Iron Isotope Fractionation during Fe(II) Oxidation Mediated by the Oxygen-Producing Marine Cyanobacterium Synechococcus PCC 7002.

In this study, we couple iron isotope analysis to microscopic and mineralogical investigation of iron speciation during circumneutral Fe(II) oxidation and Fe(III) precipitation with photosynthetically produced oxygen. In the presence of the cyanobacterium Synechococcus PCC 7002, aqueous Fe(II) (Fe(II)aq) is oxidized and precipitated as amorphous Fe(III) oxyhydroxide minerals (iron precipitates, Feppt), with distinct isotopic fractionation (ε56Fe) values determined from fitting the δ56Fe(II)aq (1.79‰ and 2.15‰) and the δ56Feppt (2.44‰ and 2.98‰) data trends from two replicate experiments. Additional Fe(II) and Fe(III) phases were detected using microscopy and chemical extractions and likely represent Fe(II) and Fe(III) sorbed to minerals and cells. The iron desorbed with sodium acetate (FeNaAc) yielded heavier δ56Fe compositions than Fe(II)aq. Modeling of the fractionation during Fe(III) sorption to cells and Fe(II) sorption to Feppt, combined with equilibration of sorbed iron and with Fe(II)aq using published fractionation factors, is consistent with our resulting δ56FeNaAc. The δ56Feppt data trend is inconsistent with complete equilibrium exchange with Fe(II)aq. Because of this and our detection of microbially excreted organics (e.g., exopolysaccharides) coating Feppt in our microscopic analysis, we suggest that electron and atom exchange is partially suppressed in this system by biologically produced organics. These results indicate that cyanobacteria influence the fate and composition of iron in sunlit environments via their role in Fe(II) oxidation through O2 production, the capacity of their cell surfaces to sorb iron, and the interaction of secreted organics with Fe(III) minerals.

Chromium geochemistry of the ca. 1.85 Ga Flin Flon paleosol.

Fractionation of stable Cr isotopes has been measured in Archaean paleosols and marine sedimentary rocks and interpreted to record the terrestrial oxidation of Cr(III) to Cr(VI), providing possible indirect evidence for the emergence of oxygenic photosynthesis. However, these fractionations occur amidst evidence from other geochemical proxies for a pervasively anoxic atmosphere. This study examined the Cr geochemistry of the ca. 1.85 Ga Flin Flon paleosol, which developed under an atmosphere unambiguously oxidising enough to quantitatively convert Fe(II) to Fe(III) during pedogenesis. The paleosol shows an extreme range in Cr isotope composition of 2.76 ‰ δ53/52 Cr. The protolith greenstone (δ53/52 Cr: -0.23 ‰), the deepest weathering horizon (δ53/52 Cr: -0.15 to -0.23 ‰) and a residual corestone in the upper paleosol (δ53/52 Cr: -0.01 ‰) all exhibit Cr isotopic compositions comparable to unaltered igneous rocks. The most significant isotopic fractionation is preserved in the areas influenced by oxidative subaerial weathering (i.e. increase in Fe(III)/Fe(II)) and the greatest loss of mobile elements. The uppermost paleosol horizon is both Cr and Mn depleted and offset to significantly 53 Cr-enriched compositions (δ53/52 Cr values between +1.50 and +2.38 ‰), which is not easily modelled with the oxidation of Cr(III) and loss of isotopically heavy Cr(VI). Instead, the currently preferred model for these data invokes the open-system removal of isotopically light aqueous Cr(III) during either pedogenesis or subsequent hydrothermal/metamorphic alteration. The 53 Cr enrichment would then represent the preferential dissolution or complexation of isotopically light aqueous Cr(III) species (enhanced by lower pH conditions and possibly the presence of complexing ligands) and/or the residual signature from preferential adsorption of isotopically heavy Cr(III). Both scenarios would contradict the widely held assumption that only redox reactions of Cr can generate large magnitude isotopic fractionations and, if substantiated, non-redox isotope effects would complicate the conclusive fingerprinting of ancient atmospheric O2 from Cr isotope data alone.

Does a Heavy Fe-Isotope Composition of Akilia Quartz-Amphibole-Pyroxene Rocks Necessitate a BIF Origin?

The age and origin of the quartz-amphibole-pyroxene (qap) gneiss from the island of Akilia, southern West Greenland, have been the subject of intense debate since the light C-isotope composition of graphite inclusions in apatite was interpreted to indicate the presence of Earth's earliest biological activity. Although this claim for biogenic relicts has been vigorously challenged, the possibility that the rocks might represent some of Earth's earliest water-lain sediments and, hence, a suitable repository for life remains an open question. While some workers have suggested that the entire sequence represents an originally mafic-ultramafic igneous precursor subsequently modified by metasomatism, quartz injection, high-grade metamorphism, and extreme ductile deformation, others maintain that at least a small part of the sequence retains geochemical characteristics indicative of a chemical sedimentary origin. Fractionated Fe isotopes with δ(56)Fe values similar to those observed in Isua BIF have been reported from high-SiO2 units of qap and used to support a chemical sedimentary protolith for the qap unit. Here, we present new Fe isotope data from all lithologic variants in the qap gneiss on Akilia, including layers of undisputed ultramafic igneous origin. Since the latter require introduction of fractionated Fe into at least part of the qap unit, we argue that Fe isotopes must therefore be treated with considerable caution when used to infer BIF for part or all of the qap protolith.

First global forum on education on organ donation and transplantation for schools.

The Transplantation Society, in collaboration with the Canadian Society of Transplantation, organized a forum on education on ODT for schools. The forum included participants from around the world, school boards, and representatives from different religions. Participants presented on their countries' experience in the area of education on ODT. Working groups discussed about technologies for education, principles for sharing of resources globally, and relationships between education, and health authorities and non-governmental organizations. The forum concluded with a discussion about how to best help existing programs and those wishing to start educational programs on ODT.

Simplified method for the determination of Ru, Pd, Re, Os, Ir and Pt in chromitites and other geological materials by isotope dilution ICP-MS and acid digestion.

A method for the determination of low Ru, Pd, Re, Os, Ir and Pt abundances in geological reference materials by isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) after acid digestion in a high pressure asher (HPA-S) is presented. The digestion technique is similar to that using Carius tubes but easier to handle and reaches higher temperatures. Osmium can be determined as OsO4 with ICP-MS directly after digestion through a sparging technique. The remaining elements are preconcentrated by means of anion column chromatography. The resin is digested directly without elution leading to high yields but this causes problems if Zr is present at higher levels in the silicate rich materials. The analytical results for international platinum group element (PGE) reference materials, chromitite CHR-Bkg, basalt TDB-1 and gabbro WGB-1, are presented and compared with literature data, demonstrating the validity of the described method. Although higher in concentration, PGEs determined for reference material WGB-1 were worse than for TDB-1 indicating a more inhomogeneous distribution of the platinum group mineral phases. The low PGE abundance chromitite standard, CHR-Bkg, is likely to be homogeneous for Ru, Re, Os and Ir and is recommended as a reference material for the study of chromitites. Detection limits (3s x total procedure blank) range from 0.012 ng (Re and Os) to 0.77 ng (Pt), which could be further improved by applying higher quality acids.

Weaving the Web into legacy information systems.

For many years, client-server systems were developed as the backbone of clinical computing in leading hospitals around the country. Beth Israel Deaconess Medical Center now faces the challenge of bridging the technology gap between such systems and the Internet. While developing Web interfaces to legacy clinical systems gives a taste of the future, it is clear that complete institutional migration to the Web is not imminent. Asking clinicians to utilize two different systems, Web-based and legacy, in the interim phase is just one of the difficulties in such transition. This paper describes "Mbridge", a solution that allows legacy system users to exploit the benefits of the Internet in a fashion that does not interfere with their workflow and is both simple and affordable to implement. The service allows clinicians to work on the legacy platform while context-sensitive clinical content is streamed to the browser without their intervention. Using the system, we can gradually expose clinicians to new Web-based applications and resources without forcing them to operate two computing environments simultaneously. The service achieves these goals by means of linkage and coordination rather than by code-translation, data exchange or replication.

Studying clinician-computer interaction in Web-based systems.

A growing of health-care organizations are in the process of modifying their clinical information systems (CIS) to support browser-based access. Consequently, care-providers are expected to modify their workflow to take advantage of the new technology. Intuitive interfaces, fast response and new functionality are few of the features used to promote endorsement of the change. In parallel, administrators are required to constantly assess user compliance and intervene where necessary to prevent rejection. Such monitoring translates to frequent surveys, analysis of logs and prudent utilization of user-groups. These methods tend to further burden users, suffer from "post-hoc" temporality and are difficult to maintain. In this paper we suggest an alternative approach to such data acquisition. "CareQuest" is an interactive Web-based service that can be woven into clinical applications without coding. It acquires information from the clinician at the relevant point in her workflow. It allows extensive interaction customization, data-driven response, real-time Web-based data-analysis, and full Web-based administration.

Making ICU alarms meaningful: a comparison of traditional vs. trend-based algorithms.

Much of the work in the ICU revolves around information that is recorded by electronic devices. Such devices typically incorporate simple alarm functions that trigger when a value exceeds predefined limits. Depending on the parameter followed, these "boundary based" alarms tend to produce vast numbers of false alarms. Some are the result of false reading and some the result of true but clinically insignificant readings. We present a computerized module that analyzes real-time data from multiple monitoring devices using a customizable logic engine. The module was tested on 6 intensive care unit patients over 5 days, running alarm algorithms for heart rate, systolic and diastolic blood pressure as well as arterial oxygen saturation. Results show a ten-fold increase in positive predictive value of alarms from 3% using monitor alarms to 32% using the module. The module's overall sensitivity was 82%, failing to detect 18% of significant alarms as defined by the ICU staff. The results suggests that implementation of such methodology may assist in filtering false and insignificant alarms in the ICU setting.

Statistical issues for research on social drinkers.

The crucial problem in alcohol research is the large amount of inherently uncontrolled variation in the dependent variables. Because randomization with respect to key independent variables is frequently impractical or impossible, quasi-experimental and survey methods are being used to control residual variation statistically. For various reasons, however, the methods have often not been properly applied in alcohol research, endangering the replicability of true findings and prolonging the life of false claims. Ill-advised practices found in alcohol research that are discussed here are the use of partial correlations and standardized regression coefficients, of categorization or truncation of independent variables, and of available or convenient samples. It is recommended that researchers use unstandardized regression models, avoid categorizing independent variables, and scale them either to agreed on units of measure or use natural units (e.g., ounces or deciliters of alcohol consumed per occasion), and employ randomization or random sampling.

Alcohol use and cognitive loss among employed men and women.

A representative sample of 1,367 employed men and women in Detroit responded to questions about their drinking practices and then completed a cognitive test which measures abstraction abilities. Abstraction, tested while respondents were sober, decreased significantly as reported quantity of alcohol usually consumed per drinking occasion increased. (Am J Public Health 1983; 73:521-526.)