Reform Teaching Strategies Used by Student Teachers

The purposes of this study were to observe the teaching practices occurring in student teachers' science and mathematics K‐12 classrooms, compare the student teachers' perceptions of their teaching with what was actually occurring in their classrooms, and determine which college faculty members and courses these student teachers felt contributed to the teaching methods they used. Data on each student teacher were gathered via field notes of three classes, an observation protocol completed after each lesson, and an interview. Composites were written for each of the students. The total data set of all composites was examined to see if any patterns generalizable to the whole were evident. Differences between and among grade levels and content areas surfaced and are discussed.     

Short-length microstructured phosphate glass fiber lasers with large mode areas

We report fabrication and testing of the first phosphate glass microstructured fiber lasers with large Er-Yb-codoped cores. For an 11-cm-long cladding-pumped fiber laser, more than 3 W of continuous wave output power is demonstrated, and near single-mode beam quality is obtained for an active core area larger than 400 microm2.     

Volumetrische Bestimmung des Alkohols

Ohne Zusammenfassung     

The diffraction of elastic waves by an imperfect fusion bond

We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material.     

Terpentin?l und Harze

Ohne Zusammenfassung     

Gamma radiation induced effects on silica and on silica-polymer interfacial interactions in filled polysiloxane rubber

We report in our studies to assess the impact of gamma radiation on silica and on the silica-polymer interface in filled polysiloxane rubber. Electron spin resonance (ESR) and solid-state nuclear magnetic resonance (NMR) studies have been performed on samples exposed to gamma radiation. In an effort to probe directly the effect of gamma radiation on the silica surface, we employed ¹H and ²⁹Si NMR. Our ESR studies show trapped paramagnetic species (positive holes and/or trapped electrons) within the host silica matrix for all samples exposed to gamma radiation. A sample of pure cab-o-sil irradiated to a dose of 50 kGy also shows an ESR signal. Our studies on real-time aged samples (derived from field trials) also show ESR signatures indicative of silica based trapped paramagnetic species. The growth of trapped paramagnetic species as a function of gamma dose was investigated. This shows that the build up of trapped species occurs rapidly at low gamma dose before reaching saturation at about 20-30 kGy. Radiation induced band gap excitation is the likely process leading to the creation of these paramagnetic species which may be trapped in regions of local charge deficit within the silica matrix. Species that are not trapped may take part in silica surface reactions leading to changes in filler-polymer interfacial interactions. NMR studies combined with ammonia modified swell studies have shown increased polymer segmental chain mobility (softening) at low gamma dose indicative of a possible reduction in filler-polymer interfacial interactions. For those samples exposed to high gamma dose, our ammonia modified swell studies suggest increased polymer-filler interactions presumably through silica-polymer crosslinking effects. Our ¹H and ²⁹Si NMR studies on irradiated silica suggest that the silica surface is sensitive to gamma radiation. Our observations are important as they highlight the need to better control the quality (size, purity, etc.) of the silica constituent in filled polymer components used in gamma radiation environments.