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.     

Early childhood education for at-risk four-year-olds? Yes.

Extends E. F. Zigler's (see record 1987-23352-001) discussion of early childhood education, concluding, contrary to Zigler, that early childhood education for at-risk children is a positive step in helping them resist the harmful effects of poverty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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.     

Age-related differences in lexical access, spreading activation, and simple pronunciation.

An experiment was conducted to address age-related differences in lexical access, spreading activation, and pronunciation. Both young and older adults participated in a delayed pronunciation task to trace the time course of lexical access and a semantic priming task to trace the time course of spreading activation. In the delayed pronunciation task, subjects were presented a word and then, after varying delays, were presented a cue to pronounce the word aloud. Older adults benefited considerably more from the preexposure to the word than did the younger adults, suggesting an age-related difference in lexical access time. In the semantic priming pronunciation task, semantic relatedness (related vs. neutral), strength of the relationship (high vs. low), and prime–target stimulus onset asynchrony (200 ms, 350 ms, 500 ms, 650 ms, and 800 ms) were factorially crossed with age to investigate age-related differences in the buildup of semantic activation across time. The results from this task indicated that the activation pattern of the older adults closely mimicked that of the younger adults. Finally, the results of both tasks indicated that older adults were slower at both their onset to pronounce and their actual production durations (i.e., from onset to offset) in the pronunciation task. The results were interpreted as suggesting that input and output processes are slowed with age, but that the basic retrieval mechanism of spreading activation is spared by age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Personality similarity in twins reared apart and together.

We administered the Multidimensional Personality Questionnaire (MPQ) to 217 monozygotic and 114 dizygotic reared-together adult twin pairs and 44 monozygotic reared-apart adult twin pairs. A four-parameter biometric model (incorporating genetic, additive versus nonadditive, shared family-environment, and unshared environment components) and five reduced models were fitted through maximum-likelihood techniques to data obtained with the 11 primary MPQ scales and its 3 higher order scales. Solely environmental models did not fit any of the scales. Although the other reduced models, including the simple additive model, did fit many of the scales, only the full model provided a satisfactory fit for all scales. Heritabilities estimated by the full model ranged from .39 to .58. Consistent with previous reports, but contrary to widely held beliefs, the overall contribution of a common family-environment component was small and negligible for all but 2 of the 14 personality measures. Evidence of significant nonadditive genetic effects, possibly emergenic (epistatic) in nature, was obtained for 3 of the measures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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.     

Landmark-based spatial memory in birds (Parus atricapillus and Columba livia): The use of edges and distances to represent spatial positions.

Birds' use of landmarks to identify spatial locations was examined. Black-capped chickadees (Parus atricapillus) and pigeons (Columba livia) searched for hidden food on a 120-cm–2 tray. In each task the target was near an edge with a nearby landmark. On occasional unrewarded tests the landmark was either left in its usual position, shifted parallel to the edge, shifted perpendicular to the edge, or shifted diagonally. On diagonal landmark shifts the birds shifted their searching more in the parallel direction than in the perpendicular, which violates the predictions of the vector sum model (K. Cheng, 1989). In some cases the birds maintained their searching at a constant perpendicular distance under all landmark shifts. This suggests that perpendicular distance to an edge forms an element in determining where to search on the basis of landmarks. Chickadees and pigeons performed similarly, which suggests similarity in the way they encode locations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)