Colorado School of Mines

The capillary break-up of complex fluid filaments occurs in many scientific and industrial applications, particularly in bio-printing where both liquid and polymerized droplets exist in the fluid. The simultaneous presence...

Here, we explore how differences in morphologic heterogeneity due to logjams and secondary channels drive transient storage across discharge in two stream reaches within the Front Range of Colorado, USA. During three tracer tests conducted from baseflow to near‐peak snowmelt, we collected instream fluid conductivity measurements and conducted electrical resistivity surveys to characterize tracer movement in the surface and subsurface of the stream system. The reach with two logjams and an intermittent secondary channel exhibited greater heterogeneity in surface transient storage, driving heterogeneity in hyporheic exchange flows, compared to the reach with a single logjam and a perennial secondary channel. As discharge increased, (a) backwater pools created by logjams increased in size in both systems, (b) channel complexity increased as logjams forced flow into secondary channels, and (c) subsurface flowpath distribution increased. Various transient storage indices provide some insight on solute retention but compressing data from this system into simple values was unintuitive given the noise in breakthrough‐curve tails and secondary peaks in concentration. While subsurface exchange increases with discharge in both reaches, retention may not. Flushing of subsurface tracers is highest at medium discharge as interpreted from the electrical resistivity inversions in both reaches, perhaps because of a tradeoff between the increasing extent of subsurface flowpaths with discharge and larger pressure gradients for driving flow. This work is one of the first to explore controls on exchange and retention in stream systems with multiple logjams and evolving channel planform using geophysical data to constrain the subsurface movement of solutes.

Lake surface conditions are critical for representing lake‐atmosphere interactions in numerical weather prediction. The Community Land Model's 1‐D lake component (CLM‐lake) is part of NOAA's High‐Resolution Rapid Refresh (HRRR) 3‐km weather/earth‐system model, which assumes that virtually all the two thousand lakes represented in CONUS have distinct (for each lake) but spatially uniform depth. To test the sensitivity of CLM‐lake to bathymetry, we ran CLM‐lake as a stand‐alone model for all of 2019 with two bathymetry data sets for 23 selected lakes: the first had default (uniform within each lake) bathymetry while the second used a new, spatially varying bathymetry. We validated simulated lake surface temperature (LST) with both remote and in situ observations to evaluate the skill of both runs and also intercompared modeled ice cover and evaporation. Though model skill varied considerably from lake to lake, using the new bathymetry resulted in marginal improvement over the default. The more important finding is the influence bathymetry has on modeled LST (i.e., differences between model simulations) where lake‐wide LST deviated as much as 10°C between simulations and individual grid cells experienced even greater departures. This demonstrates the sensitivity of surface conditions in atmospheric models to lake bathymetry. The new bathymetry also improved lake depths over the (often too deep) previous value assumed for unknown‐depth lakes. These results have significant implications for numerical weather prediction, especially in regions near large lakes where lake surface conditions often influence the state of the atmosphere via thermal regulation and lake effect precipitation.

We introduce a new system of surface integral equations for Maxwell’s transmission problem in three dimensions (3-D). This system has two remarkable features, both of which we prove. First, it is well-posed at all frequencies. Second, the underlying linear operator has a uniformly bounded inverse as the frequency approaches zero, ensuring that there is no low-frequency breakdown. The system is derived from a formulation we introduced in our previous work, which required additional integral constraints to ensure well-posedness across all frequencies. In this study, we eliminate those constraints and demonstrate that our new self-adjoint, constraints-free linear system—expressed in the desirable form of an identity plus a compact weakly-singular operator—is stable for all frequencies. Furthermore, we propose and analyze a fully discrete numerical method for these systems and provide a proof of spectrally accurate convergence for the computational method. We also computationally demonstrate the high-order accuracy of the algorithm using benchmark scatterers with curved surfaces.

Functionalization is poised to play a prominent role in MOF development as it could become the to-go strategy to bestow extant MOF with new properties, and to control MOF pore shape and size by modulating polymorph selection. Thus, to speed up MOF development through computational work, a better (predictive) understanding on how functionalization impacts MOF synthesizability is needed. Here we use a data-driven approach where molecular dynamics simulations on 5,000+ MOFs are used to shed light on how functionalization affects MOF free energy, as the latter has been largely tied to MOF synthesizability and polymorph selection. More consistently in MOFs with higher void fractions, we find that functionalization generally reduces free energy, with entropy contributing significantly to this thermodynamic stabilization. Although with some functionalizations (-CF3, -F, -Br, -SH, -OH) the role of entropy is more apparent than with others (-CN, -CH3, -NO2, -NH3). Through uneven stabilization of polymorphs, we also find functionalization (more often with -Br, -CN and -CF3) as capable of altering polymorph (topology) selection relative to original non-functionalized polymorphic families. However, no switch in polymorph stability ever occurred when the original (unfunctionalized) polymorphs were separated by more than 1.42 kJ/mol per MOF atom. We show that machine learning can predict functionalization-induced free energy change of a parent MOF with a mean absolute error of 0.16 kJ/mol per atom, using only physical properties of the parent MOF and the functional group as input. The ML-based SHAP analysis agrees with human analysis on the functionalization molecular mass and the hydrogen fraction of the parent MOF being among the factors that influence change in free energy the most. Finally, we present a publicly accessible dynamic interface to visualize and navigate the free energy data , thereby encouraging the research community to engage with and utilize the data to help uncover new insights.

Protonic ceramic electrochemical cells (PCECs) can operate at intermediate temperatures (450° to 600°C) for power generation and hydrogen production. However, the operating temperature is still too high to revolutionize ceramic electrochemical cell technology. Lowering the operating temperature to <450°C will enable a wider material choice and reduce system costs. We present approaches to redesigning PCECs via readily fabricated single-grain–thick, chemically homogeneous, and robust electrolytes and a nano-micro positive electrode. At 450°C, the PCECs achieve a peak power density of 1.6 watt per square centimeter on H 2 fuel, 0.5 watt per square centimeter on NH 3 fuel, and 0.3 watt per square centimeter on CH 4 fuel in fuel cell mode. In steam electrolysis mode, a current density of >0.6 ampere per square centimeter with a Faradaic efficiency of >90% is achievable at 1.4 volt and 400°C. In addition, exceptional durability (>2000 hours) has been demonstrated, with a degradation rate of <0.01 millivolt per 100 hours in fuel cell mode at 400°C.

Emissions reductions may be met with relatively small costs

Although the sensitivity of the circadian system to the characteristics of light (e.g., biological timing, intensity, duration, spectrum) has been well studied in adults, data in early childhood remain limited. Utilizing a crossover, within-subjects design, we examined differences in the circadian response to evening light exposure at two different correlated color temperatures (CCT) in preschool-aged children. Healthy, good sleeping children ( n = 10, 3.0-5.9 years) completed two 10-day protocols. In each protocol, after maintaining a stable sleep schedule for 7 days, a 3-day in-home dim-light circadian assessment was performed. On the first and third evenings of the in-home protocol, dim-light melatonin onset (DLMO) was assessed. On the second evening, children received a 1-h light exposure of 20 lux from either 2700 K (low CCT) or 5000 K (high CCT) (~9 and ~16 melanopic equivalent daylight illuminance (mEDI lux), respectively) centered around their habitual bedtime. Children received the remaining light condition during their second protocol, with the order counterbalanced across participants. Salivary melatonin was collected to compute melatonin suppression and circadian phase shift resulting from each experimental light condition. Melatonin suppression across the 1-h light stimulus was significantly greater during exposure to the high CCT light ( M = 56.3%, SD = 19.25%) than during the low CCT light ( M = 23.90%, SD = 41.06%). Both light conditions resulted in marked delays of circadian timing, but only a small difference ( d = −0.25) was observed in the delay between the 5000 K ( M = 35.3 min, SD = 34.3 min) and 2700 K ( M = 26.7 min, SD = 15.9 min) conditions. Together, these findings add to a growing literature demonstrating high responsivity of the circadian clock to evening light exposure in early childhood and provide preliminary evidence of melatonin suppression sensitivity to differences in light spectrum in preschool-aged children.

Shelley A. Claridge, Jianbin Huang, Serena Margadonna, Ryan Richards and Federico Rosei share their retrospective in an editorial celebrating the first year of publication of RSC Applied Interfaces.

Sunnyside is a well-preserved Miocene polymetallic vein deposit located in the Western San Juan Mountains of Colorado, USA. The steeply dipping veins extend vertically for ~ 600 m and can be traced laterally over a combined length of ~ 2100 m. Fracture-controlled fluid flow dominated during the pre-ore stage. Subsequent ore deposition along major extensional structures took place at far-from-equilibrium conditions resulting in the formation of ore mineral dendrites in a silica matrix that was originally noncrystalline. Recrystallization of the noncrystalline silica to quartz caused extensive microtextural modification of the veins during and after the ore-stage. Microtextural evidence suggests that essentially all quartz in the ore-stage veins originated from a noncrystalline silica precursor. The deposition of ore mineral dendrites and noncrystalline silica is interpreted to have occurred during repeated fluid flashing events over the lifetime of the hydrothermal system. A period of quasi steady-state fluid flow occurred during the post-ore stage resulting in the formation of gangue minerals in open spaces in the veins. Fluid inclusion evidence suggests that the veins at Sunnyside formed at the transition between the epithermal and porphyry environments at ~ 1300–1900 m below the paleowater table at temperatures ranging up to ~ 345 °C.

The solidification microstructures of plain and inoculated 6061 aluminum builds manufactured with gas metal arc-directed energy deposition were studied with a combination of models and experiments. Electron back-scatter diffraction (EBSD) showed that the plain 6061 build had large, columnar grains with intergranular solidification cracking, while the inoculated build had a near-equiaxed, fine grain microstructure with no solidification cracks. By combining EBSD and energy dispersive spectrometry, the inoculated build has been shown to have exhibited globular growth while the non-inoculated build displayed a dendritic microstructure. A combination of heat transfer and modified grain morphology models were employed to predict the solidification morphology of the 6061 builds, which closely matched experimental results. A modification is proposed to the criterion marking the transition from globular to dendritic growth that better matches experimental results in this work. The results of this study are expected to provide improved methods to predict solidification microstructure for the development of new materials and processing parameters for additive manufacturing.

Slickwater, a low viscosity fracturing fluid, is prevalent in the stimulation of hydraulic fracturing operations due to its efficacy in penetrating tight formations and providing the necessary fracture conductivity. However, its proppant-suspending capabilities, which are crucial for transporting proppants to the intended locations within induced fractures, pose a significant challenge. A comprehensive understanding of proppant transport behavior during fracturing is essential for successfully creating the desired geometry of fractures that are kept open by the proppants, thereby enhancing the productivity of the well. This paper offers a comprehensive review of the intricacies of proppant transport in slickwater-based fracturing treatments, drawing upon experimental data, numerical simulations, and analytical models. It delves into the multifaceted interactions between slickwater and proppants, exploring the impact of factors like injection rate, proppant size and concentration, fluid viscosity, and fracture complexity on the effectiveness of hydraulic fracturing treatments. Through a synthesis of existing knowledge and the identification of future research directions, this paper seeks to refine proppant distribution strategies, addressing the constraints of slickwater use and promoting sustainable, efficient resource extraction in the continually advancing field of hydraulic fracturing. Additionally, it aims to optimize fracturing treatments by mitigating slickwater's limitations, thereby ensuring improved fracture treatment outcomes.