3-D Tracking and Visualization of Hundreds of Pt-Co Fuel Cell Nanocatalysts During Electrochemical Aging

We present an electron tomography method that allows for the identification of hundreds of electrocatalyst nanoparticles with one-to-one correspondence before and after electrochemical aging. This method allows us to track, in three-dimensions (3-D), the trajectories and morphologies of each Pt-Co nanocatalyst on a fuel cell carbon support. The use of atomic-scale electron energy loss spectroscopic imaging enables the correlation of performance degradation of the catalyst with changes in particle/inter-particle morphologies, particle-support interactions and the near-surface chemical composition. We found that, aging of the catalysts under normal fuel cell operating conditions (potential scans from +0.6 V to +1.0 V for 30,000 cycles) gives rise to coarsening of the nanoparticles, mainly through coalescence, which in turn leads to the loss of performance. The observed coalescence events were found to be the result of nanoparticle migration on the carbon support during potential cycling. This method provides detailed insights into how nanocatalyst degradation occurs in proton exchange membrane fuel cells (PEMFCs), and suggests that minimization of particle movement can potentially slow down the coarsening of the particles, and the corresponding performance degradation.Comment: Nano Letters, accepte

Exoplanet Classification and Yield Estimates for Direct Imaging Missions

Future NASA concept missions that are currently under study, like Habitable Exoplanet Imaging Mission (HabEx) & Large Ultra-Violet Optical Infra Red (LUVOIR) Surveyor, would discover a large diversity of exoplanets. We propose here a classification scheme that distinguishes exoplanets into different categories based on their size and incident stellar flux, for the purpose of providing the expected number of exoplanets observed (yield) with direct imaging missions. The boundaries of this classification can be computed using the known chemical behavior of gases and condensates at different pressures and temperatures in a planetary atmosphere. In this study, we initially focus on condensation curves for sphalerite ZnS, H2O, CO2 and CH4. The order in which these species condense in a planetary atmosphere define the boundaries between different classes of planets. Broadly, the planets are divided into rocky (0.5 - 1.0RE), super-Earths (1.0- 1.75RE), sub-Neptunes (1.75-3.5RE), sub-Jovians (3.5 - 6.0RE) and Jovians (6-14.3RE) based on their planet sizes, and 'hot', 'warm' and 'cold' based on the incident stellar flux. We then calculate planet occurrence rates within these boundaries for different kinds of exoplanets, \eta_{planet}, using the community co-ordinated results of NASA's Exoplanet Program Analysis Group's Science Analysis Group-13 (SAG-13). These occurrence rate estimates are in turn used to estimate the expected exoplanet yields for direct imaging missions of different telescope diameter.Comment: Accepted to Astrophysical Journal. 30 pages, 4 tables. Online tool for classification boundaries can be found at: http://www3.geosc.psu.edu/~ruk15/planets

Exoplanet Diversity in the Era of Space-based Direct Imaging Missions

This whitepaper discusses the diversity of exoplanets that could be detected by future observations, so that comparative exoplanetology can be performed in the upcoming era of large space-based flagship missions. The primary focus will be on characterizing Earth-like worlds around Sun-like stars. However, we will also be able to characterize companion planets in the system simultaneously. This will not only provide a contextual picture with regards to our Solar system, but also presents a unique opportunity to observe size dependent planetary atmospheres at different orbital distances. We propose a preliminary scheme based on chemical behavior of gases and condensates in a planet's atmosphere that classifies them with respect to planetary radius and incident stellar flux.Comment: A white paper submitted to the National Academy of Sciences Exoplanet Science Strateg

Measurement of cortisol in saliva: a comparison of measurement error within and between international academic-research laboratories

Objective: Hundreds of scientific publications are produced annually that involve the measurement of cortisol in saliva. Intra- and inter-laboratory variation in salivary cortisol results has the potential to contribute to cross- study inconsistencies in findings, and the perception that salivary cortisol results are unreliable. This study rigor- ously estimates sources of measurement variability in the assay of salivary cortisol within and between established international academic-based laboratories that specialize in saliva analyses. One hundred young adults (Mean age: 23.10 years; 62 females) donated 2 mL of whole saliva by passive drool. Each sample was split into multiple- 100 µL aliquots and immediately frozen. One aliquot of each of the 100 participants’ saliva was transported to academic laboratories (N = 9) in the United States, Canada, UK, and Germany and assayed for cortisol by the same commercially available immunoassay. Results: 1.76% of the variance in salivary cortisol levels was attributable to differences between duplicate assays of the same sample within laboratories, 7.93% of the variance was associated with differences between laboratories, and 90.31% to differences between samples. In established-qualified laboratories, measurement error of salivary cortisol is minimal, and inter-laboratory differences in measurement are unlikely to have a major influence on the determined values

Subcortical brain volume, regional cortical thickness, and cortical surface area across disorders: findings from the ENIGMA ADHD, ASD, and OCD Working Groups

Objective Attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and obsessive-compulsive disorder (OCD) are common neurodevelopmental disorders that frequently co-occur. We aimed to directly compare all three disorders. The ENIGMA consortium is ideally positioned to investigate structural brain alterations across these disorders. Methods Structural T1-weighted whole-brain MRI of controls (n=5,827) and patients with ADHD (n=2,271), ASD (n=1,777), and OCD (n=2,323) from 151 cohorts worldwide were analyzed using standardized processing protocols. We examined subcortical volume, cortical thickness and surface area differences within a mega-analytical framework, pooling measures extracted from each cohort. Analyses were performed separately for children, adolescents, and adults using linear mixed-effects models adjusting for age, sex and site (and ICV for subcortical and surface area measures). Results We found no shared alterations among all three disorders, while shared alterations between any two disorders did not survive multiple comparisons correction. Children with ADHD compared to those with OCD had smaller hippocampal volumes, possibly influenced by IQ. Children and adolescents with ADHD also had smaller ICV than controls and those with OCD or ASD. Adults with ASD showed thicker frontal cortices compared to adult controls and other clinical groups. No OCD-specific alterations across different age-groups and surface area alterations among all disorders in childhood and adulthood were observed. Conclusion Our findings suggest robust but subtle alterations across different age-groups among ADHD, ASD, and OCD. ADHD-specific ICV and hippocampal alterations in children and adolescents, and ASD-specific cortical thickness alterations in the frontal cortex in adults support previous work emphasizing neurodevelopmental alterations in these disorders

In Situ Neutron Reflectometry Study of a Tungsten Oxide/Li-Ion Battery Electrolyte Interface

The solid electrolyte interface/interphase (SEI) is of great importance to the viable operation of lithium-ion batteries. In the present work, the interface between a tungsten oxide electrode and an electrolyte solution consisting of LiPF6 in a deuterated ethylene carbonate/diethyl carbonate solvent was characterized with in situ neutron reflectometry (NR) at a series of applied electrochemical potentials. NR data were fit to yield neutron scattering length density (SLD) depth profiles in the surface normal direction, from which composition depth profiles were inferred. The goals of this work were to characterize SEI formation on a model transition-metal oxide, an example of a conversion electrode, to characterize the lithiation of WO3, and to help interpret the results of an earlier study of tungsten electrodes without an intentionally grown surface oxide. The WO3 electrode was produced by thermal oxidation of a W thin film. Co-analysis of NR and X-ray reflectivity data indicated that the stoichiometry of the thermal oxide was WO3. As the electrode was polarized to progressively more reducing potentials, starting from open circuit and down to +0.25 V versus Li/Li+, the layer that was originally WO3 expanded and increased in lithium content. The reduced electrode consisted of two to three layers: an inner layer (the evolving conversion electrode) which may have been mixed W and Li2O and unreacted WO3 or LixWO3, a layer rich in protons and/or lithium, possibly corresponding to LiOH or LiH (the inner SEI), and an outermost layer adjacent to the solution with an SLD close to that of the solution, possibly consisting of lower SLD species with solution-filled porosity or deuteron-rich species derived from the solvents (the outer SEI), though the presence of this layer was tenuous. For the steps in the direction of more oxidizing potentials, the evolution of the layer structure was qualitatively the reverse of that seen when stepping toward more negative potentials, though with hysteresis. The SLD gradient suggested that the reaction was not limited by diffusion within the film. No clear phase boundary was evident in the evolving conversion electrode

Leading groups and teams towards successful innovation

Among the many factors that can affect teams' creative and innovative performance, leadership may be the most powerful. In this chapter, we review the literature on leadership and team innovation, distinguishing between task-focused and person-focused leadership styles and behaviors. We discuss three roles of leadership in the innovation process: as a predictor of team innovation, as a moderator of the effects of other variables on team innovation, and as a transition catalyst in moving from creativity to implementation. Having reviewed the literature in this manner, we discuss methodological and theoretical trends and gaps in the literature, and identify some important avenues for future research

Electrochemical Behavior of Electrolytic Manganese Dioxide in Aqueous KOH and LiOH Solutions: A Comparative Study

As an inexpensive and high capacity oxidant, electrolytic manganese dioxide (γ-MnO2) is of interest as a cathode for secondary aqueous batteries. Electrochemical behavior of γ-MnO2 was characterized in aqueous 5.0 M KOH and LiOH solutions, and found to depend strongly upon cation identity. In LiOH and mixed LiOH / KOH solutions, Li-ion intercalation appeared to operate in competition with proton intercalation, being favored at higher [Li+] and, for mixed electrolytes, lower sweep rates. Electrochemical and in situ X-ray diffraction data indicated that γ-MnO2 underwent a chemically irreversible transformation upon the first reduction in LiOH solution, while in KOH solution, structure was largely unchanged after the first cycle. These experiments with γ-MnO2 as well as with a closely-related, ramsdellite-like sample, suggest that depending on sample morphology/rate capability, the irreversible process proceeds either through a solid-solution reaction or a two-phase reaction followed by a solid-solution reaction. While discharge capacity and capacity retention during galvanostatic cycling of γ-MnO2 were worse in LiOH than in KOH solution, some improvement was noted in a mixed LiOH/KOH solution

CO₂ and O₂ Evolution at High Voltage Cathode Materials of Li-Ion Batteries: A Differential Electrochemical Mass Spectrometry Study

A three-electrode differential electrochemical mass spectrometry (DEMS) cell has been developed to study the oxidative decomposition of electrolytes at high voltage cathode materials of Li-ion batteries. In this DEMS cell, the working electrode used was the same as the cathode electrode in real Li-ion batteries, i.e., a lithium metal oxide deposited on a porous aluminum foil current collector. A charged LiCoO₂ or LiMn₂O₄ was used as the reference electrode, because of their insensitivity to air, when compared to lithium. A lithium sheet was used as the counter electrode. This DEMS cell closely approaches real Li-ion battery conditions, and thus the results obtained can be readily correlated with reactions occurring in real Li-ion batteries. Using DEMS, the oxidative stability of three electrolytes (1 M LiPF₆ in EC/DEC, EC/DMC, and PC) at three cathode materials including LiCoO₂, LiMn₂O₄, and LiNi_0.5Mn_1.5O₄ were studied. We found that 1 M LiPF₆ + EC/DMC electrolyte is quite stable up to 5.0 V, when LiNi_0.5Mn_1.5O₄ is used as the cathode material. The EC/DMC solvent mixture was found to be the most stable for the three cathode materials, while EC/DEC was the least stable. The oxidative decomposition of the EC/DEC mixture solvent could be readily observed under operating conditions in our cell even at potentials as low as 4.4 V in 1 M LiPF₆ + EC/DEC electrolyte on a LiCoO₂ cathode, as indicated by CO₂ and O₂ evolution. The features of this DEMS cell to unveil solvent and electrolyte decomposition pathways are also described