Untersuchung von Getreide, Mehl und Bachwaren

Ohne Zusammenfassung     

On the stoichiometry of the organic metal bis(ethylenedioxy)-tetrathiafulvalene chloride

We report on Shubnikov-de Haas and de Haas-van Alphen measurements of an organic metal based on the molecular donor bis(ethylenedioxy)-tetrathiavulvalene (= BEDO-TTF) and the anion Cl^- with H₂O molecules. The observed single oscillation frequency perfectly follows the two-dimensional dependence with T. The Fermi-surface area of of the first Brillouin zone proves a quarter-filled band, i.e., a 2:1 stoichiometry of the BEDO-TTF donor with respect to the anion. The apparent discrepancy to X-ray data which give a 1:1 ratio between BEDO-TTF and Cl^- is understood by replacement of H₂O molecules with (H₃O)⁺ ions. The proposed stoichiometry therefore is (BEDO-TTF)₂ ⁺(H₅O₂)⁺(Cl^-)₂. The cyclotron effective mass is when deduced from the temperature dependence of the fundamental oscillation amplitude, but strongly reduced when extracted from higher harmonics. This and the strong harmonic content of the oscillations signals an influence of the two-dimensional electronic structure and can be qualitatively understood by applying the concept of magnetic interaction to the effect of the oscillatory chemical potential. Received: 16 April 1998 / Revised: 7 July 1998 / Accepted: 9 July 1998     

Zur Untersuchung von Drogen und daraus hergestellten Produkten

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Preservation of bone collagen from the late Cretaceous period studied by immunological techniques and atomic force microscopy

Late Cretaceous avian bone tissues from Argentina demonstrate exceptional preservation. Skeletal elements are preserved in partial articulation and suspended in three dimensions in a medium-grained sandstone matrix, indicating unusual perimortem taphonomic conditions. Preservation extends to the microstructural and molecular levels. Bone tissues respond to collagenase digestion and histochemical stains. In situ immunohistochemistry localizes binding sites for avian collagen antibodies in fossil tissues. Immunohistochemical studies do not, however, guarantee the preservation of molecular integrity. A protein may retain sufficient antigenicity for antibody binding even though degradation may render it incapable of original function. Therefore, we have applied atomic force microscopy to address the integrity and functionality of retained organic structures. Collagen pull-off measurements not only support immunochemical evidence for collagen preservation for antibody recognition but also imply preservation of the whole molecular integrity. No appreciable differences in collagen pull-off properties were measured between fossil and extant bone samples under physiological conditions.     

Zum schnellen Nachweis von Bromiden in Alkalijodiden

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Universal conductance and conductivity at critical points in integer quantum Hall systems

The sample averaged longitudinal two-terminal conductance and the respective Kubo conductivity are calculated at quantum critical points in the integer quantum Hall regime. In the limit of large system size, both transport quantities are found to be the same within numerical uncertainty in the lowest Landau band, and , respectively. In the second-lowest Landau band, a critical conductance is obtained which indeed supports the notion of universality. However, these numbers are significantly at variance with the hitherto commonly believed value . We argue that this difference is due to the multifractal structure of critical wave functions, a property that should generically show up in the conductance at quantum critical points.     

The photoelectron spectra of gaseous zinc(II) and cadmium(II) chlorides,bromides, and iodides

The He I photoelectron spectra of the gaseous chlorides, bromides, and iodides of zinc(II) and cadmium(II) have been obtained using a high-temperature spectrometer equipped with an internally-located, laser-beam heated, sample oven. The spectral peaks have been assigned molecular-orbital origins by use of qualitatively-derived molecular-orbital diagrams.     

Nonstationary Markov decision problems with converging parameters

This paper considers the solution of Markov decision problems whose parameters can be obtained only via approximating schemes, or where it is computationally preferable to approximate the parameters, rather than employing exact algorithms for their computation.Various models are presented in which this situation occurs. Furthermore, it is shown that a modified value-iteration method may be employed, both for the discounted version and for the undiscounted version of the model, in order to solve the optimality equation and to find optimal policies. In both cases, the convergence rate is determined.As a side result, we characterize the asymptotic behavior of backward products of a geometrically convergent sequence of Markov matrices.