Untersuchung von Trinkwasser, Abwasser, Mineralwasser

Ohne Zusammenfassung     

Accuracy of the multipole expansion applied to a sphere in a creeping flow parallel to a wall

An example system is studied to discuss precision of the multipoleexpansion, applied to determine forces exerted on particlesby a viscous low-Reynolds-number fluid flow. A single spherein an ambient flow (pure shear, quadratic, and modulated shear)parallel to a close plane wall is considered. Forces and torquesexerted by the ambient flow on a motionless sphere are evaluated.Their precision is determined and related to a multipole orderof the truncation. Similar analysis is performed for a movingsphere with no ambient flow and for a freely moving sphere.Relative motion of the sphere with respect to the wall givesrise to strong lubrication interactions. It is analysed howthese interactions affect accuracy of the pure multipole expansion,and what are the smallest distances where it becomes insufficient.An alternative precise method is applied, in which lubricationexpressions are subtracted from the hydrodynamic forces andtorques, and the residue is evaluated as a fast-convergent seriesof inverse powers of the distance between the sphere centreand the wall. The accuracy of this procedure is carefully analysed.     

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.     

Expanded understanding of student conceptions of engineers: Validation of the modified draw-an-engineer test (mDAET) scoring rubric

With this research, we sought to expand the pool of engineering education assessment instruments. We drew upon earlier efforts to define an expanded protocol for prompting children's drawings of engineers; and evaluate the reliability of a new scoring rubric for the modified Draw-an-Engineer Test (mDAET). An earlier paper introduced our ground theory approach in gathering theoretical propositions derived from children's drawings, explanations of engineers (n = 940) to develop the mDAET Scoring Rubric. Here we evaluate the reliability of the mDAET, a component of the larger mDAET rubric validation process. In the current study, eight participants scored twelve sets (including anchor sets) of drawings (n = 36) and, scores across drawings were evaluated by percentage match with the known-score and interrater reliability. Kappa values for exact matches across eight raters met the threshold for “substantial” agreement and matches that were exact or adjacent indicated “almost perfect” agreement. Notably, 92% of the possible matches among common anchor items were either exact or adjacent matches. These results indicate adequate inter-rater reliability evidence of the mDAET scoring rubric and demonstrate the feasibility of largescale administration that may no longer require individual child interviews.