Oxidation of Silicon Carbide in Environments Containing Potassium Salt Vapor

At high temperatures in clean oxidizing environments, SiC forms a very protective SiO₂ film, but, in environments containing low levels of gaseous alkali salt contaminants or where condensed salts may deposit on the surface, the resistance of the film is significantly reduced. Oxidation kinetics of SiC were measured by continuous thermogravimetric analysis in a controlled environment containing CO₂, H₂O, and O₂ plus low levels of potassium-containing salts. Potassium was found to be incorporated into the SiO₂ scale and to significantly change its transport properties and its morphology. The rate of scale formation was found to increase directly in proportion to K in the scale. A change in mechanism was observed when water vapor was added to the reacting gas stream.     

Oxygen Tracer Diffusion in Vitreous Silica

Oxygen diffusion in vitreous silica glass is studied using the gas exchange technique. The tracer concentration profiles are consistent with a model based on two mechanisms, one network and the other interstitial. These processes are coupled through limited network–interstitial exchange. Nuclear reaction analysis and secondary ion mass spectrometry techniques are performed and compared. These results are compared to experiments on transport in thin silica films grown on single-crystal silicon.     

Nuclear Magnetic Resonance Studies of Silicon Carbide Polytypes

The ²⁹Si MAS NMR spectra of the 2H, 4H, 6H, and 3C polytypes of silicon carbide are presented. An attempt is made to correlate differences in the chemical shifts with local atomic environment. The results of the analysis of the spectra of pure polytypes are used as a basic for the interpretation of the spectra of mixed polytypes and a discussion of the crystallinity and impurity levels of different samples. Carbon-13 chemical shifts obtained from spectra of the same polytypes are also tabulated.     

Casual reasoning in planning1

Reasoning about actions necessarily involves tracking the truth of assertions about the world over time. The SIPE planning system retains the efficiency of the STRIPS assumption for this while enhancing expressive power by allowing the specification of a causl theory. Separation of knowledge about causality from knowledge about actions relieves operators of much of their representational burden and allows them to be applicable in a wide range of contexts. The implementation of causal theories is described, together with examples and evaluations of the system's expressive power and efficiency.     

Rapid assessment of infant predictors of adult IQ: Midtwin-midparent analyses.

Assessed infant predictors of adult IQ with same-sex infant twins (114 pairs) and their parents. The midtwin–midparent design permits the rapid assessment of infant measures to predict later behavior, because the midparent score serves as a proxy for the infant's potential score at maturity. At 5, 7, and 9 mo, Ss were observed on the Fagan Test of Infant Intelligence, hand preference, vocalizations, selected Bayley Scales of Infant Development items, and a modified Bayley Infant Behavior Record. At 8 mo, Ss received the Visual Expectation Paradigm and an auditory discrimination task. Their parents received the Wechsler Adult Intelligence Scale—Revised (WAIS—R). Some infant measures, indicative of information processing, language ability, and temperament, predicted midparent IQ. This study extended and partially replicated findings from a previous midtwin–midparent cohort (L. F. DiLalla et al; see record 1991-04066-001). (PsycINFO Database Record (c) 2010 APA, all rights reserved)