268 research outputs found
Pion Exchange Effects in Elastic Backward Proton-Deuteron Scattering
The elastic backward proton-deuteron scattering is analyzed within a
covariant approach based on the Bethe-Salpeter equation with realistic
meson-exchange interaction. Contributions of the one-nucleon and one-pion
exchange mechanisms to the cross section and polarization observables are
investigated in explicit form. Results of numerical calculations for the cross
section, tensor analyzing power and spin transfers are presented. The one-pion
exchange contribution is essential for describing the spin averaged cross
section, while in polarization observables it is found to be less important.Comment: 19 LaTeX pages, including 5 eps figure
Field induced phase transition in the few photon regime
Some features of the field induced phase transition accompanied by the vacuum
creation of an electron-positron plasma (EPP) in strong time-dependent electric
fields have been discussed in the work [1] in the domain of the tunneling
mechanism (, where is the characteristic frequency of
the external field and is the electron mass). In the present contribution
the features of the this process will be considered in the few photon domain
where . We observe a narrowing of the transient domain of the
fast oscillations and, mainly, a considerable growth of the effectiveness of
the EPP production. Under these circumstances, we see an increase of the
effectiveness of the EPP creation in the particular case of a bifrequent
excitation, where both mechanisms (tunneling and few photon) act simultaneously
[2,3].Comment: 6 pages, 4 figures, contribution to the Proceedings of the XXIII
International Baldin Seminar on "High Energy Physics Problems", Dubna,
Russia, September 19-24, 201
Staphylococcal enterotoxin B (SEB) activates TCR- and CD28-mediated inflammatory signals in the absence of MHC class II molecules
The inflammatory activity of staphylococcal enterotoxin B (SEB) relies on its capacity to trigger polyclonal T‐cell activation by binding both T‐cell receptor (TCR) and costimulatory
receptor CD28 on T cells and MHC class II and B7 molecules on antigen presenting cells (APC). Previous studies highlighted that SEB may bind TCR and CD28 molecules independently
of MHC class II, yet the relative contribution of these interactions to the pro‐inflammatory function of SEB remained unclear. Here, we show that binding to MHC class II is dispensable
for the inflammatory activity of SEB, whereas binding to TCR, CD28 and B7 molecules is pivotal, in both human primary T cells and Jurkat T cell lines. In particular, our finding is that
binding of SEB to B7 molecules suffices to trigger both TCR‐ and CD28‐mediated inflammatory signalling. We also provide evidence that, by strengthening the interaction between
CD28 and B7, SEB favours the recruitment of the TCR into the immunological synapse, thus inducing lethal inflammatory signallin
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