Contribution to the analytical characterization of coatings produced by thermal spraying

This paper reports on the use of Auger electron spectroscopy (AES)/ depth profile analysis for the investigation of plasma-sprayed coatings. Prior to spraying the St 37 substrates are heated to 300 °C or 500 °C for ceramic or metallic layers, respectively. Studies of the starting materials and of the interfaces are important if the adhesion mechanism is to be understood. Therefore the initial components—the unheated and heated substrates and the powder particles NiCrAl, Al₂O₃ and ZrO₂-7.25Y₂O₃—are analyzed. Depth profiles obtained from two coatings St 37/NiCrAl and St 37/Al₂O₃ show the influence of plasmaspraying on substrate surfaces and sprayed particles. Plasma-spraying mainly causes a decrease of superficial carbon contamination for both coating layers. In the case of St 37/NiCrAl incorporation of carbon in the sprayed layer is observed. The whole layer is almost completely oxidized except for some areas where substrate and particle material are present. It is assumed that these areas are identical with so-called adherence zones.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Geometric construction of the global base of the quantum modified algebra of\hat gl_N

A geometric construction of the modified quantum algebra ofgln was given in [BLM]. It was then observed independentely by Lusztig and Ginzburg-Vasserot (see [L1], [GV]) that this construction admits an affine analogue in terms of periodic flags of lattices. However the compatibility of the canonical base of the modified algebra and of the geometric base given by intersection cohomology sheaves on the affine flag variety was never proved. The aim of the paper is to prove this compatibility. As a consequence we prove a recent conjecture of Lusztig (see [L1]). Of course, our proof would work also in the finite type case.Partially supported by EEC grant no. ERB FMRX-CT97-0100.     

Adsorption of hydrogen and of oxygen on an open metal surface-HREELS investigation at Ni(311)

The adsorption behavior of hydrogen and oxygen on the stepped Ni(311) surface has been investigated by HREELS. A series of metastable phases was found for hydrogen adsorption at low temperatures with a succession of different adsorption sites indicated by the following loss peaks: 55 and 149 meV for the threefold site, shifting with higher coverage to 65 and 155 meV, respectively; 40 and 90 meV for the fourfold site, shifting to 35 and 85 meV with coverage; and 110 and 124 meV for an additional site between close packed rows. Room temperature adsorption of hydrogen leads to the reconstruction of the surface with occupation of three- and fourfold sites, represented by loss peaks at 60 and 145 meV for the threefold site and 74 meV for the fourfold site. This phase is the thermodynamically stable one. Oxygen is most likely initially adsorbed on a bridge site (loss peak at 66 meV). The stepped surface is already oxidized at very low exposures to oxygen, as seen by the characteristic vibration for oxide islands at 55 meV and later by the Fuchs-Kliewer mode of NiO at 68 meV.     

Study of metal containing hydrogenated carbon films by STM/AFM and SAXS

Metal-containing amorphous hydrogenated carbon films are of high interest for industrial applications because of their excellent frictional properties, their high abrasive wear resistance and their electrical conductivity, which can be adjusted in a range of 10–12 orders of magnitude. In order to get insight into the mechanical and electrical properties it is necessary to study the nanostructure of the films. The structure consists of small nanometer sized metallic or carbidic particles, which are embedded in a three dimensional amorphous hydrogen-carbon matrix. Anomalous small angle X-ray scattering (ASAXS) and scanning tunneling microscopy (STM) have been used to determine size- and distance-distributions of the particles as a function of metal content. Problems and restrictions of both methods will be discussed. Furthermore the capabilities of scanning probe techniques to distinguish different materials on a nanometer scale (material contrast) have been studied employing barrier height imaging (dI/dz) and friction force microscopy.Dedicated to Professor Dr. rer. nat. Dr. h. c. Hubertus Nickel on the occasion of his 65th birthday     

How are theoretical approaches expressed in research practices? A report on an experience in comparing theoretical approaches with respect to the construction of research problems

This article explores the idea that theoretical approaches might be usefully compared in terms of the ways in which they lead researchers to construe commonsense classroom problems. It reports an experience when one such problem was posed to a range of researchers with different theoretical backgrounds. They were invited to propose an answer, and to reframe the classroom problem as a research problem. As anticipated, responses adopted particular theoretical perspectives that “privileged” certain objects of study and modes of explanation. Nevertheless, where responses did appeal to a common theoretical perspective, sometimes used in combination with others, there could be quite sharp differences in conceptualisation, proposed action, and research intention.     

Identification of Structure–Activity Relationships from Screening a Structurally Compact DNA‐Encoded Chemical Library

Methods for the rapid and inexpensive discovery of hit compounds are essential for pharmaceutical research and DNA‐encoded chemical libraries represent promising tools for this purpose. We here report on the design and synthesis of DAL‐100K, a DNA‐encoded chemical library containing 103 200 structurally compact compounds. Affinity screening experiments and DNA‐sequencing analysis provided ligands with nanomolar affinities to several proteins, including prostate‐specific membrane antigen and tankyrase 1. Correlations of sequence counts with binding affinities and potencies of enzyme inhibition were observed and enabled the identification of structural features critical for activity. These results indicate that libraries of this type represent a useful source of small‐molecule binders for target proteins of pharmaceutical interest and information on structural features important for binding.