts for scattering obtained by Colangelo,
Gasser and Leutwyler (CGL) from the Roy equations and chiral perturbation
theory, plus experiment and Regge behaviour at high energy, or directly, using
the CGL parameters for s and s. We find mismatch, both among the CGL
phases themselves and with the results obtained from the pion form factor. This
reaches the level of several (2 to 5) standard deviations, and is essentially
independent of the details of the intermediate energy region ( GeV) and, in some cases, of the high energy behaviour assumed. We discuss
possible reasons for this mismatch, in particular in connection with an
alternate set of phase shifts.Comment: Version to appear in Phys. Rev. D. Graphs and sum rule added. Plain
TeX fil
Study of below 1 GeV using Integral Equation Approach
The scattering of is studied using the axial
anomaly, elastic unitarity, analyticity and crossing symmetry. Using the
technique to derive the Roy's equation, an integral equation for the P-wave
amplitude is obtained in terms of the strong P-wave pion pion phase shifts. Its
solution is obtained numerically by an iteration procedure using the starting
point as the solution of the integral equation of the Muskelshsvilli-Omnes
type. It is, however, ambiguous and depends sensitively on the second
derivative of the P-wave amplitude at which cannot directly be
measured.Comment: 26 pages, 10 figure
On the precision of the theoretical predictions for pi pi scattering
In a recent paper, Pelaez and Yndurain evaluate some of the low energy
observables of pi pi scattering and obtain flat disagreement with our earlier
results. The authors work with unsubtracted dispersion relations, so that their
results are very sensitive to the poorly known high energy behaviour of the
scattering amplitude. They claim that the asymptotic representation we used is
incorrect and propose an alternative one. We repeat their calculations on the
basis of the standard, subtracted fixed-t dispersion relations, using their
asymptotics. The outcome fully confirms our earlier findings. Moreover, we show
that the Regge parametrization proposed by these authors for the region above
1.4 GeV violates crossing symmetry: Their ansatz is not consistent with the
behaviour observed at low energies.Comment: Added more material, mostly in Sects. 7, 8 and 9, in support of the
same conclusions. Latex, 28 pages, 3 figure
The Inverse Amplitude Method in Scattering in Chiral Perturbation Theory to Two Loops
The inverse amplitude method is used to unitarize the two loop
scattering amplitudes of SU(2) Chiral Perturbation Theory in the ,
and channels. An error analysis in terms of the low energy
one-loop parameters and existing experimental data is
undertaken. A comparison to standard resonance saturation values for the two
loop coefficients is also carried out. Crossing
violations are quantified and the convergence of the expansion is discussed.Comment: (Latex, epsfig) 30 pages, 13 figures, 8 table
Analyticity, Crossing Symmetry and the Limits of Chiral Perturbation Theory
The chiral Lagrangian for Goldstone boson scattering is a power series
expansion in numbers of derivatives. Each successive term is suppressed by
powers of a scale, , which must be less than of order where is the Goldstone boson decay constant and is the
number of flavors. The chiral expansion therefore breaks down at or below . We argue that the breakdown of the chiral expansion is
associated with the appearance of physical states other than Goldstone bosons.
Because of crossing symmetry, some ``isospin'' channels will deviate from their
low energy behavior well before they approach the scale at which their low
energy amplitudes would violate unitarity. We argue that the estimates of
``oblique'' corrections from technicolor obtained by scaling from QCD are
untrustworthy.Comment: harvmac, 18 pages (3 figures), HUTP-92/A025, BUHEP-92-18, new version
fixes a TeX problem in little mod
Another look at scattering in the scalar channel
We set up a general framework to describe scattering below 1 GeV
based on chiral low-energy expansion with possible spin-0 and 1 resonances.
Partial wave amplitudes are obtained with the method, which satisfy
unitarity, analyticity and approximate crossing symmetry. Comparison with the
phase shift data in the J=0 channel favors a scalar resonance near the
mass.Comment: 17 pages, 5 figures, REVTe
Personalised service? Changing the role of the government librarian
Investigates the feasibility of personalised information service in a government department. A qualitative methodology explored stakeholder opinions on the remit, marketing, resourcing and measurement of the service. A questionnaire and interviews gathered experiences of personalised provision across the government sector. Potential users were similarly surveyed to discuss how the service could meet their needs. Data were analysed using coding techniques to identify emerging theory. Lessons learned from government librarians centred on clarifying requirements, balancing workloads and selective marketing. The user survey showed low usage and awareness of existing specialist services, but high levels of need and interest in services repackaged as a tailored offering. Fieldwork confirmed findings from the literature on the scope for adding value through information management advice, information skills training and substantive research assistance and the need to understand business processes and develop effective partnerships. Concluding recommendations focus on service definition, strategic marketing, resource utilisation and performance measurement
Pion and Kaon Vector Form Factors
We develop a unitarity approach to consider the final state interaction
corrections to the tree level graphs calculated from Chiral Perturbation Theory
() allowing the inclusion of explicit resonance fields. The method is
discussed considering the coupled channel pion and kaon vector form factors.
These form factors are then matched with the one loop results. A very
good description of experimental data is accomplished for the vector form
factors and for the P-wave phase shifts up to
GeV, beyond which multiparticle states play a non negligible role. In
particular the low and resonance energy regions are discussed in detail and for
the former a comparison with one and two loop is made showing a
remarkable coincidence with the two loop results.Comment: 20 pages, 7 figs, to appear in Phys. Rev.
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