Optimal Convergence of Basic Schemes for Elliptic Boundary Value Problems with Strong Parabolic Layers

We consider a convection-diffusion problem with strong parabolic boundary layers and its discretization using upwind finite differences or bilinear finite elements on a layer-adapted mesh. Based on a new decomposition of the solution we are able to prove optimal uniform convergence results.     

Quantitative determination of specified chlorobiphenyls in fish with capillary gas chromatography and its use for monitoring and tolerance purposes

A gel permeation (GPC) clean-up procedure of fish samples in combination with capillary gas chromatography is used for the determination of individual chlorobiphenyls. The described method is compared with a more universal method based on saponification. Starting from a tolerance for PCB's expressed as a technical Aroclor, tolerance for some specified individual chlorobiphenyls are derived. It is shown that these tolerances for specified individual chlorobiphenyls can be used for monitoring and tolerance purposes. Rejection obtained with the Dutch PCB tolerance agree with rejections obtained with individual tolerances.     

Determination of soil fumigants in air using tandem capillary gas chromatography after charcoal trapping

Soil fumigants, like 1,3-dichloropropene and metham-sodium (forming methyl isothiocyanate) diffuse into the atmosphere, thus presenting a hazard to people in the surroundings. A method is described in which a large volume (50 μl) of extractant, used to desorb the compounds from charcoal, is injected into a GC, equipped with two capillary columns. By way of Deans switching, the solvent is separated from the compounds of interest. Modification of a GC sampler makes unattended analyses possible.     

A Facile Diagnostic 1H NMR Method for Syn and anti Hydroxy Systems

In diastereomeric hydroxyl-containing systems, the relative ¹H-NMR chemical shift of the carbamate NH of the in situ generated trichloroacetylisocyanate derivatives appear to be diagnostic for the syn and anti stereochemistry.     

An analytically oriented discretization technique for boundary value problems

Dedicated to ProfessorJ.W. Schmidt on the occasion of his 60 ^th birthday