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We discuss the recent first principles calculations of the properties of interfaces between metals and oxides. This type of calculation is parameter-free, und exploits the density functional theory in the local density approximation to obtain the electronic structure of the system. At the same time the equilibrium atomic structure is sought, which minimises the excess energy of the interface. Up to now calculations of this type have been made for a few model interfaces which are atomically coherent, that is with commensurate lattices. Examples are Ag/MgO and Nb/Al2O3. In these cases it has been possible to predict the structures observed by high resolution electron microscopy. Besides the electronic structure of the interface, such calculations have provided values of the ideal work of adhesion. Electrostatic image forces in conjunction with the elementary ionic model provide a simple framework for understanding the results.

Molecular-dynamics simulations of the \ensuremath{\Sigma}3〈110〉(211) twin boundary in Ag predict a thin (1 nm) boundary phase of the 9R (\ensuremath{\alpha}-Sm) structure. High-resolution electron microscopy shows the presence of the predicted structure. We also calculate the energy ab initio for several hypothetical structures of Cu and Ag. Low energies of the 9R structure and other polytypes, low experimental stacking-fault energies, and the hcp-fcc energy difference are correlated and explained in terms of an effective nearest-neighbor Ising interaction.

We have performed ab initio local density-functional calculations of the equilibrium geometries, force constants, interface energies and works of adhesion for lattice-matched interfaces between rocksalt-structured MgO and a f.c.c. transition or noble metal (M=Ti or Ag). The interfaces had (001)M ‖(001)MgO and [100]M ‖ [100]MgO. We used the full-potential LMTO method. Both Ti and Ag are found to bind on top of oxygen. The interface force constants are 3–4 times larger for Ti|MgO than for Ag|MgO. These, as well as the M-O distances (2.18A˚for Ti O and 2.5A˚for Ag O), indicate that the Ti O bonding is predominantly covalent with the Ti oxidation state less than +1, and that the Ag-bonding is predominantly ionic, as in Ag2O, with the Ag oxidation state close to +1. The calculated interface energies are both 0.8 eV/M|MgO and the interface adhesions are, rspectively, 1.2 eV/Ti|MgO and 0.9 eV/Ag|MgO. The calculated (strained) surface energies are, respectively, 1.1 eV/Ti|, 0.7 eV/Ag| and 1.0 eV/MgO|.

The Hubbard \emph{U} of the \emph{3d} transition metal series as well as SrVO$_{3}$, YTiO$_{3}$, Ce and Gd has been estimated using a recently proposed scheme based on the random-phase approximation. The values obtained are generally in good accord with the values often used in model calculations but for some cases the estimated values are somewhat smaller than those used in the literature. We have also calculated the frequency-dependent \emph{U} for some of the materials. The strong frequency dependence of \emph{U} in some of the cases considered in this paper suggests that the static value of \emph{U} may not be the most appropriate one to use in model calculations. We have also made comparison with the constrained LDA method and found some discrepancies in a number of cases. We emphasize that our scheme and the constrained LDA method theoretically ought to give similar results and the discrepancies may be attributed to technical difficulties in performing calculations based on currently implemented constrained LDA schemes., Comment: 24 pages, 13 figures; Submitted to Phys. Rev. B

Grenzen und Grenzsituationen sind kein neues Aufgabengebiet der Ernahrungswissenschaft. Schon lange beschaftigt man sich mit korperlichen und gesundheitlichen Grenzen, erarbeitet Grenzwerte und Grenzkosten. Doch die in diesem Band thematisierten Grenzsituationen der Ernahrung greifen neue Fragen auf, die eine Chance fur Forschung und Wissenschaft darstellen.

Dicke Menschen haben es schwer. Denn ihre extremen Korpermase sind selten mit Waren aus Massenproduktion zu vereinbaren. „Stop size discrimination“ ist deshalb ein Slogan, mit dem sich Gruppen in den USA nicht nur gegen Kleider-, Schuh- und Mobelproduzenten, sondern neuerdings auch gegen die Autoindustrie wehren. Grund fur die Proteste sind die serienmasigen Autogurte. Sie sind zu kurz und halten auserdem einem uberdurchschnittlich grosen Korpergewicht im Falle eines Unfalls nicht stand. Extrem schwere Menschen stosen hier auf Grenzen, bedingt durch ihren Korper und sanktioniert durch die Gesellschaft.

Die Zukunft der Ernahrung oder der Ernahrungswissenschaft steht nicht zum ersten Mal im Mittelpunkt wissenschaftlicher Diskussion. Wahrend der Vorbereitung fur diesen Beitrag wurde deutlich, dass es in den letzten Jahren eine ganze Reihe von ahnlichen Veranstaltungen gab (Tab. 1). So fand 1994 in Giesen ein Forum zum Thema „Experimentelle Ernahrungsforschung 2000“ statt. Drei Jahre spater lud die DGE vor dem Hintergrund politischer Veranderungen zur Arbeitstagung „Ernahrungsberatung — quo vadis?“ ein. Die in Giesen stattgefundene Veranstaltung „Reflexionen Visionen“ war ebenfalls zukunftsgewandt konzipiert Anlass war damals die akademische Verabschiedung von Prof. Claus Leitzmann. Aber nicht nur die Wissenschaft, sondern auch Politik und Wirtschaft blicken in die Zukunft.

Recent large-scale mutagenesis screens have made the zebrafish the first vertebrate organism to allow a forward genetic approach to the discovery of developmental control genes. Mutations can be cloned positionally, or placed on a simple sequence length polymorphism (SSLP) map to match them with mapped candidate genes and expressed sequence tags (ESTs). To facilitate the mapping of candidate genes and to increase the density of markers available for positional cloning, we have created a radiation hybrid (RH) map of the zebrafish genome. This technique is based on somatic cell hybrid lines produced by fusion of lethally irradiated cells of the species of interest with a rodent cell line. Random fragments of the donor chromosomes are integrated into recipient chromosomes or retained as separate minichromosomes. The radiation-induced breakpoints can be used for mapping in a manner analogous to genetic mapping, but at higher resolution and without a need for polymorphism. Genome-wide maps exist for the human, based on three RH panels of different resolutions, as well as for the dog, rat and mouse. For our map of the zebrafish genome, we used an existing RH panel and 1,451 sequence tagged site (STS) markers, including SSLPs, cloned candidate genes and ESTs. Of these, 1,275 (87.9%) have significant linkage to at least one other marker. The fraction of ESTs with significant linkage, which can be used as an estimate of map coverage, is 81.9%. We found the average marker retention frequency to be 18.4%. One cR3000 is equivalent to 61 kb, resulting in a potential resolution of approximately 350 kb.

We have investigated the energies of a number of phases of ${\mathrm{ZrO}}_{2}$ using models of an increasing degree of sophistication: the simple ionic model, the polarizable ion model, the compressible ion model, and finally a model including quadrupole polarizability of the oxygen ions. The three structures which are observed with increasing temperatures are monoclinic, tetragonal, and cubic (fluorite). Besides these we have studied some hypothetical structures which certain potentials erroneously predict or which occur in other oxides with this stoichiometry, e.g., the \ensuremath{\alpha}-${\mathrm{PbO}}_{2}$ structure and rutile. We have also performed ab initio density functional calculations with the full-potential linear combination of muffin-tin orbitals method to investigate the cubic-tetragonal distortion. A detailed comparison is made between the results using classical potentials, the experimental data, and our own and other ab initio results. The factors which stabilize the various structure are analyzed. We find the only genuinely transferable model is the one including compressible ions and anion polarizability to the quadrupole level. \textcopyright{} 1996 The American Physical Society.

In order to get a better understanding of the energetics of ZrO2 (zirconia) ab initio calculations with the full potential linear muffin tin orbital method ( fp LMTO) have been performed on the tetragonal structure over a range of c/a and sublattice displacement. A new semi-empirical shell model is developed which makes use of Hartree-Fock calculations and includes compressible anions and quadrupolar distortions. The empirical model predicts energies for tetragonal distortion in agreement with the fp LMTO calculations. Furthermore, it enables us to understand why the seven-fold coordinated monoclinic phase is the low temperature equilibrium structure.

We discuss the recent first principles calculations of the properties of interfaces between metals and oxides. This type of calculation is parameter-free, and exploits the density functional theory in the local density approximation to obtain the electronic structure of the system. At the same time the equilibrium atomic structure is sought, which minimises the excess energy of the interface. Up to now calculations of this type have been made for a few model interfaces which are atomically coherent, that is with commensurate lattices. Examples are Ag/MgO and Nb/Al2O3. In these cases it has been possible to predict the structures observed by high resolution electron microscopy. The calculations are actually made in a supercell geometry, in which there are alternating nanolayers of metal and ceramic. Because of the effectiveness of metallic screening in particular, the interfaces between the nanolayers do not interfere much with each other.Besides the electronic structure of the interface, such calculations have provided values of the ideal work of adhesion. Electrostatic image forces in conjunction with the elementary ionic model provide a simple framework for understanding the results.An important role of such calculations is to develop intuition about the nature of the bonding, including the effects of charge transfer, which has formerly only been described in an empirical way. It may then be possible to build atomistic models of the metal/ceramic interaction which have a sound physical basis and can be calibrated against ab initio results. Simpler models are necessary if larger systems, including misfit dislocations and other defects, are to be simulated, with a view to understanding the atomic processes of growth and failure. Another area in which ab initio calculations can be expected to contribute is in the chemistry of impurity segregation and its effect at interfaces. Such theoretical tools are a natural partner to the experimental technique of high resolution electron energy loss spectroscopy for studying the local chemical environment at an interface.