Relativistic corrections of one-nucleon current in low-energy three-nucleon photonuclear reactions

Proton-deuteron radiative capture and two- and three-body photodisintegration of 3He at low energy are described using realistic hadronic dynamics and including the Coulomb force. The sensitivity of the observables to the relativistic corrections of one-nucleon electromagnetic current operator is studied. Significant effects of the relativistic spin-orbit charge are found for the vector analyzing powers in the proton-deuteron radiative capture and for the beam-target parallel-antiparallel spin asymmetry in the three-body photodisintegration of 3He.Comment: 7 figures, accepted for publication in Phys. Rev.

Meson and Quark Degrees of Freedom and the Radius of the Deuteron

The existing experimental data for the deuteron charge radius are discussed. The data of elastic electron scattering are inconsistent with the value obtained in a recent atomic physics experiment. Theoretical predictions based on a nonrelativistic description of the deuteron with realistic nucleon-nucleon potentials and with a rather complete set of meson-exchange contributions to the charge operator are presented. Corrections arising from the quark-gluon substructure of the nucleon are explored in a nonrelativistic quark model; the quark-gluon corrections, not accounted for by meson exchange, are small. Our prediction for the deuteron charge radius favors the value of a recent atomic physics experiment.Comment: 20 pages, LaTeX, 4 Postscript figures, to appear in Few-Body-System

Overexpression of the ATP-dependent helicase RecG improves resistance to weak organic acids in Escherichia coli

Increased resistance to several weak organic acids was conferred on Escherichia coli by overexpression of the ATP-dependent helicase RecG and, to a lesser extent, by overexpressing the helicase RuvAB. This property of helicases was identified by reproducible selection of recG-bearing clones from genomic libraries of the acetate-resistant species Acetobacter aceti and Staphylococcus capitis. We show that overexpression of RecG from both species, but also from E. coli, increased the maximum biomass concentration attained by E. coli cultures that were grown in the presence of various weak organic acids and uncouplers. Furthermore, overexpression of RecG from A. aceti significantly improved the maximum growth rates of E. coli under weak organic acid challenge. Based on the known role of RecG in DNA replication/repair, our data provide a first indication that weak organic acids negatively affect DNA replication and/or repair, and that these negative effects may be counteracted by helicase activit