Reactions of water molecules in silica-based network glasses.

Given that H(2)O dissolves minimally in quartz, the mechanism for the ubiquitous dissolution of H(2)O in silica glasses has been a long-standing puzzle. We report first-principles calculations in prototype silica glass networks and identify the ring topologies that allow the exothermic dissolution of H(2)O as geminate Si-O-H groups. The topological constraints of these reactions explain both the observed saturation of Si-O-H concentrations and the observed increase in the average Si-Si distance. In addition, calculations of H(2)O and Si-O-H dissociation account for the observed response to radiation by wet thermally grown SiO(2).

Theory of hydrogen-related metastability in disordered silicon.

Density functional electronic structure calculations are employed to examine hydrogen for a variety of configurations in silicon. A novel complex is found for hydrogen in amorphous silicon. The complex involves the breaking of a weak silicon bond to form two Si-H bonds with both hydrogens in between the original silicon atoms. This complex provides a microscopic model for new metastable complexes observed in amorphous silicon. Mechanisms for hydrogen-related metastability are discussed for amorphous and polycrystalline silicon.

The influence of maternal drinking and drug use on the quality of the home environment of school-aged children.

BACKGROUND: Although many studies have examined the development of children of male alcoholics, few studies have considered substance use by the female caregiver. This study evaluated the relationship between substance use by female caregivers and factors that affect the child-rearing environment. METHODS: A total of 480 inner-city African-American women were recruited during pregnancy for a longitudinal study of the effects of prenatal alcohol use and substance use by caregivers on the development of their children. All women were screened for alcohol consumption at their first prenatal visit to a large urban maternity hospital. Those who averaged seven or more drinks per week (0.5 oz absolute alcohol per day) at the time of conception were invited to participate in the study, as was a 5% random sample of lighter drinkers and abstainers. At the 7.5-year follow-up assessment, the quantity and frequency of alcohol consumption and drug use, as well as several measures of the child-rearing environment, were assessed for 231 of the caregivers. RESULTS: Current alcohol use was uncorrelated with standard demographic factors, such as socioeconomic status, but was related to poorer family functioning, lower quality of parental intellectual stimulation, and higher levels of domestic violence. There were independent effects of illicit drug use on family environment, domestic violence, and caregiver depression. History of drinking during pregnancy, however, was not related to the current child-rearing environment. Poorer parental functioning generally was found only among the caregivers who currently drank both heavily (six or more drinks/occasion) and frequently (three or more days/week). After controlling for lifetime alcohol problems, current drinking still predicted a less cohesive and organized family environment and higher levels of domestic violence. CONCLUSIONS: Current heavy, frequent drinking in this relatively homogenous, economically disadvantaged sample was unrelated to demographics and seemed to have an important negative impact on the quality of the child-rearing environment, whereas drinking during pregnancy was unrelated to the current child-rearing environment.

Preparation and characterization of chemically derived (Pb,La)TiO (3) thin films.

Ferroelectric lead lanthanum titanate (PLT) thin films with composition varying from pure PbTiO(3) to PLT 25/100 (0 to 25 mol.% La) were prepared by spin-casting 0.25M solutions containing metallo-organic precursors of Pb, La, and Ti. The dielectric and ferroelectric properties of the thin (410-nm) films were characterized. The dielectric constants of the films varied from ~80 to ~690 for La contents varying from 0 to 25 mol%, respectively. Dissipation factors varied from ~0.03 to ~0.09 over the same compositional range. The temperature dependence of the dielectric properties was also studied to determine the effects of La content on the Curie point (T(c)). As expected, T(c ) was found to decrease with increasing La concentration. Coercive field and remanent polarization also decreased with increased La concentration.