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1. Generation of Archean TTGs via sluggish subduction

   https://doi.org/10.1130/G52196.1  

   Foley, Bradford J (June 2024, Geology)

   Abstract The trondhjemite-tonalite-granodiorite (TTG) suite of rocks prominent in Earth’s Archean continents is thought to form by melting of hydrated basalt, but the specific tectonic settings of formation are unclear. Models for TTG genesis range from melting of downgoing mafic crust during subduction into a hotter mantle to melting at the base of a thick crustal plateau; while neither uniquely defines a global tectonic regime, the former is consistent with mobile lid tectonics and the latter a stagnant lid. One major problem for a subduction model is slabs sinking too quickly and steeply in a hotter mantle to melt downgoing crust. I show, however, that grain size reduction in the lithosphere leads to relatively strong plate boundaries on the early Earth, which slow slab sinking. During this “sluggish subduction,” sinking plates can heat up enough to melt when the mantle temperature is ≳1600 °C. Crustal melting via sluggish subduction can thus explain TTG formation during the Archean due to elevated mantle temperatures and the paucity of TTG production since due to mantle cooling. 

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2. Interactions Between Fire Refugia and Climate-Environment Conditions Determine Mesic Subalpine Forest Recovery After Large and Severe Wildfires

   https://doi.org/10.3389/ffgc.2022.890893  

   Busby, Sebastian U.; Holz, Andrés (May 2022, Frontiers in Forests and Global Change)

   Infrequent stand-replacing wildfires are characteristic of mesic and/or cool conifer forests in western North America, where forest recovery within high-severity burn patch interiors can be slow, yet successful over long temporal periods (decades to centuries). Increasing fire frequency and high-severity burn patch size, under a warming climate, however, may challenge post-fire forest recovery, promoting landscape-level shifts in forest structure, composition, and distribution of non-forest patches. Crucial to a delay and/or impediment to this shift, fire refugia (i.e., remnant seed sources) may determine forest recovery trajectories and potential forest state-transitions. To examine how fire refugia attributes (i.e. extent, composition, and structure) interact with local climate and environmental conditions to determine post-fire forest recovery responses, we developed fine-grain maps of fire refugia via remote sensing and conducted field-based assessment of post-fire conifer tree establishment largely originating (i.e., dispersed) from fire refugium in the Central Cascade Range of the Pacific Northwest United States. We found that limitations on seed availability, represented by the distance 2 -weighted density (D 2 WD) of fine-grain refugia extent, largely explained post-fire tree establishment responses within our relatively mesic and cool subalpine study sites. Interactions between seed availability, climate, and environmental conditions indicated that the structural attributes of refugia (e.g., tree height) and site abiotic/biotic environmental controls (e.g., climate water deficit, canopy cover, and coarse woody debris cover) interplayed to constrain or enhance species-specific tree establishment responses. Importantly, these interactions illustrate that when seed availability is critically low for a given area, climate-environment conditions may strongly determine whether forests recover following fire(s). Toward modelling and predicting tree establishment responses and potential forest state-transitions after large stand-replacing fires(s), our study demonstrates the importance of accurately quantifying seed availability via the fine-grain extent, configuration, and attributes of remnant seed source legacies. 

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3. Generalized Flow-Graph Programming Using Template Task-Graphs: Initial Implementation and Assessment

   https://doi.org/10.1109/IPDPS53621.2022.00086  

   Schuchart, Joseph; Nookala, Poornima; Javanmard, Mohammad Mahdi; Herault, Thomas; Valeev, Edward F.; Bosilca, George; Harrison, Robert J. (May 2022, 2021 IEEE International Parallel and Distributed Processing Symposium Workshops (IPDPSW))

   We present and evaluate TTG, a novel programming model and its C++ implementation that by marrying the ideas of control and data flowgraph programming supports compact specification and efficient distributed execution of dynamic and irregular applications. Programming interfaces that support task-based execution often only support shared memory parallel environments; a few support distributed memory environments, either by discovering the entire DAG of tasks on all processes, or by introducing explicit communications. The first approach limits scalability, while the second increases the complexity of programming. We demonstrate how TTG can address these issues without sacrificing scalability or programmability by providing higher-level abstractions than conventionally provided by task-centric programming systems, without impeding the ability of these runtimes to manage task creation and execution as well as data and resource management efficiently. TTG supports distributed memory execution over 2 different task runtimes, PaRSEC and MADNESS. Performance of four paradigmatic applications (in graph analytics, dense and block-sparse linear algebra, and numerical integrodifferential calculus) with various degrees of irregularity implemented in TTG is illustrated on large distributed-memory platforms and compared to the state-of-the-art implementations. 

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4. Synthesis of pigeonites for spectroscopic studies

   https://doi.org/10.2138/am-2019-6869CCBYNCND  

   Lindsley, D. H.; Nekvasil, H.; Glotch, T. D. (January 2019, The American mineralogist)

   Pigeonite (P21/c clinopyroxene) crystallizes in various terrestrial and extraterrestrial rocks. However, because it breaks down (“inverts”) in slowly cooled rocks, bulk natural samples of pigeonite from coarse-grained rocks are not available. We have synthesized eight samples of pigeonite with compositions of Wo8 and Wo10 [where Wo (mol%) = 100Ca/(Ca+Mg+Fe2+)] and X ranging from 20 to 60 [where X = 100Fe2+/(Mg+Fe2+)]. These samples are suitable for spectroscopic and other studies that require bulk samples. Because of relatively fine grain size (mainly 5–50 mm) and slight grain-to grain variation in composition, they are generally not suitable for studies requiring individual crystals. We will make samples available for appropriate investigations, especially if the techniques used are non-destructive and the samples can be returned after use. 

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5. Process-microstructure relationship of laser processed thermoelectric material Bi2Te3

   https://doi.org/10.3389/femat.2022.1046694  

   Oztan, Cagri; Şişik, Bengisu; Welch, Ryan; LeBlanc, Saniya (December 2022, Frontiers in Electronic Materials)

   Additive manufacturing allows fabrication of custom-shaped thermoelectric materials while minimizing waste, reducing processing steps, and maximizing integration compared to conventional methods. Establishing the process-structure-property relationship of laser additive manufactured thermoelectric materials facilitates enhanced process control and thermoelectric performance. This research focuses on laser processing of bismuth telluride (Bi 2 Te 3 ), a well-established thermoelectric material for low temperature applications. Single melt tracks under various parameters (laser power, scan speed and number of scans) were processed on Bi 2 Te 3 powder compacts. A detailed analysis of the transition in the melting mode, grain growth, balling formation, and elemental composition is provided. Rapid melting and solidification of Bi 2 Te 3 resulted in fine-grained microstructure with preferential grain growth along the direction of the temperature gradient. Experimental results were corroborated with simulations for melt pool dimensions as well as grain morphology transitions resulting from the relationship between temperature gradient and solidification rate. Samples processed at 25 W, 350 mm/s with 5 scans resulted in minimized balling and porosity, along with columnar grains having a high density of dislocations. 

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