Axial vector nuclear sum rules and exchange effects

The nuclear pionic vertex and its relation to the π-nuclear (charge exchange) scattering length are investigated using dispersion techniques. The aim is to extract information on mesonic (exchange current) effects in the pionic vertex and in the axial vector current matrix element.     

Pauli principle and renormalization of the pion nucleon interaction in nuclei

We show that the exclusion principle provides an alternative mechanism to the Lorentz-Lorenz effect for the renormalization of the pion-nucleon coupling constant in nuclei. This mechanism proves to be less sensitive to the range of the π - N forces. The implications for pion-nucleus scattering are discussed.     

Quenching and hardening in the transverse quasi-elastic peak

We study in the RPA framework the collective response of symmetric, infinite nuclear matter to a spin-isospin sensitive probe with both σ · q and σ × q couplings. The two responses, similar in the low-q region, differ markedly for moderate momenta (?1 fm^?1). Indeed the collective effect manifests itself quite differently in the two responses; whereas the longitudinal one displays a softening and an enhancement (due to the attractive character of the associated particle-hole force), the transverse response is quenched and hardened with respect to the free Fermi gas. The existing experimental data, which we analyze, are compatible with our results. We also explore the total strengths and find that for repulsive forces they are appreciably reduced by the RPA correlations. A large part of this quenching comes from the Δ-excitation (LLEE effect), but some reduction is still present even when the nucleonic degrees of freedom are neglected. This illustrates a violation of strength conservation brought about by the RPA correlations in the spin-isospin channel.     

Capillary electrochromatography of hydrophobic amines on continuous beds

The capillary electrochromatographic separation performance of hydrophobic amines and a related quaternary ammonium compound on continuous beds based on polymers of acrylamide has been studied. The chromatographic bed is polymerized in situ and the character of the polymers with regard to hydrophobicity and charge has been systematically changed by regulating its content of isopropyl and sulfonate ligands, respectively. The best performance was obtained for columns with a molar ratio of 1:80 for the sulfonate and isopropyl groups, and resulted in efficiencies up to 200000 plates per meter. The effects on retention, resolution and elution order by ionic strength, pH, and content of acetonitrile in the mobile phase have been investigated. The quaternary ammonium compound was always the least retained irrespective of pH. By increasing the pH, a reversal of the migration order between the tertiary and secondary amine was obtained. The results indicate a complex migration/retention mechanism where ion-exchange, adsorption and electrophoretic mobilities play a role. The concentration limit of detection could be lowered from 1.3 microg/mL to 50 pg/mL by using a high content of 2-propanol (96%) in the sample compared to dissolving the analytes in the mobile phase.     

Zur Bestimmung und Trennung des Titans

Ohne Zusammenfassung     

Nonlinear wave motion in magnetoelasticity

Archive for Rational Mechanics and Analysis -     

Quark spin-isospin sum rules and the adler-weisberger relation in nuclei

We use a quark model to extend the classical Gamow-Teller sum rule for the difference of the β^?andβ⁺ strengths to excitations of the nucleon (mainly the Δ isobar).A schematic model illustrates the realization of the new sum rule when a particle-hole force is introduced. We discuss the connection of our result with the model-independent Adler-Weisberger sum rule.     

Evidence against the existence of a low mass scalar boson from neutron-nucleus scattering

The existence of a weakly-coupled scalar boson, recently proposed to explain the apparent discrepancy in X-rays from muonic atoms is shown to be inconsistent with the angular distribution measurements in low energy neutron-nucleus scattering. Other negative evidence from various different physical situatiions is also briefly reviewed.