Zur Kenntnis der Kaliumthiochromite

KCrS₂, KCr₅S₈ and the new compound KCr₃S₅ were prepared by the reaction of H₂S with chromium in K₂CO₃ melts. KCr₃S₅ (space group C2/m,a=19.16 Å,b=3.49 Å,c=12.02 Å, β=123.0°) is isotypic with TlCr₃S₅ having a psilomelane like channel structure. The thermal degradation: $$KCrS_2 \xrightarrow{{ - K_2 S}}KCr_3 S_5 \xrightarrow{{ - K_2 S}}KCr_5 S_8$$ was studied and the topochemical relations between the products are discussed. A new layered phase K_0.5(H₂O)_0.2CrS₂ having a 2 H stacking sequence (space group P6₃/mmc,a=3.36 Å,c=16.83 Å) was prepared from polysulfide melts. The dehydration of this phase was studied by TGA and X-rays.     

Simultaneous co-extraction of organometallic species of different elements by accelerated solvent extraction and analysis by inductively coupled plasma mass spectrometry coupled to liquid and gas chromatography

This paper describes the development of an accelerated solvent extraction methodology that is capable of simultaneously extracting organometallic species of As, Sn and Hg in a semi-automated manner. Accelerated solvent extraction (ASE) methods based on previous research on the separate extraction of organotin and -arsenic species in our laboratory were adapted for the co-extraction of six different species from an oyster tissue certified reference material (BCR 710). For the first time, the extraction of MeHg by this technique is also investigated. The proposed ASE conditions employed 50% acetic acid in methanol at a temperature of 100 degrees C with up to five consecutive extraction cycles of 3 minutes. Extraction efficiencies for organoarsenic species ranged from 80% (dimethylarsinic acid, DMA) to 99% for arsenobetaine (AsB). Species of toxicological interest, such as dibutyltin (DBT), tributyltin (TBT) and methylmercury (MeHg), were extracted with mean recoveries of 81, 84 and 76%, respectively. The extracted species were analysed by gas chromatography/inductively coupled plasma mass spectrometry (GC/ICPMS; DBT, TBT and MeHg) and liquid chromatography/inductively coupled plasma mass spectrometry (LC/ICPMS; MMA, DMA, AsB) after ethylation with sodium tetraethylborate or dilution with water, respectively. In addition to those species for which the extraction efficiency was assessed during this study, a further five arsenic species (arsenite, arsenate and three unidentified species), as well as monobutyltin (MBT) and mono-, di- and triphenyltin, could also be extracted from other matrices. The developed ASE method provides a significant improvement over many currently available routine monitoring methods for trace element speciation due to the fact that it is capable of extracting several species of toxicological interest simultaneously and quantitatively.     

Multiresolution schemes for an extended clarifier-thickener model

A fully adaptive finite volume multiresolution scheme for one-dimensional strongly degenerate parabolic equations with discontinuous flux modelling an extended clarifier-thickener, is presented. The numerical scheme is based on a finite volume discretization using the approximation of Engquist-Osher for the flux and explicit time stepping. Cell averages multiresolution scheme speeds up CPU time and memory requirements. A particular feature of our scheme is the storage of the multiresolution representation of the solution in a dynamic graded tree. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical Approximation of Oscillatory Solutions of Hyperbolic-Elliptic Systems of Conservation Laws by Multiresolution Schemes

The generic structure of solutions of initial value problems of hyperbolic-elliptic systems, also called mixed systems, of conservation laws is not yet fully understood. One reason for the absence of a core well-posedness theory for these equations is the sensitivity of their solutions to the structure of a parabolic regularization when attempting to single out an admissible solution by the vanishing viscosity approach. There is, however, theoretical and numerical evidence for the appearance of solutions that exhibit persistent oscillations, so-called oscillatory waves, which are (in general, measure-valued) solutions that emerge from Riemann data or slightly perturbed constant data chosen from the interior of the elliptic region. To capture these solutions, usually a fine computational grid is required. In this work, a version of the multiresolution method applied to a WENO scheme for systems of conservation laws is proposed as a simulation tool for the efficient computation of solutions of oscillatory wave type. The hyperbolic-elliptic $2 \times 2$ systems of conservation laws considered are a prototype system for three-phase flow in porous media and a system modeling the separation of a heavy-buoyant bidisperse suspension. In the latter case, varying one scalar parameter produces elliptic regions of different shapes and numbers of points of tangency with the borders of the phase space, giving rise to different kinds of oscillation waves.     

Spectral Polarimeters Based on Integrated Acousto-Optical Ti:LiNbO3 TE-TM Converters

An integrated Ti:LiNbO3 acousto-optical TE-TM converter followed by a polarizer was used to realize a wavelength-selective polarimeter. The stop-band attenuation was shown to increase to > 28 dB when more mode converters were integrated on a chip. Based on this experience, a four-stage demonstration unit was built, and polarimetric spectra as well as the time evolution of the state of polarization were measured. Finally, a simple optical spectrum analyzer is proposed.     

The Influence of Hydrogen Adsorption on Magnetic Properties of Ni/Cu(001) Surface

Ni/Cu(001) is known as a unique system showing the spin-reorientation transition from an in-plane to out-of-plane magnetization direction when the Ni-overlayer thickness is increased. We investigate different relaxed multilayer structures with a hydrogen adlayer using the full-potential linearized augmented plane-wave method. The relaxed geometries, determined by total energy and atomic force calculations, show that H-monolayer strongly influences the interlayer distance between the Ni-surface and sub-surface layers yielding the outward relaxation of Ni-layer at H/Ni interface. Furthermore, large decrease of local magnetic moments at the top surface area is found for the surface covered by H. The magneto-crystalline anisotropy energies are calculated for fully relaxed H/Ni-films. The spin-reorientation transition critical thickness of 4 ML is found in good quantitative agreement with the experiment.     

Applications of Normal Forms for Weighted Leavitt Path Algebras: Simple Rings and Domains

Weighted Leavitt path algebras (wLpas) are a generalisation of Leavitt path algebras (with graphs of weight 1) and cover the algebras L _K (n, n + k) constructed by Leavitt. Using Bergman’s diamond lemma, we give normal forms for elements of a weighted Leavitt path algebra. This allows us to produce a basis for a wLpa. Using the normal form we classify the wLpas which are domains, simple and graded simple rings. For a large class of weighted Leavitt path algebras we establish a local valuation and as a consequence we prove that these algebras are prime, semiprimitive and nonsingular but contrary to Leavitt path algebras, they are not graded von Neumann regular.