Quantification of Olivine Using Fe Lα in Electron Probe Microanalysis (EPMA)

AbstractQuantification of first series transition metal Lα X-rays is hampered by absorption and in some cases transition probabilities (fluorescence yields) varying with chemical bonding. Compound mass absorption coefficients for Fe Lα were measured in the olivine solid solution series [Forsterite (Mg2SiO4) to Fayalite (Fe2SiO4)] and the mass absorption coefficients for Fe Lα absorbed by Fe were calculated. The mass absorption coefficients vary systematically between Fo83 and Fo0. Using the measured mass absorption coefficients for both standard and unknown and by correcting for a systematic discrepancy, consistent with varying partial fluorescence yields, a good agreement between calculated k-ratios and measured k-ratios is achieved. The systematic variations allow quantification of unknown k-ratios. The described method of quantification requires modification of matrix correction routines to allow standards and unknowns to have different mass absorption coefficients, and to incorporate solid solution mass absorption coefficients and partial fluorescence yield corrections derived from regression of experimental data.</jats:p

The Accuracy of Al and Cu Film Thickness Determinations and the Implications for Electron Probe Microanalysis

AbstractThe accuracy to which Cu and Al coatings can be determined, and the effect this has on the quantification of the substrate, is investigated. Cu and Al coatings of nominally 5, 10, 15, and 20 nm were sputter coated onto polished Bi using two configurations of coater: One with the film thickness monitor (FTM) sensor colocated with the samples, and one where the sensor is located to one side. The FTM thicknesses are compared against those calculated from measured Cu Lαand Al Kα k-ratios using PENEPMA, GMRFilm, and DTSA-II. Selected samples were also cross-sectioned using focused ion beam. Both systems produced repeatable coatings, the thickest coating being approximately four times the thinnest coating. The side-located FTM sensor indicated thicknesses less than half those of the software modeled results, propagating on to 70% errors in substrate quantification at 5 kV. The colocated FTM sensor produced errors in film thickness and substrate quantification of 10–20%. Over the range of film thicknesses and accelerating voltages modeled both the substrate and coatingk-ratios can be approximated by linear trends as functions of film thickness. The Al films were found to have a reduced density of ~2 g/cm2.</jats:p

Apparent preservation of primary foraminiferal Mg/Ca ratios and Mg-banding in recrystallized foraminifera

Trace element and δ18O values of foraminifera are widely used to reconstruct oceanic temperatures throughout the Cenozoic and beyond. Previous work evaluating the geochemistry of foraminifera with differing degrees of physical preservation have shown that Mg/Ca and δ18O paleothermometers give discrepant values in recrystallized tests, with planktonic oxygen isotopes often yielding significantly lower temperatures than Mg/Ca ratios. To study the mobility of elements during diagenesis, we performed microspatial trace element analyses in Eocene Morozovella. Element maps show that trace element banding is readily identifiable and preserved, to an extent, in texturally recrystallized tests. A reaction-diffusion model was used to test whether the preservation of Mg-banding and the decoupling of δ18O and Mg/Ca values could be the result of diffusively limited “closed-system” recrystallization. Results show that, in a closed system, internal features (such as Mg-banding) will dissipate prior to changes in bulk Mg/Ca composition, while the bulk δ18O value will typically change faster than Mg/Ca. This is observed regardless of what partitioning coefficient is used for Mg and demonstrates that the planktonic Mg/Ca proxy is more diagenetically robust than the δ18O proxy. Thus, this model can explain the observed decoupling of these two proxies. Furthermore, the preservation of intra-test Mg-banding shows potential for use in evaluating the preservation of primary Mg/Ca values and hence the accuracy of paleotemperature reconstructions

A method for comparing multiple imputation techniques: A case study on the U.S. national COVID cohort collaborative.

Healthcare datasets obtained from Electronic Health Records have proven to be extremely useful for assessing associations between patients’ predictors and outcomes of interest. However, these datasets often suffer from missing values in a high proportion of cases, whose removal may introduce severe bias. Several multiple imputation algorithms have been proposed to attempt to recover the missing information under an assumed missingness mechanism. Each algorithm presents strengths and weaknesses, and there is currently no consensus on which multiple imputation algorithm works best in a given scenario. Furthermore, the selection of each algorithm’s pa- rameters and data-related modeling choices are also both crucial and challenging

Addressing the environmental, community and health impacts of resource development: Challenges across scales, sectors and sites

Work that addresses the cumulative impacts of resource extraction on environment, community, and health is necessarily large in scope. This paper presents experiences from initiating research at this intersection and explores implications for the ambitious, integrative agenda of planetary health. The purpose is to outline origins, design features, and preliminary insights from our intersectoral and international project, based in Canada and titled the “Environment, Community, Health Observatory” (ECHO) Network. With a clear emphasis on rural, remote, and Indigenous communities, environments, and health, the ECHO Network is designed to answer the question: How can an Environment, Community, Health Observatory Network support the integrative tools and processes required to improve understanding and response to the cumulative health impacts of resource development? The Network is informed by four regional cases across Canada where we employ a framework and an approach grounded in observation, “taking notice for action”, and collective learning. Sharing insights from the foundational phase of this five-year project, we reflect on the hidden and obvious challenges of working across scales, sectors, and sites, and the overlap of generative and uncomfortable entanglements associated with health and resource development. Yet, although intersectoral work addressing the cumulative impacts of resource extraction presents uncertainty and unresolved tensions, ultimately we argue that it is worth staying with the trouble

High spatial resolution analysis of the iron oxidation state in silicate glasses using the electron probe

The iron oxidation state in silicate melts is important for understanding their physical properties, although it is most often used to estimate the oxygen fugacity of magmatic systems. Often high spatial resolution analyses are required, yet the available techniques, such as μXANES and μMössbauer, require synchrotron access. The flank method is an electron probe technique with the potential to measure Fe oxidation state at high spatial resolution but requires careful method development to reduce errors related to sample damage, especially for hydrous glasses. The intensity ratios derived from measurements on the flanks of FeLα and FeLβ X-rays (FeLβf/FeLαf) over a time interval (time-dependent ratio flank method) can be extrapolated to their initial values at the onset of analysis. We have developed and calibrated this new method using silicate glasses with a wide range of compositions (43–78 wt% SiO2, 0–10 wt% H2O, and 2–18 wt% FeOT, which is all Fe reported as FeO), including 68 glasses with known Fe oxidation state. The Fe oxidation state (Fe2+/FeT) of hydrous (0–4 wt% H2O) basaltic (43–56 wt% SiO2) and peralkaline (70–76 wt% SiO2) glasses with FeOT > 5 wt% can be quantified with a precision of ±0.03 (10 wt% FeOT and 0.5 Fe2+/FeT) and accuracy of ±0.1. We find basaltic and peralkaline glasses each require a different calibration curve and analysis at different spatial resolutions (∼20 and ∼60 μm diameter regions, respectively). A further 49 synthetic glasses were used to investigate the compositional controls on redox changes during electron beam irradiation, where we found that the direction of redox change is sensitive to glass composition. Anhydrous alkali-poor glasses become reduced during analysis, while hydrous and/or alkali-rich glasses become oxidized by the formation of magnetite nanolites identified using Raman spectroscopy. The rate of reduction is controlled by the initial oxidation state, whereas the rate of oxidation is controlled by SiO2, Fe, and H2O content

Addressing the environmental, community and health impacts of resource development: Challenges across scales, sectors and sites

Work that addresses the cumulative impacts of resource extraction on environment, community, and health is necessarily large in scope. This paper presents experiences from initiating research at this intersection and explores implications for the ambitious, integrative agenda of planetary health. The purpose is to outline origins, design features, and preliminary insights from our intersectoral and international project, based in Canada and titled the “Environment, Community, Health Observatory” (ECHO) Network. With a clear emphasis on rural, remote, and Indigenous communities, environments, and health, the ECHO Network is designed to answer the question: How can an Environment, Community, Health Observatory Network support the integrative tools and processes required to improve understanding and response to the cumulative health impacts of resource development? The Network is informed by four regional cases across Canada where we employ a framework and an approach grounded in observation, “taking notice for action”, and collective learning. Sharing insights from the foundational phase of this five-year project, we reflect on the hidden and obvious challenges of working across scales, sectors, and sites, and the overlap of generative and uncomfortable entanglements associated with health and resource development. Yet, although intersectoral work addressing the cumulative impacts of resource extraction presents uncertainty and unresolved tensions, ultimately we argue that it is worth staying with the trouble