Ames National Laboratory

Abstract Our recent work on molecular evolution and population genetics postulated that individuals with a specific mutation exhibit a fluctuation in fitness, short for FSI (fluctuating selection among individuals), whereas the fitness effect of wildtype remains a constant. An intriguing phenomenon called selection-duality emerges, that is, a slightly beneficial mutation could be a negative selection (the substitution rate less than the mutation rate). It appears that selection-duality is bounded by two bounds: the generic neutrality where the mutation is neutral by the means of fitness on average, and the substitution neutrality where the substitution rate equals to the mutation rate. In addition, the middle point of generic neutrality and substitution neutrality is called the FSI- neutrality . An important problem is about the age profile of allele frequency, i.e., the arising timing of a mutation whose frequency in the current population is given ( the allele-age problem for short). Solving this problem under selection duality would help extend the standard coalescent theory that based on strict neutrality to a more general form under selection duality. In this paper, we studied the allele-age problem under selection-duality by the first arrival time approach and the mean age approach, respectively. Since the general solution of allele-age problem under selection duality is not available, we focused on solving the problem at the substitution neutrality (the up-bound of selection duality), the FSI-neutrality (the middle-point) and the generic neutrality (the low-bound), respectively. Our analysis results in an overall picture that the mean first-arrival age of a mutation at the substitution neutrality is theoretically identical to that at the FSI-neutrality, which is numerically close to that at the generic neutrality. For illustration, we calculated the mean age of nonsynonymous mutations in the human population and demonstrated that the estimated allele-age could be overestimated considerably when the effect of FSI was neglected.

Transition metal borides with a tetragonal structure are emerging as a strong candidate for rare-earth-free permanent magnet applications due to their inherently high magnetization, magnetocrystalline anisotropy, and Curie temperature. In this study, we developed (Fe0.7-xCo0.3Zrx)2 B (x = 0, 0.01, 0.02, 0.03, and 0.04) hard magnetic phase through arc melting followed by rapid solidification using melt spinning. X-ray diffraction (XRD) confirms the formation of a single phase tetragonal structure, with an average crystallite size in the range of ∼30-40 nm. Singular point detection (SPD) measurement showed that Zr incorporation enhances magnetocrystalline anisotropy, increasing the anisotropy field (Ha) from 7.5 to 9.5 kOe with an increase of Zr content from x = 0 to x = 0.03. Room-temperature magnetization loops reveal saturation magnetization (Ms) of 139–144 emu/g and an optimum coercivity of approximately 0.39 kOe. Additionally, Bloch’s law fitting of temperature-dependent saturation magnetization data suggests weakened ferromagnetic exchange interactions with increasing Zr content. These findings demonstrate that minor Zr incorporation significantly improves magnetic anisotropy, suggesting (Fe0.7Co0.3)2B-based alloys as promising candidates for next-generation, high-performance permanent magnets.

Chalcohalide semiconductors are rapidly gaining traction as stable, biocompatible materials for energy conversion applications. While the solid-state synthesis of bulk chalcohalides is relatively well-developed, the colloidal chemistry of these materials is still in its early stages. Colloidal semiconductors are often advantageous in device fabrication due to the cost effectiveness of solution processing. Thus, we aim to increase the utility of chalcohalides in device fabrication by establishing solution phase chemistry of promising compositions. We show that silyl-mediated deacetylation is a versatile and effective method of making colloidal PnChI (Pn = Sb, Bi; Ch = S, Se) and Sn2PnS2I3 (Pn = Sb, Bi) chalcohalides of tunable sizes and compositions. Furthermore, we demonstrate the preparation of mixed-pnictide chalcohalides through silyl-mediated deacetylation and/or cation exchange, the latter being one of the few reported instances in chalcohalides. Additionally, we use the thiocyanate heat up approach in combination with density functional theory to study halide mixing in quaternary tin chalcohalides. By pushing the limits of each synthetic technique, we have designed more soluble chalcohalides with tunable compositions while also gaining a better understanding of the efficacy of each procedure in respect to thin film and subsequent device fabrication. In addition to size and composition tuning, silyl-mediated deacetylation can help facilitate the future development and wide-scale application of chalcohalide-based devices by expanding the selection of solution-processable chalcohalides.

C-H bond functionalization of arenes with boranes continues to be a challenge in catalysis, with late and rare earth metals shown to be catalytically active. In this study, group IV metallocenes grafted onto acidic sulfated zirconia (SZO) are demonstrated to catalyze arene borylation with pinacolborane (HBpin). Catalysis studies at partial HBpin conversions (59-68%) using Cp₂M(Me)/SZO (M = Ti, Zr, or Hf; Cp = cyclopentadienyl) catalysts reveal that Zr exhibits greater selectivity and activity than Ti and Hf. At 0.16 mol% of Zr, Cp2ZrMe/SZO achieves 332 turnovers at high HBpin conversion (86 %), making this catalyst comparably active to previously reported Ir and Rh C-H borylation catalysts. At 160 °C, a maximum chemoselectivity of 82 % for PhBpin 2 was observed at 24% HBpin conversion. The superior activity of ionic Cp2ZrMe/SZO compared to neutral Cp2ZrMe/SiO2 demonstrates the borylation mechanism relies on the highly electrophilic, coordinatively unsaturated cationic sites stabilized by the weakly coordinating sulfated support. Furthermore, both catalysts significantly outperform their molecular analogues, Cp2ZrMe2 and [Cp2ZrMe][B(C6F5)4], suggesting that the support enhances catalytic performance by stabilizing the active species.

Phase-change memory (PCM) has emerged as a promising non-volatile memory technology, offering significant potential for next-generation artificial intelligence and neuromorphic computing systems. However, conventional Ge1Sb4Te7 (GST), a prototypical stoichiometric phase-change chalcogenide, suffers from intrinsic limitations such as inadequate thermal stability and pronounced resistance drift, hindering its practical applications in high-performance devices and chips. In this study, we demonstrate that carbon (C) doping in GST markedly enhances its thermal robustness and data retention, while elucidating the underlying microstructure property relationships. Carbon doping significantly increases the crystallization temperature of GST, shifting it to and beyond 200 °C with increasing carbon content. Higher carbon incorporation also yields up to a fourfold improvement in data retention, achieving 10-year stability at 100 °C. Moreover, GST-C-based PCM devices exhibit excellent electrical stability, featuring ultralow resistance drift (ν = 0.03) and highly reproducible multilevel resistance states. Through ab initio simulations, we uncover the atomic-scale mechanisms governing these enhancements: carbon incorporation induces the formation of robust, shortened bonds with Ge/Sb/Te, promoting tetrahedral C clusters that impede crystallization by elevating the activation energy barrier. This work identifies GST-C as a promising candidate for reliable, high-density PCM and highlights its potential for neuromorphic computing applications.