Discrete duality finite volume schemes for Leray−Lions−type elliptic problems on general 2D meshes

Discrete duality finite volume schemes on general meshes, introduced by Hermeline and Domelevo and Omnès for the Laplace equation, are proposed for nonlinear diffusion problems in 2D with nonhomogeneous Dirichlet boundary condition. This approach allows the discretization of non linear fluxes in such a way that the discrete operator inherits the key properties of the continuous one. Furthermore, it is well adapted to very general meshes including the case of nonconformal locally refined meshes. We show that the approximate solution exists and is unique, which is not obvious since the scheme is nonlinear. We prove that, for general W^?1,p′(Ω) source term and W^1‐(1/p),p(?Ω) boundary data, the approximate solution and its discrete gradient converge strongly towards the exact solution and its gradient, respectively, in appropriate Lebesgue spaces. Finally, error estimates are given in the case where the solution is assumed to be in W^2,p(Ω). Numerical examples are given, including those on locally refined meshes. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007     

Recycling in telomerization of butadiene with D‐xylose: Pd(TPPTS)n‐KF/Al2O3 as an active catalyst

A palladium‐TPPTS catalyst heterogenized on KF/alumina has been shown to be effective and recyclable for the selective formation of monooctadienylxylopyranosides via the telomerization of butadiene with D ‐xylose. Copyright © 2007 John Wiley & Sons, Ltd.     

Solid-phase extraction on alkyl-bonded silica gels in inorganic analysis.

Solid-phase extraction (SPE) is an effective tool for the preconcentration of trace elements and their separation from various sample constituents. Octadecyl and other alkyl-bonded silica gels are most widely used for these purposes. The fundamentals of the SPE of inorganic ions are reviewed and compared with those of related techniques (liquid-liquid extraction and reversed-phase liquid chromatography). The extraction of ions in the form of chelate compounds, inorganic salts solvated by neutral reagents, and ion-pair compounds is considered. Numerous applications of SPE to the separation and preconcentration of different elements and their species, including on-line combinations with instrumental determination techniques, are described and tabulated.     

Simultane Ionen-Chromatographie von Kationen und Anionen mit Komplexonen als Elutionsmittel und selektiver UV-Detektion

Summary The complexones EDTA, DCTA and EGTA were investigated as eluting agents at various pH-values for the simultaneous separation of 9 cations and 6 anions using ion chromatography on a silica gel based anion exchanger (Nucleosil 10-Anion II). 1,2-Diaminocyclohexanetetraacetic acid (DCTA) proved to be the best eluting agent. UV spectrophotometry was used for both direct and indirect detection of the anions and anionic metal complexes and a detailed study was carried out with respect to selectivity of detection. This was facilitated by referring to the UV absorption spectra of the anions and metal complexes involved. By choice of a suitable wavelength between 203 and 270 nm and taking into account pH effects, a number of selective determinations were possible. Examples include Pb and Cu in the presence of excess of Ca and Mg as well as nitrate, nitrite and bromide in a large excess of chloride and sulphate. Some examples of detection limits are (g/l) nitrate 2, Fe(III) 3, Cu 9 and Pb 12 (sample volume 20 l, direct UV-detection). The Chromatographie behaviour of Fe(II) and Fe(III) was studied and discussed. Drinking water was analysed for chloride, nitrate and sulphate as well as Ca and Mg using DCTA in the eluent. Complete analyses can be carried out in less than 15 min.

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Herrn Prof. Dr. R. Neeb zum 60. Geburtstag gewidmet     

The formation of lactams of N-(2-amino)benzoylamino acids

N-(2-Nitro)benzoylamino acids were prepared by 2-nitrobenzoylation of amino acids via the mixed ethylcarbonic anhydride procedure. They were reduced catalytically to N-(2-amino)benzoylamino acids which underwent cyclization to the corresponding lactams under a variety of conditions. The use of this reaction sequence for stepwise degradation of peptides seems possible.     

Oxidative coupling of malononitrile with formation of 1,1,2,3,3-pentacyanopropene salts

A simple and convenient route for the synthesis of 1,1,2,3,3-pentacyanopropene salts is reported. These salts are formed by interaction of malononitrile with SeO₂ in presence of organic N-containing bases or pyridinium salts.