Particle-in-cell direct simulation Monte Carlo simulations reveal that ion-acoustic instabilities excited in presheaths can cause significant ion heating. Ion-acoustic instabilities are excited by the ion flow toward ...
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The physical growth of Polycyclic Aromatic Compounds (PACs) to soot particles plays a significant role in understanding the chemistry of soot formation. Insights into the process can be gained from PACs’ free energy ...
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The physical growth of Polycyclic Aromatic Compounds (PACs) to soot particles plays a significant role in understanding the chemistry of soot formation. Insights into the process can be gained from PACs’ free energy of dimerization landscape. However, because the infeasibly large space of possible PAC dimers cannot be exhaustively simulated, researchers must train machine learning models on a subset of data to impute the rest. To this end, we propose and assess an active learning approach to discovering the optimal PACs for training a machine learning model to predict PACs’ association and dissociation free energies. The comparison between active learning and random sampling showed that active learning has faster loss convergence, requiring fewer training samples to reach the same level of accuracy. The trained model accurately modeled unseen PACs and exhibited robustness against changes in the sampling space used to train the model. More broadly, this work shows how active learning can optimize the design and improve the understanding of more expensive models in specific domains.
The imidophosphorane ligand, [NP t Bu 3 ] − ( t Bu= tert -butyl), enables isolation of a pseudo-tetrahedral, tetravalent praseodymium complex, [Pr 4+ (NP t Bu 3 ) 4 ] ( 1-Pr ), which is characterized by a suite of phy...
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The imidophosphorane ligand, [NP t Bu 3 ] − ( t Bu= tert -butyl), enables isolation of a pseudo-tetrahedral, tetravalent praseodymium complex, [Pr 4+ (NP t Bu 3 ) 4 ] ( 1-Pr ), which is characterized by a suite of physical characterization methods including single-crystal X-ray diffraction, electron paramagnetic resonance, and L 3 -edge X-ray near-edge spectroscopies. Variable-temperature direct-current magnetic susceptibility data, supported by multiconfigurational quantum chemical calculations, demonstrate that the electronic structure diverges from the isoelectronic Ce 3+ analogue, driven by increased crystal field. The four-coordinate environment around Pr 4+ in 1-Pr , which is unparalleled in reported extended solid systems, provides a unique opportunity to study the interplay between crystal field splitting and spin-orbit coupling in a molecular tetravalent lanthanide within a pseudo-tetrahedral coordination geometry.
Transmission radiography using megaelectronvolt radiation is a powerful nondestructive method for determining elemental composition. Radiography is typically performed with either neutrons or photons, but neither of t...
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Transmission radiography using megaelectronvolt radiation is a powerful nondestructive method for determining elemental composition. Radiography is typically performed with either neutrons or photons, but neither of these probes is universally applicable. We experimentally demonstrate that a significant increase in the contrast for small elemental variations in object composition can be realized by combining the multiple-monoenergetic-neutron and multiple-monoenergetic-photon transmission radiography techniques. The multimodal source is based on deuteron-driven low-energy nuclear reactions that produce both neutrons and photons at discrete energies. The neutron time-of-flight technique is used to measure the transmission over a broad range of neutron energies and is combined with spectroscopic photon transmission radiography. This work demonstrates the use of a single, multiparticle, multiple-monoenergetic-radiation source and a single type of radiation detector to simultaneously perform neutron and photon spectroscopic radiography. Four different material-identification metrics are used, which show a factor-of-3-or-greater increase in sensitivity to changes in material composition when compared with traditional dual-energy photon radiography, and are in agreement with simulations that establish a direct correspondence to known photon and neutron interaction cross sections. Furthermore, the ability to infer the presence of objects consisting of impure elements, layers of different elements, or non-natural isotope concentrations is demonstrated.
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