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Creators/Authors contains: "Thomas, J."

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  1. ; ; ; ( , Physical Review E)
    Free, publicly-accessible full text available July 1, 2023
  2. ; ; ; ; ; ; ( , Journal of Materials Chemistry A)
    Redox flow batteries are attractive for grid-scale energy storage, but ongoing work on materials discovery is hampered by the difficulty of measuring electron-transfer rates under battery-relevant conditions. We have developed an experimental approach for collecting continuous voltammetric measurements of flow battery electrolytes by placing a 3-electrode cell containing an ultramicroelectrode into the flow loop of a functioning redox flow battery. We further developed an empirical approach for extracting electron-transfer rate constants from each voltammetric cycle, thereby enabling continuous measurements as a function of state of charge and cycle time. Benchmarking these approaches with iron-based aqueous flow battery electrolytes using platinummore »and carbon fiber ultramicroelectrodes yielded rate constants that varied in the order Pt > electrochemically oxidized carbon > pristine carbon, in good agreement with prior work. We also found that Pt electrodes become more catalytically active upon cycling for several hours, whereas carbon fiber electrodes with and without oxidative pretreatments remained stable over the same interval. We expect these experimental approaches can be used to measure kinetics and other figures of merit for most electrodes and electrolytes of interest for redox flow batteries as well as in other systems where it is useful to evaluate the properties of a flowing electrolyte in real time.« less
    Free, publicly-accessible full text available July 5, 2023
  3. ; ; ; ; ; ; ( , Geochimica et Cosmochimica Acta)
    Free, publicly-accessible full text available June 1, 2023
  4. ; ; ; ( , Physical Chemistry Chemical Physics)
    Ligand selectivity to specific lanthanide (Ln) ions is key to the separation of rare earth elements from each other. Ligand selectivity can be quantified with relative stability constants (measured experimentally) or relative binding energies (calculated computationally). The relative stability constants of EDTA (ethylenediaminetetraacetic acid) with La 3+ , Eu 3+ , Gd 3+ , and Lu 3+ were predicted from relative binding energies, which were quantified using electronic structure calculations with relativistic effects and based on the molecular structures of Ln–EDTA complexes in solution from density functional theory molecular dynamics simulations. The protonation state of an EDTA amine group wasmore »varied to study pH ∼7 and ∼11 conditions. Further, simulations at 25 °C and 90 °C were performed to elucidate how structures of Ln–EDTA complexes varying with temperature are related to complex stabilities at different pH conditions. Relative stability trends are predicted from computation for varying Ln 3+ ions (La, Eu, Gd, Lu) with a single ligand (EDTA at pH ∼11), as well as for a single Ln 3+ ion (La) with varying ligands (EDTA at pH ∼7 and ∼11). Changing the protonation state of an EDTA amine site significantly changes the solution structure of the Ln–EDTA complex resulting in a reduction of the complex stability. Increased Ln–ligand complex stability is correlated to reduced structural variations in solution upon an increase in temperature.« less
    Free, publicly-accessible full text available May 4, 2023
  5. ; ; ; ; ; ; ; ; ; ; et al ( , Inorganic Chemistry)
    Free, publicly-accessible full text available July 18, 2023
  6. ; ; ; ; ( , IEEE Transactions on Neural Networks and Learning Systems)
    Numerical models based on physics represent the state of the art in Earth system modeling and comprise our best tools for generating insights and predictions. Despite rapid growth in computational power, the perceived need for higher model resolutions overwhelms the latest generation computers, reducing the ability of modelers to generate simulations for understanding parameter sensitivities and characterizing variability and uncertainty. Thus, surrogate models are often developed to capture the essential attributes of the full-blown numerical models. Recent successes of machine learning methods, especially deep learning (DL), across many disciplines offer the possibility that complex nonlinear connectionist representations may be ablemore »to capture the underlying complex structures and nonlinear processes in Earth systems. A difficult test for DL-based emulation, which refers to function approximation of numerical models, is to understand whether they can be comparable to traditional forms of surrogate models in terms of computational efficiency while simultaneously reproducing model results in a credible manner. A DL emulation that passes this test may be expected to perform even better than simple models with respect to capturing complex processes and spatiotemporal dependencies. Here, we examine, with a case study in satellite-based remote sensing, the hypothesis that DL approaches can credibly represent the simulations from a surrogate model with comparable computational efficiency. Our results are encouraging in that the DL emulation reproduces the results with acceptable accuracy and often even faster performance. We discuss the broader implications of our results in light of the pace of improvements in high-performance implementations of DL and the growing desire for higher resolution simulations in the Earth sciences.« less
    Free, publicly-accessible full text available May 5, 2023
  7. ; ( , The Journal of Chemical Physics)
    If a binary liquid mixture, composed of two alternative species with equal amounts, is quenched from a high temperature to a low temperature, below the critical point of demixing, then the mixture will phase separate through a process known as spinodal decomposition. However, if the two alternative species are allowed to interconvert, either naturally (e.g., the equilibrium interconversion of enantiomers) or forcefully (e.g., via an external source of energy or matter), then the process of phase separation may drastically change. In this case, depending on the nature of interconversion, two phenomena could be observed: either phase amplification, the growth ofmore »one phase at the expense of another stable phase, or microphase separation, the formation of nongrowing (steady-state) microphase domains. In this work, we phenomenologically generalize the Cahn–Hilliard theory of spinodal decomposition to include the molecular interconversion of species and describe the physical properties of systems undergoing either phase amplification or microphase separation. We apply the developed phenomenology to accurately describe the simulation results of three atomistic models that demonstrate phase amplification and/or microphase separation. We also discuss the application of our approach to phase transitions in polyamorphic liquids. Finally, we describe the effects of fluctuations of the order parameter in the critical region on phase amplification and microphase separation.« less
    Free, publicly-accessible full text available February 28, 2023
  8. ; ; ( , Frontiers in Political Science)
    Ethnographers have ably documented the great extent and diversity of social institutions that contemporary fishers and shellfishers employ to collectively manage common property resources. However, the collective action regimes developed among ancient maritime societies remain understudied by archaeologists. We summarize research into the development and form of collective action among the maritime societies of the western peninsular coast of Florida, USA, drawing on our own recent work in the Tampa Bay area and previous work elsewhere in the region, especially the Calusa area to the south. Archaeological evidence suggests that collective action became more important in Tampa Bay in themore »first centuries CE, probably owing to a marine transgression that resulted in more productive estuaries. Groups here staked claims to productive estuarine locations through the founding of villages, the building of mounds, and the construction of relatively simple marine enclosures. Historically, these changes resulted in societies of relatively small scale and limited authoritarian government. In contrast, collective action developed later in the Calusa area, may have begun in relation to resource scarcity than plenty, and may been founded in kinship rather than in public ritual. Collective action in the Calusa area resulted in projects of greater scale and complexity, providing a foundation for more hierarchical and authoritarian social formations.« less
    Free, publicly-accessible full text available March 8, 2023
  9. ; ; ( , Journal of Hymenoptera Research)
    Establishing a higher classification of bees based on morphology alone can fail to capture evolutionary relationships when morphological characters either vary very little between distantly related groups, or conversely vary greatly between closely related species. This problem is well represented in the subfamily Panurginae, for which a recent global revision based on phylogenomic data unexpectedly revealed that two Old World species previously placed in Camptopoeum Spinola and Flavipanurgus Warncke, are in fact most closely related to each other, and together form a sister group relationship to the remaining Flavipanurgus and Panurgus Panzer combined. To rectify this situation, we here establishmore »an expanded phylogenomic data set of Old World Panurgini and re-assess generic and subgeneric concepts for the tribe. To solve the paraphyly of Camptopoeum and Flavipanurgus , we establish the new genus Halopanurgus gen. nov. containing the species H. baldocki (Wood & Cross), comb. nov. and H. fuzetus (Patiny), comb. nov. , both of which are restricted to coastal sands, saltmarshes, and inland saline lagoons in the extreme south of Portugal and south-west of Spain. Re-evaluation of four recently used subgenera in Panurgus strongly supports a simplified classification of two subgenera; Pachycephalopanurgus Patiny, stat. rev. including Micropanurgus Patiny syn. nov. , and Panurgus s. str. including Euryvalvus Patiny. Pachycephalopanurgus species seem to be oligoleges of Asteroideae (Asteraceae), whereas Panurgus s. str. may be oligoleges of Cichorieae (Asteraceae). Our findings reinforce the challenges of establishing a phylogenetically sound classification of Panurginae using morphology alone and illustrate that even in well-studied regions like Europe unrecognised genera can persist in underexplored corners of the continent.« less
    Free, publicly-accessible full text available February 28, 2023
  10. ; ; ; ( , Physical Review Letters)
    Free, publicly-accessible full text available March 1, 2023