Die Bestimmung des Fluors

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Untersuchung von Trinkwasser, Abwasser, Mineralwasser

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Mathematics Teachers' Reasoning About Fractions and Decimals Using Drawn Representations

This qualitative study considers middle grades mathematics teachers' reasoning about drawn representations of fractions and decimals. We analyzed teachers' strategies based on their response to multiple-choice tasks that required analysis of drawn representations. We found that teachers' flexibility with referent units played a significant role in understanding drawn representations with fractions and decimals. Teachers who could correctly identify or flexibly use the referent unit could better adapt their mathematical knowledge of fractions validating their choice, whereas teachers who did not attend to the referent unit demonstrated four problem-solving strategies for making sense of the tasks. These four approaches all proved to be limited in their generalizability, leading teachers to make incorrect assumptions about and choices on the tasks.     

Multiple peak analysis in gel permeation chromatography

Summary This paper describes the resolution of multimodal GPC chromatograms into their individual components through the use of two optimization techniques, applied sequentially. The principle of the method can be applied to any form of curve but only the mathematics for Gaussian curves is given. The method has been successfully tested against both model and real chromatograms. The model chromatograms consisted of overlapping, perfectly Gaussian, curves whilst the real chromatograms were obtained from oligomeric polyesters submitted for routine GPC analysis and contained from three to five components. These chromatograms, which would have been too complex to resolve by “pencil and ruler” techniques, were resolved by this method to a precision within experimental error.     

Zum Nachweis und zur Bestimmung des Thalliums

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