Oxidation of low-index FeAl surfaces

The oxidation of the (100), (110) and (111) surfaces of the intermetallic compound FeAl has been investigated using LEED and XPS. On all three surfaces, oxidation at room temperature leads to the formation of an amorphous oxide film on top of an Al-depleted interlayer. The film growth can be divided into two regions of differing kinetics, i.e. the initial formation of a closed oxide film and a subsequent thickening. In the first region, the oxygen-uptake rate varies significantly with surface orientation, while in the thickening regime the uptake is the same for all surfaces. The maximum thickness as well as the composition of the oxide films were found to depend on the initial oxidation rate. At higher oxidation temperatures, ordered oxide films of around 5–8 Å in thickness are formed, very similar to those observed on NiAl. Photoemission spectra from these ordered phases showed evidence for Al atoms in two different chemical environments, i.e. the well-known oxide species in the interior of the film and an additional species present at the oxide/alloy interface.     

Chiral ordering in the nematic and an optically isotropic mesophase of bent-core mesogens with a halogen substituent at the central core

Two new homologous series of bent-core compounds have been synthesized. Their mesophase behaviour has been investigated by polarizing microscopy, differential scanning calorimetry, X-ray diffraction, NMR spectroscopy, and by dielectric and electro-optical measurements. It was found that, with one exception, all the chlorine-substituted compounds form a nematic phase and an optically isotropic 'banana phase'. The latter phase shows spontaneously chiral domains of opposite handedness. This phase may be considered as a type of smectic blue phase. The mesophase behaviour of the homologous bromine-substituted compounds is more complicated. Depending on the chain length, B₆, columnar, nematic or the isotropic 'banana phase' occur.     

Fractional Penetrations for Electrostatically Charged Fibrous Filters in the Submicron Particle Size Range

Particle penetrations through commercially available, electrically charged fibrous filters have been measured. The particles were monodisperse and in charge equilibrium. Tests were conducted for several particle sizes in the range 0.02 μm ≤ x ≤ 1 μm. The face velocity was varied in the range of 2 cm/s to 30 cm/s. The penetration has a bimodal dependence on particle size. This behaviour is not found for uncharged filters. The reduction in penetration and bimodal dependence is attributed to electrical collection effects. As the face velocity is increased, the electrostatic collection effects are significantly reduced. The results agree quantitatively with a model for particle penetration through charged fibrous filters recently presented in the literature by the authors.     

Geometrische Extremwertaufgaben in dynamischer Behandlung

There are some shortcomings in the treatment of extreme value problems in current schoolbooks. Most extreme value problems are geometrical problems. The methods of dynamic geometry open up new possibilities of preformal treatment of geometrical extreme value problems. Figures made movable by direct manipulation permit an experimental investigation of their quantitative characteristics with the goal of detecting extremal properties and determining them approximatively. Illustration of quasi-empirical functions in the form of graphical representations is an important technique. Cabri Géomètre II is recommended as an appropriate tool.     

Nickel(0)-induzierte C---C-verknüpfung von heterokumulenen: Bildung von oxanilid aus phenylisocyanat

In the presence of small amounts of aromatic N-heterocycles, nickel(0) couples two phenylisocyanate molecules with C---C bond formation. After hydrolysis oxanilide is obtained.     

High temperature gluon matter in the background gauge

The polarisation tensor of gluons in high temperature QCD matter is discussed in the back-ground gauge and compared with that in the temporal axialA ₀=0 gauge. In both of these the gluon polarisation tensor alone is sufficient to give the asymptotically free sign of the QCD beta function. In the former the beta function and the imaginary part of the polarisation tensor are coupled in such a way that asymptotic freedom implies instability of plasma oscillations. In the latter, due to the non-covariance of the gauge condition, the beta function and the imaginary part are decoupled in such a way that the sign of the imaginary part corresponds to stable plasma oscillations.     

Characterization of rhenium-silicon thin films

Rhenium-silicon thin films have been characterized as promising compounds of thermoelectric applications by means of analytical transmission electron microscopy and X-ray diffraction referring to composition, morphology, short-range order and phase formation. Beyond the discussion of the results some methodical aspects and problems are presented.     

The approach to equilibrium in a quark-gluon plasma

I review work done during the last year on the problem of color equilibration in a quarkgluon plasma.