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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. RackSched: A Microsecond-Scale Scheduler for Rack-Scale Computers

   Zhu, Hang; Kaffes, Kostis; Chen, Zixu; Liu, Zhenming; Kozyrakis, Christos; Stoica, Ion (January 2021, OSDI 2021)

   null (Ed.)
3. RackSched: A Microsecond-Scale Scheduler for Rack-Scale Computers

   Zhu, Hang; Kaffes, Kostis; Chen, Zixu; Liu, Zhenming; Kozyrakis, Christos; Stoica, Ion; Jin, Xin (November 2020, 14th USENIX Symposium on Operating Systems Design and Implementation)

   null (Ed.)

   Low-latency online services have strict Service Level Objectives (SLOs) that require datacenter systems to support high throughput at microsecond-scale tail latency. Dataplane operating systems have been designed to scale up multi-core servers with minimal overhead for such SLOs. However, as application demands continue to increase, scaling up is not enough, and serving larger demands requires these systems to scale out to multiple servers in a rack. We present RackSched, the first rack-level microsecond-scale scheduler that provides the abstraction of a rack-scale computer (i.e., a huge server with hundreds to thousands of cores) to an external service with network-system co-design. The core of RackSched is a two-layer scheduling framework that integrates inter-server scheduling in the top-of-rack (ToR) switch with intra-server scheduling in each server. We use a combination of analytical results and simulations to show that it provides near-optimal performance as centralized scheduling policies, and is robust for both low-dispersion and high-dispersion workloads. We design a custom switch data plane for the inter-server scheduler, which realizes power-of-k- choices, ensures request affinity, and tracks server loads accurately and efficiently. We implement a RackSched prototype on a cluster of commodity servers connected by a Barefoot Tofino switch. End-to-end experiments on a twelve-server testbed show that RackSched improves the throughput by up to 1.44x, and scales out the throughput near linearly, while maintaining the same tail latency as one server until the system is saturated. 

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4. 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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5. 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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