• Transit Time Distributions Estimation Exploiting Flow-Weighted Time: Theory and Proof-of-Concept

      Kim, M.; Troch, P.A.; Biosphere 2, University of Arizona; Department of Hydrology and Atmospheric Sciences, University of Arizona (Blackwell Publishing Ltd, 2020)
      Time-variable transit time distributions (TTDs) have been utilized as a tool to understand how catchments transmit water. However, most of the existing TTD estimation methods require to impose certain structures on those TTDs a priori, which could lead to misinterpreting data. We present a data-based method to estimate time-variable TTDs without imposing their structure a priori. The core of the method is the use of a revised flow-weighted time, where TTDs do not reflect variable external forcings directly. The functional forms of the TTDs are much simpler in flow-weighted time, compared to those in calendar time, and this allows for easier estimation of TTDs. Dynamic (state-dependent) multiple linear regression methods were applied to estimate the time-variable TTDs in flow-weighted time, which can eventually be transformed back to calendar time. The method performs well in a proof-of-concept demonstration with synthetic data sets. We also discuss potential generalizations of the proposed method. © 2020. American Geophysical Union. All Rights Reserved.
    • Potential of Hydraulic Tomography in Identifying Boundary Conditions of Groundwater Basins

      Liu, F.; Yeh, T.-C.J.; Wang, Y.-L.; Song, X.; Lei, X.; Wen, J.-C.; Wang, W.; Hao, Y.; University of Arizona (Blackwell Publishing Ltd, 2020)
      This study investigates the potential of hydraulic tomography (HT) in identifying the boundary conditions of groundwater basins using numerical experiments. The experiment mimics the scenario of groundwater exploitation reduction in a pilot area of groundwater overexploitation control in the North China Plain. In this study, we propose an approach that integrates the HT concept and readily available groundwater monitoring data to identify the constant head and impermeable boundaries by mapping anomalously high- and low-permeability zones from HT surveys in a large-scale domain that encompasses the true groundwater basin. The resulting boundaries and conditions were then used in inversion of steady-state and transient-state simultaneous pumping tests and HT surveys of heterogeneity within the groundwater basin. The inversion results demonstrated significant advantages of HT surveys over multiple simultaneous pumping tests to identify boundary conditions and heterogeneity in the groundwater basin. Moreover, steady HT inversion outperforms transient HT inversion in capturing the true boundary conditions, leading to the better T estimates from steady HT inversion than those from transient HT inversion. Additionally, the study shows that accurate geological zonation information can significantly improve HT parameter estimations. ©2020. American Geophysical Union. All Rights Reserved.
    • Tree Ring-Based Historic Hydroclimatic Variability of the Baja California Peninsula

      Gutierrez-Garcia, G.; Leavitt, S.W.; Trouet, V.; Carriquiry, J.D.; Laboratory of Tree-Ring Research, University of Arizona (Blackwell Publishing Ltd, 2020)
      The Baja California Peninsula is one of the most arid regions in Mexico, receiving an average of only 168 mm of precipitation annually. Climate change scenarios project drier and warmer conditions in the region at the end of this century driven by anthropogenic emissions of greenhouse gases. The growing demand for limited water supplies and the impacts of climate change pose a challenge to manage the already scarce water resources in the Peninsula. Analysis of historical hydroclimatic variability in the Peninsula is limited because most of the early instrumental climate data collection started only in the 1950s. In this study, we reconstruct past precipitation variability for the Peninsula using two tree ring chronologies from northern (Pinus monophylla) and southern (Pinus lagunae) Baja California. Our two reconstructions document multicentury hydroclimatic variability in the Peninsula, including events that turned out to be more extreme than those captured by modern instrumental records. Drought episodes are longer, more frequent, and more intense in the northern peninsula compared to the southern region. Multiyear dry and wet events in our two reconstructions exhibit broad spatial extent, affecting most of northwest Mexico and the western United States, which are mainly caused by broad-scale atmospheric circulation patterns such as El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). The results of this study allow framing current and projected droughts in a longer-term context, thus providing a better understanding of past climate variability and a basis for robust water resource management in the region. ©2020. American Geophysical Union. All Rights Reserved.
    • Predicting Drivers of Collective Soil Function With Woody Plant Encroachment in Complex Landscapes

      Farella, M.M.; Breshears, D.D.; Gallery, R.E.; School of Natural Resources and the Environment, Environment and Natural Resources 2, The University of Arizona; Department of Ecology and Evolutionary Biology, The University of Arizona (Blackwell Publishing Ltd, 2020)
      Dryland (arid and semiarid) ecosystems are extensive, home to a third of the human population, and a major contributor to terrestrial net primary productivity and associated biogeochemical cycles. Many dryland systems are undergoing woody plant encroachment, which can substantially alter landscape-scale soil nutrient dynamics via long-recognized “islands of fertility” mechanisms. To effectively constrain soil biogeochemistry responses to woody plant encroachment, predictions are needed for microbial biomass and especially microbial activity in addition to existing predictions for soil nutrients—referred to collectively hereafter as “collective soil functioning.” Here we evaluated whether collective soil functioning could be predicted from a suite of metrics including plant cover, precipitation, soil physiochemical characteristics, and topographic variables across complex landscapes undergoing woody plant encroachment by mesquite (Prosopis velutina). Plant cover alone predicted nearly half of the variability (R2 = 48.5%) in collective soil functioning and had a significant effect on each component of this index (soil nutrients, microbial biomass, and microbial activity). Prediction strength for collective soil functioning increased to 55.4%, and the error term decreased by 13.4% when precipitation, soil physiochemical characteristics, and topographic metrics were also included in models (plant and environment model). Besides the expected effects of plant cover, other significant predictors of collective soil functioning included state factors such as topography, precipitation, and parent material along with soil age and bulk density. These results illustrate that mesquites influence many components of soil functionality but the strength of this effect depends on which component is analyzed and which environmental variables are considered. ©2020. American Geophysical Union. All Rights Reserved.
    • Unraveling Glacial Hydroclimate in the Indo-Pacific Warm Pool: Perspectives From Water Isotopes

      Windler, G.; Tierney, J.E.; Zhu, J.; Poulsen, C.J.; Department of Geosciences, University of Arizona (John Wiley and Sons Inc, 2020)
      The Indo-Pacific Warm Pool (IPWP) is home to the warmest sea surface temperatures in the world oceans, favoring strong tropospheric convection and heavy rainfall. The mechanisms controlling long-term change in the region's hydroclimate are still uncertain. Here, we present a 450,000-year record of precipitation δD from southern Sumatra that records a consistent pattern of glacial isotopic enrichment and interglacial depletion. We synthesize existing paleo-indicators of precipitation δD and δ18O in the IPWP and compare results with water isotope-enabled climate simulations of the Last Glacial Maximum (LGM). The simulations show glacial isotopic enrichment over the eastern Indian Ocean extending into the southern IPWP and isotopic depletion over Southeast Asia, the west Pacific, and Australia. The pattern of simulated LGM isotopic change agrees generally well with our proxy synthesis. We conclude that reorganization of regional circulation under glacial conditions controls precipitation isotope variability in the IPWP: Low-level tropospheric convergence dominates the signal in the north/east, whereas divergence controls the response in the south/west. Additional sensitivity simulations suggest that the LGM ice sheets and the associated lowering in sea level, rather than decreased greenhouse gases, are responsible for the distinctive spatial pattern in glacial changes of precipitation isotopes and hydroclimate across the IPWP. ©2020. American Geophysical Union. All Rights Reserved.
    • The multi-scale infrastructure for chemistry and aerosols (MUSICA)

      Pfister, G.G.; Eastham, S.D.; Arellano, A.F.; Aumont, B.; Barsanti, K.C.; Barth, M.C.; Conley, A.; Davis, N.A.; Emmons, L.K.; Fast, J.D.; et al. (American Meteorological Society, 2020)
      To explore the various couplings across space and time and between ecosystems in a consistent manner, atmospheric modeling is moving away from the fractured limited-scale modeling strategy of the past toward a unification of the range of scales inherent in the Earth system. This paper describes the forward-looking Multi-Scale Infrastructure for Chemistry and Aerosols (MUSICA), which is intended to become the next-generation community infrastructure for research involving atmospheric chemistry and aerosols. MUSICA will be developed collaboratively by the National Center for Atmospheric Research (NCAR) and university and government researchers, with the goal of serving the international research and applications communities. The capability of unifying various spatiotemporal scales, coupling to other Earth system components, and process-level modularization will allow advances in both fundamental and applied research in atmospheric composition, air quality, and climate and is also envisioned to become a platform that addresses the needs of policy makers and stakeholders. © 2020 American Meteorological Society
    • Why Is the Terrestrial Water Storage in Dryland Regions Declining? A Perspective Based on Gravity Recovery and Climate Experiment Satellite Observations and Noah Land Surface Model With Multiparameterization Schemes Model Simulations

      Chang, L.-L.; Yuan, R.; Gupta, H.V.; Winter, C.L.; Niu, G.-Y.; Department of Hydrology and Atmospheric Sciences, University of Arizona (Blackwell Publishing Ltd, 2020)
      Drylands cover over 40% of the global land area and are home to more than 2 billion humans. Here, we use the terrestrial water storage (TWS) anomaly data derived from GRACE satellites to assess water storage changes globally and find that drylands lost ~15.9 ± 9.1 mm of water between April 2002 and January 2017. The TWS trends are more significant and apparent in dry regions than in humid regions. The decrease in TWS occurred mainly in hyperarid and arid regions. Exact causes to the observed declines in TWS remain elusive due to anthropogenic water withdrawals, atmospheric demand (potential evapotranspiration, PET) in contrast to supply (precipitation, P) caused by the warming, and terrestrial ecohydrological responses. Therefore, we use a process-based model forced by climate data to interpret the causes over three selected dryland regions showing the strongest drying trends. We find that the modeled TWS without considering anthropogenic water withdrawals explains most of the declining GRACE TWS over the southwestern North America (NA) and Middle East but underestimates the drying trend over North China. This suggests that TWS declines in the southwestern NA and the Middle East were primarily driven by the contrast between atmospheric demand and supply, whereas anthropogenic water withdrawals may have played a relatively more dominant role in TWS declines over North China. Additional model experiments indicate that terrestrial ecohydrological processes that help extract deep substrate water are critical for providing water supply additional to precipitation to sustain ET in the drying drylands at decadal scales. ©2020. American Geophysical Union. All Rights Reserved.
    • Evolution of the Oligotrophic West Pacific Warm Pool During the Pliocene-Pleistocene Boundary

      Bali, H.; Gupta, A.K.; Mohan, K.; Thirumalai, K.; Tiwari, S.K.; Panigrahi, M.K.; Department of Geosciences, University of Arizona (John Wiley and Sons Inc, 2020)
      This study investigates the development of oligotrophic conditions, thickening, and zonal and meridional contraction of the West Pacific Warm Pool (WPWP) during the Pliocene. It has been hypothesized that the evolution of the WPWP and the establishment of strong equatorial Pacific zonal gradients are closely related to the narrowing of the Indonesian Gateway (IG) as well as the closure of the Central American Seaway (CAS). However, the timing of the development of these events remains unclear. Here we report Pliocene-to-Recent relative abundances of planktic foraminifera at Deep Sea Drilling Project (DSDP) Site 214 in the eastern Indian Ocean and at Ocean Drilling Program (ODP) Site 807, in the western Pacific. A comparison of the abundance of mixed-layer species (MLS) from both sites indicates a pronounced increase in their population between ~3.15 and 1.6 Ma. There is a contemporaneous decrease in the Globigerinita glutinata population during this time, which together with the MLS data suggest the development of oligotrophic conditions in the western tropical Pacific. Our data suggest that the oligotrophic WPWP, resembling present-day conditions, developed around 3.15 Ma and was closely linked to the gradual constriction of the IG. ©2020. American Geophysical Union. All Rights Reserved.
    • Cosmic Ray Neutron Soil Moisture Estimation Using Physically Based Site-Specific Conversion Functions

      Andreasen, M.; Jensen, K.H.; Bogena, H.; Desilets, D.; Zreda, M.; Looms, M.C.; Department of Hydrology and Atmospheric Sciences, University of Arizona (Blackwell Publishing Ltd, 2020)
      In order to advance the use of the cosmic ray neutrons (CRNs) to map soil moisture in heterogeneous landscapes, we need to develop a methodology that reliably estimates soil moisture without having to collect 100+ soil samples for each point along the survey route. In this study, such an approach is developed using physically based modeling with the numerical MCNP neutron transport code. The objective is to determine site-specific conversion functions to estimate soil moisture from CRNs for the dominant land covers. Here, we assess this methodology at three field sites with similar mineral soil composition, but different land covers. First, we ensure that the developed models capture the most important differences in neutron transport behavior across sites. For this, we use measured time series and height profiles of thermal and epithermal neutrons. Then, we compare the estimates obtained from the site-specific conversion functions with the standard N0-calibration function. Finally, we compare the CRN soil moisture estimates with independent soil moisture estimates. Overall, the site-specific models are in agreement with the observed trends in neutron intensities. The site-specific soil moisture is similar to the N0-estimated soil moisture, which results in comparable statistical measures. We show that various land covers have a significant impact on the amount and soil moisture sensitivity of epithermal neutrons, while the thermal neutrons are affected to a less degree. Thereby, thermal-to-epithermal neutron ratios can be used to identify the land cover type and thereby the appropriate conversion function for soil moisture estimation for each point along the survey route. ©2020. American Geophysical Union. All Rights Reserved.
    • Coronene-uracil complexes embedded in argon matrices: FTIR spectroscopy and quantum-mechanical calculations

      Stepanian, S.G.; Ivanov, A.Y.; Karachevtsev, V.A.; Adamowicz, L.; Department of Chemistry and Biochemistry, University of Arizona (American Institute of Physics Inc., 2021)
      We employ low-temperature matrix-isolation FTIR spectroscopy and quantum chemical calculations to study the interaction between nucleobase uracil and coronene which models the graphene surface. To observe the dimer FTIR spectrum, we use a quartz microbalance that allows us to produce matrix samples with precisely determined concentrations of coronene and uracil (with the concentration ratio of 2.5:1:1000 for coronene:uracil:argon). The interaction between coronene and uracil results in spectral shifts of uracil spectral bands. These shifts do not exceed 10 cm−1. The maximum shifts are observed for the C=O stretching and NH out-of-plane vibrations of uracil. The structures and interaction energies of stacked and H-bonded coronene-uracil complexes are calculated at the DFT/B3LYP(GD3BJ)/aug-cc-pVDZ and MP2/aug-cc-pVDZ levels of theory. In total, 19 stable stacked and two H-bonded coronene-uracil dimer structures are found in the calculations. The interaction energy obtained for the most stable stacked dimer is −12.1 and −14.3 kcal/mol at the DFT and MP2 levels, respectively. The interaction energies of the H-bonded dimers do not exceed − 3 kcal/mol. The IR spectra of the studied monomeric molecules and of all the dimers are calculated at the DFT/B3LYP(GD3BJ)/aug-cc-pVDZ level of theory. The spectral shifts of the most stable stacked coronene-uracil dimer obtained in the calculations are in good agreement with the experimental results. © 2021 Author(s).
    • Estimating the Effects of Forest Structure Changes From Wildfire on Snow Water Resources Under Varying Meteorological Conditions

      Moeser, C.D.; Broxton, P.D.; Harpold, A.; Robertson, A.; School of Natural Resources and the Environment, University of Arizona (Blackwell Publishing Ltd, 2020)
      Modeling forest change effects on snow is critical to resource management. However, many models either do not appropriately model canopy structure or cannot represent fine-scale changes in structure following a disturbance. We applied a 1 m2 resolution energy budget snowpack model at a forested site in New Mexico, USA, affected by a wildfire, using input data from lidar to represent prefire and postfire canopy conditions. Both scenarios were forced with 37 years of equivalent meteorology to simulate the effect of fire-mediated canopy change on snowpack under varying meteorology. Postfire, the simulated snow distribution was substantially altered, and despite an overall increase in snow, 32% of the field area displayed significant decreases, resulting in higher snowpack variability. The spatial differences in snow were correlated with the change in several direction-based forest structure metrics (aspect-based canopy edginess and gap area). Locations with decreases in snow following the fire were on southern aspects that transitioned to south facing canopy edges, canopy gaps that increased in size to the south, or where large trees were removed. Locations with largest increases in snow occurred where all canopy was removed. Changes in canopy density metrics, typically used in snow models to represent the forest, did not fully explain the effects of fire on snow distribution. This explains why many models are not able to represent greater postfire variability in snow distribution and tend to predict only increases in snowpack following a canopy disturbance event despite observational studies showing both increases and decreases. ©2020. American Geophysical Union. All Rights Reserved.
    • Fully Implicit Dynamic Pore-Network Modeling of Two-Phase Flow and Phase Change in Porous Media

      Chen, S.; Qin, C.; Guo, B.; Department of Hydrology and Atmospheric Sciences, University of Arizona; Department of Hydrology and Atmospheric Sciences, University of Arizona (Blackwell Publishing Ltd, 2020)
      Dynamic pore-network model (PNM) has been widely used to model pore-scale two-phase flow. Numerical algorithms commonly used for dynamic PNM including IMPES (implicit pressure explicit saturation) and IMP-SIMS (implicit pressure semi-implicit saturation) can be numerically unstable or inaccurate for challenging flow regimes such as low capillary number (Ca) flow and unfavorable displacements. We perform comprehensive analyses of IMPES and IMP-SIMS for a wide range of flow regimes under drainage conditions and develop a novel fully implicit (FI) algorithm to address their limitations. Our simulations show the following: (1) While IMPES was reported to be numerically unstable for low Ca flow, using a smoothed local pore-body capillary pressure curve appears to produce stable simulations. (2) Due to an approximation for the capillary driving force, IMP-SIMS can deviate from quasi-static solutions at equilibrium states especially in heterogeneous networks. (3) Both IMPES and IMP-SIMS introduce mass conservation errors. The errors are small for networks with cubic pore bodies (less than 1.4% for IMPES and 1.2% for IMP-SIMS). They become much greater for networks with square-tube pore bodies (up to 45% for IMPES and 46% for IMP-SIMS). Conversely, the new FI algorithm is numerically stable and mass conservative regardless of the flow regimes and pore geometries. It also precisely recovers the quasi-static solutions at equilibrium states. The FI framework has been extended to include compressible two-phase flow, multicomponent transport, and phase change dynamics. Example simulations of two-phase displacements accounting for phase change show that evaporation and condensation can suppress fingering patterns generated during invasion. ©2020. American Geophysical Union. All Rights Reserved.
    • Electron heating and cooling in hypersonic flows

      Parent, B.; Department of Aerospace and Mechanical Engineering (American Institute of Physics Inc., 2021)
      Using recently developed advanced numerical methods for plasma flows and sheaths, the first detailed study of electron cooling and heating taking place within hypersonic non-neutral flows is presented here. The numerical simulations fully couple the Navier-Stokes equations for the neutrals to the drift-diffusion model for the electrons and ions and include a 11-species finite-rate chemical solver along with a transport equation for the electron temperature in non-equilibrium. Results for Mach 18 airflow around a wedge with a sharp leading edge show that at low flight dynamic pressure the electron temperature remains close to the freestream temperature in the stagnation region. Such is attributed to the product of the electric field and the electron current being dominantly negative within the plasma sheaths and acting as an electron energy sink. This cooling effect leads to a significant portion of the flow downstream of the shock exhibiting electron temperatures much lower than expected. This study is the first to show a large impact of the non-neutral plasma sheaths on the post-shock electron temperature. This study also shows that the common approach to set the electron temperature equal to the vibrational temperature can result in the electron temperature being over-predicted by one order of magnitude or more in hypersonic flows. © 2021 Author(s).
    • Physics-informed neural networks for rarefied-gas dynamics: Thermal creep flow in the Bhatnagar-Gross-Krook approximation

      De, Florio, M.; Schiassi, E.; Ganapol, B.D.; Furfaro, R.; Department of Systems and Industrial Engineering, University of Arizona; Department of Aerospace and Mechanical Engineering, University of Arizona (American Institute of Physics Inc., 2021)
      This work aims at accurately solve a thermal creep flow in a plane channel problem, as a class of rarefied-gas dynamics problems, using Physics-Informed Neural Networks (PINNs). We develop a particular PINN framework where the solution of the problem is represented by the Constrained Expressions (CE) prescribed by the recently introduced Theory of Functional Connections (TFC). CEs are represented by a sum of a free-function and a functional (e.g., function of functions) that analytically satisfies the problem constraints regardless to the choice of the free-function. The latter is represented by a shallow Neural Network (NN). Here, the resulting PINN-TFC approach is employed to solve the Boltzmann equation in the Bhatnagar-Gross-Krook approximation modeling the Thermal Creep Flow in a plane channel. We test three different types of shallow NNs, i.e., standard shallow NN, Chebyshev NN (ChNN), and Legendre NN (LeNN). For all the three cases the unknown solutions are computed via the extreme learning machine algorithm. We show that with all these networks we can achieve accurate solutions with a fast training time. In particular, with ChNN and LeNN we are able to match all the available benchmarks. © 2021 Author(s).
    • The influence of low-temperature argon matrix on embedded water clusters. A DFT theoretical study

      Vasylieva, A.; Doroshenko, I.; Stepanian, S.; Adamowicz, L.; Department of Chemistry and Biochemistry, University of Arizona (American Institute of Physics Inc., 2021)
      Computer simulations of an argon fcc crystal fragment with embedded water clusters of different sizes are performed using the quantum mechanical DFT/M06-2X method. The effect of the argon matrix on the structural, energy, and spectral parameters of individual water clusters are investigated. The formation energies of (H2O)n@Arm complexes, as well as deformation energies of water clusters and of the argon crystal involved in the embedment, are computed for n = 1-7. Matrix shifts of the IR vibrational frequencies of water clusters isolated in argon matrices are predicted based on the results of the calculations. The predictions indicate a possibility of the formation of small stable water complexes in low-temperature argon matrices. © 2021 Author(s).
    • Extended aging of Ge-Se glasses below the glass transition temperature

      King, E.A.; Sen, S.; Takeda, W.; Boussard-Pledel, C.; Bureau, B.; Guin, J.-P.; Lucas, P.; Department of Materials Science and Engineering, University of Arizona (American Institute of Physics Inc., 2021)
      Germanium selenide glasses of compositions spanning the whole glass-formation range are aged at room temperature for up to 20 years. A prominent enthalpy relaxation process is observed in all glasses, and its structural origin is analyzed by Raman spectroscopy. The structural relaxation is manifested in the Raman spectra as a decrease in the ratio of edge- to corner-sharing GeSe4/2 tetrahedral units. This structural evolution can be explained in terms of configurational entropy and density changes. Changes in Raman features and enthalpy follow an identical stretched exponential relaxation function characteristic of aging in glasses. The compositional dependence of enthalpy relaxation after 20 years is in agreement with kinetic considerations based on the glass transition temperature of each glass. The relaxation behavior and heat capacity curves are consistent with standard glass relaxation models for all compositions. These results indicate that the non-reversing enthalpy obtained by modulated differential scanning calorimetry (MDSC), which suggests the existence of non-aging glasses, is not a reliable measure of the ability of a glass to relax. Instead, it is suggested that an interpretation of MDSC data in terms of complex heat capacity provides a more complete and reliable assessment of the relaxation properties of glasses. © 2021 Author(s).
    • Beyond tomb and relic: Anthropological and pedagogical approaches to Archaeogaming

      Rassalle, T.; University of Arizona (University of Chicago Press, 2021)
      The advent of the computer chip has radically altered human life at a global scale, and with increasing access to digital platforms it was inevitable that digitization would reshape popular culture. The video game industry is one of the fastest growing sectors in technological and entertainment industries, reaching an enormous audience. It is now estimated that some 2.5 billion people play games worldwide, with 211 million American adults, 52 percent of whom are college educated (see Rassalle in this issue) (fig. 1). © 2021, University of Chicago Press. All rights reserved.
    • Microscopic modeling of non-normal incidence vertical external cavity surface-emitting laser cavities

      McLaren, S.; Kilen, I.; Moloney, J.V.; Program in Applied Mathematics, University of Arizona; Arizona Center for Mathematical Sciences; College of Optical Sciences, University of Arizona (American Institute of Physics Inc., 2021)
      The optimization of a V-cavity geometry to obtain intense ultrafast pulses for a modelocked vertical external-cavity surface-emitting laser is studied using an expanded form of the transverse Maxwell semiconductor Bloch equations. The influence of the incidence angle and relative cavity arm lengths is considered with respect to both the pump-probe computed instantaneous gain and group delay dispersion and the converged modelocked state. Changes in the angle are seen to lead to modest changes in dispersion but significant deformations of the modelocked pulse. Large changes in relative arm lengths are seen to lead to modest changes in the modelocked pulse with optimal pulses being observed with a 1:1 arm length ratio. The underlying microscopic dynamics are shown to drive these behaviors. This work provides a theoretical means to optimize experimental cavity geometry for desirable modelocking behaviors. © 2021 Author(s).
    • Beyond 3 μ m Dy3 +/Er3 +co-doped ZBLAN fiber lasers pumped by 976 nm laser diode

      Wang, J.; Zhu, X.; Norwood, R.A.; Peyghambarian, N.; James C. Wyant College of Optical Sciences, University of Arizona (American Institute of Physics Inc., 2021)
      Dysprosium-erbium (Dy3+/Er3+) co-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fiber lasers operating at 3.2-3.35 μm were demonstrated by pumping at the 980 nm Er3+ absorption band. A maximum output power of 260 mW at 3.27 μm with a slope efficiency of 5.73% was achieved with 3.6 m 0.25 mol. % Dy3+/4 mol. % Er3+ co-doped ZBLAN fiber. Lasers operating at 3.23 μm and 3.35 μm were also demonstrated with 2 m and 9 m gain fibers, respectively, but with lower slope efficiencies. Our experiments confirm the possibility of pumping the Dy3+/Er3+-doped ZBLAN fiber laser with a low-cost high efficiency diode laser at 976 nm. © 2021 Author(s).
    • Voicing the supply chain

      Cotter, W.M.; University of Arizona (University of Chicago Press, 2021)
      The specialty coffee industry emphasizes the importance of personal relationships that span disparate levels of the supply chain and production models that focus on the wellbeing of coffee producers. This emphasis presents specialty coffee as a socially progressive form of consumption that is often represented as superior to mass-produced coffee. Discourses that emphasize relationships between baristas and professionals at other levels of the supply chain serve as a tool in marketing specialty coffee, with baristas serving as an interface between consumers and other levels of the supply chain. The somewhat recent elevation of baristas to professional status is due, in part, to the growth of barista competitions. This article takes barista competitions as a context for analysis, highlighting how baristas incorporate voices from across the supply chain into their competition performances. I argue that in voicing individuals from across the supply chain, baristas draw on the expertise and authority represented by coffee farmers and roasters to support the development of their own authentic professional persona. This article also shows that, by voicing the supply chain, baristas respond to consumer desires for more ethical forms of consumption through these narratives, providing the moral and emotional experience of coffee that consumers crave. © 2021 by Semiosis Research Center at Hankuk University of Foreign Studies.