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  1. Free, publicly-accessible full text available September 1, 2023
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  3. The ability of symbionts to recolonize their hosts after a period of dysbiosis is essential to maintain a resilient partnership. Many cnidarians rely on photosynthate provided from a large algal symbiont population. Under periods of thermal stress, symbiont densities in host cnidarians decline, and the recovery of hosts is dependent on the re-establishment of symbiosis. The cellular mechanisms that govern this process of colonization are not well-defined and require further exploration. To study this process in the symbiotic sea anemone model Exaiptasia diaphana , commonly called Aiptasia, we developed a non-invasive, efficient method of imaging that uses autofluorescence to measuremore »the abundance of symbiont cells, which were spatially distributed into distinct cell clusters within the gastrodermis of host tentacles. We estimated cell cluster sizes to measure the occurrence of singlets, doublets, and so on up to much larger cell clusters, and characterized colonization patterns by native and non-native symbionts. Native symbiont Breviolum minutum rapidly recolonized hosts and rapidly exited under elevated temperature, with increased bleaching susceptibility for larger symbiont clusters. In contrast, populations of non-native symbionts Symbiodinium microadriaticum and Durusdinium trenchii persisted at low levels under elevated temperature. To identify mechanisms driving colonization patterns, we simulated symbiont population changes through time and determined that migration was necessary to create observed patterns (i.e., egression of symbionts from larger clusters to establish new clusters). Our results support a mechanism where symbionts repopulate hosts in a predictable cluster pattern, and provide novel evidence that colonization requires both localized proliferation and continuous migration.« less
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  6. The Renewable Fuel Standard (RFS) specifies the use of biofuels in the United States and thereby guides nearly half of all global biofuel production, yet outcomes of this keystone climate and environmental regulation remain unclear. Here we combine econometric analyses, land use observations, and biophysical models to estimate the realized effects of the RFS in aggregate and down to the scale of individual agricultural fields across the United States. We find that the RFS increased corn prices by 30% and the prices of other crops by 20%, which, in turn, expanded US corn cultivation by 2.8 Mha (8.7%) and totalmore »cropland by 2.1 Mha (2.4%) in the years following policy enactment (2008 to 2016). These changes increased annual nationwide fertilizer use by 3 to 8%, increased water quality degradants by 3 to 5%, and caused enough domestic land use change emissions such that the carbon intensity of corn ethanol produced under the RFS is no less than gasoline and likely at least 24% higher. These tradeoffs must be weighed alongside the benefits of biofuels as decision-makers consider the future of renewable energy policies and the potential for fuels like corn ethanol to meet climate mitigation goals.« less
    Free, publicly-accessible full text available March 1, 2023
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  8. This study aimed to investigate the effects of thermal annealing on a film of squaraine (SQ) molecules in a polymethyl methacrylate (PMMA) matrix. Molecular aggregation is inferred from in situ absorption measurements, and excited state dynamics are measured using a spatially encoded transient absorption (TA) spectroscopy. TA spectra were well-replicated using a kinetic model that evolves as a function of annealing time and extent of aggregation. While linear absorbance spectra indicate that the SQ molecules are primarily uncoupled or weakly-coupled when initially deposited in a PMMA matrix, the kinetic model shows that some pi-stacked aggregates are already present. Excitons aremore »funnelled by energy transfer to these aggregates in just a few picoseconds. The amount of pi-stacked aggregates increases during thermal annealing, further increasing the population of excitons that end up in these aggregates.« less
    Free, publicly-accessible full text available January 1, 2023
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  10. Abstract

    Tool wear in machining is generally observed as early and late stage tool wear. During early stage tool wear, the tool is rapidly worn during a break-in period, followed by a stable region of tool wear. After machining more material, the tool reaches late stage tool wear. At this point, tool wear becomes unstable; tool failure occurs quickly or it may take some time. Therefore, late stage tool wear represents a bifurcation point, making it difficult to predict tool wear past this point.

    Tool wear is well known to be stochastically influenced. Due to this effect, it is difficultmore »to perform studies on late stage tool wear since machining tools will be affected differently up to this point, introducing unknown variables. A novel method is presented in this research which utilized artificial wear to reach late stage tool wear. This method, termed contrived tool wear, may be capable of reducing the stochastic tool wear that occurs during early stage tool wear. As an initial investigation, machining tool inserts were worn by taking several passes over a grinding wheel with the tool rotating in reverse. Several parameters were tested in an attempt to match the natural worn state as close as possible. Subsequent to artificial wear, the inserts were used to machine IN718. The presented method of contrived wear was found to be a good approach, but could not sufficiently replicate the tool wear typically produced in IN718 machining. Future work should aim at implementing a multi-axis approach to enable grinding at various angles to the rake face of the insert.

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    Free, publicly-accessible full text available November 1, 2022