Surface and depth fallout distribution of137Cs and90Sr in soils of Caceres (Spain). Dose commitments due to external irradiation

An analysis has been made of the surface distribution of¹³⁷Cs and⁹⁰Sr in soils of the province of Cáceres (Spain), of some 20.000 km² area, situated on the frontier with Portugal. From the distribution of depth profiles of concentrations of these radionuclides and their fit to a negative exponential, determination was made of the mean values of the respective inventories and of the corresponding¹³⁷Cs/⁹⁰Sr ratio. The external dose rates from the presence of these man-made isotopes in the soil are calculated and compared with that originating from the concentrations of natural radioisotopes.     

A noncommutative deformation of topological field theory

Cohomological Yang–Mills theory is formulated on a noncommutative differentiable four manifold through the -deformation of its corresponding BRST algebra. The resulting noncommutative field theory is a natural setting to define the -deformation of Donaldson invariants and they are interpreted as a mapping between the Chevalley–Eilenberg homology of noncommutative spacetime and the Chevalley–Eilenberg cohomology of noncommutative moduli of instantons. In the process we find that in the weak coupling limit the quantum theory is localized at the moduli space of noncommutative instantons.     

Preparation and application of silicalite-1 micromembranes on laser-perforated stainless steel sheets

Silicalite-1 micromembranes of approximately 80 μm in diameter have been prepared by synthesizing the zeolite material inside a network of perforations created by using a Nd–YAG laser on 75 μm thick stainless steel sheets. Several strategies have been introduced here to reduce the thickness of the micromembranes synthesized; among these the most successful involved using a polyamide filling to reduce the volume of the microperforations accessible to the synthesis solution. The density of microperforations could be tailored to prepare arrays of micromembranes of different overall porosity (1.8, 3.7, 6.6 and 7.7%). The micromembranes performed well in the propane/N₂ separation, showing a maximum propane/N₂ separation factor of 46, at a propane permeance of about 5 × 10⁻⁶ mol/(m² s Pa).     

New mass spectrometric approaches to structural analysis in mixtures

Structural analysis of minor components in mixtures is a vital requirement in the development of any pharmaceutical compound. Mass spectrometry is uniquely able to give this kind of information on the trace amounts of material present as minor impurities in a drug substance. In this study we show that a combination of mass spectrometric analysers with different characteristics is an even more powerful approach with a higher chance of establishing a potential structure. In particular the advent of analysers capable of accurate mass measurement on small amounts of material has enabled structures to be proposed in situations where previously no real conclusions could be made. Copyright 1999 John Wiley & Sons, Ltd.