Up to now lasers have not achieved any practical importance in dentistry for drilling teeth because of considerable damage to the surrounding tissue. We studied the application of pulsed 2.94 microns Er:YAG laser radiation in vitro on extracted teeth to remove enamel, dentin, and carious lesions. The depth and diameter of laser-drilled holes were measured as a function of pulse number and radiant exposure. The tissue removal is very effective both for dentin and enamel.

No abstract

Many studies have been undertaken trying to use various laser systems as optical drills on dental enamel and dentin, but the high radiant exposure needed and subsequent high temperature rises lead to fractures of the hard substances and possible damages to the pulp. Compared to the other laser systems, the use of the Er:Yag laser has given encouraging results. Optical and scanning electron microscopy showed only minimal if any damage of the surrounding tissue.

Distributional assumptions for the returns on the underlying assets play a key role in valuation theories for derivative securities. Based on a data set consisting of daily prices of the 30 DAX shares over a three-year period, we investigate the distributional form of compound returns. After performing a number of statistical tests, it becomes clear that some of the standard assumptions cannot be justi ed. Instead, we introduce the class of hyperbolic distributions which can be tted to the empirical returns with high accuracy. Two models based on hyperbolic L evy motion are discussed. By studying the Esscher transform of the process with hyperbolic returns, we derive a valuation formula for derivative securities. The result suggests a correction of standard Black{Scholes pricing, especially for options close to expiration.

Because testing time in educational research is typically scarce, the use of long scales to assess motivational affective constructs can be problematic. The goal of the present study was to scrutinize the psychometric properties of short scales (with three items) and single item measures for two core motivational affective constructs (i.e., academic anxiety and academic self concept) by conducting sys tematic comparisons with corresponding long scales across school subjects and within different subject domains (i.e., mathematics, German, French). Statistical analyses were based on representative data from 3879 ninth grade students. All short forms possessed satisfactory levels of reliability (range: .75 .89) and substantial correlations with the long scales (range: .88 .97); correlational patterns with educational stu dent characteristics (e.g., achievement, school satisfaction, gender, academic track, and socioeconomic status) were comparable to those obtained with the corresponding long scales (all average differences in correlations below .07). The correlational patterns between all single item measures and the external criteria were similar to those obtained with the corresponding long scales (all average differences in correlations below .08), yet the single item measures demonstrated low to modest score reliabilities (estimated with the model based omega coefficient; range: .22 .72) and correlations with full scales (range: .50 .88). When long scales are not applicable, short forms and perhaps even single item measures may represent psychometrically sound alternatives for assessing academic anxiety and academic self concept for educational research purposes.