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In 2023, Jenny Hoffman ran across the United States in 47 days, smashing the women's world record. But she still found time to lead a research team. [ABSTRACT FROM AUTHOR]

Machine learning interatomic force fields are promising for combining high computational efficiency and accuracy in modeling quantum interactions and simulating atomistic dynamics. Active learning methods have been recently developed to train force fields efficiently and automatically. Among them, Bayesian active learning utilizes principled uncertainty quantification to make data acquisition decisions. In this work, we present a general Bayesian active learning workflow, where the force field is constructed from a sparse Gaussian process regression model based on atomic cluster expansion descriptors. To circumvent the high computational cost of the sparse Gaussian process uncertainty calculation, we formulate a high-performance approximate mapping of the uncertainty and demonstrate a speedup of several orders of magnitude. We demonstrate the autonomous active learning workflow by training a Bayesian force field model for silicon carbide (SiC) polymorphs in only a few days of computer time and show that pressure-induced phase transformations are accurately captured. The resulting model exhibits close agreement with both ab initio calculations and experimental measurements, and outperforms existing empirical models on vibrational and thermal properties. The active learning workflow readily generalizes to a wide range of material systems and accelerates their computational understanding. [ABSTRACT FROM AUTHOR]

Caroli-de Gennes-Matricon (CdGM) states were predicted in 1964 as low-energy excitations within vortex cores of type-II superconductors. In the quantum limit, the energy levels of these states were predicted to be discrete with the basic levels at ±μΔ2/EF (μ = 1/2, 3/2, 5/2, ...) with Δ the superconducting energy gap and EF the Fermi energy. However, due to the small ratio of Δ/EF in most type-II superconductors, it is very difficult to observe the discrete CdGM states, but rather a symmetric peak which appears at zero bias at the vortex center. Here we report the clear observation of these discrete energy levels of CdGM states in FeTe0.55Se0.45. The rather stable energies of these bound state peaks vs. space clearly validate our conclusion. Analysis based on the energies of these CdGM states indicates that the Fermi energy in the present system is very small. [ABSTRACT FROM AUTHOR]

The copepod genus Eurytemora occupies a wide range of habitat types throughout the Northern Hemisphere, with among the broadest salinity ranges of any known copepod. The epicenter of diversity for this genus lies along coastal Alaska, where several species are endemic. Systematic analysis has been difficult, however, because of a tendency toward morphological stasis in this genus, despite large genetic divergences among populations and species. The goals of this study were to (1) analyze patterns of morphological variation and divergence within this genus, focusing on Eurytemora species that occur in North America, and (2) determine patterns of geographic and salinity distribution of Eurytemora species within the ancestral range in Alaska. We applied a comparative multivariate morphological analysis using 16–26 characters from 125 specimens from 20 newly collected sites in Alaska and 15 existing samples predominantly from North America. Results from principal component and hierarchical cluster analyses identified seven distinct morphological species of Eurytemora in North America ( E. affinis, E. americana, E. canadensis, E. composita, E. herdmani, E. pacifica, and E. raboti), and identified diagnostic characters that distinguish the species (forming the basis for a new identification key). Several previously named species were regarded as synonyms. The sites we sampled in Alaska were remarkable in the high levels of sympatry of Eurytemora species, to a degree not seen outside of Alaska. Future studies of Eurytemora should shed light on patterns of habitat invasions and physiological evolution within the genus, and yield insights into mechanisms leading to its remarkably broad geographic and habitat range. [ABSTRACT FROM AUTHOR]