Effect of Cu Content on the Structure,and Performance of Substoichiometric Cr–N Coatings

Cu–Cr–N coatings with Cu contents between 3 and 65 at.%, Cu/Cr ratios in the 0.04–4.5 range and 21–27 at.% N, synthesized by twin electron-beam Physical Vapor Deposition at 450 °C, were investigated and compared against substoichiometric Cr–N reference samples. The main objective of this study is to study the influence of Cu on the structure, and the subsequent effects on the mechanical properties, room (22 °C) and high temperature (500 and 840 °C) tribological performance of Cu–Cr–N coatings. Using X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and scanning electron microscopy, in combination with nanoindentation mechanical property measurements and laboratory-controlled ball-on-disc sliding experiments, it is shown that Cu–Cr–N coatings with low Cu content (3 at.%) possess sufficient wear resistance for high-temperature demanding tribological applications. The lubricious effect of oxide formation at high temperatures is also evaluated.     

Synthesis and characterization of niobium-doped potassium tetragonal tungsten bronzes, KxNbyW1?yO3

Needle-shaped crystals of sizes up to 5 μm × 5 μm × 40 μm of nominal composition K _x Nb _y W_1−y O₃ were synthesized by solid state method at 800 °C using appropriate amount of WO₃, WO₂, Nb₂O₅, and K₂WO₄. The samples were characterized with XRD, SEM, microprobe analysis, optical spectroscopy, and Raman spectroscopy. The XRD patterns of the samples show single phase of tetragonal tungsten bronze (TTB) type (P4/mbm, No. 127) up to y = 0.07. Structure refinements reveal an increase in cell parameter with increasing nominal niobium content within the TTB phase. The elemental compositions of the crystals determined by electron microprobe analysis also show an increase in Nb content with increasing y. With increasing Nb content the reflectivity minimum in the near infrared spectral range shifts towards lower wavenumber indicating the effect of decreasing carrier concentration. Pyrochlore type phase (KNbWO₆) is obtained as a second phase when nominal composition y > 0.07.     

Utilization and transformation of aquatic humic substances by autochthonous microorganisms

Aquatic humic substances (HS) from a bog lake water, a riverwater, and a groundwater were isolated after enrichment on XAD 8 columns and added to a Czapek-Dox nutrient broth which was used either in full strength or without glucose and/or NaNO3. The individual flasks were inoculated with natural microbial populations of corresponding water samples or with a Pseudomonas fluorescens strain isolated from groundwater. The presence of HS resulted in an increase of bacterial numbers in nearly all cultures incubated for 3 weeks at 25 degrees C on a shaker. HS reisolated from cultures without glucose or NaNO3 showed no or only minor quantitative differences as compared to those from sterile controls. In full strength nutrient broth up to 27% of HS were utilized. Data obtained by spectroscopic methods (UV/vis/FTIR) and elemental analysis indicated a decrease in particle size and a loss in aromaticity and aliphatic carbon in HS reisolated from the microbial cultures. Simultaneously an increase in the N content of HS was observed, which probably originated from some constituents of microbial biomass such as proteins and amino sugars. The NMR data also documented that significant transformations of HS occurred in the individual microbial cultures. After incubation, increased amounts of aromatic acids were detected in some liquid media and residual HS by GC/MS or capillary electrophoresis. 1H NMR spectroscopy was less effective in indicating structural differences in the HS than 13C NMR but revealed considerable detail of the microbial degradation of riverine HS, when limited sample was available. The newly developed NMR increment analysis provided substantial detail of aromatic structures in a microbially altered HS. The microbial degradation of HS strongly depended on the composition of the HS, the species selection of the microorganisms, and to a lesser extent on the culture conditions. For any series of identical inoculum and HS, full broth media initiated the most extensive alteration of HS.     

Amplitude and phase recovery of rotationally symmetric beams

Two methods are presented for the amplitude and phase recovery of optical beams with rotational symmetry. These are the tomographic method based on the ambiguity function and the one-step wavefront recovery based on the measurement of a phase-space distribution closely related to the Wigner distribution function. The results obtained from these two methods are compared, and the appropriateness of using either one of them for specific situations is discussed.     

Adsorption kinetics and mechanical properties of thiol-modified DNA-oligos on gold investigated by microcantilever sensors

Immobilised DNA-oligo layers are scientifically and technologically appealing for a wide range of sensor applications such as DNA chips. Using microcantilever-based sensors with integrated readout, we demonstrate in situ quantitative studies of surface-stress formation during self-assembly of a 25-mer thiol-modified DNA-oligo layer. The self-assembly induces a surface-stress change, which closely follows Langmuir adsorption model. The adsorption results in compressive surface-stress formation, which might be due to intermolecular repulsive forces in the oligo layer. The rate constant of the adsorption depends on the concentration of the oligo solution. Based on the calculated rate constants a surface free energy of the thiol-modified DNA-oligo adsorption on gold is found to be -32.4 kJ mol(-1). The adsorption experiments also indicate that first a single layer of DNA-oligos is assembled on the gold surface after which a significant unspecific adsorption takes place on top of the first DNA-oligo layer. The cantilever-based sensor principle has a wide range of applications in real-time local monitoring of chemical and biological interactions as well as in the detection of specific DNA sequences, proteins and particles.     

The Haskell Refactorer, HaRe, and its API

We demonstrate the Haskell Refactorer, HaRe, both as an example of a fully-functional tool for a complete (functional) programming language, and to show the API which HaRe provides for building source-level program transformations for Haskell. We comment on the challenges presented by the construction of this and similar tools for language frameworks and processors.