155 research outputs found
Exclusive measurement of coherent eta photoproduction from the deuteron
Coherent photoproduction of eta mesons from the deuteron has been measured
from threshold up to incident photon energies of 750 MeV using the photon
spectrometer TAPS at the tagged photon facility at the Mainz microtron MAMI.
For the first time, differential coherent cross sections have been deduced from
the coincident detection of the eta meson and the recoil deuteron. A missing
energy analysis was used for the suppression of background events so that a
very clean identification of coherent eta-photoproduction was achieved. The
resulting cross sections agree with previous experimental results except for
angles around 90 deg in the photon-deuteron cm-system where they are smaller.
They are compared to various model calculations.Comment: 4 pages, 4 figure
CXCL5 limits macrophage foam cell formation in atherosclerosis
The ELR+-CXCL chemokines have been described typically as potent chemoattractants and activators of neutrophils during the acute phase of inflammation. Their role in atherosclerosis, a chronic inflammatory vascular disease, has been largely unexplored. Using a mouse model of atherosclerosis, we found that CXCL5 expression was upregulated during disease progression, both locally and systemically, but was not associated with neutrophil infiltration. Unexpectedly, inhibition of CXCL5 was not beneficial but rather induced a significant macrophage foam cell accumulation in murine atherosclerotic plaques. Additionally, we demonstrated that CXCL5 modulated macrophage activation, increased expression of the cholesterol efflux regulatory protein ABCA1, and enhanced cholesterol efflux activity in macrophages. These findings reveal a protective role for CXCL5, in the context of atherosclerosis, centered on the regulation of macrophage foam cell formation
Study of nucleon resonances with electromagnetic interactions
Recent developments in using electromagnetic meson production reactions to
study the structure of nucleon resonances are reviewed. Possible future works
are discussed.Comment: 25 pages, 19 figure
Threshold enhancement in eta photoproduction from 2H and 4He
The photoproduction of eta-mesons from 2H and 4He has been studied for
energies close to the production thresholds. The experiments were carried out
with the tagged photon beam of the Mainz MAMI accelerator. The eta-mesons were
detected via their two photon decays with the electromagnetic calorimeter TAPS.
Total cross sections, angular and momentum distributions of the eta-mesons have
been determined for both reactions. The total cross sections in the threshold
region show a large enhancement over the predictions of a participant -
spectator model, indicating significant final state interaction effects. The
results are compared to recent model calculations taking into account
nucleon-nucleon and nucleon-eta final state interaction effects on different
levels of sophistication.Comment: 8 pages, 6 figure
The helicity amplitudes A and A for the D resonance obtained from the reaction}
The helicity dependence of the reaction
has been measured for the first time in the photon energy range from 550 to 790
MeV. The experiment, performed at the Mainz microtron MAMI, used a
4-detector system, a circularly polarized, tagged photon beam, and a
longitudinally polarized frozen-spin target. These data are predominantly
sensitive to the resonance and are used to determine its
parameters.Comment: 5 pages, 4 figure
First measurement of the Gerasimov-Drell-Hearn integral for Hydrogen from 200 to 800 MeV
A direct measurement of the helicity dependence of the total photoabsorption
cross section on the proton was carried out at MAMI (Mainz) in the energy range
200 < E_gamma < 800 MeV. The experiment used a 4 detection system, a
circularly polarized tagged photon beam and a frozen spin target.
The contributions to the Gerasimov-Drell-Hearn sum rule and to the forward
spin polarizability determined from the data are 226 \pm 5 (stat)\pm
12(sys) \mu b and -187 \pm 8 (stat)\pm 10(sys)10^{-6} fm^4, respectively, for
200 < E_\gamma < 800 MeV.Comment: 6 pages, 3 figures, 3 table
Coherent \pi^\circ photoproduction from ^4He
Differential cross sections and beam asymmetries for coherent \pi^\circ
photoproduction from ^4He in the \Delta energy-range have been measured with
high statistical and systematic precisions using both decay photons for
identifying the process.The experiment was performed at the MAinz MIcrotron
using the TAPS photon spectrometer and the Glasgow/Mainz tagged photon
facility. The differential cross sections are in excellent agreement with
predictions based on the DWIA if an appropriate parametrization of the
\Delta-nuclear interaction is applied. The beam asymmetries are interpreted in
terms of degrees of linear polarization of collimated coherent bremsstrahlung.
The expected increase of the degree of linear polarization with decreasing
collimation angle is confirmed. Agreement with calculations is obtained on a
few-percent level of precision in the maxima of the coherent peaks.Comment: 22 pages, 6 figure
The Different Function of Single Phosphorylation Sites of Drosophila melanogaster Lamin Dm and Lamin C
Lamins' functions are regulated by phosphorylation at specific sites but our understanding of the role of such modifications is practically limited to the function of cdc 2 (cdk1) kinase sites in depolymerization of the nuclear lamina during mitosis. In our study we used Drosophila lamin Dm (B-type) to examine the function of particular phosphorylation sites using pseudophosphorylated mutants mimicking single phosphorylation at experimentally confirmed in vivo phosphosites (S25E, S45E, T435E, S595E). We also analyzed lamin C (A-type) and its mutant S37E representing the N-terminal cdc2 (mitotic) site as well as lamin Dm R64H mutant as a control, non-polymerizing lamin. In the polymerization assay we could observe different effects of N-terminal cdc2 site pseudophosphorylation on A- and B-type lamins: lamin Dm S45E mutant was insoluble, in contrast to lamin C S37E. Lamin Dm T435E (C-terminal cdc2 site) and R64H were soluble in vitro. We also confirmed that none of the single phosphorylation site modifications affected the chromatin binding of lamin Dm, in contrast to the lamin C N-terminal cdc2 site. In vivo, all lamin Dm mutants were incorporated efficiently into the nuclear lamina in transfected Drosophila S2 and HeLa cells, although significant amounts of S45E and T435E were also located in cytoplasm. When farnesylation incompetent mutants were expressed in HeLa cells, lamin Dm T435E was cytoplasmic and showed higher mobility in FRAP assay
Helicity dependence of the γ→p→→nπ+π0 reaction in the second resonance region
The helicity dependence of the total cross section for the reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D13 resonance.
peerReviewe
Dynamical properties of algebraic systems : a study in closed geodesics
To a great extent, rigidity theory is the study of boundaries of semisimple groups. Here we investigate the action of a lattice on such a boundary. While we can construct topological factors for real rank 1 groups we show the nonexistence of such factors in higher rank for some cases.
We also study the geodesic flow on a compact locally symmetric manifold of the noncompact type. He calculate metric and topological entropies and see that the Liouville measure is a measure or maximal entropy. This leads to a study of compact maximal flats. We give a new proof of their density in the space of all flats. We prove specification and expansiveness theorems for the geodesic flow and apply them to determine a growth rate for compact maximal flats. Finally, we give an example of a space with infinitely many closed singular geodesics
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