Att konstruera ett historiskt tänkande

Skolverket för i en artikel fram hur film har blivit ett alltmer vanligt inslag i historieundervisningen. På grund av detta har även den historiedidaktiska forskningen intresserat sig för de problem och möjligheter detta ger i klassrummet. Flera undersökningar har gjorts inom området för att ta reda på användbara metoder samt filmens inverkan på eleverna.1 Dock har dessa i stor utsträckning fokuserat på historisk empati medan andra områden lämnats outforskade. På så sätt valde vi att undersöka vilken inverkan läromedelstexter och spelfilmer har när elever tolkar det förflutna. Med detta vill vi komparativt undersöka hur elevernas uppfattning av historia påverkas av dessa två medier. Därför genomfördes studien i en klass som delades in i två grupper, en som såg film och en som läste text. För att mäta elevernas kunskapsutveckling användes ett förtest och ett eftertest. Dessa analyserades med teoretiska verktyg som var konstruerade utifrån historiedidaktiska teorier och förklaringsmodeller. Resultaten behandlas kvalitativt och analyseras genom att använda kodning. Detta genom att göra om våra teoretiska perspektiv till analysverktyg bland annat i en kunskapsmatris. De resultat studien får fram visar att eleverna som läste text kunde föra mer komplexa resonemang än de som såg filmklipp

End-Group Cleavage in MALDI of ATRP-Made Polystyrene: A Silver-Catalyzed Reaction during Sample Preparation

Cleavage of the labile halide termination upon matrix-assisted laser desorption/ionization (MALDI) has always been reported as a major concern in mass analysis of polystyrene prepared by atom transfer radical polymerization (ATRP). By studying this issue using nuclear magnetic resonance (NMR) and electrospray ionization–mass spectrometry, we evidence here that the ionization step is not involved in this deleterious process. Instead, removal of the halogen was shown to readily occur upon interaction of the silver salt (AgTFA) used as the cationizing agent in mass spectrometry, either in solution or in the solid-state when performing solvent-free sample preparation. In solution, this silver-induced reaction mostly consists of a nucleophilic substitution, leading to polystyrene molecules holding different terminations, depending on relative nucleophilicity of species present in the liquid-phase solution composition. In chloroform supplemented with AgTFA, trifluoroacetate-terminated PS were evidenced in ESI-MS spectra but experienced end-group cleavage in MALDI. In contrast, the major methoxy-terminated PS macromolecules formed when the silver-catalyzed nucleophilic substitution was performed in methanol were generated as intact gas-phase ions using both ionization techniques. This controlled and fast modification could hence be advantageously used as a rapid sample pretreatment for safe MALDI mass analysis of ATRP-made polystyrene

Improved Structural Elucidation of Synthetic Polymers by Dynamic Nuclear Polarization Solid-State NMR Spectroscopy

Dynamic nuclear polarization (DNP) is shown to greatly improve the solid-state nuclear magnetic resonance (SSNMR) analysis of synthetic polymers by allowing structural assignment of intrinsically diluted NMR signals, which are typically not detected in conventional SSNMR. Specifically, SSNMR and DNP SSNMR were comparatively used to study functional polymers for which precise structural elucidation of chain ends is essential to control their reactivity and to eventually obtain advanced polymeric materials of complex architecture. Results show that the polymer chain-end signals, while hardly observable in conventional SSNMR, could be clearly identified in the DNP SSNMR spectrum owing to the increase in sensitivity afforded by the DNP setup (a factor ∼10 was achieved here), hence providing access to detailed structural characterization within realistic experimental times. This sizable gain in sensitivity opens new avenues for the characterization of “smart” functional polymeric materials and new analytical perspectives in polymer science

Optimizing Sample Preparation Methods for Dynamic Nuclear Polarization Solid-state NMR of Synthetic Polymers

This work compares the overall sensitivity enhancements provided by dynamic nuclear polarization (DNP) for the solid-state NMR characterization of polymer samples doped with biradicals and prepared either by <i>film casting</i> (FC), or by <i>glass forming</i> (GF) using 1,1,2,2-tetrachloroethane as the solvent. Analysis of amorphous and semicrystalline polymers (polystyrene, poly­(ethylene oxide), polylactide, poly­(methyl methacrylate)) of varying molecular weights showed that GF provided larger sensitivity enhancements than FC but yielded DNP-enhanced ¹³C CPMAS spectra of lower resolution for semicrystalline polymers, owing to line-broadening due to conformational distribution of the polymer chains in frozen solution. Moreover, use of deuterated solvents significantly reduced the intensity of the solvent signals in the DNP-enhanced ¹³C CPMAS spectra of polymers prepared by GF, while preserving the sensitivity enhancement observed for the polymer signals. For the polymers investigated here, both FC and GF performed better than <i>incipient wetness impregnation</i>, yielding overall sensitivity enhancements between 5 and 40