NBC News Scripts
WBAP-TV (Television station : Fort Worth, Tex.)
1954-12-31
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3,273 records were found.
We present the 1.55-μm GaInNAs/GaAs multiple quantum well (QW) heterostructures with GaNAs or GaInNAs barrier and space layer (BSL). An enhancement of photoluminescence intensity and a remarkable reduction of emission linewidth of GaInNAs multiple QWs have been demonstrated by using GaInNAs quaternary BSL, instead of GaNAs BSL. These effects of GaInNAs BSL could be understood in term of the improvement of structural properties of GaInNAs QWs. These results present to us a variable approach to further developing GaAs-based light sources in the telecommunication wavelength range near 1.55 μm.
Various techniques on the growth of self-assembled compound semiconductor nano-structures (quantum dots, QDs) have been tried to enhance the controlling on size, density, emitting wavelength, uniformity in size and ordering in location of the QDs. Optimized growth conditions have been used in the application of the QD materials in opto-electronic devices. High-power, long-lifetime quantum-dot laser-diodes (QD-LDs) emitting near 1 μm, QD-LDs emitting in red-light range, 1.3 μm QD-LDs on GaAs substrate and quantum-dot super-luminescent diodes (QD-SLDs) have successfully been achieved.
This tutorial-like presentation provides a survey of acoustical correlates of word and sentence stress, with emphasis on Germanic languages such as Dutch and English. It also reviews what is known about the perceptual cue value of the acoustic correlates of stress, and show that highly reliable correlates are not necessarily strong perceptual cues, and conversely that the strongest perceptual cue (pitch change) is an unreliable correlate.
Circulation time (Ct) between lung and periphery may be a surrogate for cardiac output, estimated here, for the most part, as the time between taking a breath of nitrogen and peripheral detection of a desaturation pulse. Use of pulse oximetry involves an internal, instrument delay; however, using the ear, we found shortening with exercise (12.1 +/- 0.37 sec, at rest; 9.1 +/- 0.25 sec at 100 watts), lengthening after beta-blockade, and lengthening in patients with echocardiographic and clinical left heart failure (8 patients 16.2 +/- 1.1 sec; 6 controls 12.0 +/- 0.5 sec). Pulse oximetry failed, however, to discriminate heart failure from normal in several patients. In patients referred to a department of nuclear medicine for assessment of chest pain, pulse oximetry (finger and ear) showed unacceptable variability. Nuclide delays between...
