SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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We calculated the kinetics of the simplest atmospheric reaction of a Criegee intermediate with a ketone by using our recently developed dual-level variational transition state theory scheme with the beyond-CCSD(T) electronic structure method W3X-L.
Detailed experimental and computational information on the response of lithium surfaces to irradiation by slow hydrogenic particles (ions, atoms, molecules) is sparse and mainly speculative. In this work, we present a computational study of the reflection and retention of deuterium (D) atoms at crystalline and amorphous lithium surfaces at 300 and 500 K, where the D atoms have an impact energy in the range of 0.025–5 eV and incident angles of 0° (perpendicular incidence) or 85° (near-grazing incidence). Classical molecular dynamics simulations are performed with the reactive bond-order force field (ReaxFF) potentials. This study provides quantitative information on the deuterium sticking probability and recycling coefficient for lithium surfaces. Further, our results support the ongoing work at the Lithium Tokamak eXperiment-β fusion experiment as well as relevant experiments in the laboratory setting.
Significance The kinetics of the structural evolution from crystalline ice (ice VII or ice VIII) toward thermodynamically stable ice I at ambient pressure have been characterized using time-resolved in situ X-ray diffraction. The time resolution captures events that were not observed previously and reveals a complex kinetic pathway with three distinctive transitions, i.e., amorphization, amorphous–amorphous, and crystallization of amorphous ice into ice I. The first two transitions exhibit different thermally activated mechanism above and below 110 K. Molecular-dynamics simulations show the transition involves a large change in density and substantial displacements of water at the nanoscale. This study presents a perspective on the metastability and complexity of the energy landscape in temperature/time-dependent structural evolution in amorphous ices.
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Higher-order topological insulators (HOTIs) have enticed enormous research interests owing to their novelty in supporting gapless states along the hinges of a crystal. Despite several theoretical predictions, enough experimental confirmation of the HOTI state in crystalline solids is still lacking. Here, it is shown that interplay between topology and magnetism can give rise to various magnetic topological states, including HOTI and axion insulator states. Here, using high-resolution angle-resolved photoemission spectroscopy combined with the first-principles calculations, we report a systematic study of the electronic structure and its evolution across the magnetic phase transition in EuIn 2 As 2 which possesses an antiferromagnetic ground state below 16 K. Antiferromagnetic EuIn 2 As 2 has been predicted to host both the axion insulator and the HOTI states.We directly observe the linearly dispersing holelike bands crossing the Fermi level and the change in their dispersion across the magnetic phase transition. Our paper points to EuIn 2 As 2 as being a promising material for the exploration of interplay between topology and magnetism.
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Zirconium nitride holds promise for improving nuclear reactor components, where thermal conductivity is important, highlighting the need for a detailed understanding of its phonons. However, the phonon dispersion derived from previous inelastic neutron scattering data is in disagreement with modern theoretical calculations, pointing to the necessity for further experimental validation. Here, in this study, we use inelastic neutron scattering experiments on polycrystalline ZrN at 6, 100, 300, 400, and 600 K, and density functional theory (DFT) calculations to study the momentum-resolved scattering and the phonon density of states. Both experimental and theoretical results reveal a phonon cutoff energy near 65 meV, in stark disagreement with previous single-crystal neutron scattering measurements indicating a cutoff near 75 meV. The 65 meV cutoff energy is, however, in reasonable agreement with previous measurements on ZrN 0.9 . Consistency between our theoretical and experimental results confirms that ZrN is a wide phonon band gap system and that DFT provides a reliable description of its phonons.
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Capacitance–voltage (C–V ) characteristics and carrier transport properties of 2-D electron gases (2DEGs) in an undoped Si/SiGe heterostructure at T = 4 – 35 K are presented here. In this work, two capacitance plateaus due to density saturation of the 2DEG in the buried Si quantum well (QW) are observed and explained by a model of surface tunneling. The peak mobility at 4 K is 4.1 × 10 5 cm 2 /V·s and enhanced by a factor of 1.97 at an even lower carrier density compared to the saturated carrier density, which is attributed to the effect of remote carrier screening. At T = 35 K, the mobility enhancement with a factor of 1.35 is still observed, which suggests the surface tunneling is still dominant.
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This data package contains temperature, moisture content, matric potential, and carbon dioxide (CO2) concentration data from the Rifle, Colorado field site and from a 2 meter tall laboratory soil/sediment column designed to simulate field conditions. In addition, redox potential data from the laboratory column are included. The purpose of the data and paper is to demonstrate how a laboratory column was constructed to reproduce the dynamics of nonisothermal conditions in the field, such that CO2 production above a variable-depth water table can be studied in the laboratory. The data package contains 3 data files corresponding to the figures in the related paper (Tokunaga, T. et al. 2018) and 1 README file with the paper information.
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