We investigated the effect of deep-etched mesa sidewall profile and oxide overhang length on the regrowth structural characteristics for buriedheterostructure (BH) quantum cascade lasers (QCLs) grown by metalorganic chemical vapor deposition (MOCVD). The relationship between etched mesa sidewall geometry, oxide overhang length, oxide thickness, and growth uniformity was examined and is extensively discussed. In particular, anomalous growth in the vicinity of the oxide edge resulting from insufficient oxide overhang length was identified and studied. An ideal ratio of mesa height to oxide overhang length between 2.5 and 3.0 is proposed and experimentally justified to yield satisfactory planar regrowths without anomalous growth. Mesas in the ½011 direction with smoothly etched entrant profile yield a higher degree of growth uniformity than mesas in the [011] direction with the re-entrant profile.
The Solar TErrestrial RElations Observatory (STEREO), the third mission in NASA's Solar Terrestrial Probes program, was launched in 2006 on a two year mission to study solar phenomena. STEREO consists of two nearly identical satellites, each carrying an Extreme Ultraviolet Imager (EUVI) telescope as part of the Sun Earth Connection Coronal and Heliospheric Investigation instrument suite. EUVI is a normal incidence, 98mm diameter, Ritchey-Chretien telescope designed to obtain wide field of view images of the Sun at short wavelengths (17.1-30.4nm) using a CCD detector. The telescope entrance aperture is divided into four quadrants by a mask near the secondary mirror spider veins. A mechanism that rotates another mask allows only one of these sub-apertures to accept light over an exposure. The EUVI contains no focus mechanism. Mechanical models predict a difference in telescope focus between ambient integration conditions and on-orbit operation. We describe an independent check of the ambient, ultraviolet, absolute focus setting of the EUVI telescopes after they were integrated with their respective spacecraft. A scanning Hartmann-like test design resulted from constraints implied by the EUVI aperture select mechanism. This inexpensive test was simultaneously coordinated with other NASA integration and test activities in a high-vibration, clean room environment. The total focus test error was required to be better than +/-0.05 mm. We describe the alignment and test procedure, sources of statistical and systematic error, and then the focus determination results using various algorithms. The results are consistent with other tests of focus alignment and indicate that the EUVI telescopes meet the ambient focus offset requirements. STEREO is functioning well on-orbit and the EUVI telescopes meet their on-orbit image quality requirements.
Plants exhibit complex responses to change in environmental conditions such as radiant heat flux, water quality, airborne pollutants, and soil contents. We seek to utilize natural chemical and electrophysiological response of plants to develop novel plant-based sensor networks. Our present work focuses on plant responses to nuclear radiation—with the goal of monitoring plant responses as benchmarks for detection and dosimetry. In our study, we used plants including Cactus, Arabidopsis, Dwarf mango (pine), Euymus, and Azela. We demonstrated that these plants Chlorophyll-a (F680) to Chlorophyll-b (F735) ratio can be changed according to the radiation dose amount. The recovery processes and speed are different for different plants.
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