Latitudinal and sediment depth gradients in foraminiferal assemblage of the southeast Atlantic

Abstrac

Calibrated Microwave Reflectance in Low-Temperature Scanning Tunneling Microscopy

We outline calibrated measurements of the microwave reflection coefficient from the tunnel junction of an ultra-high vacuum low temperature scanning tunneling microscope. The microwave circuit design is described in detail, including an interferometer for enhanced signal-to-noise and a demodulation scheme for lock-in detection. A quantitative, in-situ procedure for impedance calibration based on the numerical 3-error-term model is presented. Our procedure exploits the response of the microwave reflection signal due to the change of the tunneling conductance caused by sub-nm variation of the tunneling distance. Experimental calibration is achieved by a least-squares numerical fit of simultaneously measured conductance and microwave reflection retraction curves at finite conductance. Our method paves the way for nanoscale microscopy and spectroscopy of dielectric surface properties at GHz frequencies and cryogenic temperatures. This opens a promising pathway even for dielectric fingerprinting at the single molecule limit.Comment: The manuscript has been improved in response to reviewer comments. Changes include addition of extra details and verification, updated figure layout to improve clarity, and additional context added to the introduction and conclusion. The conclusions and the underlying data remain the same. 12 pages, 4 figures, submitted to Review of Scientific Instrument

Preserving Charge and Oxidation State of Au(III) Ions in an Agent-Functionalized Nanocrystal Model System

Supporting functional molecules on crystal facets is an established technique in nanotechnology. To preserve the original activity of ionic metallorganic agents on a supporting template, conservation of the charge and oxidation state of, the active center is indispensable. We. present a model system of a metallorganic agent that, indeed, fulfills this design criterion on a technologically relevant metal support With potential Impact on Au(III)-porphyrin-functionalized nanoparticles for an improved anticancer-drug delivery. Employing scanning tunneling microscopy and -spectroscopy in combination with photoemission spectroscopy,we clarify at the single-molecule level the underlying mechanisms of this exceptional adsorption mode. It is based on the balance between a high-energy oxidation state and an electrostatic screening-response of the surface (image charge). Modeling with first principles methods reveals submolecular details of the metal-ligand bonding interaction and completes the study by providing an Illustrative electrostatic.. model relevant for ionic metalorganic agent molecules, in general

The SE-Atlantic in the late pleistocene and holocene : paleoceanographic interpretations based on sedimentological, geochemical and foraminiferal data

Die ozeanographische und sedimentologische Entwicklung der drei Tiefseebecken des südöstlichen Atlantiks (Kapbecken, Angolabecken, Guineabecken) während des Holozäns wurde anhand der Foraminiferenfauna und geochemisch-sedimentologischer Parameter rekonstruiert. Im Golf von Guinea spiegeln die Schwankungen der Werte des stabilen Sauerstoffs 18O in planktonischen Foraminiferenschalen ein klimagekoppeltes Heben und Senken der Thermokline (Temperatursprungschicht) wider. Sedimentologische Daten belegen deutliche Veränderungen der Tiefenwasserströme während des späten Pleistozäns und Holozäns. Das Guineabecken und das Angolabecken werden von Nordatlantischem Tiefenwasser dominiert während das Kapbecken von Antarktischem Bodenwasser durchströmt wird. Die Foraminiferenfauna zeigt einen deutlichen Trend: eine Zunahme der Diversität Richtung Äquator.The Southeast Atlantic deep-sea basins are the goal of thorough investigations concerning biodiversity as well as the oceanographic evolution during the youngest part of earth history, the Late Pleistocene and Holocene. The South Atlantic is considered to be a key region concerning ocean circulation and coupled climatic processes due to the special position in the mixing area of deep water currents from the North (North Atlantic Deep Water) and South Atlantic (Antarctic Bottom Water), both tightly connected by the Thermohaline Circulation. In the presented study we tried to link geochemical, sedimentological and faunistic data to draw a picture of the evolution of the main water currents in the region focussing on shallow water layers by the use of temperature differences stored in planktonic foraminiferal tests and on deep water by the evaluation of the effect of deep water corrosiveness fluctuations on the sediments. A second focus is on the temporal and spatial distribution patterns of benthic foraminiferal and their possible correlations to water mass and sediment properties. Due to different habitat preferences, test shapes and material as well as feeding habits abundances of specific foraminiferal taxa show a correlation with sediment properties such as sand content, organic carbon content, and carbonate content. In most cases it is difficult to clarify if a correlation is based on a direct interplay or is triggered by secondary effects as for example taphonomic processes such as dissolution. A combination of various sedimentological and geochemical proxies helps to decipher these interactions.by Stefan MülleggerAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersGraz, Univ., Diss., 2008OeBB(VLID)20126