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  1. Free, publicly-accessible full text available December 1, 2022
  2. Abstract We study a possible calibration technique for the nEXO experiment using a 127 Xe electron capture source. nEXO is a next-generation search for neutrinoless double beta decay (0 νββ ) that will use a 5-tonne, monolithic liquid xenon time projection chamber (TPC). The xenon, used both as source and detection medium, will be enriched to 90% in 136 Xe. To optimize the event reconstruction and energy resolution, calibrations are needed to map the position- and time-dependent detector response. The 36.3 day half-life of 127 Xe and its small Q-value compared to that of 136 Xe 0 νββ would allow a small activity to be maintained continuously in the detector during normal operations without introducing additional backgrounds, thereby enabling in-situ calibration and monitoring of the detector response. In this work we describe a process for producing the source and preliminary experimental tests. We then use simulations to project the precision with which such a source could calibrate spatial corrections to the light and charge response of the nEXO TPC.
    Free, publicly-accessible full text available July 1, 2023
  3. Abstract We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Ly α emitting galaxies between 1.88 < z < 3.52, in a 540 deg 2 area encompassing a comoving volume of 10.9 Gpc 3 . No preselection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project’s observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra.
    Free, publicly-accessible full text available December 1, 2022
  4. Abstract. Global ecosystems vary in their function, and therefore resilience to disturbance, as a result of their location on Earth, structure, and anthropogenic legacy. Resilience can therefore be difficult to describe solely based on energy partitioning, as it fails to effectively describe how ecosystems use available resources, such as soil moisture. Maximum entropy production (MEP) has been shown to be a better metric to describe these differences as it relates energy use efficiencies of ecosystems to the availability of resources. We studied three sites in a longleaf pine ecosystem with varying levels of anthropogenic legacy and biodiversity, all of which were exposed to extreme drought. We quantified their resilience from radiative, metabolic and overall MEP ratios. Sites with anthropogenic legacy had ~10% lower overall and metabolic energy use efficiency compared to more biodiverse sites. This resulted in lower resilience and a delay in recovery from drought by ~1 year. Additionally, a set of entropy ratios to determine metabolic and overall energy use efficiency explained more clearly site-specific ecosystem function, whereas the radiative entropy budget gave more insights about structural complexities at the sites. Our study provides foundational evidence of how MEP can be used to determine resiliencymore »across ecosystems globally.

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  5. Coaker, Gitta (Ed.)
  6. Abstract. Ecosystems are open systems that exchange matter and energy with theirenvironment. They differ in their efficiency in doing so as a result of theirlocation on Earth, structure and disturbance, including anthropogenic legacy.Entropy has been proposed to be an effective metric to describe thesedifferences as it relates energy use efficiencies of ecosystems to theirthermodynamic environment (i.e., temperature) but has rarely been studied tounderstand how ecosystems with different disturbance legacies respond whenconfronted with environmental variability. We studied three sites in alongleaf pine ecosystem with varying levels of anthropogenic legacy and plantfunctional diversity, all of which were exposed to extreme drought. Wequantified radiative (effrad), metabolic and overall entropychanges – as well as changes in exported to imported entropy(effflux) in response to drought disturbance and environmentalvariability using 24 total years of eddy covariance data (8 years per site).We show that structural and functional characteristics contribute todifferences in energy use efficiencies at the three study sites. Our resultsdemonstrate that ecosystem function during drought is modulated by decreasedabsorbed solar energy and variation in the partitioning of energy and entropyexports owing to differences in site enhanced vegetation index and/or soilwater content. Low effrad and metabolic entropy as well as slowadjustment of effflux at themore »anthropogenically altered siteprolonged its recovery from drought by approximately 1 year. In contrast,stands with greater plant functional diversity (i.e., the ones that includedboth C3 and C4 species) adjusted their entropy exports when facedwith drought, which accelerated their recovery. Our study provides a pathforward for using entropy to determine ecosystem function across differentglobal ecosystems.

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