A geophysical survey within the Mesozoic magnitic anomaly sequence south of Bermuda

Also published as: Journal of Geophysical Research 84 (1979): 5487-5496This geophysical survey of an approximate 1° square covers Mesozoic magnetic anomalies M0, M2, and M4 south of Bermuda. Bathymetry, magnetics, seismic reflection profiling, and seismic refraction data are presented. The isochron trend within the survey area at magnetic anomaly M4 time is 025°. Two left lateral fracture zones exist: the southern fracture zone has an offset of <10 km at M4 time and 33 km at M0 time. The northern fracture zone has an offset of 37 km at M4 time and 26 km at M0 time. These changes in offset are accounted for by asymmetric spreading, an 11° change in trend of anomaly M0 relative to M4, and by M0 time, growth of a small right lateral fracture zone. Seismic refraction data provide poor control on the shallow crustal structure but suggest the presence of significant lateral inhomogeneities within layer 2.Prepared for the Office of Naval Research under Contract N00014-74-C-0262; NR 083-004

Relativistic nucleon optical potentials with isospin dependence in Dirac Brueckner Hartree-Fock approach

The relativistic optical model potential (OMP) for nucleon-nucleus scattering is investigated in the framework of Dirac-Brueckner-Hartree-Fock (DBHF) approach using the Bonn-B One-Boson- Exchange potential for the bare nucleon-nucleon interaction. Both real and imaginary parts of isospin-dependent nucleon self-energies in nuclear medium are derived from the DBHF approach based on the projection techniques within the subtracted T -matrix representation. The Dirac potentials as well as the corresponding Schrodinger equivalent potentials are evaluated. An improved local density approximation is employed in this analysis, where a range parameter is included to account for a finite-range correction of the nucleon-nucleon interaction. As an example the total cross sections, differential elastic scattering cross sections, analyzing powers for n, p + 27Al at incident energy 100 keV < E < 250 MeV are calculated. The results derived from this microscopic approach of the OMP are compared to the experimental data, as well as the results obtained with a phenomenological OMP. A good agreement between the theoretical results and the measurements can be achieved for all incident energies using a constant value for the range parameter.Comment: 10 pages, 16 figure

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4: II. 2H and 7Li NMR stimulated-echo experiment

We use 2H NMR stimulated-echo spectroscopy to measure two-time correlation functions characterizing the polymer segmental motion in polymer electrolytes PPO-LiClO4 near the glass transition temperature Tg. To investigate effects of the salt on the polymer dynamics, we compare results for different ether oxygen to lithium ratios, namely, 6:1, 15:1, 30:1 and infinity. For all compositions, we find nonexponential correlation functions, which can be described by a Kohlrausch function. The mean correlation times show quantitatively that an increase of the salt concentration results in a strong slowing down of the segmental motion. Consistently, for the high 6:1 salt concentration, a high apparent activation energy E_a=4.1eV characterizes the temperature dependence of the mean correlation times at Tg < T< 1.1T_g, while smaller values E_a=2.5eV are observed for moderate salt contents. The correlation functions are most nonexponential for 15:1 PPO-LiClO4, whereas the stretching is reduced for higher and lower salt concentrations. A similar dependence of the correlation functions on the evolution time in the presence and in the absence of ions indicates that addition of salt hardly affects the reorientational mechanism. For all compositions, mean jump angles of about 15 degree characterize the segmental reorientation. In addition, comparison of results from 2H and 7Li NMR stimulated-echo experiments suggests a coupling of ion and polymer dynamics in 15:1 PPO-LiClO4.Comment: 14 pages, 12 figure