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1. Bridging molecular-scale interfacial science with continuum-scale models

   https://doi.org/10.1038/s41467-024-49598-y  

   Ilgen, Anastasia G; Borguet, Eric; Geiger, Franz M; Gibbs, Julianne M; Grassian, Vicki H; Jun, Young-Shin; Kabengi, Nadine; Kubicki, James D (December 2024, Nature Communications)

   Abstract Solid–water interfaces are crucial for clean water, conventional and renewable energy, and effective nuclear waste management. However, reflecting the complexity of reactive interfaces in continuum-scale models is a challenge, leading to oversimplified representations that often fail to predict real-world behavior. This is because these models use fixed parameters derived by averaging across a wide physicochemical range observed at the molecular scale. Recent studies have revealed the stochastic nature of molecular-level surface sites that define a variety of reaction mechanisms, rates, and products even across a single surface. To bridge the molecular knowledge and predictive continuum-scale models, we propose to represent surface properties with probability distributions rather than with discrete constant values derived by averaging across a heterogeneous surface. This conceptual shift in continuum-scale modeling requires exponentially rising computational power. By incorporating our molecular-scale understanding of solid–water interfaces into continuum-scale models we can pave the way for next generation critical technologies and novel environmental solutions. 

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2. Large-scale dual AGN in large-scale cosmological hydrodynamical simulations

   https://doi.org/10.1093/mnras/stae2763  

   Puerto-Sánchez, Clara; Habouzit, Mélanie; Volonteri, Marta; Ni, Yueying; Foord, Adi; Anglés-Alcázar, Daniel; Chen, Nianyi; Guetzoyan, Paloma; Davé, Romeel; Di Matteo, Tiziana; et al (December 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Detecting dual active galactic nuclei (DAGNs) in observations and understanding theoretically which massive black holes (MBHs) compose them and in which galactic and large-scale environment they reside are becoming increasingly important questions as we enter the multimessenger era of MBH astronomy. This paper presents the abundance and properties of DAGN produced in nine large-scale cosmological hydrodynamical simulations. We focus on DAGN powered by AGN with $$L_{\rm bol}\geqslant 10^{43}\, \rm erg\, s^{-1}$$ and belonging to distinct galaxies, i.e. pairs that can be characterized with current and near-future electromagnetic observations. We find that the number density of DAGN separated by a few to 30 proper kpc varies from $$10^{-8}$$ (or none) to $$10^{-3} \, \rm comoving\, Mpc^{3}$$ in the redshift range $$z=0\!-\!7$$. At a given redshift, the densities of the DAGN numbers vary by up to two orders of magnitude from one simulation to another. However, for all simulations, the DAGN peak is in the range $$z=1\!-\!3$$, right before the peak of cosmic star formation or cosmic AGN activity. The corresponding fractions of DAGN (with respect to the total number of AGN) range from 0 per cent to 6 per cent. We find that simulations could produce too few DAGN at $z=0$ (or merge pairs too quickly) compared to current observational constraints while being consistent with preliminary constraints at high redshift ($$z\sim 3$$). Next-generation observatories (e.g. Advanced X-Ray Imaging Satellite [AXIS]) will be of paramount importance to detect DAGN across cosmic times. We predict the detectability of DAGN with future X-ray telescopes and discuss DAGN as progenitors for future Laser Interferometer Space Antenna (LISA) gravitational wave detections. 

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3. Local-scale Arctic tundra heterogeneity affects regional-scale carbon dynamics

   https://doi.org/10.1038/s41467-020-18768-z  

   Lara, M. J.; McGuire, A. D.; Euskirchen, E. S.; Genet, H.; Yi, S.; Rutter, R.; Iversen, C.; Sloan, V.; Wullschleger, S. D. (December 2020, Nature Communications)

   null (Ed.)

   Abstract In northern Alaska nearly 65% of the terrestrial surface is composed of polygonal ground, where geomorphic tundra landforms disproportionately influence carbon and nutrient cycling over fine spatial scales. Process-based biogeochemical models used for local to Pan-Arctic projections of ecological responses to climate change typically operate at coarse-scales (1km 2 –0.5°) at which fine-scale (<1km 2 ) tundra heterogeneity is often aggregated to the dominant land cover unit. Here, we evaluate the importance of tundra heterogeneity for representing soil carbon dynamics at fine to coarse spatial scales. We leveraged the legacy of data collected near Utqiaġvik, Alaska between 1973 and 2016 for model initiation, parameterization, and validation. Simulation uncertainty increased with a reduced representation of tundra heterogeneity and coarsening of spatial scale. Hierarchical cluster analysis of an ensemble of 21 st -century simulations reveals that a minimum of two tundra landforms (dry and wet) and a maximum of 4km 2 spatial scale is necessary for minimizing uncertainties (<10%) in regional to Pan-Arctic modeling applications. 

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4. Scale-free behavioral dynamics directly linked with scale-free cortical dynamics

   https://doi.org/10.7554/eLife.79950  

   Jones, Sabrina A; Barfield, Jacob H; Norman, V Kindler; Shew, Woodrow L (January 2023, eLife)

   Naturally occurring body movements and collective neural activity both exhibit complex dynamics, often with scale-free, fractal spatiotemporal structure. Scale-free dynamics of both brain and behavior are important because each is associated with functional benefits to the organism. Despite their similarities, scale-free brain activity and scale-free behavior have been studied separately, without a unified explanation. Here, we show that scale-free dynamics of mouse behavior and neurons in the visual cortex are strongly related. Surprisingly, the scale-free neural activity is limited to specific subsets of neurons, and these scale-free subsets exhibit stochastic winner-take-all competition with other neural subsets. This observation is inconsistent with prevailing theories of scale-free dynamics in neural systems, which stem from the criticality hypothesis. We develop a computational model which incorporates known cell-type-specific circuit structure, explaining our findings with a new type of critical dynamics. Our results establish neural underpinnings of scale-free behavior and clear behavioral relevance of scale-free neural activity. 

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5. Continental Scale Hydrostratigraphy: Basin‐Scale Testing of Alternative Data‐Driven Approaches

   https://doi.org/10.1111/gwat.13357  

   Tijerina‐Kreuzer, Danielle; Swilley, Jackson S.; Tran, Hoang V.; Zhang, Jun; West, Benjamin; Yang, Chen; Condon, Laura E.; Maxwell, Reed M. (October 2023, Groundwater)

   Abstract Integrated hydrological modeling is an effective method for understanding interactions between parts of the hydrologic cycle, quantifying water resources, and furthering knowledge of hydrologic processes. However, these models are dependent on robust and accurate datasets that physically represent spatial characteristics as model inputs. This study evaluates multiple data‐driven approaches for estimating hydraulic conductivity and subsurface properties at the continental‐scale, constructed from existing subsurface dataset components. Each subsurface configuration represents upper (unconfined) hydrogeology, lower (confined) hydrogeology, and the presence of a vertical flow barrier. Configurations are tested in two large‐scale U.S. watersheds using an integrated model. Model results are compared to observed streamflow and steady state water table depth (WTD). We provide model results for a range of configurations and show that both WTD and surface water partitioning are important indicators of performance. We also show that geology data source, total subsurface depth, anisotropy, and inclusion of a vertical flow barrier are the most important considerations for subsurface configurations. While a range of configurations proved viable, we provide a recommended Selected National Configuration 1 km resolution subsurface dataset for use in distributed large‐and continental‐scale hydrologic modeling. 

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