The feeding behavior of antarctic knll Euphausia superba on ice algae was observed in situ and in the laboratory. Field observations by divers confirm that knll uLhze natural sea ice microalgae for food. Laboratory investigations show that melting ice releases algae into the water column which induces area-intensive foraging behavior in M1. This behavior is characterized by high speed swimming and rapid turning, accompanied by rapid opening and closing of the thoracic appendages, also known as the feedmg basket. Presentation of increased concentrations of ice algae to laboratory populations of knll significantly increased euphausiid responsiveness which led to location of and direct grazing upon the undersurfaces of ice containing microalgae. Foraging behavior of krill on ice algae appears to be affected by the spatial patchiness of the algae withln the ice and on the rate of algal cell release from ice. We propose that sea ice algae is an abundant and predictable food resource for knll during austral winters, when phytoplankton food resources are depleted.
We report high-brightness blue and green light-emitting diodes ͑LEDs͒ based on II-VI heterostructures grown by molecular beam epitaxy on ZnSe substrates. The devices consist of a 2-3 m thick layer of n-type ZnSe:Cl, a ϳ0.1 m thick active region of Zn 0.9 Cd 0.1 Se ͑blue͒ or ZnTe 0.1 Se 0.9 ͑green͒, and a 1.0 m thick p-type ZnSe:N layer. The blue LEDs produce 327 W ͑10 mA, 3.2 V͒, with the light output sharply peaked at 489 nm, and exhibit an external quantum efficiency of 1.3%. The green LEDs produce 1.3 mW ͑10 mA, 3.2 V͒ peaked at 512 nm, corresponding to an external quantum efficiency of 5.3%. In terms of photometric units, the luminous performance ͑luminous efficiency͒ of the devices is 1.6 lm/W ͑blue͒ and 17 lm/W ͑green͒, respectively, when operated at 10 mA.
Multiple-quantum-well light-emitting diode (LED) structures of InGaN/GaN were grown by metalorganic chemical vapor deposition on Si(111) substrates via ZrB2(0001) buffer layers and a GaN template comprising composite AlxGa1-xN (where x lies in the range from 0 to 1) transition layers to minimize cracking due to thermal expansion mismatch between Si and GaN. Photoluminescence and electroluminescence results from the LED structures compared favorably with similar measurements obtained on identical LED structures grown on sapphire substrates. However, in spite of all the precautions taken, cracking was still present in the LED structures. Scanning electron microscopy and transmission electron microscopy in plan-view and cross-section geometries were conducted on the LED structures to examine the presence and the influence of various defects such as microvoids, micropipes, and threading dislocations on the mechanism of cracking. Our results suggest that the crack network propagates from microvoids on the surface of the LED structure. The formation of microvoids appears to originate from imperfections in the epitaxial ZrB2(0001) buffer layer.
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