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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

The effect of polymer stiffness on magnetization reversal of magnetorheological elastomers

Ultrasoft magnetorheological elastomers (MREs) offer convenient real-time magnetic field control of mechanical properties that provides a means to mimic mechanical cues and regulators of cells in vitro. Here, we systematically investigate the effect of polymer stiffness on magnetization reversal of MREs using a combination of magnetometry measurements and computational modeling. Poly-dimethylsiloxane-based MREs with Young’s moduli that range over two orders of magnitude were synthesized using commercial polymers Sylgard™ 527, Sylgard 184, and carbonyl iron powder. The magnetic hysteresis loops of the softer MREs exhibit a characteristic pinched loop shape with almost zero remanence and loop widening at intermediate fields that monotonically decreases with increasing polymer stiffness. A simple two-dipole model that incorporates magneto-mechanical coupling not only confirms that micrometer-scale particle motion along the applied magnetic field direction plays a defining role in the magnetic hysteresis of ultrasoft MREs but also reproduces the observed loop shapes and widening trends for MREs with varying polymer stiffnesses.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Tunability and Long-Range Enhancement of Resonance Energy Transfer Facilitated by Plasmonic Nanorods

Resonance energy transfer (RET) between molecules or quantum dots is an important process in many energy-related applications. Different environmental structures have been studied and demonstrated to be able to enhance the RET rates between a nearby donor–acceptor pair. In particular, cylindrical silver nanorods and nanowires have shown an extraordinary ability to transfer energy along their longitudinal axes over large distances. However, the detailed mechanism of such transfer and the effects on the molecular RET process are as yet elusive. In this study, we use the recently developed computational tool based on the plasmon-coupled RET method to systematically study the effects of nanorods with different dimensions on the RET rates. We find that highly frequency-dependent coupling factor (CF) spectra, whose amplitudes determine RET rates, can be obtained due to the localized surface plasmon polariton modes of the rods with nanoscale dimensions. Simple phenomenological models can be derived for the wavelengths of CF peaks in relation to the length and width of the nanorods, providing easy tunability for enhancing the RET rate in specific wavelength ranges. When coupled to longer rods with mesoscale lengths, exponential decay of the CF over long donor–acceptor distances with a small decay constant is observed, leading to the possibility of long-range RET processes. Furthermore, drumhead resonance modes emerge on the flat ends of the rod when the rod’s diameter reaches 300 nm, resulting in extra enhancement to RET rate compared to certain thinner rods. Furthermore, these findings shed new light on the mechanism of plasmonic enhancement with silver nanorods and establish design principles for how to optimally utilize these structures to manipulate RET processes for various applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Impact of Dispersion Solvent on Ionomer Thin Films and Membranes

Perfluorosulfonic acid (PFSA) ionomers are an important class of materials that many electrochemical devices rely on as their ion-conducting electrolyte. Often, PFSA films are prepared through solution-processing techniques. Previous research has demonstrated that the solvent environment affects PFSA dispersion conformation, but it is not clear to what extent (if at all) these conformational effects persist for thin films and membranes upon casting, nor how dispersion solvent impacts film formation during the drying process. Here in this paper, we explore these questions by systematically examining the effect of Thin Film all length scales affected by dispersion solvent water and n-propanol mixtures on PFSA thin-film formation and structure, membrane structure, and resulting properties. Using a combination of in situ, time-resolved grazing incidence X-ray scattering and tender wide-angle X-ray scattering, it is shown that films prepared from high-water-concentration dispersions exhibit stronger interactions and arrangement upon drying, and possess larger network domain sizes than those prepared from low-water-concentration dispersions. These stronger interactions likely manifest in greater network connectivity, as evidenced by enhanced conductivity for membranes and decreased water uptake for thin films. Significantly, these solvent-induced differences persist even after thermal annealing. It is clear that the dispersion solvent choice is a critical parameter controlling PFSA nano- and mesoscale structure and presents an important dial with which to direct PFSA macroscale properties.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Effect of recoils on soft-drop-groomed observables in 𝛾-tagged jets in a multistage approach

We investigate medium-induced modifications to jet substructure observables that characterize hard components in central Pb-Pb collisions at $\sqrt{𝑠_{𝑁⁢𝑁}}$ = 5.02 TeV. Using a multistage Monte Carlo simulation of in-medium jet shower evolution, we explore flavor-dependent medium effects through simulations of inclusive and 𝛾-tagged jets. The results show that quark jets undergo a nonmonotonic modification compared with gluon jets in observables such as the Pb-Pb to 𝑝−𝑝 ratio of the soft drop prong angle 𝑟 𝑔 , the relative prong transverse momentum 𝑘 𝑇,𝑔 , and the groomed mass 𝑚 𝑔 distributions. Due to this nonmonotonic modification, 𝛾-tagged jets, enriched in quark jets, provide surprisingly clear signals of medium-induced structural modifications, distinct from effects dominated by selection bias. Further systematic studies demonstrate that these effects are dominated by recoil medium response. This work highlights the potential of hard substructures in 𝛾-tagged jets as powerful tools for probing the jet-medium interactions in high-energy heavy-ion collisions, in particular by enabling detailed investigations of jet-medium parton scatterings via their associated medium response. All simulations for 𝛾-tagged jet analyses carried out in this paper used triggered events containing at least one hard photon, which highlights the utility of these observables for future Bayesian analysis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Effect of substrate tilt on sputter-deposited AuTa films

Gold-tantalum alloy films are of interest for biomedical and magnetically-assisted inertial confinement fusion applications. However, growth mechanisms of such Au-Ta alloy films are not well understood. Here, we systematically study the effect of substrate tilt on properties of films deposited by direct current magnetron sputtering from a AuTa alloy target. Experimental data is correlated with distributions of landing energies and incident angles of sputtered and backscattered species calculated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. Results reveal that the deposition rate and film density monotonically decrease with increasing substrate tilt. Properties are similar for films with a tilt of 40° and below: films are amorphous, with an average compressive stress of 0.5 GPa, a density of 16 g/cm 3 , and electrical resistivity of 200 μΩ cm. The critical substrate tilt angle for the onset of porosity, a transition to a reduced stress state, and an increase in electrical resistivity lies between 40 and 60°. Based on Monte Carlo simulations, these changes in film properties are correlated with an increase in the average impact angle of the ballistic component of atomic flux. Implications of these results to deposition onto non-planar substrates are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Investigating Kinetic Mechanisms of Soot Formation in Plasma Pyrolysis of Methane via Active Learning (Final Technical Report)

Plasma pyrolysis of methane is an effective route for zero-carbon hydrogen production. Yet, soot generated from pyrolysis of hydrocarbons is detrimental to the climate and human health. There is ample experimental and theoretical evidence that suggests polycyclic aromatic hydrocarbons (PAHs) are the molecular precursors to soot particles. The reaction pathways of PAH formation are intricately dependent on a multitude of process parameters, whose kinetic mechanisms are not well-understood in plasma pyrolysis. This project aims to leverage advances in the kinetic modeling of soot formation in combustion, as well as in surrogate modeling and active learning, to systematically investigate the effects of process parameter on the kinetics of PAH formation in plasma pyrolysis of methane. To this end, we propose to use the PAH formation kinetics model developed by the PPPL/PU group based on the well-established ABF and HACA mechanisms, coupled with low-temperature plasma models. We will develop an active learning (AL) framework based on Bayesian optimization to systematically and data-efficiently explore the complex and multivariable parameter space of plasma pyrolysis in order to quantify the effects of plasma and feed parameters on the ABF and HACA kinetic pathways. AL is the branch of machine learning concerned with systematically querying samples from a system (experimental or computational) to train a data-driven model that maps design parameters to a performance criterion. We will use the data generated via AL to perform global sensitivity analysis, combined with uncertainty quantification, to elucidate the impact of different reaction pathways on minimizing formation of soot precursors. This study will result in an improved understanding of kinetics of PAH formation in plasma pyrolysis and can pave the way for more advanced mechanistic studies (e.g., soot nucleation mechanisms). Additionally, the findings will be useful for establishing practical strategies for increasing the pyrolysis efficiency and producing high-grade carbon for synthesis of nanomaterials.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Simultaneous compression of NaCl, Au, and ruby: toward mutually consistent pressure scales

Here, we evaluate pressure consistency of equations of state (EOS) for NaCl and Au at 300 K. The simultaneous measurements of unit-cell volumes (V) with ruby R1 line shifts (Δλ) in a helium (He) loaded diamond cell effectively remove potential systematic errors. Compression and decompression data were automatically collected at 1 sec interval, yielding a dense dataset with >8,000 (V, Δλ) pairs each for NaCl and Au. Solidification of He has noticeable effects on both V and Delta lambda (hence P). Only data up to similar to 14 GPa, or 6000 (V, P) pairs, can be considered hydrostatic within the resolution. The P-V data are fitted to the Rydberg-Vinet and the 3 rd order Birch-Murnaghan EOS. Predicted pressures of these EOSs agree with those given by the Ruby2020 ruby scale to within +/- 0.05 GPa. Overall, pressures predicted by the Rydberg-Vinet EOS are in better agreement with the average of commonly used NaCl and Au pressure scales.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Influence of triangularity on the plasma response to resonant magnetic perturbations

The effect of the axisymmetric plasma shape on the non-axisymmetric plasma response to resonant magnetic perturbations is investigated in experiment and modeling for the DIII-D, EAST and ASDEX Upgrade tokamaks. Systematically modeling the effect of the triangularity, whilst keeping other equilibrium quantities largely unchanged, reveals that the plasma response is strongly suppressed at high triangularity compared to that at low triangularity. This is validated through targeted comparison with experiments at DIII-D, EAST, and ASDEX Upgrade. DIII-D and EAST magnetic measurements are used to validate simulations, while at ASDEX Upgrade the plasma edge displacement is measured. Both experiments and modeling find a reduced magnetic plasma response on the high-field side at high triangularity across devices. Multi-modal analysis of the simulation results extracts the mode structure and applied spectrum dependence of each mode. The amplitude of the dominant mode reveals similar trends with the edge resonance and radial displacement near the X-point, which suggests that the multi-mode plasma response provides another way to understand the edge localized mode (ELM) control physics. The plasma response is strongly reduced at high triangularity compared to that at low triangularity, which implies different ELM control effects as shaping is varied. Furthermore, these findings indicate that the plasma shape should be taken into consideration when designing an RMP-ELM control strategy in experiment, and that predictive plasma response calculations can be used to maximize access to RMP-ELM control in future devices by maximizing the coupling between coils and the plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1993

Comment on 'The semiannual variation of great geomagnetic storms and the postshock Russell-McPherron effect preceding coronal mass ejecta' by N. U. Crooker, E. W. Cliver and B. T. Tsurutani

It is proposed by Crooker et al. (1992) that for a subgroup of great geomagnetic storms, for which the associated strong southward IMF (B(S)) fields reside in the postshock plasma, preceding the driver gas of coronal mass ejections, such strong B(S) fields result from a 'major increase in the Russell-McPherron polarity effect, through a systematic pattern of compression and draping' of the Archimedean field in the x-y plane. The critics test the scenario proposed by Crooker et al., namely, that the Russell-McPherron polarity effect is a major contribution to the semiannual variable of intense geomagnetic storms. It is found by the critics that in the cases studied there is little difference between the B(S) values as measured in geocentric solar ecliptic and geocentric solar magnetospheric coordinates, and it is concluded that the Russell-McPherron mechanism cannot explain by itself the seasonal dependence of intense storms, for which the variation is the largest. Crooker et al. present arguments to show that the combined preshock and postshock Russell-McPherron effect remains the sole cause of the semiannual variation of great storm occurrence.

Gonzalez, W. D.↗
DOE OSTI2024

Mesoscale simulation of granular materials under weak shock compaction–pore size distribution effects

This research established a systematic method to generate various pore-size distributions (PSDs) and studied the effect of PSDs on the shock compaction response of granular materials using two-dimensional mesoscale simulations under identical porosity. Simulations utilized various PSDs for three particle shapes (circle, ellipse, and square). Contacting particle configurations using three PSDs, characterized by spatially uniform distributed pores to heterogeneous distributed pores, and non-contacting particle configurations under a single case of PSD were tested. The PSD of generated particle sets was characterized using coordination number, mean diameter, and bimodality coefficient as statistical metrics. Mesoscale simulations showed that regardless of the conditions of pore distributions, shock compaction of granular materials consistently demonstrates a precursor, shock compaction front, and end. However, the shock compaction velocity of contacting particles was dependent on the PSDs despite the constant initial porosity. The compaction velocity was faster in particle configurations with relatively uniform pore distributions than in heterogeneous pore distributions, which our study demonstrated can be attributed to particle rearrangement during compaction. Circular-shaped particles had high sensitivity in shock compaction response to the various PSDs. Furthermore, a contacting particle configuration tended to propagate the shock compaction wave relatively faster than particles that were in a non-contact configuration. This study established the relative importance of considering PSD as a metric over the coordination number in studies of the shock compaction response of granular materials. Further, insights are provided on the evolving shock substructure to characterize the shock compaction response of granular materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Using Substituted [Fe 4 N(CO) 12 ] – as a Platform To Probe the Effect of Cation and Lewis Acid Location on Redox Potential

The impact of cationic and Lewis acidic functional groups installed in the primary or secondary coordination sphere (PCS or SCS) of an (electro)catalyst is known to vary depending on the precise positioning of those groups. However, it is difficult to systematically probe the effect of that position. In this report we probe the effect of the functional group position and identity on the observed reduction potentials (E p,c ) using substituted iron clusters, [Fe 4 N(CO) 11 R] n , where R = NO + , PPh 2 -CH 2 CH 2–9 BBN, ( Me PTA + ) 2 , ( Me PTA + ) 4 , and H + , where n = 0, -1, +1, or +3 (9-BBN is 9-borabicyclo(3.3.1)nonane and Me PTA + is 1-methyl-1 azonia-3,5-diaza-7-phosphaadamantane). The cationic NO + and H + ligands cause anodic shifts of 700 and 320 mV, respectively, in E p,c relative to unsubstituted [Fe 4 N(CO) 12 ] – . Infra-red absorption band data, νCO, suggests that some of the 700 mV shift by NO + results from electronic changes to the cluster core. Furthermore, this contrasts with the effects of cationic MePTA + and H + which cause primarily electrostatic effects on E p,c . Lewis acidic 9-BBN in the SCS had almost no effect on E p,c .

14 SOLAR ENERGY↗
NASA NTRS1992

Propagation effects for land mobile satellite systems: Overview of experimental and modeling results

Models developed and experiments performed to characterize the propagation environment associated with land mobile communication using satellites are discussed. Experiments were carried out with transmitters on stratospheric balloons, remotely piloted aircraft, helicopters, and geostationary satellites. This text is comprised of compiled experimental results for the expressed use of communications engineers, designers of planned Land Mobile Satellite Systems (LMSS), and modelers of propagation effects. The results presented here are mostly derived from systematic studies of propagation effects for LMSS geometries in the United States associated with rural and suburban regions. Where applicable, the authors also draw liberally from the results of other related investigations in Canada, Europe, and Australia. Frequencies near 1500 MHz are emphasized to coincide with frequency bands allocated for LMSS by the International Telecommunication Union, although earlier experimental work at 870 MHz is also included.

Goldhirsh, Julius↗
NASA NTRS1995

Functional relationships among monitoring performance: Subjective report of thought process and compromising states of awareness

A biocybernetic system for use in adaptive automation was evaluated using EEG indices based on the beta, alpha, and theta bandwidths. Subjects performed a compensatory tracking task while their EEG was recorded and one of three engagement indices was derived: beta/(alpha + theta), beta/alpha, or 1/alpha. The task was switched between manual and automatic modes as a function of the subjects' level of engagement and whether they were under a positive or negative feedback condition. It was hypothesized that negative feedback would produce more switches between manual and automatic modes, and that the beta/(alpha + theta) index would produce the strongest effect. The results confirmed these hypotheses. There were no systematic changes in these effects over three 16-minute trials. Tracking performance was found to be better under negative feedback. An analysis of the different EEG bands under positive and negative feedback in manual and automatic modes found more beta power in the positive feedback/manual condition and less in the positive feedback/automatic condition. The opposite effect was observed for alpha and theta power. The implications of biocybernetic systems for adaptive automation are discussed.

Freeman, Frederick↗
DOE OSTI2026

Improving unfolding and systematic uncertainty estimation using generative diffusion networks (Final Technical Report)

This final technical report summarizes the key accomplishments on the unfolding using diffusion model project, a DOE award received by PI Pierre-Hugues Beauchemin at Tufts University. This project main goal was to investigate the potential of diffusion models for unfolding experimental High Energy Physics data from detector effects while controlling systematics uncertainties. The project accomplished its goals by completing the following objectives: 1) Performing an object-by-object, event-by-event unfolding of various kinematic distributions reconstructed from detector data in HEP in a way that keeps correlations between unfolded observables while demonstrating competitive performance compared to standard algorithms used in the field; 2) Address the generalization problem by developing an unfolding algorithm capable to correctly infer the underlying distributions of observables and processes never seen before, while controlling the dominant theoretical uncertainties affecting the process, therefore increasing the effectiveness, the precision, and the applicability of the developed algorithm; 3) Understand the theoretical foundations between the developed algorithm so to extend it to applications beyond experimental HEP, for broader benefits to the society. This report provides an overview of the accomplishments related to each of these key objectives.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

A systems genetics approach to deciphering the effect of dosage variation on leaf morphology in Populus

Abstract Gene copy number variation is frequent in plant genomes of various species, but the impact of such gene dosage variation on morphological traits is poorly understood. We used a large population of Populus carrying genomically characterized insertions and deletions across the genome to systematically assay the effect of gene dosage variation on a suite of leaf morphology traits. A systems genetics approach was used to integrate insertion and deletion locations, leaf morphology phenotypes, gene expression, and transcriptional network data, to provide an overview of how gene dosage influences morphology. Dosage-sensitive genomic regions were identified that influenced individual or pleiotropic morphological traits. We also identified cis-expression quantitative trait loci (QTL) within these dosage QTL regions, a subset of which modulated trans-expression QTL as well. Integration of data types within a gene co-expression framework identified co-expressed gene modules that are dosage sensitive, enriched for dosage expression QTL, and associated with morphological traits. Functional description of these modules linked dosage-sensitive morphological variation to specific cellular processes, as well as candidate regulatory genes. Together, these results show that gene dosage variation can influence morphological variation through complex changes in gene expression, and suggest that frequently occurring gene dosage variation has the potential to likewise influence quantitative traits in nature.

Biochemistry & Molecular Biology↗
DOE OSTI2021

Layer-Dependent Pressure Effect on the Electronic Structure of 2D Black Phosphorus

Through infrared spectroscopy, we systematically study the pressure effect on electronic structures of few-layer black phosphorus (BP) with layer number ranging from 2 to 13. We reveal that the pressure-induced shift of optical transitions exhibits strong layer dependence. In sharp contrast to the bulk counterpart which undergoes a semiconductor to semimetal transition under ~1.8 GPa, the band gap of 2 L increases with increasing pressure until beyond 2 GPa. Meanwhile, for a sample with a given layer number, the pressure-induced shift also differs for transitions with different indices. Through the tight-binding model in conjunction with a Morse potential for the interlayer coupling, this layer- and transition-index-dependent pressure effect can be fully accounted. Our study paves a way for versatile van der Waals engineering of two-dimensional BP.

2-dimensional systems↗
DOE OSTI2026

Process-driven roadmap for depositing super duplex stainless steel via wire Arc additive manufacturing

Here, this study systematically investigates the effects of shielding gas, bead spacing, weld mode, and travel speed on the phase balance, porosity, and hardness of wire arc additively manufactured (WAAM) super duplex stainless steel (ER2594). Robotic WAAM was employed to fabricate multilayer walls under systematically varied process conditions, followed by phase transformation simulations, X-ray computed tomography (XCT), electron backscatter diffraction (EBSD), and microhardness evaluation. Thermodynamic simulations predicted rapid cooling of AM process can suppress the potential formation of deleterious precipitates which was later validated via cross-sectional microstructure analyses of printed samples. XCT revealed porosity levels below 0.2% for all deposits, with reduced travel speed significantly lowering defect volume. Microstructural analyses revealed the evolution of various austenite precipitates, including grain boundary austenite (GBA), Widmanstätten austenite (WA), and intergranular austenite (IGA), sequentially upon cooling of the ferrite phase. Among all process parameters, weld transfer mode exhibited the strongest influence on phase balance; pulsed mode promoted higher ferrite retention (~ 36%) compared to RapidX mode. No consistent relationship between stabilized phase fraction and captured microhardness was observed. This work provides critical insights for optimizing WAAM parameters to control phase balance and mechanical performance, which is essential for producing high-integrity super duplex stainless-steel components for nuclear and marine applications.

Grain orientation↗
DOE OSTI2023

Macroscale property assessment and indentation characteristics of thick section friction stir welded AA 5083

The spatial gradients in microstructure have been proven to be effective in optimizing the performance of components, and several techniques have been developed to achieve this microstructure. Nevertheless, the local microstructural modification methods inevitably result in the formation of gradient microstructure leading to a variation in the property. Herein this work systematically investigates the effect of gradient microstructure formed during thick section friction stir weld Al5083 alloy on its mechanical properties. A novel macro-indentation technique, profilometer-based indentation plastometry (PIP), is utilized to capture the variation in the mechanical properties in the feedstock (rolled plate) and weld region. The feedstock exhibited a gradient microstructure owing to different stress states during rolling. Additionally, the stirring of the tool resulted in a complex material flow pattern producing a microstructure gradient in the weld region. The aspect ratio of the grains was identified as the primary factor causing variation in indentation response in the feedstock. In contrast, variation in the grain size in the weld region resulted in property variation. Overall, the stir zone has a lower yield strength (158±4MPa) than the base material (173±3MPa). In addition, microstructure heterogeneity in the stir zone resulted in lower elongation than the base material.

36 MATERIALS SCIENCE↗