Intense ultraviolet photoluminescence at 314 nm in Gd^3+-doped Silica

Photoluminescence (PL) of Gd-doped silica in the ultraviolet (UV) is investigated. The efficient emission detected at 314 nm is due to the 6P7/2 to 8S7/2 transition of a 4f electron of the Gd3+ ion

Fluxes and distribution of dissolved iron in the eastern (sub-) tropical North Atlantic Ocean

Aeolian dust transport from the Saharan/Sahel desert regions is considered the dominant external input of iron (Fe) to the surface waters of the eastern (sub-) tropical North Atlantic Ocean. To test this hypothesis, we investigated the sources of dissolved Fe (DFe) and quantified DFe fluxes to the surface ocean in this region. In winter 2008, surface water DFe concentrations varied between <0.1 nM and 0.37 nM, with an average of 0.13 ± 0.07 nM DFe (n = 194). A strong correlation between mixed layer averaged concentrations of dissolved aluminum (DAl), a proxy for dust input, and DFe indicated dust as a source of DFe to the surface ocean. The importance of Aeolian nutrient input was further confirmed by an increase of 0.1 nM DFe and 0.05 ?M phosphate during a repeat transect before and after a dust event. An exponential decrease of DFe with increasing distance from the African continent, suggested that continental shelf waters were a source of DFe to the northern part of our study area. Relatively high Fe:C ratios of up to 3 × 10?5 (C derived from apparent oxygen utilization (AOU)) indicated an external source of Fe to these African continental shelf waters. Below the wind mixed layer along 12°N, enhanced DFe concentrations (>1.5 nM) correlated positively with apparent oxygen utilization (AOU) and showed the importance of organic matter remineralization as an DFe source. As a consequence, vertical diffusive mixing formed an important Fe flux to the surface ocean in this region, even surpassing that of a major dust event

Rapid prototyping Lab-on-Chip devices for the future: A numerical optimisation of bulk optical parameters in microfluidic systems

Nuclear reactor process control is typically monitored for pure β-emitting radionuclides via manual sampling followed by laboratory analysis, leading to delays in data availability and response times. The development of an in situ microfluidic Lab on Chip (LoC) system with integrated detection capable of measuring pure β-emitting radionuclides presents a promising solution, enabling a reduction in occupational exposure and cost of monitoring whilst providing improved temporal resolution through near real-time data acquisition. However, testing prototypes with radioactive sources is time-consuming, requires specialist facilities/equipment, generates contaminated waste, and cannot rapidly evaluate a wide range of designs or configurations. Despite this, modelling multiple design parameters and testing their impact on detection with non-radioactive substitutes has yet to be adopted as best practice. The measurement of pure β emitters in aqueous media relies on the efficient transport of photons generated by the Cherenkov effect or liquid scintillators to the detector. Here we explore the role of numerical modelling to assess the impact of optical cell geometry and design on photon transmission and detection through the microfluidic system, facilitating improved designs to realise better efficiency of integrated detectors and overall platform design. Our results demonstrate that theoretical modelling and an experimental evaluation using non-radiogenic chemiluminescence are viable for system testing design parameters and their impact on photon transport. These approaches enable reduced material consumption and requirement for specialist facilities for handling radioactive materials during the prototyping process. This method establishes proof of concept and the first step towards numerical modelling approaches for the design optimisation of microfluidic LoC systems with integrated detectors for the measurement of pure β emitting radionuclides via scintillation-based detection

Der Effekt saurer Polysaccharide auf die Biogeochemie von Eisen im Meer

In large areas of the ocean, the so called high nutrient low chlorophyll (HNLC) areas, phytoplankton growth is partly limited by depleted iron (Fe) conditions due to very low Fe input to surface waters. Fe is an important nutrient for marine phytoplankton, being essential in many metabolic reactions. Fast hydrolysis and scavenging onto particles constantly remove Fe from the surface ocean. More than 99% of the remaining dissolved Fe is found to be bound by organic compounds. Photochemical reactions involving dissolved organic matter (DOM) and oxygen form hydrogen peroxide (HOOH). HOOH acts as strong oxidant or reductant in the cycling of organic compounds and trace metals like Fe. The objective of this PhD project was to investigate the role of acidic polysaccharides, main constituents of phytoplankton exudates, on the redox photochemistry of Fe and as Fe ligands

THE EFFECT OF ACIDIC POLYSACCHARIDES ON THE BIOGEOCHEMISTRY OF IRONIN THE MARINE ENVIRONMENT

In large areas of the ocean, the so called high nutrient low chlorophyll (HNLC) areas, phytoplankton growth is partly limited by depleted iron (Fe) conditions due to very low Fe input to surface waters. Fe is an important nutrient for marine phytoplankton, being essential in many metabolic reactions. Fast hydrolysis and scavenging onto particles constantly remove Fe from the surface ocean. More than 99% of the remaining dissolved Fe is found to be bound by organic compounds. Photochemical reactions involving dissolved organic matter (DOM) and oxygen form hydrogen peroxide (HOOH). HOOH acts as strong oxidant or reductant in the cycling of organic compounds and trace metals like Fe. The objective of this PhD project was to investigate the role of acidic polysaccharides, main constituents of phytoplankton exudates, on the redox photochemistry of Fe and as Fe ligands

Effect of algal polysaccharides and UVA+B radiation on iron speciation in seawater

UVA/B, hydrogen peroxide, ferrous iron, algal exudates, polysaccharide

Characterization of phytoplankton exudates and carbohydrates in relation to their complexation of copper, cadmium and iron

The goal of this study was to investigate if transparent exopolymer particles (TEP), carbohydrates, surface active substances (SAS), reduced sulfur species (RSS) or thio/amino groups contribute significantly to the complexing capacity of phytoplankton exudates for copper (LTOTCu), cadmium (LTOTCd) or iron (LTOTFe). Complexing capacities and apparent stability constants (Kapp) were determined electrochemically for Cu and Cd in cultures of the marine diatoms Thalassiosira weissflogii and Skeletonema costatum, and in a culture of the coccolithophore Emiliana huxleyi. Furthermore, the complexing capacity with Fe, Cu and Cd of four marine polysaccharides (PS) (phytagel, carrageenan, laminarin and alginic acid) were investigated. As expected more Cu than Cd was complexed in the three phytoplankton cultures and in the phytagel solution. Size fractionation of the phytagel solution suggests that the binding capacity for Cu was more significant in the particulate fraction (> 0.7 µm), indicating that Cu was preferably trapped within pores and channel of large hydrogels. In contrast Cd binding sites were predominantly found in the fraction < 0.7 µm, suggesting binding to the outer surfaces of gel particles to be of greater importance for larger ions. The Kapp of the Cd complexes were higher than those of Cu, indicating stronger binding of Cd ions than of Cu ions. Solutions of carrageenan, laminarin and alginic acid did not form complexes with either Cu or Cd and Fe-binding properties could not be detected for any of the four polysaccharide solutions. Thio/amino groups of sulfur-rich “glutathione” type ligands were found in all phytoplankton cultures and were presumably responsible for the complexation of Cu. No consistent relationship was observed between TEP, carbohydrate concentration, SAS or sulfur content, or with the complexing capacity, emphasizing the high degree of heterogeneity of substance classes responsible for metal binding