Cerium hydride has a variety of interesting properties, including a known lattice contraction and densification with increasing hydrogen content. However, precise stoichiometric control is not experimentally straightforward and ab initio approaches are not computationally feasible for many properties such as melting and low temperature diffusion. Therefore, we develop a machine-learned interatomic potential for cerium hydride that is valid for H to Ce ratios from 2.0 to 3.0. A query-by-committee active learning approach is used to develop the training set. Leveraging classical molecular dynamics simulations, we assess a range of properties and provide fundamental mechanisms for the trends with stoichiometry. A majority of the properties follow the trend of lattice contraction, being governed by the stronger lattice binding induced by adding octahedral atoms.

Depleted hydrocarbon reservoirs offer a promising solution for large-scale hydrogen (H2) storage, providing sufficient gas containment typically achieved through porous reservoir rocks and impermeable caprocks. However, the impact of high H2 diffusion coefficients on caprock sealing efficiency is often overlooked, leading to oversimplifications in underground hydrogen storage (UHS) modeling and assessments. A comprehensive literature review reveals significant variability in H2 diffusion coefficients in caprocks, ranging from 1 x 10-10 to 1 x 10-7m2/s. To address this uncertainty, we present a multi-dimensional statistical framework to assess caprock sealing efficiency across various caprock properties, using the Morrow reservoir in Texas as a case study. Based on 500 Monte Carlo simulations, we identified the H2 diffusion coefficient, initial water/gas saturation, and caprock permeability as key factors affecting caprock sealing efficiency. We find that the presence of free gas provides connected gas-phase pathways that substantially enhance upward H2 diffusion into caprocks, increasing diffusion losses and reducing energy storage efficiency from 86% to 73%. We further optimize storage efficiency and enhance the annual storage capacity from 29 GWh to 34 GWh by implementing UHS in reservoirs with water-saturated caprocks. Accurate characterization of hydrogen diffusion behavior and initial water saturation is essential for assessing UHS performance and ensuring reliable energy storage capacity estimations. Overall, this study provides critical insights into caprock seal integrity, emphasizing its pivotal role in enhancing energy storage efficiency and optimizing the performance of UHS systems across diverse geological settings.

Defects and roughness at a material's surface can allow for the formation of a material jet when a shockwave reaches a surface. The formation of a jet can lead to significant material damage of the shocked material, as well as the downstream material that the jet impacts. Here, we utilize planar shocks in single crystal aluminum to assess initial jetting formation for surface notches and sub-surface porosity. In the case of surface notches, we find that changing the width of the notch can cause the shock breakout response to transition from a standard jetting mechanism to an atomic atomization at high velocities. This transition occurs due to the mechanisms associated with lateral relaxations within the notch and how this interacts with the shock focusing event that induces jetting. For sub-surface pores, the pore collapse induces a re-shock, localized near the pore, that is stronger than the initial shock, but unsupported. Changing the pore dimensions and location relative to the surface influences the strength of the shock that emanates from its collapse when it reaches the surface, leading to a variety of different breakout conditions including jetting and localized material failure.

Geological hydrogen (H2) storage is a vital component of the transition to a zero-emission economy. A key challenge is the potential chemical interactions between the stored H2 and reservoir minerals, which can impact storage feasibility and long-term reservoir integrity. To evaluate these interactions, we employ ab initio calculations based on density functional theory (DFT) to investigate H2 adsorption on representative minerals. Our findings classify H2-mineral interactions into three categories: (i) weak physisorption through van der Waals (vdW) forces on kaolinite, muscovite, and alpha-quartz, indicating a minimal risk of H2 loss in reservoirs dominated by these minerals; (ii) intermediate interactions with charge redistribution on calcite, edenite, augite, and fayalite, which may influence prospects for H2 retrieval; and (iii) chemisorption with H2 dissociation on albite, anorthite, fluorite, and pyrite, posing risks of H2 loss and mineral corrosion. These insights enhance our understanding of H2 interactions with minerals in geological settings, aiding in the selection of suitable storage sites and development of mitigation strategies for safety, efficiency, and long-term underground H2 storage.

This study explores hydrogen adsorption on mineral surfaces (pyrite, calcite, and quartz varieties) for potential storage in subsurface sites with these rock types. Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) simulations are used to investigate the system across a range of temperatures, pressures, and pore sizes. The findings show that pore size significantly impacts hydrogen density, with nanopores facilitating higher adsorption due to stronger interactions with mineral surfaces. Temperature and surface chemistry also influence storage performance, with adsorption decreasing by 12-19% as temperatures rise. Pyrite, exhibiting weaker hydrogen-sulfur interactions, has the lowest adsorption capacity, while calcite and quartz, with stronger hydrogen-oxygen bonds, show higher capacities. Notably, non-hydroxylated Q4 quartz outperforms hydroxylated Q2 and Q3 in hydrogen storage. Additionally, isosteric heat of adsorption (Qst) analysis reveals that pyrite has significantly lower Qst values compared to calcite and quartz, indicating weaker hydrogen interactions. These findings provide insights into the role of mineral surface characteristics and temperature in optimizing hydrogen storage in geological formations.

As global energy systems undergo a transition to cleaner alternatives, geologic hydrogen storage has emerged as a promising solution for large-scale energy storage. A critical factor in determining the feasibility of this approach is the effectiveness of caprock formations, such as shale, in preventing hydrogen migration. This study investigates the diffusion behavior of hydrogen through shale to assess its suitability as a caprock for geologic hydrogen storage. Using a novel double-seal core holder design and a through-diffusion apparatus, hydrogen diffusion was measured through shale rock from the Eagle Ford and Wolfcamp Formations under dry conditions. These measurements were complemented by microstructural and mineralogical analyses using low-pressure nitrogen adsorption and X-ray diffraction. The effective diffusion coefficient of hydrogen in these shale caprocks ranged from 2.51 x 10-8 to 9.85 x 10-8 m2/s. Notably, we observed that the diffusion behavior was more related to the pore network structure and could not be attributed to differences in the total pore volume between shale types alone. To further understand the role of pore network complexity, a fractal pore model was developed to correlate tortuosity with the fractal dimension of the pore structure (a measure of pore network complexity). The proposed model closely matched tortuosity values obtained from diffusion experiments, outperforming existing theoretical tortuosity-porosity correlations. These findings provide key quantitative parameters needed to assess the feasibility of geologic hydrogen storage as well as insights that can be applied to hydrogen storage in a range of geologic formations.

Relative permeability is a crucial two‐phase property in porous media that can be significantly impacted by wettability conditions. While traditional research has predominantly examined homogeneous wettability, this work explores the less studied pore‐size dependent (PSD) wettability, featured by a pore‐size dependent wettability distribution. Leveraging high‐fidelity Lattice Boltzmann simulations on CT‐scanned porous samples, we demonstrate how PSD wettability would impact relative permeability at the pore scale. Our findings reveal that the deviation of relative permeability from the homogeneous wettabilitity induced by PSD wettability can be 5%–20%. The deviation of relative permeability curves increases as the spanning range of the contact angle increases. We also find that this impact is less pronounced as the capillary number increases. By adopting a pore‐size‐dependent contact angle relationship, our approach provides a more accurate and nuanced understanding of how PSD wettability would impact two‐phase flow. These findings discovered at the pore scale may also provide valuable insights on relative permeability at the core to reservoir scales.

The recent history of respiratory pathogen epidemics, including those caused by influenza and SARS-CoV-2, has highlighted the urgent need for advanced modeling approaches that can accurately capture heterogeneous disease dynamics and outcomes at the national scale, thereby enhancing the effectiveness of resource allocation and decision-making. In this paper, we describe Epicast 2.0, an agent-based model that utilizes a highly detailed, synthetic population and high-performance computing techniques to simulate respiratory pathogen transmission across the entire United States. This model replicates the contact patterns of over 320 million agents as they engage in daily activities at school, work, and within their communities. Epicast 2.0 supports vaccination and an array of non-pharmaceutical interventions that can be promoted or relaxed via highly granular, user specified policies. We illustrate the model's capabilities using a wide range of outbreak scenarios, highlighting the model's varied dynamics as well as its extensive support for policy exploration. This model provides a robust platform for conducting what if scenario analysis and providing insights into potential strategies for mitigating the impacts of infectious diseases.

High-pressure shear band formation is a critical phenomenon in energetic materials because of its ability to form hotspots and influence mechanical strength. Shear banding is known to occur in a variety of these materials, but the governing dynamics of the mechanisms are not well defined for molecular crystals. Our previous work has found that at high pressures in 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), the initial formation sites for shear bands, called "embryos", form in excess and rapidly lower deviatoric stresses prior to shear band formation and growth, suppressing the shear banding nucleation and growth. Here, we assess the influence of a variety of changes to the material state on this phenomenon, including altered initial temperature, lateral strain that confines the system in tension or pressure, and initial molecular vacancies throughout the crystal. Shear band suppression and the nature of the shear band network are assessed as a function of each of these.

This study investigates the reaction of hydrogen (H-2) with pyrite (FeS2), focusing on how temperature and the presence of water influence the reaction pathways and kinetics. Utilizing computational molecular simulations and kinetic analyses, we explore the impact of these factors on the formation of hydrogen sulfide (H2S) and related species. First, grand canonical Monte Carlo/molecular dynamics (GCMC/MD) simulations reveal that physical H-2 adsorption occurs in distinct layers on the pyrite surface. In addition, increased temperatures reduce the absolute adsorption capacities. Reactive MD simulations demonstrate that H-2 interacts differently with pyrite under varying conditions. At 298 K, H-2 reacts with pyrite to form HS-, leading to the formation of HS- through covalent bonding with sulfur of pyrite. However, no H2S is produced at this temperature, suggesting that a kinetic barrier (i.e., activation energy) may prevent this reaction. At higher temperatures, H2S production significantly increases. The presence of water introduces additional complexity to the reaction mechanism. Unlike dry conditions, water enhances H2S generation, even at low temperatures. Water also facilitates the formation of additional products, such as SOH, indicating a more intricate chemical environment on the pyrite surface. Our findings identify the association of HS- ions to form H2S as the rate-limiting step, with temperature influencing this process. This finding suggests that while the presence of water can create a more dynamic reaction environment, the overall mechanisms leading to H2S formation remain consistent. These outcomes suggest the need for developing targeted strategies to manage and control H2S emissions within the context of underground hydrogen storage.

Disease surveillance systems allow public health agencies to respond to emerging diseases before they become widespread. Developing such systems requires identifying optimal ways to monitor in the context of an epidemic outbreak; this problem is known as sensor selection. Contact networks represent the dynamics of interaction in a population and are used to model how a disease spreads in a population and to explore strategies of sensor selection. We evaluated five sensor selection strategies on their ability to provide an early warning of a COVID-like outbreak in synthetic contact networks encapsulated in four network scenarios. Three of these scenarios assessed different aspects of community structure. The fourth scenario employed a contact network representing the population and interactions of 6.8 million people in New York City, constructed from an agent-based simulation using census and transportation data. This scenario exemplifies how sensor selection strategies may perform in a real-world, urban context. Our findings suggest that the choice of the optimal strategy depends heavily on the community structure of the network. Strategies that select highly connected nodes or maximize network coverage are the optimal surveillance strategy for outbreak detection in many network community structures. However, a naive implementation of these strategies may fail to provide an early warning at all—including in the New York City scenario. Moreover, these methods are impractical for real-world use as they require knowledge of the underlying contact network. Instead, a selection strategy that starts with a set of random nodes and then performs a random walk through a chain of neighbors reliably provides early warnings without requiring prior knowledge of the network. We find this method, called "random chain", to be the most pragmatic for implementation in a real-world disease surveillance context.

High pressure shear band formation is a critical phenomenon in energetic materials due to its influence on both mechanical strength and mechanochemical activation. While shear banding is know to occur in a variety of these materials, the governing dynamics of the mechanisms is not well defined for molecular crystals. We conduct molecular dynamics simulations of shock wave induced shear band formation in the energetic material 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) to assess shear band nucleation processes. We find, that at high pressures, the initial formation sites for shear bands 'over-nucleate' and rapidly lower deviatoric stresses prior to shear band formation and growth. This results in the suppression of plastic deformation. A local cluster analysis is used to quantify and contrast this mechanism with a more typical shear banding seen at lower pressures. These results demonstrate a mechanism that is reversible in nature and that supersedes shear band formation at increased pressures. We anticipate that these results will have a broad impact on the modeling and development of high strain rate application materials such as those for high explosives and hypersonic systems.

Background Nonpharmaceutical interventions (NPIs) may be considered as part of national pandemic preparedness as a first line defense against influenza pandemics. Preemptive school closures (PSCs) are an NPI reserved for severe pandemics and are highly effective in slowing influenza spread but have unintended consequences. Methods We used results of simulated PSC impacts for a 1957-like pandemic (i.e., an influenza pandemic with a high case fatality rate) to estimate population health impacts and quantify PSC costs at the national level using three geographical scales, four closure durations, and three dismissal decision criteria (i.e., the number of cases detected to trigger closures). At the Chicago regional level, we also used results from simulated 1957-like, 1968-like, and 2009-like pandemics. Our net estimated economic impacts resulted from educational productivity costs plus loss of income associated with providing childcare during closures after netting out productivity gains from averted influenza illness based on the number of cases and deaths for each mitigation strategy. Results For the 1957-like, national-level model, estimated net PSC costs and averted cases ranged from $7.5 billion (2016 USD) averting 14.5 million cases for two-week, community-level closures to $97 billion averting 47 million cases for 12-week, county-level closures. We found that 2-week school-by-school PSCs had the lowest cost per discounted life-year gained compared to county-wide or school district–wide closures for both the national and Chicago regional-level analyses of all pandemics. The feasibility of spatiotemporally precise triggering is questionable for most locales. Theoretically, this would be an attractive early option to allow more time to assess transmissibility and severity of a novel influenza virus. However, we also found that county-wide PSCs of longer durations (8 to 12 weeks) could avert the most cases (31–47 million) and deaths (105,000–156,000); however, the net cost would be considerably greater ($88-$103 billion net of averted illness costs) for the national-level, 1957-like analysis. Conclusions We found that the net costs per death averted ($180,000-$4.2 million) for the national-level, 1957-like scenarios were generally less than the range of values recommended for regulatory impact analyses ($4.6 to 15.0 million). This suggests that the economic benefits of national-level PSC strategies could exceed the costs of these interventions during future pandemics with highly transmissible strains with high case fatality rates. In contrast, the PSC outcomes for regional models of the 1968-like and 2009-like pandemics were less likely to be cost effective; more targeted and shorter duration closures would be recommended for these pandemics.

High pressure shear band formation is a critical phenomenon in energetic materials due to its influence on both mechanical strength and mechanochemical activation. While shear banding is known to occur in a variety of these materials, the governing dynamics of the mechanisms are not well defined for molecular crystals. We conduct molecular dynamics simulations of shock wave induced shear band formation in the energetic material 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) to assess shear band nucleation processes. We find, that at high pressures, the initial formation sites for shear bands, "embryos", form in excess and rapidly lower deviatoric stresses prior to shear band formation and growth. This results in the suppression of plastic deformation. A local cluster analysis is used to quantify and contrast this mechanism with a more typical shear banding seen at lower pressures. These results demonstrate a mechanism that is reversible in nature and that supersedes shear band formation at increased pressures. We anticipate that these results will have a broad impact on the modeling and development of high-strain rate application materials such as those for high explosives and hypersonic systems.

Abstract Geologic storage of CO2 and H2 are climate‐positive techniques for meeting the energy transition. While similar formations could be considered for both gases, the flow dynamics could differ due to differences in their thermophysical properties. We conduct a rigorous pore‐scale study of water/CO2 and water/H2 systems at relevant reservoir conditions in a Bentheimer rock sample using the lattice Boltzmann method to quantify the effects of capillary, viscous, inertial, and wetting forces during gas invasion. At similar conditions, H2 invasion is weaker compared to CO2 due to unfavorable viscosity ratios. Increasing flow rate, however, increases the breakthrough saturation for both gas systems in the range of capillary numbers studied. At isolated conditions of flow rate, viscosity ratio, and wettability, local inertial effects are found to be critical and show consistent increase in the invaded gas saturation. The effect of inertial forces persits for both gases across all field conditions tested.

Subsurface formations are promising for large-scale H2 storage, balancing the energy demand and supply. Wettability is vital in ensuring storage safety, efficiency, and capacity, whereas noticeable discrepancies exist in the literature. This work reconciles these discrepancies by revealing the mechanisms of quartz wettability alteration with surface chemistry and pressure using classical molecular dynamics simulation. We find that the fully rigid quartz substrate results in much lower hydrophilicity than the fully flexible and the hydroxyl group flexible quartz substrates due to the lower probability of hydrogen bond formation between water and hydroxyl groups. Also, quartz wettability relies on not only the area density but also the arrangement of the surface hydroxyl groups. Monolayer water adsorption on both hydrophilic and hydrophobic quartz surfaces is observed, whereas the structure of the adsorbed water film is different. Dissolved H2 prefers to move to the quartz surface rather than staying in bulk water. The water contact angle on the fully hydroxylated quartz fluctuates between 30.7 and 37.1(degrees) with pressure ranging from 1-30 MPa, without a monotonic trend. We reveal that the dominant mechanism of wettability alteration within this pressure range is due to the pinning effect induced by the microstructures on the quartz surface.

Diffusion of hydrogen (H2) is important to understand the leakage risk and transport behavior for H2 geologic storage. We applied molecular dynamics simulations to investigate the influencing factors of H2 diffusion in the slit pores of calcite, hematite, and quartz, owing to their abundance. It is revealed that the H2 self-diffusion coefficient increases with the temperature, regardless of the type of pore minerals. The diffusion of H2 in the 20 nm slit pores falls into the bulk diffusion regime when the pressure is 10 MPa. The self-diffusion of H2 decreases with pressure in all three types of slit pores, following a power law model with the exponents ranging from -0.825 to -0.964. Furthermore, the impact of confinement on H2 diffusion is more pronounced for the slit pores with stronger interactions with H2-like calcite. The role of surface roughness in H2 diffusion depends on the slit aperture. The rough surface enhances H2 diffusion in the larger slit pores due to the enlarged effective pore space, whereas it weakens H2 diffusion in the small slit pores due to stronger adsorption. These findings will fill the knowledge gap on the coupling effect of different factors influencing H2 diffusion.