Congruence and non-congruence subgroups of the (2,3,7)-group

Let [DELTA] denote the (2,3,7)-group. We establish an upper bound for the number of congruence subgroups of index n and a lower bound for the total number of subgroups of index n. Since the latter grows more quickly, there exist non-congruence subgroups of index n for all n greater than some n0

On the pulsation hypothesis for massive red supergiants

Red supergiant pulsar hypothesis using Q values derived from stellar luminosity, period, and spectru

Evolution of stars with suppressed core convection

Stellar evolution on the upper main sequence was computed for models of stars with cores assumed to be in radiative equilibrium, up to the point of central helium ignition. The role of the Schonberg-Chandrasekhar limit for an isothermal core is found to be critical for the evolutionary tracks. Observational data are used to rule out the hypothesis of evolution with radiative cores (in upper main-sequence stars) and, by implication, of magnetic fields that are sufficiently strong to have suppressed the core convention

Pulsational Instabilities in Hydrogen-poor Massive Blue Stars. 1

Structure and pulsational properties of hydrogen poor massive blue stars with helium core

Flood basalt eruptions, comet showers, and mass extinction events

A chronology of initiation dates of the major continental flood basalt episodes has been established from compilation of published K-Ar and Ar-Ar ages of basaltic flows and related basic intrusions. The dating is therefore independent of the biostratigraphic and paleomagnetic time scales, and the estimated errors of the inititation dates are approximately + or - 4 pct. There are 11 distinct episodes of continental flood basalts known during the past 250 Myr. The data show that flood basalt episodes are generally relatively brief geologic events, with intermittent eruptions during peak output periods lasting ony 2 to 3 Myr or less. Statistical analyses suggest that these episodes may have occurred quasi-periodically with a mean cycle time of 32 + or - 1 Myr. The initiation dates of the flood basalts are close to the estimated dates of marine mass extinctions and impact-crater clusters. Although a purely internal forcing might be argued for the flood basalt volcanism, quasi-periodic comet impacts may be the trigger for both the flood basalts and the extinctions. Impact cratering models suggest that large-body impactors lead to deep initial cratering, and therefore may cause mantle disturbances and initiate mantle plume activity. The flood basalt episodes commonly mark the initiation or jump of a mantle hotspot, and are often followed by continental rifting and separation. Evidence from dynamical studies of impacts, occurrences of craters and hotspots, and the geochemistry of boundary layers is synthesized to provide a possible model of impact-generated volcanism. Flood basalt eruptions may themselves have severe effects on climate, and possibly on life. Impacts might, as a result, have led to mass extinctions through direct atmospheric disturbances, and/or indirectly through prolonged flood basalt volcanism

Solar neutrinos and the influence of radiative opacities on solar models

Use of new radiative opacities based on the hot Thomas-Fermi model of the atom yields a predicted solar neutrino flux which is still considerably larger than the flux observed in Davis's Cl-37 experiment

Semantic Integration in Adults with Nonverbal Learning Disabilities and Autism Spectrum Disorder: Influence of Word Knowledge and Gestalt Perception

Language in individuals with nonverbal learning disabilities (NLD) and autism spectrum disorder (ASD) has been described as semantically empty and impoverished, despite apparently average word knowledge. Here, inter-related studies explored semantic representations in adults with these disorders of social perception. Studies highlighted semantic integration, a form of gestalt perception in which new concepts are developed by connecting familiar terms in novel ways. Semantic integration was compared to vocabulary breadth, and to nonverbal gestalt perception, comparing clinical groups to each other and to adults without a diagnosis. Because weaknesses in gestalt perception have been seen in NLD and ASD, it was expected that the clinical groups would show difficulty with semantic integration compared to controls, but that vocabulary would not differ between groups. Chapter 2 presents results from two surveys administered to investigate autism symptoms in adults with NLD, ASD, or no diagnosis. Results corroborated social perception impairments in both clinical groups, and adults with NLD had survey scores above thresholds for potential ASD. Chapter 3 found no differences between groups in breadth of vocabulary, as hypothesized. The NLD group had lower scores for tests of semantic integration and gestalt perception than controls. The ASD group, however, had equal or better scores than the other groups for semantic integration, an unexpected result potentially related to formulaic language. In Chapter 4, adults with NLD provided fewer meanings for polysemous words than controls, and scores for this measure were predicted by nonverbal perceptual reasoning. Results supported clinical observations that individuals with NLD are less likely to form links between unlike but familiar words, and suggested a specific cognitive underpinning for this difficulty. Overall, there was little to no difference between clinical groups for either quantitative or observational data concerning vocabulary breadth, but quantitative differences were seen for underlying cognitive measures. Outcomes suggested different cognitive paths by which these adults arrive at similar destinations in regard to their linguistic strengths and weaknesses