Systematics of quadrupolar correlation energies

We calculate correlation energies associated with the quadrupole shape degrees of freedom with a view to improving the self-consistent mean-field theory of nuclear binding energies. Systematic results are presented for 605 even-even nuclei from mass number 16 to the heaviest whose mass has been measured, using the Skyrme SLy4 interaction and the generator coordinate method. Correlation energies range from 0.5 to 6.0 MeV, and their inclusion improves two qualitative deficiencies of the mean-field theory, namely, the exaggerated shell effect at neutron magic numbers and the failure of mean-field theory to describe mutually enhanced magicity. For the mass table as a whole, the quadrupolar correlations improve binding energies, separation energies, and separation energy differences by 20%30%.     

Morphological and Thermal Properties of Vesicular Phospholipid Gels Studied by DSC,Rheometry and Electron Microscopy

Semisolid phospholipid preparations have been well known for several years and are still investigated as drug carrier systems, e.g. for potential cancer therapy. They may be applied parenterally as semisolid vesicular phospholipid gels suitable as implants for sustained drug release or as liposomal preparations after redisperging the stable storage form. Due to enhanced stability, mixtures of hydrated phospholipids and cholesterol are more suitable than natural unsaturated phospholipids. In order to describe characteristics of vesicular phospholipid gels, only a few techniques may be useful. Especially the structure of the semisolid preparation is not yet completely understood. We tried to get some more information about these systems by using a combination of freeze-fracture electron microscopy, differential scanning calorimetry and rheometry to elucidate, on the one hand, the inner structure or homogeneity and, on the other, the thermotropic phase transition of the three-dimensional lipid network and the temperature dependency of the fluidity/viscosity of the samples. Using freeze-fracture electron microscopy we found coexisting phospholipid domains of lamellar sheets and vesicular structures. With the help of differential scanning calorimetry the reasons for the different phase behaviour were elucidated. Rheometric measurements show increased intermediate viscosity at the thermotropic phase transition of the lipid bilayers, possibly induced by interacting membrane defects. This revised version was published online in August 2006 with corrections to the Cover Date.     

Finite element error bounds for a curve shrinking with prescribed normal contact to a fixed boundary

We approximate the evolution of a curve subject to motion bycurvature by linear finite elements. The curve evolves insidea given domain and meets orthogonally. We derive optimal boundsfor the error with respect to the L²- and H¹-norms and presentsome computed examples.     

Heated nontronite: Possible relations to the magnetic phase in the Martian soil

We have modified the iron-containing layer silicate nontronite into a magnetic sample by heat treatment at 900 C for 5 minutes and studied the properties of the sample by Mössbauer spectroscopy, X-ray powder diffraction and infrared spectroscopy. Mössbauer spectra obtained in applied magnetic fields show that the majority of the iron is situated in a ferrimagnetic phase, related to maghemite.     

Chemisorption and the properties of metal clusters

In an earlier [C.W. Bauschlicher, D.H. Liskow, C.F. Bender and H.F. Schaefer, J. Chem. Phys. 62 (1975) 4815] we reported model studies of the chemisorption of atomic hydrogen on the (0001) surface of metallic beryllium. Four distinct sites for chemisorption were considered and the surface was modeled by clusters as large as Be₁₀. In the present paper, this work has been extended in two directions. First, two distint Be₁₃ clusters have been studied in an analogous manner. Second, the predicted chemisorption characteristics have been correlated with several properties of the isolated metal clusters. Metal cluster properties investigated include the ionization potential, cohesive energy, and singlet—triplet separation. The various sites for chemisorption are compared and electronic structure considerations discussed.