236 research outputs found
Long Range Structure of the Nucleon
The long range structure of the nucleon is discussed starting from the old
model of a quark bag with a pion cloud (``cloudy bag'') carrying on to the more
recent ideas of the parton model of the nucleon. On the basis of the most
recent measurements of the form factors at MAMI, JLab and MIT quantitative
results for nucleon charge densities are presented within both non-relativistic
and relativistic frameworks.Comment: 14 pages, 14 figure
The Decay of Unstable Noncommutative Solitons
We study the classical decay of unstable scalar solitons in noncommutative
field theory in 2+1 dimensions. This can, but does not have to, be viewed as a
toy model for the decay of D-branes in string theory. In the limit that the
noncommutativity parameter \theta is infinite, the gradient term is absent,
there are no propagating modes and the soliton does not decay at all. If \theta
is large, but finite, the rotationally symmetric decay channel can be described
as a highly excited nonlinear oscillator weakly coupled to a continuum of
linear modes. This system is closely akin to those studied in the context of
discrete breathers. We here diagonalize the linear problem and compute the
decay rate to first order using a version of Fermi's Golden Rule, leaving a
more rigorous treatment for future work.Comment: 36 pages, 7 figures, dedicated to Rudolf Haag. v2: uniform estimate
for Weyl criterion provided, refs adde
Hadron structure at small momentum transfer
Giving three examples, the form factors of the nucleon, the polarisability of
the charged pion and the interference of the with the
excitation of the nucleon in the -decay channel, it is
argued that the hadron structure at low momentum transfer is highly significant
for studying QCD.Comment: 7 pages, 9 figures. Contribution to the International School of
Nuclear Physics, 29th Ccourse, "Quarks in Hadrons and Nuclei", Erice, Sicily,
16 - 24 September 200
Ivabradine Reduces Chemokine-Induced CD4-Positive Lymphocyte Migration
Aims. Migration of CD4-positive lymphocytes into the vessel wall is a critical step in atherogenesis. Recent data suggest that ivabradine, a selective I(f)-channel blocker, reduces atherosclerotic plaque formation in apolipoprotein E-deficient mice, hitherto nothing is known about the mechanism by which ivabradine modulates plaque formation. Therefore, the present study investigated whether ivabradine regulates chemokine-induced migration of lymphocytes. Methods and results. Stimulation of CD4-positive lymphocytes with SDF-1 leads to a 2.0 ± 0.1 fold increase in cell migration (P < .01; n = 7). Pretreatment of cells with ivabradine reduces this effect to a maximal 1.2 ± 0.1 fold induction at 0.1 µmol/L ivabradine (P < .01 compared to SDF-1-treated cells, n = 7). The effect of ivabradine on CD4-positive lymphocyte migration was mediated through an early inhibition of chemokine-induced PI-3 kinase activity as determined by PI-3 kinase activity assays. Downstream, ivabradine inhibits activation of the small GTPase Rac and phosphorylation of the Myosin Light Chain (MLC). Moreover, ivabradine treatment reduces f-actin formation as well as ICAM3 translocation to the uropod of the cell, thus interfering with two important steps in T cell migration. Conclusion. Ivabradine inhibits chemokine-induced migration of CD4-positive lymphocytes. Given the crucial importance of chemokine-induced T-cell migration in early atherogenesis, ivabradine may be a promising tool to modulate this effect
Differential stellar population models: how to reliably measure [Fe/H] and [alpha/Fe] in galaxies
We present differential stellar population models, which allow improved
determinations of the ages, iron and alpha-element abundances of old stellar
populations from spectral fitting. These new models are calibrated at solar
abundances using the predictions from classical, semi-empirical stellar
population models. We then use the predictive power of fully synthetic models
to compute predictions for different [Fe/H] and [alpha/Fe]. We show that these
new differential models provide remarkably accurate fits to the integrated
optical spectra of the bulge globular clusters NGC6528 and NGC6553, and that
the inferred [Fe/H] and [alpha/Fe] agree with values derived elsewhere from
stellar photometry and spectroscopy. The analysis of a small sample of SDSS
early-type galaxies further confirms that our alpha-enhanced models provide a
better fit to the spectra of massive ellipticals than the solar-scaled ones.
Our approach opens new opportunities for precision measurements of abundance
ratios in galaxies.Comment: 5 pages, 5 figures, MNRAS in pres
Reproducibility of mild to moderate regurgitation of all heart valves by magnetic resonance imaging
Ultrasound simulation of peripheral nerves: development of a novel technology for training in regional anaesthesia
- …