Synthesis and characterization of fillers of controlled structure based on polyhedral oligomeric silsesquioxane cages and their use in reinforcing siloxane elastomers

Four polyhedral oligomeric silsesquioxane (POSS) cages with vinyl groups were linked to a central siloxane core by hydrosilylation. The goal was to obtain filler particles of sizes between those of the POSS cages themselves and the much larger silica particles typically used to reinforce elastomers. The hydrosilylation reaction was monitored with Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, and the resulting structure was confirmed by mass spectrometry. Simply blending these POSS-based fillers into silanol-terminated poly(dimethylsiloxane) (PDMS) had little effect on the mechanical properties, but bonding them to PDMS provided considerable reinforcement. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3314–3323, 2003     

Production of calibration standards for x-ray fluorescence analysis of aerosol particles precipitated on different filter materials

Calibration results are presented for a method producing filter standards of two different materials. The first filter type is a membranous filter, the second a quartz fibre filter. Multielement solutions with predetermined elemental concentrations have been produced by an aerosol generator and preciptiated onto the respective filter materials. Additionally, the particle size-distribution in the aerosol generator, depending on the salt concentration in the nebulized solution, is presented.     

Statistical analyses of electromyographic activity in spasmodic dysphonic and normal control subjects

Heterogeneity in the quality and task sensitivity of vocal symptoms in the spasmodic dysphonia (SD) population contributes to controversy as to whether this is a single disorder or two disorders with different etiologies (neurogenic versus psychogenic). Perceptual and acoustic assessments of vocal symptoms are inadequate to resolve this controversy. However, myoelectric events are intimately proximal to the source of vocal disruption and may be informative. The present report employs statistical modeling of quantitative amplitude measures of electromyographic activity recorded from thyroarytenoid to examine neuromotor bases of vocal symptoms in SD. Consideration of perceptual ratings of the quality and task sensitivity of vocal symptoms in the context of statistical models provides support for the conclusion that the range of vocal symptoms identified as SD represents a single, neurogenic disorder.     

Comparison of time-dependent effects of (+)-methamphetamine or forced swim on monoamines,corticosterone, glucose,creatine, and creatinine in rats

Background  

Methamphetamine (MA) use is a worldwide problem. Abusers can have cognitive deficits, monoamine reductions, and altered magnetic resonance spectroscopy findings. Animal models have been used to investigate some of these effects, however many of these experiments have not examined the impact of MA on the stress response. For example, numerous studies have demonstrated (+)-MA-induced neurotoxicity and monoamine reductions, however the effects of MA on other markers that may play a role in neurotoxicity or cell energetics such as glucose, corticosterone, and/or creatine have received less attention. In this experiment, the effects of a neurotoxic regimen of (+)-MA (4 doses at 2 h intervals) on brain monoamines, neostriatal GFAP, plasma corticosterone, creatinine, and glucose, and brain and muscle creatine were evaluated 1, 7, 24, and 72 h after the first dose. In order to compare MA's effects with stress, animals were subjected to a forced swim test in a temporal pattern similar to MA administration [i.e., (30 min/session) 4 times at 2 h intervals].     

Electronic and structural properties of hydrogen on semiconductor surfaces

In this paper we will review the scientific literature which addresses the atomic geometry and electronic structure of clean and hydrogenated semiconductor surfaces. In particular, results related to vibrational studies will be presented. First, surfaces of elemental semiconductors (Ge, Si), Ge/Si-alloys, and III–V compound semiconductors chemisorb in a first stage atomic hydrogen by saturating surface atom dangling bonds. In a second step surface bonds are broken and a change of the geometrical structure results. Finally, higher hydrogen exposures are able to etch semiconductor surfaces. Best understood to date are surfaces of Si(1 0 0), Si(1 1 1), Ge_xSi_1−x(1 0 0), and III–V's after cleavage which have been modeled by dimerized and undimerized structures. (1 0 0) surfaces of III–V semiconductors, like GaAs and InP, tend to be dimerized, too.     

Coverage- and temperature-dependent vibrational spectra of hydrogen chemisorbed on Si(100)2 × 1

The adsorption of atomic hydrogen at Si(100)2 × 1 has been studied for coverages at and below one monolayer at temperatures between 300 and 1200 K using high-resolution Electron Energy Loss Spectroscopy (EELS) and Low Energy Electron Diffraction (LEED). Measurements of EELS frequencies, linewidths and intensities are discussed for different coverages and temperatures during exposure as well as subsequent annealing. Formation of a monohydride Si(100)2 × 1 : H adsorption phase is observed at room temperature in the sub-monolayer range, at 650 K for all coverages up to the saturation, and during thermal decomposition of the low temperature dihydride Si(100)1 × 1 : : 2H adsorption phase. The latter is formed by saturating Si(100) at 300 K with atomic hydrogen.