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Clusters of nitrogen- and carbon-coordinated transition metals dispersed in a carbon matrix (e. g., Fe−N−C) have emerged as an inexpensive class of electrocatalysts for the oxygen reduction reaction (ORR). Here, it was shown that optimizing the interaction between the nitrogen-coordinated transition metal clusters embedded in a more stable and corrosion-resistant carbide matrix yielded an ORR electrocatalyst with enhanced activity and stability compared to Fe−N−C catalysts. Utilizing first-principles calculations, an electrostatics-based descriptor of catalytic activity was identified, and nitrogen-coordinated iron (FeN4) clusters embedded in a TiC matrix were predicted to be an efficient platinum-group metal (PGM)-free ORR electrocatalyst. Guided by theory, selected catalyst formulations were synthesized, and it was demonstrated that the experimentally observed trends in activity fell exactly in line with the descriptor-derived theoretical predictions. The Fe−N−TiC catalyst exhibited enhanced activity (20 %) and durability (3.5-fold improvement) compared to a traditional Fe−N−C catalyst. It was posited that the electrostatics-based descriptor provides a powerful platform for the design of active and stable PGM-free electrocatalysts and heterogenous single-atom catalysts for other electrochemical reactions. 

We present Grapple, a new and powerful framework for explicit-state model checking on GPUs. Grapple is based on swarm verification (SV), a model-checking technique wherein a collection or swarm of small, memory- and time-bounded verification tests (VTs) are run in parallel to perform state-space exploration. SV achieves high state-space coverage via diversification of the search strategies used by constituent VTs. Grapple represents a swarm implementation for the GPU. In particular, it runs a parallel swarm of internally-parallel VTs, which are implemented in a manner that specifically targets the GPU architecture and the SIMD parallelism its computing cores offer. Grapple also makes effective use of the GPU shared memory, eliminating costly inter-block communication overhead. We conducted a comprehensive performance analysis of Grapple focused on the various design parameters, including the size of the queue structure, implementation of guard statements, and nondeterministic exploration order. Tests are run with multiple hardware configurations, including on the Amazon cloud. Our results show that Grapple performs favorably compared to the SPIN swarm and a prior non-swarm GPU implementation. Although a recently debuted FPGA swarm is faster, the deployment process to the FPGA is much more complex than Grapple's. 

We measure the branching fraction of the decay $B^{-}\to D^0\rho (770{)}^{-}$using data collected with the Belle II detector. The data contain 387 million $B\overline{B}$pairs produced in $e^{+}{e}^{-}$collisions at the $\mathrm{\Upsilon }\left(4S\right)$resonance. We reconstruct $8360\pm 180$decays from an analysis of the distributions of the $B^{-}$energy and the $\rho (770{)}^{-}$helicity angle. We determine the branching fraction to be $(0.939\pm 0.021\left(\mathrm{stat}\right)\pm 0.050\left(\mathrm{syst}\right))\%$, in agreement with previous results. Our measurement improves the relative precision of the world average by more than a factor of two. Published by the American Physical Society2024 

We report on a search for a resonance $X$decaying to a pair of muons in $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}X$events in the $0.212–9.000\mathrm{GeV}/c^2$mass range, using $178{\mathrm{fb}}^{-1}$of data collected by the Belle II experiment at the SuperKEKB collider at a center of mass energy of 10.58 GeV. The analysis probes two different models of $X$beyond the standard model: a $Z^{\prime }$vector boson in the $L_{\mu }-L_{\tau }$model and a muonphilic scalar. We observe no evidence for a signal and set exclusion limits at the 90% confidence level on the products of cross section and branching fraction for these processes, ranging from 0.046 fb to 0.97 fb for the $L_{\mu }-L_{\tau }$model and from 0.055 fb to 1.3 fb for the muonphilic scalar model. For masses below $6\mathrm{GeV}/c^2$, the corresponding constraints on the couplings of these processes to the standard model range from 0.0008 to 0.039 for the $L_{\mu }-L_{\tau }$model and from 0.0018 to 0.040 for the muonphilic scalar model. These are the first constraints on the muonphilic scalar from a dedicated search. Published by the American Physical Society2024