Soluble silicates are complex mixtures of silicate anions. The larger anions are two- or three-dimensional condensation products of silicate monomer, SiO4 -4. In more siliceous silicate solutions, i.e., SiO2:Na2O ratio >2.0, some of the silicate condenses to polymeric (colloidal) silica. Negative charges on the anions are balanced by protons or by cations, typically alkali metal or quaternary alkylammonium cations. The distribution of these anions varies with the concentration of dissolved silicate solids, the relative molar concentrations of cations and silica, and to a lesser extent, trace impurities. 29Silicon NMR spectroscopy of silicate solutions has been a powerful method for studying the connectivity of silicon and oxygen atoms in silicate solutions. In this paper we will show how variations in silicate band shape and peak location in the mid-infrared spectrum from 700 to 1300 cm-1 depend on concentration and silica:alkali ratio. We will interpret the infrared data in consonance with NMR results. We will also relate these variations in anion distribution to the average molecular weight of silicate solutions.

To describe the psychosocial impact of acne on adolescents, and, in particular, to assess whether self-concept is affected by medical treatment, we evaluated 39 teenagers presenting for care to a community-based dermatologist. Prior to and following treatment, subjects completed a self-assessment questionnaire, the Piers-Harris self-concept scale, and underwent an objective assessment of acne severity. Fifty-eight percent of subjects were dissatisfied with their facial appearance and this in turn was correlated with feelings of embarrassment and social inhibition (for each, r = 0.48, P less than or equal to 0.005). Subjects' rating of acne severity, but not the dermatologist's, was correlated with dissatisfaction with facial appearance (r = 0.45, P less than or equal to 0.005). Despite these findings, the mean Piers-Harris total t-score (55.4 +/- 7.4) was within the normal range. Fourteen subjects (36%) returned for follow-up and 71% of these were judged by both the dermatologist and themselves to have improved. Following therapy, significant reductions in the adverse consequences of acne were observed with 42% of subjects reporting that their facial appearance was more acceptable to peers, 50% being less embarrassed, and 58% feeling less socially inhibited. Minimal improvement in mean Piers-Harris total t-score was observed (54.6 to 57.4, P = 0.004, paired t-test). Our data demonstrate that acne is perceived by adolescents to have important negative personal and social consequences, and that improvement in these areas may accompany medical treatment.

A systematic study of the transition in silicate solutions from a solution containing a highly complex mixture of silicate species to one dominated by a single symmetric cubic octamer has been completed. Infrared and NMR results have been analyzed and compared with each other and literature values. The FT-IR band locations are dependent on many factors, particularly the dominant band near 1000 cm(-1). The analysis supports Dent Glasser's hypothesis that silica polymerization results from changes in distribution between the larger colloidal silica and intermediate sized anionic fraction rather than the continuous stepwise growth seen with organic polymerization. A constant value of silica monomer seen in all solutions independent of the complexity of the species or their distribution suggests equilibrium between the monomeric form and larger anions and polymers that is independent of their structure. No evidence is uncovered for specific silicate species dependent IR band assignments.

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Objective: To determine if changes in histologic parameters obtained from intermittent sampling of the entire block correlated with differences in prognosis and management.

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The effects of several thermal and hydrothermal treatments of low soda Y zeolites of different lanthanum content have been investigated by infrared and X-ray powder methods. The absorption maxima of the framework vibrational bands shifted toward higher frequencies after steaming at 540 and 820°. The cationic and framework atom coordinates, interatomic distances, and angles of low and high lanthanum Y zeolites steamed at 540°were determined. The changes in location of infrared absorption maxima are attributed to partial framework dealumination. Observed unit cell shrinkage supports this assumption. The detection of a nonframework position at X -Y = Z = 0.028 in the structure of steamed, low-lanthanum Y has been attributed to nonframework aluminum. We conclude that steaming results in partial framework dealumination and possible structural rearrangement in the framework. These effects are more pronounced for low-lanthanum zeolites.

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