Colorado School of Mines
  • Golden, CO, United States
Recent publications
Understanding public activities and developing thoughtful public health strategies are key goals in efforts to manage the COVID-19 pandemic. This paper explores how seismic noise data can be used as part of such efforts. We show that the fluctuation of seismic noise levels has the capacity to demonstrate aggregate human movement. When considered in relation to major public health efforts, these data can help us evaluate the effectiveness of public health communication strategies that seek to limit social activity. We show evidence that, broadly speaking, Mexican national efforts to encourage “lockdown” worked for a few months in areas around seismic stations, and broke down as time went on. Further, we suggest that changes in the levels of human activity detected in seismic noise can be read alongside social data that provide some clues as to why people respond or not to health recommendations. Our findings have implications for both efforts to understand the nature and effects of public trust in the Mexican state and also the practicalities of using seismic noise data in this manner. An interdisciplinary analysis allows us to address these data and their possible use in a way that takes seriously the opportunities and challenges that emerge in the context of contemporary biopolitics and emerging configurations of surveillance technologies. Analyzing anthropogenic seismic activity opens up new opportunities for ethical data collection and use.
The atmosphere contains a diverse reservoir of microbes but the sources and factors contributing to microbial aerosol variability are not well constrained. To advance understanding of microbial emissions in wildfire smoke, we used unmanned aircraft systems to analyze the aerosols above high-intensity forest fires in the western United States. Our results show that samples of the smoke contained ~four-fold higher concentrations of cells (1.02 ± 0.26 × 10 ⁵ m ⁻³ ) compared to background air, with 78% of microbes in smoke inferred to be viable. Fivefold higher taxon richness and ~threefold enrichment of ice nucleating particle concentrations in smoke implies that wildfires are an important source of diverse bacteria and fungi as well as meteorologically relevant aerosols. We estimate that such fires emit 3.71 × 10 ¹⁴ microbial cells ha ⁻¹ under typical wildfire conditions in western US forests and demonstrate that wildland biomass combustion has a large-scale influence on the local atmospheric microbial assemblages. Given the long-range transport of wildfire smoke emissions, these results expand the concept of a wildfire’s perimeter of biological impact and have implications to biogeography, gene flow, the dispersal of plant, animal, and human pathogens, and meteorology.
Earth’s crust responds to perturbations from various environmental factors. To evaluate this response, seismic velocity changes offer an indirect diagnostic, especially where velocity can be monitored on an ongoing basis from ambient seismic noise. Investigating the connection between the seismic velocity changes and external perturbations could be useful for characterizing dynamic activities in the crust. The seismic velocity is known to be sensitive to variations in meteorological signals such as temperature, snow, and precipitation as well as changes in sea level. Among these perturbations, the impact of variations in sea level on velocity changes inferred from seismic interferometry of ambient noise is not well known. This study investigates the influence of the ocean in a 3-year record of ambient noise seismic velocity monitoring in the Chugoku and Shikoku regions of southwest Japan. First, we applied a bandpass filter to determine the optimal period band for discriminating among different influences on seismic velocity. Then, we applied a regression analysis between the proximity of seismic station pairs to the coast and the ocean influence, as indicated by the correlation of sea level to seismic velocity changes between pairs of stations. Our study suggests that for periods between 0.0036 to 0.0155 cycle/day (64–274 days), the ocean’s influence on seismic velocity decreases with increasing distance of station pairs from the coast. The increasing sea level deforms the ocean floor, affecting the stress in the adjacent coast. The stress change induced by the ocean loading may extend at least dozens of kilometers from the coast. The correlation between sea level and inland seismic velocity changes is negative or positive. Although it is difficult to clearly interpret the correlation based on a simple model, they could depend on the in situ local stress, orientation of dominant crack, and hydraulic conductivity. Our study shows that seismic monitoring may be useful for evaluating the perturbation in the crust associated with an external load. Graphical abstract
Study Region Rio Grande Headwaters Study Focus In the western US wildfires are increasing in duration and frequency, insect inducted forest mortality is widespread, and both wildfires and forest mortality are exacerbated by drought. These forest disturbances have hydrologic implications that are not always evident in the post-disturbance water budget – especially at the watershed outlet. In this study we evaluate two snow dominated paired catchment systems in the forested Rio Grande headwaters – where each impacted site was severely burned by the 2013 West Fork Complex (WFC) fire, and all sites (including control sites) were severely impacted by spruce beetle induced forest mortality from approximately 2005 to 2010. A combination of observed runoff, reanalysis precipitation, and remotely sensed evapotranspiration and vegetation metrics are used to evaluate the post-fire surface water budget (runoff and evapotranspiration) in paired catchments. New hydrological insights for the region Significant changes in post-fire surface water budget partitioning are not detectable, which is likely the result of decreased evapotranspiration due to insect-induced vegetation change in all study catchments prior to the fire. Our findings highlight the importance of considering overlapping disturbances, especially in paired catchment studies, and in alpine and subalpine forest regions like the Rio Grande headwaters that are increasingly prone to drought, insect mortality and wildfire. Our results also illustrate that insect induced forest mortality has significant implications for post-fire hydrology studies that rely on control-impact or before-and-after comparisons.
Underground oil storage is a viable technique to increase energy security in the context of global concern for oil demand and supply. When the economic conditions permit, it makes sense to store oil in water-flooded, water-wet sandstone reservoirs that are geographically ubiquitous and abundant, structurally safe, and cost-effective for storing large amounts of crude oil safely. Due to long-term restoring oil contacting with the surface of rocks in such reservoirs, the property of the reservoir rocks may be changed, and the performance of oil reproduction may be different. These important factors are related to the change of wetting behavior of reservoirs, which directly affects the recovery rate of stored oil and the relative permeability characteristic of oil and water flow during the reproduction of stored crude oil in a water-wet depleted petroleum reservoir. Unfortunately, there is a lack of study on these research areas. This study investigates the change of wettability in such reservoirs and its influence on the production of stored oil by a second water flooding process. Several experimental techniques, including NMR and centrifuge measurements (USBM), and two-phase flow relative permeability measurement, are employed to investigate wetting behavior in crude oil/water/rock systems and two-phase flow characteristics when the crude oil is reinjected and stored oil is reproduced by water flooding in the present work. Based on the results of NMR and centrifuge experiments, the wettability of the core aged with crude oil was altered from strongly water-wet to weakly water-wet with an increase in aging time. NMR and USBM wettability indexes showed a good agreement suggesting a change into weakly water wetness. It is consistent with the change of relative permeability characteristics for first and second water flooding. We also reported that 77.5% of stored oil is recovered by second water flooding. Oil recovery factors and the characteristic parameters, Swi, Ko(Swi), Soi, Sor, Sw(max), and Kw(Sor) were experimentally determined for initial and second water flooding. Although not all of the stored crude oil has been recovered due to wettability change and oil film left the pore’s surface on the rock, the desired recovery factor has been achieved during the second water flooding.
Home energy management systems (HEMS) have been shown to reduce energy bills and to provide grid services including peak demand reduction and demand flexibility. However, uncertainty in residential energy systems is a significant issue and can reduce the benefits of a HEMS to the homeowner or grid operator. Sources of uncertainty include weather forecasts, predictions of energy-related occupant activities (e.g., hot water draws), and parameter estimation for the building envelope and energy-consuming equipment. This paper tackles the problem of uncertainty by developing a framework that simulates HEMS in uncertain conditions and evaluates the performance of multiple control strategies. A linear, reduced-order residential building model for model predictive control applications is derived and compared to a full-order model. Stochastic model predictive control is shown to perform better than deterministic and heuristic methods when considering realistic forecasts with uncertainty. The framework can evaluate the performance of HEMS in real-world applications, which can help de-risk HEMS deployment.
Intensive big data nanoindentation (BDNi) characterization was performed to reveal the cross-scale mechanical properties of, and hence distinguish the different phases in, inorganic-organic hybrid oilwell cement-elastomer composites, hydrothermally cured at 160 • C and 20 MPa for 28 days. Totally-three emulsified and particulate elastomers, including styrene-butadiene latex (SBL) emulsion (6, 12, and 14 wt.%), polypropylene (PP) powder (12 wt.%), and nitrile rubber (NR) powder (6 wt.%), and a weighting agent, hematite (50 wt.%), were used as additives to finely adjust the mechanical properties and microstructure of the hybrid composites, which were respectively examined by the BDNi and mercury intrusion porosimetry and scanning electron microscopy. BDNi data were statistically deconvoluted by the Gaussian mixture modeling (GMM) to discern mechanically distinct phases and their Young's moduli and hardness at the micro/nano scale and the bulk composites' properties at the macro scale. Results show that the SBL emulsion can be more homogeneously dispersed into the cement matrix, due to its emulsified soft consistency and hydrophilicity, resulting in the formation of soft coatings on, and softer infills intermixed with, the cement hydration products (CHPs). In contrast, the two hydrophobic, inert, particulate elastomers, PP and NR powders, only act as isolated soft inclusions embedded in the hydrated cement matrix. The NR melts at high temperatures and permeates into the pores of the cement matrix, leading to the formation of complex intervened micromorphology and hence functions better than the PP. All elastomers can effectively reduce the composites' Young's moduli: with increasing the elastomer contents, while the modulus of a BDNi-identified major CHP phase decreases from 20.9 to 11.3 GPa, the bulk composites' counterpart from 17.3 to 10.7 GPa. The BDNi enables the identification of multiple mechanically distinct phases in the hybrid composites and quantification of the property changes of these phases.
In this study, the guest exchange behaviors in the hydrate-bearing sediment of a one-dimensional reactor specially designed for depressurization-assisted replacement were experimentally investigated for CH4 production and CO2 storage. The longitudinal distributions of vapor compositions, replacement efficiency, and hydrate weight fractions, as well as the average efficiency for depressurization-assisted replacement, were examined using gas chromatography and powder X-ray diffraction (PXRD). The immediate re-formation of gas hydrates after CO2 injection implied a rapid recovery of the geo-mechanical strength of the sediment. The unique changes in the gas compositions in the pore space caused by the re-formation of gas hydrates resulted in a distinctive longitudinal distribution of the replacement efficiency in the hydrate-bearing sediment. PXRD analysis of the hydrate samples revealed that the gas hydrate saturation nearly recovered after depressurization-assisted replacement. Despite CH4 re-enclathration, the replacement efficiency was remarkably enhanced through depressurization-assisted replacement, and a larger amount of CO2 was stored in the hydrate-bearing sediment than the amount of CH4 produced. Furthermore, the production rate of CH4 through depressurization-assisted replacement was significantly higher than that through replacement only, and the guest exchange rate increased with an increase in the initial hydrate dissociation ratio. The experimental results demonstrated that depressurization-assisted replacement could solve the weakening of the geo-mechanical strength of the sediment for depressurization only and the slow production rate for replacement only; thus, it would be useful for low-carbon energy production from natural gas hydrate-bearing sediments.
We describe the factors researchers should consider in deciding when and how to use computational general equilibrium (CGE) models for environmental policy analysis instead of partial equilibrium or engineering models. Special attention is given to modeling the social costs and benefits of regulations and the role played by labor markets. CGE models excel at quantifying interactions across different sectors of the economy, factor-market outcomes, and the distributional consequences of policy, all using a comprehensive set of the resource constraints faced by agents. The ceteris paribus nature of these experiments allows a skilled modeler to develop a systematic understanding of the connection between model assumptions and policy outcomes. Using CGE models to address environmental policy questions involves challenges, including the representation of narrow and technology-specific regulatory designs, data and aggregation issues, and the development of methods to improve model transparency and validity. Expected final online publication date for the Annual Review of Resource Economics, Volume 14 is October 2022. Please see for revised estimates.
This article presents a computational study of saturated flow boiling in non-circular microchannels. The unit channel of a multi-microchannel evaporator, consisting of the fluidic channel and surrounding evaporator walls, is simulated and the conjugate heat transfer problem is solved. Simulations are performed using OpenFOAM v2106 and the built-in geometric Volume Of Fluid method, augmented with self-developed libraries to include liquid-vapour phase-change and improve the surface tension force calculation. A systematic study is conducted by employing water at atmospheric pressure, a channel hydraulic diameter of Dh=229 µm, a uniform base heat flux of qb=100 kW/m2, and by varying the channel width-to-height aspect-ratio and channel fin thickness in the range ϵ=0.25–4 and Wf=Dh/8−Dh, respectively. The effects of conjugate heat transfer and channel aspect-ratio on the bubble and evaporative film dynamics, heat transfer, and evaporator temperature are investigated in detail. This study reveals that, when the flow is single-phase, higher Nusselt numbers and lower evaporator base temperatures are achieved for smaller channel aspect-ratios, from Nu≃4 and Tb−Tsat≃9K when ϵ=4, to Nu≃6 and Tb−Tsat≃2K when ϵ=0.25, for same fin thickness Wf=Dh/8. In the two-phase flow regime, Nusselt numbers in the range Nu=12−36 are achieved. The trends of the Nusselt number versus the aspect-ratio are non-monotonic and exhibit a marked dependence on the channel fin thickness. For small fin thicknesses, Wf=Dh/8 and Wf=Dh/4, an overall ascending trend of Nu for increasing aspect-ratios is apparent, although in the narrower range ϵ=0.5–2 the Nusselt number appears weakly dependent on ϵ. For thicker fins, Wf=Dh/2 and Wf=Dh, the Nusselt number decreases slightly when increasing the aspect-ratio in the range ϵ=0.5–2, although this trend is not monotonic when considering the entire range of aspect-ratios investigated. Nonetheless, due to conjugate heat transfer, Nusselt numbers and evaporator base temperatures follow different trends when varying the aspect-ratio, and channels with ϵ<1 seem to promote lower evaporator temperatures than higher aspect-ratio conduits.
Paper has shaped society for centuries and is considered one of humanity's most important inventions. However, pulp and paper products can be damaging to social and natural systems along their lifecycle of material extraction, processing, transportation, and waste handling. The pulp and paper industry is among the top five most energy-intensive industries globally and is the fourth largest industrial energy user. This industry accounts for approximately 6% of global industrial energy use and 2% of direct industrial CO 2 emissions. The pulp and paper industry is also the largest user of original or virgin wood, with deleterious impacts on both human health and local flora and fauna, including aquatic ecosystems. This critical and systematic review seeks to identify alternatives for mitigating the climate impacts of pulp and paper processes and products, thus making the pulp and paper industry more environmentally sustainable. This study reviews 466 studies to answer the following questions: what are the main determinants of energy and carbon emissions emerging from the pulp and paper industry? What are the benefits of this industry adopting low-carbon manufacturing processes, and what barriers will need to be tackled to enable such adoption? Using a sociotechnical lens, we answer these questions, identify barriers for the pulp and paper industry's decarbonization, and present promising avenues for future research.
This paper combined data-driven modeling and optimal control for performance enhancement of earth pressure balance tunnel boring machine (EPBM). Two coupled processes, EPBM advance rate (AR) and cutterhead rotation torque, are modeled using support vector regression (SVR). An optimal control framework was formulated to maximize the AR, solved with particle swarm algorithm. Using the Seattle N125 project as case study, it is found the SVR model can predict EPBM AR with R² = 0.90, normalized root mean square error (nRMSE) = 0.30 and mean absolute percentage error (MAPE) = 31.2%, and R² = 0.65, nRMSE = 0.59 and MAPE = 6.7% for torque prediction. Compared to human operator, EPBM with optimal control can increase AR by 0.6–23.3 mm∕min on average, accompanied by an average torque reduction of 83.1 kN - m. It is found higher cutterhead rotation and lower chamber pressure always contribute to faster tunneling, but the optimal total thrust force to apply depends on the chamber pressure.
Substantial energy subsidies are recognised as the leading cause of Iran's inefficient electricity generation and consumption. This paper investigates the impacts of subsidy removal on future electricity demand and the required generation mix. A hybrid modelling framework is developed to analyse supply and demand sides under harmonised assumptions. An autoregressive distributed lag (ARDL) model combined with an autoregressive integrated moving average (ARIMA) model forecast electricity demand under subsidy removal scenarios at different paces. A partial equilibrium energy systems model (MESSAGE) offers a cost-optimal configuration of power generation technologies to meet the forecasted demand during the period 2017–2050. The findings demonstrate that energy subsidy reforms can reduce total electricity demand by 16% and could ensure a 31% cut in cumulative CO2 emissions. The scenario analysis also shows that under an early and steady reform scenario and with gradual removal, the development of renewable energy technologies and energy efficiency plans become cost-competitive. In contrast, the late and rapid subsidy removal path should tackle the lock-in effect's risk. This reveals that the early action in energy subsidy reform should be considered a priority over the removal speed. Finally, this paper discusses the potential policy implications beyond Iran.
Metallic additive manufacturing (AM) provides a customizable and tailorable manufacturing process for new engineering designs and technologies. The greatest challenge currently facing metallic AM is maintaining control of microstructural evolution during solidification and any solid state phase transformations during the build process. Ti-6Al-4V has been extensively surveyed in this regard, with the potential solid state and solidification microstructures explored at length. This work evaluates the applicability of previously determined crystallographic markers of microstructural condition observed in electron beam melting powder bed fusion (PBF-EB) builds of Ti-6Al-4V in a directed energy deposition (DED) build process. The aim of this effort is to elucidate whether or not these specific crystallographic textures are useful tools for indicating microstructural conditions in AM variants beyond PBF-EB. Parent β-Ti grain size was determined to be directly related to α-Ti textures in the DED build process, and the solid state microstructural condition could be inferred from the intensity of specific α-Ti orientations. Qualitative trends on the as-solidified β-Ti grain size were also determined to be related to the presence of a fiber texture, and proposed as a marker for as-solidified grain size in any cubic metal melted by AM. Analysis of the DED Ti-6Al-4V build also demonstrated a near complete fracture of the build volume, suspected to originate from accumulated thermal stresses in the solid state. Crack propagation was found to only appreciably occur in regions of slow cooling with large α+β colonies. Schmid factors for the basal and prismatic α-Ti systems explained the observed crack pathway, including slower bifurcation in colonies with lower Schmid factors of both slip systems. Colony morphologies and localized equiaxed β-Ti solidification were also found to originate from build pauses during production and uneven heating of the build edges during deposition. Tailoring of DED Ti-6Al-4V microstructures with the insight gained here is proposed, along with cautionary insight on preventing unplanned build pauses to maintain an informed and controlled thermal environment for microstructural control.
Bayesian inference with Sequential Monte Carlo was used to determine the single crystal elastic constants of additively manufactured (AM) cobalt‑nickel-based superalloy specimens from only the resonant frequencies and texture data. This novel framework enables the quantification of the single crystal elastic constants for AM and polycrystalline specimens using only electron backscatter diffraction (EBSD) and Resonant Ultrasound Spectroscopy (RUS), avoiding the expense of bulk single crystal fabrication or synchrotron experiments. A parallelizable and open-source Python package (SMCPy) was used to perform Bayesian inference of the single crystal elastic constants from resonant frequencies of AM specimens. The single crystal elastic constants determined from AM cobalt‑nickel-base superalloy specimens were validated with measurements of the single crystal elastic constants on a bulk single crystal specimen. EBSD texture data was used to determine the single crystal elastic constants from the resonant frequencies of AM specimens, and validated with neutron diffraction data by considering the experimental uncertainty in both the EBSD and neutron diffraction data. The robustness of this framework for varied texture orientations relative to the build direction (BD) was demonstrated for AM specimens printed at 0° and 20° BD-inclinations.
The United States is affected by an average of almost seven severe weather events a year, often resulting in billions of dollars in physical and economic damages, a subset of which are related to grid outages. There is a need for power and energy system stakeholders to better understand and implement the strategies that help reduce net-economic and societal consequences associated with grid outages by improving the resilience of their systems. In addition, there are incentives to reduce emissions and meet climate goals, several pathways of which include resilient technologies. Including resilience constraints and metrics in energy system planning models may help inform the design of more resilient systems that are also more renewable and sustainable. This paper reviews qualitative definitions of resilience, quantitative approaches to resilience, recent examples of the inclusion of resilience in energy system models with respect to acute climatological threats, and the gaps in fully articulating resilience in current modeling tools. We then outline steps to effectively improve resilience considerations against such threats into energy sector modeling tools. Based on the findings, the authors propose a novel framework for energy system resilience assessment and future areas of research to bridge the current modeling gaps.
Gasoline subsidies distort the gasoline market resulting in inefficiencies and a costly burden in government budget. In Indonesia, they have taken up to 15 % of the government expenditures that arguably could be better spent elsewhere. Governments are aware of these costs, yet face difficulties in removing the policy. Governments would like to release the subsidy fund for other programs while still maintaining political power. Simultaneously, a reform will reduce the purchasing of the population and thus, it is commonly met with strong public resistance. The general population can influence the government's decision to carry out a reform by exerting pressure that may affect the country's political stability. There is a vast economics literature analysing the economic impact from a subsidy reform. Meanwhile, the government's hesitancy is analysed in the political science literature. We combined these two fields by developing a quantitative game theory model to show the interaction between the government and the general population. The model is based on Indonesian data but provides a framework that can be applied elsewhere. Different policy removal schemes are simulated including completely or partially phasing-out the subsidy with and without compensation. An important take-away from our analysis is that it provides a framework showing governments what they have to quantify in order to make an informed policy decision. Another important implication is that the success of the policy reform is highly dependent on the selectorates trust to the government. It strongly supports the political science recommendations of building trust through transparency and inclusion.
Despite their maturity and popularity, security remains a critical concern in container adoption. To address this concern, secure container runtimes have emerged, offering superior guest isolation, as well as host protection, via system call policing through the surrogate kernel layer. Whether or not an adversary can bypass this protection depends on the effectiveness of the system call policy being enforced by the container runtime. In this work, we propose a novel method to quantify this container system call exposure. Our technique combines the analysis of a large number of exploit codes with comprehensive experiments designed to uncover the syscall pass-through behaviors of container runtimes. Our exploit code analysis uses information retrieval techniques to rank system calls by their risk weights. Our study shows that secure container runtimes are about 4.2 to 7.5 times more secure than others, using our novel quantification metric. We additionally uncover changing security trends across a 4.5 year version history of the container runtimes.KeywordsSecure container runtimeSecurity quantificationSystem callContainer escapeExploit code analysis
Through systematic linker substitution in a flexible zeolitic imidazolate framework (ZIF) with step-shaped adsorption-desorption, structural intermediates between the known open and closed phases were isolated. Reflecting this, modulative sorption behaviour with an inverting adsorption pressure trend-in which the step pressure decreases and then increases again with increasing mixed linker concentration-is observed, highlighting how linker substitution modifies the energetic landscape of framework flexibility.
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3,723 members
Kevin Cannon
  • Department of Geology and Geological Engineering
Lincoln D Carr
  • Department of Physics
Jason M Porter
  • Department of Mechanical Engineering
Joel M Bach
  • College of Engineering and Computational Sciences (CECS)
Mark T. Lusk
  • Department of Physics
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