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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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At least 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Effect of Synthesis Method Using Varying Types of Micropore Level Sulfur Infiltration on Electrochemical Performance in Lithium–Sulfur Batteries

The role of physically restrained, noncrystalline sulfur species in rechargeable lithium–sulfur batteries is examined by electrochemical and high‐resolution material characterizations. Carbon–sulfur composites are created by melting and sublimation of sulfur in an isochoric reactor via the autogenic process. These noncrystalline sulfur cathodes demonstrate a high specific capacity of ≈1000 Ah kg −1 after 100 cycles with a gravimetric current of 557 A kg −1 . Interestingly, this high‐performance sulfur allotrope lacks a long‐range structural order: high‐resolution X‐ray diffraction, performed at the Advanced Photon Source, indicates the lack of crystalline (i.e., orthorhombic or monoclinic) sulfur in the nanoscale domain. Electrochemical and material characterizations suggest that noncrystalline sulfur is a consequence of synthesis and not necessarily evidence of electrochemical efficacy. Rather, a high rate capacity depends on sulfur distribution, in turn, controlled by synthesis pathway. At higher sulfur content, the performance of carbon–sulfur composites is limited by the available surface area in which crystalline sulfur coincides with reduced gravimetric capacity and greater charge transport impedance, suggesting suboptimal sulfur containment.

Dysart, Arthur Dence↗
DOE OSTI2021

Approximation of periodic Green's operator in real space using numerical integration and its use in fast Fourier transform-based micromechanical models

In this work, we propose an expression for the periodic first derivative of Green's function in real space. The proposed expression allows an alternative way of computing the periodic Green's operator based on periodically summing the free-space Green's operator in terms of an appropriate quadrature rule. We provide computational examples, which show the accuracy of the proposed approach, together with reduced spurious oscillations in the solution fields.

42 ENGINEERING↗
DOE OSTI2012

Event detection and sub-state discovery from biomolecular simulations using higher-order statistics: Application to enzyme adenylate kinase

Biomolecular simulations at millisecond and longer time-scales can provide vital insights into functional mechanisms. Because post-simulation analyses of such large trajectory datasets can be a limiting factor in obtaining biological insights, there is an emerging need to identify key dynamical events and relating these events to the biological function online, that is, as simulations are progressing. Recently, we have introduced a novel computational technique, quasi-anharmonic analysis (QAA) (Ramanathan et al., PLoS One 2011;6:e15827), for partitioning the conformational landscape into a hierarchy of functionally relevant sub-states. The unique capabilities of QAA are enabled by exploiting anharmonicity in the form of fourth-order statistics for characterizing atomic fluctuations. In this article, we extend QAA for analyzing long time-scale simulations online. In particular, we present HOST4MD—a higher-order statistical toolbox for molecular dynamics simulations, which (1) identifies key dynamical events as simulations are in progress, (2) explores potential sub-states, and (3) identifies conformational transitions that enable the protein to access those sub-states. We demonstrate HOST4MD on microsecond timescale simulations of the enzyme adenylate kinase in its apo state. HOST4MD identifies several conformational events in these simulations, revealing how the intrinsic coupling between the three subdomains (LID, CORE, and NMP) changes during the simulations. Further, it also identifies an inherent asymmetry in the opening/closing of the two binding sites. We anticipate that HOST4MD will provide a powerful and extensible framework for detecting biophysically relevant conformational coordinates from long time-scale simulations.

Ramanathan, Arvind↗
DOE OSTI2019

Assessing the mechanisms governing the daytime evolution of marine stratocumulus using large‐eddy simulation

Large‐eddy simulation (LES) output for a case of thin stratocumulus off the coast of California is examined in a mixed‐layer analysis framework to identify the specific mechanisms responsible for governing the evolution of the cloud system. An equation for cloud‐base height tendency isolates the individual cloud‐modulating mechanisms that control the evolution of boundary‐layer liquid‐water static energy ( S l ) and total water mixing ratio ( q T ). With a suitable spin‐up procedure, the control simulation performs admirably compared with observed estimates of liquid water content, vertical velocity variance, and radiative fluxes sampled during an aircraft field campaign. Investigation of the cloud response to various environmental forcing scenarios was addressed through a suite of sensitivity simulations, including variations in subsidence velocity, surface fluxes, wind shear near the inversion, and radiative forcing. In the control simulation, rising cloud‐base tendencies are associated with entrainment warming/drying and short‐wave absorption, whereas lowering cloud‐base tendencies are driven by long‐wave cooling. Even in the presence of substantial afternoon solar heating, entrainment fluxes remained active. The thin cloud demonstrated unexpected resiliency, with mixed‐layer analysis indicating that, as the short‐wave flux decreases later in the afternoon, the relative contribution of long‐wave cooling often becomes large enough to offset entrainment warming/drying and result in a reversal of cloud‐base tendency. The evolution of cloud‐base tendency is found to be insensitive to the net radiative flux divergence for most of the simulations (liquid water path ranging from ~10–50 g/m 2 ). Error analysis in comparison with LES S l and q T budgets suggests that our method of entrainment flux calculation could be improved by a more complete understanding of entrainment‐layer physics.

McMichael, Lucas A.↗