Oxide crystals for electro-optic <Emphasis Type="Italic">Q</Emphasis>-switching of lasers

A new generation of oxide crystals is emerging for electro-optic Q-switching or control of high-power pulsed lasers. Unlike the acousto-optic Q-switches in which the total turn-off time is limited by the duration of sound wave propagation (110–220 ns/mm) across the beam diameter, the electro-optic devices provide a short (<10 ns) response needed for minimum losses. Extinction ratios of better than 100 : 1 for electro-optic crystals ensure their reliable hold-off. By contrast, acousto-optic devices are characterized by single-pass dynamic losses of approximately 40%, which hinders their use in high-gain lasers. The basic principles of electro-optic Pockels cells are discussed. The performance characteristics of Q-switching for traditional electro-optic materials [deuterated potassium dihydrogen phosphate (DKDP), lithium niobate (LNB)] and other new electro-optic crystals, such as barium metaborate (BBO) and crystals belonging to the langasite (LGS) and potassium titanyl phosphate (KTP) families, are reviewed comparatively. Particular emphasis is placed on KTP-type electro-optic crystals, primarily on rubidium titanyl phosphate RbTiOPO₄ (RTP), which stand out in their ability to provide Q-switching at extremely high frequencies or repetition rates up to 200 kHz. The use of both X- and Y-oriented double crystals as Q-switches in order to combine large electro-optic coefficients and low quarter-wave hold-off voltages with excellent thermal stability of the device is considered.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Roth, Tseitlin, Angert.     

College grade point average as a personnel selection device: Ethnic group differences and potential adverse impact.

College grade point average (GPA) is often used in a variety of ways in personnel selection. Unfortunately, there is little empirical research literature in human resource management that informs researchers or practitioners about the magnitude of ethnic group differences and any potential adverse impact implications when using cumulative GPA for selection. Data from a medium-sized university in the Southeast (N= 7,498) indicate that the standardized average Black-White difference for cumulative GPA in the senior year is d= 0.78. The authors also conducted analyses at 3 GPA screens (3.00, 3.25, and 3.50) to demonstrate that employers (or educators) might face adverse impact at all 3 levels if GPA continues to be implemented as part of a selection system. Implications and future research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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Longitudinal predictors of word reading development.

The authors review the scientific evidence regarding the prediction of reading development from six cognitive constructs: phonological awareness, phonological decoding, naming speed, orthographic processing, morphological awareness, and vocabulary. The authors describe the theoretical connexions amongst these indicators and word reading. The authors conclude that there is substantial evidence of each contributing to reading, and in most cases, this contribution is above and beyond that of the other predictor constructs. These findings have implications for early and regular cognitive assessment, and for curriculum development and teacher education. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

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