Kodierte Anregung in der photoakustischen Bildgebung

Der photoakustische Effekt basiert auf der Erzeugung akustischer Wellen durch die Bestrahlung eines Objektes mit gepulster elektromagnetischer Strahlung. Im Rahmen dieser Arbeit wurde erstmals eine kodierte photoakustische Bildgebung mittels gepulster Laserdioden entwickelt. Die vorgeschlagene Messmethode ermöglicht eine Erhöhung des SNR-Gewinns pro Zeiteinheit gegenüber konventionellen Mittelungsmethoden. Die Konzepte zur kodierten Anregung wurden in einem experimentellen Aufbau realisiert. Die theoretisch vorhergesagten Kodiergewinne konnten erfolgreich experimentell verifiziert werden. Es konnte gezeigt werden, dass insbesondere die unipolaren, orthogonalen, komplementären Sätze von Sequenzen eine artefaktfreie, multispektrale, kodierte photoakustische Bildgebung ermöglichen. Beim Einsatz kommerziell verfügbarer Komponenten ermöglicht die Kodierung eine Reduktion der Anzahl notwendiger Laserdioden verglichen mit nicht kodierten Systemen um 30%

Mesopelagic prokaryotic bulk and single-cell heterotrophic activity and community composition in the NW Africa–Canary Islands coastal-transition zone

8 pages, 3 figures, 2 tablesMesopelagic prokaryotic communities have often been assumed to be relatively inactive in comparison to those from epipelagic waters, and therefore unresponsive to the presence of nearby upwelled waters. We have studied the zonal (shelf-ocean), latitudinal, and depth (epipelagic–mesopelagic) variability of microbial assemblages in the NW Africa–Canary Islands coastal-transition zone (CTZ). Vertical profiles of bacterial bulk and single-cell activity through the epi- and mesopelagic waters were combined with point measurements of bacterial respiration, leucine-to-carbon conversion factors and leucine-to-thymidine incorporation ratios. The overall picture that emerges from our study is that prokaryotes in the mesopelagic zone of this area are less abundant than in the epipelagic but have comparable levels of activity. The relationship between prokaryotes and heterotrophic nanoflagellates, their main predators, remains constant throughout the water column, further contradicting the assumption that deep ocean bacterial communities are mostly inactive. Both bulk and single-cell activity showed clear differences between stations, with higher mesopelagic activities closer to the shelf or affected by upwelling features. We also tested whether differences in microbial function between stations could be related to differences in bacterial community structure, and conclude that bacterial communities are very similar at similar depths in the deep ocean, even if the stations present order-of-magnitude differences in bacterial functionThis work was supported by Grants COCA (REN2000 1471-CO2-O1-MAR), RODA (CTM 2004-06842-C03/MAR) and MODIVUS (CTM2005-04795/MAR), and is a contribution to EU Networks of Excellence EUROCEANS and MARBEFPeer reviewe