Measurement of polarization observables T, P, and H in π0 and η photoproduction off quasi-free nucleons.

The target asymmetry T, recoil asymmetry P, and beam-target double polarization observable H were determined in exclusive π0 and η photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the γp→π0p and γp→ηp reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the ηn system at W=1.68GeV. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the S11(1535) and S11(1650) resonances within the S11-partial wave.

Observation of the pη

Data on the beam asymmetry Σ in the photoproduction of η mesons off protons are reported for tagged photon energies from 1130 to 1790 MeV (mass range from W=1748 MeV to W=2045 MeV). The data cover the full solid angle that allows for a precise moment analysis. For the first time, a strong cusp effect in a polarization observable has been observed that is an effect of a branch-point singularity at the pη^{'} threshold [E_{γ}=1447 MeV (W=1896 MeV)]. The latest BnGa partial wave analysis includes the new beam asymmetry data and yields a strong indication for the N(1895)1/2^{-} nucleon resonance, demonstrating the importance of including all singularities for a correct determination of partial waves and resonance parameters.

Application of a fibrinogen-thrombin-collagen-based hemostyptic agent in experimental injuries of liver and spleen.

FTCH is a recently developed material which consists of a collagen fleece containing fibrinogen, thrombin, and aprotinin integrated into its surface. FTCH is highly effective in sealing of tissues and in establishing hemostasis. We evaluated FTCH in experimentally produced liver (n = 6) and splenic (n = 12) injuries in 18 adult mongrel dogs. The stability of the parenchymal seal of the splenic injuries was tested by splenic tissue pressure elevation after temporary ligation of the splenic vein. No breakthrough bleeding occurred up to a parenchymal pressure of 16.3 +/- 5 mm Hg. Complete hemostasis was easily achieved in all animals before closure. When the dogs were re-explored postoperatively at intervals of either 14 or 30 days, there was no gross evidence of recurrent bleeding. Histologic examinations demonstrated a partially regenerated capsule covering an unspecific fibrovascular granulation tissue and progressive resorption of FTCH without significant inflammatory response. We conclude the following: FTCH provides adequate hemostatic control of experimental liver and splenic injuries. FTCH has excellent tissue compatibility and can be applied easily and safely to hemorrhaging parenchymal wounds. It will not replace adequate surgical techniques, but could be useful as a quickly available and easily applicable hemostatic means in diffuse or acute bleeding of liver and spleen.

The effectiveness of a fibrinogen-thrombin-collagen-based hemostatic agent in an experimental arterial bleeding model.

The hemostyptic agent used in this study is a recently developed material that consists of a collagen fleece containing fibrinogen, thrombin, and aprotinin integrated into its surface (FTCH) with excellent topical hemostyptic properties. The potential use of this substance for cardiovascular surgery was evaluated in a canine arterial bleeding model, which allowed comparison of the new agent with previously used pure collagen (CHF) as well as study of the hemostyptic under elevated blood pressure conditions. The results revealed that FTCH induced reliable hemostasis in 10-mm injuries of the canine hypogastric artery up to a systolic blood pressure of 260 mmHg, whereas bleeding control by CHF alone was impossible. To assess the long-term reliability of FTCH, the dogs were re-explored at intervals of 14 and 31 days after operation. At relaparotomy, the arteries were patent and there was no evidence of recurrent bleeding, thrombosis formation, or aneurysmatic changes. Histologic examinations showed well-healed vascular lesions covered by cell-depleted collagen tissue and a partially resorped hemostyptic. FTCH will not replace adequate surgical techniques but could be useful as a quickly available and easily applicable hemostatic means in otherwise uncontrollable diffuse or acute bleeding in cardiovascular surgery.