1,118 research outputs found
Mg/Ca ratios in freshwater microbial carbonates: Thermodynamic, kinetic and vital effects
The ratio of magnesium to calcium (Mg/Ca) in carbonate minerals in an abiotic setting is conventionally assumed to be predominantly controlled by (Mg/Ca)solution and a temperature dependant partition coefficient. This temperature dependence suggests that both marine (e.g. foraminiferal calcite and corals) and freshwater (e.g. speleothems and surface freshwater deposits, âtufasâ) carbonate deposits may be important archives of palaeotemperature data. However, there is considerable uncertainty in all these settings. In surface freshwater deposits this uncertainty is focussed on the influence of microbial biofilms. Biogenic or âvitalâ effects may arise from microbial metabolic activity and/or the presence of extracellular polymeric substances (EPS). This study addresses this key question for the first time, via a series of unique through-flow microcosm and agitated flask experiments where freshwater calcite was precipitated under controlled conditions. These experiments reveal there is no strong relationship between (Mg/Ca)calcite and temperature, so the assumption of thermodynamic fractionation is not viable. However, there is a pronounced influence on (Mg/Ca)calcite from precipitation rate, so that rapidly forming precipitates develop with very low magnesium content indicating kinetic control on fractionation. Calcite precipitation rate in these experiments (where the solution is only moderately supersaturated) is controlled by biofilm growth rate, but occurs even when light is excluded indicating that photosynthetic influences are not critical. Our results thus suggest the apparent kinetic fractionation arises from the electrochemical activity of EPS molecules, and are therefore likely to occur wherever these molecules occur, including stromatolites, soil and lake carbonates and (via colloidal EPS) speleothems
Evaluation des impacts Ă©cologiques et hydrologiques de la collecte des eaux pluviales sur une zone humide artificielle
Obesity and Albuminuria Among Adults With Type 2 Diabetes: The Look AHEAD (Action for Health in Diabetes) Study
This is an uncopyedited electronic version of an article accepted for publication in Diabetes Care. The American Diabetes Association, publisher of Diabetes Care, is not responsible for any errors or omissions in this version of the manuscript or any version derived from it by third parties. The definitive publisher-authenticated version will be available in a future issue of Diabetes Care in print and online a
Lower Total Adipocyte Number but No Evidence for Small Adipocyte Depletion in Patients With Type 2 Diabetes
Trunk Versus Extremity Adiposity and Cardiometabolic Risk Factors in White and African American Adults
Microscreening toxicity system based on living magnetic yeast and gradient chips
There is an increasing demand for easy and cost-effective methods to screen the toxicological impact of the growing number of chemical mixtures being generated by industry. Such a screening method has been developed using viable, genetically modified green fluorescent protein (GFP) reporter yeast that was magnetically functionalised and held within a microfluidic device. The GFP reporter yeast was used to detect genotoxicity by monitoring the exposure of the cells to a well-known genotoxic chemical (methyl methane sulfonate, MMS). The cells were magnetised using biocompatible positively charged PAH-stabilised magnetic nanoparticles with diameters around 15 nm. Gradient mixing was utilised to simultaneously expose yeast to a range of concentrations of toxins, and the effective fluorescence emitted from the produced GFP was measured. The magnetically enhanced retention of the yeast cells, with their facile subsequent removal and reloading, allowed for very convenient and rapid toxicity screening of a wide range of chemicals. This is the first report showing magnetic yeast within microfluidic devices in a simple bioassay, with potential applications to other types of fluorescent reporter yeast in toxicological and biomedical research. The microfluidic chip offers a simple and low-cost screening test that can be automated to allow multiple uses (adapted to different cell types) of the device on a wide range of chemicals and concentrations. © 2010 Springer-Verlag
Short intense ion pulses for materials and warm dense matter research
We have commenced experiments with intense short pulses of ion beams on the
Neutralized Drift Compression Experiment-II at Lawrence Berkeley National
Laboratory, by generating beam spots size with radius r < 1 mm within 2 ns FWHM
and approximately 10^10 ions/pulse. To enable the short pulse durations and
mm-scale focal spot radii, the 1.2 MeV Li+ ion beam is neutralized in a
1.6-meter drift compression section located after the last accelerator magnet.
An 8-Tesla short focal length solenoid compresses the beam in the presence of
the large volume plasma near the end of this section before the target. The
scientific topics to be explored are warm dense matter, the dynamics of
radiation damage in materials, and intense beam and beam-plasma physics
including selected topics of relevance to the development of heavy-ion drivers
for inertial fusion energy. Here we describe the accelerator commissioning and
time-resolved ionoluminescence measurements of yttrium aluminium perovskite
using the fully integrated accelerator and neutralized drift compression
components.Comment: 7 pages, 9 figure
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