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The beam divergence in the vertical direction from a graded index separate confinement heterostructure (GRINSCH) multiquantum-well (MQW) laser has been studied. It is demonstrated both theoretically and experimentally that a circular beam MQW laser can be produced by choosing appropriate thicknesses for the GRINSCH layers, while maintaining other desired laser characteristics. The beam divergence is found to be more affected by the index change induced by injected carriers than by strain in the MQW active layer. Theoretical results are in good agreement with the measurements for 1.3-μm InGaAsP strained MQW lasers 相似文献
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Mann-Fu Rau David Rieck James W. Evans 《Metallurgical and Materials Transactions B》1987,18(1):257-278
An “environmental cell” located in a high voltage transmission electron microscope has been used to study the reduction of
single crystal iron oxides by hydrogen and hydrogen-argon mixtures. The cell enables a direct observation of the solid during
reaction, thus permitting the nucleation and growth of solid reaction products to be observed. Hematite was reduced at temperatures
in the range 387 to 610°C with gas pressures up to 5.3 kP. Reduction with pure hydrogen was considerably faster than when
argon was present. Lath magnetite which rapidly transforms to porous magnetite and thence (more slowly) to porous iron was
observed. The reduction of magnetite and of wustite single crystals was observed in the temperature range 300 to 514°C using
both hydrogen and hydrogen-argon mixtures at gas pressures up to 6.6 kP. Incubation periods were found for magnetite reduction;
during these periods faceted pits formed in the oxide. Iron formed in the early stages was epitaxial with the host magnetite;
at later stages the epitaxy was lost and fissures frequently formed in the metal. The morphology of the iron differed between
the gas mixtures. Disproportionation accompanied the reduction of wustite, producing intermediate polycrystalline magnetite
despite reducing conditions. The disproportionation appeared to be promoted by the reduction reaction. For both oxides, reduction
in the hydrogen-argon mixture was slower than in pure hydrogen. 相似文献
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P Dhordain O Albagli RJ Lin S Ansieau S Quief A Leutz JP Kerckaert RM Evans D Leprince 《Canadian Metallurgical Quarterly》1997,94(20):10762-10767
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An automatic procedure for target data association is presented here. The procedure is particularly appropriate for shallow water applications, where navigation errors are limited and where sufficient overlap is present between successively surveyed areas. The proposed method includes a performance check that can be used to confirm that solutions are meaningful and also to produce a time-bounded implementation suitable for real-time operation. Main applications for the procedure include change detection and navigation enhancements (for example, by concurrent mapping and localisation/simultaneous localisation and mapping procedures). Results are presented for different survey platforms. 相似文献