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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 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Surface acetone reactions on ZnxZryOz: A DRIFTS-MS study

We report a systematic DRIFTS-MS study of surface acetone aldolization and self-deoxygenation reactions on ZrO2 and Zn1Zr10Oz, using temperature programmed surface reactions of both acetone reactant and possible intermediate compounds including diacetone alcohol, mesityl oxide, phorone, and isophorone. DRIFTS was used to monitor the evolution of surface species while MS was used to track corresponding gas phase products, in an attempt to identify the distinct reaction pathways observed on the two catalysts as well as the role zinc plays in the corresponding reaction pathways. It is found that aldol condensation (or aldolization) of acetone occurs readily at low temperature (298?K), forming mainly acetone dimers (i.e., diacetone alcohol, DAA/mesityl oxide, MSO) on both ZrO2 and Zn1Zr10Oz with the latter being more active. At elevated temperatures, secondary MSO reactions are diverted, mainly caused by the different Lewis basicity on the two catalysts. Over ZrO2, MSO reacts with activated acetone (acetone enolate) to form a surface 4,4-dimethyl-2,6-heptadione (phorone-C), which is further converted into a stable isophorone intermediate. At temperatures above 473?K, polymerization/oligomerization of isophorone along with basic hydroxyl promoted decomposition reactions occur, leading to the formation of heavier carbonaceous surface species and gas-phase side products (methane and CO2). The addition of zinc balances the surface acid-base properties on ZnxZryOz (i.e., Zn1Zr10Oz) via not only enhancing the surface Lewis basicity but passivating the strong acidity. This balance, especially the enhanced surface Lewis basicity largely promotes the a-H abstraction of MSO to form MSO enolate on the Zn1Zr10Oz, which thus favors the aldolization of MSO enolate and acetone, a reaction tends to form 2,6-dimethyl-2,5-heptadien-4-one (phorone-A). Phorone-A then readily decomposes to produce isobutene as a major product at temperature as low as 373?K. Note that, despite the facile formation of isobutene at low temperatures, a high temperature (673?K) is still necessary to release the strongly adsorbed formate/carbonate/acetate species via CO2 formation.

Li, Houqian↗
DOE OSTI2018

Microstructure evolution and a new mechanism of B2 phase on room temperature mechanical properties of Ti-47Al-2Cr-2Nb alloy prepared by hot isostatic pressing

Highlights: • The microstructure evolution of Ti-47Al-2Cr-2Nb alolly was investigated in detail. • The foramtion of B{sub 2} phase can be adjusted in Ti-47Al-2Cr-2Nb alloy. • A new mechanism of B{sub 2} phase on room temperature mechanical properties of Ti-47Al-2Cr-2Nb alloy was proposed. - Abstract: The formation of B{sub 2} phase was adjusted via various hot isostatic pressing processes in Ti-47Al-2Cr-2Nb alloy. The microstructure evolution and a new mechanism of B{sub 2} phase on room temperature mechanical properties was investigated by BSE, EBSD and TEM in detail. The result shows that the formation of B{sub 2} phase leads to Cr element content decrease in γ matrix phase, which results in lattice parameter increase, namely the c/a ratio of γ matrix phase. Finally, at room temperature the mechanical properties of Ti-47Al-2Cr-2Nb alloy deteriorates.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Porous NaTi2(PO4)3@C nanocubes as improved anode for sodium-ion batteries

Highlights: • Porous NaTi{sub 2}(PO{sub 4}){sub 3}@C nanocubes are synthesized. • Oleic acid is utilized as the carbon source. • NaTi{sub 2}(PO{sub 4}){sub 3}@C is to be measured at 0.01–3 V for SIBs. • NaTi{sub 2}(PO{sub 4}){sub 3}@C achieves 201 mAh g{sup −1} at 100 mA g{sup −1} after 100 cycles. • NaTi{sub 2}(PO{sub 4}){sub 3}@C delivers 140 mAh g{sup −1} at 1 A g{sup −1} for 1000 times. - Abstract: The NASICON-type NaTi{sub 2}(PO{sub 4}){sub 3} has drawn much attention as anode material for sodium-ion batteries owing to its stable structural characteristics and low cost. Nevertheless, the insulating property of NaTi{sub 2}(PO{sub 4}){sub 3} and the high working potential of about 2.1 V vs. Na{sup +}/Na lead to its poor cycling stability, low rate performance as well as inferior capacity. In this work, we synthesize the porous NaTi{sub 2}(PO{sub 4}){sub 3}@C nanocubes by hydrothermal method and a subsequent coating process with using oleic acid as the carbon source. When utilized as the anode for sodium-ion battery in the voltage range between 0.01 V and 3.0 V, The as-synthesized porous NaTi{sub 2}(PO{sub 4}){sub 3}@C nanocubes deliver a discharge capacity of 201 mAh·g{sup −1} at the current density of 100 mA g{sup −1} after 100 cycles. Additionally, the reserved capacity of 140 mAh·g{sup −1} could be achieved at the current density of 1 A g{sup −1} after 1000 cycles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Enhanced DSSCs performance of TiO2 nanostructure by surface passivation layers

Highlights: • Passivation layers of MgO, CaCO{sub 3}, ZrO{sub 2} and SnO{sub 2} on TiO{sub 2} electrode deposited in copper container by spin coating method. • XRD and EDX analysis give detail information about surface passivation layers deposition on TiO{sub 2} electrode. • Achieved highest efficiency for electrode with MgO passivation layer it is about 6.05%. • Highest electron lifetime of 0.65 ms. - Abstract: Rutile titanium oxide (TiO{sub 2}) synthesized in copper containers, was spin-coated with different surface passivation layers such as magnesium oxide (MgO), calcium carbonate (CaCO{sub 3}), zirconium oxide (ZrO{sub 2}), and tin oxide (SnO{sub 2}). The deposition of these passivation layers on TiO{sub 2} confirmed with the help of XRD and EDX analysis, leads to changes in surface morphology induced by the passivation layers demonstrated by FE-SEM imaging. The highest photoconversion efficiency obtained for TiO{sub 2} electrode with MgO passivation layer (6.05%), respective incident photon conversion efficiency was 52%. After introduction of passivation layers on the TiO{sub 2} nanostructure, electron lifetime increased from 0.48 ms to 0.65 ms and charge transfer resistance decreased from 36.9 Ω cm (pristine TiO{sub 2} electrode) to 20.16 Ω cm (MgO passivation layer).

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Witnessing light-driven entanglement using time-resolved resonant inelastic X-ray scattering

Abstract Characterizing and controlling entanglement in quantum materials is crucial for the development of next-generation quantum technologies. However, defining a quantifiable figure of merit for entanglement in macroscopic solids is theoretically and experimentally challenging. At equilibrium the presence of entanglement can be diagnosed by extracting entanglement witnesses from spectroscopic observables and a nonequilibrium extension of this method could lead to the discovery of novel dynamical phenomena. Here, we propose a systematic approach to quantify the time-dependent quantum Fisher information and entanglement depth of transient states of quantum materials with time-resolved resonant inelastic x-ray scattering. Using a quarter-filled extended Hubbard model as an example, we benchmark the efficiency of this approach and predict a light-enhanced many-body entanglement due to the proximity to a phase boundary. Our work sets the stage for experimentally witnessing and controlling entanglement in light-driven quantum materials via ultrafast spectroscopic measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Rejuvenation as the origin of planar defects in the CrCoNi medium entropy alloy

Abstract High or medium- entropy alloys (HEAs/MEAs) are multi-principal element alloys with equal atomic elemental composition, some of which have shown record-breaking mechanical performance. However, the link between short-range order (SRO) and the exceptional mechanical properties of these alloys has remained elusive. The local destruction of SRO by dislocation glide has been predicted to lead to a rejuvenated state with increased entropy and free energy, creating softer zones within the matrix and planar fault boundaries that enhance the ductility, but this has not been verified. Here, we integrate in situ nanomechanical testing with energy-filtered four-dimensional scanning transmission electron microscopy (4D-STEM) and directly observe the rejuvenation during cyclic mechanical loading in single crystal CrCoNi at room temperature. Surprisingly, stacking faults (SFs) and twin boundaries (TBs) are reversible in initial cycles but become irreversible after a thousand cycles, indicating SF energy reduction and rejuvenation. Molecular dynamics (MD) simulation further reveals that the local breakdown of SRO in the MEA triggers these SF reversibility changes. As a result, the deformation features in HEAs/MEAs remain planar and highly localized to the rejuvenated planes, leading to the superior damage tolerance characteristic in this class of alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Rising atmospheric moisture escalates the future impact of atmospheric rivers in the Antarctic climate system

Abstract Despite their relative rarity, atmospheric rivers are key contributors to the surface mass balance of Antarctica. However, the future role of atmospheric rivers in modulating Antarctic sea-level contributions is a major area of uncertainty. Here, we leverage high-resolution climate simulations to show that Antarctic atmospheric rivers are highly sensitive to future increases in atmospheric moisture, leading to a doubling of atmospheric river frequencies and 2.5 × increase in precipitation from 2066–2100 under present-day thresholds for atmospheric river detection. However, future precipitation impacts are critically dependent on the detection threshold: accounting for moisture increases in the threshold produces smaller, regional changes in atmospheric river frequency, primarily resulting from an eastward shift in the polar jet maximum wind speeds. Our results underscore the importance of using large ensembles to quantify Antarctic atmospheric river responses to variability in projected moisture, which may not be captured when using only a few ensemble members.

Environmental Sciences & Ecology↗
DOE OSTI2024

Dipolar focusing in laser-assisted positronium formation

Abstract We consider positronium formation in collisions of positrons with excited hydrogen atoms H(n) in an infrared laser field theoretically. This process is assisted by the dipolar focusing effect: a positron moving in a superposition of a laser field and the dipolar field can approach the atomic target even if its trajectory starts with a very large impact parameter, leading to a significant enhancement of the Ps formation cross section. The classical trajectory Monte Carlo method, which is justified for n ⩾ 3 , allows efficient calculation of this enhancement. A similar effect can occur in collisions of positrons with other atoms in excited states, which can lead to improvements in the efficiency of positronium formation.

Optics↗
DOE OSTI2021

The cosmological evolution of self-interacting dark matter

We study the evolution of cosmological perturbations in dark-matter models with elastic and velocity-independent self interactions. Such interactions are imprinted in the matter-power spectrum as dark acoustic oscillations, which can be experimentally explored to determine the strength of the self scatterings. Models with self interactions have similarities to warm dark matter, as they lead to suppression of power on small scales when the dark-matter velocity dispersion is sizable. Nonetheless, both the physical origin and the extent of the suppression differ for self-interacting dark matter from conventional warm dark matter, with a dark sound horizon controlling the reduction of power in the former case, and a free-streaming length in the latter. We thoroughly analyze these differences by performing computations of the linear power spectrum using a newly developed Boltzmann code. We find that while current Lyman-α data disfavor conventional warm dark matter with a mass less than 5.3 keV, when self interactions are included at their maximal value consistent with bounds from the Bullet Cluster, the limits are relaxed to 4.4 keV. Lastly, we make use of our analysis to set novel bounds on light scalar singlet dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

SDSS J0159 as an outlier in the M BH–σ space: further clues to support a central tidal disruption event?

ABSTRACT In this Letter, properties of black hole (BH) mass are well checked for the interesting object SDSS J0159, a changing-look active galactic nuclei and also a host galaxy of a tidal disruption event (TDE). Through spectral absorption features, the stellar velocity dispersion of SDSS J0159 can be well measured as $\sigma \sim 81~{\rm km\, s}^{-1}$, leading to SDSS J0159 being an apparent outlier in the MBH–σ space, because of the BH mass estimated through the MBH–σ relation about two magnitudes lower than the reported virial BH mass of about 108 M⊙. After considerations of contributions of stellar debris from the central TDE to broad line emission clouds, the overestimated virial BH mass could be well explained in SDSS J0159. Therefore, overestimated virial BH masses through broad-line properties in the MBH–σ space could be treated as interesting clues to support central TDEs.

Zhang, Xue-Guang↗
DOE OSTI2017

Triple collinear emissions in parton showers

A framework to include triple collinear splitting functions into parton showers is presented, and the implementation of flavor-changing next-to-leading-order (NLO) splitting kernels is discussed as a first application. The correspondence between the Monte Carlo integration and the analytic computation of NLO DGLAP evolution kernels is made explicit for both timelike and spacelike parton evolution. Numerical simulation results are obtained with two independent implementations of the new algorithm, using the two independent event generation frameworks PYTHIA and SHERPA.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Attributes of Securable Architectures

As cyber-security is becoming more and more important in systems development, engineers have begun to recognize and understand the types of errors they can introduce through hurried coding technique and design. This overall trend is certainly moving the software industry in the right direction and can lead to developing higher quality software-centric systems. Unfortunately, we have barely begun to examine the results of poor architectural choices, nor do we have much insight into what secure and securable architectures look like. In this paper, based on the past 40 years of work identifying specific security principles, we create a taxonomy of principles that address the abstract cyber-security needs of systems. We then tie these principles to studies of insecure systems architectures to demonstrate applicability. We close the paper with a description of other cyber-security taxonomies, how they specifically differ from this presented taxonomy, and add new principles to address gaps shown in taxonomic comparisons.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Better calibration of cloud parameterizations and subgrid effects increases the fidelity of the E3SM Atmosphere Model version 1

Abstract. Realistic simulation of the Earth's mean-state climate remains a major challenge, and yet it is crucial for predicting the climate system in transition. Deficiencies in models' process representations, propagation of errors from one process to another, and associated compensating errors can often confound the interpretation and improvement of model simulations. These errors and biases can also lead to unrealistic climate projections and incorrect attribution of the physical mechanisms governing past and future climate change. Here we show that a significantly improved global atmospheric simulation can be achieved by focusing on the realism of process assumptions in cloud calibration and subgrid effects using the Energy Exascale Earth System Model (E3SM) Atmosphere Model version 1 (EAMv1). The calibration of clouds and subgrid effects informed by our understanding of physical mechanisms leads to significant improvements in clouds and precipitation climatology, reducing common and long-standing biases across cloud regimes in the model. The improved cloud fidelity in turn reduces biases in other aspects of the system. Furthermore, even though the recalibration does not change the global mean aerosol and total anthropogenic effective radiative forcings (ERFs), the sensitivity of clouds, precipitation, and surface temperature to aerosol perturbations is significantly reduced. This suggests that it is possible to achieve improvements to the historical evolution of surface temperature over EAMv1 and that precise knowledge of global mean ERFs is not enough to constrain historical or future climate change. Cloud feedbacks are also significantly reduced in the recalibrated model, suggesting that there would be a lower climate sensitivity when it is run as part of the fully coupled E3SM. This study also compares results from incremental changes to cloud microphysics, turbulent mixing, deep convection, and subgrid effects to understand how assumptions in the representation of these processes affect different aspects of the simulated atmosphere as well as its response to forcings. We conclude that the spectral composition and geographical distribution of the ERFs and cloud feedback, as well as the fidelity of the simulated base climate state, are important for constraining the climate in the past and future.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1983

Asymptotic unbounded root loci - Formulas and computation

A new geometric way of computing the asymptotic behavior of unbounded root loci of a strictly proper linear time-invariant control system as loop gain goes to infinity is presented. Properties of certain restricted linear maps and nested restrictions of linear maps are developed, and formulas are obtained for the leading coefficient of the asymptotic values of the unbounded multivariable root loci are obtained in terms of eigenvalues of those maps. Published results and a certain simple null structure assumption are used to relate these asymptotic values to the structure at infinity of the Smith-McMillan form of the open loop transfer function. Explicit matrix formulas for the more abstract derived formulas are given and additional geometric insights are developed with orthogonal projections and singular value decomposition. Formulas for the pivots of the unbounded root loci are calculated and shown to have the same form as the coefficients of the unbounded asymptotic root loci.

Sastry, S. S.↗
NASA NTRS2003

NASA Tech Briefs, August 2003

Topics covered include: Stable, Thermally Conductive Fillers for Bolted Joints; Connecting to Thermocouples with Fewer Lead Wires; Zipper Connectors for Flexible Electronic Circuits; Safety Interlock for Angularly Misdirected Power Tool; Modular, Parallel Pulse-Shaping Filter Architectures; High-Fidelity Piezoelectric Audio Device; Photovoltaic Power Station with Ultracapacitors for Storage; Time Analyzer for Time Synchronization and Monitor of the Deep Space Network; Program for Computing Albedo; Integrated Software for Analyzing Designs of Launch Vehicles; Abstract-Reasoning Software for Coordinating Multiple Agents; Software Searches for Better Spacecraft-Navigation Models; Software for Partly Automated Recognition of Targets; Antistatic Polycarbonate/Copper Oxide Composite; Better VPS Fabrication of Crucibles and Furnace Cartridges; Burn-Resistant, Strong Metal-Matrix Composites; Self-Deployable Spring-Strip Booms; Explosion Welding for Hermetic Containerization; Improved Process for Fabricating Carbon Nanotube Probes; Automated Serial Sectioning for 3D Reconstruction; and Parallel Subconvolution Filtering Architectures.

Source record↗