A convergence study of two ocean models applied to a density driven flow

A three‐dimensional, baroclinic and rotational benchmark for hydrostatic coastal ocean models is suggested. The computational domain is a quadratic basin 200×200 km horizontally and 200 m deep. The lateral boundaries are closed. Solutions to the problems are estimated with two different sigma co‐ordinate models, both for the diagnostic and the prognostic case. Grid‐ and time‐converged results are presented. For the transports, convergence within two significant digits is reported. Copyright © 2001 John Wiley & Sons, Ltd.     

Krypton incorporation in sputtered silicon films

The incorporation of Kr in sputtered a-Si films has been investigated in a systematic way by varying the Kr to Si flux, yielding Kr concentrations up to 5 at%. Compositions were determined with X-ray microanalysis. A model has been applied to describe the composition of the growing film. The layers were characterized by positron annihilation, Raman spectroscopy and Mössbauer spectroscopy. The present results clearly indicate that ion assisted growth leads to a strong reduction of open volume defects, and that the Kr resides in very small clusters.     

Solvent and lipid dynamics of hydrated lipid bilayers by incoherent quasielastic neutron scattering

The microscopic dynamics of the planar, multilamellar lipid bilayer system 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) has been investigated using quasielastic neutron scattering. The DMPC was hydrated to a level corresponding to approximately nine water molecules per lipid molecule. Selective deuteration has been used to separately extract the dynamics of the water, the acyl chains, and the polar head groups from the strong incoherent scattering of the remaining hydrogen atoms. Furthermore, the motions parallel and perpendicular to the bilayers were probed by using two different sample orientations relative to the incident neutron beam. For both sample orientations, the results showed an onset of water motions at 260 K on the experimental time scale of about 100 ps. From lack of wave-vector dependence of the onset temperature for water motions, it is evident that the observed water dynamics is of mainly rotational character at such low temperatures. At 290 K, i.e., slightly below the gel-to-liquid transition around 295 K, the nature of the water dynamics had changed to a more translational character, well described by a jump-diffusion model. On the limited experimental time and length (about 10 A) scales, this jump-diffusion process was isotropic, despite the very anisotropic system. The acyl chains exhibited a weak onset of anharmonic motions already at 120 K, probably due to conformational changes (trans-gauche and/or syn-anti) in the plane of the lipid bilayers. Other anharmonic motions were not observed on the experimental time scale until temperature had been reached above the gel-to-liquid transition around 295 K, where the acyl chains start to show more substantial motions.