Gender bias in teaching evaluations: the causal role of department gender composition.

Women are underrepresented in academia's higher ranks. Promotion oftentimes requires positive student-provided course evaluations. At a U.S. university, both an archival and an experimental investigation uncovered gender discrimination that affected both men and women. A department's gender composition and the course levels being taught interacted to predict biases in evaluations. However, women were disproportionately impacted because women were more often in the gender minority. A subsequent audit of the university's promotion guidelines suggested a disproportionate impact on women's career trajectories. Our framework was guided by role congruity theory, which poses that workplace positions are gendered by the ratios of men and women who fill them. We hypothesized that students would expect educators in a department's gender majority to fill more so essential positions of teaching upper-level courses and those in the minority to fill more so supportive positions of teaching lower-level courses. Consistent with role congruity theory when an educator's gender violated expected gendered roles, we generally found discrimination in the form of lower evaluation scores. A follow-up experiment demonstrated that it was possible to change students' expectations about which gender would teach their courses. When we assigned students randomly to picture themselves as students in a male-dominated, female-dominated, or gender-parity department, we shifted their expectations of whether men or women would teach upper- and lower-level courses. Violating students' expectations created negative biases in teaching evaluations. This provided a causal link between department gender composition and discrimination. The importance of gender representation and ameliorating strategies are discussed.

Tissue-Specific Toxicokinetics of Aqueous Radium-226 in an Estuarine Mussel, Geukensia demissa.

Radiological contamination of coastal habitats poses potential risk for native fauna, but the bioavailability of aqueous radium (Ra) and other dissolved metals to marine bivalves remains unclear. This study was the first to examine the tissue-specific disposition of aqueous 226Ra in a coastal mussel, specifically the Atlantic ribbed mussel Geukensia demissa. Most organ groups reached steady-state concentrations within 7 days during experimental exposure, with an average uptake rate constant of 0.0013 mL g-1 d-1. When moved to Ra-free synthetic seawater, mussels rapidly eliminated aqueous 226Ra (average elimination rate constant 1.56 d-1). The biological half-life for aqueous 226Ra ranged from 8.9 h for the gills and labial palps to 15.4 h for the muscle. Although previous field studies have demonstrated notable 226Ra accumulation in the soft tissues of marine mussels and that, for freshwater mussels, tissue-incorporated 226Ra derives primarily from the aqueous phase, our tissue-specific bioconcentration factors (BCFs) were on the order of (8.3 ± 1.5) × 10-4 indicating low accumulation potential of aqueous 226Ra in estuarine mussels. This suggests marine and estuarine mussels obtain 226Ra from an alternate route, such as particulate-sorbed Ra ingested during filter-feeding or from a contaminated food source.

Functionalized Polymer Thin Films for Plutonium Capture and Isotopic Screening from Aqueous Sources.

The rapid screening of plutonium from aqueous sources remains a critical challenge for nuclear nonproliferation efforts. The determination of trace-level Pu isotopes in water requires offsite sample preparation and analysis; therefore, new methods that combine plutonium purification, concentration, and isotopic screening in a fieldable detection system will provide an invaluable tool for nuclear safeguards. This contribution describes the development and characterization of thin polymer-ligand films for the isolation and concentration of waterborne Pu for direct spectroscopic analyses. Submicron thin films were prepared through spin coating onto Si wafers and consisted of combinations of polystyrene (PS) with dibenzoylmethane, thenoyltrifluoroacetone, and di(2-ethylhexyl)phosphoric acid (HDEHP). Pu uptake studies from solutions at pH from 2.3 to 6.3 indicated that only films containing HDEHP exhibited significant recovery of Pu. High alpha spectroscopy peak energy resolutions were achieved for PS-HDEHP films over a range of film thicknesses from 30 to 250 nm. A separate study was performed to evaluate uptake from a primarily Pu(V) solution where it was observed that doubling the HDEHP loading in the film increased uptake of Pu by an order of magnitude. X-ray photoelectron spectroscopy (XPS) analysis revealed that HDEHP was highly concentrated within the first few nanometers of the film at the higher loading. XPS analysis also revealed that, in the presence of water, HDEHP was stripped from the surface layer of the film at circumneutral pH. While significant losses of ligand were seen in all samples, higher loadings of HDEHP resulted in measurable amounts of ligand retained after a 12-h soak in water. Findings of this study are being used to guide the development of thin-film composite membrane-based detection methods for the rapid, fieldable analysis of Pu in water.

Enthalpy of Uranium Adsorption onto Hematite.

The influence of temperature on the adsorption of metal ions at the solid-water interface is often overlooked, despite the important role that adsorption plays in metal-ion fate and transport in the natural environment where temperatures vary widely. Herein, we examine the temperature-dependent adsorption of uranium, a widespread radioactive contaminant, onto the ubiquitous iron oxide, hematite. The multitemperature batch adsorption data and surface complexation models indicate that the adsorption of uranium, as the hexavalent uranyl (UO22+) ion, increases significantly with increasing temperature, with an adsorption enthalpy (ΔHads) of +71 kJ mol-1. We suggest that this endothermic, entropically driven adsorption behavior is linked to reorganization of the uranyl-ion hydration and interfacial water structures upon UVI adsorption at the hematite surface. Overall, this work provides fundamental insight into the thermodynamics driving metal-ion adsorption reactions and provides the specific enthalpy value necessary for improved predictive geochemical modeling of UVI adsorption in the environment.

Dissolution and Vertical Transport of Uranium from Stable Mineral Forms by Plants as Influenced by the Co-occurrence of Uranium with Phosphorus.

Plants could mobilize (dissolution followed by vertical transport) uranium (U) from mineral forms that are otherwise stable. However, the variability of this plant-mediated mobilization of U as a function of the presence of various essential plant nutrients contained in these minerals remains unknown. A series of column experiments were conducted using Andropogon virginicus to quantify the vertical transport of U from stable mineral forms as influenced by the chemical and physical coexistence of U with the essential nutrient, phosphorus (P). The presence of plants significantly increased the vertical migration of U only when U was precipitated with P (UO2HPO4·4H2O; chernikovite) but not from UO2 (uraninite) that lacks any essential plant nutrient. The U dissolution was further increased when chernikovite co-occurred with a sparingly available form of P (FePO4) under P-limited growing conditions. Similarly, A. virginicus accumulated the highest amount of U from chernikovite (0.05 mg/g) in the presence of FePO4 compared to that of uraninite (no-P) and chernikovite supplemented with KH2PO4. These results signify an increased plant-mediated dissolution, uptake, and leaching of radioactive contaminants in soils that are nutrient deficient, a key factor that should be considered in management at legacy contamination sites.

Impact of Natural Organic Matter on Plutonium Vadose Zone Migration from an NH4Pu(V)O2CO3(s) Source.

We investigated the influence of natural organic matter (NOM) on the behavior of Pu(V) in the vadose zone through a combination of the field lysimeter and laboratory studies. Well-defined solid sources of NH4Pu(V)O2CO3(s) were placed in two 5-L lysimeters containing NOM-amended soil collected from the Savannah River Site (SRS) or unamended vadose zone soil and exposed to 3 years of natural South Carolina, USA, meteorological conditions. Lysimeter soil cores were removed from the field, used in desorption experiments, and characterized using wet chemistry methods and X-ray absorption spectroscopy. For both lysimeters, Pu migrated slowly with the majority (>95%) remaining within 2 cm of the source. However, without the NOM amendment, Pu was transported significantly farther than in the presence of NOM. Downward Pu migration appears to be influenced by the initial source oxidation state and composition. These Pu(V) sources exhibited significantly greater migration than previous studies using Pu(IV) or Pu(III) sources. However, batch laboratory experiments demonstrated that Pu(V) is reduced by the lysimeter soil in the order of hours, indicating that downward migration of Pu may be due to cycling between Pu(V) and Pu(IV). Under the conditions of these experiments, NOM appeared to both enhance reduction of the Pu(V) source as well as Pu sorption to soils. This indicates that NOM will tend to have a stabilizing effect on Pu migration under SRS vadose zone field conditions.

Thermodynamics and Electronic Properties of Heterometallic Multinuclear Actinide-Containing Metal-Organic Frameworks with "Structural Memory".

Thermodynamic studies of actinide-containing metal-organic frameworks (An-MOFs), reported herein for the first time, are a step toward addressing challenges related to effective nuclear waste administration. In addition to An-MOF thermochemistry, enthalpies of formation were determined for the organic linkers, 2,2'-dimethylbiphenyl-4,4'-dicarboxylic acid (H2Me2BPDC) and biphenyl-4,4'-dicarboxylic acid (H2BPDC), which are commonly used building blocks for MOF preparation. The electronic structure of the first example of An-MOF with mixed-metal AnAn'-nodes was influenced through coordination of transition metals as shown by the density of states near the Fermi edge, changes in the Tauc plot, conductivity measurements, and theoretical calculations. The "structural memory" effect (i.e., solvent-directed crystalline-amorphous-crystalline structural dynamism) was demonstrated as a function of node coordination degree, which is the number of organic linkers per metal node. Remarkable three-month water stability was reported for Th-containing frameworks herein, and the mechanism is also considered for improvement of the behavior of a U-based framework in water. Mechanistic aspects of capping linker installation were highlighted through crystallographic characterization of the intermediate, and theoretical calculations of free energies of formation (ΔGf) for U- and Th-MOFs with 10- and 12-coordinated secondary building units (SBUs) were performed to elucidate experimentally observed transformations during the installation processes. Overall, these results are the first thermochemical, electronic, and mechanistic insights for a relatively young class of actinide-containing frameworks.

Mobility of Aqueous and Colloidal Neptunium Species in Field Lysimeter Experiments.

Due to its radiotoxicity, long half-life, and potentially high environmental mobility, neptunium transport is of paramount importance for risk assessment and safety. Environmental transport of neptunium through field lysimeters at the Savannah River Site was observed from both oxidized (Np(V)) and reduced (Np(IV)) source materials. While transport from oxidized neptunium sources was expected, the unexpected transport from reduced neptunium sources spurred further investigation into transport mechanisms. Partial oxidation of the reduced neptunium source resulted in significant release and transport into the mobile aqueous phase, though a reduced colloidal neptunium species appears to have also been present, enhancing neptunium mobility over shorter distances. These field and laboratory experiments demonstrate the multiple controls on neptunium vadose zone transport and chemical behavior, as well as the need for thorough understanding of radionuclide source terms for long-term risk prediction.

Phosphorus Stress-Induced Changes in Plant Root Exudation Could Potentially Facilitate Uranium Mobilization from Stable Mineral Forms.

Apparent deficiency of soil mineral nutrients often triggers specific physio-morphological changes in plants, and some of these changes could also inadvertently increase the ability of plants to mobilize radionuclides from stable mineral forms. This work, through a series of sand-culture, hydroponics, and batch-equilibration experiments, investigated the differential ability of root exudates of Andropogon virginicus grown under conditions with variable phosphorus (P) availability (KH2PO4, FePO4, Ca3(PO4)2, and no P) to solubilize uranium (U) from the uranyl phosphate mineral Chernikovite. The mineral form of P, and hence the bioavailability of P, affected the overall composition of the root exudates. The lower bioavailable forms of P (FePO4 and Ca3(PO4)2), but not the complete absence of P, resulted in a higher abundance of root metabolites with chelating capacity at 72 hrs after treatment application. In treatments with lower P-bioavailability, the physiological amino acid concentration inside of the roots increased, whereas the concentration of organic acids in the roots decreased due to the active exudation. In batch dissolution experiments, the organic acids, but not amino acids, increase the dissolution U from Chernikovite. The root exudate matrix of plants exposed to low available forms of P induced a >60% increase in U dissolution from Chernikovite due to 5-16 times greater abundance of organic acids in these treatments. However, this was ca. 70% of the theoretical dissolution achievable by this exudate matrix. These results highlight the potential of using active management of soil P as an effective tool to alter the plant-mediated mobilization of U in contaminated soil.

Anion-Exchange Fibers for Improved Sample Loading in Ultra-Trace Analysis of Plutonium by Thermal Ionization Mass Spectrometry.

A new sample loading procedure was developed for isotope ratio measurements of ultratrace amounts of plutonium with thermal ionization mass spectrometry (TIMS). The goal was to determine the efficacy of a polymer fiber architecture for TIMS sample loading by following similar sample loading procedures as those used in bead loading. Fibers with diameter of approximately 100 µm were prepared from triethylamine-quaternized-poly(vinylbenzyl chloride) cross-linked with diazabicyclo[2.2.2]octane. Fiber sections (2.5 mm) were loaded with 10 pg of New Brunswick Laboratory certified reference material (NBL CRM) 128 from an 8 M HNO3 matrix and affixed to rhenium filaments with collodion. A single filament assembly was used for these analyses. Total ion counts (239Pu + 242Pu) and isotope ratios obtained from fiber-loaded filaments were compared to those measured by depositing Pu amended resin beads on the filament. Fiber loading was found to improve sensitivity, accuracy, and precision of isotope ratio measurements of plutonium when compared to the established resin bead loading method, while maintaining its simplicity. The average number of detected Pu+ counts was 180% greater, and there was a 72% reduction in standard deviation of ratio measurements when using fiber loading. An average deviation of 0.0012 (0.117%) from the certified isotope ratio value of NBL CRM Pu128 was measured when fiber loading versus a deviation of 0.0028 (0.284%) when bead loading. The fiber formation method presented in this study can be extended to other anion-exchange polymer chemistries and, therefore, offers a convenient platform to investigate the efficacy of novel polymer chemistries in sample loading for TIMS.

Plant litter chemistry alters the content and composition of organic carbon associated with soil mineral and aggregate fractions in invaded ecosystems.

Through the input of disproportionate quantities of chemically distinct litter, invasive plants may potentially influence the fate of organic matter associated with soil mineral and aggregate fractions in some of the ecosystems they invade. Although context dependent, these native ecosystems subjected to prolonged invasion by exotic plants may be instrumental in distinguishing the role of plant-microbe-mineral interactions from the broader edaphic and climatic influences on the formation of soil organic matter (SOM). We hypothesized that the soils subjected to prolonged invasion by an exotic plant that input recalcitrant litter (Japanese knotweed, Polygonum cuspidatum) would have a greater proportion of plant-derived carbon (C) in the aggregate fractions, as compared with that in adjacent soil inhabited by native vegetation that input labile litter, whereas the soils under an invader that input labile litter (kudzu, Pueraria lobata) would have a greater proportion of microbial-derived C in the silt-clay fraction, as compared with that in adjacent soils that receive recalcitrant litter. At the knotweed site, the higher C content in soils under P. cuspidatum, compared with noninvaded soils inhabited by grasses and forbs, was limited to the macroaggregate fraction, which was abundant in plant biomarkers. The noninvaded soils at this site had a higher abundance of lignins in mineral and microaggregate fractions and suberin in the macroaggregate fraction, partly because of the greater root density of the native species, which might have had an overriding influence on the chemistry of the above-ground litter input. At the kudzu site, soils under P. lobata had lower C content across all size fractions at a 0-5 cm soil depth despite receiving similar amounts of Pinus litter. Contrary to our prediction, the noninvaded soils receiving recalcitrant Pinus litter had a similar abundance of plant biomarkers across both mineral and aggregate fractions, potentially because of the higher surface area of soil minerals at this site. The plant biomarkers were lower in the aggregate fractions of the P. lobata-invaded soils, compared with noninvaded pine stands, potentially suggesting a microbial co-metabolism of pine-derived compounds. These results highlight the complex interactions among litter chemistry, soil biota, and minerals in mediating soil C storage in unmanaged ecosystems; these interactions are particularly important under global changes that may alter plant species composition and hence the quantity and chemistry of litter inputs in terrestrial ecosystems.

Effect of Natural Organic Matter on Plutonium Sorption to Goethite.

The effect of citric acid (CA), desferrioxamine B (DFOB), fulvic acid (FA), and humic acid (HA) on plutonium (Pu) sorption to goethite was studied as a function of organic carbon concentration and pH using batch sorption experiments at 5 mgC·L-1 and 50 mgC·L-1 natural organic matter (NOM), 10-9-10-10 M 238Pu, and 0.1 g·L-1 goethite concentrations, at pH 3, 5, 7, and 9. Low sorption of ligands coupled with strong Pu complexation decreased Pu sorption at pH 5 and 7, relative to a ligand-free system. Conversely, CA, FA, and HA increased Pu sorption to goethite at pH 3, suggesting ternary complex formation or, in the case of humic acid, incorporation into HA aggregates. Mechanisms for ternary complex formation were characterized by Fourier transform infrared spectroscopy in the absence of Pu. CA and FA demonstrated clear surface interactions at pH 3, HA appeared unchanged suggesting HA aggregates had formed, and no DFOB interactions were observed. Plutonium sorption decreased in the presence of DFOB (relative to a ligand free system) at all pH values examined. Thus, DFOB does not appear to facilitate formation of ternary Pu-DFOB-goethite complexes. At pH 9, Pu sorption in the presence of all NOM increased relative to pH 5 and 7; speciation models attributed this to Pu(IV) hydrolysis competing with ligand complexation, increasing sorption. The results indicate that in simple Pu-NOM-goethite ternary batch systems, NOM will decrease Pu sorption to goethite at all but particularly low pH conditions.

High-Resolution 4D Preclinical Single-Photon Emission Computed Tomography/X-ray Computed Tomography Imaging of Technetium Transport within a Heterogeneous Porous Media.

A dynamic 99mTc tracer experiment was performed to investigate the capabilities of combined preclinical single photon emission computed tomography (SPECT) and X-ray computed tomography (CT) for investigating transport in a heterogeneous porous medium. The experiment was conducted by continuously injecting a 99mTc solution into a column packed with eight layers (i.e., soil, silica gel, and 0.2-4 mm glass beads). Within the imaging results it was possible to correlate observed features with objects as small as 2 mm for the SPECT and 0.2 mm for the CT. Time-lapse SPECT imaging results illustrated both local and global nonuniform transport phenomena and the high-resolution CT data were found to be useful for interpreting the cause of variations in the 99mTc concentration associated with structural features within the materials, such as macropores. The results of this study demonstrate SPECT/CT as a novel tool for 4D (i.e., transient three-dimensional) noninvasive imaging of fate and transport processes in porous media. Despite its small scale, an experiment with such high resolution data allows us to better understand the pore scale transport which can then be used to inform larger scale studies.

A Novel Method for Tracer Concentration Plutonium(V) Solution Preparation.

Preparation of relatively pure low concentration Pu(V) solutions for environmental studies is nontrivial due to the complex redox chemistry of Pu. Ozone gas generated by an inexpensive unit designed for household-use was used to oxidize a 2 × 10(-8) M Pu(IV) solution to predominantly Pu(VI) with some Pu(V) present. Over several days, the Pu(VI) in the solution reduced to Pu(V) without further reducing to Pu(IV). The reduction from Pu(VI) to Pu(V) could be accelerated by raising the pH of the solution, which led to an immediate conversion without substantial conversion to Pu(IV). The aqueous Pu was found to be stable as predominately Pu(V) for greater than one month from pH 3-7; however, at circumneutral pH, a sizable fraction of Pu was lost from solution by either precipitation or sorption to the vial walls. This method provides a fast means of preparing Pu(V) solutions for tracer concentration studies without numerous extraction or cleanup steps.

Implantable Cardioverter Defibrillator Programming Characteristics, Shocked Rhythms, and Survival Among Patients Under Thirty Years of Age.

INTRODUCTION: Indications for implantable cardioverter defibrillators (ICDs) in young patients have expanded and differ from those in older adults. We sought to provide descriptive characteristics and data regarding ICD therapy and outcomes among younger and older ICD recipients. METHODS AND RESULTS: Demographics, device type and programming, remotely transmitted data, shock events, and survival were compared among younger (≤30 years) and older (>30 years) cohorts with ICDs from a single manufacturer followed on a remote network. The younger cohort included 904 patients (1.6% of all implants). This group had more females (46% vs. 25%; P < 0.01), single-coil leads (21% vs. 4%; P < 0.01), and single-chamber devices (46% vs. 34%; P < 0.01). Shock incidence was higher (40% younger vs. 32% older at 4 years; P < 0.01) and survival was better over comparable follow-up (88% vs. 72%; P < 0.01). Remote monitoring was associated with improved survival in both groups (93% vs. 86% ≤ 30 years, P < 0.01; 73% vs. 66% > 30 years, P < 0.01). Shock for polymorphic ventricular tachycardia/fibrillation (VT/VF) was more frequent in younger patients (12% vs. 5%; P < 0.01); 39% of all shocks were inappropriate. A 10-fold increased risk of mortality was seen among young patients with shocks for atrial fibrillation/flutter (AF/AFL). CONCLUSIONS: Differences in survival, shock incidence, and prognostic significance of VT/VF and AF/AFL exist between younger and older ICD recipients. These suggest distinct differences in myocardial substrates and diseases that ultimately impact ICD management.