University of Colorado Boulder
  • Boulder, CO, United States
Recent publications
Proxy reconstructions and model simulations of precipitation during Earth's glacial periods suggest that the locations and mechanisms of atmospheric moisture transport have changed considerably during Earth's past. We investigate the hydroclimate of the Last Glacial Maximum (LGM) using simulations with the Community Earth System Model, with a focus on the extratropics and the influence of atmospheric rivers (ARs), a key driver of modern‐day moisture transport globally. Mean and extreme precipitation increase significantly over southwestern Patagonia, Iberia, and southwestern North America—mid‐latitude regions affected by ARs in the modern climate—despite overall decreases elsewhere. In each, the associated moisture transport changes are different, with increased transport and AR activity mainly occurring in the North Atlantic. The overall LGM response is dominated by the response to ice sheets, with other forcings causing additional cooling and drying over the extratropics and a strong decrease of moisture transport over the subpolar North Atlantic.
Enhanced transport of warm subsurface Atlantic Water (AW) into Greenland fjords has driven glacier mass loss, but the mechanisms transporting AW to the fjords remain poorly characterized. Here, we provide the first direct satellite‐based observations of rapid ( ∼0.2 m/s) AW intrusion toward Sermilik Fjord abutting Helheim Glacier, one of Greenland’s largest glaciers. The intrusions arise when coastal upwelling — through interactions with Sermilik’s bathymetric trough on the continental shelf — triggers enhanced AW upwelling and inflow that can travel tens of kilometers along the trough within hours. A weakening or reversal of northeasterly alongshore winds stimulates the intrusions and is often associated with the passing of cyclones and subsequent sea surface lowering. Mooring data show that these intrusions produce subsurface ocean warming both at Sermilik Fjord mouth and within the fjord and that the warming signal in the fjord does not diminish during subsequent coastal downwelling events. Satellite imagery captures near‐synchronous AW intrusions at multiple troughs rimming southeast Greenland suggesting that these wind‐driven processes may play a substantial role in ocean heat transport toward the Greenland Ice Sheet.
Background To increase uptake of implementation science (IS) methods by researchers and implementers, many have called for ways to make it more accessible and intuitive. The purpose of this paper is to describe the iPRISM webtool (Iterative, Practical, Robust Implementation and Sustainability Model) and how this interactive tool operationalizes PRISM to assess and guide a program’s (a) alignment with context, (b) progress on pragmatic outcomes, (c) potential adaptations, and (d) future sustainability across the stages of the implementation lifecycle. Methods We used an iterative human-centered design process to develop the iPRISM webtool. Results We conducted user-testing with 28 potential individual and team-based users who were English and Spanish speaking from diverse settings in various stages of implementing different types of programs. Users provided input on all aspects of the webtool including its purpose, content, assessment items, visual feedback displays, navigation, and potential application. Participants generally expressed interest in using the webtool and high likelihood of recommending it to others. The iPRISM webtool guides English and Spanish-speaking users through the process of iteratively applying PRISM across the lifecycle of a program to facilitate systematic assessment and alignment with context. The webtool summarizes assessment responses in graphical and tabular displays and then guides users to develop feasible and impactful adaptations and corresponding action plans. Equity considerations are integrated throughout. Conclusions The iPRISM webtool can intuitively guide individuals and teams from diverse settings through the process of using IS methods to iteratively assess and adapt different types of programs to align with the context across the implementation lifecycle. Future research and application will continue to develop and evaluate this IS resource.
Kinesin-5 motor proteins play essential roles during mitosis in most organisms. Their tetrameric structure and plus-end-directed motility allow them to bind to and move along antiparallel microtubules, thereby pushing spindle poles apart to assemble a bipolar spindle. Recent work has shown that the C-terminal tail is particularly important to kinesin-5 function: The tail affects motor domain structure, ATP hydrolysis, motility, clustering, and sliding force measured for purified motors, as well as motility, clustering, and spindle assembly in cells. Because previous work has focused on presence or absence of the entire tail, the functionally important regions of the tail remain to be identified. We have therefore characterized a series of kinesin-5/Cut7 tail truncation alleles in fission yeast. Partial truncation causes mitotic defects and temperature-sensitive growth, while further truncation that removes the conserved BimC motif is lethal. We compared the sliding force generated by cut7 mutants using a kinesin-14 mutant background in which some microtubules detach from the spindle poles and are pushed into the nuclear envelope. These Cut7-driven protrusions decreased as more of the tail was truncated, and the most severe truncations produced no observable protrusions. Our observations suggest that the C-terminal tail of Cut7p contributes to both sliding force and midzone localization. In the context of sequential tail truncation, the BimC motif and adjacent C-terminal amino acids are particularly important for sliding force. In addition, moderate tail truncation increases midzone localization, but further truncation of residues N-terminal to the BimC motif decreases midzone localization.
Hydrogel adhesion that can be easily modulated in magnitude, space, and time is desirable in many emerging applications ranging from tissue engineering and soft robotics to wearable devices. In synthetic materials, these complex adhesion behaviors are often achieved individually with mechanisms and apparatus that are difficult to integrate. Here, we report a universal strategy to embody multifaceted adhesion programmability in synthetic hydrogels. By designing the surface network topology of a hydrogel, supramolecular linkages that result in contrasting adhesion behaviors are formed on the hydrogel interface. The incorporation of different topological linkages leads to dynamically tunable adhesion with high-resolution spatial programmability without alteration of bulk mechanics and chemistry. Further, the association of linkages enables stable and tunable adhesion kinetics that can be tailored to suit different applications. We rationalize the physics of polymer chain slippage, rupture, and diffusion at play in the emergence of the programmable behaviors. With the understanding, we design and fabricate various soft devices such as smart wound patches, fluidic channels, drug-eluting devices, and reconfigurable soft robotics. Our study presents a simple and robust platform in which adhesion controllability in multiple aspects can be easily integrated into a single design of a hydrogel network.
This issue contains a series of articles describing the various resources, studies, results, and future directions for the collaborative study on the genetics of alcoholism (COGA). The collaborative and integrative approach initiated by this group ~30 years ago serves as an excellent example of the strength of team science. Individually, various aspects of COGA would be limited in their impact toward improved understanding of alcohol use disorder. Collectively, their wholistic approach which spans deep longitudinal phenotypic assessments in families to include the application of large‐scale omics technologies and cell‐culture based molecular studies has demonstrated the power of working together.
Agricultural and prescribed burning activities emit large amounts of trace gases and aerosols on regional to global scales. We present a compilation of emission factors (EFs) and emission ratios (ERs) from the eastern portion of the Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) campaign in 2019 in the United States, which sampled burning of crop residues and other prescribed fire fuels. FIREX‐AQ provided comprehensive chemical characterization of 53 crop residue and 22 prescribed fires. Crop residues burned at different modified combustion efficiencies (MCE), with corn residue burning at higher MCE than other fuel types. Prescribed fires burned at lower MCE (<0.90) which is typical, while grasslands burned at lower MCE (0.90) than normally observed due to moist, green, growing season fuels. Most non‐methane volatile organic compounds (NMVOCs) were significantly anticorrelated with MCE except for ethanol and NMVOCs that were measured with less certainty. We identified 23 species where crop residue fires differed by more than 50% from prescribed fires at the same MCE. Crop residue EFs were greater for species related to agricultural chemical use and fuel composition as well as oxygenated NMVOCs possibly due to the presence of metals such as potassium. Prescribed EFs were greater for monoterpenes (5×). FIREX‐AQ crop residue average EFs generally agreed with the previous agricultural fire study in the US but had large disagreements with global compilations. FIREX‐AQ observations show the importance of regionally‐specific and fuel‐specific EFs as first steps to reduce uncertainty in modeling the air quality impacts of fire emissions.
Air‐sea exchange of carbon dioxide (CO2) in the Southern Ocean plays an important role in the global carbon budget. Previous studies have suggested that flow around topographic features of the Southern Ocean enhances the upward supply of carbon from the deep to the surface, influencing air‐sea CO2 exchange. Here, we investigate the role of seafloor topography on the transport of carbon and associated air‐sea CO2 flux in an idealized channel model. We find elevated CO2 outgassing upstream of a seafloor ridge, driven by anomalous advection of dissolved inorganic carbon. Argo‐like Lagrangian particles in our channel model sample heterogeneously in the vicinity of the seafloor ridge, which could impact float‐based estimates of CO2 flux.
Governments, regulatory bodies, and manufacturers are proposing plans to accelerate the adoption of electric vehicles (EVs), with the goal of reducing the impact of greenhouse gases and pollutants from internal combustion engines on human health and climate change. In this context, the paper considers a scenario where ride-sharing enterprises utilize a 100%-electrified fleet of vehicles, and seeks responses to the following key question: How can renewable-based EV charging be maximized without disrupting the quality of the ride-sharing services? We propose a new mechanism to promote EV charging during hours of high renewable generation, and we introduce the concept of charge request, which is issued by a power utility company. Our mechanism is inspired by a game-theoretic approach where the power utility company proposes incentives and the ride-sharing platform assigns vehicles to both ride and charge requests; the bargaining mechanism leads to prices and EV assignments that are aligned with the notion of Nash equilibria. Numerical results show that it is possible to shift the EV charging during periods of high renewable generation and adapt to intermittent generation while minimizing the impact on the quality of service. The paper also investigates how the users’ willingness to ride-share affects the charging strategy and the quality of service.
Background Sexual assault (SA) is experienced by a substantial proportion of emerging adult college students and is associated with elevated rates of Post‐Traumatic Stress Disorder (PTSD) and alcohol use. The current study examines the mediating role of posttraumatic stress symptoms (PTSS) in the associations among SA severity, drinking to cope with anxiety, and average weekly drinks while considering the moderating roles of gender identity and sexual orientation. Methods 2160 college students diverse in gender (cisgender women, 64.4%; cisgender men, 30.6%, and transgender and gender diverse (TGD) individuals = 4.9%) and sexual orientation (heterosexual = 68.0%, LGBQ+ = 32.0%) completed measures of SA severity, PTSS, drinking to cope with anxiety motives, and average weekly drinks. Results The mediation model for the full sample indicated significant indirect effects of SA severity on drinking to cope with anxiety through PTSS, but not on average weekly drinks. Moderation analyses revealed differential relationships between the variables based on both gender identity and sexual orientation. For instance, the association between SA severity and PTSS was stronger for cisgender women and TGD individuals compared to cisgender men, and for LGBQ+ individuals compared to heterosexual individuals. While the association between PTSS and average weekly drinks was only significant for cisgender men, the association between PTSS and drinking to cope with anxiety was significant for both cisgender men and women but not TGD individuals. Further, the association between SA severity and drinking to cope with anxiety was stronger for cisgender women than cisgender men. Conclusions Findings from the current study demonstrate sexual orientation and gender identity differences and similarities in the associations of SA severity, PTSS, drinking to cope with anxiety, and alcohol use. Results are discussed in relation to the self‐medication hypothesis and tailoring interventions for diverse groups.
In Part 1 of this Perspective, I discussed basic principles of scientific peer review. In Part 2, I focused specifically on the peer review of manuscripts. Here in Part 3, I complete the Perspective by sharing my thoughts on peer review of grant applications. I begin by emphasizing the goals of grant peer review and then describe the 2-stage organizational structure involved. The objective of stage 1 of the process is to establish the scientific merit of the grant proposal. For that phase, I discuss grant review panels, reviewer qualifications and responsibilities, how reviewers are identified and selected, pre-review meeting activities, activities during the review panel meeting, grant review criteria and scoring scales, and post-meeting activities. I also note 2 mechanisms that provide "pre-peer review" advice and recommendations for grant applications under development. I then describe the events associated with stage 2 of the peer review process in which grant funding agencies consider application merit scores (from stage 1) along with other factors including their research mission, priority areas of investigation, and available funds. Tips for early-career reviewers are discussed next and include questions to ask before accepting a review assignment, the importance of following reviewer guidelines, considerations when working through applications, issues involved in writing the critique, scoring the application, and how to approach evaluating resubmitted grant applications. Finally, I identify options for gaining skills and experience in peer review of grant proposals.
A principal challenge facing the control of floating offshore wind turbines (FOWTs) is the problem of instability, or “negative damping,” when using blade pitch feedback to control generator speed. This closed‐loop instability can be attributed to non‐minimum phase zeros in the transfer function from blade pitch to generator speed. Standard approaches to improving stability and performance include robust tuning of control gains and introducing multiple feedback loops to respond to platform motion. Combining these approaches is nontrivial because multiple control loops complicate the impact of coupling in the system dynamics. The single‐loop approach to analyzing stability robustness neglects inter‐loop coupling, while a simplistic multi‐loop approach is highly sensitive to dimensional scaling and overestimates the robustness of the single‐loop controller. This work proposes a sensitivity representation that separates some of the natural FOWT dynamic coupling into a parallel feedback loop in the sensitivity function loop to address both of these concerns. The modified robustness measure is used with a simplified linear FOWT model to optimize scheduled multi‐loop control parameters in an automated tuning procedure. This controller is implemented for the 10‐MW Ultraflexible Smart FLoating Offshore Wind Turbine (USFLOWT) and compared against conventional single‐ and multi‐loop controllers tuned using frequency‐domain analysis and high‐fidelity OpenFAST simulations. The multi‐loop robust controller shows the highest overall performance in generator speed regulation and tower load reduction, though consideration of power quality, actuator usage, and other structural loading leads to additional trade‐offs.
Foraging is a universal behaviour that has co‐evolved with predation pressure. We investigated the role of the bed nucleus of the stria terminalis (BNST) GABA neurons in robotic and live predator threat processing and their consequences in post‐threat encounter foraging. Both robotic and live predator interactions increased BNST GABA neuron activity. Mice were trained to procure food in a laboratory‐based foraging apparatus in which food pellets were placed at incrementally greater distances from a nest zone. After mice learned to forage, they were exposed to a robotic or live predator threat, while BNST GABA neurons were chemogenetically inhibited. Post‐robotic threat encounter, mice spent more time in the nest zone, but other foraging parameters were unchanged compared with pre‐encounter behaviour. Inhibition of BNST GABA neurons had no effect on foraging behaviour post‐robotic threat encounter. Following live predator exposure, control mice spent significantly more time in the nest zone, increased their latency to successfully forage, and significantly altered their overall foraging performance. Inhibition of BNST GABA neurons during live predator exposure prevented changes in foraging behaviour from developing after a live predator threat. BNST GABA neuron inhibition did not alter foraging behaviour during robotic or live predator threats. We conclude that these results demonstrate that while both robotic and live predator encounters effectively intrude on foraging behaviour, the perceived risk and behavioural consequences of the threat are distinguishable. Additionally, BNST GABA neurons may play a role in the integration of prior innate predator threat experience that results in hypervigilance during post‐encounter foraging behaviour.
Indium phosphide quantum dots have become an industrially relevant material for solid-state lighting and wide color gamut displays. The synthesis of indium phosphide quantum dots from indium carboxylates and tris(trimethylsilyl)phosphine (P(SiMe3)3) is understood to proceed through the formation of magic-sized clusters, with In37P20(O2CR)51 being the key isolable intermediate. The reactivity of the In37P20(O2CR)51 cluster is a vital parameter in controlling conversion to quantum dots. Here, we report structural perturbations to In37P20(O2CR)51 clusters induced by tuning the steric properties of a series of substituted phenylacetate ligands. This approach allows for control over reactivity with P(SiMe3)3, where meta-substituents enhance the susceptibility to ligand displacement and para-substituents hinder phosphine diffusion to the core. Thermolysis studies show that with complete cluster dissolution, steric profile can modulate the nucleation period, whereas partial dissolution from indium carboxylate loss results in conversion to uniform InP cores with a narrow, 419 nm absorbance. The enhanced stability from ligand engineering also allows for the isolation and structural characterization by single-crystal X-ray diffraction of a new III-V magic-sized cluster with formula In26P13(O2CR)39. This intermediate is thought to precede the In37P20(O2CR)51 cluster on the InP reaction coordinate. The physical and electronic structure of this cluster are analyzed, providing new insight into previously unrecognized relationships between II-VI and III-V materials and the discrete growth of III-V cluster intermediates.
Using MMS orbits in the Earth’s magnetotail from 2017 to 2020, plasma conditions and the 3D spatial structure of inner‐magnetotail plasma environments (with a focus on the plasma sheet) are studied with different approaches. Threshold conditions for distinguishing the plasma sheet, plasma sheet boundary layers, and lobes are derived from the statistical properties of background plasma parameters. Our results support previous studies that employed similar methods using Cluster data. However, stronger currents are observed in both the lobes and plasma sheet, likely due to the smaller spacecraft separation ( ≲ 70 km) that can resolve thin electron‐scale currents. Threshold conditions are used together with magnetic field and electric field measurements to image the spatial structure of the plasma sheet. Results are in good agreement with a global neutral sheet model based on solar wind conditions and magnetospheric configurations. Furthermore, the Earth’s dipole tilts towards the Sun around June solstice, which warps the magnetotail as much as ∼ 2–4 R˙E in Z GSM. This warping effect is relaxed towards September equinox. Consequently, as MMS travels through the magnetotail from dawn to dusk during this period, there is an apparent dawn‐dusk asymmetry in plasma conditions between June and September. Kink‐like flapping waves and IMF twisting are other mesoscale processes attributed with a few R E of flaring near the flanks. These findings reveal important insights into the mesoscale structure and dynamics of the magnetotail.
Improving the scalability of probabilistic model checking (PMC) tools is crucial to the verification of real-world system designs. The Stamina infinite-state PMC tool achieves scalability by iteratively constructing a partial state space for an unbounded continuous-time Markov chain model, where a majority of the probability mass resides. It then performs time-bounded transient PMC. It can efficiently produce an accurate probability bound to the property under verification. We present a new software architecture design and the C++ implementation of the Stamina 2.0 algorithm, integrated with the Storm model checker. This open-source Stamina implementation offers a high degree of modularity and provides significant optimizations to the Stamina 2.0 algorithm. Performance improvements are demonstrated on multiple challenging benchmark examples, including hazard analysis of infinite-state combinational genetic circuits, over the previous Stamina implementation. Additionally, its design allows for future customizations and optimizations to the Stamina algorithm.
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Philip Graves
  • Department of Economics
Mihaly Horanyi
  • Department of Physics
Zoltan Sternovsky
  • Laboratory for Atmospheric and Space Physics (LASP)
Dragan Maksimovic
  • Department of Electrical, Computer, and Energy Engineering (ECEE)
Mingwei Min
  • Department of Chemistry and Biochemistry
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