582 research outputs found
Baryon form factors: Model-independent results
Baryon form factors can be analyzed in a largely model-independent fashion in
terms of two complementary approaches. These are chiral perturbation theory and
dispersion relations. I review the status of dispersive calculations of the
nucleon electromagnetic form factors in the light of new data. Then, I present
the leading one-loop chiral perturbation theory analysis of the hyperon and the
strange nucleon form factors. Open problems and challenges are also discussed.Comment: 10 pp, LaTeX, 10 figures, plenary talk, NUCLEON '99, Frascati, June
1999, to appear in the proceedings (Nucl. Phys. A), typos corrected,
references update
Low energy analysis of the nucleon electromagnetic form factors
We analyze the electromagnetic form factors of the nucleon to fourth order in
relativistic baryon chiral perturbation theory. We employ the recently proposed
infrared regularization scheme and show that the convergence of the chiral
expansion is improved as compared to the heavy fermion approach. We also
discuss the inclusion of vector mesons and obtain an accurate description of
all four nucleon form factors for momentum transfer squared up to Q^2 \simeq
0.4 GeV^2.Comment: 44 pp, LaTeX2e, uses epsf and amsbs
Spectral functions of isoscalar scalar and isovector electromagnetic form factors of the nucleon at two-loop order
We calculate the imaginary parts of the isoscalar scalar and isovector
electromagnetic form factors of the nucleon up to two-loop order in chiral
perturbation theory. Particular attention is paid on the correct behavior of Im
and Im at the two-pion threshold
in connection with the non-relativistic 1/M-expansion. We recover the
well-known strong enhancement near threshold originating from the nearby
anomalous singularity at . In the
case of the scalar spectral function Im one finds a significant
improvement in comparison to the lowest order one-loop result. Higher order
-rescattering effects are however still necessary to close a remaining
20%-gap to the empirical scalar spectral function. The isovector electric and
magnetic spectral functions Im get additionally enhanced near
threshold by the two-pion-loop contributions. After supplementing their
two-loop results by a phenomenological -meson exchange term one can
reproduce the empirical isovector electric and magnetic spectral functions
fairly well.Comment: 10 pages, 6 figures, submitted to Physical Review
Transcriptomic Profiling in Childhood H1N1/09 Influenza Reveals Reduced Expression of Protein Synthesis Genes
We compared the blood RNA transcriptome of children hospitalized with influenza A H1N1/09, respiratory syncytial virus (RSV) or bacterial infection, and healthy controls. Compared to controls, H1N1/09 patients showed increased expression of inflammatory pathway genes and reduced expression of adaptive immune pathway genes. This was validated on an independent cohort. The most significant function distinguishing H1N1/09 patients from controls was protein synthesis, with reduced gene expression. Reduced expression of protein synthesis genes also characterized the H1N1/09 expression profile compared to children with RSV and bacterial infection, suggesting that this is a key component of the pathophysiological response in children hospitalized with H1N1/09 infection
Nucleon electromagnetic form factors and polarization observables in space-like and time-like regions
We perform a global analysis of the experimental data of the electromagnetic
nucleon form factors, in space-like and time-like regions. We give the
expressions of the observables in annihilation processes, such as , or , in terms of form factors. We discuss some
of the phenomenological models proposed in the literature for the space-like
region, and consider their analytical continuation to the time-like region.
After determining the parameters through a fit on the available data, we give
predictions for the observables which will be experimentally accessible with
large statistics, polarized annihilation reactions.Comment: 25 pages, 5 figures 7 table
Extraction of electromagnetic neutron form factors through inclusive and exclusive polarized electron scattering on polarized 3He target
Inclusive 3He(e,e') and exclusive 3He(e,e'n) processes with polarized
electrons and 3He have been theoretically analyzed and values for the magnetic
and electric neutron form factors have been extracted. In both cases the form
factor values agree well with the ones extracted from processes on the
deuteron. Our results are based on Faddeev solutions, modern NN forces and
partially on the incorporation of mesonic exchange currents.Comment: 28 pages, 29 Postscript figure
Extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
Nucleon electromagnetic form factor data (including recent data) is fitted
with models that respect the confinement and asymptotic freedom properties of
QCD. Gari-Krumpelmann (GK) type models, which include the major vector meson
pole contributions and at high momentum transfer conform to the predictions of
perturbative QCD, are combined with Hohler-Pietarinen (HP) models, which also
include the width of the rho meson and the addition of higher mass vector meson
exchanges, but do not evolve into the explicit form of PQCD at high momentum
transfer. Different parameterizations of the GK model's hadronic form factors,
the effect of including the width of the rho meson and the addition of the next
(in mass) isospin 1 vector meson are considered. The quality of fit and the
consistency of the parameters select three of the combined HP/GK type models.
Projections are made to the higher momentum transfers which are relevant to
electron-deuteron experiments. The projections vary little for the preferred
models, removing much of the ambiguity in electron-nucleus scattering
predictions.Comment: 18pp, 7 figures, using RevTeX with BoxedEPS macros; 1 new figure,
minor textual changes; email correspondence to [email protected]
Effect of recent R_p and R_n measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
The Gari-Krumpelmann (GK) models of nucleon electromagnetic form factors, in
which the rho, omega, and phi vector meson pole contributions evolve at high
momentum transfer to conform to the predictions of perturbative QCD (pQCD), was
recently extended to include the width of the rho meson by substituting the
result of dispersion relations for the pole and the addition of rho' (1450)
isovector vector meson pole. This extended model was shown to produce a good
overall fit to all the available nucleon electromagnetic form factor (emff)
data. Since then new polarization data shows that the electric to magnetic
ratios R_p and R_n obtained are not consistent with the older G_{Ep} and G_{En}
data in their range of momentum transfer. The model is further extended to
include the omega' (1419) isoscalar vector meson pole. It is found that while
this GKex cannot simultaneously fit the new R_p and the old G_{En} data, it can
fit the new R_p and R_n well simultaneously. An excellent fit to all the
remaining data is obtained when the inconsistent G_{Ep} and G_{En} is omitted.
The model predictions are shown up to momentum transfer squared, Q^2, of 8
GeV^2/c^2.Comment: 14 pages, 8 figures, using RevTeX4; email correspondence to
[email protected] ; minor typos corrected, figures added, conclusions
extende
Logarithmic corrections and soft photon phenomenology in the multipole model of the nucleon form factors
We analyzed the presently available experimental data on nucleon
electromagnetic form factors within a multipole model based on dispersion
relations. A good fit of the data is achieved by considering the coefficients
of the multipole expansions as logarithmic functions of the momentum transfer
squared. The superconvergence relations, applied to this coefficients, makes
the model agree with unitary constraints and pQCD asymptotics for the Dirac and
Pauli form factors. The soft photon emission is proposed as a mechanism
responsible for the difference between the Rosenbluth, polarization and
beam--target--asymmetry data. It is shown, that the experimentally measured
cross sections depend not only on the Dirac and Pauli form factors, but also on
the average number of the photons emitted. For proton this number is shown to
be different for different types of experimental measurements and then
estimated phenomenologically. For neutron the same mechanism predicts, that the
data form different types of experiments must coincide with high accuracy. A
joint fit of all the experimental data reproduce the dependence with the
accuracy . Predictions of the model, that 1) the ratios of the
proton form factors are different for Rosenbluth, polarization and
beam--target--asymmetry experiments and 2) similar ratios are nearly the same
for neutron, can be used for experimental verification of the model.Comment: 14 pages in 2-column format, 4 figures, references added, typos
corrected, minor changes in the text, accepted in Eur. Phys. Journal
3D Real-Time Echocardiography Combined with Mini Pressure Wire Generate Reliable Pressure-Volume Loops in Small Hearts
BACKGROUND:
Pressure-volume loops (PVL) provide vital information regarding ventricular performance and pathophysiology in cardiac disease. Unfortunately, acquisition of PVL by conductance technology is not feasible in neonates and small children due to the available human catheter size and resulting invasiveness. The aim of the study was to validate the accuracy of PVL in small hearts using volume data obtained by real-time three-dimensional echocardiography (3DE) and simultaneously acquired pressure data.
METHODS:
In 17 piglets (weight range: 3.6–8.0 kg) left ventricular PVL were generated by 3DE and simultaneous recordings of ventricular pressure using a mini pressure wire (PVL3D). PVL3D were compared to conductance catheter measurements (PVLCond) under various hemodynamic conditions (baseline, alpha-adrenergic stimulation with phenylephrine, beta-adrenoreceptor-blockage using esmolol). In order to validate the accuracy of 3D volumetric data, cardiac magnetic resonance imaging (CMR) was performed in another 8 piglets.
RESULTS:
Correlation between CMR- and 3DE-derived volumes was good (enddiastolic volume: mean bias -0.03ml ±1.34ml). Computation of PVL3D in small hearts was feasible and comparable to results obtained by conductance technology. Bland-Altman analysis showed a low bias between PVL3D and PVLCond. Systolic and diastolic parameters were closely associated (Intraclass-Correlation Coefficient for: systolic myocardial elastance 0.95, arterial elastance 0.93, diastolic relaxation constant tau 0.90, indexed end-diastolic volume 0.98). Hemodynamic changes under different conditions were well detected by both methods (ICC 0.82 to 0.98). Inter- and intra-observer coefficients of variation were below 5% for all parameters.
CONCLUSIONS:
PVL3D generated from 3DE combined with mini pressure wire represent a novel, feasible and reliable method to assess different hemodynamic conditions of cardiac function in hearts comparable to neonate and infant size. This methodology may be integrated into clinical practice and cardiac catheterization programs and has the capability to contribute to clinical decision making even in small hearts
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