Search

Udgivelsesdato: June 2006, phosphorus loading and a shift in the nitrogen loading from DIN to DON. Such a change in land use would also increase theexport of DOC and CDOM to the estuary having the potential to increase

Upwelling of cold. saline, and nutrient rich water was observed in late September 1999 along an east-west transect in the SW Kattegat. The Kattegat forms part of the transitional zone between the high saline North Sea and the low saline Baltic Sea. The upwelling occurred after an extended period of northward flow and eastern winds in the Kattegat, that changed into a southward flow as wind ceased. The upwelling was the result of a combination of high current speeds and bottom topography whereby the high-speed inflow water was forced towards the surface at the slope. Nutrient data show that the upwelling brought nutrient rich bottom water to the light exposed surface and a related strong (1943.5 ml(-1)) bloom of Pseudo-nitzschia pseudodelicatissima was observed. Surface (1.0 m) chlorophyll-a values increased from 3.7 to 10.0 mug l(-1) during upwelling. A frontal structure developed during the upwelling with raised fluorescence values at the front related to convergence. The present upwelling front was only indirectly related to the wind conditions and the front propagated off shore as compared to other upwelling fronts., Un upwelling d’eau froide riche en nutriments a été observé fin septembre 1999 le long d’une section d'est en ouest au sud-ouest du Kattegat. Le Kattegat fait partie de la zone de transition entre la mer du Nord, de forte salinité, et la mer Baltique, de faible salinité. L’upwelling se produit après une longue période de courant de nord et de vents d’est dans le Kattegat, ce qui génére un courant de sud lorsque le vent cesse. L’upwelling est le résultat d’une combinaison de forts courants et d’une topographie du fond qui permet la remontée de l’eau vers la surface au niveau de la pente. Les résultats montrent que la remontée d’eau riche en nutriments vers la surface exposée à la lumière permet une floraison de Pseudo-nitzschia pseudodelicatissima. La teneur en chlorophylle a en surface de 3.7 à 10.0 g l–1 pendant l’upwelling. Une structure se développe au front de l’upwelling avec des valeurs élevées de fluorescence en relation avec la convergence. L’upwelling actuel est seulement indirectement corrélé au vent et le front se propage au large comme dans le cas des autres fronts d’upwelling.

An optical waveguide switch/modulator is an important element for photonic switching systems. It is very important for these devices to be compatible with other electronic and optical components. In particular, it is desirable to have them monolithically integrated with lasers, transistors, and detectors. Implementation of a modulator is typically done using the Quantum Confined Stark Effect(QCSE) in a reverse biased PIN structure or using free carrier effects, both electrons and holes, in a forward biased PN structure. It has also been demonstrated that control of only electrons in a single quantum well via a gate electrode in an FET configuration can dramatically affect the optical absorption. A detailed analysis of the physical mechanisms controlling the changes in absorption due to the channel charge has also been given. Modulators using gate control of a channel charge benefit from both the high contrast available due to free carriers as well as high speed due to FET action. Recently the Heterostructure Field Effect Transistor (HFET) was reported as an ideal transistor for optoelectronic integration because of its unique waveguiding properties. We report here the operation of the HFET as an optical absorption modulator using its waveguiding capability., This article is from 'Organization of the Optical Society of America Photonic Science Topical Meeting Series. Volume 7. Quantum Optoelectronics Held in Salt Lake City, Utah on 11-13 March 1991,' AD-A253 823, p62-65.